# ssh_config

## NAME



           **ssh_config** — OpenSSH client configuration file
    


## DESCRIPTION



           _ssh_(1) obtains configuration data from the following sources in
           the following order:
    
                 1.   command-line options
                 2.   user's configuration file (_~/.ssh/config_)
                 3.   system-wide configuration file (_/etc/ssh/ssh_config_)
    
           Unless noted otherwise, for each parameter, the first obtained
           value will be used.  The configuration files contain sections
           separated by **Host** specifications, and that section is only applied
           for hosts that match one of the patterns given in the
           specification.  The matched host name is usually the one given on
           the command line (see the **CanonicalizeHostname** option for
           exceptions).
    
           Since the first obtained value for each parameter is used, more
           host-specific declarations should be given near the beginning of
           the file, and general defaults at the end.
    
           The file contains keyword-argument pairs, one per line.  Lines
           starting with ‘#’ and empty lines are interpreted as comments.
           Arguments may optionally be enclosed in double quotes (") in order
           to represent arguments containing spaces.  Configuration options
           may be separated by whitespace or optional whitespace and exactly
           one ‘=’; the latter format is useful to avoid the need to quote
           whitespace when specifying configuration options using the **ssh** ,
           **scp** , and **sftp -o** option.
    
           The possible keywords and their meanings are as follows (note that
           keywords are case-insensitive and arguments are case-sensitive):
    
           **Host** Restricts the following declarations (up to the next **Host**
                   or **Match** keyword) to be only for those hosts that match
                   one of the patterns given after the keyword.  If more than
                   one pattern is provided, they should be separated by
                   whitespace.  A single ‘*’ as a pattern can be used to
                   provide global defaults for all hosts.  The host is
                   usually the _hostname_ argument given on the command line
                   (see the **CanonicalizeHostname** keyword for exceptions).
    
                   A pattern entry may be negated by prefixing it with an
                   exclamation mark (‘!’).  If a negated entry is matched,
                   then the **Host** entry is ignored, regardless of whether any
                   other patterns on the line match.  Negated matches are
                   therefore useful to provide exceptions for wildcard
                   matches.
    
                   See “PATTERNS” for more information on patterns.
    
           **Match** Restricts the following declarations (up to the next **Host**
                   or **Match** keyword) to be used only when the conditions
                   following the **Match** keyword are satisfied.  Match
                   conditions are specified using one or more criteria or the
                   single token **all** which always matches.  The available
                   criteria keywords are: **canonical** , **final** , **exec** ,
                   **localnetwork** , **host** , **originalhost** , **tagged** , **user** , and
                   **localuser**.  The **all** criteria must appear alone or
                   immediately after **canonical** or **final**.  Other criteria may
                   be combined arbitrarily.  All criteria but **all** , **canonical** ,
                   and **final** require an argument.  Criteria may be negated by
                   prepending an exclamation mark (‘!’).
    
                   The **canonical** keyword matches only when the configuration
                   file is being re-parsed after hostname canonicalization
                   (see the **CanonicalizeHostname** option).  This may be useful
                   to specify conditions that work with canonical host names
                   only.
    
                   The **final** keyword requests that the configuration be re-
                   parsed (regardless of whether **CanonicalizeHostname** is
                   enabled), and matches only during this final pass.  If
                   **CanonicalizeHostname** is enabled, then **canonical** and **final**
                   match during the same pass.
    
                   The **exec** keyword executes the specified command under the
                   user's shell.  If the command returns a zero exit status
                   then the condition is considered true.  Commands
                   containing whitespace characters must be quoted.
                   Arguments to **exec** accept the tokens described in the
                   “TOKENS” section.
    
                   The **localnetwork** keyword matches the addresses of active
                   local network interfaces against the supplied list of
                   networks in CIDR format.  This may be convenient for
                   varying the effective configuration on devices that roam
                   between networks.  Note that network address is not a
                   trustworthy criteria in many situations (e.g. when the
                   network is automatically configured using DHCP) and so
                   caution should be applied if using it to control security-
                   sensitive configuration.
    
                   The other keywords' criteria must be single entries or
                   comma-separated lists and may use the wildcard and
                   negation operators described in the “PATTERNS” section.
                   The criteria for the **host** keyword are matched against the
                   target hostname, after any substitution by the **Hostname** or
                   **CanonicalizeHostname** options.  The **originalhost** keyword
                   matches against the hostname as it was specified on the
                   command-line.  The **tagged** keyword matches a tag name
                   specified by a prior **Tag** directive or on the _ssh_(1)
                   command-line using the **-P** flag.  The **user** keyword matches
                   against the target username on the remote host.  The
                   **localuser** keyword matches against the name of the local
                   user running _ssh_(1) (this keyword may be useful in system-
                   wide **ssh_config** files).
    
           **AddKeysToAgent**
                   Specifies whether keys should be automatically added to a
                   running _ssh-agent_(1).  If this option is set to **yes** and a
                   key is loaded from a file, the key and its passphrase are
                   added to the agent with the default lifetime, as if by
                   _ssh-add_(1).  If this option is set to **ask** , _ssh_(1) will
                   require confirmation using the SSH_ASKPASS program before
                   adding a key (see _ssh-add_(1) for details).  If this option
                   is set to **confirm** , each use of the key must be confirmed,
                   as if the **-c** option was specified to _ssh-add_(1).  If this
                   option is set to **no** , no keys are added to the agent.
                   Alternately, this option may be specified as a time
                   interval using the format described in the “TIME FORMATS”
                   section of _sshd_config_(5) to specify the key's lifetime in
                   _ssh-agent_(1), after which it will automatically be
                   removed.  The argument must be **no**(the default), **yes** ,
                   **confirm**(optionally followed by a time interval), **ask** or a
                   time interval.
    
           **AddressFamily**
                   Specifies which address family to use when connecting.
                   Valid arguments are **any**(the default), **inet**(use IPv4
                   only), or **inet6**(use IPv6 only).
    
           **BatchMode**
                   If set to **yes** , user interaction such as password prompts
                   and host key confirmation requests will be disabled.  This
                   option is useful in scripts and other batch jobs where no
                   user is present to interact with _ssh_(1).  The argument
                   must be **yes** or **no**(the default).
    
           **BindAddress**
                   Use the specified address on the local machine as the
                   source address of the connection.  Only useful on systems
                   with more than one address.
    
           **BindInterface**
                   Use the address of the specified interface on the local
                   machine as the source address of the connection.
    
           **CanonicalDomains**
                   When **CanonicalizeHostname** is enabled, this option
                   specifies the list of domain suffixes in which to search
                   for the specified destination host.
    
           **CanonicalizeFallbackLocal**
                   Specifies whether to fail with an error when hostname
                   canonicalization fails.  The default, **yes** , will attempt to
                   look up the unqualified hostname using the system
                   resolver's search rules.  A value of **no** will cause _ssh_(1)
                   to fail instantly if **CanonicalizeHostname** is enabled and
                   the target hostname cannot be found in any of the domains
                   specified by **CanonicalDomains**.
    
           **CanonicalizeHostname**
                   Controls whether explicit hostname canonicalization is
                   performed.  The default, **no** , is not to perform any name
                   rewriting and let the system resolver handle all hostname
                   lookups.  If set to **yes** then, for connections that do not
                   use a **ProxyCommand** or **ProxyJump** , _ssh_(1) will attempt to
                   canonicalize the hostname specified on the command line
                   using the **CanonicalDomains** suffixes and
                   **CanonicalizePermittedCNAMEs** rules.  If
                   **CanonicalizeHostname** is set to **always** , then
                   canonicalization is applied to proxied connections too.
    
                   If this option is enabled, then the configuration files
                   are processed again using the new target name to pick up
                   any new configuration in matching **Host** and **Match** stanzas.
                   A value of **none** disables the use of a **ProxyJump** host.
    
           **CanonicalizeMaxDots**
                   Specifies the maximum number of dot characters in a
                   hostname before canonicalization is disabled.  The
                   default, 1, allows a single dot (i.e. hostname.subdomain).
    
           **CanonicalizePermittedCNAMEs**
                   Specifies rules to determine whether CNAMEs should be
                   followed when canonicalizing hostnames.  The rules consist
                   of one or more arguments of
                   _source_domain_list_ :_target_domain_list_ , where
                   _source_domain_list_ is a pattern-list of domains that may
                   follow CNAMEs in canonicalization, and _target_domain_list_
                   is a pattern-list of domains that they may resolve to.
    
                   For example,
                   "*.a.example.com:*.b.example.com,*.c.example.com" will
                   allow hostnames matching "*.a.example.com" to be
                   canonicalized to names in the "*.b.example.com" or
                   "*.c.example.com" domains.
    
                   A single argument of "none" causes no CNAMEs to be
                   considered for canonicalization.  This is the default
                   behaviour.
    
           **CASignatureAlgorithms**
                   Specifies which algorithms are allowed for signing of
                   certificates by certificate authorities (CAs).  The
                   default is:
    
                         ssh-ed25519,ecdsa-sha2-nistp256,
                         ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                         sk-ssh-ed25519@openssh.com,
                         sk-ecdsa-sha2-nistp256@openssh.com,
                         rsa-sha2-512,rsa-sha2-256
    
                   If the specified list begins with a ‘+’ character, then
                   the specified algorithms will be appended to the default
                   set instead of replacing them.  If the specified list
                   begins with a ‘-’ character, then the specified algorithms
                   (including wildcards) will be removed from the default set
                   instead of replacing them.
    
                   _ssh_(1) will not accept host certificates signed using
                   algorithms other than those specified.
    
           **CertificateFile**
                   Specifies a file from which the user's certificate is
                   read.  A corresponding private key must be provided
                   separately in order to use this certificate either from an
                   **IdentityFile** directive or **-i** flag to _ssh_(1), via
                   _ssh-agent_(1), or via a **PKCS11Provider** or
                   **SecurityKeyProvider**.
    
                   Arguments to **CertificateFile** may use the tilde syntax to
                   refer to a user's home directory, the tokens described in
                   the “TOKENS” section and environment variables as
                   described in the “ENVIRONMENT VARIABLES” section.
    
                   It is possible to have multiple certificate files
                   specified in configuration files; these certificates will
                   be tried in sequence.  Multiple **CertificateFile** directives
                   will add to the list of certificates used for
                   authentication.
    
           **ChannelTimeout**
                   Specifies whether and how quickly _ssh_(1) should close
                   inactive channels.  Timeouts are specified as one or more
                   “type=interval” pairs separated by whitespace, where the
                   “type” must be the special keyword “global” or a channel
                   type name from the list below, optionally containing
                   wildcard characters.
    
                   The timeout value “interval” is specified in seconds or
                   may use any of the units documented in the “TIME FORMATS”
                   section.  For example, “session=5m” would cause
                   interactive sessions to terminate after five minutes of
                   inactivity.  Specifying a zero value disables the
                   inactivity timeout.
    
                   The special timeout “global” applies to all active
                   channels, taken together.  Traffic on any active channel
                   will reset the timeout, but when the timeout expires then
                   all open channels will be closed.  Note that this global
                   timeout is not matched by wildcards and must be specified
                   explicitly.
    
                   The available channel type names include:
    
                   **agent-connection**
                           Open connections to _ssh-agent_(1).
    
                   **direct-tcpip** , **direct-streamlocal@openssh.com**
                           Open TCP or Unix socket (respectively) connections
                           that have been established from a _ssh_(1) local
                           forwarding, i.e. **LocalForward** or **DynamicForward**.
    
                   **forwarded-tcpip** , **forwarded-streamlocal@openssh.com**
                           Open TCP or Unix socket (respectively) connections
                           that have been established to a _sshd_(8) listening
                           on behalf of a _ssh_(1) remote forwarding, i.e.
                           **RemoteForward**.
    
                   **session**
                           The interactive main session, including shell
                           session, command execution, _scp_(1), _sftp_(1), etc.
    
                   **tun-connection**
                           Open **TunnelForward** connections.
    
                   **x11-connection**
                           Open X11 forwarding sessions.
    
                   Note that in all the above cases, terminating an inactive
                   session does not guarantee to remove all resources
                   associated with the session, e.g. shell processes or X11
                   clients relating to the session may continue to execute.
    
                   Moreover, terminating an inactive channel or session does
                   not necessarily close the SSH connection, nor does it
                   prevent a client from requesting another channel of the
                   same type.  In particular, expiring an inactive forwarding
                   session does not prevent another identical forwarding from
                   being subsequently created.
    
                   The default is not to expire channels of any type for
                   inactivity.
    
           **CheckHostIP**
                   If set to **yes** , _ssh_(1) will additionally check the host IP
                   address in the _known_hosts_ file.  This allows it to detect
                   if a host key changed due to DNS spoofing and will add
                   addresses of destination hosts to _~/.ssh/known_hosts_ in
                   the process, regardless of the setting of
                   **StrictHostKeyChecking**.  If the option is set to **no**(the
                   default), the check will not be executed.
    
           **Ciphers**
                   Specifies the ciphers allowed and their order of
                   preference.  Multiple ciphers must be comma-separated.  If
                   the specified list begins with a ‘+’ character, then the
                   specified ciphers will be appended to the default set
                   instead of replacing them.  If the specified list begins
                   with a ‘-’ character, then the specified ciphers
                   (including wildcards) will be removed from the default set
                   instead of replacing them.  If the specified list begins
                   with a ‘^’ character, then the specified ciphers will be
                   placed at the head of the default set.
    
                   The supported ciphers are:
    
                         3des-cbc
                         aes128-cbc
                         aes192-cbc
                         aes256-cbc
                         aes128-ctr
                         aes192-ctr
                         aes256-ctr
                         aes128-gcm@openssh.com
                         aes256-gcm@openssh.com
                         chacha20-poly1305@openssh.com
    
                   The default is:
    
                         chacha20-poly1305@openssh.com,
                         aes128-ctr,aes192-ctr,aes256-ctr,
                         aes128-gcm@openssh.com,aes256-gcm@openssh.com
    
                   The list of available ciphers may also be obtained using
                   "ssh -Q cipher".
    
           **ClearAllForwardings**
                   Specifies that all local, remote, and dynamic port
                   forwardings specified in the configuration files or on the
                   command line be cleared.  This option is primarily useful
                   when used from the _ssh_(1) command line to clear port
                   forwardings set in configuration files, and is
                   automatically set by _scp_(1) and _sftp_(1).  The argument
                   must be **yes** or **no**(the default).
    
           **Compression**
                   Specifies whether to use compression.  The argument must
                   be **yes** or **no**(the default).
    
           **ConnectionAttempts**
                   Specifies the number of tries (one per second) to make
                   before exiting.  The argument must be an integer.  This
                   may be useful in scripts if the connection sometimes
                   fails.  The default is 1.
    
           **ConnectTimeout**
                   Specifies the timeout (in seconds) used when connecting to
                   the SSH server, instead of using the default system TCP
                   timeout.  This timeout is applied both to establishing the
                   connection and to performing the initial SSH protocol
                   handshake and key exchange.
    
           **ControlMaster**
                   Enables the sharing of multiple sessions over a single
                   network connection.  When set to **yes** , _ssh_(1) will listen
                   for connections on a control socket specified using the
                   **ControlPath** argument.  Additional sessions can connect to
                   this socket using the same **ControlPath** with **ControlMaster**
                   set to **no**(the default).  These sessions will try to reuse
                   the master instance's network connection rather than
                   initiating new ones, but will fall back to connecting
                   normally if the control socket does not exist, or is not
                   listening.
    
                   Setting this to **ask** will cause _ssh_(1) to listen for
                   control connections, but require confirmation using
                   _ssh-askpass_(1).  If the **ControlPath** cannot be opened,
                   _ssh_(1) will continue without connecting to a master
                   instance.
    
                   X11 and _ssh-agent_(1) forwarding is supported over these
                   multiplexed connections, however the display and agent
                   forwarded will be the one belonging to the master
                   connection i.e. it is not possible to forward multiple
                   displays or agents.
    
                   Two additional options allow for opportunistic
                   multiplexing: try to use a master connection but fall back
                   to creating a new one if one does not already exist.
                   These options are: **auto** and **autoask**.  The latter requires
                   confirmation like the **ask** option.
    
           **ControlPath**
                   Specify the path to the control socket used for connection
                   sharing as described in the **ControlMaster** section above or
                   the string **none** to disable connection sharing.  Arguments
                   to **ControlPath** may use the tilde syntax to refer to a
                   user's home directory, the tokens described in the
                   “TOKENS” section and environment variables as described in
                   the “ENVIRONMENT VARIABLES” section.  It is recommended
                   that any **ControlPath** used for opportunistic connection
                   sharing include at least %h, %p, and %r (or alternatively
                   %C) and be placed in a directory that is not writable by
                   other users.  This ensures that shared connections are
                   uniquely identified.
    
           **ControlPersist**
                   When used in conjunction with **ControlMaster** , specifies
                   that the master connection should remain open in the
                   background (waiting for future client connections) after
                   the initial client connection has been closed.  If set to
                   **no**(the default), then the master connection will not be
                   placed into the background, and will close as soon as the
                   initial client connection is closed.  If set to **yes** or 0,
                   then the master connection will remain in the background
                   indefinitely (until killed or closed via a mechanism such
                   as the "ssh -O exit").  If set to a time in seconds, or a
                   time in any of the formats documented in _sshd_config_(5),
                   then the backgrounded master connection will automatically
                   terminate after it has remained idle (with no client
                   connections) for the specified time.
    
           **DynamicForward**
                   Specifies that a TCP port on the local machine be
                   forwarded over the secure channel, and the application
                   protocol is then used to determine where to connect to
                   from the remote machine.
    
                   The argument must be [_bind_address_ :]_port_.  IPv6 addresses
                   can be specified by enclosing addresses in square
                   brackets.  By default, the local port is bound in
                   accordance with the **GatewayPorts** setting.  However, an
                   explicit _bind_address_ may be used to bind the connection
                   to a specific address.  The _bind_address_ of **localhost**
                   indicates that the listening port be bound for local use
                   only, while an empty address or ‘*’ indicates that the
                   port should be available from all interfaces.
    
                   Currently the SOCKS4 and SOCKS5 protocols are supported,
                   and _ssh_(1) will act as a SOCKS server.  Multiple
                   forwardings may be specified, and additional forwardings
                   can be given on the command line.  Only the superuser can
                   forward privileged ports.
    
           **EnableEscapeCommandline**
                   Enables the command line option in the **EscapeChar** menu for
                   interactive sessions (default ‘~C’).  By default, the
                   command line is disabled.
    
           **EnableSSHKeysign**
                   Setting this option to **yes** in the global client
                   configuration file _/etc/ssh/ssh_config_ enables the use of
                   the helper program _ssh-keysign_(8) during
                   **HostbasedAuthentication**.  The argument must be **yes** or **no**
                   (the default).  This option should be placed in the non-
                   hostspecific section.  See _ssh-keysign_(8) for more
                   information.
    
           **EscapeChar**
                   Sets the escape character (default: ‘~’).  The escape
                   character can also be set on the command line.  The
                   argument should be a single character, ‘^’ followed by a
                   letter, or **none** to disable the escape character entirely
                   (making the connection transparent for binary data).
    
           **ExitOnForwardFailure**
                   Specifies whether _ssh_(1) should terminate the connection
                   if it cannot set up all requested dynamic, tunnel, local,
                   and remote port forwardings, (e.g. if either end is unable
                   to bind and listen on a specified port).  Note that
                   **ExitOnForwardFailure** does not apply to connections made
                   over port forwardings and will not, for example, cause
                   _ssh_(1) to exit if TCP connections to the ultimate
                   forwarding destination fail.  The argument must be **yes** or
                   **no**(the default).
    
           **FingerprintHash**
                   Specifies the hash algorithm used when displaying key
                   fingerprints.  Valid options are: **md5** and **sha256**(the
                   default).
    
           **ForkAfterAuthentication**
                   Requests **ssh** to go to background just before command
                   execution.  This is useful if **ssh** is going to ask for
                   passwords or passphrases, but the user wants it in the
                   background.  This implies the **StdinNull** configuration
                   option being set to “yes”.  The recommended way to start
                   X11 programs at a remote site is with something like **ssh**
                   **-f host xterm** , which is the same as **ssh host xterm** if the
                   **ForkAfterAuthentication** configuration option is set to
                   “yes”.
    
                   If the **ExitOnForwardFailure** configuration option is set to
                   “yes”, then a client started with the
                   **ForkAfterAuthentication** configuration option being set to
                   “yes” will wait for all remote port forwards to be
                   successfully established before placing itself in the
                   background.  The argument to this keyword must be **yes**
                   (same as the **-f** option) or **no**(the default).
    
           **ForwardAgent**
                   Specifies whether the connection to the authentication
                   agent (if any) will be forwarded to the remote machine.
                   The argument may be **yes** , **no**(the default), an explicit
                   path to an agent socket or the name of an environment
                   variable (beginning with ‘$’) in which to find the path.
    
                   Agent forwarding should be enabled with caution.  Users
                   with the ability to bypass file permissions on the remote
                   host (for the agent's Unix-domain socket) can access the
                   local agent through the forwarded connection.  An attacker
                   cannot obtain key material from the agent, however they
                   can perform operations on the keys that enable them to
                   authenticate using the identities loaded into the agent.
    
           **ForwardX11**
                   Specifies whether X11 connections will be automatically
                   redirected over the secure channel and DISPLAY set.  The
                   argument must be **yes** or **no**(the default).
    
                   X11 forwarding should be enabled with caution.  Users with
                   the ability to bypass file permissions on the remote host
                   (for the user's X11 authorization database) can access the
                   local X11 display through the forwarded connection.  An
                   attacker may then be able to perform activities such as
                   keystroke monitoring if the **ForwardX11Trusted** option is
                   also enabled.
    
           **ForwardX11Timeout**
                   Specify a timeout for untrusted X11 forwarding using the
                   format described in the “TIME FORMATS” section of
                   _sshd_config_(5).  X11 connections received by _ssh_(1) after
                   this time will be refused.  Setting **ForwardX11Timeout** to
                   zero will disable the timeout and permit X11 forwarding
                   for the life of the connection.  The default is to disable
                   untrusted X11 forwarding after twenty minutes has elapsed.
    
           **ForwardX11Trusted**
                   If this option is set to **yes** , remote X11 clients will have
                   full access to the original X11 display.
    
                   If this option is set to **no**(the default), remote X11
                   clients will be considered untrusted and prevented from
                   stealing or tampering with data belonging to trusted X11
                   clients.  Furthermore, the _xauth_(1) token used for the
                   session will be set to expire after 20 minutes.  Remote
                   clients will be refused access after this time.
    
                   See the X11 SECURITY extension specification for full
                   details on the restrictions imposed on untrusted clients.
    
           **GatewayPorts**
                   Specifies whether remote hosts are allowed to connect to
                   local forwarded ports.  By default, _ssh_(1) binds local
                   port forwardings to the loopback address.  This prevents
                   other remote hosts from connecting to forwarded ports.
                   **GatewayPorts** can be used to specify that ssh should bind
                   local port forwardings to the wildcard address, thus
                   allowing remote hosts to connect to forwarded ports.  The
                   argument must be **yes** or **no**(the default).
    
           **GlobalKnownHostsFile**
                   Specifies one or more files to use for the global host key
                   database, separated by whitespace.  The default is
                   _/etc/ssh/ssh_known_hosts_ , _/etc/ssh/ssh_known_hosts2_.
    
           **GSSAPIAuthentication**
                   Specifies whether user authentication based on GSSAPI is
                   allowed.  The default is **no**.
    
           **GSSAPIDelegateCredentials**
                   Forward (delegate) credentials to the server.  The default
                   is **no**.
    
           **HashKnownHosts**
                   Indicates that _ssh_(1) should hash host names and addresses
                   when they are added to _~/.ssh/known_hosts_.  These hashed
                   names may be used normally by _ssh_(1) and _sshd_(8), but they
                   do not visually reveal identifying information if the
                   file's contents are disclosed.  The default is **no**.  Note
                   that existing names and addresses in known hosts files
                   will not be converted automatically, but may be manually
                   hashed using _ssh-keygen_(1).
    
           **HostbasedAcceptedAlgorithms**
                   Specifies the signature algorithms that will be used for
                   hostbased authentication as a comma-separated list of
                   patterns.  Alternately if the specified list begins with a
                   ‘+’ character, then the specified signature algorithms
                   will be appended to the default set instead of replacing
                   them.  If the specified list begins with a ‘-’ character,
                   then the specified signature algorithms (including
                   wildcards) will be removed from the default set instead of
                   replacing them.  If the specified list begins with a ‘^’
                   character, then the specified signature algorithms will be
                   placed at the head of the default set.  The default for
                   this option is:
    
                      ssh-ed25519-cert-v01@openssh.com,
                      ecdsa-sha2-nistp256-cert-v01@openssh.com,
                      ecdsa-sha2-nistp384-cert-v01@openssh.com,
                      ecdsa-sha2-nistp521-cert-v01@openssh.com,
                      sk-ssh-ed25519-cert-v01@openssh.com,
                      sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
                      rsa-sha2-512-cert-v01@openssh.com,
                      rsa-sha2-256-cert-v01@openssh.com,
                      ssh-ed25519,
                      ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                      sk-ssh-ed25519@openssh.com,
                      sk-ecdsa-sha2-nistp256@openssh.com,
                      rsa-sha2-512,rsa-sha2-256
    
                   The **-Q** option of _ssh_(1) may be used to list supported
                   signature algorithms.  This was formerly named
                   HostbasedKeyTypes.
    
           **HostbasedAuthentication**
                   Specifies whether to try rhosts based authentication with
                   public key authentication.  The argument must be **yes** or **no**
                   (the default).
    
           **HostKeyAlgorithms**
                   Specifies the host key signature algorithms that the
                   client wants to use in order of preference.  Alternately
                   if the specified list begins with a ‘+’ character, then
                   the specified signature algorithms will be appended to the
                   default set instead of replacing them.  If the specified
                   list begins with a ‘-’ character, then the specified
                   signature algorithms (including wildcards) will be removed
                   from the default set instead of replacing them.  If the
                   specified list begins with a ‘^’ character, then the
                   specified signature algorithms will be placed at the head
                   of the default set.  The default for this option is:
    
                      ssh-ed25519-cert-v01@openssh.com,
                      ecdsa-sha2-nistp256-cert-v01@openssh.com,
                      ecdsa-sha2-nistp384-cert-v01@openssh.com,
                      ecdsa-sha2-nistp521-cert-v01@openssh.com,
                      sk-ssh-ed25519-cert-v01@openssh.com,
                      sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
                      rsa-sha2-512-cert-v01@openssh.com,
                      rsa-sha2-256-cert-v01@openssh.com,
                      ssh-ed25519,
                      ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                      sk-ecdsa-sha2-nistp256@openssh.com,
                      sk-ssh-ed25519@openssh.com,
                      rsa-sha2-512,rsa-sha2-256
    
                   If hostkeys are known for the destination host then this
                   default is modified to prefer their algorithms.
    
                   The list of available signature algorithms may also be
                   obtained using "ssh -Q HostKeyAlgorithms".
    
           **HostKeyAlias**
                   Specifies an alias that should be used instead of the real
                   host name when looking up or saving the host key in the
                   host key database files and when validating host
                   certificates.  This option is useful for tunneling SSH
                   connections or for multiple servers running on a single
                   host.
    
           **Hostname**
                   Specifies the real host name to log into.  This can be
                   used to specify nicknames or abbreviations for hosts.
                   Arguments to **Hostname** accept the tokens described in the
                   “TOKENS” section.  Numeric IP addresses are also permitted
                   (both on the command line and in **Hostname** specifications).
                   The default is the name given on the command line.
    
           **IdentitiesOnly**
                   Specifies that _ssh_(1) should only use the configured
                   authentication identity and certificate files (either the
                   default files, or those explicitly configured in the
                   **ssh_config** files or passed on the _ssh_(1) command-line),
                   even if _ssh-agent_(1) or a **PKCS11Provider** or
                   **SecurityKeyProvider** offers more identities.  The argument
                   to this keyword must be **yes** or **no**(the default).  This
                   option is intended for situations where ssh-agent offers
                   many different identities.
    
           **IdentityAgent**
                   Specifies the Unix-domain socket used to communicate with
                   the authentication agent.
    
                   This option overrides the SSH_AUTH_SOCK environment
                   variable and can be used to select a specific agent.
                   Setting the socket name to **none** disables the use of an
                   authentication agent.  If the string "SSH_AUTH_SOCK" is
                   specified, the location of the socket will be read from
                   the SSH_AUTH_SOCK environment variable.  Otherwise if the
                   specified value begins with a ‘$’ character, then it will
                   be treated as an environment variable containing the
                   location of the socket.
    
                   Arguments to **IdentityAgent** may use the tilde syntax to
                   refer to a user's home directory, the tokens described in
                   the “TOKENS” section and environment variables as
                   described in the “ENVIRONMENT VARIABLES” section.
    
           **IdentityFile**
                   Specifies a file from which the user's ECDSA,
                   authenticator-hosted ECDSA, Ed25519, authenticator-hosted
                   Ed25519 or RSA authentication identity is read.  You can
                   also specify a public key file to use the corresponding
                   private key that is loaded in _ssh-agent_(1) when the
                   private key file is not present locally.  The default is
                   _~/.ssh/id_rsa_ , _~/.ssh/id_ecdsa_ , _~/.ssh/id_ecdsa_sk_ ,
                   _~/.ssh/id_ed25519_ and _~/.ssh/id_ed25519_sk_.  Additionally,
                   any identities represented by the authentication agent
                   will be used for authentication unless **IdentitiesOnly** is
                   set.  If no certificates have been explicitly specified by
                   **CertificateFile** , _ssh_(1) will try to load certificate
                   information from the filename obtained by appending
                   _-cert.pub_ to the path of a specified **IdentityFile**.
    
                   Arguments to **IdentityFile** may use the tilde syntax to
                   refer to a user's home directory or the tokens described
                   in the “TOKENS” section.  Alternately an argument of **none**
                   may be used to indicate no identity files should be
                   loaded.
    
                   It is possible to have multiple identity files specified
                   in configuration files; all these identities will be tried
                   in sequence.  Multiple **IdentityFile** directives will add to
                   the list of identities tried (this behaviour differs from
                   that of other configuration directives).
    
                   **IdentityFile** may be used in conjunction with
                   **IdentitiesOnly** to select which identities in an agent are
                   offered during authentication.  **IdentityFile** may also be
                   used in conjunction with **CertificateFile** in order to
                   provide any certificate also needed for authentication
                   with the identity.
    
           **IgnoreUnknown**
                   Specifies a pattern-list of unknown options to be ignored
                   if they are encountered in configuration parsing.  This
                   may be used to suppress errors if **ssh_config** contains
                   options that are unrecognised by _ssh_(1).  It is
                   recommended that **IgnoreUnknown** be listed early in the
                   configuration file as it will not be applied to unknown
                   options that appear before it.
    
           **Include**
                   Include the specified configuration file(s).  Multiple
                   pathnames may be specified and each pathname may contain
                   _glob_(7) wildcards, tokens as described in the “TOKENS”
                   section, environment variables as described in the
                   “ENVIRONMENT VARIABLES” section and, for user
                   configurations, shell-like ‘~’ references to user home
                   directories.  Wildcards will be expanded and processed in
                   lexical order.  Files without absolute paths are assumed
                   to be in _~/.ssh_ if included in a user configuration file
                   or _/etc/ssh_ if included from the system configuration
                   file.  **Include** directive may appear inside a **Match** or **Host**
                   block to perform conditional inclusion.
    
           **IPQoS** Specifies the IPv4 type-of-service or DSCP class for
                   connections.  Accepted values are **af11** , **af12** , **af13** , **af21** ,
                   **af22** , **af23** , **af31** , **af32** , **af33** , **af41** , **af42** , **af43** , **cs0** , **cs1** ,
                   **cs2** , **cs3** , **cs4** , **cs5** , **cs6** , **cs7** , **ef** , **le** , **lowdelay** ,
                   **throughput** , **reliability** , a numeric value, or **none** to use
                   the operating system default.  This option may take one or
                   two arguments, separated by whitespace.  If one argument
                   is specified, it is used as the packet class
                   unconditionally.  If two values are specified, the first
                   is automatically selected for interactive sessions and the
                   second for non-interactive sessions.  The default is **af21**
                   (Low-Latency Data) for interactive sessions and **cs1**(Lower
                   Effort) for non-interactive sessions.
    
           **KbdInteractiveAuthentication**
                   Specifies whether to use keyboard-interactive
                   authentication.  The argument to this keyword must be **yes**
                   (the default) or **no**.  **ChallengeResponseAuthentication** is a
                   deprecated alias for this.
    
           **KbdInteractiveDevices**
                   Specifies the list of methods to use in keyboard-
                   interactive authentication.  Multiple method names must be
                   comma-separated.  The default is to use the server
                   specified list.  The methods available vary depending on
                   what the server supports.  For an OpenSSH server, it may
                   be zero or more of: **bsdauth** and **pam**.
    
           **KexAlgorithms**
                   Specifies the permitted KEX (Key Exchange) algorithms that
                   will be used and their preference order.  The selected
                   algorithm will be the first algorithm in this list that
                   the server also supports.  Multiple algorithms must be
                   comma-separated.
    
                   If the specified list begins with a ‘+’ character, then
                   the specified algorithms will be appended to the default
                   set instead of replacing them.  If the specified list
                   begins with a ‘-’ character, then the specified algorithms
                   (including wildcards) will be removed from the default set
                   instead of replacing them.  If the specified list begins
                   with a ‘^’ character, then the specified algorithms will
                   be placed at the head of the default set.
    
                   The default is:
    
                         sntrup761x25519-sha512,sntrup761x25519-sha512@openssh.com,
                         mlkem768x25519-sha256,
                         curve25519-sha256,curve25519-sha256@libssh.org,
                         ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
                         diffie-hellman-group-exchange-sha256,
                         diffie-hellman-group16-sha512,
                         diffie-hellman-group18-sha512,
                         diffie-hellman-group14-sha256
    
                   The list of supported key exchange algorithms may also be
                   obtained using "ssh -Q kex".
    
           **KnownHostsCommand**
                   Specifies a command to use to obtain a list of host keys,
                   in addition to those listed in **UserKnownHostsFile** and
                   **GlobalKnownHostsFile**.  This command is executed after the
                   files have been read.  It may write host key lines to
                   standard output in identical format to the usual files
                   (described in the “VERIFYING HOST KEYS” section in
                   _ssh_(1)).  Arguments to **KnownHostsCommand** accept the tokens
                   described in the “TOKENS” section.  The command may be
                   invoked multiple times per connection: once when preparing
                   the preference list of host key algorithms to use, again
                   to obtain the host key for the requested host name and, if
                   **CheckHostIP** is enabled, one more time to obtain the host
                   key matching the server's address.  If the command exits
                   abnormally or returns a non-zero exit status then the
                   connection is terminated.
    
           **LocalCommand**
                   Specifies a command to execute on the local machine after
                   successfully connecting to the server.  The command string
                   extends to the end of the line, and is executed with the
                   user's shell.  Arguments to **LocalCommand** accept the tokens
                   described in the “TOKENS” section.
    
                   The command is run synchronously and does not have access
                   to the session of the _ssh_(1) that spawned it.  It should
                   not be used for interactive commands.
    
                   This directive is ignored unless **PermitLocalCommand** has
                   been enabled.
    
           **LocalForward**
                   Specifies that a TCP port on the local machine be
                   forwarded over the secure channel to the specified host
                   and port from the remote machine.  The first argument
                   specifies the listener and may be [_bind_address_ :]_port_ or a
                   Unix domain socket path.  The second argument is the
                   destination and may be _host_ :_hostport_ or a Unix domain
                   socket path if the remote host supports it.
    
                   IPv6 addresses can be specified by enclosing addresses in
                   square brackets.  Multiple forwardings may be specified,
                   and additional forwardings can be given on the command
                   line.  Only the superuser can forward privileged ports.
                   By default, the local port is bound in accordance with the
                   **GatewayPorts** setting.  However, an explicit _bind_address_
                   may be used to bind the connection to a specific address.
                   The _bind_address_ of **localhost** indicates that the listening
                   port be bound for local use only, while an empty address
                   or ‘*’ indicates that the port should be available from
                   all interfaces.  Unix domain socket paths may use the
                   tokens described in the “TOKENS” section and environment
                   variables as described in the “ENVIRONMENT VARIABLES”
                   section.
    
           **LogLevel**
                   Gives the verbosity level that is used when logging
                   messages from _ssh_(1).  The possible values are: QUIET,
                   FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and
                   DEBUG3.  The default is INFO.  DEBUG and DEBUG1 are
                   equivalent.  DEBUG2 and DEBUG3 each specify higher levels
                   of verbose output.
    
           **LogVerbose**
                   Specify one or more overrides to LogLevel.  An override
                   consists of one or more pattern lists that matches the
                   source file, function and line number to force detailed
                   logging for.  For example, an override pattern of:
    
                         kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
    
                   would enable detailed logging for line 1000 of _kex.c_ ,
                   everything in the **kex_exchange_identification**() function,
                   and all code in the _packet.c_ file.  This option is
                   intended for debugging and no overrides are enabled by
                   default.
    
           **MACs** Specifies the MAC (message authentication code) algorithms
                   in order of preference.  The MAC algorithm is used for
                   data integrity protection.  Multiple algorithms must be
                   comma-separated.  If the specified list begins with a ‘+’
                   character, then the specified algorithms will be appended
                   to the default set instead of replacing them.  If the
                   specified list begins with a ‘-’ character, then the
                   specified algorithms (including wildcards) will be removed
                   from the default set instead of replacing them.  If the
                   specified list begins with a ‘^’ character, then the
                   specified algorithms will be placed at the head of the
                   default set.
    
                   The algorithms that contain "-etm" calculate the MAC after
                   encryption (encrypt-then-mac).  These are considered safer
                   and their use recommended.
    
                   The default is:
    
                         umac-64-etm@openssh.com,umac-128-etm@openssh.com,
                         hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
                         hmac-sha1-etm@openssh.com,
                         umac-64@openssh.com,umac-128@openssh.com,
                         hmac-sha2-256,hmac-sha2-512,hmac-sha1
    
                   The list of available MAC algorithms may also be obtained
                   using "ssh -Q mac".
    
           **NoHostAuthenticationForLocalhost**
                   Disable host authentication for localhost (loopback
                   addresses).  The argument to this keyword must be **yes** or
                   **no**(the default).
    
           **NumberOfPasswordPrompts**
                   Specifies the number of password prompts before giving up.
                   The argument to this keyword must be an integer.  The
                   default is 3.
    
           **ObscureKeystrokeTiming**
                   Specifies whether _ssh_(1) should try to obscure inter-
                   keystroke timings from passive observers of network
                   traffic.  If enabled, then for interactive sessions,
                   _ssh_(1) will send keystrokes at fixed intervals of a few
                   tens of milliseconds and will send fake keystroke packets
                   for some time after typing ceases.  The argument to this
                   keyword must be **yes** , **no** or an interval specifier of the
                   form **interval:milliseconds**(e.g. **interval:80** for 80
                   milliseconds).  The default is to obscure keystrokes using
                   a 20ms packet interval.  Note that smaller intervals will
                   result in higher fake keystroke packet rates.
    
           **PasswordAuthentication**
                   Specifies whether to use password authentication.  The
                   argument to this keyword must be **yes**(the default) or **no**.
    
           **PermitLocalCommand**
                   Allow local command execution via the **LocalCommand** option
                   or using the **!**_command_ escape sequence in _ssh_(1).  The
                   argument must be **yes** or **no**(the default).
    
           **PermitRemoteOpen**
                   Specifies the destinations to which remote TCP port
                   forwarding is permitted when **RemoteForward** is used as a
                   SOCKS proxy.  The forwarding specification must be one of
                   the following forms:
    
                         **PermitRemoteOpen** _host_ :_port_
                         **PermitRemoteOpen** _IPv4_addr_ :_port_
                         **PermitRemoteOpen** _[IPv6_addr]_ :_port_
    
                   Multiple forwards may be specified by separating them with
                   whitespace.  An argument of **any** can be used to remove all
                   restrictions and permit any forwarding requests.  An
                   argument of **none** can be used to prohibit all forwarding
                   requests.  The wildcard ‘*’ can be used for host or port
                   to allow all hosts or ports respectively.  Otherwise, no
                   pattern matching or address lookups are performed on
                   supplied names.
    
           **PKCS11Provider**
                   Specifies which PKCS#11 provider to use or **none** to
                   indicate that no provider should be used (the default).
                   The argument to this keyword is a path to the PKCS#11
                   shared library _ssh_(1) should use to communicate with a
                   PKCS#11 token providing keys for user authentication.
    
           **Port** Specifies the port number to connect on the remote host.
                   The default is 22.
    
           **PreferredAuthentications**
                   Specifies the order in which the client should try
                   authentication methods.  This allows a client to prefer
                   one method (e.g. **keyboard-interactive**) over another method
                   (e.g. **password**).  The default is:
    
                         gssapi-with-mic,hostbased,publickey,
                         keyboard-interactive,password
    
           **ProxyCommand**
                   Specifies the command to use to connect to the server.
                   The command string extends to the end of the line, and is
                   executed using the user's shell ‘exec’ directive to avoid
                   a lingering shell process.
    
                   Arguments to **ProxyCommand** accept the tokens described in
                   the “TOKENS” section.  The command can be basically
                   anything, and should read from its standard input and
                   write to its standard output.  It should eventually
                   connect an _sshd_(8) server running on some machine, or
                   execute **sshd -i** somewhere.  Host key management will be
                   done using the **Hostname** of the host being connected
                   (defaulting to the name typed by the user).  Setting the
                   command to **none** disables this option entirely.  Note that
                   **CheckHostIP** is not available for connects with a proxy
                   command.
    
                   This directive is useful in conjunction with _nc_(1) and its
                   proxy support.  For example, the following directive would
                   connect via an HTTP proxy at 192.0.2.0:
    
                      ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
    
           **ProxyJump**
                   Specifies one or more jump proxies as either
                   [_user_ @]_host_[:_port_] or an ssh URI.  Multiple proxies may be
                   separated by comma characters and will be visited
                   sequentially.  Setting this option will cause _ssh_(1) to
                   connect to the target host by first making a _ssh_(1)
                   connection to the specified **ProxyJump** host and then
                   establishing a TCP forwarding to the ultimate target from
                   there.  Setting the host to **none** disables this option
                   entirely.
    
                   Note that this option will compete with the **ProxyCommand**
                   option - whichever is specified first will prevent later
                   instances of the other from taking effect.
    
                   Note also that the configuration for the destination host
                   (either supplied via the command-line or the configuration
                   file) is not generally applied to jump hosts.
                   _~/.ssh/config_ should be used if specific configuration is
                   required for jump hosts.
    
           **ProxyUseFdpass**
                   Specifies that **ProxyCommand** will pass a connected file
                   descriptor back to _ssh_(1) instead of continuing to execute
                   and pass data.  The default is **no**.
    
           **PubkeyAcceptedAlgorithms**
                   Specifies the signature algorithms that will be used for
                   public key authentication as a comma-separated list of
                   patterns.  If the specified list begins with a ‘+’
                   character, then the algorithms after it will be appended
                   to the default instead of replacing it.  If the specified
                   list begins with a ‘-’ character, then the specified
                   algorithms (including wildcards) will be removed from the
                   default set instead of replacing them.  If the specified
                   list begins with a ‘^’ character, then the specified
                   algorithms will be placed at the head of the default set.
                   The default for this option is:
    
                      ssh-ed25519-cert-v01@openssh.com,
                      ecdsa-sha2-nistp256-cert-v01@openssh.com,
                      ecdsa-sha2-nistp384-cert-v01@openssh.com,
                      ecdsa-sha2-nistp521-cert-v01@openssh.com,
                      sk-ssh-ed25519-cert-v01@openssh.com,
                      sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
                      rsa-sha2-512-cert-v01@openssh.com,
                      rsa-sha2-256-cert-v01@openssh.com,
                      ssh-ed25519,
                      ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                      sk-ssh-ed25519@openssh.com,
                      sk-ecdsa-sha2-nistp256@openssh.com,
                      rsa-sha2-512,rsa-sha2-256
    
                   The list of available signature algorithms may also be
                   obtained using "ssh -Q PubkeyAcceptedAlgorithms".
    
           **PubkeyAuthentication**
                   Specifies whether to try public key authentication.  The
                   argument to this keyword must be **yes**(the default), **no** ,
                   **unbound** or **host-bound**.  The final two options enable
                   public key authentication while respectively disabling or
                   enabling the OpenSSH host-bound authentication protocol
                   extension required for restricted _ssh-agent_(1) forwarding.
    
           **RekeyLimit**
                   Specifies the maximum amount of data that may be
                   transmitted or received before the session key is
                   renegotiated, optionally followed by a maximum amount of
                   time that may pass before the session key is renegotiated.
                   The first argument is specified in bytes and may have a
                   suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes,
                   Megabytes, or Gigabytes, respectively.  The default is
                   between ‘1G’ and ‘4G’, depending on the cipher.  The
                   optional second value is specified in seconds and may use
                   any of the units documented in the TIME FORMATS section of
                   _sshd_config_(5).  The default value for **RekeyLimit** is
                   **default none** , which means that rekeying is performed after
                   the cipher's default amount of data has been sent or
                   received and no time based rekeying is done.
    
           **RemoteCommand**
                   Specifies a command to execute on the remote machine after
                   successfully connecting to the server.  The command string
                   extends to the end of the line, and is executed with the
                   user's shell.  Arguments to **RemoteCommand** accept the
                   tokens described in the “TOKENS” section.
    
           **RemoteForward**
                   Specifies that a TCP port on the remote machine be
                   forwarded over the secure channel.  The remote port may
                   either be forwarded to a specified host and port from the
                   local machine, or may act as a SOCKS 4/5 proxy that allows
                   a remote client to connect to arbitrary destinations from
                   the local machine.  The first argument is the listening
                   specification and may be [_bind_address_ :]_port_ or, if the
                   remote host supports it, a Unix domain socket path.  If
                   forwarding to a specific destination then the second
                   argument must be _host_ :_hostport_ or a Unix domain socket
                   path, otherwise if no destination argument is specified
                   then the remote forwarding will be established as a SOCKS
                   proxy.  When acting as a SOCKS proxy, the destination of
                   the connection can be restricted by **PermitRemoteOpen**.
    
                   IPv6 addresses can be specified by enclosing addresses in
                   square brackets.  Multiple forwardings may be specified,
                   and additional forwardings can be given on the command
                   line.  Privileged ports can be forwarded only when logging
                   in as root on the remote machine.  Unix domain socket
                   paths may use the tokens described in the “TOKENS” section
                   and environment variables as described in the “ENVIRONMENT
                   VARIABLES” section.
    
                   If the _port_ argument is 0, the listen port will be
                   dynamically allocated on the server and reported to the
                   client at run time.
    
                   If the _bind_address_ is not specified, the default is to
                   only bind to loopback addresses.  If the _bind_address_ is
                   ‘*’ or an empty string, then the forwarding is requested
                   to listen on all interfaces.  Specifying a remote
                   _bind_address_ will only succeed if the server's
                   **GatewayPorts** option is enabled (see _sshd_config_(5)).
    
           **RequestTTY**
                   Specifies whether to request a pseudo-tty for the session.
                   The argument may be one of: **no**(never request a TTY), **yes**
                   (always request a TTY when standard input is a TTY), **force**
                   (always request a TTY) or **auto**(request a TTY when opening
                   a login session).  This option mirrors the **-t** and **-T** flags
                   for _ssh_(1).
    
           **RequiredRSASize**
                   Specifies the minimum RSA key size (in bits) that _ssh_(1)
                   will accept.  User authentication keys smaller than this
                   limit will be ignored.  Servers that present host keys
                   smaller than this limit will cause the connection to be
                   terminated.  The default is **1024** bits.  Note that this
                   limit may only be raised from the default.
    
           **RevokedHostKeys**
                   Specifies revoked host public keys.  Keys listed in this
                   file will be refused for host authentication.  Note that
                   if this file does not exist or is not readable, then host
                   authentication will be refused for all hosts.  Keys may be
                   specified as a text file, listing one public key per line,
                   or as an OpenSSH Key Revocation List (KRL) as generated by
                   _ssh-keygen_(1).  For more information on KRLs, see the KEY
                   REVOCATION LISTS section in _ssh-keygen_(1).  Arguments to
                   **RevokedHostKeys** may use the tilde syntax to refer to a
                   user's home directory, the tokens described in the
                   “TOKENS” section and environment variables as described in
                   the “ENVIRONMENT VARIABLES” section.
    
           **SecurityKeyProvider**
                   Specifies a path to a library that will be used when
                   loading any FIDO authenticator-hosted keys, overriding the
                   default of using the built-in USB HID support.
    
                   If the specified value begins with a ‘$’ character, then
                   it will be treated as an environment variable containing
                   the path to the library.
    
           **SendEnv**
                   Specifies what variables from the local _environ_(7) should
                   be sent to the server.  The server must also support it,
                   and the server must be configured to accept these
                   environment variables.  Note that the TERM environment
                   variable is always sent whenever a pseudo-terminal is
                   requested as it is required by the protocol.  Refer to
                   **AcceptEnv** in _sshd_config_(5) for how to configure the
                   server.  Variables are specified by name, which may
                   contain wildcard characters.  Multiple environment
                   variables may be separated by whitespace or spread across
                   multiple **SendEnv** directives.
    
                   See “PATTERNS” for more information on patterns.
    
                   It is possible to clear previously set **SendEnv** variable
                   names by prefixing patterns with _-_.  The default is not to
                   send any environment variables.
    
           **ServerAliveCountMax**
                   Sets the number of server alive messages (see below) which
                   may be sent without _ssh_(1) receiving any messages back
                   from the server.  If this threshold is reached while
                   server alive messages are being sent, ssh will disconnect
                   from the server, terminating the session.  It is important
                   to note that the use of server alive messages is very
                   different from **TCPKeepAlive**(below).  The server alive
                   messages are sent through the encrypted channel and
                   therefore will not be spoofable.  The TCP keepalive option
                   enabled by **TCPKeepAlive** is spoofable.  The server alive
                   mechanism is valuable when the client or server depend on
                   knowing when a connection has become unresponsive.
    
                   The default value is 3.  If, for example,
                   **ServerAliveInterval**(see below) is set to 15 and
                   **ServerAliveCountMax** is left at the default, if the server
                   becomes unresponsive, ssh will disconnect after
                   approximately 45 seconds.
    
           **ServerAliveInterval**
                   Sets a timeout interval in seconds after which if no data
                   has been received from the server, _ssh_(1) will send a
                   message through the encrypted channel to request a
                   response from the server.  The default is 0, indicating
                   that these messages will not be sent to the server.
    
           **SessionType**
                   May be used to either request invocation of a subsystem on
                   the remote system, or to prevent the execution of a remote
                   command at all.  The latter is useful for just forwarding
                   ports.  The argument to this keyword must be **none**(same as
                   the **-N** option), **subsystem**(same as the **-s** option) or
                   **default**(shell or command execution).
    
           **SetEnv** Directly specify one or more environment variables and
                   their contents to be sent to the server.  Similarly to
                   **SendEnv** , with the exception of the TERM variable, the
                   server must be prepared to accept the environment
                   variable.
    
           **StdinNull**
                   Redirects stdin from _/dev/null_ (actually, prevents reading
                   from stdin).  Either this or the equivalent **-n** option must
                   be used when **ssh** is run in the background.  The argument
                   to this keyword must be **yes**(same as the **-n** option) or **no**
                   (the default).
    
           **StreamLocalBindMask**
                   Sets the octal file creation mode mask (umask) used when
                   creating a Unix-domain socket file for local or remote
                   port forwarding.  This option is only used for port
                   forwarding to a Unix-domain socket file.
    
                   The default value is 0177, which creates a Unix-domain
                   socket file that is readable and writable only by the
                   owner.  Note that not all operating systems honor the file
                   mode on Unix-domain socket files.
    
           **StreamLocalBindUnlink**
                   Specifies whether to remove an existing Unix-domain socket
                   file for local or remote port forwarding before creating a
                   new one.  If the socket file already exists and
                   **StreamLocalBindUnlink** is not enabled, **ssh** will be unable
                   to forward the port to the Unix-domain socket file.  This
                   option is only used for port forwarding to a Unix-domain
                   socket file.
    
                   The argument must be **yes** or **no**(the default).
    
           **StrictHostKeyChecking**
                   If this flag is set to **yes** , _ssh_(1) will never
                   automatically add host keys to the _~/.ssh/known_hosts_
                   file, and refuses to connect to hosts whose host key has
                   changed.  This provides maximum protection against man-in-
                   the-middle (MITM) attacks, though it can be annoying when
                   the _/etc/ssh/ssh_known_hosts_ file is poorly maintained or
                   when connections to new hosts are frequently made.  This
                   option forces the user to manually add all new hosts.
    
                   If this flag is set to **accept-new** then ssh will
                   automatically add new host keys to the user's _known_hosts_
                   file, but will not permit connections to hosts with
                   changed host keys.  If this flag is set to **no** or **off** , ssh
                   will automatically add new host keys to the user known
                   hosts files and allow connections to hosts with changed
                   hostkeys to proceed, subject to some restrictions.  If
                   this flag is set to **ask**(the default), new host keys will
                   be added to the user known host files only after the user
                   has confirmed that is what they really want to do, and ssh
                   will refuse to connect to hosts whose host key has
                   changed.  The host keys of known hosts will be verified
                   automatically in all cases.
    
           **SyslogFacility**
                   Gives the facility code that is used when logging messages
                   from _ssh_(1).  The possible values are: DAEMON, USER, AUTH,
                   LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6,
                   LOCAL7.  The default is USER.
    
           **TCPKeepAlive**
                   Specifies whether the system should send TCP keepalive
                   messages to the other side.  If they are sent, death of
                   the connection or crash of one of the machines will be
                   properly noticed.  However, this means that connections
                   will die if the route is down temporarily, and some people
                   find it annoying.
    
                   The default is **yes**(to send TCP keepalive messages), and
                   the client will notice if the network goes down or the
                   remote host dies.  This is important in scripts, and many
                   users want it too.
    
                   To disable TCP keepalive messages, the value should be set
                   to **no**.  See also **ServerAliveInterval** for protocol-level
                   keepalives.
    
           **Tag** Specify a configuration tag name that may be later used by
                   a **Match** directive to select a block of configuration.
    
           **Tunnel** Request _tun_(4) device forwarding between the client and
                   the server.  The argument must be **yes** , **point-to-point**
                   (layer 3), **ethernet**(layer 2), or **no**(the default).
                   Specifying **yes** requests the default tunnel mode, which is
                   **point-to-point**.
    
           **TunnelDevice**
                   Specifies the _tun_(4) devices to open on the client
                   (_local_tun_) and the server (_remote_tun_).
    
                   The argument must be _local_tun_[:_remote_tun_].  The devices
                   may be specified by numerical ID or the keyword **any** , which
                   uses the next available tunnel device.  If _remote_tun_ is
                   not specified, it defaults to **any**.  The default is
                   **any:any**.
    
           **UpdateHostKeys**
                   Specifies whether _ssh_(1) should accept notifications of
                   additional hostkeys from the server sent after
                   authentication has completed and add them to
                   **UserKnownHostsFile**.  The argument must be **yes** , **no** or **ask**.
                   This option allows learning alternate hostkeys for a
                   server and supports graceful key rotation by allowing a
                   server to send replacement public keys before old ones are
                   removed.
    
                   Additional hostkeys are only accepted if the key used to
                   authenticate the host was already trusted or explicitly
                   accepted by the user, the host was authenticated via
                   **UserKnownHostsFile**(i.e. not **GlobalKnownHostsFile**) and the
                   host was authenticated using a plain key and not a
                   certificate.
    
                   **UpdateHostKeys** is enabled by default if the user has not
                   overridden the default **UserKnownHostsFile** setting and has
                   not enabled **VerifyHostKeyDNS** , otherwise **UpdateHostKeys**
                   will be set to **no**.
    
                   If **UpdateHostKeys** is set to **ask** , then the user is asked to
                   confirm the modifications to the known_hosts file.
                   Confirmation is currently incompatible with
                   **ControlPersist** , and will be disabled if it is enabled.
    
                   Presently, only _sshd_(8) from OpenSSH 6.8 and greater
                   support the "hostkeys@openssh.com" protocol extension used
                   to inform the client of all the server's hostkeys.
    
           **User** Specifies the user to log in as.  This can be useful when
                   a different user name is used on different machines.  This
                   saves the trouble of having to remember to give the user
                   name on the command line.
    
           **UserKnownHostsFile**
                   Specifies one or more files to use for the user host key
                   database, separated by whitespace.  Each filename may use
                   tilde notation to refer to the user's home directory, the
                   tokens described in the “TOKENS” section and environment
                   variables as described in the “ENVIRONMENT VARIABLES”
                   section.  A value of **none** causes _ssh_(1) to ignore any
                   user-specific known hosts files.  The default is
                   _~/.ssh/known_hosts_ , _~/.ssh/known_hosts2_.
    
           **VerifyHostKeyDNS**
                   Specifies whether to verify the remote key using DNS and
                   SSHFP resource records.  If this option is set to **yes** , the
                   client will implicitly trust keys that match a secure
                   fingerprint from DNS.  Insecure fingerprints will be
                   handled as if this option was set to **ask**.  If this option
                   is set to **ask** , information on fingerprint match will be
                   displayed, but the user will still need to confirm new
                   host keys according to the **StrictHostKeyChecking** option.
                   The default is **no**.
    
                   See also “VERIFYING HOST KEYS” in _ssh_(1).
    
           **VisualHostKey**
                   If this flag is set to **yes** , an ASCII art representation of
                   the remote host key fingerprint is printed in addition to
                   the fingerprint string at login and for unknown host keys.
                   If this flag is set to **no**(the default), no fingerprint
                   strings are printed at login and only the fingerprint
                   string will be printed for unknown host keys.
    
           **XAuthLocation**
                   Specifies the full pathname of the _xauth_(1) program.  The
                   default is _/usr/X11R6/bin/xauth_.
    


## PATTERNS



           A _pattern_ consists of zero or more non-whitespace characters, ‘*’
           (a wildcard that matches zero or more characters), or ‘?’ (a
           wildcard that matches exactly one character).  For example, to
           specify a set of declarations for any host in the ".co.uk" set of
           domains, the following pattern could be used:
    
                 **Host *.co.uk**
    
           The following pattern would match any host in the 192.168.0.[0-9]
           network range:
    
                 **Host 192.168.0.?**
    
           A _pattern-list_ is a comma-separated list of patterns.  Patterns
           within pattern-lists may be negated by preceding them with an
           exclamation mark (‘!’).  For example, to allow a key to be used
           from anywhere within an organization except from the "dialup"
           pool, the following entry (in authorized_keys) could be used:
    
                 **from="!*.dialup.example.com,*.example.com"**
    
           Note that a negated match will never produce a positive result by
           itself.  For example, attempting to match "host3" against the
           following pattern-list will fail:
    
                 **from="!host1,!host2"**
    
           The solution here is to include a term that will yield a positive
           match, such as a wildcard:
    
                 **from="!host1,!host2,*"**
    


## TOKENS



           Arguments to some keywords can make use of tokens, which are
           expanded at runtime:
    
                 %%    A literal ‘%’.
                 %C    Hash of %l%h%p%r%j.
                 %d    Local user's home directory.
                 %f    The fingerprint of the server's host key.
                 %H    The _known_hosts_ hostname or address that is being
                       searched for.
                 %h    The remote hostname.
                 %I    A string describing the reason for a **KnownHostsCommand**
                       execution: either **ADDRESS** when looking up a host by
                       address (only when **CheckHostIP** is enabled), **HOSTNAME**
                       when searching by hostname, or **ORDER** when preparing
                       the host key algorithm preference list to use for the
                       destination host.
                 %i    The local user ID.
                 %j    The contents of the ProxyJump option, or the empty
                       string if this option is unset.
                 %K    The base64 encoded host key.
                 %k    The host key alias if specified, otherwise the
                       original remote hostname given on the command line.
                 %L    The local hostname.
                 %l    The local hostname, including the domain name.
                 %n    The original remote hostname, as given on the command
                       line.
                 %p    The remote port.
                 %r    The remote username.
                 %T    The local _tun_(4) or _tap_(4) network interface assigned
                       if tunnel forwarding was requested, or "NONE"
                       otherwise.
                 %t    The type of the server host key, e.g.  **ssh-ed25519**.
                 %u    The local username.
    
           **CertificateFile** , **ControlPath** , **IdentityAgent** , **IdentityFile** ,
           **Include** , **KnownHostsCommand** , **LocalForward** , **Match exec** ,
           **RemoteCommand** , **RemoteForward** , **RevokedHostKeys** , and
           **UserKnownHostsFile** accept the tokens %%, %C, %d, %h, %i, %j, %k,
           %L, %l, %n, %p, %r, and %u.
    
           **KnownHostsCommand** additionally accepts the tokens %f, %H, %I, %K
           and %t.
    
           **Hostname** accepts the tokens %% and %h.
    
           **LocalCommand** accepts all tokens.
    
           **ProxyCommand** and **ProxyJump** accept the tokens %%, %h, %n, %p, and
           %r.
    
           Note that some of these directives build commands for execution
           via the shell.  Because _ssh_(1) performs no filtering or escaping
           of characters that have special meaning in shell commands (e.g.
           quotes), it is the user's responsibility to ensure that the
           arguments passed to _ssh_(1) do not contain such characters and that
           tokens are appropriately quoted when used.
    


## ENVIRONMENT VARIABLES



           Arguments to some keywords can be expanded at runtime from
           environment variables on the client by enclosing them in **${}** , for
           example **${HOME}/.ssh** would refer to the user's .ssh directory.  If
           a specified environment variable does not exist then an error will
           be returned and the setting for that keyword will be ignored.
    
           The keywords **CertificateFile** , **ControlPath** , **IdentityAgent** ,
           **IdentityFile** , **Include** , **KnownHostsCommand** , and **UserKnownHostsFile**
           support environment variables.  The keywords **LocalForward** and
           **RemoteForward** support environment variables only for Unix domain
           socket paths.
    


## FILES



           _~/.ssh/config_
                   This is the per-user configuration file.  The format of
                   this file is described above.  This file is used by the
                   SSH client.  Because of the potential for abuse, this file
                   must have strict permissions: read/write for the user, and
                   not writable by others.
    
           _/etc/ssh/ssh_config_
                   Systemwide configuration file.  This file provides
                   defaults for those values that are not specified in the
                   user's configuration file, and for those users who do not
                   have a configuration file.  This file must be world-
                   readable.
    


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