.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
-.\" $OpenBSD: sshd_config.5,v 1.29 2004/03/08 10:18:57 dtucker Exp $
+.\" $OpenBSD: sshd_config.5,v 1.44 2005/07/25 11:59:40 markus Exp $
.Dd September 25, 1999
.Dt SSHD_CONFIG 5
.Os
keywords and their meanings are as follows (note that
keywords are case-insensitive and arguments are case-sensitive):
.Bl -tag -width Ds
+.It Cm AcceptEnv
+Specifies what environment variables sent by the client will be copied into
+the session's
+.Xr environ 7 .
+See
+.Cm SendEnv
+in
+.Xr ssh_config 5
+for how to configure the client.
+Note that environment passing is only supported for protocol 2.
+Variables are specified by name, which may contain the wildcard characters
+.Ql \&*
+and
+.Ql \&? .
+Multiple environment variables may be separated by whitespace or spread
+across multiple
+.Cm 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.
+.It Cm AddressFamily
+Specifies which address family should be used by
+.Nm sshd .
+Valid arguments are
+.Dq any ,
+.Dq inet
+(use IPv4 only) or
+.Dq inet6
+(use IPv6 only).
+The default is
+.Dq any .
.It Cm AllowGroups
This keyword can be followed by a list of group name patterns, separated
by spaces.
wildcards in the patterns.
Only group names are valid; a numerical group ID is not recognized.
By default, login is allowed for all groups.
-.Pp
.It Cm AllowTcpForwarding
Specifies whether TCP forwarding is permitted.
The default is
Note that disabling TCP forwarding does not improve security unless
users are also denied shell access, as they can always install their
own forwarders.
-.Pp
.It Cm AllowUsers
This keyword can be followed by a list of user name patterns, separated
by spaces.
If the pattern takes the form USER@HOST then USER and HOST
are separately checked, restricting logins to particular
users from particular hosts.
-.Pp
.It Cm AuthorizedKeysFile
Specifies the file that contains the public keys that can be used
for user authentication.
authentication is allowed.
This option is only available for protocol version 2.
By default, no banner is displayed.
-.Pp
.It Cm ChallengeResponseAuthentication
Specifies whether challenge response authentication is allowed.
All authentication styles from
.It Cm Ciphers
Specifies the ciphers allowed for protocol version 2.
Multiple ciphers must be comma-separated.
+The supported ciphers are
+.Dq 3des-cbc ,
+.Dq aes128-cbc ,
+.Dq aes192-cbc ,
+.Dq aes256-cbc ,
+.Dq aes128-ctr ,
+.Dq aes192-ctr ,
+.Dq aes256-ctr ,
+.Dq arcfour128 ,
+.Dq arcfour256 ,
+.Dq arcfour ,
+.Dq blowfish-cbc ,
+and
+.Dq cast128-cbc .
The default is
-.Pp
.Bd -literal
- ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
- aes192-cbc,aes256-cbc,aes128-ctr,aes192-ctr,aes256-ctr''
+ ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
+ arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
+ aes192-ctr,aes256-ctr''
.Ed
-.It Cm ClientAliveInterval
-Sets a timeout interval in seconds after which if no data has been received
-from the client,
-.Nm 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.
.It Cm ClientAliveCountMax
Sets the number of client alive messages (see above) which may be
sent without
.Cm ClientAliveCountMax
is left at the default, unresponsive ssh clients
will be disconnected after approximately 45 seconds.
+.It Cm ClientAliveInterval
+Sets a timeout interval in seconds after which if no data has been received
+from the client,
+.Nm 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.
.It Cm Compression
-Specifies whether compression is allowed.
+Specifies whether compression is allowed, or delayed until
+the user has authenticated successfully.
The argument must be
-.Dq yes
+.Dq yes ,
+.Dq delayed ,
or
.Dq no .
The default is
-.Dq yes .
+.Dq delayed .
.It Cm DenyGroups
This keyword can be followed by a list of group name patterns, separated
by spaces.
wildcards in the patterns.
Only group names are valid; a numerical group ID is not recognized.
By default, login is allowed for all groups.
-.Pp
.It Cm DenyUsers
This keyword can be followed by a list of user name patterns, separated
by spaces.
.Cm GatewayPorts
can be used to specify that
.Nm sshd
-should bind remote port forwardings to the wildcard address,
-thus allowing remote hosts to connect to forwarded ports.
-The argument must be
+should allow remote port forwardings to bind to non-loopback addresses, thus
+allowing other hosts to connect.
+The argument may be
+.Dq no
+to force remote port forwardings to be available to the local host only,
.Dq yes
-or
-.Dq no .
+to force remote port forwardings to bind to the wildcard address, or
+.Dq clientspecified
+to allow the client to select the address to which the forwarding is bound.
The default is
.Dq no .
.It Cm GSSAPIAuthentication
Specifies whether
.Nm sshd
should ignore the user's
-.Pa $HOME/.ssh/known_hosts
+.Pa ~/.ssh/known_hosts
during
.Cm RhostsRSAAuthentication
or
Multiple algorithms must be comma-separated.
The default is
.Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
+.It Cm MaxAuthTries
+Specifies the maximum number of authentication attempts permitted per
+connection.
+Once the number of failures reaches half this value,
+additional failures are logged.
+The default is 6.
.It Cm MaxStartups
Specifies the maximum number of concurrent unauthenticated connections to the
.Nm sshd
The default is
.Dq no .
.It Cm PermitRootLogin
-Specifies whether root can login using
+Specifies whether root can log in using
.Xr ssh 1 .
The argument must be
.Dq yes ,
.Pp
If this option is set to
.Dq without-password
-password authentication is disabled for root. Note that other authentication
-methods (e.g., keyboard-interactive/PAM) may still allow root to login using
-a password.
+password authentication is disabled for root.
.Pp
If this option is set to
.Dq forced-commands-only
.Pp
If this option is set to
.Dq no
-root is not allowed to login.
+root is not allowed to log in.
.It Cm PermitUserEnvironment
Specifies whether
.Pa ~/.ssh/environment
.It Cm PrintLastLog
Specifies whether
.Nm sshd
-should print the date and time when the user last logged in.
+should print the date and time of the last user login when a user logs
+in interactively.
The default is
.Dq yes .
.It Cm PrintMotd
.It Cm UseDNS
Specifies whether
.Nm sshd
-should lookup the remote host name and check that
+should look up the remote host name and check that
the resolved host name for the remote IP address maps back to the
very same IP address.
The default is
.Cm UsePrivilegeSeparation
is specified, it will be disabled after authentication.
.It Cm UsePAM
-Enables PAM authentication (via challenge-response) and session set up.
-If you enable this, you should probably disable
-.Cm PasswordAuthentication .
-If you enable
-.CM UsePAM
-then you will not be able to run sshd as a non-root user. The default is
+Enables the Pluggable Authentication Module interface.
+If set to
+.Dq yes
+this will enable PAM authentication using
+.Cm ChallengeResponseAuthentication
+and PAM account and session module processing for all authentication types.
+.Pp
+Because PAM challenge-response authentication usually serves an equivalent
+role to password authentication, you should disable either
+.Cm PasswordAuthentication
+or
+.Cm ChallengeResponseAuthentication.
+.Pp
+If
+.Cm UsePAM
+is enabled, you will not be able to run
+.Xr sshd 8
+as a non-root user.
+The default is
.Dq no .
.It Cm UsePrivilegeSeparation
Specifies whether
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