sshd_config.0

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SSHD_CONFIG(5)            OpenBSD Programmer's Manual           SSHD_CONFIG(5)

NAME
     sshd_config - OpenSSH SSH daemon configuration file

SYNOPSIS
     /etc/ssh/sshd_config

DESCRIPTION
     sshd reads configuration data from /etc/ssh/sshd_config (or the file
     specified with -f on the command line).  The file contains keyword-argu-
     ment pairs, one per line.  Lines starting with `#' and empty lines are
     interpreted as comments.

     The possible keywords and their meanings are as follows (note that key-
     words are case-insensitive and arguments are case-sensitive):

     AcceptEnv
             Specifies what environment variables sent by the client will be
             copied into the session's environ(7).  See SendEnv in
             ssh_config(5) for how to configure the client.  Note that envi-
             ronment passing is only supported for protocol 2.  Variables are
             specified by name, which may contain the wildcard characters `*'
             and `?'.  Multiple environment variables may be separated by
             whitespace or spread across multiple AcceptEnv directives.  Be
             warned that some environment variables could be used to bypass
             restricted user environments.  For this reason, care should be
             taken in the use of this directive.  The default is not to accept
             any environment variables.

     AddressFamily
             Specifies which address family should be used by sshd.  Valid ar-
             guments are ``any'', ``inet'' (use IPv4 only) or ``inet6'' (use
             IPv6 only).  The default is ``any''.

     AllowGroups
             This keyword can be followed by a list of group name patterns,
             separated by spaces.  If specified, login is allowed only for
             users whose primary group or supplementary group list matches one
             of the patterns.  `*' and `?' can be used as wildcards in the
             patterns.  Only group names are valid; a numerical group ID is
             not recognized.  By default, login is allowed for all groups.

     AllowTcpForwarding
             Specifies whether TCP forwarding is permitted.  The default is
             ``yes''.  Note that disabling TCP forwarding does not improve se-
             curity unless users are also denied shell access, as they can al-
             ways install their own forwarders.

     AllowUsers
             This keyword can be followed by a list of user name patterns,
             separated by spaces.  If specified, login is allowed only for us-
             er names that match one of the patterns.  `*' and `?' can be used
             as wildcards in the patterns.  Only user names are valid; a nu-
             merical user ID is not recognized.  By default, login is allowed
             for all users.  If the pattern takes the form USER@HOST then USER
             and HOST are separately checked, restricting logins to particular
             users from particular hosts.

     AuthorizedKeysFile
             Specifies the file that contains the public keys that can be used
             for user authentication.  AuthorizedKeysFile may contain tokens
             of the form %T which are substituted during connection set-up.
             The following tokens are defined: %% is replaced by a literal
             '%', %h is replaced by the home directory of the user being au-
             thenticated and %u is replaced by the username of that user.  Af-
             ter expansion, AuthorizedKeysFile is taken to be an absolute path
             or one relative to the user's home directory.  The default is
             ``.ssh/authorized_keys''.

     Banner  In some jurisdictions, sending a warning message before authenti-
             cation may be relevant for getting legal protection.  The con-
             tents of the specified file are sent to the remote user before
             authentication is allowed.  This option is only available for
             protocol version 2.  By default, no banner is displayed.

     ChallengeResponseAuthentication
             Specifies whether challenge response authentication is allowed.
             All authentication styles from login.conf(5) are supported.  The
             default is ``yes''.

     Ciphers
             Specifies the ciphers allowed for protocol version 2.  Multiple
             ciphers must be comma-separated.  The supported ciphers are
             ``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'', ``aes256-cbc'',
             ``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'', ``arcfour'',
             ``blowfish-cbc'', and ``cast128-cbc''.  The default is

               ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
                 aes192-cbc,aes256-cbc,aes128-ctr,aes192-ctr,aes256-ctr''

     ClientAliveInterval
             Sets a timeout interval in seconds after which if no data has
             been received from the client, sshd will send a message through
             the encrypted channel to request a response from the client.  The
             default is 0, indicating that these messages will not be sent to
             the client.  This option applies to protocol version 2 only.

     ClientAliveCountMax
             Sets the number of client alive messages (see above) which may be
             sent without sshd receiving any messages back from the client.
             If this threshold is reached while client alive messages are be-
             ing sent, sshd will disconnect the client, terminating the ses-
             sion.  It is important to note that the use of client alive mes-
             sages is very different from TCPKeepAlive (below).  The client
             alive messages are sent through the encrypted channel and there-
             fore will not be spoofable.  The TCP keepalive option enabled by
             TCPKeepAlive is spoofable.  The client alive mechanism is valu-
             able when the client or server depend on knowing when a connec-
             tion has become inactive.

             The default value is 3.  If ClientAliveInterval (above) is set to
             15, and ClientAliveCountMax is left at the default, unresponsive
             ssh clients will be disconnected after approximately 45 seconds.

     Compression
             Specifies whether compression is allowed.  The argument must be
             ``yes'' or ``no''.  The default is ``yes''.

     DenyGroups
             This keyword can be followed by a list of group name patterns,
             separated by spaces.  Login is disallowed for users whose primary
             group or supplementary group list matches one of the patterns.
             `*' and `?' can be used as wildcards in the patterns.  Only group
             names are valid; a numerical group ID is not recognized.  By de-
             fault, login is allowed for all groups.

     DenyUsers
             This keyword can be followed by a list of user name patterns,
             separated by spaces.  Login is disallowed for user names that
             match one of the patterns.  `*' and `?' can be used as wildcards
             in the patterns.  Only user names are valid; a numerical user ID
             is not recognized.  By default, login is allowed for all users.
             If the pattern takes the form USER@HOST then USER and HOST are
             separately checked, restricting logins to particular users from
             particular hosts.

     GatewayPorts
             Specifies whether remote hosts are allowed to connect to ports
             forwarded for the client.  By default, sshd binds remote port
             forwardings to the loopback address.  This prevents other remote
             hosts from connecting to forwarded ports.  GatewayPorts can be
             used to specify that sshd should allow remote port forwardings to
             bind to non-loopback addresses, thus allowing other hosts to con-
             nect.  The argument may be ``no'' to force remote port forward-
             ings to be available to the local host only, ``yes'' to force re-
             mote port forwardings to bind to the wildcard address, or
             ``clientspecified'' to allow the client to select the address to
             which the forwarding is bound.  The default is ``no''.

     GSSAPIAuthentication
             Specifies whether user authentication based on GSSAPI is allowed.
             The default is ``no''.  Note that this option applies to protocol
             version 2 only.

     GSSAPICleanupCredentials
             Specifies whether to automatically destroy the user's credentials
             cache on logout.  The default is ``yes''.  Note that this option
             applies to protocol version 2 only.

     HostbasedAuthentication
             Specifies whether rhosts or /etc/hosts.equiv authentication to-
             gether with successful public key client host authentication is
             allowed (hostbased authentication).  This option is similar to
             RhostsRSAAuthentication and applies to protocol version 2 only.
             The default is ``no''.

     HostKey
             Specifies a file containing a private host key used by SSH.  The
             default is /etc/ssh/ssh_host_key for protocol version 1, and
             /etc/ssh/ssh_host_rsa_key and /etc/ssh/ssh_host_dsa_key for pro-
             tocol version 2.  Note that sshd will refuse to use a file if it
             is group/world-accessible.  It is possible to have multiple host
             key files.  ``rsa1'' keys are used for version 1 and ``dsa'' or
             ``rsa'' are used for version 2 of the SSH protocol.

     IgnoreRhosts
             Specifies that .rhosts and .shosts files will not be used in
             RhostsRSAAuthentication or HostbasedAuthentication.

             /etc/hosts.equiv and /etc/shosts.equiv are still used.  The de-
             fault is ``yes''.

     IgnoreUserKnownHosts
             Specifies whether sshd should ignore the user's
             $HOME/.ssh/known_hosts during RhostsRSAAuthentication or
             HostbasedAuthentication.  The default is ``no''.

     KerberosAuthentication
             Specifies whether the password provided by the user for
             PasswordAuthentication will be validated through the Kerberos
             KDC.  To use this option, the server needs a Kerberos servtab
             which allows the verification of the KDC's identity.  Default is
             ``no''.

     KerberosGetAFSToken
             If AFS is active and the user has a Kerberos 5 TGT, attempt to
             aquire an AFS token before accessing the user's home directory.
             Default is ``no''.

     KerberosOrLocalPasswd
             If set then if password authentication through Kerberos fails
             then the password will be validated via any additional local
             mechanism such as /etc/passwd.  Default is ``yes''.

     KerberosTicketCleanup
             Specifies whether to automatically destroy the user's ticket
             cache file on logout.  Default is ``yes''.

     KeyRegenerationInterval
             In protocol version 1, the ephemeral server key is automatically
             regenerated after this many seconds (if it has been used).  The
             purpose of regeneration is to prevent decrypting captured ses-
             sions by later breaking into the machine and stealing the keys.
             The key is never stored anywhere.  If the value is 0, the key is
             never regenerated.  The default is 3600 (seconds).

     ListenAddress
             Specifies the local addresses sshd should listen on.  The follow-
             ing forms may be used:

                   ListenAddress host|IPv4_addr|IPv6_addr
                   ListenAddress host|IPv4_addr:port
                   ListenAddress [host|IPv6_addr]:port

             If port is not specified, sshd will listen on the address and all
             prior Port options specified.  The default is to listen on all
             local addresses.  Multiple ListenAddress options are permitted.
             Additionally, any Port options must precede this option for non
             port qualified addresses.

     LoginGraceTime
             The server disconnects after this time if the user has not suc-
             cessfully logged in.  If the value is 0, there is no time limit.
             The default is 120 seconds.

     LogLevel
             Gives the verbosity level that is used when logging messages from
             sshd.  The possible values are: QUIET, FATAL, ERROR, INFO, VER-
             BOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.  The default is INFO.
             DEBUG and DEBUG1 are equivalent.  DEBUG2 and DEBUG3 each specify
             higher levels of debugging output.  Logging with a DEBUG level
             violates the privacy of users and is not recommended.

     MACs    Specifies the available MAC (message authentication code) algo-
             rithms.  The MAC algorithm is used in protocol version 2 for data
             integrity protection.  Multiple algorithms must be comma-separat-
             ed.  The default is ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-
             sha1-96,hmac-md5-96''.

     MaxAuthTries