ssh_config

SSH_CONFIG(5) File Formats Manual SSH_CONFIG(5)

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.

   Note that the Debian openssh-client package sets several options as standard in /etc/ssh/ssh_config which are not the default in ssh(1):

         •   Include /etc/ssh/ssh_config.d/*.conf
         •   SendEnv LANG LC_* COLORTERM NO_COLOR
         •   HashKnownHosts yes
         •   GSSAPIAuthentication yes

   /etc/ssh/ssh_config.d/*.conf files are included at the start of the system-wide configuration file, so options set there will override those in /etc/ssh/ssh_config.

   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, command, user, localuser, and version.  The all criteria must appear alone or immediately after canonical or final.  Other criteria may be combined arbi‐
           trarily.  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  automati
           cally 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 command keyword matches the remote command  that
           has  been  requested,  or the subsystem name that is being invoked (e.g. "sftp" for an SFTP session).  The empty string will match the case where a command or tag has not been
           specified, i.e. ‘Match tag ""’.  The version keyword matches against the version string of ssh(1), for example “OpenSSH_10.0”.

           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).

           Finally,  the  sessiontype  keyword  matches the requested session type, which may be one of shell for interactive sessions, exec for command execution sessions, subsystem for
           subsystem invocations such as sftp(1), or none for transport-only sessions, such as when ssh(1) is started with the -N flag.

   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.  In addition, the ServerAliveInterval option will be set to 300
           seconds by default (Debian-specific).  This option is useful in scripts and other batch jobs where no user is present to interact with ssh(1), and where it is desirable to de
           tect a broken network swiftly.  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 ad‐
           dresses 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-gcm@openssh.com,aes256-gcm@openssh.com,
                 aes128-ctr,aes192-ctr,aes256-ctr

           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.  SetupTimeOut is a Debian-specific compatibility alias for this option.

   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 con
           tinue 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 ini‐
           tial 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  termi‐
           nate 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  lis‐
           tening 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 lo
           cal 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 authen
           ticate 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, (the Debian-specific default), remote X11 clients will have full access to the original X11 display.

           If this option is set to no (the upstream 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.

   GSSAPIClientIdentity
           If set, specifies the GSSAPI client identity that ssh should use when connecting to the server. The default is unset, which means that the default identity will be used.

   GSSAPIDelegateCredentials
           Forward (delegate) credentials to the server.  The default is no.

   GSSAPIKeyExchange
           Specifies whether key exchange based on GSSAPI may be used. When using GSSAPI key exchange the server need not have a host key.  The default is “no”.

   GSSAPIRenewalForcesRekey
           If set to “yes” then renewal of the client's GSSAPI credentials will force the rekeying of the ssh connection. With a compatible server, this will delegate the renewed creden
           tials to a session on the server.

           Checks  are  made to ensure that credentials are only propagated when the new credentials match the old ones on the originating client and where the receiving server still has
           the old set in its cache.

           The default is no.

           For this to work GSSAPIKeyExchange needs to be enabled in the server and also used by the client.

   GSSAPIServerIdentity
           If set, specifies the GSSAPI server identity that ssh should expect when connecting to the server. The default is unset, which means that the expected GSSAPI  server  identity
           will be determined from the target hostname.

   GSSAPITrustDns
           Set  to  yes  to indicate that the DNS is trusted to securely canonicalize the name of the host being connected to. If no, the hostname entered on the command line will be
           passed untouched to the GSSAPI library.  The default is no.

   GSSAPIKexAlgorithms
           The list of key exchange algorithms that are offered for GSSAPI key exchange. Possible values are

              gss-gex-sha1-,
              gss-group1-sha1-,
              gss-group14-sha1-,
              gss-group14-sha256-,
              gss-group16-sha512-,
              gss-nistp256-sha256-,
              gss-curve25519-sha256-

           The default is gss-group14-sha256-,gss-group16-sha512-,gss-nistp256-sha256-,gss-curve25519-sha256-,gss-gex-sha1-,gss-group14-sha1-.  This option only applies to  connections
           using GSSAPI.

   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).  Use of this option may break facilities such as tab-completion that rely on being able to read un‐
           hashed host names from ~/.ssh/known_hosts.

   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 spec‐
           ified 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  al‐
           gorithms (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 certifi‐
           cates.  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  be‐
           gins 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 authen‐
           tication 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 con
           junction 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  be
           fore 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 lowdelay for interactive sessions and throughput 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:

                 mlkem768x25519-sha256,
                 sntrup761x25519-sha512,sntrup761x25519-sha512@openssh.com,
                 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 or Unix-domain socket on the local machine be forwarded over the secure channel to the specified host and port (or Unix-domain socket) from the re
           mote machine.  For a TCP port, the first argument must 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.

           If either argument contains a '/' in it, that argument will be interpreted as a Unix-domain socket (on the corresponding host) rather than a TCP port.

           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 spec
           ified  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  fol
           lowing 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 argu
           ment  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  li‐
           brary 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.   Set‐
           ting  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  (in‐
           cluding  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, re‐
           spectively.  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 or Unix-domain socket on the remote machine be forwarded over the secure channel.  The remote port may either be forwarded to a  specified  host  and
           port  or  Unix-domain  socket  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.

           If either argument contains a '/' in it, that argument will be interpreted as a Unix-domain socket (on the corresponding host) rather than a TCP port.

           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  re‐
           mote 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 au
           thentication 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  environ‐
           ment  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, or 300 if the BatchMode option is set (Debian-specific).  ProtocolKeepAlives
           is a Debian-specific compatibility alias for this option.

   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 in the form “NAME=VALUE”.  Similarly to SendEnv, with the exception of the  TERM
           variable, the server must be prepared to accept the environment variable.

           The “VALUE” may use the tokens described in the “TOKENS” section and environment variables as described in the “ENVIRONMENT VARIABLES” section.

   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 pro
           ceed, 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.  This option only uses TCP keepalives (as opposed to using ssh level keepalives), so takes a long time to notice when the connection dies.  As such, you probably want
           the ServerAliveInterval option as well.  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  pub
           lic 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.  Arguments to User may use the tokens described in the “TOKENS” section (with the exception of %r and %C) and environment variables as described in
           the “ENVIRONMENT VARIABLES” section.

   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-spe
           cific 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  fin
           gerprint  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).

   VersionAddendum
           Optionally specifies additional text to append to the SSH protocol banner sent by the client upon connection.  The default is none.

   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/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 exam
   ple, 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, UserKnownHostsFile  and
   VersionAddendum 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 com
   mands (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 direc
   tory.  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.  It may be group-writable provided that the group in question contains only the user.

   /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.

SEE ALSO

   ssh(1)

AUTHORS

   OpenSSH is a derivative of the original and free ssh 1.2.12 release by Tatu Ylonen.  Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo de Raadt and  Dug  Song  removed  many
   bugs, re-added newer features and created OpenSSH.  Markus Friedl contributed the support for SSH protocol versions 1.5 and 2.0.

Debian March 3, 2025 SSH_CONFIG(5)