{ "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. Unless noted\notherwise, for each keyword, the first obtained value will be used. Lines starting with ‘#’\nand empty lines are interpreted as comments. Arguments may optionally be enclosed in double\nquotes (\") in order to represent arguments containing spaces.\n\n## Sections\n\n- **NAME**\n- **DESCRIPTION** (93 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": 10 }, { "name": "AllowStreamLocalForwarding", "lines": 7 }, { "name": "AllowTcpForwarding", "lines": 7 }, { "name": "AllowUsers", "lines": 12 }, { "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": "ChannelTimeout", "lines": 49 }, { "name": "ChrootDirectory", "lines": 20 }, { "name": "Ciphers", "lines": 29 }, { "name": "ClientAliveCountMax", "lines": 14 }, { "name": "ClientAliveInterval", "lines": 5 }, { "name": "Compression", "lines": 4 }, { "name": "DebianBanner", "lines": 3 }, { "name": "DenyGroups", "lines": 9 }, { "name": "DenyUsers", "lines": 12 }, { "name": "DisableForwarding", "lines": 4 }, { "name": "ExposeAuthInfo", "lines": 5 }, { "name": "FingerprintHash", "lines": 3 }, { "name": "ForceCommand", "lines": 8 }, { "name": "GatewayPorts", "lines": 10 }, { "name": "GSSAPIAuthentication", "lines": 2 }, { "name": "GSSAPICleanupCredentials", "lines": 3 }, { "name": "GSSAPIKeyExchange", "lines": 3 }, { "name": "GSSAPIStrictAcceptorCheck", "lines": 7 }, { "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": 12 }, { "name": "HostKeyAgent", "lines": 4 }, { "name": "HostKeyAlgorithms", "lines": 20 }, { "name": "IgnoreRhosts", "lines": 8 }, { "name": "IgnoreUserKnownHosts", "lines": 4 }, { "name": "Include", "lines": 15 }, { "name": "KbdInteractiveAuthentication", "lines": 4 }, { "name": "KerberosAuthentication", "lines": 5 }, { "name": "KerberosGetAFSToken", "lines": 3 }, { "name": "KerberosOrLocalPasswd", "lines": 3 }, { "name": "KerberosTicketCleanup", "lines": 3 }, { "name": "KexAlgorithms", "lines": 35 }, { "name": "ListenAddress", "lines": 12 }, { "name": "LoginGraceTime", "lines": 3 }, { "name": "LogLevel", "lines": 6 }, { "name": "LogVerbose", "lines": 86 }, { "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": 17 }, { "name": "PermitOpen", "lines": 14 }, { "name": "PermitRootLogin", "lines": 14 }, { "name": "PermitTTY", "lines": 2 }, { "name": "PermitTunnel", "lines": 7 }, { "name": "PermitUserEnvironment", "lines": 7 }, { "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": 17 }, { "name": "PubkeyAuthentication", "lines": 2 }, { "name": "RekeyLimit", "lines": 10 }, { "name": "RequiredRSASize", "lines": 4 }, { "name": "RevokedKeys", "lines": 7 }, { "name": "SecurityKeyProvider", "lines": 9 }, { "name": "StreamLocalBindMask", "lines": 8 }, { "name": "StreamLocalBindUnlink", "lines": 8 }, { "name": "StrictModes", "lines": 6 }, { "name": "Subsystem", "lines": 12 }, { "name": "SyslogFacility", "lines": 4 }, { "name": "TCPKeepAlive", "lines": 15 }, { "name": "TrustedUserCAKeys", "lines": 9 }, { "name": "UnusedConnectionTimeout", "lines": 33 }, { "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": 28, "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. Unless noted\notherwise, for each keyword, the first obtained value will be used. Lines starting with ‘#’\nand empty lines are interpreted as comments. Arguments may optionally be enclosed in double\nquotes (\") in order to represent arguments 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\noptions 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 re‐\nquests a pseudo-terminal as it is required by the protocol. Variables are specified\nby name, which may contain the wildcard characters ‘*’ and ‘?’. Multiple environment\nvariables may be separated by whitespace or spread across multiple AcceptEnv direc‐\ntives. Be warned that some environment variables could be used to bypass restricted\nuser environments. For this reason, care should be taken in the use of this direc‐\ntive. The default 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\n(the default), 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\nthat disabling agent forwarding does not improve security unless users are also de‐\nnied shell access, 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.\nIf specified, login is allowed only for users whose primary group or supplementary\ngroup list matches one of the patterns. Only group names are valid; a numerical\ngroup ID is not recognized. By default, login is allowed for all groups. The al‐\nlow/deny groups directives are processed in the following order: DenyGroups,\nAllowGroups.\n\nSee PATTERNS in sshconfig(5) for more information on patterns. This keyword may ap‐\npear multiple times in sshdconfig with each instance appending to the list.\n" }, { "name": "AllowStreamLocalForwarding", "content": "Specifies whether StreamLocal (Unix-domain socket) forwarding is permitted. The\navailable options are yes (the default) or all to allow StreamLocal forwarding, no to\nprevent all StreamLocal forwarding, local to allow local (from the perspective of\nssh(1)) forwarding only or remote to allow remote forwarding only. Note that dis‐\nabling StreamLocal forwarding does not improve security unless users are also denied\nshell access, as they can always install their own forwarders.\n" }, { "name": "AllowTcpForwarding", "content": "Specifies whether TCP forwarding is permitted. The available options are yes (the\ndefault) or all to allow TCP forwarding, no to prevent all TCP forwarding, local to\nallow local (from the perspective of ssh(1)) forwarding only or remote to allow re‐\nmote forwarding only. Note that disabling TCP forwarding does not improve security\nunless users are also denied shell access, as they can always install their own for‐\nwarders.\n" }, { "name": "AllowUsers", "content": "This keyword can be followed by a list of user name patterns, separated by spaces.\nIf specified, login is allowed only for user names that match one of the patterns.\nOnly user names are valid; a numerical user ID is not recognized. By default, login\nis allowed for all users. If the pattern takes the form USER@HOST then USER and HOST\nare separately checked, restricting logins to particular users from particular hosts.\nHOST criteria may additionally contain addresses to match in CIDR address/masklen\nformat. The allow/deny users directives are processed in the following order:\nDenyUsers, AllowUsers.\n\nSee PATTERNS in sshconfig(5) for more information on patterns. This keyword may ap‐\npear multiple times in sshdconfig with each instance appending to the list.\n" }, { "name": "AuthenticationMethods", "content": "Specifies the authentication methods that must be successfully completed for a user\nto be granted access. This option must be followed by one or more lists of comma-\nseparated authentication method names, or by the single string any to indicate the\ndefault behaviour of accepting any single authentication method. If the default is\noverridden, then successful authentication requires completion of every method in at\nleast one of these lists.\n\nFor example, \"publickey,password publickey,keyboard-interactive\" would require the\nuser to complete public key authentication, followed by either password or keyboard\ninteractive authentication. Only methods that are next in one or more lists are of‐\nfered at each stage, so for this example it would not be possible to attempt password\nor keyboard-interactive authentication before public key.\n\nFor keyboard interactive authentication it is also possible to restrict authentica‐\ntion to a specific device by appending a colon followed by the device identifier\nbsdauth or pam. 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\nhave been used successfully are not reused for subsequent authentications. For exam‐\nple, \"publickey,publickey\" requires successful authentication using two different\npublic keys.\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\nbe owned by root, not writable by group or others and specified by an absolute path.\nArguments to AuthorizedKeysCommand accept the tokens described in the “TOKENS” sec‐\ntion. If no 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 rec‐\nommended to use a dedicated user that has no other role on the host than running au‐\nthorized 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 ex‐\npansion, AuthorizedKeysFile is taken to be an absolute path or one relative to the\nuser's home directory. Multiple files may be listed, separated by whitespace. Al‐\nternately this option may be set to none to skip checking for user keys in files.\nThe default is \".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\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\nAuthorizedPrincipalsFile output. If either AuthorizedPrincipalsCommand or\nAuthorizedPrincipalsFile is specified, then certificates offered by the client for\nauthentication 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\nauthorized 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 authen‐\ntication. When using certificates signed by a key listed in TrustedUserCAKeys, this\nfile lists names, one of which must appear in the certificate for it to be accepted\nfor authentication. Names are listed one per line preceded by key options (as de‐\nscribed in “AUTHORIZEDKEYS FILE FORMAT” in sshd(8)). Empty lines and comments\nstarting with ‘#’ are ignored.\n\nArguments to AuthorizedPrincipalsFile accept the tokens described in the “TOKENS”\nsection. After expansion, AuthorizedPrincipalsFile is taken to be an absolute path\nor one relative to the user's home directory. The default is none, i.e. not to use a\nprincipals file – in this case, the username of the user must appear in a certifi‐\ncate's principals list for it to be accepted.\n\nNote that AuthorizedPrincipalsFile is only used when authentication proceeds using a\nCA listed in TrustedUserCAKeys and is not consulted for certification authorities\ntrusted via ~/.ssh/authorizedkeys, though the principals= key option offers a simi‐\nlar facility (see sshd(8) for details).\n\nBanner The contents of the specified file are sent to the remote user before authentication\nis allowed. If the argument is none then no banner is displayed. By default, no\nbanner is 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 be‐\ngins with a ‘-’ character, then the specified algorithms (including wildcards) will\nbe removed from the default set instead of replacing them.\n\nCertificates signed using other algorithms will not be accepted for public key or\nhost-based authentication.\n" }, { "name": "ChannelTimeout", "content": "Specifies whether and how quickly sshd(8) should close inactive channels. Timeouts\nare specified as one or more “type=interval” pairs separated by whitespace, where the\n“type” must be a channel type name (as described in the table below), optionally con‐\ntaining wildcard characters.\n\nThe timeout value “interval” is specified in seconds or may use any of the units doc‐\numented in the “TIME FORMATS” section. For example, “session:*=5m” would cause all\nsessions to terminate after five minutes of inactivity. Specifying a zero value dis‐\nables the inactivity timeout.\n\nThe available channel types include:\n\nagent-connection\nOpen connections to ssh-agent(1).\n\ndirect-tcpip, direct-streamlocal@openssh.com\nOpen TCP or Unix socket (respectively) connections that have been established\nfrom a ssh(1) local forwarding, i.e. LocalForward or DynamicForward.\n\nforwarded-tcpip, forwarded-streamlocal@openssh.com\nOpen TCP or Unix socket (respectively) connections that have been established\nto a sshd(8) listening on behalf of a ssh(1) remote forwarding, i.e.\nRemoteForward.\n\nsession:command\nCommand execution sessions.\n\nsession:shell\nInteractive shell sessions.\n\nsession:subsystem:...\nSubsystem sessions, e.g. for sftp(1), which could be identified as\nsession:subsystem:sftp.\n\nx11-connection\nOpen X11 forwarding sessions.\n\nNote that in all the above cases, terminating an inactive session does not guarantee\nto remove all resources associated with the session, e.g. shell processes or X11\nclients relating to the session may continue to execute.\n\nMoreover, terminating an inactive channel or session does not necessarily close the\nSSH connection, nor does it prevent a client from requesting another channel of the\nsame type. In particular, expiring an inactive forwarding session does not prevent\nanother identical forwarding from being subsequently created. See also\nUnusedConnectionTimeout, which may be used in conjunction with this option.\n\nThe default is not to expire channels of any type for inactivity.\n" }, { "name": "ChrootDirectory", "content": "Specifies the pathname of a directory to chroot(2) to after authentication. At ses‐\nsion startup sshd(8) checks that all components of the pathname are root-owned direc‐\ntories which are not writable by any other user or group. After the chroot, sshd(8)\nchanges the working directory to the user's home directory. Arguments to\nChrootDirectory accept 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 configura‐\ntion of the environment is necessary if the in-process sftp-server is used, though\nsessions which use logging may require /dev/log inside the chroot directory on some\noperating systems (see sftp-server(8) for details).\n\nFor safety, it is very important that the directory hierarchy be prevented from modi‐\nfication by other processes on the system (especially those outside the jail). Mis‐\nconfiguration 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\nspecified list begins with a ‘+’ character, then the specified ciphers will be ap‐\npended to the default set instead of replacing them. If the specified list begins\nwith a ‘-’ character, then the specified ciphers (including wildcards) will be re‐\nmoved from the default set instead of replacing them. If the specified list begins\nwith a ‘^’ character, then the specified ciphers will be placed at the head of the\ndefault 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.\nIt is 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\non knowing 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 termina‐\ntion.\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 re‐\nsponse from the client. The default is 0, indicating that these messages will not be\nsent to the client.\n" }, { "name": "Compression", "content": "Specifies whether compression is enabled after the user has authenticated success‐\nfully. The argument must be yes, delayed (a legacy synonym for yes) or no. The de‐\nfault is yes.\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 direc‐\ntives are processed in the following order: DenyGroups, AllowGroups.\n\nSee PATTERNS in sshconfig(5) for more information on patterns. This keyword may ap‐\npear multiple times in sshdconfig with each instance appending to the list.\n" }, { "name": "DenyUsers", "content": "This keyword can be followed by a list of user name patterns, separated by spaces.\nLogin is disallowed for user names that match one of the patterns. Only user names\nare valid; a numerical user ID is not recognized. By default, login is allowed for\nall users. 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,\nAllowUsers.\n\nSee PATTERNS in sshconfig(5) for more information on patterns. This keyword may ap‐\npear multiple times in sshdconfig with each instance appending to the list.\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 re‐\nstricted configurations.\n" }, { "name": "ExposeAuthInfo", "content": "Writes a temporary file containing a list of authentication methods and public cre‐\ndentials (e.g. keys) used to authenticate the user. The location of the file is ex‐\nposed to the user session through the SSHUSERAUTH environment variable. The de‐\nfault 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\nby the client is available in the SSHORIGINALCOMMAND environment variable. Speci‐\nfying a command of internal-sftp will force the use of an in-process SFTP server that\nrequires no 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\ncan be used to specify that sshd should allow remote port forwardings to bind to non-\nloopback addresses, thus allowing other hosts to connect. The argument may be no to\nforce remote port forwardings to be available to the local host only, yes to force\nremote port forwardings to bind to the wildcard address, or clientspecified to allow\nthe client to select the address to which the forwarding is bound. The default is\nno.\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.\nThe default is yes.\n" }, { "name": "GSSAPIKeyExchange", "content": "Specifies whether key exchange based on GSSAPI is allowed. GSSAPI key exchange\ndoesn't rely 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\nauthenticates against. If set to yes then the client must authenticate against the\nhost service on the current hostname. If set to no then the client may authenticate\nagainst any service key stored in the machine's default store. This facility is pro‐\nvided to assist with operation on multi homed machines. The default is yes. This\noption may not be effective in Windows Active Directory environments.\n" }, { "name": "GSSAPIStoreCredentialsOnRekey", "content": "Controls whether the user's GSSAPI credentials should be updated following a success‐\nful connection rekeying. This option can be used to accepted renewed or updated cre‐\ndentials from 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. Possi‐\nble values 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\na ‘+’ character, then the specified signature algorithms will be appended to the de‐\nfault set instead of replacing them. If the specified list begins with a ‘-’ charac‐\nter, then the specified signature algorithms (including wildcards) will be removed\nfrom the default set instead of replacing them. If the specified list begins with a\n‘^’ character, then the specified signature algorithms will be placed at the head of\nthe 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\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\ndefault is no.\n" }, { "name": "HostbasedUsesNameFromPacketOnly", "content": "Specifies whether or not the server will attempt to perform a reverse name lookup\nwhen matching 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\nby the client rather than attempting to resolve the name from the TCP connection it‐\nself. The 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\nsshd(8).\n\nIt is possible to have multiple host key files. It is also possible to specify pub‐\nlic host key files instead. In this case operations on the private key will be dele‐\ngated to an ssh-agent(1).\n" }, { "name": "HostKeyAgent", "content": "Identifies the UNIX-domain socket used to communicate with an agent that has access\nto the private host keys. If the string \"SSHAUTHSOCK\" is specified, the location\nof the socket 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\nallow the use of .shosts but to ignore .rhosts or no to allow both .shosts and\nrhosts.\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/sshknownhosts. 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\nlexical order. Files without absolute paths are assumed to be in /etc/ssh. An\nInclude directive 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 automati‐\ncally selected for interactive sessions and the second for non-interactive sessions.\nThe default is lowdelay for interactive sessions and throughput for non-interactive\nsessions.\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\nbe validated through the Kerberos KDC. To use this option, the server needs a Ker‐\nberos servtab which allows the verification of the KDC's identity. The default is\nno.\n" }, { "name": "KerberosGetAFSToken", "content": "If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire an AFS token\nbefore 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.\nThe default 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\nthem. If the specified list begins with a ‘-’ character, then the specified algo‐\nrithms (including wildcards) will be removed from the default set instead of replac‐\ning them. If the specified list begins with a ‘^’ character, then the specified al‐\ngorithms will be placed at the head of the default set. The supported algorithms\nare:\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\nsntrup761x25519-sha512@openssh.com,\ncurve25519-sha256,curve25519-sha256@libssh.org,\necdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,\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 op‐\ntions are permitted.\n" }, { "name": "LoginGraceTime", "content": "The server disconnects after this time if the user has not successfully logged in.\nIf the 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 pos‐\nsible values are: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DE‐\nBUG3. The default is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each\nspecify higher levels of debugging output. Logging with a DEBUG level violates the\nprivacy of users 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 op‐\ntion is 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 speci‐\nfied 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\nat the 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. 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 key‐\nword appears in multiple Match blocks that are satisfied, only the first instance of\nthe keyword 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\nsshconfig(5).\n\nThe patterns in an Address criteria may additionally contain addresses to match in\nCIDR address/masklen format, such as 192.0.2.0/24 or 2001:db8::/32. Note that the\nmask length provided must be consistent with the address - it is an error to specify\na mask length that is too long for the address or one with bits set in this host por‐\ntion of the 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,\nAuthorizedPrincipalsFile, Banner, CASignatureAlgorithms, ChannelTimeout,\nChrootDirectory, ClientAliveCountMax, ClientAliveInterval, DenyGroups, DenyUsers,\nDisableForwarding, ExposeAuthInfo, ForceCommand, GatewayPorts, GSSAPIAuthentication,\nHostbasedAcceptedAlgorithms, HostbasedAuthentication,\nHostbasedUsesNameFromPacketOnly, 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,\nUnusedConnectionTimeout, X11DisplayOffset, X11Forwarding and X11UseLocalhost.\n" }, { "name": "MaxAuthTries", "content": "Specifies the maximum number of authentication attempts permitted per connection.\nOnce the number of failures reaches half this value, additional failures are logged.\nThe default 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\nthat support connection multiplexing. Setting MaxSessions to 1 will effectively dis‐\nable session multiplexing, whereas setting it to 0 will prevent all shell, login and\nsubsystem sessions while still permitting forwarding. The default is 10.\n" }, { "name": "MaxStartups", "content": "Specifies the maximum number of concurrent unauthenticated connections to the SSH\ndaemon. 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 sepa‐\nrated values start:rate:full (e.g. \"10:30:60\"). sshd(8) will refuse connection at‐\ntempts with a probability of rate/100 (30%) if there are currently start (10) unau‐\nthenticated connections. The probability increases linearly and all connection at‐\ntempts are refused if 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\nexchange 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 argu‐\nment of any can be used to remove all restrictions and permit any listen requests.\nAn argument of none can be used to prohibit all listen requests. The host name may\ncontain wildcards as described in the PATTERNS section in sshconfig(5). The wild‐\ncard ‘*’ can also be used in place of a port number to allow all ports. By default\nall port forwarding listen requests are permitted. Note that the GatewayPorts option\nmay further restrict which addresses may be listened on. Note also that ssh(1) will\nrequest a listen host of “localhost” if no listen host was specifically requested,\nand this name is treated differently to explicit localhost addresses of “127.0.0.1”\nand “::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\nof any can be used to remove all restrictions and permit any forwarding requests. An\nargument of none can be used to prohibit all forwarding requests. The wildcard ‘*’\ncan be used for host or port to allow all hosts or ports respectively. Otherwise, no\npattern matching or address lookups are performed on supplied names. By default all\nport forwarding 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,\nwithout-password), password and keyboard-interactive authentication are disabled for\nroot.\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\n~/.ssh/authorizedkeys are processed by sshd(8). Valid options are yes, no or a pat‐\ntern-list specifying which environment variable names to accept (for example\n\"LANG,LC*\"). The default is no. Enabling environment processing may enable users\nto bypass access restrictions in some configurations using mechanisms such as\nLDPRELOAD.\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\nmay be specified, separated by a colon. The default is 32:128, which means each ad‐\ndress is considered individually.\n" }, { "name": "PidFile", "content": "Specifies the file that contains the process ID of the SSH daemon, or none to not\nwrite one. 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\na user 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 authentica‐\ntion as a list of comma-separated patterns. Alternately if the specified list begins\nwith a ‘+’ character, then the specified algorithms will be appended to the default\nset instead of replacing them. If the specified list begins with a ‘-’ character,\nthen the specified algorithms (including wildcards) will be removed from the default\nset instead of replacing them. If the specified list begins with a ‘^’ character,\nthen the specified algorithms will be placed at the head of the default set. The de‐\nfault 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": "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\nthat a physically present user explicitly confirmed the authentication (usually by\ntouching the authenticator). By default, sshd(8) requires user presence unless over‐\nridden with an authorizedkeys option. The touch-required flag disables this over‐\nride.\n\nThe verify-required option requires a FIDO key signature attest that the user was\nverified, 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 or received before the\nsession key is renegotiated, optionally followed by a maximum amount of time that may\npass before the session key is renegotiated. The first argument is specified in\nbytes and may have a suffix of ‘K’, ‘M’, or ‘G’ to indicate Kilobytes, Megabytes, or\nGigabytes, respectively. The default is between ‘1G’ and ‘4G’, depending on the ci‐\npher. The optional second value is specified in seconds and may use any of the units\ndocumented in the “TIME FORMATS” section. The default value for RekeyLimit is\ndefault none, which means that rekeying is performed after the cipher's default\namount of data has been sent or received and no time based rekeying is done.\n" }, { "name": "RequiredRSASize", "content": "Specifies the minimum RSA key size (in bits) that sshd(8) will accept. User and\nhost-based authentication keys smaller than this limit will be refused. The default\nis 1024 bits. Note that this limit may only be raised from the default.\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 read‐\nable, then public key authentication will be refused for all users. Keys may be\nspecified as a text file, listing one public key per line, or as an OpenSSH Key Revo‐\ncation List (KRL) as generated by ssh-keygen(1). For more information on KRLs, see\nthe KEY REVOCATION LISTS section in ssh-keygen(1).\n" }, { "name": "SecurityKeyProvider", "content": "Specifies a path to a library that will be used when loading FIDO authenticator-\nhosted keys, 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\nsshd(8) as “NAME=VALUE”. The environment value may be quoted (e.g. if it contains\nwhitespace characters). Environment variables set by SetEnv override the default en‐\nvironment and any variables specified by the user via AcceptEnv or\nPermitUserEnvironment.\n" }, { "name": "StreamLocalBindMask", "content": "Sets the octal file creation mode mask (umask) used when creating a Unix-domain\nsocket file for local or remote port forwarding. This option is only used for port\nforwarding to a Unix-domain socket file.\n\nThe default value is 0177, which creates a Unix-domain socket file that is readable\nand writable only by the owner. Note that not all operating systems honor the file\nmode on Unix-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-do‐\nmain socket 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\nand home directory before accepting login. This is normally desirable because\nnovices sometimes accidentally leave their directory or files world-writable. The\ndefault is yes. Note that this does not apply to ChrootDirectory, whose permissions\nand ownership are 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\nsimplify 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 possi‐\nble values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5,\nLOCAL6, LOCAL7. The default is AUTH.\n" }, { "name": "TCPKeepAlive", "content": "Specifies whether the system should send TCP keepalive messages to the other side.\nIf they are sent, death of the connection or crash of one of the machines will be\nproperly noticed. However, this means that connections will die if the route is down\ntemporarily, and some people find it annoying. On the other hand, if TCP keepalives\nare not sent, sessions may hang indefinitely on the server, leaving \"ghost\" users and\nconsuming server resources.\n\nThe default is yes (to send TCP keepalive messages), and the server will notice if\nthe network goes down or the client host crashes. This avoids infinitely hanging\nsessions.\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\nto sign user certificates for authentication, or none to not use one. Keys are\nlisted one per line; empty lines and comments starting with ‘#’ are allowed. If a\ncertificate is presented for authentication and has its signing CA key listed in this\nfile, then it may be used for authentication for any user listed in the certificate's\nprincipals list. Note that certificates that lack a list of principals will not be\npermitted for authentication using TrustedUserCAKeys. For more details on certifi‐\ncates, see the CERTIFICATES section in ssh-keygen(1).\n" }, { "name": "UnusedConnectionTimeout", "content": "Specifies whether and how quickly sshd(8) should close client connections with no\nopen channels. Open channels include active shell, command execution or subsystem\nsessions, connected network, socket, agent or X11 forwardings. Forwarding listeners,\nsuch as those from the ssh(1) -R flag, are not considered as open channels and do not\nprevent the timeout. The timeout value is specified in seconds or may use any of the\nunits documented in the “TIME FORMATS” section.\n\nNote that this timeout starts when the client connection completes user authentica‐\ntion but before the client has an opportunity to open any channels. Caution should\nbe used when using short timeout values, as they may not provide sufficient time for\nthe client to request and open its channels before terminating the connection.\n\nThe default none is to never expire connections for having no open channels. This\noption may be useful in conjunction with ChannelTimeout.\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\nbe used in ~/.ssh/authorizedkeys from and sshdconfig Match Host directives.\n\nUsePAM Enables the Pluggable Authentication Module interface. If set to yes this will en‐\nable PAM authentication using KbdInteractiveAuthentication and PasswordAuthentication\nin addition to PAM account and session module processing for all authentication\ntypes.\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\ndefault 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 traf‐\nfic, as users can always install their own forwarders.\n" }, { "name": "X11UseLocalhost", "content": "Specifies whether sshd(8) should bind the X11 forwarding server to the loopback ad‐\ndress or to the wildcard address. By default, sshd binds the forwarding server to\nthe loopback address and sets the hostname part of the DISPLAY environment variable\nto localhost. This prevents remote hosts from connecting to the proxy display. How‐\never, some older X11 clients may not function with this configuration.\nX11UseLocalhost may be set to no to specify that the forwarding server should be\nbound to the wildcard address. 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%C Identifies the connection endpoints, containing four space-separated values:\nclient address, client port number, server address, and server port number.\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 %%, %C, %D, %f, %h, %k, %t, %U, and %u.\n\nAuthorizedKeysFile accepts the tokens %%, %h, %U, and %u.\n\nAuthorizedPrincipalsCommand accepts the tokens %%, %C, %D, %F, %f, %h, %i, %K, %k, %s, %T,\n%t, %U, and %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\nbugs, re-added newer features and created OpenSSH. Markus Friedl contributed the support for\nSSH protocol versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support for\nprivilege separation.\n\nDebian July 28, 2023 SSHDCONFIG(5)", "subsections": [] } } } }