neulab/tldr huggingface dataset:
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, pty, stderr, ctty, setsid, pipes, login, sigint, sigquit See also: SYSTEM
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, 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. 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: 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, 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: cipher, verify, commonname, cafile, capath, certificate, key, compress, bind, pf, sourceport, retry 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, cipher, verify, commonname, cafile, capath, certificate, key, compress, fork, bind, range, tcpwrap, su, reuseaddr, retry 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 appeares 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
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. 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
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, cool-write 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
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: 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
STDERR Uses file descriptor 2. Option groups: FD (TERMIOS,REG,SOCKET) See also: FD
STDIN  Uses file descriptor 0. 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. Option groups: FD (TERMIOS,REG,SOCKET) See also: FD
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, pty, stderr, ctty, setsid, pipes, sigint, sigquit See also: EXEC
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: crnl, bind, pf, connect-timeout, tos, mtudiscover, mss, nodelay, nonblock, sourceport, retry, 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 assignes 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 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, 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. 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. 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. 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
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 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. 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 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, pf, 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, pf, max-children, backlog, su, reuseaddr, retry, cool-write 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.
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  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 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 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 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 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 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 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 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   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() . These calls might require ownership or root privilege.
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 Opens the file in binary mode to avoid implicit line terminator conversions (Cygwin).
text   Opens the file in text mode to force implicit line terminator conversions (Cygwin).
noinherit Does not keep this file open in a spawned process (Cygwin).
cool-write 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. This option is experimental.
end-close 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 Changes the (address dependent) method of shutting down the write part of a connection to not do anything.
shut-down 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 Changes the (address dependent) method of shutting down the write part of a connection to close(fd).
shut-null 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 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.
umask=<mode> Sets the umask of the process to <mode> [mode_t] before accessing the file system entry (useful with UNIX domain sockets!). This call might affect all further operations of the socat process!
unlink-early Unlinks (removes) the file before opening it and even before applying user-early etc.
unlink Unlinks (removes) the file before accessing it, but after user-early etc.
unlink-late Unlinks (removes) the file after opening it to make it inaccessible for other processes after a short race condition.
unlink-close Removes 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 1; for created files, opened files, and generic opened files the default is 0.
OPEN option group
The OPEN group options allow setting flags with the open() system call. E.g., option `creat’ sets the O_CREAT flag. 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 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  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.
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 setgit 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).
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 lastest 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