{ "content": [ { "type": "text", "text": "# SSH_CONFIG (man)\n\n## NAME\n\nsshconfig — OpenSSH client configuration file\n\n## DESCRIPTION\n\nssh(1) obtains configuration data from the following sources in the following order:\n\n## Sections\n\n- **NAME**\n- **DESCRIPTION** (94 subsections)\n- **PATTERNS**\n- **TOKENS**\n- **ENVIRONMENT VARIABLES**\n- **FILES**\n- **SEE ALSO**\n- **AUTHORS**\n\nUse structuredContent.sections for detailed options, examples, and full documentation.\n" } ], "structuredContent": { "command": "SSH_CONFIG", "section": "", "mode": "man", "summary": "sshconfig — OpenSSH client configuration file", "synopsis": null, "tldr_summary": null, "tldr_examples": [], "tldr_source": null, "flags": [], "examples": [], "see_also": [ { "name": "ssh", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/ssh/1/json" } ], "section_outline": [ { "name": "NAME", "lines": 2, "subsections": [] }, { "name": "DESCRIPTION", "lines": 80, "subsections": [ { "name": "AddKeysToAgent", "lines": 12 }, { "name": "AddressFamily", "lines": 3 }, { "name": "BatchMode", "lines": 6 }, { "name": "BindAddress", "lines": 3 }, { "name": "BindInterface", "lines": 3 }, { "name": "CanonicalDomains", "lines": 3 }, { "name": "CanonicalizeFallbackLocal", "lines": 6 }, { "name": "CanonicalizeHostname", "lines": 12 }, { "name": "CanonicalizeMaxDots", "lines": 3 }, { "name": "CanonicalizePermittedCNAMEs", "lines": 13 }, { "name": "CASignatureAlgorithms", "lines": 17 }, { "name": "CertificateFile", "lines": 13 }, { "name": "CheckHostIP", "lines": 6 }, { "name": "Ciphers", "lines": 29 }, { "name": "ClearAllForwardings", "lines": 6 }, { "name": "Compression", "lines": 2 }, { "name": "ConnectionAttempts", "lines": 4 }, { "name": "ConnectTimeout", "lines": 4 }, { "name": "ControlMaster", "lines": 20 }, { "name": "ControlPath", "lines": 9 }, { "name": "ControlPersist", "lines": 11 }, { "name": "DynamicForward", "lines": 15 }, { "name": "EnableSSHKeysign", "lines": 5 }, { "name": "EscapeChar", "lines": 5 }, { "name": "ExitOnForwardFailure", "lines": 7 }, { "name": "FingerprintHash", "lines": 3 }, { "name": "ForkAfterAuthentication", "lines": 13 }, { "name": "ForwardAgent", "lines": 11 }, { "name": "ForwardX11", "lines": 9 }, { "name": "ForwardX11Timeout", "lines": 6 }, { "name": "ForwardX11Trusted", "lines": 11 }, { "name": "GatewayPorts", "lines": 7 }, { "name": "GlobalKnownHostsFile", "lines": 3 }, { "name": "GSSAPIAuthentication", "lines": 2 }, { "name": "GSSAPIClientIdentity", "lines": 3 }, { "name": "GSSAPIDelegateCredentials", "lines": 2 }, { "name": "GSSAPIKeyExchange", "lines": 3 }, { "name": "GSSAPIRenewalForcesRekey", "lines": 13 }, { "name": "GSSAPIServerIdentity", "lines": 4 }, { "name": "GSSAPITrustDns", "lines": 4 }, { "name": "GSSAPIKexAlgorithms", "lines": 15 }, { "name": "HashKnownHosts", "lines": 8 }, { "name": "HostbasedAcceptedAlgorithms", "lines": 26 }, { "name": "HostbasedAuthentication", "lines": 3 }, { "name": "HostKeyAlgorithms", "lines": 29 }, { "name": "HostKeyAlias", "lines": 5 }, { "name": "Hostname", "lines": 5 }, { "name": "IdentitiesOnly", "lines": 7 }, { "name": "IdentityAgent", "lines": 13 }, { "name": "IdentityFile", "lines": 22 }, { "name": "IgnoreUnknown", "lines": 6 }, { "name": "Include", "lines": 17 }, { "name": "KbdInteractiveAuthentication", "lines": 4 }, { "name": "KbdInteractiveDevices", "lines": 5 }, { "name": "KexAlgorithms", "lines": 18 }, { "name": "KnownHostsCommand", "lines": 11 }, { "name": "LocalCommand", "lines": 10 }, { "name": "LocalForward", "lines": 16 }, { "name": "LogLevel", "lines": 5 }, { "name": "LogVerbose", "lines": 32 }, { "name": "NoHostAuthenticationForLocalhost", "lines": 3 }, { "name": "NumberOfPasswordPrompts", "lines": 3 }, { "name": "PasswordAuthentication", "lines": 3 }, { "name": "PermitLocalCommand", "lines": 3 }, { "name": "PermitRemoteOpen", "lines": 14 }, { "name": "PKCS11Provider", "lines": 7 }, { "name": "PreferredAuthentications", "lines": 7 }, { "name": "ProxyCommand", "lines": 17 }, { "name": "ProxyJump", "lines": 14 }, { "name": "ProxyUseFdpass", "lines": 3 }, { "name": "PubkeyAcceptedAlgorithms", "lines": 25 }, { "name": "PubkeyAuthentication", "lines": 5 }, { "name": "RekeyLimit", "lines": 10 }, { "name": "RemoteCommand", "lines": 5 }, { "name": "RemoteForward", "lines": 25 }, { "name": "RequestTTY", "lines": 5 }, { "name": "RevokedHostKeys", "lines": 7 }, { "name": "SecurityKeyProvider", "lines": 6 }, { "name": "SendEnv", "lines": 13 }, { "name": "ServerAliveCountMax", "lines": 13 }, { "name": "ServerAliveInterval", "lines": 7 }, { "name": "SessionType", "lines": 9 }, { "name": "StdinNull", "lines": 4 }, { "name": "StreamLocalBindMask", "lines": 8 }, { "name": "StreamLocalBindUnlink", "lines": 8 }, { "name": "StrictHostKeyChecking", "lines": 16 }, { "name": "SyslogFacility", "lines": 4 }, { "name": "TCPKeepAlive", "lines": 18 }, { "name": "TunnelDevice", "lines": 7 }, { "name": "UpdateHostKeys", "lines": 26 }, { "name": "UserKnownHostsFile", "lines": 5 }, { "name": "VerifyHostKeyDNS", "lines": 9 }, { "name": "VisualHostKey", "lines": 5 }, { "name": "XAuthLocation", "lines": 2 } ] }, { "name": "PATTERNS", "lines": 27, "subsections": [] }, { "name": "TOKENS", "lines": 38, "subsections": [] }, { "name": "ENVIRONMENT VARIABLES", "lines": 9, "subsections": [] }, { "name": "FILES", "lines": 11, "subsections": [] }, { "name": "SEE ALSO", "lines": 2, "subsections": [] }, { "name": "AUTHORS", "lines": 6, "subsections": [] } ], "sections": { "NAME": { "content": "sshconfig — OpenSSH client configuration file\n", "subsections": [] }, "DESCRIPTION": { "content": "ssh(1) obtains configuration data from the following sources in the following order:\n\n1. command-line options\n2. user's configuration file (~/.ssh/config)\n3. system-wide configuration file (/etc/ssh/sshconfig)\n\nFor each parameter, the first obtained value will be used. The configuration files contain\nsections separated by Host specifications, and that section is only applied for hosts that\nmatch one of the patterns given in the specification. The matched host name is usually the one\ngiven on the command line (see the CanonicalizeHostname option for exceptions).\n\nSince the first obtained value for each parameter is used, more host-specific declarations\nshould be given near the beginning of the file, and general defaults at the end.\n\nNote that the Debian openssh-client package sets several options as standard in\n/etc/ssh/sshconfig which are not the default in ssh(1):\n\n•• Include /etc/ssh/sshconfig.d/*.conf\n•• SendEnv LANG LC*\n•• HashKnownHosts yes\n•• GSSAPIAuthentication yes\n\n/etc/ssh/sshconfig.d/*.conf files are included at the start of the system-wide configuration\nfile, so options set there will override those in /etc/ssh/sshconfig.\n\nThe file contains keyword-argument pairs, one per line. Lines starting with ‘#’ and empty\nlines are interpreted as comments. Arguments may optionally be enclosed in double quotes (\")\nin order to represent arguments containing spaces. Configuration options may be separated by\nwhitespace or optional whitespace and exactly one ‘=’; the latter format is useful to avoid the\nneed to quote whitespace when specifying configuration options using the ssh, scp, and sftp -o\noption.\n\nThe possible keywords and their meanings are as follows (note that keywords are case-insensi‐\ntive and arguments are case-sensitive):\n\nHost Restricts the following declarations (up to the next Host or Match keyword) to be only\nfor those hosts that match one of the patterns given after the keyword. If more than\none pattern is provided, they should be separated by whitespace. A single ‘*’ as a\npattern can be used to provide global defaults for all hosts. The host is usually the\nhostname argument given on the command line (see the CanonicalizeHostname keyword for\nexceptions).\n\nA pattern entry may be negated by prefixing it with an exclamation mark (‘!’). If a\nnegated entry is matched, then the Host entry is ignored, regardless of whether any\nother patterns on the line match. Negated matches are therefore useful to provide ex‐\nceptions for wildcard matches.\n\nSee PATTERNS for more information on patterns.\n\nMatch Restricts the following declarations (up to the next Host or Match keyword) to be used\nonly when the conditions following the Match keyword are satisfied. Match conditions\nare specified using one or more criteria or the single token all which always matches.\nThe available criteria keywords are: canonical, final, exec, host, originalhost, user,\nand localuser. The all criteria must appear alone or immediately after canonical or\nfinal. Other criteria may be combined arbitrarily. All criteria but all, canonical,\nand final require an argument. Criteria may be negated by prepending an exclamation\nmark (‘!’).\n\nThe canonical keyword matches only when the configuration file is being re-parsed after\nhostname canonicalization (see the CanonicalizeHostname option). This may be useful to\nspecify conditions that work with canonical host names only.\n\nThe final keyword requests that the configuration be re-parsed (regardless of whether\nCanonicalizeHostname is enabled), and matches only during this final pass. If\nCanonicalizeHostname is enabled, then canonical and final match during the same pass.\n\nThe exec keyword executes the specified command under the user's shell. If the command\nreturns a zero exit status then the condition is considered true. Commands containing\nwhitespace characters must be quoted. Arguments to exec accept the tokens described in\nthe TOKENS section.\n\nThe other keywords' criteria must be single entries or comma-separated lists and may\nuse the wildcard and negation operators described in the PATTERNS section. The crite‐\nria for the host keyword are matched against the target hostname, after any substitu‐\ntion by the Hostname or CanonicalizeHostname options. The originalhost keyword matches\nagainst the hostname as it was specified on the command-line. The user keyword matches\nagainst the target username on the remote host. The localuser keyword matches against\nthe name of the local user running ssh(1) (this keyword may be useful in system-wide\nsshconfig files).\n", "subsections": [ { "name": "AddKeysToAgent", "content": "Specifies whether keys should be automatically added to a running ssh-agent(1). If\nthis option is set to yes and a key is loaded from a file, the key and its passphrase\nare added to the agent with the default lifetime, as if by ssh-add(1). If this option\nis set to ask, ssh(1) will require confirmation using the SSHASKPASS program before\nadding a key (see ssh-add(1) for details). If this option is set to confirm, each use\nof the key must be confirmed, as if the -c option was specified to ssh-add(1). If this\noption is set to no, no keys are added to the agent. Alternately, this option may be\nspecified as a time interval using the format described in the TIME FORMATS section of\nsshdconfig(5) to specify the key's lifetime in ssh-agent(1), after which it will auto‐\nmatically be removed. The argument must be no (the default), yes, confirm (optionally\nfollowed by a time interval), ask or a time interval.\n" }, { "name": "AddressFamily", "content": "Specifies which address family to use when connecting. Valid arguments are any (the\ndefault), inet (use IPv4 only), or inet6 (use IPv6 only).\n" }, { "name": "BatchMode", "content": "If set to yes, user interaction such as password prompts and host key confirmation re‐\nquests will be disabled. In addition, the ServerAliveInterval option will be set to\n300 seconds by default (Debian-specific). This option is useful in scripts and other\nbatch jobs where no user is present to interact with ssh(1), and where it is desirable\nto detect a broken network swiftly. The argument must be yes or no (the default).\n" }, { "name": "BindAddress", "content": "Use the specified address on the local machine as the source address of the connection.\nOnly useful on systems with more than one address.\n" }, { "name": "BindInterface", "content": "Use the address of the specified interface on the local machine as the source address\nof the connection.\n" }, { "name": "CanonicalDomains", "content": "When CanonicalizeHostname is enabled, this option specifies the list of domain suffixes\nin which to search for the specified destination host.\n" }, { "name": "CanonicalizeFallbackLocal", "content": "Specifies whether to fail with an error when hostname canonicalization fails. The de‐\nfault, yes, will attempt to look up the unqualified hostname using the system re‐\nsolver's search rules. A value of no will cause ssh(1) to fail instantly if\nCanonicalizeHostname is enabled and the target hostname cannot be found in any of the\ndomains specified by CanonicalDomains.\n" }, { "name": "CanonicalizeHostname", "content": "Controls whether explicit hostname canonicalization is performed. The default, no, is\nnot to perform any name rewriting and let the system resolver handle all hostname\nlookups. If set to yes then, for connections that do not use a ProxyCommand or\nProxyJump, ssh(1) will attempt to canonicalize the hostname specified on the command\nline using the CanonicalDomains suffixes and CanonicalizePermittedCNAMEs rules. If\nCanonicalizeHostname is set to always, then canonicalization is applied to proxied con‐\nnections too.\n\nIf this option is enabled, then the configuration files are processed again using the\nnew target name to pick up any new configuration in matching Host and Match stanzas. A\nvalue of none disables the use of a ProxyJump host.\n" }, { "name": "CanonicalizeMaxDots", "content": "Specifies the maximum number of dot characters in a hostname before canonicalization is\ndisabled. The default, 1, allows a single dot (i.e. hostname.subdomain).\n" }, { "name": "CanonicalizePermittedCNAMEs", "content": "Specifies rules to determine whether CNAMEs should be followed when canonicalizing\nhostnames. The rules consist of one or more arguments of\nsourcedomainlist:targetdomainlist, where sourcedomainlist is a pattern-list of\ndomains that may follow CNAMEs in canonicalization, and targetdomainlist is a pat‐\ntern-list of domains that they may resolve to.\n\nFor example, \"*.a.example.com:*.b.example.com,*.c.example.com\" will allow hostnames\nmatching \"*.a.example.com\" to be canonicalized to names in the \"*.b.example.com\" or\n\"*.c.example.com\" domains.\n\nA single argument of \"none\" causes no CNAMEs to be considered for canonicalization.\nThis is the default behaviour.\n" }, { "name": "CASignatureAlgorithms", "content": "Specifies which algorithms are allowed for signing of certificates by certificate au‐\nthorities (CAs). The default is:\n\nssh-ed25519,ecdsa-sha2-nistp256,\necdsa-sha2-nistp384,ecdsa-sha2-nistp521,\nsk-ssh-ed25519@openssh.com,\nsk-ecdsa-sha2-nistp256@openssh.com,\nrsa-sha2-512,rsa-sha2-256\n\nIf the specified list begins with a ‘+’ character, then the specified algorithms will\nbe appended to the default set instead of replacing them. If the specified list begins\nwith a ‘-’ character, then the specified algorithms (including wildcards) will be re‐\nmoved from the default set instead of replacing them.\n\nssh(1) will not accept host certificates signed using algorithms other than those spec‐\nified.\n" }, { "name": "CertificateFile", "content": "Specifies a file from which the user's certificate is read. A corresponding private\nkey must be provided separately in order to use this certificate either from an\nIdentityFile directive or -i flag to ssh(1), via ssh-agent(1), or via a PKCS11Provider\nor SecurityKeyProvider.\n\nArguments to CertificateFile may use the tilde syntax to refer to a user's home direc‐\ntory, the tokens described in the TOKENS section and environment variables as described\nin the ENVIRONMENT VARIABLES section.\n\nIt is possible to have multiple certificate files specified in configuration files;\nthese certificates will be tried in sequence. Multiple CertificateFile directives will\nadd to the list of certificates used for authentication.\n" }, { "name": "CheckHostIP", "content": "If set to yes ssh(1) will additionally check the host IP address in the knownhosts\nfile. This allows it to detect if a host key changed due to DNS spoofing and will add\naddresses of destination hosts to ~/.ssh/knownhosts in the process, regardless of the\nsetting of StrictHostKeyChecking. If the option is set to no (the default), the check\nwill not be executed.\n" }, { "name": "Ciphers", "content": "Specifies the ciphers allowed and their order of preference. Multiple ciphers must be\ncomma-separated. If the specified list begins with a ‘+’ character, then the specified\nciphers will be appended to the default set instead of replacing them. If the speci‐\nfied list begins with a ‘-’ character, then the specified ciphers (including wildcards)\nwill be removed from the default set instead of replacing them. If the specified list\nbegins with a ‘^’ character, then the specified ciphers will be placed at the head of\nthe default set.\n\nThe supported ciphers are:\n\n3des-cbc\naes128-cbc\naes192-cbc\naes256-cbc\naes128-ctr\naes192-ctr\naes256-ctr\naes128-gcm@openssh.com\naes256-gcm@openssh.com\nchacha20-poly1305@openssh.com\n\nThe default is:\n\nchacha20-poly1305@openssh.com,\naes128-ctr,aes192-ctr,aes256-ctr,\naes128-gcm@openssh.com,aes256-gcm@openssh.com\n\nThe list of available ciphers may also be obtained using \"ssh -Q cipher\".\n" }, { "name": "ClearAllForwardings", "content": "Specifies that all local, remote, and dynamic port forwardings specified in the config‐\nuration files or on the command line be cleared. This option is primarily useful when\nused from the ssh(1) command line to clear port forwardings set in configuration files,\nand is automatically set by scp(1) and sftp(1). The argument must be yes or no (the\ndefault).\n" }, { "name": "Compression", "content": "Specifies whether to use compression. The argument must be yes or no (the default).\n" }, { "name": "ConnectionAttempts", "content": "Specifies the number of tries (one per second) to make before exiting. The argument\nmust be an integer. This may be useful in scripts if the connection sometimes fails.\nThe default is 1.\n" }, { "name": "ConnectTimeout", "content": "Specifies the timeout (in seconds) used when connecting to the SSH server, instead of\nusing the default system TCP timeout. This timeout is applied both to establishing the\nconnection and to performing the initial SSH protocol handshake and key exchange.\n" }, { "name": "ControlMaster", "content": "Enables the sharing of multiple sessions over a single network connection. When set to\nyes, ssh(1) will listen for connections on a control socket specified using the\nControlPath argument. Additional sessions can connect to this socket using the same\nControlPath with ControlMaster set to no (the default). These sessions will try to re‐\nuse the master instance's network connection rather than initiating new ones, but will\nfall back to connecting normally if the control socket does not exist, or is not lis‐\ntening.\n\nSetting this to ask will cause ssh(1) to listen for control connections, but require\nconfirmation using ssh-askpass(1). If the ControlPath cannot be opened, ssh(1) will\ncontinue without connecting to a master instance.\n\nX11 and ssh-agent(1) forwarding is supported over these multiplexed connections, how‐\never the display and agent forwarded will be the one belonging to the master connection\ni.e. it is not possible to forward multiple displays or agents.\n\nTwo additional options allow for opportunistic multiplexing: try to use a master con‐\nnection but fall back to creating a new one if one does not already exist. These op‐\ntions are: auto and autoask. The latter requires confirmation like the ask option.\n" }, { "name": "ControlPath", "content": "Specify the path to the control socket used for connection sharing as described in the\nControlMaster section above or the string none to disable connection sharing. Argu‐\nments to ControlPath may use the tilde syntax to refer to a user's home directory, the\ntokens described in the TOKENS section and environment variables as described in the\nENVIRONMENT VARIABLES section. It is recommended that any ControlPath used for oppor‐\ntunistic connection sharing include at least %h, %p, and %r (or alternatively %C) and\nbe placed in a directory that is not writable by other users. This ensures that shared\nconnections are uniquely identified.\n" }, { "name": "ControlPersist", "content": "When used in conjunction with ControlMaster, specifies that the master connection\nshould remain open in the background (waiting for future client connections) after the\ninitial client connection has been closed. If set to no (the default), then the master\nconnection will not be placed into the background, and will close as soon as the ini‐\ntial client connection is closed. If set to yes or 0, then the master connection will\nremain in the background indefinitely (until killed or closed via a mechanism such as\nthe \"ssh -O exit\"). If set to a time in seconds, or a time in any of the formats docu‐\nmented in sshdconfig(5), then the backgrounded master connection will automatically\nterminate after it has remained idle (with no client connections) for the specified\ntime.\n" }, { "name": "DynamicForward", "content": "Specifies that a TCP port on the local machine be forwarded over the secure channel,\nand the application protocol is then used to determine where to connect to from the re‐\nmote machine.\n\nThe argument must be [bindaddress:]port. IPv6 addresses can be specified by enclosing\naddresses in square brackets. By default, the local port is bound in accordance with\nthe GatewayPorts setting. However, an explicit bindaddress may be used to bind the\nconnection to a specific address. The bindaddress of localhost indicates that the\nlistening port be bound for local use only, while an empty address or ‘*’ indicates\nthat the port should be available from all interfaces.\n\nCurrently the SOCKS4 and SOCKS5 protocols are supported, and ssh(1) will act as a SOCKS\nserver. Multiple forwardings may be specified, and additional forwardings can be given\non the command line. Only the superuser can forward privileged ports.\n" }, { "name": "EnableSSHKeysign", "content": "Setting this option to yes in the global client configuration file /etc/ssh/sshconfig\nenables the use of the helper program ssh-keysign(8) during HostbasedAuthentication.\nThe argument must be yes or no (the default). This option should be placed in the non-\nhostspecific section. See ssh-keysign(8) for more information.\n" }, { "name": "EscapeChar", "content": "Sets the escape character (default: ‘~’). The escape character can also be set on the\ncommand line. The argument should be a single character, ‘^’ followed by a letter, or\nnone to disable the escape character entirely (making the connection transparent for\nbinary data).\n" }, { "name": "ExitOnForwardFailure", "content": "Specifies whether ssh(1) should terminate the connection if it cannot set up all re‐\nquested dynamic, tunnel, local, and remote port forwardings, (e.g. if either end is un‐\nable to bind and listen on a specified port). Note that ExitOnForwardFailure does not\napply to connections made over port forwardings and will not, for example, cause ssh(1)\nto exit if TCP connections to the ultimate forwarding destination fail. The argument\nmust be yes or no (the default).\n" }, { "name": "FingerprintHash", "content": "Specifies the hash algorithm used when displaying key fingerprints. Valid options are:\nmd5 and sha256 (the default).\n" }, { "name": "ForkAfterAuthentication", "content": "Requests ssh to go to background just before command execution. This is useful if ssh\nis going to ask for passwords or passphrases, but the user wants it in the background.\nThis implies the StdinNull configuration option being set to “yes”. The recommended\nway to start X11 programs at a remote site is with something like ssh -f host xterm,\nwhich is the same as ssh host xterm if the ForkAfterAuthentication configuration option\nis set to “yes”.\n\nIf the ExitOnForwardFailure configuration option is set to “yes”, then a client started\nwith the ForkAfterAuthentication configuration option being set to “yes” will wait for\nall remote port forwards to be successfully established before placing itself in the\nbackground. The argument to this keyword must be yes (same as the -f option) or no\n(the default).\n" }, { "name": "ForwardAgent", "content": "Specifies whether the connection to the authentication agent (if any) will be forwarded\nto the remote machine. The argument may be yes, no (the default), an explicit path to\nan agent socket or the name of an environment variable (beginning with ‘$’) in which to\nfind the path.\n\nAgent forwarding should be enabled with caution. Users with the ability to bypass file\npermissions on the remote host (for the agent's Unix-domain socket) can access the lo‐\ncal agent through the forwarded connection. An attacker cannot obtain key material\nfrom the agent, however they can perform operations on the keys that enable them to au‐\nthenticate using the identities loaded into the agent.\n" }, { "name": "ForwardX11", "content": "Specifies whether X11 connections will be automatically redirected over the secure\nchannel and DISPLAY set. The argument must be yes or no (the default).\n\nX11 forwarding should be enabled with caution. Users with the ability to bypass file\npermissions on the remote host (for the user's X11 authorization database) can access\nthe local X11 display through the forwarded connection. An attacker may then be able\nto perform activities such as keystroke monitoring if the ForwardX11Trusted option is\nalso enabled.\n" }, { "name": "ForwardX11Timeout", "content": "Specify a timeout for untrusted X11 forwarding using the format described in the TIME\nFORMATS section of sshdconfig(5). X11 connections received by ssh(1) after this time\nwill be refused. Setting ForwardX11Timeout to zero will disable the timeout and permit\nX11 forwarding for the life of the connection. The default is to disable untrusted X11\nforwarding after twenty minutes has elapsed.\n" }, { "name": "ForwardX11Trusted", "content": "If this option is set to yes, (the Debian-specific default), remote X11 clients will\nhave full access to the original X11 display.\n\nIf this option is set to no (the upstream default), remote X11 clients will be consid‐\nered untrusted and prevented from stealing or tampering with data belonging to trusted\nX11 clients. Furthermore, the xauth(1) token used for the session will be set to ex‐\npire after 20 minutes. Remote clients will be refused access after this time.\n\nSee the X11 SECURITY extension specification for full details on the restrictions im‐\nposed on untrusted clients.\n" }, { "name": "GatewayPorts", "content": "Specifies whether remote hosts are allowed to connect to local forwarded ports. By de‐\nfault, ssh(1) binds local port forwardings to the loopback address. This prevents\nother remote hosts from connecting to forwarded ports. GatewayPorts can be used to\nspecify that ssh should bind local port forwardings to the wildcard address, thus al‐\nlowing remote hosts to connect to forwarded ports. The argument must be yes or no (the\ndefault).\n" }, { "name": "GlobalKnownHostsFile", "content": "Specifies one or more files to use for the global host key database, separated by\nwhitespace. The default is /etc/ssh/sshknownhosts, /etc/ssh/sshknownhosts2.\n" }, { "name": "GSSAPIAuthentication", "content": "Specifies whether user authentication based on GSSAPI is allowed. The default is no.\n" }, { "name": "GSSAPIClientIdentity", "content": "If set, specifies the GSSAPI client identity that ssh should use when connecting to the\nserver. The default is unset, which means that the default identity will be used.\n" }, { "name": "GSSAPIDelegateCredentials", "content": "Forward (delegate) credentials to the server. The default is no.\n" }, { "name": "GSSAPIKeyExchange", "content": "Specifies whether key exchange based on GSSAPI may be used. When using GSSAPI key ex‐\nchange the server need not have a host key. The default is “no”.\n" }, { "name": "GSSAPIRenewalForcesRekey", "content": "If set to “yes” then renewal of the client's GSSAPI credentials will force the rekeying\nof the ssh connection. With a compatible server, this will delegate the renewed creden‐\ntials to a session on the server.\n\nChecks are made to ensure that credentials are only propagated when the new credentials\nmatch the old ones on the originating client and where the receiving server still has\nthe old set in its cache.\n\nThe default is “no”.\n\nFor this to work GSSAPIKeyExchange needs to be enabled in the server and also used by\nthe client.\n" }, { "name": "GSSAPIServerIdentity", "content": "If set, specifies the GSSAPI server identity that ssh should expect when connecting to\nthe server. The default is unset, which means that the expected GSSAPI server identity\nwill be determined from the target hostname.\n" }, { "name": "GSSAPITrustDns", "content": "Set to “yes” to indicate that the DNS is trusted to securely canonicalize the name of\nthe host being connected to. If “no”, the hostname entered on the command line will be\npassed untouched to the GSSAPI library. The default is “no”.\n" }, { "name": "GSSAPIKexAlgorithms", "content": "The list of key exchange algorithms that are offered for GSSAPI key exchange. Possible\nvalues are\n\ngss-gex-sha1-,\ngss-group1-sha1-,\ngss-group14-sha1-,\ngss-group14-sha256-,\ngss-group16-sha512-,\ngss-nistp256-sha256-,\ngss-curve25519-sha256-\n\nThe default is\n“gss-group14-sha256-,gss-group16-sha512-,gss-nistp256-sha256-,gss-curve25519-sha256-,gss-gex-sha1-,gss-group14-sha1-”.\nThis option only applies to connections using GSSAPI.\n" }, { "name": "HashKnownHosts", "content": "Indicates that ssh(1) should hash host names and addresses when they are added to\n~/.ssh/knownhosts. These hashed names may be used normally by ssh(1) and sshd(8), but\nthey do not visually reveal identifying information if the file's contents are dis‐\nclosed. The default is no. Note that existing names and addresses in known hosts\nfiles will not be converted automatically, but may be manually hashed using\nssh-keygen(1). Use of this option may break facilities such as tab-completion that\nrely on being able to read unhashed host names from ~/.ssh/knownhosts.\n" }, { "name": "HostbasedAcceptedAlgorithms", "content": "Specifies the signature algorithms that will be used for hostbased authentication as a\ncomma-separated list of patterns. Alternately if the specified list begins with a ‘+’\ncharacter, then the specified signature algorithms will be appended to the default set\ninstead of replacing them. If the specified list begins with a ‘-’ character, then the\nspecified signature algorithms (including wildcards) will be removed from the default\nset instead of replacing them. If the specified list begins with a ‘^’ character, then\nthe specified signature algorithms will be placed at the head of the default set. The\ndefault for this option is:\n\nssh-ed25519-cert-v01@openssh.com,\necdsa-sha2-nistp256-cert-v01@openssh.com,\necdsa-sha2-nistp384-cert-v01@openssh.com,\necdsa-sha2-nistp521-cert-v01@openssh.com,\nsk-ssh-ed25519-cert-v01@openssh.com,\nsk-ecdsa-sha2-nistp256-cert-v01@openssh.com,\nrsa-sha2-512-cert-v01@openssh.com,\nrsa-sha2-256-cert-v01@openssh.com,\nssh-ed25519,\necdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,\nsk-ssh-ed25519@openssh.com,\nsk-ecdsa-sha2-nistp256@openssh.com,\nrsa-sha2-512,rsa-sha2-256\n\nThe -Q option of ssh(1) may be used to list supported signature algorithms. This was\nformerly named HostbasedKeyTypes.\n" }, { "name": "HostbasedAuthentication", "content": "Specifies whether to try rhosts based authentication with public key authentication.\nThe argument must be yes or no (the default).\n" }, { "name": "HostKeyAlgorithms", "content": "Specifies the host key signature algorithms that the client wants to use in order of\npreference. Alternately if the specified list begins with a ‘+’ character, then the\nspecified signature algorithms will be appended to the default set instead of replacing\nthem. If the specified list begins with a ‘-’ character, then the specified signature\nalgorithms (including wildcards) will be removed from the default set instead of re‐\nplacing them. If the specified list begins with a ‘^’ character, then the specified\nsignature algorithms will be placed at the head of the default set. The default for\nthis option is:\n\nssh-ed25519-cert-v01@openssh.com,\necdsa-sha2-nistp256-cert-v01@openssh.com,\necdsa-sha2-nistp384-cert-v01@openssh.com,\necdsa-sha2-nistp521-cert-v01@openssh.com,\nsk-ssh-ed25519-cert-v01@openssh.com,\nsk-ecdsa-sha2-nistp256-cert-v01@openssh.com,\nrsa-sha2-512-cert-v01@openssh.com,\nrsa-sha2-256-cert-v01@openssh.com,\nssh-ed25519,\necdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,\nsk-ecdsa-sha2-nistp256@openssh.com,\nsk-ssh-ed25519@openssh.com,\nrsa-sha2-512,rsa-sha2-256\n\nIf hostkeys are known for the destination host then this default is modified to prefer\ntheir algorithms.\n\nThe list of available signature algorithms may also be obtained using \"ssh -Q\nHostKeyAlgorithms\".\n" }, { "name": "HostKeyAlias", "content": "Specifies an alias that should be used instead of the real host name when looking up or\nsaving the host key in the host key database files and when validating host certifi‐\ncates. This option is useful for tunneling SSH connections or for multiple servers\nrunning on a single host.\n" }, { "name": "Hostname", "content": "Specifies the real host name to log into. This can be used to specify nicknames or ab‐\nbreviations for hosts. Arguments to Hostname accept the tokens described in the TOKENS\nsection. Numeric IP addresses are also permitted (both on the command line and in\nHostname specifications). The default is the name given on the command line.\n" }, { "name": "IdentitiesOnly", "content": "Specifies that ssh(1) should only use the configured authentication identity and cer‐\ntificate files (either the default files, or those explicitly configured in the\nsshconfig files or passed on the ssh(1) command-line), even if ssh-agent(1) or a\nPKCS11Provider or SecurityKeyProvider offers more identities. The argument to this\nkeyword must be yes or no (the default). This option is intended for situations where\nssh-agent offers many different identities.\n" }, { "name": "IdentityAgent", "content": "Specifies the UNIX-domain socket used to communicate with the authentication agent.\n\nThis option overrides the SSHAUTHSOCK environment variable and can be used to select\na specific agent. Setting the socket name to none disables the use of an authentica‐\ntion agent. If the string \"SSHAUTHSOCK\" is specified, the location of the socket\nwill be read from the SSHAUTHSOCK environment variable. Otherwise if the specified\nvalue begins with a ‘$’ character, then it will be treated as an environment variable\ncontaining the location of the socket.\n\nArguments to IdentityAgent may use the tilde syntax to refer to a user's home direc‐\ntory, the tokens described in the TOKENS section and environment variables as described\nin the ENVIRONMENT VARIABLES section.\n" }, { "name": "IdentityFile", "content": "Specifies a file from which the user's DSA, ECDSA, authenticator-hosted ECDSA, Ed25519,\nauthenticator-hosted Ed25519 or RSA authentication identity is read. The default is\n~/.ssh/idrsa, ~/.ssh/idecdsa, ~/.ssh/idecdsask, ~/.ssh/ided25519,\n~/.ssh/ided25519sk and ~/.ssh/iddsa. Additionally, any identities represented by\nthe authentication agent will be used for authentication unless IdentitiesOnly is set.\nIf no certificates have been explicitly specified by CertificateFile, ssh(1) will try\nto load certificate information from the filename obtained by appending -cert.pub to\nthe path of a specified IdentityFile.\n\nArguments to IdentityFile may use the tilde syntax to refer to a user's home directory\nor the tokens described in the TOKENS section.\n\nIt is possible to have multiple identity files specified in configuration files; all\nthese identities will be tried in sequence. Multiple IdentityFile directives will add\nto the list of identities tried (this behaviour differs from that of other configura‐\ntion directives).\n\nIdentityFile may be used in conjunction with IdentitiesOnly to select which identities\nin an agent are offered during authentication. IdentityFile may also be used in con‐\njunction with CertificateFile in order to provide any certificate also needed for au‐\nthentication with the identity.\n" }, { "name": "IgnoreUnknown", "content": "Specifies a pattern-list of unknown options to be ignored if they are encountered in\nconfiguration parsing. This may be used to suppress errors if sshconfig contains op‐\ntions that are unrecognised by ssh(1). It is recommended that IgnoreUnknown be listed\nearly in the configuration file as it will not be applied to unknown options that ap‐\npear before it.\n" }, { "name": "Include", "content": "Include the specified configuration file(s). Multiple pathnames may be specified and\neach pathname may contain glob(7) wildcards and, for user configurations, shell-like\n‘~’ references to user home directories. Wildcards will be expanded and processed in\nlexical order. Files without absolute paths are assumed to be in ~/.ssh if included in\na user configuration file or /etc/ssh if included from the system configuration file.\nInclude directive may appear inside a Match or Host block to perform conditional inclu‐\nsion.\n\nIPQoS Specifies the IPv4 type-of-service or DSCP class for connections. Accepted values are\naf11, af12, af13, af21, af22, af23, af31, af32, af33, af41, af42, af43, cs0, cs1, cs2,\ncs3, cs4, cs5, cs6, cs7, ef, le, lowdelay, throughput, reliability, a numeric value, or\nnone to use the operating system default. This option may take one or two arguments,\nseparated by whitespace. If one argument is specified, it is used as the packet class\nunconditionally. If two values are specified, the first is automatically selected for\ninteractive sessions and the second for non-interactive sessions. The default is\nlowdelay for interactive sessions and throughput for non-interactive sessions.\n" }, { "name": "KbdInteractiveAuthentication", "content": "Specifies whether to use keyboard-interactive authentication. The argument to this\nkeyword must be yes (the default) or no. ChallengeResponseAuthentication is a depre‐\ncated alias for this.\n" }, { "name": "KbdInteractiveDevices", "content": "Specifies the list of methods to use in keyboard-interactive authentication. Multiple\nmethod names must be comma-separated. The default is to use the server specified list.\nThe methods available vary depending on what the server supports. For an OpenSSH\nserver, it may be zero or more of: bsdauth and pam.\n" }, { "name": "KexAlgorithms", "content": "Specifies the available KEX (Key Exchange) algorithms. Multiple algorithms must be\ncomma-separated. If the specified list begins with a ‘+’ character, then the specified\nalgorithms will be appended to the default set instead of replacing them. If the spec‐\nified list begins with a ‘-’ character, then the specified algorithms (including wild‐\ncards) will be removed from the default set instead of replacing them. If the speci‐\nfied list begins with a ‘^’ character, then the specified algorithms will be placed at\nthe head of the default set. The default is:\n\ncurve25519-sha256,curve25519-sha256@libssh.org,\necdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,\nsntrup761x25519-sha512@openssh.com,\ndiffie-hellman-group-exchange-sha256,\ndiffie-hellman-group16-sha512,\ndiffie-hellman-group18-sha512,\ndiffie-hellman-group14-sha256\n\nThe list of available key exchange algorithms may also be obtained using \"ssh -Q kex\".\n" }, { "name": "KnownHostsCommand", "content": "Specifies a command to use to obtain a list of host keys, in addition to those listed\nin UserKnownHostsFile and GlobalKnownHostsFile. This command is executed after the\nfiles have been read. It may write host key lines to standard output in identical for‐\nmat to the usual files (described in the VERIFYING HOST KEYS section in ssh(1)). Argu‐\nments to KnownHostsCommand accept the tokens described in the TOKENS section. The com‐\nmand may be invoked multiple times per connection: once when preparing the preference\nlist of host key algorithms to use, again to obtain the host key for the requested host\nname and, if CheckHostIP is enabled, one more time to obtain the host key matching the\nserver's address. If the command exits abnormally or returns a non-zero exit status\nthen the connection is terminated.\n" }, { "name": "LocalCommand", "content": "Specifies a command to execute on the local machine after successfully connecting to\nthe server. The command string extends to the end of the line, and is executed with\nthe user's shell. Arguments to LocalCommand accept the tokens described in the TOKENS\nsection.\n\nThe command is run synchronously and does not have access to the session of the ssh(1)\nthat spawned it. It should not be used for interactive commands.\n\nThis directive is ignored unless PermitLocalCommand has been enabled.\n" }, { "name": "LocalForward", "content": "Specifies that a TCP port on the local machine be forwarded over the secure channel to\nthe specified host and port from the remote machine. The first argument specifies the\nlistener and may be [bindaddress:]port or a Unix domain socket path. The second argu‐\nment is the destination and may be host:hostport or a Unix domain socket path if the\nremote host supports it.\n\nIPv6 addresses can be specified by enclosing addresses in square brackets. Multiple\nforwardings may be specified, and additional forwardings can be given on the command\nline. Only the superuser can forward privileged ports. By default, the local port is\nbound in accordance with the GatewayPorts setting. However, an explicit bindaddress\nmay be used to bind the connection to a specific address. The bindaddress of\nlocalhost indicates that the listening port be bound for local use only, while an empty\naddress or ‘*’ indicates that the port should be available from all interfaces. Unix\ndomain socket paths may use the tokens described in the TOKENS section and environment\nvariables as described in the ENVIRONMENT VARIABLES section.\n" }, { "name": "LogLevel", "content": "Gives the verbosity level that is used when logging messages from ssh(1). The possible\nvalues are: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The\ndefault is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify\nhigher levels of verbose output.\n" }, { "name": "LogVerbose", "content": "Specify one or more overrides to LogLevel. An override consists of a pattern lists\nthat matches the source file, function and line number to force detailed logging for.\nFor example, an override pattern of:\n\nkex.c:*:1000,*:kexexchangeidentification():*,packet.c:*\n\nwould enable detailed logging for line 1000 of kex.c, everything in the\nkexexchangeidentification() function, and all code in the packet.c file. This option\nis intended for debugging and no overrides are enabled by default.\n\nMACs Specifies the MAC (message authentication code) algorithms in order of preference. The\nMAC algorithm is used for data integrity protection. Multiple algorithms must be\ncomma-separated. If the specified list begins with a ‘+’ character, then the specified\nalgorithms will be appended to the default set instead of replacing them. If the spec‐\nified list begins with a ‘-’ character, then the specified algorithms (including wild‐\ncards) will be removed from the default set instead of replacing them. If the speci‐\nfied list begins with a ‘^’ character, then the specified algorithms will be placed at\nthe head of the default set.\n\nThe algorithms that contain \"-etm\" calculate the MAC after encryption (encrypt-then-\nmac). These are considered safer and their use recommended.\n\nThe default is:\n\numac-64-etm@openssh.com,umac-128-etm@openssh.com,\nhmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,\nhmac-sha1-etm@openssh.com,\numac-64@openssh.com,umac-128@openssh.com,\nhmac-sha2-256,hmac-sha2-512,hmac-sha1\n\nThe list of available MAC algorithms may also be obtained using \"ssh -Q mac\".\n" }, { "name": "NoHostAuthenticationForLocalhost", "content": "Disable host authentication for localhost (loopback addresses). The argument to this\nkeyword must be yes or no (the default).\n" }, { "name": "NumberOfPasswordPrompts", "content": "Specifies the number of password prompts before giving up. The argument to this key‐\nword must be an integer. The default is 3.\n" }, { "name": "PasswordAuthentication", "content": "Specifies whether to use password authentication. The argument to this keyword must be\nyes (the default) or no.\n" }, { "name": "PermitLocalCommand", "content": "Allow local command execution via the LocalCommand option or using the !command escape\nsequence in ssh(1). The argument must be yes or no (the default).\n" }, { "name": "PermitRemoteOpen", "content": "Specifies the destinations to which remote TCP port forwarding is permitted when\nRemoteForward is used as a SOCKS proxy. The forwarding specification must be one of\nthe following forms:\n\nPermitRemoteOpen host:port\nPermitRemoteOpen IPv4addr:port\nPermitRemoteOpen [IPv6addr]:port\n\nMultiple forwards may be specified by separating them with whitespace. An argument of\nany can be used to remove all restrictions and permit any forwarding requests. An ar‐\ngument of none can be used to prohibit all forwarding requests. The wildcard ‘*’ can\nbe used for host or port to allow all hosts or ports respectively. Otherwise, no pat‐\ntern matching or address lookups are performed on supplied names.\n" }, { "name": "PKCS11Provider", "content": "Specifies which PKCS#11 provider to use or none to indicate that no provider should be\nused (the default). The argument to this keyword is a path to the PKCS#11 shared li‐\nbrary ssh(1) should use to communicate with a PKCS#11 token providing keys for user au‐\nthentication.\n\nPort Specifies the port number to connect on the remote host. The default is 22.\n" }, { "name": "PreferredAuthentications", "content": "Specifies the order in which the client should try authentication methods. This allows\na client to prefer one method (e.g. keyboard-interactive) over another method (e.g.\npassword). The default is:\n\ngssapi-with-mic,hostbased,publickey,\nkeyboard-interactive,password\n" }, { "name": "ProxyCommand", "content": "Specifies the command to use to connect to the server. The command string extends to\nthe end of the line, and is executed using the user's shell ‘exec’ directive to avoid a\nlingering shell process.\n\nArguments to ProxyCommand accept the tokens described in the TOKENS section. The com‐\nmand can be basically anything, and should read from its standard input and write to\nits standard output. It should eventually connect an sshd(8) server running on some\nmachine, or execute sshd -i somewhere. Host key management will be done using the\nHostname of the host being connected (defaulting to the name typed by the user). Set‐\nting the command to none disables this option entirely. Note that CheckHostIP is not\navailable for connects with a proxy command.\n\nThis directive is useful in conjunction with nc(1) and its proxy support. For example,\nthe following directive would connect via an HTTP proxy at 192.0.2.0:\n\nProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p\n" }, { "name": "ProxyJump", "content": "Specifies one or more jump proxies as either [user@]host[:port] or an ssh URI. Multi‐\nple proxies may be separated by comma characters and will be visited sequentially.\nSetting this option will cause ssh(1) to connect to the target host by first making a\nssh(1) connection to the specified ProxyJump host and then establishing a TCP forward‐\ning to the ultimate target from there. Setting the host to none disables this option\nentirely.\n\nNote that this option will compete with the ProxyCommand option - whichever is speci‐\nfied first will prevent later instances of the other from taking effect.\n\nNote also that the configuration for the destination host (either supplied via the com‐\nmand-line or the configuration file) is not generally applied to jump hosts.\n~/.ssh/config should be used if specific configuration is required for jump hosts.\n" }, { "name": "ProxyUseFdpass", "content": "Specifies that ProxyCommand will pass a connected file descriptor back to ssh(1) in‐\nstead of continuing to execute and pass data. The default is no.\n" }, { "name": "PubkeyAcceptedAlgorithms", "content": "Specifies the signature algorithms that will be used for public key authentication as a\ncomma-separated list of patterns. If the specified list begins with a ‘+’ character,\nthen the algorithms after it will be appended to the default instead of replacing it.\nIf the specified list begins with a ‘-’ character, then the specified algorithms (in‐\ncluding wildcards) will be removed from the default set instead of replacing them. If\nthe specified list begins with a ‘^’ character, then the specified algorithms will be\nplaced at the head of the default set. The default for this option is:\n\nssh-ed25519-cert-v01@openssh.com,\necdsa-sha2-nistp256-cert-v01@openssh.com,\necdsa-sha2-nistp384-cert-v01@openssh.com,\necdsa-sha2-nistp521-cert-v01@openssh.com,\nsk-ssh-ed25519-cert-v01@openssh.com,\nsk-ecdsa-sha2-nistp256-cert-v01@openssh.com,\nrsa-sha2-512-cert-v01@openssh.com,\nrsa-sha2-256-cert-v01@openssh.com,\nssh-ed25519,\necdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,\nsk-ssh-ed25519@openssh.com,\nsk-ecdsa-sha2-nistp256@openssh.com,\nrsa-sha2-512,rsa-sha2-256\n\nThe list of available signature algorithms may also be obtained using \"ssh -Q\nPubkeyAcceptedAlgorithms\".\n" }, { "name": "PubkeyAuthentication", "content": "Specifies whether to try public key authentication. The argument to this keyword must\nbe yes (the default), no, unbound or host-bound. The final two options enable public\nkey authentication while respectively disabling or enabling the OpenSSH host-bound au‐\nthentication protocol extension required for restricted ssh-agent(1) forwarding.\n" }, { "name": "RekeyLimit", "content": "Specifies the maximum amount of data that may be transmitted before the session key is\nrenegotiated, optionally followed by a maximum amount of time that may pass before the\nsession key is renegotiated. The first argument is specified in bytes and may have a\nsuffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes, Megabytes, or Gigabytes, respec‐\ntively. The default is between ‘1G’ and ‘4G’, depending on the cipher. The optional\nsecond value is specified in seconds and may use any of the units documented in the\nTIME FORMATS section of sshdconfig(5). The default value for RekeyLimit is default\nnone, which means that rekeying is performed after the cipher's default amount of data\nhas been sent or received and no time based rekeying is done.\n" }, { "name": "RemoteCommand", "content": "Specifies a command to execute on the remote machine after successfully connecting to\nthe server. The command string extends to the end of the line, and is executed with\nthe user's shell. Arguments to RemoteCommand accept the tokens described in the TOKENS\nsection.\n" }, { "name": "RemoteForward", "content": "Specifies that a TCP port on the remote machine be forwarded over the secure channel.\nThe remote port may either be forwarded to a specified host and port from the local ma‐\nchine, or may act as a SOCKS 4/5 proxy that allows a remote client to connect to arbi‐\ntrary destinations from the local machine. The first argument is the listening speci‐\nfication and may be [bindaddress:]port or, if the remote host supports it, a Unix do‐\nmain socket path. If forwarding to a specific destination then the second argument\nmust be host:hostport or a Unix domain socket path, otherwise if no destination argu‐\nment is specified then the remote forwarding will be established as a SOCKS proxy.\nWhen acting as a SOCKS proxy the destination of the connection can be restricted by\nPermitRemoteOpen.\n\nIPv6 addresses can be specified by enclosing addresses in square brackets. Multiple\nforwardings may be specified, and additional forwardings can be given on the command\nline. Privileged ports can be forwarded only when logging in as root on the remote ma‐\nchine. Unix domain socket paths may use the tokens described in the TOKENS section and\nenvironment variables as described in the ENVIRONMENT VARIABLES section.\n\nIf the port argument is 0, the listen port will be dynamically allocated on the server\nand reported to the client at run time.\n\nIf the bindaddress is not specified, the default is to only bind to loopback ad‐\ndresses. If the bindaddress is ‘*’ or an empty string, then the forwarding is re‐\nquested to listen on all interfaces. Specifying a remote bindaddress will only suc‐\nceed if the server's GatewayPorts option is enabled (see sshdconfig(5)).\n" }, { "name": "RequestTTY", "content": "Specifies whether to request a pseudo-tty for the session. The argument may be one of:\nno (never request a TTY), yes (always request a TTY when standard input is a TTY),\nforce (always request a TTY) or auto (request a TTY when opening a login session).\nThis option mirrors the -t and -T flags for ssh(1).\n" }, { "name": "RevokedHostKeys", "content": "Specifies revoked host public keys. Keys listed in this file will be refused for host\nauthentication. Note that if this file does not exist or is not readable, then host\nauthentication will be refused for all hosts. Keys may be specified as a text file,\nlisting one public key per line, or as an OpenSSH Key Revocation List (KRL) as gener‐\nated by ssh-keygen(1). For more information on KRLs, see the KEY REVOCATION LISTS sec‐\ntion in ssh-keygen(1).\n" }, { "name": "SecurityKeyProvider", "content": "Specifies a path to a library that will be used when loading any FIDO authenticator-\nhosted keys, overriding the default of using the built-in USB HID support.\n\nIf the specified value begins with a ‘$’ character, then it will be treated as an envi‐\nronment variable containing the path to the library.\n" }, { "name": "SendEnv", "content": "Specifies what variables from the local environ(7) should be sent to the server. The\nserver must also support it, and the server must be configured to accept these environ‐\nment variables. Note that the TERM environment variable is always sent whenever a\npseudo-terminal is requested as it is required by the protocol. Refer to AcceptEnv in\nsshdconfig(5) for how to configure the server. Variables are specified by name, which\nmay contain wildcard characters. Multiple environment variables may be separated by\nwhitespace or spread across multiple SendEnv directives.\n\nSee PATTERNS for more information on patterns.\n\nIt is possible to clear previously set SendEnv variable names by prefixing patterns\nwith -. The default is not to send any environment variables.\n" }, { "name": "ServerAliveCountMax", "content": "Sets the number of server alive messages (see below) which may be sent without ssh(1)\nreceiving any messages back from the server. If this threshold is reached while server\nalive messages are being sent, ssh will disconnect from the server, terminating the\nsession. It is important to note that the use of server alive messages is very differ‐\nent from TCPKeepAlive (below). The server alive messages are sent through the en‐\ncrypted channel and therefore will not be spoofable. The TCP keepalive option enabled\nby TCPKeepAlive is spoofable. The server alive mechanism is valuable when the client\nor server depend on knowing when a connection has become unresponsive.\n\nThe default value is 3. If, for example, ServerAliveInterval (see below) is set to 15\nand ServerAliveCountMax is left at the default, if the server becomes unresponsive, ssh\nwill disconnect after approximately 45 seconds.\n" }, { "name": "ServerAliveInterval", "content": "Sets a timeout interval in seconds after which if no data has been received from the\nserver, ssh(1) will send a message through the encrypted channel to request a response\nfrom the server. The default is 0, indicating that these messages will not be sent to\nthe server, or 300 if the BatchMode option is set (Debian-specific).\nProtocolKeepAlives and SetupTimeOut are Debian-specific compatibility aliases for this\noption.\n" }, { "name": "SessionType", "content": "May be used to either request invocation of a subsystem on the remote system, or to\nprevent the execution of a remote command at all. The latter is useful for just for‐\nwarding ports. The argument to this keyword must be none (same as the -N option),\nsubsystem (same as the -s option) or default (shell or command execution).\n\nSetEnv Directly specify one or more environment variables and their contents to be sent to the\nserver. Similarly to SendEnv, with the exception of the TERM variable, the server must\nbe prepared to accept the environment variable.\n" }, { "name": "StdinNull", "content": "Redirects stdin from /dev/null (actually, prevents reading from stdin). Either this or\nthe equivalent -n option must be used when ssh is run in the background. The argument\nto this keyword must be yes (same as the -n option) or no (the default).\n" }, { "name": "StreamLocalBindMask", "content": "Sets the octal file creation mode mask (umask) used when creating a Unix-domain socket\nfile for local or remote port forwarding. This option is only used for port forwarding\nto a Unix-domain socket file.\n\nThe default value is 0177, which creates a Unix-domain socket file that is readable and\nwritable only by the owner. Note that not all operating systems honor the file mode on\nUnix-domain socket files.\n" }, { "name": "StreamLocalBindUnlink", "content": "Specifies whether to remove an existing Unix-domain socket file for local or remote\nport forwarding before creating a new one. If the socket file already exists and\nStreamLocalBindUnlink is not enabled, ssh will be unable to forward the port to the\nUnix-domain socket file. This option is only used for port forwarding to a Unix-domain\nsocket file.\n\nThe argument must be yes or no (the default).\n" }, { "name": "StrictHostKeyChecking", "content": "If this flag is set to yes, ssh(1) will never automatically add host keys to the\n~/.ssh/knownhosts file, and refuses to connect to hosts whose host key has changed.\nThis provides maximum protection against man-in-the-middle (MITM) attacks, though it\ncan be annoying when the /etc/ssh/sshknownhosts file is poorly maintained or when\nconnections to new hosts are frequently made. This option forces the user to manually\nadd all new hosts.\n\nIf this flag is set to accept-new then ssh will automatically add new host keys to the\nuser's knownhosts file, but will not permit connections to hosts with changed host\nkeys. If this flag is set to no or off, ssh will automatically add new host keys to\nthe user known hosts files and allow connections to hosts with changed hostkeys to pro‐\nceed, subject to some restrictions. If this flag is set to ask (the default), new host\nkeys will be added to the user known host files only after the user has confirmed that\nis what they really want to do, and ssh will refuse to connect to hosts whose host key\nhas changed. The host keys of known hosts will be verified automatically in all cases.\n" }, { "name": "SyslogFacility", "content": "Gives the facility code that is used when logging messages from ssh(1). The possible\nvalues are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6,\nLOCAL7. The default is USER.\n" }, { "name": "TCPKeepAlive", "content": "Specifies whether the system should send TCP keepalive messages to the other side. If\nthey are sent, death of the connection or crash of one of the machines will be properly\nnoticed. This option only uses TCP keepalives (as opposed to using ssh level\nkeepalives), so takes a long time to notice when the connection dies. As such, you\nprobably want the ServerAliveInterval option as well. However, this means that connec‐\ntions will die if the route is down temporarily, and some people find it annoying.\n\nThe default is yes (to send TCP keepalive messages), and the client will notice if the\nnetwork goes down or the remote host dies. This is important in scripts, and many\nusers want it too.\n\nTo disable TCP keepalive messages, the value should be set to no. See also\nServerAliveInterval for protocol-level keepalives.\n\nTunnel Request tun(4) device forwarding between the client and the server. The argument must\nbe yes, point-to-point (layer 3), ethernet (layer 2), or no (the default). Specifying\nyes requests the default tunnel mode, which is point-to-point.\n" }, { "name": "TunnelDevice", "content": "Specifies the tun(4) devices to open on the client (localtun) and the server\n(remotetun).\n\nThe argument must be localtun[:remotetun]. The devices may be specified by numerical\nID or the keyword any, which uses the next available tunnel device. If remotetun is\nnot specified, it defaults to any. The default is any:any.\n" }, { "name": "UpdateHostKeys", "content": "Specifies whether ssh(1) should accept notifications of additional hostkeys from the\nserver sent after authentication has completed and add them to UserKnownHostsFile. The\nargument must be yes, no or ask. This option allows learning alternate hostkeys for a\nserver and supports graceful key rotation by allowing a server to send replacement pub‐\nlic keys before old ones are removed.\n\nAdditional hostkeys are only accepted if the key used to authenticate the host was al‐\nready trusted or explicitly accepted by the user, the host was authenticated via\nUserKnownHostsFile (i.e. not GlobalKnownHostsFile) and the host was authenticated using\na plain key and not a certificate.\n\nUpdateHostKeys is enabled by default if the user has not overridden the default\nUserKnownHostsFile setting and has not enabled VerifyHostKeyDNS, otherwise\nUpdateHostKeys will be set to no.\n\nIf UpdateHostKeys is set to ask, then the user is asked to confirm the modifications to\nthe knownhosts file. Confirmation is currently incompatible with ControlPersist, and\nwill be disabled if it is enabled.\n\nPresently, only sshd(8) from OpenSSH 6.8 and greater support the \"hostkeys@openssh.com\"\nprotocol extension used to inform the client of all the server's hostkeys.\n\nUser Specifies the user to log in as. This can be useful when a different user name is used\non different machines. This saves the trouble of having to remember to give the user\nname on the command line.\n" }, { "name": "UserKnownHostsFile", "content": "Specifies one or more files to use for the user host key database, separated by white‐\nspace. Each filename may use tilde notation to refer to the user's home directory, the\ntokens described in the TOKENS section and environment variables as described in the\nENVIRONMENT VARIABLES section. The default is ~/.ssh/knownhosts, ~/.ssh/knownhosts2.\n" }, { "name": "VerifyHostKeyDNS", "content": "Specifies whether to verify the remote key using DNS and SSHFP resource records. If\nthis option is set to yes, the client will implicitly trust keys that match a secure\nfingerprint from DNS. Insecure fingerprints will be handled as if this option was set\nto ask. If this option is set to ask, information on fingerprint match will be dis‐\nplayed, but the user will still need to confirm new host keys according to the\nStrictHostKeyChecking option. The default is no.\n\nSee also VERIFYING HOST KEYS in ssh(1).\n" }, { "name": "VisualHostKey", "content": "If this flag is set to yes, an ASCII art representation of the remote host key finger‐\nprint is printed in addition to the fingerprint string at login and for unknown host\nkeys. If this flag is set to no (the default), no fingerprint strings are printed at\nlogin and only the fingerprint string will be printed for unknown host keys.\n" }, { "name": "XAuthLocation", "content": "Specifies the full pathname of the xauth(1) program. The default is /usr/bin/xauth.\n" } ] }, "PATTERNS": { "content": "A pattern consists of zero or more non-whitespace characters, ‘*’ (a wildcard that matches zero\nor more characters), or ‘?’ (a wildcard that matches exactly one character). For example, to\nspecify a set of declarations for any host in the \".co.uk\" set of domains, the following pat‐\ntern could be used:\n\nHost *.co.uk\n\nThe following pattern would match any host in the 192.168.0.[0-9] network range:\n\nHost 192.168.0.?\n\nA pattern-list is a comma-separated list of patterns. Patterns within pattern-lists may be\nnegated by preceding them with an exclamation mark (‘!’). For example, to allow a key to be\nused from anywhere within an organization except from the \"dialup\" pool, the following entry\n(in authorizedkeys) could be used:\n\nfrom=\"!*.dialup.example.com,*.example.com\"\n\nNote that a negated match will never produce a positive result by itself. For example, at‐\ntempting to match \"host3\" against the following pattern-list will fail:\n\nfrom=\"!host1,!host2\"\n\nThe solution here is to include a term that will yield a positive match, such as a wildcard:\n\nfrom=\"!host1,!host2,*\"\n", "subsections": [] }, "TOKENS": { "content": "Arguments to some keywords can make use of tokens, which are expanded at runtime:\n\n%% A literal ‘%’.\n%C Hash of %l%h%p%r.\n%d Local user's home directory.\n%f The fingerprint of the server's host key.\n%H The knownhosts hostname or address that is being searched for.\n%h The remote hostname.\n%I A string describing the reason for a KnownHostsCommand execution: either ADDRESS\nwhen looking up a host by address (only when CheckHostIP is enabled), HOSTNAME when\nsearching by hostname, or ORDER when preparing the host key algorithm preference\nlist to use for the destination host.\n%i The local user ID.\n%K The base64 encoded host key.\n%k The host key alias if specified, otherwise the original remote hostname given on\nthe command line.\n%L The local hostname.\n%l The local hostname, including the domain name.\n%n The original remote hostname, as given on the command line.\n%p The remote port.\n%r The remote username.\n%T The local tun(4) or tap(4) network interface assigned if tunnel forwarding was re‐\nquested, or \"NONE\" otherwise.\n%t The type of the server host key, e.g. ssh-ed25519.\n%u The local username.\n\nCertificateFile, ControlPath, IdentityAgent, IdentityFile, KnownHostsCommand, LocalForward,\nMatch exec, RemoteCommand, RemoteForward, and UserKnownHostsFile accept the tokens %%, %C, %d,\n%h, %i, %k, %L, %l, %n, %p, %r, and %u.\n\nKnownHostsCommand additionally accepts the tokens %f, %H, %I, %K and %t.\n\nHostname accepts the tokens %% and %h.\n\nLocalCommand accepts all tokens.\n\nProxyCommand accepts the tokens %%, %h, %n, %p, and %r.\n", "subsections": [] }, "ENVIRONMENT VARIABLES": { "content": "Arguments to some keywords can be expanded at runtime from environment variables on the client\nby enclosing them in ${}, for example ${HOME}/.ssh would refer to the user's .ssh directory.\nIf a specified environment variable does not exist then an error will be returned and the set‐\nting for that keyword will be ignored.\n\nThe keywords CertificateFile, ControlPath, IdentityAgent, IdentityFile, KnownHostsCommand, and\nUserKnownHostsFile support environment variables. The keywords LocalForward and RemoteForward\nsupport environment variables only for Unix domain socket paths.\n", "subsections": [] }, "FILES": { "content": "~/.ssh/config\nThis is the per-user configuration file. The format of this file is described above.\nThis file is used by the SSH client. Because of the potential for abuse, this file\nmust have strict permissions: read/write for the user, and not writable by others. It\nmay be group-writable provided that the group in question contains only the user.\n\n/etc/ssh/sshconfig\nSystemwide configuration file. This file provides defaults for those values that are\nnot specified in the user's configuration file, and for those users who do not have a\nconfiguration file. This file must be world-readable.\n", "subsections": [] }, "SEE ALSO": { "content": "ssh(1)\n", "subsections": [] }, "AUTHORS": { "content": "OpenSSH is a derivative of the original and free ssh 1.2.12 release by Tatu Ylonen. Aaron\nCampbell, Bob Beck, Markus Friedl, Niels Provos, Theo de Raadt and Dug Song removed many bugs,\nre-added newer features and created OpenSSH. Markus Friedl contributed the support for SSH\nprotocol versions 1.5 and 2.0.\n\nBSD February 15, 2022 BSD", "subsections": [] } } } }