# socat

## NAME



           socat - Multipurpose relay (SOcket CAT)
    


## SYNOPSIS



           socat [options] <address> <address>
           socat -V
           socat -h[h[h]] | -?[?[?]]
           filan
           procan
    


## DESCRIPTION



           **Socat** is a command line based utility that establishes two
           bidirectional byte streams and transfers data between them.
           Because the streams can be constructed from a large set of
           different types of data sinks and sources (see address types), and
           because lots of address options may be applied to the streams,
           socat can be used for many different purposes.
    
           **Filan** is a utility that prints information about its active file
           descriptors to stdout. It has been written for debugging **socat** ,
           but might be useful for other purposes too. Use the -h option to
           find more infos.
    
           **Procan** is a utility that prints information about process
           parameters to stdout. It has been written to better understand
           some UNIX process properties and for debugging **socat** , but might be
           useful for other purposes too.
    
           The life cycle of a **socat** instance typically consists of four
           phases.
    
           In the _init_ phase, the command line options are parsed and logging
           is initialized.
    
           During the _open_ phase, **socat** opens the first address and
           afterwards the second address. These steps are usually blocking;
           thus, especially for complex address types like socks, connection
           requests or authentication dialogs must be completed before the
           next step is started.
    
           In the _transfer_ phase, **socat** watches both streams’ read and write
           file descriptors via select() , and, when data is available on one
           side _and_ can be written to the other side, socat reads it,
           performs newline character conversions if required, and writes the
           data to the write file descriptor of the other stream, then
           continues waiting for more data in both directions.
    
           When one of the streams effectively reaches EOF, the _closing_ phase
           begins. **Socat** transfers the EOF condition to the other stream,
           i.e. tries to shutdown only its write stream, giving it a chance
           to terminate gracefully. For a defined time **socat** continues to
           transfer data in the other direction, but then closes all
           remaining channels and terminates.
    


## OPTIONS



           **Socat** provides some command line options that modify the behaviour
           of the program. They have nothing to do with so called address
           options that are used as parts of address specifications.
    
           **-V** Print version and available feature information to stdout,
                  and exit.
    
           **-h | -?**
                  Print a help text to stdout describing command line options
                  and available address types, and exit.
    
           **-hh | -??**
                  Like -h, plus a list of the short names of all available
                  address options. Some options are platform dependent, so
                  this output is helpful for checking the particular
                  implementation.
    
           **-hhh | -???**
                  Like -hh, plus a list of all available address option
                  names.
    
           **-d** Without this option, only fatal, error, and warning
                  messages are printed; applying this option also prints
                  notice messages.  See DIAGNOSTICS for more information.
    
           **-d0** With this option, only fatal and error messages are
                  printed; this restores the behaviour of **socat** up to version
                  1.7.4.
    
           **-d -d | -dd | -d2**
                  Prints fatal, error, warning, and notice messages.
    
           **-d -d -d | -ddd | -d3**
                  Prints fatal, error, warning, notice, and info messages.
    
           **-d -d -d -d | -dddd | -d4**
                  Prints fatal, error, warning, notice, info, and debug
                  messages.
    
           **-D** Logs information about file descriptors before starting the
                  transfer phase.
    
           **--experimental**
                  New features that are not well tested or are subject to
                  change in the future must be explicitly enabled using this
                  option.
    
           **-ly[ <facility>]**
                  Writes messages to syslog instead of stderr; severity as
                  defined with -d option. With optional <facility>, the
                  syslog type can be selected, default is "daemon". Third
                  party libraries might not obey this option.
    
           **-lf <logfile>**
                  Writes messages to <logfile> [filename] instead of stderr.
                  Some third party libraries, in particular libwrap, might
                  not obey this option.
    
           **-ls** Writes messages to stderr (this is the default). Some third
                  party libraries might not obey this option, in particular
                  libwrap appears to only log to syslog.
    
           **-lp <progname>**
                  Overrides the program name printed in error messages and
                  used for constructing environment variable names.
    
           **-lu** Extends the timestamp of error messages to microsecond
                  resolution. Does not work when logging to syslog.
    
           **-lm[ <facility>]**
                  Mixed log mode. During startup messages are printed to
                  stderr; when **socat** starts the transfer phase loop or daemon
                  mode (i.e. after opening all streams and before starting
                  data transfer, or, with listening sockets with fork option,
                  before the first accept call), it switches logging to
                  syslog.  With optional <facility>, the syslog type can be
                  selected, default is "daemon".
    
           **-lh** Adds hostname to log messages. Uses the value from
                  environment variable HOSTNAME or the value retrieved with
                  uname() if HOSTNAME is not set.
    
           **-v** Writes the transferred data not only to their target
                  streams, but also to stderr. The output format is text with
                  some conversions for readability, and prefixed with "> " or
                  "< " indicating flow directions.
    
           **-x** Writes the transferred data not only to their target
                  streams, but also to stderr. The output format is
                  hexadecimal, prefixed with "> " or "< " indicating flow
                  directions. Can be combined with -v .
    
           **-r <file>**
                  Dumps the raw (binary) data flowing from left to right
                  address to the given file. The file name may contain
                  references to environment variables and $$ (pid), $PROGNAME
                  (see option option -lp), $TIMESTAMP (uses format
                  %Y%m%dT%H%M%S), and MICROS (microseconds of daytime). These
                  references have to be protected from shell expansion of
                  course.
    
           **-R <file>**
                  Dumps the raw (binary) data flowing from right to left
                  address to the given file. See option -r for customization
                  of file name.
    
           **-b <size>**
                  Sets the data transfer block <size> [size_t].  At most
                  <size> bytes are transferred per step. Default is 8192
                  bytes.
    
           **-s** By default, **socat** terminates when an error occurred to
                  prevent the process from running when some option could not
                  be applied. With this option, **socat** is sloppy with errors
                  and tries to continue. Even with this option, socat will
                  exit on fatals, and will abort connection attempts when
                  security checks failed.
    
           **-S <signals-bitmap>**
                  Changes the set of signals that are caught by **socat** just
                  for printing an log message. This catching is useful to get
                  the information about the signal into **socat** s log, but
                  prevents core dump or other standard actions. The default
                  set of these signals is SIGHUP, SIGINT, SIGQUIT, SIGILL,
                  SIGABRT, SIGBUS, SIGFPE, SIGSEGV, and SIGTERM; replace this
                  set (0x89de on Linux) with a bitmap (e.g., SIGFPE has value
                  8 and its bit is 0x0080).
                  Note: Signals SIGHUP, SIGINT, SIGQUIT, SIGUSR1, SIGPIPE,
                  SIGALRM, SIGTERM, and SIGCHLD may be handled specially
                  anyway.
    
           **-t <timeout>**
                  When one channel has reached EOF, the write part of the
                  other channel is shut down. Then, **socat** waits <timeout>
                  [timeval] seconds before terminating. Default is 0.5
                  seconds. This timeout only applies to addresses where write
                  and read part can be closed independently. When during the
                  timeout interval the read part gives EOF, socat terminates
                  without awaiting the timeout.
    
           **-T <timeout>**
                  Total inactivity timeout: when **socat** is already in the
                  transfer loop and nothing has happened for <timeout>
                  [timeval] seconds (no data arrived, no interrupt
                  occurred...) then it terminates. Up to version 1.8.0.0 "0"
                  meant infinite"; since version 1.8.0.1 "0" means 0 and
                  values <0 mean infinite.
                  Useful with protocols like UDP that cannot transfer EOF.
    
           **-u** Uses unidirectional mode. The first address is only used
                  for reading, and the second address is only used for
                  writing (example).
    
           **-U** Uses unidirectional mode in reverse direction. The first
                  address is only used for writing, and the second address is
                  only used for reading.
    
           **-g** During address option parsing, don’t check if the option is
                  considered useful in the given address environment. Use it
                  if you want to force, e.g., appliance of a socket option to
                  a serial device.
    
           **-L <lockfile>**
                  If lockfile exists, exits with error. If lockfile does not
                  exist, creates it and continues, unlinks lockfile on exit.
    
           **-W <lockfile>**
                  If lockfile exists, waits until it disappears. When
                  lockfile does not exist, creates it and continues, unlinks
                  lockfile on exit.
    
           **-4** Use IP version 4 in case the addresses do not implicitly or
                  explicitly specify a version. Since version 1.8.0.1 this is
                  the default.
    
           **-6** Use IP version 6 in case the addresses do not implicitly or
                  explicitly specify a version.
    
           **-0** Do not prefer a particular IP version; this lets passive
                  addresses (LISTEN, RECV, ...) serve both versions on some
                  platforms (not BSD).
    
           **--statistics**
    
           **-S** Logs transfer statistics (bytes and blocks counters for
                  both directions) before terminating **socat**.
                  See also signal USR1.
                  This feature is experimental and might change in future
                  versions.
    


## ADDRESS SPECIFICATIONS



           With the address command line arguments, the user gives **socat**
           instructions and the necessary information for establishing the
           byte streams.
    
           An address specification usually consists of an address type
           keyword, zero or more required address parameters separated by ’:’
           from the keyword and from each other, and zero or more address
           options separated by ’,’.
    
           The keyword specifies the address type (e.g., TCP4, OPEN, EXEC).
           For some keywords there exist synonyms (’-’ for STDIO, TCP for
           TCP4). Keywords are case insensitive.  For a few special address
           types, the keyword may be omitted: Address specifications starting
           with a number are assumed to be FD (raw file descriptor)
           addresses; if a ’/’ is found before the first ’:’ or ’,’, GOPEN
           (generic file open) is assumed.
    
           The required number and type of address parameters depend on the
           address type. E.g., TCP4 requires a server specification (name or
           address), and a port specification (number or service name).
    
           Zero or more address options may be given with each address. They
           influence the address in some ways.  Options consist of an option
           keyword or an option keyword and a value, separated by ’=’. Option
           keywords are case insensitive.  For filtering the options that are
           useful with an address type, each option is member of one option
           group. For each address type there is a set of option groups
           allowed. Only options belonging to one of these address groups may
           be used (except with option -g).
    
           Address specifications following the above schema are also called
           _single_ address specifications.  Two single addresses can be
           combined with "!!" to form a _dual_ type address for one channel.
           Here, the first address is used by **socat** for reading data, and the
           second address for writing data. There is no way to specify an
           option only once for being applied to both single addresses.
    
           Usually, addresses are opened in read/write mode. When an address
           is part of a dual address specification, or when option -u or -U
           is used, an address might be used only for reading or for writing.
           Considering this is important with some address types.
    
           With socat version 1.5.0 and higher, the lexical analysis tries to
           handle quotes and parenthesis meaningfully and allows escaping of
           special characters.  If one of the characters ( { [ ’ is found,
           the corresponding closing character - ) } ] ’ - is looked for;
           they may also be nested. Within these constructs, socats special
           characters and strings : , !! are not handled specially. All those
           characters and strings can be escaped with \ or within ""
    


## ADDRESS TYPES



           This section describes the available address types with their
           keywords, parameters, and semantics.
    
           **CREATE: <filename>**
                  Opens <filename> with creat() and uses the file descriptor
                  for writing.  This is a write-only address because a file
                  opened with creat cannot be read from. See options -u and
                  -U, and dual addresses.
                  Flags like O_LARGEFILE cannot be applied. If you need them
                  use OPEN with options create,create.
                  <filename> must be a valid existing or not existing path.
                  If <filename> is a named pipe, creat() might block; if
                  <filename> refers to a socket, this is an error.
                  Option groups: FD,REG,NAMED
                  Useful options: mode, mode, user, group, unlink-early,
                  unlink-late, append
                  See also: OPEN, GOPEN
    
           **DCCP-CONNECT: <host>:<port> (DCCP:<host>:<port>)**
                  Establishes a DCCP connect to the specified <host> [IP
                  address] and <port> [DCCP service] using IP version 4 or 6
                  depending on address specification, name resolution, or
                  option pf.
                  Option groups: FD,SOCKET,IP4,IP6,SCTP,CHILD,RETRY
                  Useful options: bind, connect-timeout, tos, dccp-set-ccid,
                  nonblock, sourceport, retry, readbytes
                  See also: DCCP4-CONNECT, DCCP6-CONNECT, DCCP-LISTEN,
                  TCP-CONNECT SCTP-CONNECT
    
           **DCCP4-CONNECT: <host>:<port> (DCCP4:<host>:<port>)**
                  Like DCCP-CONNECT, but only supports IPv4 protocol.
                  Option groups: FD,SOCKET,IP4,DCCP,CHILD,RETRY
    
           **DCCP6-CONNECT: <host>:<port> (DCCP6:<host>:<port>)**
                  Like DCCP-CONNECT, but only supports IPv6 protocol.
                  Option groups: FD,SOCKET,IP6,DCCP,CHILD,RETRY
    
           **DCCP-LISTEN: <port> (DCCP-L:<port>)**
                  Listens on <port> [DCCP service] and accepts an DCCP
                  connection. The IP version is 4 or the one specified with
                  address option pf, socat option (-4, -6), or environment
                  variable SOCAT_DEFAULT_LISTEN_IP.  Note that opening this
                  address usually blocks until a client connects.
                  Option groups:
                  FD,SOCKET,LISTEN,CHILD,RANGE,IP4,IP6,DCCP,RETRY
                  Useful options: fork, bind, range, max-children, backlog,
                  accept-timeout, dccp-set-sid, su, reuseaddr, retry
                  See also: DCCP4-LISTEN, DCCP6-LISTEN, TCP-LISTEN,
                  SCTP-LISTEN, DCCP-CONNECT
    
           **DCCP4-LISTEN: <port> (DCCP4-L:<port>)**
                  Like DCCP-LISTEN, but only supports IPv4 protocol.
                  Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,DCCP,RETRY
    
           **DCCP6-LISTEN: <port> (DCCP6-L:<port>)**
                  Like DCCP-LISTEN, but only supports IPv6 protocol.
                  Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP6,DCCP,RETRY
    
           **EXEC: <command-line>**
                  Forks a sub process that establishes communication with its
                  parent process and invokes the specified program with
                  execvp() .  <command-line> is a simple command with
                  arguments separated by single spaces. If the program name
                  contains a ’/’, the part after the last ’/’ is taken as
                  ARGV[0]. If the program name is a relative path, the
                  execvp() semantics for finding the program via $PATH apply.
                  After successful program start, **socat** writes data to stdin
                  of the process and reads from its stdout using a UNIX
                  domain socket generated by socketpair() per default.
                  (example)
                  Option groups: FD,SOCKET,EXEC,FORK,TERMIOS
                  Useful options: path, fdin, fdout, chroot, su, su-d,
                  nofork, socktype, pty, stderr, ctty, setsid, pipes, umask,
                  login, sigint, sigquit, netns
                  See also: SYSTEM,SHELL
    
           **FD: <fdnum>**
                  Uses the file descriptor <fdnum>. It must already exist as
                  valid UN*X file descriptor.
                  Option groups: FD (TERMIOS,REG,SOCKET)
                  See also: STDIO, STDIN, STDOUT, STDERR
    
           **GOPEN: <filename>**
                  (Generic open) This address type tries to handle any file
                  system entry except directories usefully. <filename> may be
                  a relative or absolute path. If it already exists, its type
                  is checked.  In case of a UNIX domain socket, **socat**
                  connects; if connecting fails, **socat** assumes a datagram
                  socket and uses sendto() calls.  If the entry is not a
                  socket, **socat** opens it applying the O_APPEND flag.  If it
                  does not exist, it is opened with flag O_CREAT as a regular
                  file (example).
                  Option groups: FD,REG,SOCKET,NAMED,OPEN
                  See also: OPEN, CREATE, UNIX-CONNECT
    
           **IP-SENDTO: <host>:<protocol>**
                  Opens a raw IP socket. Depending on host specification or
                  option pf, IP protocol version 4 or 6 is used. It uses
                  <protocol> to send packets to <host> [IP address] and
                  receives packets from host, ignores packets from other
                  hosts.  Protocol 255 uses the raw socket with the IP header
                  being part of the data.
                  Option groups: FD,SOCKET,IP4,IP6
                  Useful options: pf, ttl
                  See also: IP4-SENDTO, IP6-SENDTO, IP-RECVFROM, IP-RECV,
                  UDP-SENDTO, UNIX-SENDTO
    
           **INTERFACE: <interface>**
                  Communicates with a network connected on an interface using
                  raw packets including link level data. <interface> is the
                  name of the network interface. Currently only available on
                  Linux.
                  Option groups: FD,SOCKET
                  Useful options: pf, type
                  See also: ip-recv
    
           **IP4-SENDTO: <host>:<protocol>**
                  Like IP-SENDTO, but always uses IPv4.
                  Option groups: FD,SOCKET,IP4
    
           **IP6-SENDTO: <host>:<protocol>**
                  Like IP-SENDTO, but always uses IPv6.
                  Option groups: FD,SOCKET,IP6
    
           **IP-DATAGRAM: <address>:<protocol>**
                  Sends outgoing data to the specified address which may in
                  particular be a broadcast or multicast address. Packets
                  arriving on the local socket are checked if their source
                  addresses match RANGE or TCPWRAP options. This address type
                  can for example be used for implementing symmetric or
                  asymmetric broadcast or multicast communications.
                  Option groups: FD, SOCKET, IP4, IP6, RANGE
                  Useful options: bind, range, tcpwrap, broadcast,
                  ip-multicast-loop, ip-multicast-ttl, ip-multicast-if,
                  ip-add-membership, ip-add-source-membership,
                  ipv6-join-group, ipv6-join-source-group, ttl, tos, pf
                  See also: IP4-DATAGRAM, IP6-DATAGRAM, IP-SENDTO,
                  IP-RECVFROM, IP-RECV, UDP-DATAGRAM
    
           **IP4-DATAGRAM: <host>:<protocol>**
                  Like IP-DATAGRAM, but always uses IPv4.  (example)
                  Option groups: FD,SOCKET,IP4,RANGE
    
           **IP6-DATAGRAM: <host>:<protocol>**
                  Like IP-DATAGRAM, but always uses IPv6. Please note that
                  IPv6 does not know broadcasts.
                  Option groups: FD,SOCKET,IP6,RANGE
    
           **IP-RECVFROM: <protocol>**
                  Opens a raw IP socket of <protocol>. Depending on option
                  pf, IP protocol version 4 or 6 is used. It receives one
                  packet from an unspecified peer and may send one or more
                  answer packets to that peer.  This mode is particularly
                  useful with fork option where each arriving packet - from
                  arbitrary peers - is handled by its own sub process.  This
                  allows a behaviour similar to typical UDP based servers
                  like ntpd or named.
                  Please note that the reply packets might be fetched as
                  incoming traffic when sender and receiver IP address are
                  identical because there is no port number to distinguish
                  the sockets.
                  This address works well with IP-SENDTO address peers (see
                  above).  Protocol 255 uses the raw socket with the IP
                  header being part of the data.
                  See the note about RECVFROM addresses.
                  Option groups: FD,SOCKET,IP4,IP6,CHILD,RANGE
                  Useful options: pf, fork, range, ttl, broadcast
                  See also: IP4-RECVFROM, IP6-RECVFROM, IP-SENDTO, IP-RECV,
                  UDP-RECVFROM, UNIX-RECVFROM
    
           **IP4-RECVFROM: <protocol>**
                  Like IP-RECVFROM, but always uses IPv4.
                  Option groups: FD,SOCKET,IP4,CHILD,RANGE
    
           **IP6-RECVFROM: <protocol>**
                  Like IP-RECVFROM, but always uses IPv6.
                  Option groups: FD,SOCKET,IP6,CHILD,RANGE
    
           **IP-RECV: <protocol>**
                  Opens a raw IP socket of <protocol>. Depending on option
                  pf, IP protocol version 4 or 6 is used. It receives packets
                  from multiple unspecified peers and merges the data.  No
                  replies are possible, this is a read-only address, see
                  options -u and -U, and dual addresses.  It can be, e.g.,
                  addressed by socat IP-SENDTO address peers.  Protocol 255
                  uses the raw socket with the IP header being part of the
                  data.
                  Option groups: FD,SOCKET,IP4,IP6,RANGE
                  Useful options: pf, range
                  See also: IP4-RECV, IP6-RECV, IP-SENDTO, IP-RECVFROM,
                  UDP-RECV, UNIX-RECV
    
           **IP4-RECV: <protocol>**
                  Like IP-RECV, but always uses IPv4.
                  Option groups: FD,SOCKET,IP4,RANGE
    
           **IP6-RECV: <protocol>**
                  Like IP-RECV, but always uses IPv6.
                  Option groups: FD,SOCKET,IP6,RANGE
    
           **OPEN: <filename>**
                  Opens <filename> using the open() system call (example).
                  This operation fails on UNIX domain sockets.
                  Note: This address type is rarely useful in bidirectional
                  mode.
                  Option groups: FD,REG,NAMED,OPEN
                  Useful options: creat, excl, noatime, nofollow, append,
                  rdonly, wronly, lock, readbytes, ignoreeof
                  See also: CREATE, GOPEN, UNIX-CONNECT
    
           **OPENSSL: <host>:<port>**
                  Tries to establish a SSL connection to <port> [TCP service]
                  on <host> [IP address] using TCP/IP version 4 or 6
                  depending on address specification, name resolution, or
                  option pf.
                  NOTE: Up to version 1.7.2.4 the server certificate was only
                  checked for validity against the system certificate store
                  or cafile or capath, but not for match with the server’s
                  name or its IP address.  Since version 1.7.3.0 socat checks
                  the peer certificate for match with the <host> parameter or
                  the value of the openssl-commonname option.  Socat tries to
                  match it against the certificates subject commonName, and
                  the certificates extension subjectAltName DNS names.
                  Wildcards in the certificate are supported.
                  Option groups: FD,SOCKET,IP4,IP6,TCP,OPENSSL,RETRY
                  Useful options: min-proto-version, cipher, verify,
                  commonname, cafile, capath, certificate, key, compress,
                  bind, pf, connect-timeout, sourceport, retry
                  See also: OPENSSL-LISTEN, TCP
    
           **OPENSSL-LISTEN: <port>**
                  Listens on tcp <port> [TCP service].  The IP version is 4
                  or the one specified with pf. When a connection is
                  accepted, this address behaves as SSL server.
                  Note: You probably want to use the certificate option with
                  this address.
                  NOTE: The client certificate is only checked for validity
                  against cafile or capath, but not for match with the
                  client’s name or its IP address!
                  Option groups:
                  FD,SOCKET,IP4,IP6,TCP,LISTEN,OPENSSL,CHILD,RANGE,RETRY
                  Useful options: pf, min-proto-version, cipher, verify,
                  commonname, cafile, capath, certificate, key, compress,
                  fork, bind, range, tcpwrap, su, reuseaddr, retry
                  See also: OPENSSL, TCP-LISTEN
    
           **OPENSSL-DTLS-CLIENT: <host>:<port>**
                  Tries to establish a DTLS connection to <port> [UDP
                  service] on <host> [IP address] using UDP/IP version 4 or 6
                  depending on address specification, name resolution, or
                  option pf.
                  **Socat** checks the peer certificates subjectAltName or
                  commonName against the addresses option openssl-commonname
                  or the host name.  Wildcards in the certificate are
                  supported.
                  Use **socat** option -b to make datagrams small enough to fit
                  with overhead on the network. Use option -T to prevent
                  indefinite hanging when peer went down quietly.
                  Option groups: FD,SOCKET,IP4,IP6,OPENSSL,RETRY
                  Useful options: min-proto-version, cipher, verify,
                  commonname, cafile, capath, certificate, key, compress,
                  bind, pf, sourceport, retry, rcvtimeo
                  See also: OPENSSL-DTLS-SERVER, OPENSSL-CONNECT, UDP-CONNECT
    
           **OPENSSL-DTLS-SERVER: <port>**
                  Listens on UDP <port> [UDP service].  The IP version is 4
                  or the one specified with pf. When a connection is
                  accepted, this address behaves as DTLS server.
                  Note: You probably want to use the certificate option with
                  this address.
                  NOTE: The client certificate is only checked for validity
                  against cafile or capath, but not for match with the
                  client’s name or its IP address!  Use **socat** option -b to
                  make datagrams small enough to fit with overhead on the
                  network.  Use option -T to prevent indefinite hanging when
                  peer went down quietly.
                  Option groups:
                  FD,SOCKET,IP4,IP6,LISTEN,OPENSSL,CHILD,RANGE,RETRY
                  Useful options: pf, min-proto-version, cipher, verify,
                  commonname, cafile, capath, certificate, key, compress,
                  fork, bind, range, tcpwrap, su, reuseaddr, retry
                  rcvtimeo
                  See also: OPENSSL-DTLS-CLIENT, OPENSSL-LISTEN, UDP-LISTEN
    
           **PIPE: <filename>**
                  If <filename> already exists, it is opened.  If it does not
                  exist, a named pipe is created and opened. Beginning with
                  socat version 1.4.3, the named pipe is removed when the
                  address is closed (but see option unlink-close
                  Note: When a pipe is used for both reading and writing, it
                  works as echo service.
                  Note: When a pipe is used for both reading and writing, and
                  socat tries to write more bytes than the pipe can buffer
                  (Linux 2.4: 2048 bytes), socat might block. Consider using
                  socat option, e.g., -b 2048
                  Option groups: FD,NAMED,OPEN
                  Useful options: rdonly, nonblock, group, user, mode,
                  unlink-early
                  See also: unnamed pipe
    
           **PIPE** Creates an unnamed pipe and uses it for reading and
                  writing. It works as an echo, because everything written to
                  it appears immediately as read data.
                  Note: When socat tries to write more bytes than the pipe
                  can queue (Linux 2.4: 2048 bytes), socat might block.
                  Consider, e.g., using option -b 2048
                  Option groups: FD
                  See also: named pipe, SOCKETPAIR
    
           **SOCKETPAIR**
                  Creates a socketpair and uses it for reading and writing.
                  It works as an echo, because everything written to it
                  appears immediately as read data. The default socket type
                  is datagram, so it keeps packet boundaries.
                  Option groups: FD
                  Useful options: socktype
                  See also: unnamed pipe
    
           **POSIXMQ-READ:/ <mqueue>**
                  Opens or creates the specified POSIX message queue and
                  reads messages (packets). It keeps the packet boundaries.
                  This is a read-only address, see options -u and -U and dual
                  addresses.
                  **Socat** provides this address type only on Linux because
                  POSIX MQ is based on UNIX filedescriptors there.
                  Useful options: posixmq-priority, unlink-early,
                  unlink-close, o-nonblock, o-creat, o-excl, umask
    
           **POSIXMQ-RECEIVE:/ <mqueue>**
    
           **POSIXMQ-RECV:/ <mqueue>**
                  Opens or creates the specified POSIX message queue and
                  reads one message (packet).
                  This is a read-only address. See POSIXMQ-READ for more
                  info.
                  Example: POSIX MQ recv with fork
                  Useful options: posixmq-priority, fork, max-children,
                  unlink-early, unlink-close, o-creat, o-excl, umask
    
           **POSIXMQ-SEND:/ <mqueue>**
                  Opens or creates the specified POSIX message queue and
                  writes messages (packets).
                  This is a write-only address. See POSIXMQ-READ for more
                  info.
                  (Example)
                  Useful options: posixmq-priority, posixmq-flush, fork,
                  max-children, unlink-early, unlink-close, o-creat, o-excl,
                  umask
    
           **POSIXMQ-WRITE:/ <mqueue>**
                  Does the same as POSIXMQ-SEND.
    
           **POSIXMQ-BIDIRECTIONAL:/mqueue**
    
           **POSIXMQ:/mqueue**
                  Opens or creates the specified POSIX message queue in read
                  and/or write mode depending on context, then reads and/or
                  writes messages (packets).  In bidirectional mode this is
                  just another echo service.
                  See POSIXMQ-READ and POSIXMQ-SEND for more info.
    
           **PROXY: <proxy>:<hostname>:<port>**
                  Connects to an HTTP proxy server on port 8080 using TCP/IP
                  version 4 or 6 depending on address specification, name
                  resolution, or option pf, and sends a CONNECT request for
                  hostname:port. If the proxy grants access and succeeds to
                  connect to the target, data transfer between socat and the
                  target can start (example).  Note that the traffic need not
                  be HTTP but can be an arbitrary protocol.
                  Option groups: FD,SOCKET,IP4,IP6,TCP,HTTP,RETRY
                  Useful options: proxyport, ignorecr, proxyauth, resolve,
                  crnl, bind, connect-timeout, mss, sourceport, retry
                  See also: SOCKS, TCP
    
           **PTY** Generates a pseudo terminal (pty) and uses its master side.
                  Another process may open the pty’s slave side using it like
                  a serial line or terminal.  (example). If both the ptmx and
                  the openpty mechanisms are available, ptmx is used (POSIX).
                  Option groups: FD,NAMED,PTY,TERMIOS
                  Useful options: link, openpty, wait-slave, mode, user,
                  group
                  See also: UNIX-LISTEN, PIPE, EXEC, SYSTEM, SHELL
    
           **READLINE**
                  Uses GNU readline and history on stdio to allow editing and
                  reusing input lines (example). This requires the GNU
                  readline and history libraries. Note that stdio should be a
                  (pseudo) terminal device, otherwise readline does not seem
                  to work.
                  Option groups: FD,READLINE,TERMIOS
                  Useful options: history, noecho
                  See also: STDIO
    
           **SCTP-CONNECT: <host>:<port>**
                  Establishes an SCTP stream connection to the specified
                  <host> [IP address] and <port> [TCP service] using IP
                  version 4 or 6 depending on address specification, name
                  resolution, or option pf.
                  Option groups: FD,SOCKET,IP4,IP6,SCTP,CHILD,RETRY
                  Useful options: bind, pf, connect-timeout, tos,
                  mtudiscover, sctp-maxseg, sctp-nodelay, nonblock,
                  sourceport, retry, readbytes
                  See also: SCTP4-CONNECT, SCTP6-CONNECT, SCTP-LISTEN,
                  TCP-CONNECT
    
           **SCTP4-CONNECT: <host>:<port>**
                  Like SCTP-CONNECT, but only supports IPv4 protocol.
                  Option groups: FD,SOCKET,IP4,SCTP,CHILD,RETRY
    
           **SCTP6-CONNECT: <host>:<port>**
                  Like SCTP-CONNECT, but only supports IPv6 protocol.
                  Option groups: FD,SOCKET,IP6,SCTP,CHILD,RETRY
    
           **SCTP-LISTEN: <port>**
                  Listens on <port> [TCP service] and accepts an SCTP
                  connection. The IP version is 4 or the one specified with
                  address option pf, socat option (-4, -6), or environment
                  variable SOCAT_DEFAULT_LISTEN_IP.  Note that opening this
                  address usually blocks until a client connects.
                  Option groups:
                  FD,SOCKET,LISTEN,CHILD,RANGE,IP4,IP6,SCTP,RETRY
                  Useful options: crnl, fork, bind, range, tcpwrap, pf,
                  max-children, backlog, accept-timeout, sctp-maxseg,
                  sctp-nodelay, su, reuseaddr, retry
                  See also: SCTP4-LISTEN, SCTP6-LISTEN, TCP-LISTEN,
                  SCTP-CONNECT
    
           **SCTP4-LISTEN: <port>**
                  Like SCTP-LISTEN, but only supports IPv4 protocol.
                  Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,SCTP,RETRY
    
           **SCTP6-LISTEN: <port>**
                  Like SCTP-LISTEN, but only supports IPv6 protocol.
                  Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP6,SCTP,RETRY
    
           **SOCKET-CONNECT: <domain>:<protocol>:<remote-address>**
                  Creates a stream socket using the first and second given
                  socket parameters and SOCK_STREAM (see man socket(2)) and
                  connects to the remote-address.  The two socket parameters
                  have to be specified by int numbers. Consult your OS
                  documentation and include files to find the appropriate
                  values. The remote-address must be the data representation
                  of a sockaddr structure without sa_family and (BSD) sa_len
                  components.
                  Please note that you can - beyond the options of the
                  specified groups - also use options of higher level
                  protocols when you apply socat option -g.
                  Option groups: FD,SOCKET,CHILD,RETRY
                  Useful options: bind, setsockopt,
                  See also: TCP, UDP-CONNECT, UNIX-CONNECT, SOCKET-LISTEN,
                  SOCKET-SENDTO
    
           **SOCKET-DATAGRAM: <domain>:<type>:<protocol>:<remote-address>**
                  Creates a datagram socket using the first three given
                  socket parameters (see man socket(2)) and sends outgoing
                  data to the remote-address. The three socket parameters
                  have to be specified by int numbers. Consult your OS
                  documentation and include files to find the appropriate
                  values. The remote-address must be the data representation
                  of a sockaddr structure without sa_family and (BSD) sa_len
                  components.
                  Please note that you can - beyond the options of the
                  specified groups - also use options of higher level
                  protocols when you apply socat option -g.
                  Option groups: FD,SOCKET,RANGE
                  Useful options: bind, range, setsockopt,
                  See also: UDP-DATAGRAM, IP-DATAGRAM, SOCKET-SENDTO,
                  SOCKET-RECV, SOCKET-RECVFROM
    
           **SOCKET-LISTEN: <domain>:<protocol>:<local-address>**
                  Creates a stream socket using the first and second given
                  socket parameters and SOCK_STREAM (see man socket(2)) and
                  waits for incoming connections on local-address. The two
                  socket parameters have to be specified by int numbers.
                  Consult your OS documentation and include files to find the
                  appropriate values. The local-address must be the data
                  representation of a sockaddr structure without sa_family
                  and (BSD) sa_len components.
                  Please note that you can - beyond the options of the
                  specified groups - also use options of higher level
                  protocols when you apply socat option -g.
                  Option groups: FD,SOCKET,LISTEN,RANGE,CHILD,RETRY
                  Useful options: setsockopt, setsockopt-listen,
                  See also: TCP, UDP-CONNECT, UNIX-CONNECT, SOCKET-LISTEN,
                  SOCKET-SENDTO, SOCKET-SENDTO
    
           **SOCKET-RECV: <domain>:<type>:<protocol>:<local-address>**
                  Creates a socket using the three given socket parameters
                  (see man socket(2)) and binds it to <local-address>.
                  Receives arriving data. The three parameters have to be
                  specified by int numbers. Consult your OS documentation and
                  include files to find the appropriate values. The
                  local-address must be the data representation of a sockaddr
                  structure without sa_family and (BSD) sa_len components.
                  Option groups: FD,SOCKET,RANGE
                  Useful options: range, setsockopt, setsockopt-listen
                  See also: UDP-RECV, IP-RECV, UNIX-RECV, SOCKET-DATAGRAM,
                  SOCKET-SENDTO, SOCKET-RECVFROM
    
           **SOCKET-RECVFROM: <domain>:<type>:<protocol>:<local-address>**
                  Creates a socket using the three given socket parameters
                  (see man socket(2)) and binds it to <local-address>.
                  Receives arriving data and sends replies back to the
                  sender. The first three parameters have to be specified as
                  int numbers. Consult your OS documentation and include
                  files to find the appropriate values. The local-address
                  must be the data representation of a sockaddr structure
                  without sa_family and (BSD) sa_len components.
                  See the note about RECVFROM addresses.
                  Option groups: FD,SOCKET,CHILD,RANGE
                  Useful options: fork, range, setsockopt, setsockopt-listen
                  See also: UDP-RECVFROM, IP-RECVFROM, UNIX-RECVFROM,
                  SOCKET-DATAGRAM, SOCKET-SENDTO, SOCKET-RECV
    
           **SOCKET-SENDTO: <domain>:<type>:<protocol>:<remote-address>**
                  Creates a socket using the three given socket parameters
                  (see man socket(2)). Sends outgoing data to the given
                  address and receives replies.  The three parameters have to
                  be specified as int numbers. Consult your OS documentation
                  and include files to find the appropriate values. The
                  remote-address must be the data representation of a
                  sockaddr structure without sa_family and (BSD) sa_len
                  components.
                  Option groups: FD,SOCKET
                  Useful options: bind, setsockopt, setsockopt-listen
                  See also: UDP-SENDTO, IP-SENDTO, UNIX-SENDTO,
                  SOCKET-DATAGRAM, SOCKET-RECV SOCKET-RECVFROM
    
           **ACCEPT-FD: <fdnum>**
                  Expects a listening socket in <fdnum> and accepts one or
                  (with option fork) more connections. This address type is
                  useful under systemd control with "inetd mode".
                  Example: (example)
                  Option groups: FD, SOCKET, TCP, CHILD, RETRY
                  Useful options: fork, range, sourceport, lowport, tcpwrap
    
           **SOCKS4: <socks-server>:<host>:<port>**
                  Connects via <socks-server> [IP address] to <host> [IPv4
                  address] on <port> [TCP service], using socks version 4
                  protocol over IP version 4 or 6 depending on address
                  specification, name resolution, or option pf (example).
                  Option groups: FD,SOCKET,IP4,IP6,TCP,SOCKS4,RETRY
                  Useful options: socksuser, socksport, sourceport, pf, retry
                  See also: SOCKS5, SOCKS4A, PROXY, TCP
    
           **SOCKS4A: <socks-server>:<host>:<port>**
                  like SOCKS4, but uses socks protocol version 4a, thus
                  leaving host name resolution to the socks server.
                  Option groups: FD,SOCKET,IP4,IP6,TCP,SOCKS4,RETRY
    
           **SOCKS5-CONNECT: <socks-server>:<socks-port>:<target-host>:<target-port>**
    
           **SOCKS5-CONNECT: <socks-server>:<target-host>:<target-port>**
                  Connects via <socks-server> [IP address] to <target-host>
                  [IPv4 address] on <target-port> [TCP service], using socks
                  version 5 protocol over TCP. Currently no authentication
                  mechanism is provided.
                  Option groups: FD, SOCKET, IP4, IP6, TCP, CHILD, RETRY
                  Useful options: socksport, sourceport, pf, retry
                  See also: SOCKS5-LISTEN, SOCKS4, SOCKS4A, PROXY, TCP
    
           **SOCKS5-LISTEN: <socks-server>:<socks-port>:<listen-host>:<listen-port>**
    
           **SOCKS5-LISTEN: <socks-server>:<listen-host>:<listen-port>**
                  Connects to <socks-server> [IP address] using socks version
                  5 protocol over TCP and makes it listen for incoming
                  connections on <listen-port> [TCP service], binding to
                  <-listen-host> [IPv4 address] Currently not authentication
                  mechanism is provided.
                  Option groups: FD, SOCKET, IP4, IP6, TCP, CHILD, RETRY
                  Useful options: sourceport, pf, retry
                  See also: SOCKS5-CONNECT,
    
           **STDERR** Uses file descriptor 2.
                  This is a write-only address, see options -u and -U, and
                  dual addresses.
                  Option groups: FD (TERMIOS,REG,SOCKET)
                  See also: FD
    
           **STDIN** Uses file descriptor 0.
                  This is a read-only address, see options -u and -U, and
                  dual addresses.
                  Option groups: FD (TERMIOS,REG,SOCKET)
                  Useful options: readbytes
                  See also: FD
    
           **STDIO** Uses file descriptor 0 for reading, and 1 for writing.
                  Option groups: FD (TERMIOS,REG,SOCKET)
                  Useful options: readbytes
                  See also: FD
    
           **STDOUT** Uses file descriptor 1.
                  This is a write-only address, see options -u and -U, and
                  dual addresses.
                  Option groups: FD (TERMIOS,REG,SOCKET)
                  See also: FD
    
           **SHELL: <shell-command>**
                  Forks a sub process that establishes communication with its
                  parent process and invokes the specified program with the
                  configured shell ($SHELL).  Note that <shell-command>
                  [string] must not contain ’,’ or "!!", and that shell meta
                  characters may have to be protected.  After successful
                  program start, **socat** writes data to stdin of the process
                  and reads from its stdout.
                  Option groups: FD,SOCKET,EXEC,FORK,TERMIOS
                  Useful options: path, fdin, fdout, chroot, su, su-d,
                  nofork, socktype, pty, stderr, ctty, setsid, pipes, umask,
                  sigint, sigquit
                  See also: EXEC, SYSTEM
    
           **SYSTEM: <shell-command>**
                  Forks a sub process that establishes communication with its
                  parent process and invokes the specified program with
                  system() . Please note that <shell-command> [string] must
                  not contain ’,’ or "!!", and that shell meta characters may
                  have to be protected.  After successful program start,
                  **socat** writes data to stdin of the process and reads from
                  its stdout.
                  Option groups: FD,SOCKET,EXEC,FORK,TERMIOS
                  Useful options: path, fdin, fdout, chroot, su, su-d,
                  nofork, socktype, pty, stderr, ctty, setsid, pipes, umask,
                  sigint, sigquit, netns
                  See also: EXEC, SHELL
    
           **TCP: <host>:<port>**
                  Connects to <port> [TCP service] on <host> [IP address]
                  using TCP/IP version 4 or 6 depending on address
                  specification, name resolution, or option pf.
                  Option groups: FD,SOCKET,IP4,IP6,TCP,RETRY
                  Useful options: connect-timeout, retry, sourceport, netns,
                  crnl, bind, pf, tos, mtudiscover, mss, nodelay, nonblock,
                  readbytes
                  See also: TCP4, TCP6, TCP-LISTEN, UDP, SCTP-CONNECT,
                  UNIX-CONNECT
    
           **TCP4: <host>:<port>**
                  Like TCP, but only supports IPv4 protocol (example).
                  Option groups: FD,SOCKET,IP4,TCP,RETRY
    
           **TCP6: <host>:<port>**
                  Like TCP, but only supports IPv6 protocol.
                  Option groups: FD,SOCKET,IP6,TCP,RETRY
    
           **TCP-LISTEN: <port>**
                  Listens on <port> [TCP service] and accepts a TCP/IP
                  connection. The IP version is 4 or the one specified with
                  address option pf, socat option (-4, -6), or environment
                  variable SOCAT_DEFAULT_LISTEN_IP.  Note that opening this
                  address usually blocks until a client connects.
                  Option groups:
                  FD,SOCKET,LISTEN,CHILD,RANGE,IP4,IP6,TCP,RETRY
                  Useful options: crnl, fork, bind, range, tcpwrap, pf,
                  max-children, backlog, accept-timeout, mss, su, reuseaddr,
                  retry, cool-write
                  See also: TCP4-LISTEN, TCP6-LISTEN, UDP-LISTEN,
                  SCTP-LISTEN, UNIX-LISTEN, OPENSSL-LISTEN, TCP-CONNECT
    
           **TCP4-LISTEN: <port>**
                  Like TCP-LISTEN, but only supports IPv4 protocol (example).
                  Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,TCP,RETRY
    
           **TCP6-LISTEN: <port>**
                  Like TCP-LISTEN, but only supports IPv6 protocol.
                  Additional useful option: ipv6only
                  Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP6,TCP,RETRY
    
           **TUN[: <if-addr>/<bits>]**
                  Creates a Linux TUN/TAP device and optionally assigns it
                  the address and netmask given by the parameters. The
                  resulting network interface is almost ready for use by
                  other processes; socat serves its "wire side". This address
                  requires read and write access to the tunnel cloning
                  device, usually /dev/net/tun , as well as permission to set
                  some ioctl()s.  **Option iff-up is required to immediately**
                  **activate the interface!**
                  Note: If you intend to transfer packets between two Socat
                  "wire sides" you need a protocol that keeps packet
                  boundaries, e.g.UDP; TCP might work with option nodelay.
                  Option groups: FD,NAMED,OPEN,TUN
                  Useful options: iff-up, tun-device, tun-name, tun-type,
                  iff-no-pi, netns
                  See also: ip-recv
    
           **UDP: <host>:<port>**
                  Connects to <port> [UDP service] on <host> [IP address]
                  using UDP/IP version 4 or 6 depending on address
                  specification, name resolution, or option pf.
                  Please note that, due to UDP protocol properties, no real
                  connection is established; data has to be sent for
                  `connecting’ to the server, and no end-of-file condition
                  can be transported.
                  Option groups: FD,SOCKET,IP4,IP6
                  Useful options: ttl, tos, bind, sourceport, pf
                  See also: UDP4, UDP6, UDP-LISTEN, TCP, IP
    
           **UDP4: <host>:<port>**
                  Like UDP, but only supports IPv4 protocol.
                  Option groups: FD,SOCKET,IP4
    
           **UDP6: <host>:<port>**
                  Like UDP, but only supports IPv6 protocol.
                  Option groups: FD,SOCKET,IP6
    
           **UDP-DATAGRAM: <address>:<port>**
                  Sends outgoing data to the specified address which may in
                  particular be a broadcast or multicast address. Packets
                  arriving on the local socket are checked for the correct
                  remote port only when option sourceport is used (this is a
                  change with **Socat** version 1.7.4.0) and if their source
                  addresses match RANGE or TCPWRAP options. This address type
                  can for example be used for implementing symmetric or
                  asymmetric broadcast or multicast communications.
                  Option groups: FD,SOCKET,IP4,IP6,RANGE
                  Useful options: bind, range, tcpwrap, broadcast,
                  ip-multicast-loop, ip-multicast-ttl, ip-multicast-if,
                  ip-add-membership, ip-add-source-membership,
                  ipv6-join-group, ipv6-join-source-group, ttl, tos,
                  sourceport, pf
                  See also: UDP4-DATAGRAM, UDP6-DATAGRAM, UDP-SENDTO,
                  UDP-RECVFROM, UDP-RECV, UDP-CONNECT, UDP-LISTEN,
                  IP-DATAGRAM
    
           **UDP4-DATAGRAM: <address>:<port>**
                  Like UDP-DATAGRAM, but only supports IPv4 protocol
                  (example1, example2).
                  Option groups: FD,SOCKET,IP4, RANGE
    
           **UDP6-DATAGRAM: <address>:<port>**
                  Like UDP-DATAGRAM, but only supports IPv6 protocol.
                  Option groups: FD,SOCKET,IP6,RANGE
    
           **UDP-LISTEN: <port>**
                  Waits for a UDP/IP packet arriving on <port> [UDP service]
                  and `connects’ back to sender.  The accepted IP version is
                  4 or the one specified with option pf.  Please note that,
                  due to UDP protocol properties, no real connection is
                  established; data has to arrive from the peer first, and no
                  end-of-file condition can be transported. Note that opening
                  this address usually blocks until a client connects.
                  Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4,IP6
                  Useful options: fork, bind, range, pf
                  See also: UDP, UDP4-LISTEN, UDP6-LISTEN, TCP-LISTEN
    
           **UDP4-LISTEN: <port>**
                  Like UDP-LISTEN, but only support IPv4 protocol.
                  Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP4
    
           **UDP6-LISTEN: <port>**
                  Like UDP-LISTEN, but only support IPv6 protocol.
                  Option groups: FD,SOCKET,LISTEN,CHILD,RANGE,IP6
    
           **UDP-SENDTO: <host>:<port>**
                  Communicates with the specified peer socket, defined by
                  <port> [UDP service] on <host> [IP address], using UDP/IP
                  version 4 or 6 depending on address specification, name
                  resolution, or option pf. It sends packets to and receives
                  packets from that peer socket only.  This address
                  effectively implements a datagram client.  It works well
                  with socat UDP-RECVFROM and UDP-RECV address peers.  When
                  the peer might send data first, UDP-DATAGRAM is preferable.
                  Option groups: FD,SOCKET,IP4,IP6
                  Useful options: ttl, tos, bind, sourceport, pf
                  See also: UDP4-SENDTO, UDP6-SENDTO, UDP-RECVFROM, UDP-RECV,
                  UDP-CONNECT, UDP-LISTEN, IP-SENDTO
    
           **UDP4-SENDTO: <host>:<port>**
                  Like UDP-SENDTO, but only supports IPv4 protocol.
                  Option groups: FD,SOCKET,IP4
    
           **UDP6-SENDTO: <host>:<port>**
                  Like UDP-SENDTO, but only supports IPv6 protocol.
                  Option groups: FD,SOCKET,IP6
    
           **UDP-RECVFROM: <port>**
                  Creates a UDP socket on <port> [UDP service] using UDP/IP
                  version 4 or 6 depending on option pf.  It receives one
                  packet from an unspecified peer and may send one or more
                  answer packets to that peer. This mode is particularly
                  useful with fork option where each arriving packet - from
                  arbitrary peers - is handled by its own sub process. This
                  allows a behaviour similar to typical UDP based servers
                  like ntpd or named. This address works well with socat
                  UDP-SENDTO address peers.
                  Note: When the second address fails before entering the
                  transfer loop the packet is dropped. Use option retry or
                  forever on the second address to avoid data loss.  When you
                  know the peer address, UDP-DATAGRAM is preferable.
                  Option groups: FD,SOCKET,IP4,IP6,CHILD,RANGE
                  Useful options: fork, ttl, tos, bind, sourceport, pf
                  See also: UDP4-RECVFROM, UDP6-RECVFROM, UDP-SENDTO,
                  UDP-RECV, UDP-CONNECT, UDP-LISTEN, IP-RECVFROM,
                  UNIX-RECVFROM
    
           **UDP4-RECVFROM: <port>**
                  Like UDP-RECVFROM, but only supports IPv4 protocol.
                  Option groups: FD,SOCKET,IP4,CHILD,RANGE
    
           **UDP6-RECVFROM: <port>**
                  Like UDP-RECVFROM, but only supports IPv6 protocol.
                  Option groups: FD,SOCKET,IP6,CHILD,RANGE
    
           **UDP-RECV: <port>**
                  Creates a UDP socket on <port> [UDP service] using UDP/IP
                  version 4 or 6 depending on option pf.  It receives packets
                  from multiple unspecified peers and merges the data.  No
                  replies are possible. It works well with, e.g., socat
                  UDP-SENDTO address peers; it behaves similar to a syslog
                  server.
                  This is a read-only address, see options -u and -U, and
                  dual addresses.
                  Note: if you need the fork option, use UDP-RECVFROM in
                  unidirectional mode (with option -u) instead.
                  Option groups: FD,SOCKET,IP4,IP6,RANGE
                  Useful options: pf, bind, sourceport, ttl, tos
                  See also: UDP4-RECV, UDP6-RECV, UDP-SENDTO, UDP-RECVFROM,
                  UDP-CONNECT, UDP-LISTEN, IP-RECV, UNIX-RECV
    
           **UDP4-RECV: <port>**
                  Like UDP-RECV, but only supports IPv4 protocol.
                  Option groups: FD,SOCKET,IP4,RANGE
    
           **UDP6-RECV: <port>**
                  Like UDP-RECV, but only supports IPv6 protocol.
                  Option groups: FD,SOCKET,IP6,RANGE
    
           **UDPLITE-CONNECT: <host>:<port>**
    
           **UDPLITE4-CONNECT: <host>:<port>**
    
           **UDPLITE6-CONNECT: <host>:<port>**
    
           **UDPLITE-DATAGRAM: <address>:<port>**
    
           **UDPLITE4-DATAGRAM: <address>:<port>**
    
           **UDPLITE6-DATAGRAM: <address>:<port>**
    
           **UDPLITE-LISTEN: <port>**
    
           **UDPLITE4-LISTEN: <port>**
    
           **UDPLITE6-LISTEN: <port>**
    
           **UDPLITE-SENDTO: <host>:<port>**
    
           **UDPLITE4-SENDTO: <host>:<port>**
    
           **UDPLITE6-SENDTO: <host>:<port>**
    
           **UDPLITE-RECVFROM: <port>**
    
           **UDPLITE4-RECVFROM: <port>**
    
           **UDPLITE6-RECVFROM: <port>**
    
           **UDPLITE-RECV: <port>**
    
           **UDPLITE4-RECV: <port>**
    
           **UDPLITE6-RECV: <port>**
                  The UDPLITE addresses are almost identical to the related
                  UDP addresses but they use UDP-Lite protocol and have the
                  additional UDPLITE option group.
    
           **UNIX-CONNECT: <filename>**
                  Connects to <filename> assuming it is a UNIX domain socket.
                  If <filename> does not exist, this is an error; if
                  <filename> is not a UNIX domain socket, this is an error;
                  if <filename> is a UNIX domain socket, but no process is
                  listening, this is an error.
                  Option groups: FD,SOCKET,NAMED,RETRY,UNIX
                  ) Useful options: bind
                  See also: UNIX-LISTEN, UNIX-SENDTO, TCP
    
           **UNIX-LISTEN: <filename>**
                  Listens on <filename> using a UNIX domain stream socket and
                  accepts a connection.  If <filename> exists and is not a
                  socket, this is an error.  If <filename> exists and is a
                  UNIX domain socket, binding to the address fails (use
                  option unlink-early!).  Note that opening this address
                  usually blocks until a client connects.  Beginning with
                  socat version 1.4.3, the file system entry is removed when
                  this address is closed (but see option unlink-close)
                  (example).
                  Option groups: FD,SOCKET,NAMED,LISTEN,CHILD,RETRY,UNIX
                  Useful options: fork, umask, mode, user, group,
                  unlink-early
                  See also: UNIX-CONNECT, UNIX-RECVFROM, UNIX-RECV,
                  TCP-LISTEN
    
           **UNIX-SENDTO: <filename>**
                  Communicates with the specified peer socket, defined by
                  [<filename>] assuming it is a UNIX domain datagram socket.
                  It sends packets to and receives packets from that peer
                  socket only.  Please note that it might be necessary to
                  bind the local socket to an address (e.g. /tmp/sock1, which
                  must not exist before).  This address type works well with
                  socat UNIX-RECVFROM and UNIX-RECV address peers.
                  Option groups: FD,SOCKET,NAMED,UNIX
                  Useful options: bind
                  See also: UNIX-RECVFROM, UNIX-RECV, UNIX-CONNECT,
                  UDP-SENDTO, IP-SENDTO
    
           **UNIX-RECVFROM: <filename>**
                  Creates a UNIX domain datagram socket [<filename>].
                  Receives one packet and may send one or more answer packets
                  to that peer.  This mode is particularly useful with fork
                  option where each arriving packet - from arbitrary peers -
                  is handled by its own sub process.  This address works well
                  with socat UNIX-SENDTO address peers.
                  Option groups: FD,SOCKET,NAMED,CHILD,UNIX
                  See the note about RECVFROM addresses.
                  Useful options: fork
                  umask
                  See also: UNIX-SENDTO, UNIX-RECV, UNIX-LISTEN,
                  UDP-RECVFROM, IP-RECVFROM
    
           **UNIX-RECV: <filename>**
                  Creates a UNIX domain datagram socket [<filename>].
                  Receives packets from multiple unspecified peers and merges
                  the data.  No replies are possible, this is a read-only
                  address, see options -u and -U, and dual addresses.  It can
                  be, e.g., addressed by socat UNIX-SENDTO address peers.  It
                  behaves similar to a syslog server.
                  Option groups: FD,SOCKET,NAMED,UNIX
                  Useful options: umask
                  See also: UNIX-SENDTO, UNIX-RECVFROM, UNIX-LISTEN,
                  UDP-RECV, IP-RECV
    
           **UNIX-CLIENT: <filename>**
                  Communicates with the specified peer socket, defined by
                  [<filename>] assuming it is a UNIX domain socket.  It first
                  tries to connect and, if that fails, assumes it is a
                  datagram socket, thus supporting both types.
                  Option groups: FD,SOCKET,NAMED,UNIX
                  Useful options: bind
                  See also: UNIX-CONNECT, UNIX-SENDTO, GOPEN
    
           **VSOCK-CONNECT: <cid>:<port>**
                  Establishes a VSOCK stream connection to the specified
                  <cid> [VSOCK cid] and <port> [VSOCK port].
                  Option groups: FD,SOCKET,CHILD,RETRY
                  Useful options: bind, connect-timeout, retry, readbytes
                  See also: VSOCK-LISTEN,
    
           **VSOCK-LISTEN: <port>**
                  Listens on <port> [VSOCK port] and accepts a VSOCK
                  connection.  Note that opening this address usually blocks
                  until a client connects.
                  Option groups: FD,SOCKET,LISTEN,CHILD,RETRY
                  Useful options: fork, bind, max-children, backlog, su,
                  reuseaddr, retry
                  See also: VSOCK-CONNECT
    
           **ABSTRACT-CONNECT: <string>**
    
           **ABSTRACT-LISTEN: <string>**
    
           **ABSTRACT-SENDTO: <string>**
    
           **ABSTRACT-RECVFROM: <string>**
    
           **ABSTRACT-RECV: <string>**
    
           **ABSTRACT-CLIENT: <string>**
                  The ABSTRACT addresses are almost identical to the related
                  UNIX addresses except that they do not address file system
                  based sockets but an alternate UNIX domain address space.
                  To achieve this the socket address strings are prefixed
                  with "\0" internally. This feature is available (only?) on
                  Linux.  Option groups are the same as with the related UNIX
                  addresses, except that the ABSTRACT addresses are not
                  member of the NAMED group.
                  Useful options: netns
    


## ADDRESS OPTIONS



           Address options can be applied to address specifications to
           influence the process of opening the addresses and the properties
           of the resulting data channels.
    
           For technical reasons not every option can be applied to every
           address type; e.g., applying a socket option to a regular file
           will fail. To catch most useless combinations as early as in the
           open phase, the concept of _option groups_ was introduced. Each
           option belongs to one or more option groups. Options can be used
           only with address types that support at least one of their option
           groups (but see option -g).
    
           Address options have data types that their values must conform to.
           Every address option consists of just a keyword or a keyword
           followed by "=value", where value must conform to the options
           type.  Some address options manipulate parameters of system calls;
           e.g., option sync sets the O_SYNC flag with the open() call.
           Other options cause a system or library call; e.g., with option
           `ttl=value’ the setsockopt(fd, SOL_IP, IP_TTL, value, sizeof(int))
           call is applied.  Other options set internal **socat** variables that
           are used during data transfer; e.g., `crnl’ causes explicit
           character conversions.  A few options have more complex
           implementations; e.g., su-d (substuser-delayed) inquires some user
           and group infos, stores them, and applies them later after a
           possible chroot() call.
    
           If multiple options are given to an address, their sequence in the
           address specification has (almost) no effect on the sequence of
           their execution/application. Instead, **socat** has built in an _option_
           _phase_ model that tries to bring the options in a useful order.
           Some options exist in different forms (e.g., unlink, unlink-early,
           unlink-late) to control the time of their execution.
    
           If the same option is specified more than once within one address
           specification, with equal or different values, the effect depends
           on the kind of option. Options resulting in function calls like
           setsockopt() cause multiple invocations. With options that set
           parameters for a required call like open() or set internal flags,
           the value of the last option occurrence is effective.
    
           The existence or semantics of many options are system dependent.
           **Socat** usually does NOT try to emulate missing libc or kernel
           features, it just provides an interface to the underlying system.
           So, if an operating system lacks a feature, the related option is
           simply not available on this platform.
    
           The following paragraphs introduce just the more common address
           options. For a more comprehensive reference and to find
           information about canonical option names, alias names, option
           phases, and platforms see file **xio.help**.
    
           **FD option group**
    
           This option group contains options that are applied to a UN*X
           style file descriptor, no matter how it was generated.  Because
           all current **socat** address types are file descriptor based, these
           options may be applied to any address.
           Note: Some of these options are also member of another option
           group, that provides another, non-fd based mechanism.  For these
           options, it depends on the actual address type and its option
           groups which mechanism is used. The second, non-fd based mechanism
           is prioritized.
    
           **cloexec[= <bool>]**
                  Sets the FD_CLOEXEC flag with the fcntl() system call to
                  value <bool>. If set, the file descriptor is closed on
                  exec() family function calls. **Socat** internally handles this
                  flag for the fds it controls, so in most cases there will
                  be no need to apply this option.
    
           **setlk[= <bool>]**
                  Tries to set a discretionary write lock to the whole file
                  using the fcntl(fd, F_SETLK, ...)  system call. If the file
                  is already locked, this call results in an error.  On
                  Linux, when the file permissions for group are "S"
                  (g-x,g+s), and the file system is locally mounted with the
                  "mand" option, the lock is mandatory, i.e. prevents other
                  processes from opening the file.
    
           **setlkw[= <bool>]**
                  Tries to set a discretionary waiting write lock to the
                  whole file using the fcntl(fd, F_SETLKW, ...)  system call.
                  If the file is already locked, this call blocks.  See
                  option setlk for information about making this lock
                  mandatory.
    
           **setlk-rd[= <bool>]**
                  Tries to set a discretionary read lock to the whole file
                  using the fcntl(fd, F_SETLK, ...)  system call. If the file
                  is already write locked, this call results in an error.
                  See option setlk for information about making this lock
                  mandatory.
    
           **setlkw-rd[= <bool>]**
                  Tries to set a discretionary waiting read lock to the whole
                  file using the fcntl(fd, F_SETLKW, ...)  system call. If
                  the file is already write locked, this call blocks.  See
                  option setlk for information about making this lock
                  mandatory.
    
           **flock-ex[= <bool>]**
                  Tries to set a blocking exclusive advisory lock to the file
                  using the flock(fd, LOCK_EX) system call. **Socat** hangs in
                  this call if the file is locked by another process.
    
           **flock-ex-nb[= <bool>]**
                  Tries to set a nonblocking exclusive advisory lock to the
                  file using the flock(fd, LOCK_EX|LOCK_NB) system call. If
                  the file is already locked, this option results in an
                  error.
    
           **flock-sh[= <bool>]**
                  Tries to set a blocking shared advisory lock to the file
                  using the flock(fd, LOCK_SH) system call. **Socat** hangs in
                  this call if the file is locked by another process.
    
           **flock-sh-nb[= <bool>]**
                  Tries to set a nonblocking shared advisory lock to the file
                  using the flock(fd, LOCK_SH|LOCK_NB) system call. If the
                  file is already locked, this option results in an error.
    
           **lock[= <bool>]**
                  Sets a blocking lock on the file. Uses the setlk or flock
                  mechanism depending on availability on the particular
                  platform. If both are available, the POSIX variant (setlkw)
                  is used.
    
           **user= <user>**
                  Sets the <user> (owner) of the stream.  If the address is
                  member of the NAMED option group, **socat** uses the chown()
                  system call after opening the file or binding to the UNIX
                  domain socket (race condition!).  Without filesystem entry,
                  **socat** sets the user of the stream using the fchown() system
                  call.  These calls might require root privilege.
    
           **user-late= <user>**
                  Sets the owner of the fd to <user> with the fchown() system
                  call after opening or connecting the channel.  This is
                  useful only on file system entries.
    
           **group= <group>**
                  Sets the <group> of the stream.  If the address is member
                  of the NAMED option group, **socat** uses the chown() system
                  call after opening the file or binding to the UNIX domain
                  socket (race condition!).  Without filesystem entry, **socat**
                  sets the group of the stream with the fchown() system call.
                  These calls might require group membership or root
                  privilege.
    
           **group-late= <group>**
                  Sets the group of the fd to <group> with the fchown()
                  system call after opening or connecting the channel.  This
                  is useful only on file system entries.
    
           **mode= <mode>**
                  Sets the <mode> [mode_t] (permissions) of the stream.  If
                  the address is member of the NAMED option group and uses
                  the open() or creat() call, the mode is applied with these.
                  If the address is member of the NAMED option group without
                  using these system calls, **socat** uses the chmod() system
                  call after opening the filesystem entry or binding to the
                  UNIX domain socket (race condition!).  Otherwise, **socat**
                  sets the mode of the stream using fchmod() which, btw,
                  might not have any effect.
                  These calls might require ownership or root privilege.
                  Note: this option can only tighten the permissions implied
                  by processes umask. See option umask to loosen permissions.
    
           **perm-late= <mode>**
                  Sets the permissions of the fd to value <mode> [mode_t]
                  using the fchmod() system call after opening or connecting
                  the channel.  This is useful only on file system entries.
    
           **append[= <bool>]**
                  Always writes data to the actual end of file.  If the
                  address is member of the OPEN option group, **socat** uses the
                  O_APPEND flag with the open() system call (example).
                  Otherwise, **socat** applies the fcntl(fd, F_SETFL, O_APPEND)
                  call.
    
           **nonblock[= <bool>]**
                  Tries to open or use file in nonblocking mode. Its only
                  effects are that the connect() call of TCP addresses does
                  not block, and that opening a named pipe for reading does
                  not block.  If the address is member of the OPEN option
                  group, **socat** uses the O_NONBLOCK flag with the open()
                  system call.  Otherwise, **socat** applies the fcntl(fd,
                  F_SETFL, O_NONBLOCK) call.
    
           **binary[= <bool>]**
                  Opens the file in binary mode to avoid implicit line
                  terminator conversions (Cygwin).
    
           **text[= <bool>]**
                  Opens the file in text mode to force implicit line
                  terminator conversions (Cygwin).
    
           **noinherit[= <bool>]**
                  Does not keep this file open in a spawned process (Cygwin).
    
           **cool-write[= <bool>]**
                  Takes it easy when write fails with EPIPE or ECONNRESET and
                  logs the message with _notice_ level instead of _error_.  This
                  prevents the log file from being filled with useless error
                  messages when **socat** is used as a high volume server or
                  proxy where clients often abort the connection. Use this
                  option only with option fork because otherwise it might
                  cause **socat** to exit with code 0 even on failure.
                  This option is deprecated, consider using option
                  children-shutup instead.
    
           **end-close[= <bool>]**
                  Changes the (address dependent) method of ending a
                  connection to just close the file descriptors. This is
                  useful when the connection is to be reused by or shared
                  with other processes (example).
                  Normally, socket connections will be ended with shutdown(2)
                  which terminates the socket even if it is shared by
                  multiple processes.  close(2) "unlinks" the socket from the
                  process but keeps it active as long as there are still
                  links from other processes.
                  Similarly, when an address of type EXEC or SYSTEM is ended,
                  socat usually will explicitly kill the sub process. With
                  this option, it will just close the file descriptors.
    
           **shut-none[= <bool>]**
                  Changes the (address dependent) method of shutting down the
                  write part of a connection to not do anything.
    
           **shut-down[= <bool>]**
                  Changes the (address dependent) method of shutting down the
                  write part of a connection to shutdown(fd, SHUT_WR). Is
                  only useful with sockets.
    
           **shut-close[= <bool>]**
                  Changes the (address dependent) method of shutting down the
                  write part of a connection to close(fd).
    
           **shut-null[= <bool>]**
                  When one address indicates EOF, **socat** will send a zero
                  sized packet to the write channel of the other address to
                  transfer the EOF condition. This is useful with UDP and
                  other datagram protocols. Has been tested against netcat
                  and socat with option null-eof.
    
           **null-eof[= <bool>]**
                  Normally **socat** will ignore empty (zero size payload)
                  packets arriving on datagram sockets, so it survives port
                  scans. With this option **socat** interprets empty datagram
                  packets as EOF indicator (see shut-null).
    
           **ioctl-void= <request>**
                  Calls ioctl() with the request value as second argument and
                  NULL as third argument. This option allows utilizing ioctls
                  that are not explicitly implemented in socat.
    
           **ioctl-int= <request>:<value>**
                  Calls ioctl() with the request value as second argument and
                  the integer value as third argument.
    
           **ioctl-intp= <request>:<value>**
                  Calls ioctl() with the request value as second argument and
                  a pointer to the integer value as third argument.
    
           **ioctl-bin= <request>:<value>**
                  Calls ioctl() with the request value as second argument and
                  a pointer to the given data value as third argument. This
                  data must be specified in <dalan> form.
    
           **ioctl-string= <request>:<value>**
                  Calls ioctl() with the request value as second argument and
                  a pointer to the given string as third argument.  <dalan>
                  form.
    
           **NAMED option group**
    
           These options work on file system entries.
           Please note that, with UNIX domain client addresses, this means
           the bind entry, not the target/peer entry.
           See also options user, group, and mode.
    
           **user-early= <user>**
                  Changes the <user> (owner) of the file system entry before
                  accessing it, using the chown() system call. This call
                  might require root privilege.
    
           **group-early= <group>**
                  Changes the <group> of the file system entry before
                  accessing it, using the chown() system call. This call
                  might require group membership or root privilege.
    
           **perm-early= <mode>**
                  Changes the <mode> [mode_t] of the file system entry before
                  accessing it, using the chmod() system call. This call
                  might require ownership or root privilege.
    
           **unlink-early[= <bool>]**
                  Unlinks (removes) the file before opening it and even
                  before applying user-early etc.
    
           **unlink[= <bool>]**
                  Unlinks (removes) the file before accessing it, but after
                  user-early etc.
    
           **unlink-late[= <bool>]**
                  Unlinks (removes) the file after opening it to make it
                  inaccessible for other processes after a short race
                  condition.
    
           **unlink-close[= <bool>]**
                  Controls removal of the addresses file system entry when
                  closing the address.  For named pipes, UNIX domain sockets,
                  and the symbolic links of pty addresses, the default is
                  remove (1); for created files, opened files, and generic
                  opened files the default is keep (0).  Setting this option
                  to 1 removes the entry, 0 keeps it. No value means 1.
    
           **OPEN option group**
    
           The OPEN group options allow setting flags with the open() system
           call.  E.g., option `creat’ sets the O_CREAT flag. When the used
           address does not use open() (e.g.STDIO), the fcntl(..., F_SETFL,
           ...)  call is used instead.
           See also options append and nonblock.
    
           **creat[= <bool>]**
                  Creates the file if it does not exist (example).
    
           **dsync[= <bool>]**
                  Blocks write() calls until metainfo is physically written
                  to media.
    
           **excl[= <bool>]**
                  With option creat, if file exists this is an error.
    
           **largefile[= <bool>]**
                  On 32 bit systems, allows a file larger than 2^31 bytes.
    
           **noatime[= <bool>]**
                  Sets the O_NOATIME options, so reads do not change the
                  access timestamp.
    
           **noctty[= <bool>]**
                  Does not make this file the controlling terminal.
    
           **nofollow[= <bool>]**
                  Does not follow symbolic links.
    
           **nshare[= <bool>]**
                  Does not allow sharing this file with other processes.
    
           **rshare[= <bool>]**
                  Does not allow other processes to open this file for
                  writing.
    
           **rsync[= <bool>]**
                  Blocks write() until metainfo is physically written to
                  media.
    
           **sync[= <bool>]**
                  Blocks write() until data is physically written to media.
    
           **rdonly[= <bool>]**
                  Opens the file for reading only.
    
           **wronly[= <bool>]**
                  Opens the file for writing only.
    
           **trunc[= <bool>]**
                  Truncates the file to size 0 during opening it.
    
           **REG and BLK option group**
    
           These options are usually applied to a UN*X file descriptor, but
           their semantics make sense only on a file supporting random
           access.
    
           **seek= <offset>**
                  Applies the lseek(fd, <offset>, SEEK_SET) (or lseek64 )
                  system call, thus positioning the file pointer absolutely
                  to <offset> [off_t or off64_t]. Please note that a missing
                  value defaults to 1, not 0.
    
           **seek-cur= <offset>**
                  Applies the lseek(fd, <offset>, SEEK_CUR) (or lseek64 )
                  system call, thus positioning the file pointer <offset>
                  [off_t or off64_t] bytes relatively to its current position
                  (which is usually 0). Please note that a missing value
                  defaults to 1, not 0.
    
           **seek-end= <offset>**
                  Applies the lseek(fd, <offset>, SEEK_END) (or lseek64 )
                  system call, thus positioning the file pointer <offset>
                  [off_t or off64_t] bytes relatively to the files current
                  end. Please note that a missing value defaults to 1, not 0.
    
           **ftruncate= <offset>**
                  Applies the ftruncate(fd, <offset>) (or ftruncate64 if
                  available) system call, thus truncating the file at the
                  position <offset> [off_t or off64_t]. Please note that a
                  missing value defaults to 1, not 0.
    
           **secrm[= <bool>]**
    
           **unrm[= <bool>]**
    
           **compr[= <bool>]**
    
           **fs-sync[= <bool>]**
    
           **immutable[= <bool>]**
    
           **fs-append[= <bool>]**
    
           **nodump[= <bool>]**
    
           **fs-noatime[= <bool>]**
    
           **journal-data[= <bool>]**
    
           **notail[= <bool>]**
    
           **dirsync[= <bool>]**
                  These options change non standard file attributes on
                  operating systems and file systems that support these
                  features, like Linux with ext2fs and successors, xfs, or
                  reiserfs. See man 1 chattr for information on these
                  options. Please note that there might be a race condition
                  between creating the file and applying these options.
    
           **PIPE options**
    
           These options may be applied to pipes (fifos).
    
           **f-setpipe-sz= <int>**
    
           **setpipe= <int>**
                  Set the number of bytes a pipe can buffer. Where more bytes
                  are written the writing process might block. When more
                  bytes are written in a single write() the writing process
                  blocks and might never recover.
    
           **General address options**
    
           These options may be applied to all address types. They change
           some process properties that are restored after opening the
           address.
    
           **chdir= <filename>**
    
           **cd= <filename>**
                  Changes the working directory. After opening the address
                  the master process changes back to the original working
                  directory. Sub processes inherit the temporary setting.
    
           **umask= <mode>**
                  Sets the umask of the process to <mode> [mode_t] before
                  opening the address. Useful when file system entries are
                  created or a shell or program is invoked. Usually the value
                  is specified as octal number with leading ’0’.
                  The processes umask value is inherited by child processes.
                  Note: umask is an inverted value: creating a file with
                  umask=0026 results in permissions 0640.
    
           **PROCESS option group**
    
           Options of this group change the process properties instead of
           just affecting one data channel.  For EXEC and SYSTEM addresses
           and for LISTEN and CONNECT type addresses with option fork, these
           options apply to the child processes instead of the main **socat**
           process.
    
           **chroot= <directory>**
                  Performs a chroot() operation to <directory> after
                  processing the address (example). This call might require
                  root privilege.
    
           **chroot-early= <directory>**
                  Performs a chroot() operation to <directory> before opening
                  the address. This call might require root privilege.
    
           **setgid= <group>**
                  Changes the primary <group> of the process after processing
                  the address. This call might require root privilege. Please
                  note that this option does not drop other group related
                  privileges.
    
           **setgid-early= <group>**
                  Like setgid but is performed before opening the address.
    
           **setuid= <user>**
                  Changes the <user> (owner) of the process after processing
                  the address. This call might require root privilege. Please
                  note that this option does not drop group related
                  privileges. Check if option su better fits your needs.
    
           **setuid-early= <user>**
                  Like setuid but is performed before opening the address.
    
           **su= <user>**
                  Changes the <user> (owner) and groups of the process after
                  processing the address (example). This call might require
                  root privilege.
    
           **su-d= <user>**
                  Short name for substuser-delayed.  Changes the <user>
                  (owner) and groups of the process after processing the
                  address (example).  The user and his groups are retrieved
                  _before_ a possible chroot() . This call might require root
                  privilege.
    
           **setpgid= <pid_t>**
                  Makes the process a member of the specified process group
                  <pid_t>. If no value is given, or if the value is 0 or 1,
                  the process becomes leader of a new process group.
    
           **setsid** Makes the process the leader of a new session (example).
    
           **netns= <net-namespace-name>**
                  Before opening the address it tries to switch to the named
                  network namespace.  After opening the address it switches
                  back to the previous namespace (example with TCP forwarder,
                  example with virtual network connection).
                  Only on Linux; requires root; use option --experimental.
    
           **READLINE option group**
    
           These options apply to the readline address type.
    
           **history= <filename>**
                  Reads and writes history from/to <filename> (example).
    
           **noprompt**
                  Since version 1.4.0, socat per default tries to determine a
                  prompt - that is then passed to the readline call - by
                  remembering the last incomplete line of the output. With
                  this option, socat does not pass a prompt to readline, so
                  it begins line editing in the first column of the terminal.
    
           **noecho= <pattern>**
                  Specifies a regular pattern for a prompt that prevents the
                  following input line from being displayed on the screen and
                  from being added to the history.  The prompt is defined as
                  the text that was output to the readline address after the
                  last newline character and before an input character was
                  typed. The pattern is a regular expression, e.g.
                  "^[Pp]assword:.*$" or "([Uu]ser:|[Pp]assword:)". See
                  regex(7) for details.  (example)
    
           **prompt= <string>**
                  Passes the string as prompt to the readline function.
                  readline prints this prompt when stepping through the
                  history. If this string matches a constant prompt issued by
                  an interactive program on the other socat address,
                  consistent look and feel can be achieved.
    
           **APPLICATION option group**
    
           This group contains options that work at data level.  Note that
           these options only apply to the "raw" data transferred by socat,
           but not to protocol data used by addresses like PROXY.
    
           **cr** Converts the default line termination character NL (’\n’,
                  0x0a) to/from CR (’\r’, 0x0d) when writing/reading on this
                  channel.
    
           **crnl** Converts the default line termination character NL (’\n’,
                  0x0a) to/from CRNL ("\r\n", 0x0d0a) when writing/reading on
                  this channel (example).  Note: socat simply strips all CR
                  characters.
    
           **ignoreeof**
                  When EOF occurs on this channel, **socat** ignores it and tries
                  to read more data (like "tail -f") (example).
    
           **readbytes= <bytes>**
                  **socat** reads only so many bytes from this address (the
                  address provides only so many bytes for transfer and
                  pretends to be at EOF afterwards).  Must be greater than 0.
    
           **lockfile= <filename>**
                  If lockfile exists, exits with error. If lockfile does not
                  exist, creates it and continues, unlinks lockfile on exit.
    
           **waitlock= <filename>**
                  If lockfile exists, waits until it disappears. When
                  lockfile does not exist, creates it and continues, unlinks
                  lockfile on exit.
    
           **escape= <int>**
                  Specifies the numeric code of a character that triggers EOF
                  on the input stream. It is useful with a terminal in raw
                  mode (example).
    
           **SOCKET option group**
    
           These options are intended for all kinds of sockets, e.g. IP or
           UNIX domain. Most are applied with a setsockopt() call.
    
           **bind= <sockname>**
                  Binds the socket to the given socket address using the
                  bind() system call. The form of <sockname> is socket domain
                  dependent: IP4 and IP6 allow the form
                  [hostname|hostaddress][:(service|port)] (example), VSOCK
                  allows the form [cid][:(port)].
                  See also: unix-bind-tempname
    
           **connect-timeout= <seconds>**
                  Abort the connection attempt after <seconds> [timeval] with
                  error status.
    
           **so-bindtodevice= <interface>**
                  Binds the socket to the given <interface>.  This option
                  might require root privilege.
    
           **broadcast**
                  For datagram sockets, allows sending to broadcast addresses
                  and receiving packets addressed to broadcast addresses.
    
           **debug** Enables socket debugging.
    
           **dontroute**
                  Only communicates with directly connected peers, does not
                  use routers.
    
           **keepalive**
                  Enables sending keepalives on the socket.
    
           **linger= <seconds>**
                  Blocks shutdown() or close() until data transfers have
                  finished or the given timeout [int] expired.
    
           **oobinline**
                  Places out-of-band data in the input data stream.
    
           **priority= <priority>**
                  Sets the protocol defined <priority> [<int>] for outgoing
                  packets.
    
           **rcvbuf= <bytes>**
                  Sets the size of the receive buffer after the socket() call
                  to <bytes> [int].  With TCP sockets, this value corresponds
                  to the socket’s maximal window size.
    
           **rcvbuf-late= <bytes>**
                  Sets the size of the receive buffer when the socket is
                  already connected to <bytes> [int].  With TCP sockets, this
                  value corresponds to the socket’s maximal window size.
    
           **so-rcvtimeo= <time>, rcvtimeo=<time>**
                  Specifies the time [int] until recv() , read() etc.
                  functions timeout when no data is received. Note that in
                  the transfer phase **socat** only calls these functions when
                  select() has reported that data is available. However this
                  option is useful with DTLS addresses to timeout during
                  connection negotiation.
    
           **so-sndtimeo= <time>, sndtimeo=<time>**
                  Like so-recvtimeo, but for send . Not usecase known.
    
           **rcvlowat= <bytes>**
                  Specifies the minimum number of received bytes [int] until
                  the socket layer will pass the buffered data to **socat**.
    
           **reuseaddr[=[0|1]]**
                  Allows other sockets to bind to an address even if parts of
                  it (e.g. the local port) are already in use by **socat**.
                  With version 1.8.0, this socket option is set automatically
                  for TCP LISTEN addresses. If you prefer the system default
                  (no related setsockopt(...SO_REUSEADDR...) call at all),
                  use form reuseaddr=.
                  (example).
    
           **sndbuf= <bytes>**
                  Sets the size of the send buffer after the socket() call to
                  <bytes> [int].
    
           **sndbuf-late= <bytes>**
                  Sets the size of the send buffer when the socket is
                  connected to <bytes> [int].
    
           **sndlowat= <bytes>**
                  Specifies the minimum number of bytes in the send buffer
                  until the socket layer will send the data to <bytes> [int].
    
           **pf= <string>**
                  Forces the use of the specified IP version or protocol.
                  <string> can be something like "ip4" or "ip6". The
                  resulting value is used as first argument to the socket()
                  or socketpair() calls.  This option affects address
                  resolution and the required syntax of bind and range
                  options.
    
           **socktype= <type>**
                  Sets the type of the socket, specified as second argument
                  to the socket() or socketpair() calls, to <type> [int].
                  Address resolution is not affected by this option.  Under
                  Linux, 1 means stream oriented socket, 2 means datagram
                  socket, 3 means raw socket, and 5 seqpacket (stream keeping
                  packet boundaries).  Datagrams are useful when you want to
                  keep packet boundaries.
    
           **protocol**
                  Sets the protocol of the socket, specified as third
                  argument to the socket() or socketpair() calls, to
                  <protocol> [int]. Address resolution is not affected by
                  this option.  6 means TCP, 17 means UDP.
    
           **reuseport**
                  Set the SO_REUSEPORT socket option.
    
           **so-timestamp**
                  Sets the SO_TIMESTAMP socket option. This enables receiving
                  and logging of timestamp ancillary messages.
    
           **setsockopt= <level>:<optname>:<optval>**
                  Invokes setsockopt() for the socket with the given
                  parameters. level [int] is used as second argument to
                  setsockopt() and specifies the layer, e.g. SOL_TCP for TCP
                  (6 on Linux), or SOL_SOCKET for the socket layer (1 on
                  Linux). optname [int] is the third argument to setsockopt()
                  and tells which socket option is to be set. For the actual
                  numbers you might have to look up the appropriate include
                  files of your system. For the 4th and 5th setsockopt()
                  parameters, value [dalan] specifies an arbitrary sequence
                  of bytes that are passed to the function per pointer, with
                  the automatically derived length parameter.
    
           **setsockopt-int= <level>:<optname>:<optval>**
                  Like setsockopt, but <optval> is a pointer to int [int]
    
           **setsockopt-listen= <level>:<optname>:<optval>**
                  Like setsockopt, but for listen type addresses it is
                  applied to the listening socket instead of the connected
                  socket.
    
           **setsockopt-string= <level>:<optname>:<optval>**
                  Like setsockopt, but <optval> is a string.  This string is
                  passed to the function with trailing null character, and
                  the length parameter is automatically derived from the
                  data.
    
           **setsockopt-socket= <level>:<optname>:<optval>**
                  Like setsockopt, but is applied to the socket before other
                  operations ( bind() , connect() , accept() , ...)
    
           **setsockopt-connected= <level>:<optname>:<optval>**
                  Like setsockopt, but is applied only when the socket has
                  been connected by a connect() or listen() call.
    
           **UNIX option group**
    
           These options apply to UNIX domain based addresses.
    
           **bind-tempname[=/tmp/pre-XXXXXX],**
                  unix-bind-tempname[=/tmp/pre-XXXXXX]" Binds to a random
                  path or random address (on abstract namespace sockets).
                  This is useful with datagram client addresses (SENDTO, or
                  CLIENT) that are opened in child processes forked off from
                  a common parent process where the child processes cannot
                  have different bind options.  In the path X ’s get replaced
                  with a random character sequence similar to tempnam(3).
                  When no argument is given **socat** takes a default like
                  /tmp/fileXXXXXX .
    
           **unix-tightsocklen[=(0|1)]**
                  On socket operations, pass a socket address length that
                  does not include the whole struct sockaddr_un record but
                  (besides other components) only the relevant part of the
                  filename or abstract string. Default is 1.
    
           **IP4 and IP6 option groups**
    
           These options can be used with IPv4 and IPv6 based sockets.
    
           **tos= <tos>**
                  Sets the TOS (type of service) field of outgoing packets to
                  <tos> [byte] (see RFC 791).
    
           **ttl= <ttl>**
                  Sets the TTL (time to live) field of outgoing packets to
                  <ttl> [byte].
    
           **ip-options= <data>**
                  Sets IP options like source routing. Must be given in
                  binary form, recommended format is a leading "x" followed
                  by an even number of hex digits. This option may be used
                  multiple times, data are appended.  E.g., to connect to
                  host 10.0.0.1 via some gateway using a loose source route,
                  use the gateway as address parameter and set a loose source
                  route using the option ip-options=x8307040a000001 .
                  IP options are defined in RFC 791.
    
           **mtudiscover= <0|1|2>**
                  Takes 0, 1, 2 to never, want, or always use path MTU
                  discover on this socket.
    
           **ip-pktinfo**
                  Sets the IP_PKTINFO socket option. This enables receiving
                  and logging of ancillary messages containing destination
                  address and interface (Linux) (example).
    
           **ip-recverr**
                  Sets the IP_RECVERR socket option. This enables receiving
                  and logging of ancillary messages containing detailed error
                  information.
    
           **ip-recvopts**
                  Sets the IP_RECVOPTS socket option. This enables receiving
                  and logging of IP options ancillary messages (Linux, *BSD).
    
           **ip-recvtos**
                  Sets the IP_RECVTOS socket option. This enables receiving
                  and logging of TOS (type of service) ancillary messages
                  (Linux).
    
           **ip-recvttl**
                  Sets the IP_RECVTTL socket option. This enables receiving
                  and logging of TTL (time to live) ancillary messages
                  (Linux, *BSD).
    
           **ip-recvdstaddr**
                  Sets the IP_RECVDSTADDR socket option. This enables
                  receiving and logging of ancillary messages containing
                  destination address (*BSD) (example).
    
           **ip-recvif**
                  Sets the IP_RECVIF socket option. This enables receiving
                  and logging of interface ancillary messages (*BSD)
                  (example).
    
           **ip-add-membership= <multicast-address:interface-address>**
    
           **ip-add-membership= <multicast-address:interface-name>**
    
           **ip-add-membership= <multicast-address:interface-index>**
    
           **ip-add-membership= <multicast-address:interface-address:interface-name>**
    
           **ip-add-membership= <multicast-address:interface-address:interface-index>**
                  Makes the socket member of the specified multicast group.
                  This only works for IPv4, see ipv6-join-group for the IPv6
                  variant. The option takes the IP address of the multicast
                  group and info about the desired network interface. The
                  most common syntax is the first one, while the others are
                  only available on systems that provide struct mreqn
                  (Linux).
                  The indices of active network interfaces can be shown using
                  the utility **procan**.
    
           **ip-add-source-membership= <multicast-address:interface-address:source-address>**
                  Makes the socket member of the specified multicast group
                  for the specified source, i.e. only multicast traffic from
                  this address is to be delivered. This only works for IPv4,
                  see ipv6-join-source-group for the IPv6 variant. The option
                  takes the IP address of the multicast group, the IP address
                  of the desired network interface and the source IP address
                  of the multicast traffic.
    
           **ipv6-join-group= <multicast-address:interface-name>**
    
           **ipv6-join-group= <multicast-address:interface-index>**
                  Makes the socket member of the specified multicast group.
                  This only works for IPv6, see ip-add-membership for the
                  IPv4 variant. The option takes the IP address of the
                  multicast group and info about the desired network
                  interface.  The indices of active network interfaces can be
                  shown using the utility **procan**.
    
           **ipv6-join-source-group= <multicast-address:interface-name:source-address>**
    
           **ipv6-join-source-group= <multicast-address:interface-index:source-address>**
                  Makes the socket member of the specified multicast group
                  for the specified source, i.e. only multicast traffic from
                  this address is to be delivered. This only works for IPv6,
                  see ip-add-source-membership for the IPv4 variant. The
                  option takes the IP address of the multicast group, info
                  about the desired network interface and the source IP
                  address of the multicast traffic. The indices of active
                  network interfaces can be shown using the utility **procan**.
                  This feature is experimental.
    
           **ip-multicast-if= <hostname>**
                  Specifies hostname or address of the network interface to
                  be used for multicast traffic.
    
           **ip-multicast-loop[= <bool>]**
                  Specifies if outgoing multicast traffic should loop back to
                  the interface.
    
           **ip-multicast-ttl= <byte>**
                  Sets the TTL used for outgoing multicast traffic. Default
                  is 1.
    
           **ip-transparent**
                  Sets the IP_TRANSPARENT socket option.  This option might
                  require root privilege.
    
           **Resolver options**
    
           These options temporarily change the behaviour of hostname
           resolution. The options of form ai-* affect behaviour of the
           getaddrinfo() function that includes /etc/hosts and NIS based
           lookups.
    
           The addresses of form res-* only affect DNS lookups, and only when
           the result is not cached in nscd . These options might not work on
           all operating systems or libc implementations.
    
           **ai-addrconfig[=0|1]**
    
           **addrconfig[=0|1]**
                  Sets or unsets the AI_ADDRCONFIG flag to prevent name
                  resolution to address families that are not available on
                  the computer (e.g. IPv6). Default value is 1 in case the
                  resolver does not get an address family hint from Socat
                  address or defaults.
    
           **ai-passive[=0|1]**
    
           **passive[=0|1]**
                  Sets of unsets the AI_PASSIVE flag for getaddrinfo() calls.
                  Default is 1 for LISTEN, RECV, and RECVFROM type addresses,
                  and with bind option.
    
           **ai-v4mapped[=0|1]**
    
           **v4mapped[=0|1]**
                  Sets or unsets the AI_V4MAPPED flag for getaddrinfo() .
                  With **socat** addresses requiring IPv6 addresses, this
                  resolves IPv4 addresses to the appropriate IPv6 address
                  [::ffff:*:*]. For IPv6 **socat** addresses, the default is 1.
    
           **ai-all[=0|1]**
                  Sets or unsets the AI_ALL flag for getaddrinfo() .
    
           **res-debug**
    
           **res-aaonly**
    
           **res-usevc**
    
           **res-primary**
    
           **res-igntc**
    
           **res-recurse**
    
           **res-defnames**
    
           **res-stayopen**
    
           **res-dnsrch**
                  These options set the corresponding resolver (name
                  resolution) option flags.  Append "=0" to clear a default
                  option. See man resolver(5) for more information on these
                  options. **Socat** restores the old values after finishing the
                  open phase of the address, so these options are valid just
                  for the address they are applied to.
                  Please note that these flags only affect DNS resolution,
                  but not hosts or NIS based name resolution, and they have
                  no effect when (g)libc retrieves the results from nscd .
    
           **res-retrans= <int>**
                  Sets the retransmission time interval of the DNS resolver
                  (based on an undocumented feature).
    
           **res-retry= <int>**
                  Sets the number of retransmits of the DNS resolver (based
                  on an undocumented feature).
    
           **res-nsaddr= <ipaddr>[:<port>]**
                  Tries to overwrite nameserver settings loaded from
                  /etc/resolv.conf by writing the given IPv4 address into the
                  undocumented _res:nsaddr_list[0] field.  /etc/hosts is
                  still checked by resolver. Please note that glibc’s nscd is
                  always queried first when it is running!
    
           **IP6 option group**
    
           These options can only be used on IPv6 based sockets. See IP
           options for options that can be applied to both IPv4 and IPv6
           sockets.
    
           **ipv6only[= <bool>]**
                  Sets the IPV6_V6ONLY socket option. If 0, the TCP stack
                  will also accept connections using IPv4 protocol on the
                  same port. The default is system dependent.
    
           **ipv6-recvdstopts**
                  Sets the IPV6_RECVDSTOPTS socket option. This enables
                  receiving and logging of ancillary messages containing the
                  destination options.
    
           **ipv6-recvhoplimit**
                  Sets the IPV6_RECVHOPLIMIT socket option. This enables
                  receiving and logging of ancillary messages containing the
                  hoplimit.
    
           **ipv6-recvhopopts**
                  Sets the IPV6_RECVHOPOPTS socket option. This enables
                  receiving and logging of ancillary messages containing the
                  hop options.
    
           **ipv6-recvpktinfo**
                  Sets the IPV6_RECVPKTINFO socket option. This enables
                  receiving and logging of ancillary messages containing
                  destination address and interface.
    
           **ipv6-unicast-hops=link(TYPE_INT)( <int>)**
                  Sets the IPV6_UNICAST_HOPS socket option. This sets the hop
                  count limit (TTL) for outgoing unicast packets.
    
           **ipv6-recvrthdr**
                  Sets the IPV6_RECVRTHDR socket option. This enables
                  receiving and logging of ancillary messages containing
                  routing information.
    
           **ipv6-tclass**
                  Sets the IPV6_TCLASS socket option. This sets the transfer
                  class of outgoing packets.
    
           **ipv6-recvtclass**
                  Sets the IPV6_RECVTCLASS socket option. This enables
                  receiving and logging of ancillary messages containing the
                  transfer class.
    
           **TCP option group**
    
           These options may be applied to TCP sockets. They work by invoking
           setsockopt() with the appropriate parameters.
    
           **cork** Doesn’t send packets smaller than MSS (maximal segment
                  size).
    
           **defer-accept**
                  While listening, accepts connections only when data from
                  the peer arrived.
    
           **keepcnt= <count>**
                  Sets the number of keepalives before shutting down the
                  socket to <count> [int].
    
           **keepidle= <seconds>**
                  Sets the idle time before sending the first keepalive to
                  <seconds> [int].
    
           **keepintvl= <seconds>**
                  Sets the interval between two keepalives to <seconds>
                  [int].
    
           **linger2= <seconds>**
                  Sets the time to keep the socket in FIN-WAIT-2 state to
                  <seconds> [int].
    
           **mss= <bytes>**
                  Sets the MSS (maximum segment size) after the socket() call
                  to <bytes> [int]. This value is then proposed to the peer
                  with the SYN or SYN/ACK packet (example).
    
           **mss-late= <bytes>**
                  Sets the MSS of the socket after connection has been
                  established to <bytes> [int].
    
           **nodelay**
                  Turns off the Nagle algorithm for measuring the RTT (round
                  trip time).
    
           **rfc1323**
                  Enables RFC1323 TCP options: TCP window scale, round-trip
                  time measurement (RTTM), and protect against wrapped
                  sequence numbers (PAWS) (AIX).
    
           **stdurg** Enables RFC1122 compliant urgent pointer handling (AIX).
    
           **syncnt= <count>**
                  Sets the maximal number of SYN retransmits during connect
                  to <count> [int].
    
           **md5sig** Enables generation of MD5 digests on the packets (FreeBSD).
    
           **noopt** Disables use of TCP options (FreeBSD, MacOSX).
    
           **nopush** sets the TCP_NOPUSH socket option (FreeBSD, MacOSX).
    
           **sack-disable**
                  Disables use the selective acknowledge feature (OpenBSD).
    
           **signature-enable**
                  Enables generation of MD5 digests on the packets (OpenBSD).
    
           **abort-threshold= <milliseconds>**
                  Sets the time to wait for an answer of the peer on an
                  established connection (HP-UX).
    
           **conn-abort-threshold= <milliseconds>**
                  Sets the time to wait for an answer of the server during
                  the initial connect (HP-UX).
    
           **keepinit**
                  Sets the time to wait for an answer of the server during
                  connect() before giving up. Value in half seconds, default
                  is 150 (75s) (Tru64).
    
           **paws** Enables the "protect against wrapped sequence numbers"
                  feature (Tru64).
    
           **sackena**
                  Enables selective acknowledge (Tru64).
    
           **tsoptena**
                  Enables the time stamp option that allows RTT recalculation
                  on existing connections (Tru64).
    
           **UDP option group**
    
           This option may be applied to UDP datagram sockets.
    
           **udp-ignore-peerport >**
                  Address UDP-DATAGRAM expects incoming responses to come
                  from the port specified in its second parameter. With this
                  option, it accepts packets coming from any port.
    
           **UDPLITE option group**
    
           These options may be applied to UDPLITE addresses:
    
           **udplite-send-cscov**
                  Sets the number of bytes for which the checksum is
                  calculated and sent ("checksum coverage").
    
           **udplite-recv-cscov**
                  Sets the number of bytes for which the checksum is checked
                  ("checksum coverage").
    
           **SCTP option group**
    
           These options may be applied to SCTP stream sockets.
    
           **sctp-nodelay**
                  Sets the SCTP_NODELAY socket option that disables the Nagle
                  algorithm.
    
           **sctp-maxseg= <bytes>**
                  Sets the SCTP_MAXSEG socket option to <bytes> [int].  This
                  value is then proposed to the peer with the SYN or SYN/ACK
                  packet.
    
           **DCCP option group**
    
           These options may be applied to DCCP sockets.
    
           **dccp-set-ccid= <int>**
    
           **ccid= <int>**
                  Selects the desired congestion control mechanism (CCID).
    
           **UDP, TCP, SCTP, DCCP, and UDPLITE option group**
    
           Here we find options that are related to the network port
           mechanism and thus can be used with UDP, TCP, SCTP, DCCP, and
           UDP-Lite client and server addresses.
    
           **sourceport= <port>**
                  For outgoing (client) connections, it sets the source
                  <port> using an extra bind() call.  With TCP or UDP listen
                  addresses, socat immediately shuts down the connection if
                  the client does not use this sourceport. UDP-RECV,
                  UDP-RECVFROM, UDP-SENDTO, and UDP-DATAGRAM addresses ignore
                  the packet when it does not match.  (example).
    
           **lowport**
                  Outgoing (client) connections with this option use an
                  unused random source port between 640 and 1023 incl. On
                  UNIX class operating systems, this requires root privilege,
                  and thus indicates that the client process is authorized by
                  local root.  TCP and UDP listen addresses with this option
                  immediately shut down the connection if the client does not
                  use a sourceport <= 1023.  This mechanism can provide
                  limited authorization under some circumstances.
    
           **SOCKS option group**
    
           When using SOCKS type addresses, some socks specific options can
           be set.
    
           **socksport= <tcp service>**
                  Overrides the default "socks" service or port 1080 for the
                  socks server port with <TCP service>.
    
           **socksuser= <user>**
                  Sends the <user> [string] in the username field to the
                  socks server. Default is the actual user name ($LOGNAME or
                  $USER) (example).
    
           **HTTP option group**
    
           Options that can be provided with HTTP type addresses. The only
           HTTP address currently implemented is proxy-connect.
    
           **http-version= <string>**
                  Changes the default "1.0" that is sent to the server in the
                  initial HTTP request. Currently it has not other effect, in
                  particular it does not provide any means to send a Host
                  header.
    
           **proxyport= <TCP service>**
                  Overrides the default HTTP proxy port 8080 with <TCP
                  service>.
    
           **ignorecr**
                  The HTTP protocol requires the use of CR+NL as line
                  terminator. When a proxy server violates this standard,
                  socat might not understand its answer.  This option directs
                  socat to interpret NL as line terminator and to ignore CR
                  in the answer. Nevertheless, socat sends CR+NL to the
                  proxy.
    
           **proxy-authorization= <username>:<password>**
                  Provide "basic" authentication to the proxy server. The
                  argument to the option is used with a "Proxy-Authorization:
                  Basic" header in base64 encoded form.
                  Note: username and password are visible for every user on
                  the local machine in the process list; username and
                  password are transferred to the proxy server unencrypted
                  (base64 encoded) and might be sniffed.
    
           **proxy-authorization-file= <filename>**
                  Like option proxy-authorization, but the credentials are
                  read from the file and therefore not visible in the process
                  list.
    
           **resolve**
                  Per default, socat sends to the proxy a CONNECT request
                  containing the target hostname. With this option, socat
                  resolves the hostname locally and sends the IP address.
                  Please note that, according to RFC 2396, only name
                  resolution to IPv4 addresses is implemented.
    
           **RANGE option group**
    
           These options check if a connecting client should be granted
           access. They can be applied to listening and receiving network
           sockets. tcp-wrappers options fall into this group.
    
           **range= <address-range>**
                  After accepting a connection, tests if the peer is within
                  _range_. For IPv4 addresses, address-range takes the form
                  address/bits, e.g.  10.0.0.0/8, or address:mask, e.g.
                  10.0.0.0:255.0.0.0 (example); for IPv6, it is
                  [ip6-address]/bits, e.g. [::1]/128.  If the client address
                  does not match, **socat** refuses the connection attempt,
                  issues a warning, and keeps listening/receiving.
    
           **tcpwrap[= <name>]**
                  Uses Wietse Venema’s libwrap (tcpd) library to determine if
                  the client is allowed to connect. The configuration files
                  are /etc/hosts.allow and /etc/hosts.deny per default, see
                  "man 5 hosts_access" for more information. The optional
                  <name> (type string) is passed to the wrapper functions as
                  daemon process name (example).  If omitted, the basename of
                  socats invocation (argv[0]) is passed.  If both tcpwrap and
                  range options are applied to an address, both conditions
                  must be fulfilled to allow the connection.
    
           **allow-table= <filename>**
                  Takes the specified file instead of /etc/hosts.allow.
    
           **deny-table= <filename>**
                  Takes the specified file instead of /etc/hosts.deny.
    
           **tcpwrap-etc= <directoryname>**
                  Looks for hosts.allow and hosts.deny in the specified
                  directory. Is overridden by options hosts-allow and
                  hosts-deny.
    
           **LISTEN option group**
    
           Options specific to listening sockets.
    
           **backlog= <count>**
                  Sets the backlog value passed with the listen() system call
                  to <count> [int]. Default is 5.
    
           **accept-timeout= <seconds>**
                  End waiting for a connection after <seconds> [timeval] with
                  error status.
    
           **CHILD option group**
    
           Addresses of LISTEN and CONNECT type take the fork option to
           handle multiple connections via child processes.
    
           **fork** After establishing a connection, handles its channel in a
                  child process and keeps the parent process attempting to
                  produce more connections, either by listening or by
                  connecting in a loop (example).
                  OPENSSL-CONNECT and OPENSSL-LISTEN differ in when they
                  actually fork off the child: OPENSSL-LISTEN forks _before_
                  the SSL handshake, while OPENSSL-CONNECT forks _afterwards_.
                  retry and forever options are not inherited by the child
                  process.
                  On some operating systems (e.g. FreeBSD) this option does
                  not work for UDP-LISTEN addresses.
    
           **max-children= <count>**
                  Limits the number of concurrent child processes [int].
                  Default is no limit.
    
           **children-shutup[=1|2|..]**
                  Decreases the severity of log messages produced by child
                  processes. For example, with value 1 notices are logged as
                  info (or dropped depending on option -dX), and errors are
                  logged as warnings but still cause termination of the child
                  process.
                  This option is intended to reduce logging of high volume
                  servers or proxies.
                  This option succeeds option cool-write.
    
           **EXEC option group**
    
           Options for addresses that invoke a program.
    
           **path= <string>**
                  Overrides the PATH environment variable for searching the
                  program with <string>. This $PATH value is effective in the
                  child process too.
    
           **login** Prefixes argv[0] for the execvp() call with ’-’, thus
                  making a shell behave as login shell.
    
           **FORK option group**
    
           EXEC or SYSTEM addresses invoke a program using a child process
           and transfer data between **socat** and the program. The interprocess
           communication mechanism can be influenced with the following
           options. Per default, a socketpair() is created and assigned to
           stdin and stdout of the child process, while stderr is inherited
           from the **socat** process, and the child process uses file
           descriptors 0 and 1 for communicating with the main socat process.
    
           **nofork** Does not fork a subprocess for executing the program,
                  instead calls execvp() or system() directly from the actual
                  socat instance. This avoids the overhead of another process
                  between the program and its peer, but introduces a lot of
                  restrictions:
    
           o      this option can only be applied to the second **socat**
                  address.
    
           o      it cannot be applied to a part of a dual address.
    
           o      the first socat address cannot be OPENSSL or READLINE
    
           o      socat options -b, -t, -D, -l, -v, -x become useless
    
           o      for both addresses, options ignoreeof, cr, and crnl become
                  useless
    
           o      for both addresses, address specific end/shutdown handling
                  (e.g., graceful socket shutdown) and related options become
                  useless
    
           o      for the second address (the one with option nofork),
                  options append,  cloexec, flock, user, group, mode,
                  nonblock, perm-late, setlk, and setpgid cannot be applied.
                  Some of these could be used on the first address though.
    
           **pipes** Creates a pair of unnamed pipes for interprocess
                  communication instead of a socket pair.
    
           **openpty**
                  Establishes communication with the sub process using a
                  pseudo terminal created with openpty() instead of the
                  default (socketpair or ptmx).
    
           **ptmx** Establishes communication with the sub process using a
                  pseudo terminal created by opening **/dev/ptmx** or **/dev/ptc**
                  instead of the default (socketpair).
    
           **pty** Establishes communication with the sub process using a
                  pseudo terminal instead of a socket pair. Creates the pty
                  with an available mechanism. If openpty and ptmx are both
                  available, it uses ptmx because this is POSIX compliant
                  (example).
    
           **ctty** Makes the pty the controlling tty of the sub process
                  (example).
    
           **stderr** Directs stderr of the sub process to its output channel by
                  making stderr a dup() of stdout (example).
    
           **fdin= <fdnum>**
                  Assigns the sub processes input channel to its file
                  descriptor <fdnum> instead of stdin (0). The program
                  started from the subprocess has to use this fd for reading
                  data from **socat**(example).
    
           **fdout= <fdnum>**
                  Assigns the sub processes output channel to its file
                  descriptor <fdnum> instead of stdout (1). The program
                  started from the subprocess has to use this fd for writing
                  data to **socat**(example).
    
           **sighup, sigint, sigquit**
                  Has **socat** pass signals of this type to the sub process.  If
                  no address has this option, socat terminates on these
                  signals.
    
           Options for address SHELL
    
           **shell= <filename>**
                  Overwrites use the default shell with the named executable,
                  e.g.  /bin/dash. Also sets the SHELL environment variable.
    
           **TERMIOS option group**
    
           For addresses that work on a tty (e.g., stdio, file:/dev/tty,
           exec:...,pty), the terminal parameters defined in the UN*X termios
           mechanism are made available as address option parameters.  Please
           note that changes of the parameters of your interactive terminal
           remain effective after **socat** ’s termination, so you might have to
           enter "reset" or "stty sane" in your shell afterwards.  For EXEC
           and SYSTEM addresses with option PTY, these options apply to the
           pty by the child processes.
    
           **b0** Disconnects the terminal.
    
           **b19200** Sets the serial line speed to 19200 baud. Some other rates
                  are possible; use something like socat -hh |grep ’ b[1-9]’
                  to find all speeds supported by your implementation.
                  Note: On some operating systems, these options may not be
                  available. Use ispeed or ospeed instead.
    
           **echo[= <bool>]**
                  Enables or disables local echo.
    
           **icanon[= <bool>]**
                  Sets or clears canonical mode, enabling line buffering and
                  some special characters.
    
           **raw** Sets raw mode, thus passing input and output almost
                  unprocessed. This option is obsolete, use option rawer or
                  cfmakeraw instead.
    
           **rawer** Makes terminal rawer than raw option. This option
                  implicitly turns off echo. (example).
    
           **cfmakeraw**
                  Sets raw mode by invoking cfmakeraw() or by simulating this
                  call. This option implicitly turns off echo.
    
           **ignbrk[= <bool>]**
                  Ignores or interprets the BREAK character (e.g., ^C)
    
           **brkint[= <bool>]**
    
           **bs0**
    
           **bs1**
    
           **bsdly= <0|1>**
    
           **clocal[= <bool>]**
    
           **cr0**
           **cr1**
           **cr2**
           **cr3**
    
                  Sets the carriage return delay to 0, 1, 2, or 3,
                  respectively.  0 means no delay, the other values are
                  terminal dependent.
    
           **crdly= <0|1|2|3>**
    
           **cread[= <bool>]**
    
           **crtscts[= <bool>]**
    
           **cs5**
           **cs6**
           **cs7**
           **cs8**
    
                  Sets the character size to 5, 6, 7, or 8 bits,
                  respectively.
    
           **csize= <0|1|2|3>**
    
           **cstopb[= <bool>]**
                  Sets two stop bits, rather than one.
    
           **dsusp= <byte>**
                  Sets the value for the VDSUSP character that suspends the
                  current foreground process and reactivates the shell (all
                  except Linux).
    
           **echoctl[= <bool>]**
                  Echos control characters in hat notation (e.g. ^A)
    
           **echoe[= <bool>]**
    
           **echok[= <bool>]**
    
           **echoke[= <bool>]**
    
           **echonl[= <bool>]**
    
           **echoprt[= <bool>]**
    
           **eof= <byte>**
    
           **eol= <byte>**
    
           **eol2= <byte>**
    
           **erase= <byte>**
    
           **discard= <byte>**
    
           **ff0**
    
           **ff1**
    
           **ffdly[= <bool>]**
    
           **flusho[= <bool>]**
    
           **hupcl[= <bool>]**
    
           **icrnl[= <bool>]**
    
           **iexten[= <bool>]**
    
           **igncr[= <bool>]**
    
           **ignpar[= <bool>]**
    
           **imaxbel[= <bool>]**
    
           **inlcr[= <bool>]**
    
           **inpck[= <bool>]**
    
           **intr= <byte>**
    
           **isig[= <bool>]**
    
           **ispeed= <unsigned-int>**
                  Set the baud rate for incoming data on this line.
                  See also: ospeed, b19200
    
           **istrip[= <bool>]**
    
           **iuclc[= <bool>]**
    
           **ixany[= <bool>]**
    
           **ixoff[= <bool>]**
    
           **ixon[= <bool>]**
    
           **kill= <byte>**
    
           **lnext= <byte>**
    
           **min= <byte>**
    
           **nl0** Sets the newline delay to 0.
    
           **nl1**
    
           **nldly[= <bool>]**
    
           **noflsh[= <bool>]**
    
           **ocrnl[= <bool>]**
    
           **ofdel[= <bool>]**
    
           **ofill[= <bool>]**
    
           **olcuc[= <bool>]**
    
           **onlcr[= <bool>]**
    
           **onlret[= <bool>]**
    
           **onocr[= <bool>]**
    
           **opost[= <bool>]**
                  Enables or disables output processing; e.g., converts NL to
                  CR-NL.
    
           **ospeed= <unsigned-int>**
                  Set the baud rate for outgoing data on this line.
                  See also: ispeed, b19200
    
           **parenb[= <bool>]**
                  Enable parity generation on output and parity checking for
                  input.
    
           **parmrk[= <bool>]**
    
           **parodd[= <bool>]**
    
           **pendin[= <bool>]**
    
           **quit= <byte>**
    
           **reprint= <byte>**
    
           **sane** Brings the terminal to something like a useful default
                  state.
    
           **start= <byte>**
    
           **stop= <byte>**
    
           **susp= <byte>**
    
           **swtc= <byte>**
    
           **tab0**
    
           **tab1**
    
           **tab2**
    
           **tab3**
    
           **tabdly= <unsigned-int>**
    
           **time= <byte>**
    
           **tostop[= <bool>]**
    
           **vt0**
    
           **vt1**
    
           **vtdly[= <bool>]**
    
           **werase= <byte>**
    
           **xcase[= <bool>]**
    
           **xtabs**
    
           **i-pop-all**
                  With UNIX System V STREAMS, removes all drivers from the
                  stack.
    
           **i-push= <string>**
                  With UNIX System V STREAMS, pushes the driver (module) with
                  the given name (string) onto the stack. For example, to
                  make sure that a character device on Solaris supports
                  termios etc, use the following options:
                  i-pop-all,i-push=ptem,i-push=ldterm,i-push=ttcompat
    
           **PTY option group**
    
           These options are intended for use with the pty address type.
    
           **link= <filename>**
                  Generates a symbolic link that points to the actual pseudo
                  terminal (pty). This might help to solve the problem that
                  ptys are generated with more or less unpredictable names,
                  making it difficult to directly access the socat generated
                  pty automatically. With this option, the user can specify a
                  "fix" point in the file hierarchy that helps him to access
                  the actual pty (example).  Beginning with **socat** version
                  1.4.3, the symbolic link is removed when the address is
                  closed (but see option unlink-close).
    
           **wait-slave**
                  Blocks the open phase until a process opens the slave side
                  of the pty.  Usually, socat continues after generating the
                  pty with opening the next address or with entering the
                  transfer loop. With the wait-slave option, socat waits
                  until some process opens the slave side of the pty before
                  continuing.  This option only works if the operating system
                  provides the poll() system call. And it depends on an
                  undocumented behaviour of pty’s, so it does not work on all
                  operating systems. It has successfully been tested on
                  Linux, FreeBSD, NetBSD, and on Tru64 with openpty.
    
           **pty-interval= <seconds>**
                  When the wait-slave option is set, socat periodically
                  checks the HUP condition using poll() to find if the pty’s
                  slave side has been opened. The default polling interval is
                  1s. Use the pty-interval option [timeval] to change this
                  value.
    
           **sitout-eio= <timeval>**
                  The login program in Linux closes its tty/pty and reopens
                  it for security reasons. During this time the pty master
                  would get EIO on I/O operations and might terminate. With
                  this option **socat** tolerates EIO for the specified time.
                  Please note that in this state **socat** blocks traffic in both
                  directions, even when it is not related to this channel.
    
           **OPENSSL option group**
    
           These options apply to the openssl and openssl-listen address
           types.
    
           **cipher= <cipherlist>**
                  Specifies the list of ciphers that may be used for the
                  connection.  See the man page of ciphers , section **CIPHER**
                  **LIST FORMAT** , for detailed information about syntax, values,
                  and default of <cipherlist>.
                  Several cipher strings may be given, separated by ’:’.
                  Some simple cipher strings:
    
           3DES   Uses a cipher suite with triple DES.
    
           MD5    Uses a cipher suite with MD5.
    
           aNULL  Uses a cipher suite without authentication.
    
           NULL   Does not use encryption.
    
           HIGH   Uses a cipher suite with "high" encryption.  Note that the
                  peer must support the selected property, or the negotiation
                  will fail.
    
           **method= <ssl-method>**
                  This option is based on deprecated functions and is only
                  available when **socat** was build with option
                  --with-openssl-method.  Use option min-proto-version and
                  maybe max-proto-version instead.  Sets the protocol version
                  to be used. Valid strings (not case sensitive) are:
    
           SSL2   Select SSL protocol version 2.
    
           SSL3   Select SSL protocol version 3.
    
           SSL23  Select the best available SSL or TLS protocol.
    
           TLS1   Select TLS protocol version 1.
    
           TLS1.1 Select TLS protocol version 1.1.
    
           TLS1.2 Select TLS protocol version 1.2.  When this option is not
                  provided OpenSSL negotiates the method with its peer.
    
           **min-proto-version**
                  This option tells OpenSSL to use this or a later SSL/TLS
                  protocol version and refuses to accept a lower/older
                  protocol. Valid syntax is:
    
           SSL2   Select SSL protocol version 2.
    
           SSL3   Select SSL protocol version 3.
    
           TLS1
    
           TLS1.0 Select TLS protocol version 1.
    
           TLS1.1 Select TLS protocol version 1.1.
    
           TLS1.2 Select TLS protocol version 1.2.
    
           TLS1.3 Select TLS protocol version 1.3.
    
           **openssl-max-proto-version**
                  This option is similar to min-proto-version, however, it
                  disallows use of a higher protocol version. Useful for
                  testing the peer.
    
           **verify[= <bool>]**
                  Controls check of the peer’s certificate. Default is 1
                  (true). Disabling verify might open your socket for
                  everyone, making the encryption useless!
    
           **cert= <filename>**
                  Specifies the file with the certificate and private key for
                  authentication.  The certificate must be in OpenSSL format
                  (*.pem).  With openssl-listen, use of this option is
                  strongly recommended. Except with cipher aNULL, "no shared
                  ciphers" error will occur when no certificate is given.
    
           **key= <filename>**
                  Specifies the file with the private key. The private key
                  may be in this file or in the file given with the cert
                  option. The party that has to proof that it is the owner of
                  a certificate needs the private key.
    
           **dhparams= <filename>**
                  Specifies the file with the Diffie Hellman parameters.
                  These parameters may also be in the file given with the
                  cert option in which case the dhparams option is not
                  needed.
    
           **cafile= <filename>**
                  Specifies the file with the trusted (root) authority
                  certificates. The file must be in PEM format and should
                  contain one or more certificates. The party that checks the
                  authentication of its peer trusts only certificates that
                  are in this file.
    
           **capath= <dirname>**
                  Specifies the directory with the trusted (root)
                  certificates. The directory must contain certificates in
                  PEM format and their hashes (see OpenSSL documentation)
    
           **egd= <filename>**
                  On some systems, openssl requires an explicit source of
                  random data. Specify the socket name where an entropy
                  gathering daemon like egd provides random data, e.g.
                  /dev/egd-pool.
    
           **openssl-maxfraglen= <int>, maxfraglen=<int>**
                  For client connections, make a Max Fragment Length
                  Negotiation Request to the server to limit the maximum size
                  fragment the server will send to us. Supported lengths are:
                  512, 1024, 2048, or 4096. Note that this option is not
                  applicable for OPENSSL-LISTEN.
    
           **openssl-maxsendfrag= <int>, maxsendfrag=<int>**
                  Limit the maximum size of the fragment we will send to the
                  other side. Supported length range: 512 - 16384. Note that
                  under OPENSSL-LISTEN, the maximum fragment size may be
                  further limited by the client’s Maximum Fragment Length
                  Negotiation Request, if it makes one.
    
           **pseudo** On systems where openssl cannot find an entropy source and
                  where no entropy gathering daemon can be utilized, this
                  option activates a mechanism for providing pseudo entropy.
                  This is achieved by taking the current time in microseconds
                  for feeding the libc pseudo random number generator with an
                  initial value. openssl is then fed with output from
                  random() calls.
                  NOTE:This mechanism is not sufficient for generation of
                  secure keys!
    
           **compress**
                  Enable or disable the use of compression for a connection.
                  Setting this to "none" disables compression, setting it to
                  "auto" lets OpenSSL choose the best available algorithm
                  supported by both parties. The default is to not touch any
                  compression-related settings.  NOTE: Requires OpenSSL 0.9.8
                  or higher and disabling compression with OpenSSL 0.9.8
                  affects all new connections in the process.
    
           **commonname= <string>**
                  Specify the commonname that the peer certificate must
                  match. With OPENSSL-CONNECT address this overrides the
                  given hostname or IP target address; with OPENSSL-LISTEN
                  this turns on check of peer certificates commonname. This
                  option has only meaning when option verify is not disabled
                  and the chosen cipher provides a peer certificate.
    
           **no-sni[= <bool>]**
                  Do not use the client side Server Name Indication (SNI)
                  feature that selects the desired server certificate.
                  Note: SNI is automatically used since **socat** version 1.7.4.0
                  and uses commonname or the given host name.
    
           **snihost= <string>**
                  Set the client side Server Name Indication (SNI) host name
                  different from the addressed server name or common name.
                  This might be useful when the server certificate has
                  multiple host names or wildcard names because the SNI host
                  name is passed in cleartext to the server and might be
                  eavesdropped; with this option a mock name of the desired
                  certificate may be transferred.
    
           **fips** Enables FIPS mode if compiled in. For info about the FIPS
                  encryption implementation standard see
                  http://oss-institute.org/fips-faq.html.  This mode might
                  require that the involved certificates are generated with a
                  FIPS enabled version of openssl. Setting or clearing this
                  option on one socat address affects all OpenSSL addresses
                  of this process.
    
           **RETRY option group**
    
           Options that control retry of some system calls, especially
           connection attempts.
    
           **retry= <num>**
                  Number of retries before the connection or listen attempt
                  is aborted.  Default is 0, which means just one attempt.
    
           **interval= <timespec>**
                  Time between consecutive attempts (seconds, [timespec]).
                  Default is 1 second.
    
           **forever**
                  Performs an unlimited number of retry attempts.
    
           **INTERFACE option group**
    
           These options may be applied to addresses INTERFACE and TUN. These
           address types and options are currently only implemented on Linux
           operating system.
    
           Note regarding VLANs: On incoming packets the Linux kernel strips
           off the VLAN tag before passing the data to the user space program
           on raw sockets. Special measures are required to get the VLAN
           information, see packet(7) PACKET_AUXDATA, and to optionally
           insert the tag into the packet again, use option retrieve-vlan
           when you need this.
    
           **retrieve-vlan**
                  On packets incoming on raw sockets, retrieve the VLAN
                  information and insert it into the packets for further
                  processing (Linux)
    
           **iff-up** Sets the TUN network interface status UP. Strongly
                  recommended.
    
           **iff-broadcast**
                  Sets the BROADCAST flag of the TUN network interface.
    
           **iff-debug**
                  Sets the DEBUG flag of the TUN network interface.
    
           **iff-loopback**
                  Sets the LOOPBACK flag of the TUN network interface.
    
           **iff-pointopoint**
                  Sets the POINTOPOINT flag of the TUN device.
    
           **iff-notrailers**
                  Sets the NOTRAILERS flag of the TUN device.
    
           **iff-running**
                  Sets the RUNNING flag of the TUN device.
    
           **iff-noarp**
                  Sets the NOARP flag of the TUN device.
    
           **iff-promisc**
                  Sets the PROMISC flag of the TUN device.
    
           **iff-allmulti**
                  Sets the ALLMULTI flag of the TUN device.
    
           **iff-master**
                  Sets the MASTER flag of the TUN device.
    
           **iff-slave**
                  Sets the SLAVE flag of the TUN device.
    
           **iff-multicast**
                  Sets the MULTICAST flag of the TUN device.
    
           **iff-portsel**
                  Sets the PORTSEL flag of the TUN device.
    
           **iff-automedia**
                  Sets the AUTOMEDIA flag of the TUN device.
    
           **iff-dynamic**
                  Sets the DYNAMIC flag of the TUN device.
    
           **TUN option group**
    
           Options that control Linux TUN/TAP interface device addresses.
    
           **tun-device= <device-file>**
                  Instructs socat to take another path for the TUN clone
                  device. Default is /dev/net/tun.
    
           **tun-name= <if-name>**
                  Gives the resulting network interface a specific name
                  instead of the system generated (tun0, tun1, etc.)
    
           **tun-type=[tun|tap]**
                  Sets the type of the TUN device; use this option to
                  generate a TAP device. See the Linux docu for the
                  difference between these types.  When you try to establish
                  a tunnel between two TUN devices, their types should be the
                  same.
    
           **iff-no-pi**
                  Sets the IFF_NO_PI flag which controls if the device
                  includes additional packet information in the tunnel.  When
                  you try to establish a tunnel between two TUN devices,
                  these flags should have the same values.
    
           **POSIX-MQ option group**
    
           Options that may be applied to POSIX-MQ addresses.
    
           **posixmq-priority (mq-prio)**
                  Sets the priority of messages (packets) written to the
                  queue, or the minimal priority of packet read from the
                  queue.
    
           **posixmq-flush (mq-flush)**
                  "Consumes" (drops) all messages currently in the queue
                  before starting transfers.
    
           **posixmq-maxmsg (mq-maxmsg)**
                  Sets the maxmsg parameter of the POSIX message queue when
                  creating it.
                  Note: This option applies only when the queue does not
                  already exist.
    
           **posixmq-msgsize (mq-msgsize)**
                  Sets the msgsize parameter of the POSIX message queue when
                  creating it.
                  Note: This option applies only when the queue does not
                  already exist.
    


## DATA VALUES



           This section explains the different data types that address
           parameters and address options can take.
    
           address-range
                  Is currently only implemented for IPv4 and IPv6. See
                  address-option `range’
    
           bool   "0" or "1"; if value is omitted, "1" is taken.
    
           byte   An unsigned int number, read with strtoul() , lower or
                  equal to UCHAR_MAX .
    
           command-line
                  A string specifying a program name and its arguments,
                  separated by single spaces.
    
           data   This is a more general data specification, "dalan" (low
                  level data description language). The given text string
                  contains information about the target data type and value.
                  Generally a leading character specifies the type of the
                  following data item. In its specific context a default data
                  type may exist.
                  Currently only the following specifications are
                  implemented:
    
           i      A signed integer number, stored in host byte order.
                  Example:    **i-1000**(Integer number -1000)
    
           I      An unsigned integer number, stored in host byte order.
    
           l      A signed long integer number, stored in host byte order.
    
           L      An unsigned long integer number, stored in host byte order.
    
           s      A signed short integer number, stored in host byte order.
    
           S      An unsigned short integer number, stored in host byte
                  order.
    
           b      A signed byte (signed char).
    
           B      An unsigned byte (unsigned char).
    
           x      Following is an even number of hex digits, stored as
                  sequence of bytes, the data length is the resulting number
                  of bytes.
                  Example:    **x7f000001**(IP address 127.0.0.1)
    
           "      Following is a string that is used with the common
                  conversions \n \r \t \f \b \a \e \0; the string must be
                  closed with ’"’. Please note that the quotes and
                  backslashes need to be escaped from shell and **socat**
                  conversion. No implicit \0 is appended.
                  Example:    **"Hello world!\n"**
    
           ’      A single char, with the usual conversions. Please note that
                  the quotes and backslashes need to be escaped from shell
                  and **socat** conversion.
                  Example:    **’a’** Data items may be separated with white
                  space without need to repeat the type specifier again.
    
           directory
                  A string with usual UN*X directory name semantics.
    
           facility
                  The name of a syslog facility in lower case characters.
    
           fdnum  An unsigned int type, read with strtoul() , specifying a
                  UN*X file descriptor.
    
           filename
                  A string with usual UN*X filename semantics.
    
           group  If the first character is a decimal digit, the value is
                  read with strtoul() as unsigned integer specifying a group
                  id. Otherwise, it must be an existing group name.
    
           int    A number following the rules of the strtol() function with
                  base "0", i.e. decimal number, octal number with leading
                  "0", or hexadecimal number with leading "0x". The value
                  must fit into a C int.
    
           interface
                  A string specifying the device name of a network interface
                  as shown by ifconfig or procan, e.g. "eth0".
    
           IP address
                  An IPv4 address in numbers-and-dots notation, an IPv6
                  address in hex notation enclosed in brackets, or a hostname
                  that resolves to an IPv4 or an IPv6 address.
                  Examples: 127.0.0.1, [::1], www.dest-unreach.org, dns1
    
           IPv4 address
                  An IPv4 address in numbers-and-dots notation or a hostname
                  that resolves to an IPv4 address.
                  Examples: 127.0.0.1, www.dest-unreach.org, dns2
    
           IPv6 address
                  An IPv6 address in hexnumbers-and-colons notation enclosed
                  in brackets, or a hostname that resolves to an IPv6
                  address.
                  Examples: [::1], [1234:5678:9abc:def0:1234:5678:9abc:def0],
                  ip6name.domain.org
    
           long   A number read with strtol() . The value must fit into a C
                  long.
    
           long long
                  A number read with strtoll() . The value must fit into a C
                  long long.
    
           off_t  An implementation dependent signed number, usually 32 bits,
                  read with strtol or strtoll.
    
           off64_t
                  An implementation dependent signed number, usually 64 bits,
                  read with strtol or strtoll.
    
           mode_t An unsigned integer, read with strtoul() , specifying mode
                  (permission) bits.
    
           pid_t  A number, read with strtol() , specifying a process id.
    
           port   A uint16_t (16 bit unsigned number) specifying a TCP or UDP
                  port, read with strtoul() .
    
           protocol
                  An unsigned 8 bit number, read with strtoul() .
    
           size_t An unsigned number with size_t limitations, read with
                  strtoul .
    
           sockname
                  A socket address. See address-option `bind’
    
           string A sequence of characters, not containing ’\0’ and,
                  depending on the position within the command line, ’:’,
                  ’,’, or "!!". Note that you might have to escape shell meta
                  characters in the command line.
    
           TCP service
                  A service name, not starting with a digit, that is resolved
                  by getservbyname() , or an unsigned int 16 bit number read
                  with strtoul() .
    
           timeval
                  A double float specifying seconds; the number is mapped
                  into a struct timeval, consisting of seconds and
                  microseconds.
    
           timespec
                  A double float specifying seconds; the number is mapped
                  into a struct timespec, consisting of seconds and
                  nanoseconds.
    
           UDP service
                  A service name, not starting with a digit, that is resolved
                  by getservbyname() , or an unsigned int 16 bit number read
                  with strtoul() .
    
           unsigned int
                  A number read with strtoul() . The value must fit into a C
                  unsigned int.
    
           user   If the first character is a decimal digit, the value is
                  read with strtoul() as unsigned integer specifying a user
                  id. Otherwise, it must be an existing user name.
    
           VSOCK cid
                  A uint32_t (32 bit unsigned number) specifying a VSOCK
                  Context Identifier (CID), read with strtoul() .  There are
                  several special addresses: VMADDR_CID_ANY (-1U) means any
                  address for binding; VMADDR_CID_HOST (2) is the well-known
                  address of the host.
    
           VSOCK port
                  A uint32_t (32 bit unsigned number) specifying a VSOCK
                  port, read with strtoul() .
    


## EXAMPLES



           **socat - TCP4:www.domain.org:80**
    
                  transfers data between STDIO (-) and a TCP4 connection to
                  port 80 of host www.domain.org. This example results in an
                  interactive connection similar to telnet or netcat. The
                  stdin terminal parameters are not changed, so you may close
                  the relay with ^D or abort it with ^C.
    
           **socat -d -d \**
                  **READLINE,history=$HOME/.http_history \**
                  **TCP4:www.domain.org:www,crnl**
    
                  this is similar to the previous example, but you can edit
                  the current line in a bash like manner (READLINE) and use
                  the history file .http_history; **socat** prints messages about
                  progress (-d -d). The  port is specified by service name
                  (www), and correct network line termination characters
                  (crnl) instead of NL are used.
    
           **socat \**
                  **TCP4-LISTEN:www \**
                  **TCP4:www.domain.org:www**
    
                  installs a simple TCP port forwarder. With TCP4-LISTEN it
                  listens on local port "www" until a connection comes in,
                  accepts it, then connects to the remote host (TCP4) and
                  starts data transfer. It will not accept a second
                  connection.
    
           **socat -d -d -lmlocal2 \**
                  **TCP4-LISTEN:80,bind=myaddr1,reuseaddr,fork,su=nobody,range=10.0.0.0/8 \**
                  **TCP4:www.domain.org:80,bind=myaddr2**
    
                  TCP port forwarder, each side bound to another local IP
                  address (bind). This example handles an almost arbitrary
                  number of parallel or consecutive connections by fork’ing a
                  new process after each accept() . It provides a little
                  security by su’ing to user nobody after forking; it only
                  permits connections from the private 10 network (range);
                  due to reuseaddr, it allows immediate restart after master
                  process’s termination, even if some child sockets are not
                  completely shut down.  With -lmlocal2, socat logs to stderr
                  until successfully reaching the accept loop. Further
                  logging is directed to syslog with facility local2.
    
           **socat \**
                  **TCP4-LISTEN:5555,fork,tcpwrap=script \**
                  **EXEC:/bin/myscript,chroot=/home/sandbox,su-d=sandbox,pty,stderr**
    
                  a simple server that accepts connections (TCP4-LISTEN) and
                  fork’s a new child process for each connection; every child
                  acts as single relay.  The client must match the rules for
                  daemon process name "script" in /etc/hosts.allow and
                  /etc/hosts.deny, otherwise it is refused access (see "man 5
                  hosts_access").  For EXEC’uting the program, the child
                  process chroot’s to **/home/sandbox** , su’s to user sandbox,
                  and then starts the program **/home/sandbox/bin/myscript**.
                  **Socat** and myscript communicate via a pseudo tty (pty);
                  myscript’s stderr is redirected to stdout, so its error
                  messages are transferred via **socat** to the connected client.
    
           **socat \**
                  **EXEC:"mail.sh target@domain.com",fdin=3,fdout=4 \**
                  **TCP4:mail.relay.org:25,crnl,bind=alias1.server.org,mss=512**
    
                  **mail.sh** is a shell script, distributed with **socat** , that
                  implements a simple SMTP client. It is programmed to
                  "speak" SMTP on its FDs 3 (in) and 4 (out).  The fdin and
                  fdout options tell **socat** to use these FDs for communication
                  with the program. Because mail.sh inherits stdin and stdout
                  while **socat** does not use them, the script can read a mail
                  body from stdin. **Socat** makes alias1 your local source
                  address (bind), cares for correct network line termination
                  (crnl) and sends at most 512 data bytes per packet (mss).
    
           **socat \**
                  **-,escape=0x0f \**
                  **/dev/ttyS0,rawer,crnl**
    
                  opens an interactive connection via the serial line, e.g.
                  for talking with a modem. rawer sets the console’s and
                  ttyS0’s terminal parameters to practicable values, crnl
                  converts to correct newline characters. escape allows
                  terminating the socat process with character control-O.
                  Consider using READLINE instead of the first address.
    
           **socat \**
                  **UNIX-LISTEN:/tmp/.X11-unix/X1,fork \**
                  **SOCKS4:host.victim.org:127.0.0.1:6000,socksuser=nobody,sourceport=20**
    
                  with UNIX-LISTEN, **socat** opens a listening UNIX domain
                  socket **/tmp/.X11-unix/X1**. This path corresponds to local
                  XWindow display :1 on your machine, so XWindow client
                  connections to DISPLAY=:1 are accepted. **Socat** then speaks
                  with the SOCKS4 server host.victim.org that might permit
                  sourceport 20 based connections due to an FTP related
                  weakness in its static IP filters. **Socat** pretends to be
                  invoked by socksuser nobody, and requests to be connected
                  to loopback port 6000 (only weak sockd configurations will
                  allow this). So we get a connection to the victims XWindow
                  server and, if it does not require MIT cookies or Kerberos
                  authentication, we can start work. Please note that there
                  can only be one connection at a time, because TCP can
                  establish only one session with a given set of addresses
                  and ports.
    
           **socat -u \**
                  **/tmp/readdata,seek-end=0,ignoreeof \**
                  **STDIO**
    
                  this is an example for unidirectional data transfer (-u).
                  **Socat** transfers data from file /tmp/readdata (implicit
                  address GOPEN), starting at its current end (seek-end=0
                  lets **socat** start reading at current end of file; use seek=0
                  or no seek option to first read the existing data) in a
                  "tail -f" like mode (ignoreeof). The "file" might also be a
                  listening UNIX domain socket (do not use a seek option
                  then).
    
           **(sleep 5; echo PASSWORD; sleep 5; echo ls; sleep 1) | \**
           **socat - \**
                  **EXEC:'ssh -l user server',pty,setsid,ctty**
    
                  EXEC’utes an ssh session to server. Uses a pty for
                  communication between **socat** and ssh, makes it ssh’s
                  controlling tty (ctty), and makes this pty the owner of a
                  new process group (setsid), so ssh accepts the password
                  from **socat**.
    
           **socat -u \**
                  **TCP4-LISTEN:3334,reuseaddr,fork \**
                  **OPEN:/tmp/in.log,creat,append**
    
                  implements a simple network based message collector.  For
                  each client connecting to port 3334, a new child process is
                  generated (option fork).  All data sent by the clients are
                  append’ed to the file /tmp/in.log.  If the file does not
                  exist, socat creat’s it.  Option reuseaddr allows immediate
                  restart of the server process.
    
           **socat \**
                  **READLINE,noecho='[Pp]assword:' \**
                  **EXEC:'ftp ftp.server.com',pty,setsid,ctty**
    
                  wraps a command line history (READLINE) around the
                  EXEC’uted ftp client utility.  This allows editing and
                  reuse of FTP commands for relatively comfortable browsing
                  through the ftp directory hierarchy. The password is
                  echoed!  pty is required to have ftp issue a prompt.
                  Nevertheless, there may occur some confusion with the
                  password and FTP prompts.
    
           **socat \**
                  **PTY,link=$HOME/dev/vmodem0,rawer,wait-slave \**
                  **EXEC:'"ssh modemserver.us.org socat - /dev/ttyS0,nonblock,rawer"'**
    
                  generates a pseudo terminal device (PTY) on the client that
                  can be reached under the symbolic link **$HOME/dev/vmodem0**.
                  An application that expects a serial line or modem can be
                  configured to use **$HOME/dev/vmodem0** ; its traffic will be
                  directed to a modemserver via ssh where another socat
                  instance links it to **/dev/ttyS0**.
    
           **sudo socat --experimental \**
                  **TCP4-LISTEN:8000,reuseaddr,fork,netns=namespace1 \**
                  **TCP4-CONNECT:server2:8000**
    
                  creates a listener in the given network namespace that
                  accepts TCP connections on port 8000 and forwards them to
                  server2.
    
           **sudo socat --experimental \**
                  **TUN:192.168.2.1/24,up \**
                  **TUN:192.168.2.2/24,up,netns=namespace2**
    
                  creates two virtual network interfaces, one in default
                  namespace, the other one in namespace2, and forwards
                  packets between them, acting as a virtual network
                  connection.
    
           **socat \**
                  **TCP4-LISTEN:2022,reuseaddr,fork \**
                  **PROXY:proxy.local:www.domain.org:22,proxyport=3128,proxyauth=username:s3cr3t**
    
                  starts a forwarder that accepts connections on port 2022,
                  and directs them through the proxy daemon listening on port
                  3128 (proxyport) on host proxy.local, using the CONNECT
                  method, where they are authenticated as "username" with
                  "s3cr3t" (proxyauth). proxy.local should establish
                  connections to host www.domain.org on port 22 then.
    
           **socat - \**
                  **SSL:server:4443,cafile=./server.crt,cert=./client.pem**
    
                  is an OpenSSL client that tries to establish a secure
                  connection to an SSL server. Option cafile specifies a file
                  that contains trust certificates: we trust the server only
                  when it presents one of these certificates and proofs that
                  it owns the related private key.  Otherwise the connection
                  is terminated.  With cert a file containing the client
                  certificate and the associated private key is specified.
                  This is required in case the server wishes a client
                  authentication; many Internet servers do not.
                  The first address (’-’) can be replaced by almost any other
                  socat address.
    
           **socat \**
                  **OPENSSL-LISTEN:4443,reuseaddr,pf=ip4,fork,cert=./server.pem,cafile=./client.crt \**
                  **PIPE**
    
                  is an OpenSSL server that accepts TCP connections, presents
                  the certificate from the file server.pem and forces the
                  client to present a certificate that is verified against
                  cafile.crt.
                  The second address (’PIPE’) can be replaced by almost any
                  other socat address.
                  For instructions on generating and distributing OpenSSL
                  keys and certificates see the additional socat docu
                  socat-openssl.txt.
    
           **echo |**
           **socat -u - \**
                  **FILE:/tmp/bigfile,create,largefile,seek=100000000000**
    
                  creates a 100GB+1B sparse file; this requires a file system
                  type that supports this (ext2, ext3, ext4, reiserfs, xfs;
                  not minix, vfat). The operation of writing 1 byte might
                  take long (reiserfs: some minutes; ext2: "no" time), and
                  the resulting file can consume some disk space with just
                  its inodes (reiserfs: 2MB; ext2: 16KB).
    
           **socat \**
                  **TCP-L:7777,reuseaddr,fork \**
                  **SYSTEM:'filan -i 0 -s >&2',nofork**
    
                  listens for incoming TCP connections on port 7777. For each
                  accepted connection, invokes a shell. This shell has its
                  stdin and stdout directly connected to the TCP socket
                  (nofork).  The shell starts filan and lets it print the
                  socket addresses to stderr (your terminal window).
    
           **echo -e "\0\14\0\0\c" |**
           **socat -u - \**
                  **FILE:/usr/bin/squid.exe,seek=0x00074420**
    
                  functions as primitive binary editor: it writes the 4 bytes
                  000 014 000 000 to the executable /usr/bin/squid.exe at
                  offset 0x00074420 (this was a real world patch to make the
                  squid executable from Cygwin run under Windows, in 2004).
    
           **socat - \**
                  **TCP:www.blackhat.org:31337,readbytes=1000**
    
                  connects to an unknown service and prevents being flooded.
    
           **socat -U \**
                  **TCP:target:9999,end-close \**
                  **TCP-L:8888,reuseaddr,fork**
    
                  merges data arriving from different TCP streams on port
                  8888 to just one stream to target:9999. The end-close
                  option prevents the child processes forked off by the
                  second address from terminating the shared connection to
                  9999 (close(2) just unlinks the inode which stays active as
                  long as the parent process lives; shutdown(2) would
                  actively terminate the connection).
    
           **socat \**
                  **TCP-LISTEN:10021,reuseaddr,socktype=6,protocol=33,fork PIPE**
    
                  is a simple DCCP echo server. DCCP is now directly
                  provisioned in **socat** , however this example shows how use
                  **socat** s TCP procedures and change the socket type to
                  SOCK_DCCP=6 (on Linux) and the IP protocol to
                  IPPROTO_DCCP=33.
    
           **socat - \**
                  **TCP: <server>:10021,reuseaddr,socktype=6,protocol=33,fork**
    
                  is a simple DCCP client. DCCP is now directly provisioned
                  in **socat** , however this example shows how use **socat** s TCP
                  procedures, but changes the socket type to SOCK_DCCP=6 (on
                  Linux) and the IP protocol to IPPROTO_DCCP=33.
    
           **socat - \**
                  **UDP4-DATAGRAM:192.168.1.0:123,sp=123,broadcast,range=192.168.1.0/24**
    
                  sends a broadcast to the network 192.168.1.0/24 and
                  receives the replies of the timeservers there. Ignores NTP
                  packets from hosts outside this network.
    
           **socat - \**
                  **SOCKET-DATAGRAM:2:2:17:x007bxc0a80100x0000000000000000,bind=x007bx00000000x0000000000000000,setsockopt-int=1:6:1,range=x0000xc0a80100x0000000000000000:x0000xffffff00x0000000000000000**
    
                  is semantically equivalent to the previous example, but all
                  parameters are specified in generic form. the value 6 of
                  setsockopt-int is the Linux value for SO_BROADCAST.
    
           **socat - \**
                  **IP4-DATAGRAM:255.255.255.255:44,broadcast,range=10.0.0.0/8**
    
                  sends a broadcast to the local network(s) using protocol
                  44. Accepts replies from the private address range only.
    
           **socat - \**
                  **UDP4-DATAGRAM:224.255.0.1:6666,bind=:6666,ip-add-membership=224.255.0.1:eth0**
    
                  transfers data from stdin to the specified multicast
                  address using UDP. Both local and remote ports are 6666.
                  Tells the interface eth0 to also accept multicast packets
                  of the given group. Multiple hosts on the local network can
                  run this command, so all data sent by any of the hosts will
                  be received by all the other ones. Note that there are many
                  possible reasons for failure, including IP-filters, routing
                  issues, wrong interface selection by the operating system,
                  bridges, or a badly configured switch.
    
           **socat \**
                  **UDP:host2:4443 \**
                  **TUN:192.168.255.1/24,up**
    
                  establishes one side of a virtual (but not private!)
                  network with host2 where a similar process might run, with
                  UDP-L and tun address 192.168.255.2. They can reach each
                  other using the addresses 192.168.255.1 and 192.168.255.2.
                  Note that streaming eg.via TCP or SSL does not guarantee to
                  retain packet boundaries and might thus cause packet loss.
    
           **socat - \**
                  **VSOCK-CONNECT:2:1234**
    
                  establishes a VSOCK connection with the host (host is
                  always reachable with the well-know CID=2) on 1234 port.
    
           **socat - \**
                  **VSOCK-LISTEN:1234**
    
                  listens for a VSOCK connection on 1234 port.
    
           **socat - \**
                  **VSOCK-CONNECT:31:4321,bind:5555**
    
                  establishes a VSOCK connection with the guest that have
                  CID=31 on 1234 port, binding the local socket to the 5555
                  port.
    
           **socat \**
                  **VSOCK-LISTEN:3333,reuseaddr,fork \**
                  **VSOCK-CONNECT:42,3333**
    
                  starts a forwarder that accepts VSOCK connections on port
                  3333, and directs them to the guest with CID=42 on the same
                  port.
    
           **socat \**
                  **VSOCK-LISTEN:22,reuseaddr,fork \**
                  **TCP:localhost:22**
    
                  forwards VSOCK connections from 22 port to the local SSH
                  server.  Running this in a VM allows you to connect via SSH
                  from the host using VSOCK, as in the example below.
    
           **socat \**
                  **TCP4-LISTEN:22222,reuseaddr,fork \**
                  **VSOCK-CONNECT:33:22**
    
                  forwards TCP connections from 22222 port to the guest with
                  CID=33 listening on VSOCK port 22.  Running this in the
                  host, allows you to connect via SSH running "ssh -p 22222
                  user@localhost", if the guest runs the example above.
    
           **socat \**
                  **PTY,link=/var/run/ppp,rawer \**
                  **INTERFACE:hdlc0**
    
                  circumvents the problem that pppd requires a serial device
                  and thus might not be able to work on a synchronous line
                  that is represented by a network device.  socat creates a
                  PTY to make pppd happy, binds to the network interface
                  hdlc0, and can transfer data between both devices. Use pppd
                  on device /var/run/ppp then.
    
           **socat -u \**
                  **STDIO \**
                  **POSIXMQ-SEND:/queue1,unlink-early,mq-prio=10**
    
                  Writes packets read from stdio (i.e., lines of input when
                  run interactively) into POSIX message queue, with priority
                  10.
    
           **socat -u \**
                  **POSIXMQ-RECV:/queue1,fork,max-children=3 \**
                  **SYSTEM:"worker.sh"**
    
                  Receives messages (packets) from POSIX message queue and,
                  for each message, forks a sub process that reads and
                  processes the message. At most 3 sub processes are allowed
                  at the same time.
    
           **socat -T 1 -d -d \**
                  **TCP-L:10081,reuseaddr,fork,crlf \**
                  **SYSTEM:"echo -e \"\\\"HTTP/1.0 200 OK\\\nDocumentType: text/plain\\\n\\\ndate: \$\(date\)\\\nserver:\$SOCAT_SOCKADDR:\$SOCAT_SOCKPORT\\\nclient: \$SOCAT_PEERADDR:\$SOCAT_PEERPORT\\\n\\\"\"; cat; echo -e \"\\\"\\\n\\\"\""**
    
                  creates a very primitive HTTP echo server: each HTTP client
                  that connects gets a valid HTTP reply that contains
                  information about the client address and port as it is seen
                  by the server host, the host address (which might vary on
                  multihomed servers), and the original client request.
    
           **socat -d -d \**
                  **UDP4-RECVFROM:9999,so-broadcast,so-timestamp,ip-pktinfo,ip-recverr,ip-recvopts,ip-recvtos,ip-recvttl!!- \**
                  **SYSTEM:'export; sleep 1' |**
           **grep SOCAT**
    
                  waits for an incoming UDP packet on port 9999 and prints
                  the environment variables provided by socat. On BSD based
                  systems you have to replace ip-pktinfo with
                  ip-recvdstaddr,ip-recvif. Especially of interest is
                  SOCAT_IP_DSTADDR: it contains the target address of the
                  packet which may be a unicast, multicast, or broadcast
                  address.
    
           **echo -e "M-SEARCH * HTTP/1.1\nHOST: 239.255.255.250:1900\nMAN: \"ssdp:discover\"\nMX: 4\nST: \"ssdp:all\"\n" |**
           **socat - \**
                  **UDP-DATAGRAM:239.255.255.250:1900,crlf**
    
                  sends an SSDP (Simple Service Discovery Protocol) query to
                  the local network and collects and outputs the answers
                  received.
    
           **systemd-socket-activate -l 1077 --inetd socat ACCEPT:0,fork PIPE**
    
                  systemd-socket-activate is a program for testing systemd
                  socket activation of daemons. With --inetd it waits for a
                  connection on the specified port. It does not accept the
                  connection but passes the listening file descriptor as FDs
                  0 and 1. **Socat** accepts the waiting connection and starts
                  data transfer.
    


## DIAGNOSTICS



           **Socat** uses a logging mechanism that allows filtering messages by
           severity. The severities provided are more or less compatible to
           the appropriate syslog priority. With one or up to four
           occurrences of the -d command line option, the lowest priority of
           messages that are issued can be selected. Each message contains a
           single uppercase character specifying the messages severity (one
           of F, E, W, N, I, or D)
    
           FATAL: Conditions that require unconditional and immediate program
                  termination.
    
           ERROR: Conditions that prevent proper program processing. Usually
                  the program is terminated (see option -s).
    
           WARNING:
                  Something did not function correctly or is in a state where
                  correct further processing cannot be guaranteed, but might
                  be possible.
    
           NOTICE:
                  Interesting actions of the program, e.g. for supervising
                  **socat** in some kind of server mode.
    
           INFO:  Description of what the program does, and maybe why it
                  happens. Allows monitoring the lifecycles of file
                  descriptors.
    
           DEBUG: Description of how the program works, all system or library
                  calls and their results.
    
           Log messages can be written to stderr, to a file, or to syslog.
    
           On exit, **socat** gives status 0 if it terminated due to EOF or
           inactivity timeout, with a positive value on error, and with a
           negative value on fatal error.
    


## FILES



           /usr/bin/socat
           /usr/bin/filan
           /usr/bin/procan
    


## SIGNALS



           SIGUSR1:
                  Causes logging of current transfer statistics.
                  See also option --statistics
    


## ENVIRONMENT VARIABLES



           Input variables carry information from the environment to socat,
           output variables are set by socat for use in executed scripts and
           programs.
    
           In the output variables beginning with "SOCAT" this prefix is
           actually replaced by the upper case name of the executable or the
           value of option -lp.
    
           **SOCAT_DEFAULT_LISTEN_IP**(input)
                  (Values 4 or 6) Sets the IP version to be used for listen,
                  recv, and recvfrom addresses if no pf (protocol-family)
                  option is given. Is overridden by socat options -4 or -6.
    
           **SOCAT_PREFERRED_RESOLVE_IP**(input)
                  (Values 0, 4, or 6) Sets the IP version to be used when
                  resolving target host names when version is not specified
                  by address type, option pf (protocol-family), or address
                  format. If name resolution does not return a matching
                  entry, the first result (with differing IP version) is
                  taken. With value 0, socat always selects the first record
                  and its IP version.
    
           **SOCAT_MAIN_WAIT**(input)
                  Specifies the time (seconds) to sleep the main process on
                  begin of main\(). Useful for debugging.
    
           **SOCAT_TRANSFER_WAIT**(input)
                  Specifies the time (seconds) to sleep the process after
                  opening addresses before entering the transfer loop. Useful
                  for debugging.
    
           **SOCAT_FORK_WAIT**(input)
                  Specifies the time (seconds) to sleep the parent and child
                  processes after successful fork(). Useful for debugging.
    
           **SOCAT_VERSION**(output)
                  Socat sets this variable to its version string, e.g.
                  "1.7.0.0" for released versions or e.g. "1.6.0.1+envvar"
                  for temporary versions; can be used in scripts invoked by
                  socat.
    
           **SOCAT_PID**(output)
                  Socat sets this variable to its process id. In case of fork
                  address option, SOCAT_PID gets the child processes id.
                  Forking for exec, system, and SHELL does not change
                  SOCAT_PID.
    
           **SOCAT_PPID**(output)
                  Socat sets this variable to its process id. In case of
                  fork, SOCAT_PPID keeps the pid of the master process.
    
           **SOCAT_PEERADDR**(output)
                  With passive socket addresses (all LISTEN and RECVFROM
                  addresses), this variable is set to a string describing the
                  peers socket address. Port information is not included.
    
           **SOCAT_PEERPORT**(output)
                  With appropriate passive socket addresses (TCP, UDP, and
                  SCTP - LISTEN and RECVFROM), this variable is set to a
                  string containing the number of the peer port.
    
           **SOCAT_SOCKADDR**(output)
                  With all LISTEN addresses, this variable is set to a string
                  describing the local socket address. Port information is
                  not included example
    
           **SOCAT_SOCKPORT**(output)
                  With TCP-LISTEN, UDP-LISTEN, and SCTP-LISTEN addresses,
                  this variable is set to the local port.
    
           **SOCAT_TIMESTAMP**(output)
                  With all RECVFROM addresses where address option
                  so-timestamp is applied, socat sets this variable to the
                  resulting timestamp.
    
           **SOCAT_IP_OPTIONS**(output)
                  With all IPv4 based RECVFROM addresses where address option
                  ip-recvopts is applied, socat fills this variable with the
                  IP options of the received packet.
    
           **SOCAT_IP_DSTADDR**(output)
                  With all IPv4 based RECVFROM addresses where address option
                  ip-recvdstaddr (BSD) or ip-pktinfo (other platforms) is
                  applied, socat sets this variable to the destination
                  address of the received packet. This is particularly useful
                  to identify broadcast and multicast addressed packets.
    
           **SOCAT_IP_IF**(output)
                  With all IPv4 based RECVFROM addresses where address option
                  ip-recvif (BSD) or ip-pktinfo (other platforms) is applied,
                  socat sets this variable to the name of the interface where
                  the packet was received.
    
           **SOCAT_IP_LOCADDR**(output)
                  With all IPv4 based RECVFROM addresses where address option
                  ip-pktinfo is applied, socat sets this variable to the
                  address of the interface where the packet was received.
    
           **SOCAT_IP_TOS**(output)
                  With all IPv4 based RECVFROM addresses where address option
                  ip-recvtos is applied, socat sets this variable to the TOS
                  (type of service) of the received packet.
    
           **SOCAT_IP_TTL**(output)
                  With all IPv4 based RECVFROM addresses where address option
                  ip-recvttl is applied, socat sets this variable to the TTL
                  (time to live) of the received packet.
    
           **SOCAT_IPV6_HOPLIMIT**(output)
                  With all IPv6 based RECVFROM addresses where address option
                  ipv6-recvhoplimit is applied, socat sets this variable to
                  the hoplimit value of the received packet.
    
           **SOCAT_IPV6_DSTADDR**(output)
                  With all IPv6 based RECVFROM addresses where address option
                  ipv6-recvpktinfo is applied, socat sets this variable to
                  the destination address of the received packet.
    
           **SOCAT_IPV6_TCLASS**(output)
                  With all IPv6 based RECVFROM addresses where address option
                  ipv6-recvtclass is applied, **socat** sets this variable to the
                  transfer class of the received packet.
    
           **SOCAT_OPENSSL_X509_ISSUER**(output)
                  Issuer field from peer certificate
    
           **SOCAT_OPENSSL_X509_SUBJECT**(output)
                  Subject field from peer certificate
    
           **SOCAT_OPENSSL_X509_COMMONNAME**(output)
                  commonName entries from peer certificates subject. Multiple
                  values are separated by " // ".
    
           **SOCAT_OPENSSL_X509_***(output)
                  all other entries from peer certificates subject
    
           **SOCAT_OPENSSL_X509V3_DNS**(output)
                  DNS entries from peer certificates extensions -
                  subjectAltName field. Multiple values are separated by " //
                  ".
    
           **HOSTNAME**(input)
                  Is used to determine the hostname for logging (see -lh).
    
           **LOGNAME**(input)
                  Is used as name for the socks client user name if no
                  socksuser is given.
                  With options su and su-d, LOGNAME is set to the given user
                  name.
    
           **USER**(input)
                  Is used as name for the socks client user name if no
                  socksuser is given and LOGNAME is empty.
                  With options su and su-d, USER is set to the given user
                  name.
    
           **SHELL**(output)
                  With options su and su-d, SHELL is set to the login shell
                  of the given user.
    
           **PATH**(output)
                  Can be set with option path for exec, system, and SHELL
                  addresses.
    
           **HOME**(output)
                  With options su and su-d, HOME is set to the home directory
                  of the given user.
    


## CREDITS



           The work of the following groups and organizations was invaluable
           for this project:
    
           The _FSF_ (GNU, http://www.fsf.org/) project with their free and
           portable development software and lots of other useful tools and
           libraries.
    
           The _Linux developers community_ (http://www.linux.org/) for
           providing a free, open source operating system.
    
           The _Open Group_ (http://www.unix-systems.org/) for making their
           standard specifications available on the Internet for free.
    


## VERSION



           This man page describes version 1.8.0 of **socat**.
    


## BUGS



           Addresses cannot be nested, so a single socat process cannot,
           e.g., drive ssl over socks.
    
           Address option ftruncate without value uses default 1 instead of
           0.
    
           Verbose modes (-x and/or -v) display line termination characters
           inconsistently when address options cr or crnl are used: They show
           the data _after_ conversion in either direction.
    
           The data transfer blocksize setting (-b) is ignored with address
           readline.
    
           Send bug reports to <socat@dest-unreach.org>
    


* * *