{ "content": [ { "type": "text", "text": "# sshd_config (man)\n\n## NAME\n\nsshdconfig — OpenSSH daemon configuration file\n\n## DESCRIPTION\n\nsshd(8) reads configuration data from /etc/ssh/sshdconfig (or the file specified with -f on\nthe command line). The file contains keyword-argument pairs, one per line. For each keyword,\nthe first obtained value will be used. Lines starting with ‘#’ and empty lines are interpreted\nas comments. Arguments may optionally be enclosed in double quotes (\") in order to represent\narguments containing spaces.\n\n## Sections\n\n- **NAME**\n- **DESCRIPTION** (90 subsections)\n- **TIME FORMATS**\n- **TOKENS**\n- **FILES**\n- **SEE ALSO**\n- **AUTHORS**\n\nUse structuredContent.sections for detailed options, examples, and full documentation.\n" } ], "structuredContent": { "command": "sshd_config", "section": "", "mode": "man", "summary": "sshdconfig — OpenSSH daemon configuration file", "synopsis": null, "tldr_summary": null, "tldr_examples": [], "tldr_source": null, "flags": [], "examples": [], "see_also": [ { "name": "sftp-server", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/sftp-server/8/json" }, { "name": "sshd", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/sshd/8/json" } ], "section_outline": [ { "name": "NAME", "lines": 2, "subsections": [] }, { "name": "DESCRIPTION", "lines": 23, "subsections": [ { "name": "AcceptEnv", "lines": 10 }, { "name": "AddressFamily", "lines": 3 }, { "name": "AllowAgentForwarding", "lines": 4 }, { "name": "AllowGroups", "lines": 8 }, { "name": "AllowStreamLocalForwarding", "lines": 7 }, { "name": "AllowTcpForwarding", "lines": 6 }, { "name": "AllowUsers", "lines": 11 }, { "name": "AuthenticationMethods", "lines": 31 }, { "name": "AuthorizedKeysCommand", "lines": 10 }, { "name": "AuthorizedKeysCommandUser", "lines": 5 }, { "name": "AuthorizedKeysFile", "lines": 8 }, { "name": "AuthorizedPrincipalsCommand", "lines": 12 }, { "name": "AuthorizedPrincipalsCommandUser", "lines": 5 }, { "name": "AuthorizedPrincipalsFile", "lines": 22 }, { "name": "CASignatureAlgorithms", "lines": 17 }, { "name": "ChrootDirectory", "lines": 20 }, { "name": "Ciphers", "lines": 28 }, { "name": "ClientAliveCountMax", "lines": 13 }, { "name": "ClientAliveInterval", "lines": 5 }, { "name": "Compression", "lines": 4 }, { "name": "DebianBanner", "lines": 3 }, { "name": "DenyGroups", "lines": 8 }, { "name": "DenyUsers", "lines": 10 }, { "name": "DisableForwarding", "lines": 4 }, { "name": "ExposeAuthInfo", "lines": 4 }, { "name": "FingerprintHash", "lines": 3 }, { "name": "ForceCommand", "lines": 8 }, { "name": "GatewayPorts", "lines": 9 }, { "name": "GSSAPIAuthentication", "lines": 2 }, { "name": "GSSAPICleanupCredentials", "lines": 3 }, { "name": "GSSAPIKeyExchange", "lines": 3 }, { "name": "GSSAPIStrictAcceptorCheck", "lines": 6 }, { "name": "GSSAPIStoreCredentialsOnRekey", "lines": 7 }, { "name": "GSSAPIKexAlgorithms", "lines": 15 }, { "name": "HostbasedAcceptedAlgorithms", "lines": 26 }, { "name": "HostbasedAuthentication", "lines": 4 }, { "name": "HostbasedUsesNameFromPacketOnly", "lines": 6 }, { "name": "HostCertificate", "lines": 4 }, { "name": "HostKey", "lines": 11 }, { "name": "HostKeyAgent", "lines": 4 }, { "name": "HostKeyAlgorithms", "lines": 20 }, { "name": "IgnoreRhosts", "lines": 7 }, { "name": "IgnoreUserKnownHosts", "lines": 4 }, { "name": "Include", "lines": 14 }, { "name": "KbdInteractiveAuthentication", "lines": 4 }, { "name": "KerberosAuthentication", "lines": 4 }, { "name": "KerberosGetAFSToken", "lines": 3 }, { "name": "KerberosOrLocalPasswd", "lines": 3 }, { "name": "KerberosTicketCleanup", "lines": 3 }, { "name": "KexAlgorithms", "lines": 34 }, { "name": "ListenAddress", "lines": 12 }, { "name": "LoginGraceTime", "lines": 3 }, { "name": "LogLevel", "lines": 6 }, { "name": "LogVerbose", "lines": 84 }, { "name": "MaxAuthTries", "lines": 4 }, { "name": "MaxSessions", "lines": 6 }, { "name": "MaxStartups", "lines": 10 }, { "name": "ModuliFile", "lines": 4 }, { "name": "PasswordAuthentication", "lines": 2 }, { "name": "PermitEmptyPasswords", "lines": 3 }, { "name": "PermitListen", "lines": 16 }, { "name": "PermitOpen", "lines": 14 }, { "name": "PermitRootLogin", "lines": 13 }, { "name": "PermitTTY", "lines": 2 }, { "name": "PermitTunnel", "lines": 7 }, { "name": "PermitUserEnvironment", "lines": 6 }, { "name": "PermitUserRC", "lines": 2 }, { "name": "PerSourceMaxStartups", "lines": 4 }, { "name": "PerSourceNetBlockSize", "lines": 5 }, { "name": "PidFile", "lines": 6 }, { "name": "PrintLastLog", "lines": 3 }, { "name": "PrintMotd", "lines": 4 }, { "name": "PubkeyAcceptedAlgorithms", "lines": 26 }, { "name": "PubkeyAuthOptions", "lines": 16 }, { "name": "PubkeyAuthentication", "lines": 2 }, { "name": "RekeyLimit", "lines": 10 }, { "name": "RevokedKeys", "lines": 7 }, { "name": "SecurityKeyProvider", "lines": 8 }, { "name": "StreamLocalBindMask", "lines": 8 }, { "name": "StreamLocalBindUnlink", "lines": 8 }, { "name": "StrictModes", "lines": 6 }, { "name": "Subsystem", "lines": 12 }, { "name": "SyslogFacility", "lines": 4 }, { "name": "TCPKeepAlive", "lines": 14 }, { "name": "TrustedUserCAKeys", "lines": 26 }, { "name": "VersionAddendum", "lines": 3 }, { "name": "X11DisplayOffset", "lines": 3 }, { "name": "X11Forwarding", "lines": 16 }, { "name": "X11UseLocalhost", "lines": 8 }, { "name": "XAuthLocation", "lines": 3 } ] }, { "name": "TIME FORMATS", "lines": 19, "subsections": [] }, { "name": "TOKENS", "lines": 26, "subsections": [] }, { "name": "FILES", "lines": 4, "subsections": [] }, { "name": "SEE ALSO", "lines": 2, "subsections": [] }, { "name": "AUTHORS", "lines": 7, "subsections": [] } ], "sections": { "NAME": { "content": "sshdconfig — OpenSSH daemon configuration file\n", "subsections": [] }, "DESCRIPTION": { "content": "sshd(8) reads configuration data from /etc/ssh/sshdconfig (or the file specified with -f on\nthe command line). The file contains keyword-argument pairs, one per line. For each keyword,\nthe first obtained value will be used. Lines starting with ‘#’ and empty lines are interpreted\nas comments. Arguments may optionally be enclosed in double quotes (\") in order to represent\narguments containing spaces.\n\nNote that the Debian openssh-server package sets several options as standard in\n/etc/ssh/sshdconfig which are not the default in sshd(8):\n\n•• Include /etc/ssh/sshdconfig.d/*.conf\n•• KbdInteractiveAuthentication no\n•• X11Forwarding yes\n•• PrintMotd no\n•• AcceptEnv LANG LC*\n•• Subsystem sftp /usr/lib/openssh/sftp-server\n•• UsePAM yes\n\n/etc/ssh/sshdconfig.d/*.conf files are included at the start of the configuration file, so op‐\ntions set there will override those in /etc/ssh/sshdconfig.\n\nThe possible keywords and their meanings are as follows (note that keywords are case-insensi‐\ntive and arguments are case-sensitive):\n", "subsections": [ { "name": "AcceptEnv", "content": "Specifies what environment variables sent by the client will be copied into the ses‐\nsion's environ(7). See SendEnv and SetEnv in sshconfig(5) for how to configure the\nclient. The TERM environment variable is always accepted whenever the client requests\na pseudo-terminal as it is required by the protocol. Variables are specified by name,\nwhich may contain the wildcard characters ‘*’ and ‘?’. Multiple environment variables\nmay be separated by whitespace or spread across multiple AcceptEnv directives. Be\nwarned that some environment variables could be used to bypass restricted user environ‐\nments. For this reason, care should be taken in the use of this directive. The de‐\nfault is not to accept any environment variables.\n" }, { "name": "AddressFamily", "content": "Specifies which address family should be used by sshd(8). Valid arguments are any (the\ndefault), inet (use IPv4 only), or inet6 (use IPv6 only).\n" }, { "name": "AllowAgentForwarding", "content": "Specifies whether ssh-agent(1) forwarding is permitted. The default is yes. Note that\ndisabling agent forwarding does not improve security unless users are also denied shell\naccess, as they can always install their own forwarders.\n" }, { "name": "AllowGroups", "content": "This keyword can be followed by a list of group name patterns, separated by spaces. If\nspecified, login is allowed only for users whose primary group or supplementary group\nlist matches one of the patterns. Only group names are valid; a numerical group ID is\nnot recognized. By default, login is allowed for all groups. The allow/deny groups\ndirectives are processed in the following order: DenyGroups, AllowGroups.\n\nSee PATTERNS in sshconfig(5) for more information on patterns.\n" }, { "name": "AllowStreamLocalForwarding", "content": "Specifies whether StreamLocal (Unix-domain socket) forwarding is permitted. The avail‐\nable options are yes (the default) or all to allow StreamLocal forwarding, no to pre‐\nvent all StreamLocal forwarding, local to allow local (from the perspective of ssh(1))\nforwarding only or remote to allow remote forwarding only. Note that disabling Stream‐\nLocal forwarding does not improve security unless users are also denied shell access,\nas they can always install their own forwarders.\n" }, { "name": "AllowTcpForwarding", "content": "Specifies whether TCP forwarding is permitted. The available options are yes (the de‐\nfault) or all to allow TCP forwarding, no to prevent all TCP forwarding, local to allow\nlocal (from the perspective of ssh(1)) forwarding only or remote to allow remote for‐\nwarding only. Note that disabling TCP forwarding does not improve security unless\nusers are also denied shell access, as they can always install their own forwarders.\n" }, { "name": "AllowUsers", "content": "This keyword can be followed by a list of user name patterns, separated by spaces. If\nspecified, login is allowed only for user names that match one of the patterns. Only\nuser names are valid; a numerical user ID is not recognized. By default, login is al‐\nlowed for all users. If the pattern takes the form USER@HOST then USER and HOST are\nseparately checked, restricting logins to particular users from particular hosts. HOST\ncriteria may additionally contain addresses to match in CIDR address/masklen format.\nThe allow/deny users directives are processed in the following order: DenyUsers,\nAllowUsers.\n\nSee PATTERNS in sshconfig(5) for more information on patterns.\n" }, { "name": "AuthenticationMethods", "content": "Specifies the authentication methods that must be successfully completed for a user to\nbe granted access. This option must be followed by one or more lists of comma-sepa‐\nrated authentication method names, or by the single string any to indicate the default\nbehaviour of accepting any single authentication method. If the default is overridden,\nthen successful authentication requires completion of every method in at least one of\nthese lists.\n\nFor example, \"publickey,password publickey,keyboard-interactive\" would require the user\nto complete public key authentication, followed by either password or keyboard interac‐\ntive authentication. Only methods that are next in one or more lists are offered at\neach stage, so for this example it would not be possible to attempt password or key‐\nboard-interactive authentication before public key.\n\nFor keyboard interactive authentication it is also possible to restrict authentication\nto a specific device by appending a colon followed by the device identifier bsdauth or\npam. depending on the server configuration. For example,\n\"keyboard-interactive:bsdauth\" would restrict keyboard interactive authentication to\nthe bsdauth device.\n\nIf the publickey method is listed more than once, sshd(8) verifies that keys that have\nbeen used successfully are not reused for subsequent authentications. For example,\n\"publickey,publickey\" requires successful authentication using two different public\nkeys.\n\nNote that each authentication method listed should also be explicitly enabled in the\nconfiguration.\n\nThe available authentication methods are: \"gssapi-with-mic\", \"hostbased\",\n\"keyboard-interactive\", \"none\" (used for access to password-less accounts when\nPermitEmptyPasswords is enabled), \"password\" and \"publickey\".\n" }, { "name": "AuthorizedKeysCommand", "content": "Specifies a program to be used to look up the user's public keys. The program must be\nowned by root, not writable by group or others and specified by an absolute path. Ar‐\nguments to AuthorizedKeysCommand accept the tokens described in the TOKENS section. If\nno arguments are specified then the username of the target user is used.\n\nThe program should produce on standard output zero or more lines of authorizedkeys\noutput (see AUTHORIZEDKEYS in sshd(8)). AuthorizedKeysCommand is tried after the\nusual AuthorizedKeysFile files and will not be executed if a matching key is found\nthere. By default, no AuthorizedKeysCommand is run.\n" }, { "name": "AuthorizedKeysCommandUser", "content": "Specifies the user under whose account the AuthorizedKeysCommand is run. It is recom‐\nmended to use a dedicated user that has no other role on the host than running autho‐\nrized keys commands. If AuthorizedKeysCommand is specified but\nAuthorizedKeysCommandUser is not, then sshd(8) will refuse to start.\n" }, { "name": "AuthorizedKeysFile", "content": "Specifies the file that contains the public keys used for user authentication. The\nformat is described in the AUTHORIZEDKEYS FILE FORMAT section of sshd(8). Arguments\nto AuthorizedKeysFile accept the tokens described in the TOKENS section. After expan‐\nsion, AuthorizedKeysFile is taken to be an absolute path or one relative to the user's\nhome directory. Multiple files may be listed, separated by whitespace. Alternately\nthis option may be set to none to skip checking for user keys in files. The default is\n\".ssh/authorizedkeys .ssh/authorizedkeys2\".\n" }, { "name": "AuthorizedPrincipalsCommand", "content": "Specifies a program to be used to generate the list of allowed certificate principals\nas per AuthorizedPrincipalsFile. The program must be owned by root, not writable by\ngroup or others and specified by an absolute path. Arguments to\nAuthorizedPrincipalsCommand accept the tokens described in the TOKENS section. If no\narguments are specified then the username of the target user is used.\n\nThe program should produce on standard output zero or more lines of\nAuthorizedPrincipalsFile output. If either AuthorizedPrincipalsCommand or\nAuthorizedPrincipalsFile is specified, then certificates offered by the client for au‐\nthentication must contain a principal that is listed. By default, no\nAuthorizedPrincipalsCommand is run.\n" }, { "name": "AuthorizedPrincipalsCommandUser", "content": "Specifies the user under whose account the AuthorizedPrincipalsCommand is run. It is\nrecommended to use a dedicated user that has no other role on the host than running au‐\nthorized principals commands. If AuthorizedPrincipalsCommand is specified but\nAuthorizedPrincipalsCommandUser is not, then sshd(8) will refuse to start.\n" }, { "name": "AuthorizedPrincipalsFile", "content": "Specifies a file that lists principal names that are accepted for certificate authenti‐\ncation. When using certificates signed by a key listed in TrustedUserCAKeys, this file\nlists names, one of which must appear in the certificate for it to be accepted for au‐\nthentication. Names are listed one per line preceded by key options (as described in\nAUTHORIZEDKEYS FILE FORMAT in sshd(8)). Empty lines and comments starting with ‘#’\nare ignored.\n\nArguments to AuthorizedPrincipalsFile accept the tokens described in the TOKENS sec‐\ntion. After expansion, AuthorizedPrincipalsFile is taken to be an absolute path or one\nrelative to the user's home directory. The default is none, i.e. not to use a princi‐\npals file – in this case, the username of the user must appear in a certificate's prin‐\ncipals list for it to be accepted.\n\nNote that AuthorizedPrincipalsFile is only used when authentication proceeds using a CA\nlisted in TrustedUserCAKeys and is not consulted for certification authorities trusted\nvia ~/.ssh/authorizedkeys, though the principals= key option offers a similar facility\n(see sshd(8) for details).\n\nBanner The contents of the specified file are sent to the remote user before authentication is\nallowed. If the argument is none then no banner is displayed. By default, no banner\nis displayed.\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\nCertificates signed using other algorithms will not be accepted for public key or host-\nbased authentication.\n" }, { "name": "ChrootDirectory", "content": "Specifies the pathname of a directory to chroot(2) to after authentication. At session\nstartup sshd(8) checks that all components of the pathname are root-owned directories\nwhich are not writable by any other user or group. After the chroot, sshd(8) changes\nthe working directory to the user's home directory. Arguments to ChrootDirectory ac‐\ncept the tokens described in the TOKENS section.\n\nThe ChrootDirectory must contain the necessary files and directories to support the\nuser's session. For an interactive session this requires at least a shell, typically\nsh(1), and basic /dev nodes such as null(4), zero(4), stdin(4), stdout(4), stderr(4),\nand tty(4) devices. For file transfer sessions using SFTP no additional configuration\nof the environment is necessary if the in-process sftp-server is used, though sessions\nwhich use logging may require /dev/log inside the chroot directory on some operating\nsystems (see sftp-server(8) for details).\n\nFor safety, it is very important that the directory hierarchy be prevented from modifi‐\ncation by other processes on the system (especially those outside the jail). Miscon‐\nfiguration can lead to unsafe environments which sshd(8) cannot detect.\n\nThe default is none, indicating not to chroot(2).\n" }, { "name": "Ciphers", "content": "Specifies the ciphers allowed. Multiple ciphers must be comma-separated. If the spec‐\nified list begins with a ‘+’ character, then the specified ciphers will be appended to\nthe default set instead of replacing them. If the specified list begins with a ‘-’\ncharacter, then the specified ciphers (including wildcards) will be removed from the\ndefault set instead of replacing them. If the specified list begins with a ‘^’ charac‐\nter, then the specified ciphers will be placed at the head of the 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": "ClientAliveCountMax", "content": "Sets the number of client alive messages which may be sent without sshd(8) receiving\nany messages back from the client. If this threshold is reached while client alive\nmessages are being sent, sshd will disconnect the client, terminating the session. It\nis important to note that the use of client alive messages is very different from\nTCPKeepAlive. The client alive messages are sent through the encrypted channel and\ntherefore will not be spoofable. The TCP keepalive option enabled by TCPKeepAlive is\nspoofable. The client alive mechanism is valuable when the client or server depend on\nknowing when a connection has become unresponsive.\n\nThe default value is 3. If ClientAliveInterval is set to 15, and ClientAliveCountMax\nis left at the default, unresponsive SSH clients will be disconnected after approxi‐\nmately 45 seconds. Setting a zero ClientAliveCountMax disables connection termination.\n" }, { "name": "ClientAliveInterval", "content": "Sets a timeout interval in seconds after which if no data has been received from the\nclient, sshd(8) will send a message through the encrypted channel to request a response\nfrom the client. The default is 0, indicating that these messages will not be sent to\nthe client.\n" }, { "name": "Compression", "content": "Specifies whether compression is enabled after the user has authenticated successfully.\nThe argument must be yes, delayed (a legacy synonym for yes) or no. The default is\nyes.\n" }, { "name": "DebianBanner", "content": "Specifies whether the distribution-specified extra version suffix is included during\ninitial protocol handshake. The default is yes.\n" }, { "name": "DenyGroups", "content": "This keyword can be followed by a list of group name patterns, separated by spaces.\nLogin is disallowed for users whose primary group or supplementary group list matches\none of the patterns. Only group names are valid; a numerical group ID is not recog‐\nnized. By default, login is allowed for all groups. The allow/deny groups directives\nare processed in the following order: DenyGroups, AllowGroups.\n\nSee PATTERNS in sshconfig(5) for more information on patterns.\n" }, { "name": "DenyUsers", "content": "This keyword can be followed by a list of user name patterns, separated by spaces. Lo‐\ngin is disallowed for user names that match one of the patterns. Only user names are\nvalid; a numerical user ID is not recognized. By default, login is allowed for all\nusers. If the pattern takes the form USER@HOST then USER and HOST are separately\nchecked, restricting logins to particular users from particular hosts. HOST criteria\nmay additionally contain addresses to match in CIDR address/masklen format. The al‐\nlow/deny users directives are processed in the following order: DenyUsers, AllowUsers.\n\nSee PATTERNS in sshconfig(5) for more information on patterns.\n" }, { "name": "DisableForwarding", "content": "Disables all forwarding features, including X11, ssh-agent(1), TCP and StreamLocal.\nThis option overrides all other forwarding-related options and may simplify restricted\nconfigurations.\n" }, { "name": "ExposeAuthInfo", "content": "Writes a temporary file containing a list of authentication methods and public creden‐\ntials (e.g. keys) used to authenticate the user. The location of the file is exposed\nto the user session through the SSHUSERAUTH environment variable. The default is no.\n" }, { "name": "FingerprintHash", "content": "Specifies the hash algorithm used when logging key fingerprints. Valid options are:\nmd5 and sha256. The default is sha256.\n" }, { "name": "ForceCommand", "content": "Forces the execution of the command specified by ForceCommand, ignoring any command\nsupplied by the client and ~/.ssh/rc if present. The command is invoked by using the\nuser's login shell with the -c option. This applies to shell, command, or subsystem\nexecution. It is most useful inside a Match block. The command originally supplied by\nthe client is available in the SSHORIGINALCOMMAND environment variable. Specifying a\ncommand of internal-sftp will force the use of an in-process SFTP server that requires\nno support files when used with ChrootDirectory. The default is none.\n" }, { "name": "GatewayPorts", "content": "Specifies whether remote hosts are allowed to connect to ports forwarded for the\nclient. By default, sshd(8) binds remote port forwardings to the loopback address.\nThis prevents other remote hosts from connecting to forwarded ports. GatewayPorts can\nbe used to specify that sshd should allow remote port forwardings to bind to non-loop‐\nback addresses, thus allowing other hosts to connect. The argument may be no to force\nremote port forwardings to be available to the local host only, yes to force remote\nport forwardings to bind to the wildcard address, or clientspecified to allow the\nclient to select the address to which the forwarding is bound. The default is no.\n" }, { "name": "GSSAPIAuthentication", "content": "Specifies whether user authentication based on GSSAPI is allowed. The default is no.\n" }, { "name": "GSSAPICleanupCredentials", "content": "Specifies whether to automatically destroy the user's credentials cache on logout. The\ndefault is yes.\n" }, { "name": "GSSAPIKeyExchange", "content": "Specifies whether key exchange based on GSSAPI is allowed. GSSAPI key exchange doesn't\nrely on ssh keys to verify host identity. The default is no.\n" }, { "name": "GSSAPIStrictAcceptorCheck", "content": "Determines whether to be strict about the identity of the GSSAPI acceptor a client au‐\nthenticates against. If set to yes then the client must authenticate against the host\nservice on the current hostname. If set to no then the client may authenticate against\nany service key stored in the machine's default store. This facility is provided to\nassist with operation on multi homed machines. The default is yes.\n" }, { "name": "GSSAPIStoreCredentialsOnRekey", "content": "Controls whether the user's GSSAPI credentials should be updated following a successful\nconnection rekeying. This option can be used to accepted renewed or updated credentials\nfrom a compatible client. The default is “no”.\n\nFor this to work GSSAPIKeyExchange needs to be enabled in the server and also used by\nthe client.\n" }, { "name": "GSSAPIKexAlgorithms", "content": "The list of key exchange algorithms that are accepted by 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": "HostbasedAcceptedAlgorithms", "content": "Specifies the signature algorithms that will be accepted for hostbased authentication\nas a list of comma-separated patterns. Alternately if the specified list begins with a\n‘+’ character, then the specified signature algorithms will be appended to the default\nset instead of replacing them. If the specified list begins with a ‘-’ character, then\nthe specified signature algorithms (including wildcards) will be removed from the de‐\nfault set instead of replacing them. If the specified list begins with a ‘^’ charac‐\nter, then the specified signature algorithms will be placed at the head of the default\nset. 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\nHostbasedAcceptedAlgorithms\". This was formerly named HostbasedAcceptedKeyTypes.\n" }, { "name": "HostbasedAuthentication", "content": "Specifies whether rhosts or /etc/hosts.equiv authentication together with successful\npublic key client host authentication is allowed (host-based authentication). The de‐\nfault is no.\n" }, { "name": "HostbasedUsesNameFromPacketOnly", "content": "Specifies whether or not the server will attempt to perform a reverse name lookup when\nmatching the name in the ~/.shosts, ~/.rhosts, and /etc/hosts.equiv files during\nHostbasedAuthentication. A setting of yes means that sshd(8) uses the name supplied by\nthe client rather than attempting to resolve the name from the TCP connection itself.\nThe default is no.\n" }, { "name": "HostCertificate", "content": "Specifies a file containing a public host certificate. The certificate's public key\nmust match a private host key already specified by HostKey. The default behaviour of\nsshd(8) is not to load any certificates.\n" }, { "name": "HostKey", "content": "Specifies a file containing a private host key used by SSH. The defaults are\n/etc/ssh/sshhostecdsakey, /etc/ssh/sshhosted25519key and\n/etc/ssh/sshhostrsakey.\n\nNote that sshd(8) will refuse to use a file if it is group/world-accessible and that\nthe HostKeyAlgorithms option restricts which of the keys are actually used by sshd(8).\n\nIt is possible to have multiple host key files. It is also possible to specify public\nhost key files instead. In this case operations on the private key will be delegated\nto an ssh-agent(1).\n" }, { "name": "HostKeyAgent", "content": "Identifies the UNIX-domain socket used to communicate with an agent that has access to\nthe private host keys. If the string \"SSHAUTHSOCK\" is specified, the location of the\nsocket will be read from the SSHAUTHSOCK environment variable.\n" }, { "name": "HostKeyAlgorithms", "content": "Specifies the host key signature algorithms that the server offers. 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-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\nHostKeyAlgorithms\".\n" }, { "name": "IgnoreRhosts", "content": "Specifies whether to ignore per-user .rhosts and .shosts files during\nHostbasedAuthentication. The system-wide /etc/hosts.equiv and /etc/ssh/shosts.equiv\nare still used regardless of this setting.\n\nAccepted values are yes (the default) to ignore all per-user files, shosts-only to al‐\nlow the use of .shosts but to ignore .rhosts or no to allow both .shosts and rhosts.\n" }, { "name": "IgnoreUserKnownHosts", "content": "Specifies whether sshd(8) should ignore the user's ~/.ssh/knownhosts during\nHostbasedAuthentication and use only the system-wide known hosts file\n/etc/ssh/knownhosts. The default is “no”.\n" }, { "name": "Include", "content": "Include the specified configuration file(s). Multiple pathnames may be specified and\neach pathname may contain glob(7) wildcards that will be expanded and processed in lex‐\nical order. Files without absolute paths are assumed to be in /etc/ssh. An Include\ndirective may appear inside a Match block to perform conditional inclusion.\n\nIPQoS Specifies the IPv4 type-of-service or DSCP class for the connection. Accepted values\nare af11, af12, af13, af21, af22, af23, af31, af32, af33, af41, af42, af43, cs0, cs1,\ncs2, cs3, cs4, cs5, cs6, cs7, ef, le, lowdelay, throughput, reliability, a numeric\nvalue, or none to use the operating system default. This option may take one or two\narguments, separated by whitespace. If one argument is specified, it is used as the\npacket class unconditionally. If two values are specified, the first is automatically\nselected for interactive sessions and the second for non-interactive sessions. The de‐\nfault is lowdelay for interactive sessions and throughput for non-interactive sessions.\n" }, { "name": "KbdInteractiveAuthentication", "content": "Specifies whether to allow keyboard-interactive authentication. The default is yes.\nThe argument to this keyword must be yes or no. ChallengeResponseAuthentication is a\ndeprecated alias for this.\n" }, { "name": "KerberosAuthentication", "content": "Specifies whether the password provided by the user for PasswordAuthentication will be\nvalidated through the Kerberos KDC. To use this option, the server needs a Kerberos\nservtab which allows the verification of the KDC's identity. The default is no.\n" }, { "name": "KerberosGetAFSToken", "content": "If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire an AFS token be‐\nfore accessing the user's home directory. The default is no.\n" }, { "name": "KerberosOrLocalPasswd", "content": "If password authentication through Kerberos fails then the password will be validated\nvia any additional local mechanism such as /etc/passwd. The default is yes.\n" }, { "name": "KerberosTicketCleanup", "content": "Specifies whether to automatically destroy the user's ticket cache file on logout. The\ndefault is yes.\n" }, { "name": "KexAlgorithms", "content": "Specifies the available KEX (Key Exchange) algorithms. Multiple algorithms must be\ncomma-separated. Alternately if the specified list begins with a ‘+’ character, then\nthe specified algorithms will be appended to the default set instead of replacing them.\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 supported algorithms are:\n\ncurve25519-sha256\ncurve25519-sha256@libssh.org\ndiffie-hellman-group1-sha1\ndiffie-hellman-group14-sha1\ndiffie-hellman-group14-sha256\ndiffie-hellman-group16-sha512\ndiffie-hellman-group18-sha512\ndiffie-hellman-group-exchange-sha1\ndiffie-hellman-group-exchange-sha256\necdh-sha2-nistp256\necdh-sha2-nistp384\necdh-sha2-nistp521\nsntrup761x25519-sha512@openssh.com\n\nThe 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,diffie-hellman-group18-sha512,\ndiffie-hellman-group14-sha256\n\nThe list of available key exchange algorithms may also be obtained using \"ssh -Q\nKexAlgorithms\".\n" }, { "name": "ListenAddress", "content": "Specifies the local addresses sshd(8) should listen on. The following forms may be\nused:\n\nListenAddress hostname|address\nListenAddress hostname:port\nListenAddress IPv4address:port\nListenAddress [hostname|address]:port\n\nIf port is not specified, sshd will listen on the address and all Port options speci‐\nfied. The default is to listen on all local addresses. Multiple ListenAddress options\nare permitted.\n" }, { "name": "LoginGraceTime", "content": "The server disconnects after this time if the user has not successfully logged in. If\nthe value is 0, there is no time limit. The default is 120 seconds.\n" }, { "name": "LogLevel", "content": "Gives the verbosity level that is used when logging messages from sshd(8). The possi‐\nble values are: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.\nThe default is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify\nhigher levels of debugging output. Logging with a DEBUG level violates the privacy of\nusers and is not recommended.\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 available MAC (message authentication code) algorithms. The MAC algo‐\nrithm is used for data integrity protection. Multiple algorithms must be comma-sepa‐\nrated. If the specified list begins with a ‘+’ character, then the specified algo‐\nrithms will be appended to the default set instead of replacing them. If the specified\nlist begins with a ‘-’ character, then the specified algorithms (including wildcards)\nwill be removed from the default set instead of replacing them. If the specified list\nbegins with a ‘^’ character, then the specified algorithms will be placed at the head\nof 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. The supported MACs are:\n\nhmac-md5\nhmac-md5-96\nhmac-sha1\nhmac-sha1-96\nhmac-sha2-256\nhmac-sha2-512\numac-64@openssh.com\numac-128@openssh.com\nhmac-md5-etm@openssh.com\nhmac-md5-96-etm@openssh.com\nhmac-sha1-etm@openssh.com\nhmac-sha1-96-etm@openssh.com\nhmac-sha2-256-etm@openssh.com\nhmac-sha2-512-etm@openssh.com\numac-64-etm@openssh.com\numac-128-etm@openssh.com\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\nMatch Introduces a conditional block. If all of the criteria on the Match line are satis‐\nfied, the keywords on the following lines override those set in the global section of\nthe config file, until either another Match line or the end of the file. If a keyword\nappears in multiple Match blocks that are satisfied, only the first instance of the\nkeyword is applied.\n\nThe arguments to Match are one or more criteria-pattern pairs or the single token All\nwhich matches all criteria. The available criteria are User, Group, Host,\nLocalAddress, LocalPort, and Address.\n\nThe match patterns may consist of single entries or comma-separated lists and may use\nthe wildcard and negation operators described in the PATTERNS section of sshconfig(5).\n\nThe patterns in an Address criteria may additionally contain addresses to match in CIDR\naddress/masklen format, such as 192.0.2.0/24 or 2001:db8::/32. Note that the mask\nlength provided must be consistent with the address - it is an error to specify a mask\nlength that is too long for the address or one with bits set in this host portion of\nthe address. For example, 192.0.2.0/33 and 192.0.2.0/8, respectively.\n\nOnly a subset of keywords may be used on the lines following a Match keyword. Avail‐\nable keywords are AcceptEnv, AllowAgentForwarding, AllowGroups,\nAllowStreamLocalForwarding, AllowTcpForwarding, AllowUsers, AuthenticationMethods,\nAuthorizedKeysCommand, AuthorizedKeysCommandUser, AuthorizedKeysFile,\nAuthorizedPrincipalsCommand, AuthorizedPrincipalsCommandUser, AuthorizedPrincipalsFile,\nBanner, CASignatureAlgorithms, ChrootDirectory, ClientAliveCountMax,\nClientAliveInterval, DenyGroups, DenyUsers, DisableForwarding, ExposeAuthInfo,\nForceCommand, GatewayPorts, GSSAPIAuthentication, HostbasedAcceptedAlgorithms,\nHostbasedAuthentication, HostbasedUsesNameFromPacketOnly, IgnoreRhosts, Include, IPQoS,\nKbdInteractiveAuthentication, KerberosAuthentication, LogLevel, MaxAuthTries,\nMaxSessions, PasswordAuthentication, PermitEmptyPasswords, PermitListen, PermitOpen,\nPermitRootLogin, PermitTTY, PermitTunnel, PermitUserRC, PubkeyAcceptedAlgorithms,\nPubkeyAuthentication, PubkeyAuthOptions, RekeyLimit, RevokedKeys, SetEnv,\nStreamLocalBindMask, StreamLocalBindUnlink, TrustedUserCAKeys, X11DisplayOffset,\nX11Forwarding and X11UseLocalhost.\n" }, { "name": "MaxAuthTries", "content": "Specifies the maximum number of authentication attempts permitted per connection. Once\nthe number of failures reaches half this value, additional failures are logged. The\ndefault is 6.\n" }, { "name": "MaxSessions", "content": "Specifies the maximum number of open shell, login or subsystem (e.g. sftp) sessions\npermitted per network connection. Multiple sessions may be established by clients that\nsupport connection multiplexing. Setting MaxSessions to 1 will effectively disable\nsession multiplexing, whereas setting it to 0 will prevent all shell, login and subsys‐\ntem sessions while still permitting forwarding. The default is 10.\n" }, { "name": "MaxStartups", "content": "Specifies the maximum number of concurrent unauthenticated connections to the SSH dae‐\nmon. Additional connections will be dropped until authentication succeeds or the\nLoginGraceTime expires for a connection. The default is 10:30:100.\n\nAlternatively, random early drop can be enabled by specifying the three colon separated\nvalues start:rate:full (e.g. \"10:30:60\"). sshd(8) will refuse connection attempts with\na probability of rate/100 (30%) if there are currently start (10) unauthenticated con‐\nnections. The probability increases linearly and all connection attempts are refused\nif the number of unauthenticated connections reaches full (60).\n" }, { "name": "ModuliFile", "content": "Specifies the moduli(5) file that contains the Diffie-Hellman groups used for the\n“diffie-hellman-group-exchange-sha1” and “diffie-hellman-group-exchange-sha256” key ex‐\nchange methods. The default is /etc/ssh/moduli.\n" }, { "name": "PasswordAuthentication", "content": "Specifies whether password authentication is allowed. The default is yes.\n" }, { "name": "PermitEmptyPasswords", "content": "When password authentication is allowed, it specifies whether the server allows login\nto accounts with empty password strings. The default is no.\n" }, { "name": "PermitListen", "content": "Specifies the addresses/ports on which a remote TCP port forwarding may listen. The\nlisten specification must be one of the following forms:\n\nPermitListen port\nPermitListen host:port\n\nMultiple permissions may be specified by separating them with whitespace. An argument\nof any can be used to remove all restrictions and permit any listen requests. An argu‐\nment of none can be used to prohibit all listen requests. The host name may contain\nwildcards as described in the PATTERNS section in sshconfig(5). The wildcard ‘*’ can\nalso be used in place of a port number to allow all ports. By default all port for‐\nwarding listen requests are permitted. Note that the GatewayPorts option may further\nrestrict which addresses may be listened on. Note also that ssh(1) will request a lis‐\nten host of “localhost” if no listen host was specifically requested, and this name is\ntreated differently to explicit localhost addresses of “127.0.0.1” and “::1”.\n" }, { "name": "PermitOpen", "content": "Specifies the destinations to which TCP port forwarding is permitted. The forwarding\nspecification must be one of the following forms:\n\nPermitOpen host:port\nPermitOpen IPv4addr:port\nPermitOpen [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. By default all port\nforwarding requests are permitted.\n" }, { "name": "PermitRootLogin", "content": "Specifies whether root can log in using ssh(1). The argument must be yes,\nprohibit-password, forced-commands-only, or no. The default is prohibit-password.\n\nIf this option is set to prohibit-password (or its deprecated alias, without-password),\npassword and keyboard-interactive authentication are disabled for root.\n\nIf this option is set to forced-commands-only, root login with public key authentica‐\ntion will be allowed, but only if the command option has been specified (which may be\nuseful for taking remote backups even if root login is normally not allowed). All\nother authentication methods are disabled for root.\n\nIf this option is set to no, root is not allowed to log in.\n" }, { "name": "PermitTTY", "content": "Specifies whether pty(4) allocation is permitted. The default is yes.\n" }, { "name": "PermitTunnel", "content": "Specifies whether tun(4) device forwarding is allowed. The argument must be yes,\npoint-to-point (layer 3), ethernet (layer 2), or no. Specifying yes permits both\npoint-to-point and ethernet. The default is no.\n\nIndependent of this setting, the permissions of the selected tun(4) device must allow\naccess to the user.\n" }, { "name": "PermitUserEnvironment", "content": "Specifies whether ~/.ssh/environment and environment= options in ~/.ssh/authorizedkeys\nare processed by sshd(8). Valid options are yes, no or a pattern-list specifying which\nenvironment variable names to accept (for example \"LANG,LC*\"). The default is no.\nEnabling environment processing may enable users to bypass access restrictions in some\nconfigurations using mechanisms such as LDPRELOAD.\n" }, { "name": "PermitUserRC", "content": "Specifies whether any ~/.ssh/rc file is executed. The default is yes.\n" }, { "name": "PerSourceMaxStartups", "content": "Specifies the number of unauthenticated connections allowed from a given source ad‐\ndress, or “none” if there is no limit. This limit is applied in addition to\nMaxStartups, whichever is lower. The default is none.\n" }, { "name": "PerSourceNetBlockSize", "content": "Specifies the number of bits of source address that are grouped together for the pur‐\nposes of applying PerSourceMaxStartups limits. Values for IPv4 and optionally IPv6 may\nbe specified, separated by a colon. The default is 32:128, which means each address is\nconsidered individually.\n" }, { "name": "PidFile", "content": "Specifies the file that contains the process ID of the SSH daemon, or none to not write\none. The default is /run/sshd.pid.\n\nPort Specifies the port number that sshd(8) listens on. The default is 22. Multiple op‐\ntions of this type are permitted. See also ListenAddress.\n" }, { "name": "PrintLastLog", "content": "Specifies whether sshd(8) should print the date and time of the last user login when a\nuser logs in interactively. The default is yes.\n" }, { "name": "PrintMotd", "content": "Specifies whether sshd(8) should print /etc/motd when a user logs in interactively.\n(On some systems it is also printed by the shell, /etc/profile, or equivalent.) The\ndefault is yes.\n" }, { "name": "PubkeyAcceptedAlgorithms", "content": "Specifies the signature algorithms that will be accepted for public key authentication\nas a list of comma-separated patterns. Alternately if the specified list begins with a\n‘+’ character, then the specified algorithms will be appended to the default set in‐\nstead of replacing them. If the specified list begins with a ‘-’ character, then the\nspecified algorithms (including wildcards) will be removed from the default set instead\nof replacing them. If the specified list begins with a ‘^’ character, then the speci‐\nfied algorithms will be placed at the head of the default set. The default for this\noption 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": "PubkeyAuthOptions", "content": "Sets one or more public key authentication options. The supported keywords are: none\n(the default; indicating no additional options are enabled), touch-required and\nverify-required.\n\nThe touch-required option causes public key authentication using a FIDO authenticator\nalgorithm (i.e. ecdsa-sk or ed25519-sk) to always require the signature to attest that\na physically present user explicitly confirmed the authentication (usually by touching\nthe authenticator). By default, sshd(8) requires user presence unless overridden with\nan authorizedkeys option. The touch-required flag disables this override.\n\nThe verify-required option requires a FIDO key signature attest that the user was veri‐\nfied, e.g. via a PIN.\n\nNeither the touch-required or verify-required options have any effect for other, non-\nFIDO, public key types.\n" }, { "name": "PubkeyAuthentication", "content": "Specifies whether public key authentication is allowed. The default is yes.\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. The default value for RekeyLimit is default none, which means\nthat rekeying is performed after the cipher's default amount of data has been sent or\nreceived and no time based rekeying is done.\n" }, { "name": "RevokedKeys", "content": "Specifies revoked public keys file, or none to not use one. Keys listed in this file\nwill be refused for public key authentication. Note that if this file is not readable,\nthen public key authentication will be refused for all users. Keys may be specified as\na text file, listing one public key per line, or as an OpenSSH Key Revocation List\n(KRL) as generated by ssh-keygen(1). For more information on KRLs, see the KEY REVOCA‐\nTION LISTS section in ssh-keygen(1).\n" }, { "name": "SecurityKeyProvider", "content": "Specifies a path to a library that will be used when loading FIDO authenticator-hosted\nkeys, overriding the default of using the built-in USB HID support.\n\nSetEnv Specifies one or more environment variables to set in child sessions started by sshd(8)\nas “NAME=VALUE”. The environment value may be quoted (e.g. if it contains whitespace\ncharacters). Environment variables set by SetEnv override the default environment and\nany variables specified by the user via AcceptEnv or PermitUserEnvironment.\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, sshd 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 is no.\n" }, { "name": "StrictModes", "content": "Specifies whether sshd(8) should check file modes and ownership of the user's files and\nhome directory before accepting login. This is normally desirable because novices\nsometimes accidentally leave their directory or files world-writable. The default is\nyes. Note that this does not apply to ChrootDirectory, whose permissions and ownership\nare checked unconditionally.\n" }, { "name": "Subsystem", "content": "Configures an external subsystem (e.g. file transfer daemon). Arguments should be a\nsubsystem name and a command (with optional arguments) to execute upon subsystem re‐\nquest.\n\nThe command sftp-server implements the SFTP file transfer subsystem.\n\nAlternately the name internal-sftp implements an in-process SFTP server. This may sim‐\nplify configurations using ChrootDirectory to force a different filesystem root on\nclients.\n\nBy default no subsystems are defined.\n" }, { "name": "SyslogFacility", "content": "Gives the facility code that is used when logging messages from sshd(8). The possible\nvalues are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6,\nLOCAL7. The default is AUTH.\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. However, this means that connections will die if the route is down temporar‐\nily, and some people find it annoying. On the other hand, if TCP keepalives are not\nsent, sessions may hang indefinitely on the server, leaving \"ghost\" users and consuming\nserver resources.\n\nThe default is yes (to send TCP keepalive messages), and the server will notice if the\nnetwork goes down or the client host crashes. This avoids infinitely hanging sessions.\n\nTo disable TCP keepalive messages, the value should be set to no.\n\nThis option was formerly called KeepAlive.\n" }, { "name": "TrustedUserCAKeys", "content": "Specifies a file containing public keys of certificate authorities that are trusted to\nsign user certificates for authentication, or none to not use one. Keys are listed one\nper line; empty lines and comments starting with ‘#’ are allowed. If a certificate is\npresented for authentication and has its signing CA key listed in this file, then it\nmay be used for authentication for any user listed in the certificate's principals\nlist. Note that certificates that lack a list of principals will not be permitted for\nauthentication using TrustedUserCAKeys. For more details on certificates, see the CER‐\nTIFICATES section in ssh-keygen(1).\n\nUseDNS Specifies whether sshd(8) should look up the remote host name, and to check that the\nresolved host name for the remote IP address maps back to the very same IP address.\n\nIf this option is set to no (the default) then only addresses and not host names may be\nused in ~/.ssh/authorizedkeys from and sshdconfig Match Host directives.\n\nUsePAM Enables the Pluggable Authentication Module interface. If set to yes this will enable\nPAM authentication using KbdInteractiveAuthentication and PasswordAuthentication in ad‐\ndition to PAM account and session module processing for all authentication types.\n\nBecause PAM keyboard-interactive authentication usually serves an equivalent role to\npassword authentication, you should disable either PasswordAuthentication or\nKbdInteractiveAuthentication.\n\nIf UsePAM is enabled, you will not be able to run sshd(8) as a non-root user. The de‐\nfault is no.\n" }, { "name": "VersionAddendum", "content": "Optionally specifies additional text to append to the SSH protocol banner sent by the\nserver upon connection. The default is none.\n" }, { "name": "X11DisplayOffset", "content": "Specifies the first display number available for sshd(8)'s X11 forwarding. This pre‐\nvents sshd from interfering with real X11 servers. The default is 10.\n" }, { "name": "X11Forwarding", "content": "Specifies whether X11 forwarding is permitted. The argument must be yes or no. The\ndefault is no.\n\nWhen X11 forwarding is enabled, there may be additional exposure to the server and to\nclient displays if the sshd(8) proxy display is configured to listen on the wildcard\naddress (see X11UseLocalhost), though this is not the default. Additionally, the au‐\nthentication spoofing and authentication data verification and substitution occur on\nthe client side. The security risk of using X11 forwarding is that the client's X11\ndisplay server may be exposed to attack when the SSH client requests forwarding (see\nthe warnings for ForwardX11 in sshconfig(5)). A system administrator may have a\nstance in which they want to protect clients that may expose themselves to attack by\nunwittingly requesting X11 forwarding, which can warrant a no setting.\n\nNote that disabling X11 forwarding does not prevent users from forwarding X11 traffic,\nas users can always install their own forwarders.\n" }, { "name": "X11UseLocalhost", "content": "Specifies whether sshd(8) should bind the X11 forwarding server to the loopback address\nor to the wildcard address. By default, sshd binds the forwarding server to the loop‐\nback address and sets the hostname part of the DISPLAY environment variable to\nlocalhost. This prevents remote hosts from connecting to the proxy display. However,\nsome older X11 clients may not function with this configuration. X11UseLocalhost may\nbe set to no to specify that the forwarding server should be bound to the wildcard ad‐\ndress. The argument must be yes or no. The default is yes.\n" }, { "name": "XAuthLocation", "content": "Specifies the full pathname of the xauth(1) program, or none to not use one. The de‐\nfault is /usr/bin/xauth.\n" } ] }, "TIME FORMATS": { "content": "sshd(8) command-line arguments and configuration file options that specify time may be ex‐\npressed using a sequence of the form: time[qualifier], where time is a positive integer value\nand qualifier is one of the following:\n\n⟨none⟩ seconds\ns | S seconds\nm | M minutes\nh | H hours\nd | D days\nw | W weeks\n\nEach member of the sequence is added together to calculate the total time value.\n\nTime format examples:\n\n600 600 seconds (10 minutes)\n10m 10 minutes\n1h30m 1 hour 30 minutes (90 minutes)\n", "subsections": [] }, "TOKENS": { "content": "Arguments to some keywords can make use of tokens, which are expanded at runtime:\n\n%% A literal ‘%’.\n%F The fingerprint of the CA key.\n%f The fingerprint of the key or certificate.\n%h The home directory of the user.\n%i The key ID in the certificate.\n%K The base64-encoded CA key.\n%k The base64-encoded key or certificate for authentication.\n%s The serial number of the certificate.\n%T The type of the CA key.\n%t The key or certificate type.\n%U The numeric user ID of the target user.\n%u The username.\n\nAuthorizedKeysCommand accepts the tokens %%, %f, %h, %k, %t, %U, and %u.\n\nAuthorizedKeysFile accepts the tokens %%, %h, %U, and %u.\n\nAuthorizedPrincipalsCommand accepts the tokens %%, %F, %f, %h, %i, %K, %k, %s, %T, %t, %U, and\n%u.\n\nAuthorizedPrincipalsFile accepts the tokens %%, %h, %U, and %u.\n\nChrootDirectory accepts the tokens %%, %h, %U, and %u.\n", "subsections": [] }, "FILES": { "content": "/etc/ssh/sshdconfig\nContains configuration data for sshd(8). This file should be writable by root only,\nbut it is recommended (though not necessary) that it be world-readable.\n", "subsections": [] }, "SEE ALSO": { "content": "sftp-server(8), sshd(8)\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. Niels Provos and Markus Friedl contributed support for privi‐\nlege separation.\n\nBSD December 4, 2021 BSD", "subsections": [] } } } }