.\" (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 1.26 2003/11/21 11:57:03 djm Exp $
+.\" $OpenBSD: sshd_config.5,v 1.32 2004/04/28 07:02:56 jmc 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 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
Specifies the ciphers allowed for protocol version 2.
Multiple ciphers must be comma-separated.
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''
will disconnect the client, terminating the session.
It is important to note that the use of client alive messages is very
different from
-.Cm KeepAlive
+.Cm TCPKeepAlive
(below).
The client alive messages are sent through the encrypted channel
and therefore will not be spoofable.
The TCP keepalive option enabled by
-.Cm KeepAlive
+.Cm TCPKeepAlive
is spoofable.
The client alive mechanism is valuable when the client or
server depend on knowing when a connection has become inactive.
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 HostbasedAuthentication .
The default is
.Dq no .
-.It Cm KeepAlive
-Specifies whether the system should send TCP keepalive messages to the
-other side.
-If they are sent, death of the connection or crash of one
-of the machines will be properly noticed.
-However, this means that
-connections will die if the route is down temporarily, and some people
-find it annoying.
-On the other hand, if keepalives are not sent,
-sessions may hang indefinitely on the server, leaving
-.Dq ghost
-users and consuming server resources.
-.Pp
-The default is
-.Dq yes
-(to send keepalives), and the server will notice
-if the network goes down or the client host crashes.
-This avoids infinitely hanging sessions.
-.Pp
-To disable keepalives, the value should be set to
-.Dq no .
.It Cm KerberosAuthentication
Specifies whether the password provided by the user for
.Cm PasswordAuthentication
Kerberos servtab which allows the verification of the KDC's identity.
Default is
.Dq no .
+.It Cm 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
+.Dq no .
.It Cm KerberosOrLocalPasswd
If set then if password authentication through Kerberos fails then
the password will be validated via any additional local mechanism
.Pp
If this option is set to
.Dq without-password
-password authentication is disabled for root.
+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.
.Pp
If this option is set to
.Dq forced-commands-only
The default is
.Dq yes .
Note that this option applies to protocol version 2 only.
-.Cm RhostsRSAAuthentication
-should be used
-instead, because it performs RSA-based host authentication in addition
-to normal rhosts or /etc/hosts.equiv authentication.
-The default is
-.Dq no .
-This option applies to protocol version 1 only.
.It Cm RhostsRSAAuthentication
Specifies whether rhosts or /etc/hosts.equiv authentication together
with successful RSA host authentication is allowed.
The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
The default is AUTH.
+.It Cm TCPKeepAlive
+Specifies whether the system should send TCP keepalive messages to the
+other side.
+If they are sent, death of the connection or crash of one
+of the machines will be properly noticed.
+However, this means that
+connections will die if the route is down temporarily, and some people
+find it annoying.
+On the other hand, if TCP keepalives are not sent,
+sessions may hang indefinitely on the server, leaving
+.Dq ghost
+users and consuming server resources.
+.Pp
+The default is
+.Dq yes
+(to send TCP keepalive messages), and the server will notice
+if the network goes down or the client host crashes.
+This avoids infinitely hanging sessions.
+.Pp
+To disable TCP keepalive messages, the value should be set to
+.Dq no .
.It Cm UseDNS
Specifies whether
.Nm sshd
.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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