X-Git-Url: http://andersk.mit.edu/gitweb/openssh.git/blobdiff_plain/874d319bf8e5a93c7e251f49d517052995b179f3..0303fddce97fc773965d10c0d4b40a62fc26487b:/sshd_config.5

diff --git a/sshd_config.5 b/sshd_config.5
index cbc2176f..1e5390a6 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -34,17 +34,15 @@
 .\" (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 1.64 2006/07/18 08:03:09 jmc Exp $
-.Dd September 25, 1999
+.\" $OpenBSD: sshd_config.5,v 1.116 2010/01/09 23:04:13 dtucker Exp $
+.Dd $Mdocdate$
 .Dt SSHD_CONFIG 5
 .Os
 .Sh NAME
 .Nm sshd_config
 .Nd OpenSSH SSH daemon configuration file
 .Sh SYNOPSIS
-.Bl -tag -width Ds -compact
-.It Pa /etc/ssh/sshd_config
-.El
+.Nm /etc/ssh/sshd_config
 .Sh DESCRIPTION
 .Xr sshd 8
 reads configuration data from
@@ -97,6 +95,15 @@ Valid arguments are
 (use IPv6 only).
 The default is
 .Dq any .
+.It Cm AllowAgentForwarding
+Specifies whether
+.Xr ssh-agent 1
+forwarding is permitted.
+The default is
+.Dq yes .
+Note that disabling agent forwarding does not improve security
+unless users are also denied shell access, as they can always install
+their own forwarders.
 .It Cm AllowGroups
 This keyword can be followed by a list of group name patterns, separated
 by spaces.
@@ -161,19 +168,64 @@ directory.
 The default is
 .Dq .ssh/authorized_keys .
 .It Cm Banner
-In some jurisdictions, sending a warning message before authentication
-may be relevant for getting legal protection.
 The contents of the specified file are sent to the remote user before
 authentication is allowed.
+If the argument is
+.Dq none
+then no banner is displayed.
 This option is only available for protocol version 2.
 By default, no banner is displayed.
 .It Cm ChallengeResponseAuthentication
-Specifies whether challenge-response authentication is allowed.
-All authentication styles from
-.Xr login.conf 5
-are supported.
+Specifies whether challenge-response authentication is allowed (e.g. via
+PAM or though authentication styles supported in
+.Xr login.conf 5 )
 The default is
 .Dq yes .
+.It Cm ChrootDirectory
+Specifies the pathname of a directory to
+.Xr chroot 2
+to after authentication.
+All components of the pathname must be root-owned directories that are
+not writable by any other user or group.
+After the chroot,
+.Xr sshd 8
+changes the working directory to the user's home directory.
+.Pp
+The pathname may contain the following tokens that are expanded at runtime once
+the connecting user has been authenticated: %% is replaced by a literal '%',
+%h is replaced by the home directory of the user being authenticated, and
+%u is replaced by the username of that user.
+.Pp
+The
+.Cm ChrootDirectory
+must contain the necessary files and directories to support the
+user's session.
+For an interactive session this requires at least a shell, typically
+.Xr sh 1 ,
+and basic
+.Pa /dev
+nodes such as
+.Xr null 4 ,
+.Xr zero 4 ,
+.Xr stdin 4 ,
+.Xr stdout 4 ,
+.Xr stderr 4 ,
+.Xr arandom 4
+and
+.Xr tty 4
+devices.
+For file transfer sessions using
+.Dq sftp ,
+no additional configuration of the environment is necessary if the
+in-process sftp server is used,
+though sessions which use logging do require
+.Pa /dev/log
+inside the chroot directory (see
+.Xr sftp-server 8
+for details).
+.Pp
+The default is not to
+.Xr chroot 2 .
 .It Cm Ciphers
 Specifies the ciphers allowed for protocol version 2.
 Multiple ciphers must be comma-separated.
@@ -193,9 +245,9 @@ and
 .Dq cast128-cbc .
 The default is:
 .Bd -literal -offset 3n
-aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
-arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
-aes192-ctr,aes256-ctr
+aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
+aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
+aes256-cbc,arcfour
 .Ed
 .It Cm ClientAliveCountMax
 Sets the number of client alive messages (see below) which may be
@@ -283,6 +335,25 @@ See
 in
 .Xr ssh_config 5
 for more information on patterns.
+.It Cm ForceCommand
+Forces the execution of the command specified by
+.Cm ForceCommand ,
+ignoring any command supplied by the client and
+.Pa ~/.ssh/rc
+if present.
+The command is invoked by using the user's login shell with the -c option.
+This applies to shell, command, or subsystem execution.
+It is most useful inside a
+.Cm Match
+block.
+The command originally supplied by the client is available in the
+.Ev SSH_ORIGINAL_COMMAND
+environment variable.
+Specifying a command of
+.Dq internal-sftp
+will force the use of an in-process sftp server that requires no support
+files when used with
+.Cm ChrootDirectory .
 .It Cm GatewayPorts
 Specifies whether remote hosts are allowed to connect to ports
 forwarded for the client.
@@ -323,6 +394,23 @@ This option is similar to
 and applies to protocol version 2 only.
 The default is
 .Dq no .
+.It Cm HostbasedUsesNameFromPacketOnly
+Specifies whether or not the server will attempt to perform a reverse
+name lookup when matching the name in the
+.Pa ~/.shosts ,
+.Pa ~/.rhosts ,
+and
+.Pa /etc/hosts.equiv
+files during
+.Cm HostbasedAuthentication .
+A setting of
+.Dq yes
+means that
+.Xr sshd 8
+uses the name supplied by the client rather than
+attempting to resolve the name from the TCP connection itself.
+The default is
+.Dq no .
 .It Cm HostKey
 Specifies a file containing a private host key
 used by SSH.
@@ -462,36 +550,86 @@ The MAC algorithm is used in protocol version 2
 for data integrity protection.
 Multiple algorithms must be comma-separated.
 The default is:
-.Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
+.Bd -literal -offset indent
+hmac-md5,hmac-sha1,umac-64@openssh.com,
+hmac-ripemd160,hmac-sha1-96,hmac-md5-96
+.Ed
 .It Cm Match
 Introduces a conditional block.
-Keywords on lines following a
+If all of the criteria on the
 .Cm Match
-block are only applied if all of the criteria on the
+line are satisfied, the keywords on the following lines override those
+set in the global section of the config file, until either another
 .Cm Match
-are satisfied.
+line or the end of the file.
+.Pp
 The arguments to
 .Cm Match
-block are one or more criteria-pattern pairs.
+are one or more criteria-pattern pairs.
 The available criteria are
 .Cm User ,
+.Cm Group ,
 .Cm Host ,
 and
 .Cm Address .
+The match patterns may consist of single entries or comma-separated
+lists and may use the wildcard and negation operators described in the
+.Sx PATTERNS
+section of
+.Xr ssh_config 5 .
+.Pp
+The patterns in an
+.Cm Address
+criteria may additionally contain addresses to match in CIDR
+address/masklen format, e.g.\&
+.Dq 192.0.2.0/24
+or
+.Dq 3ffe:ffff::/32 .
+Note that the mask length provided must be consistent with the address -
+it is an error to specify a mask length that is too long for the address
+or one with bits set in this host portion of the address.
+For example,
+.Dq 192.0.2.0/33
+and
+.Dq 192.0.2.0/8
+respectively.
+.Pp
 Only a subset of keywords may be used on the lines following a
 .Cm Match
 keyword.
 Available keywords are
+.Cm AllowAgentForwarding ,
 .Cm AllowTcpForwarding ,
+.Cm Banner ,
+.Cm ChrootDirectory ,
+.Cm ForceCommand ,
 .Cm GatewayPorts ,
+.Cm GSSAPIAuthentication ,
+.Cm HostbasedAuthentication ,
+.Cm KbdInteractiveAuthentication ,
+.Cm KerberosAuthentication ,
+.Cm MaxAuthTries ,
+.Cm MaxSessions ,
+.Cm PasswordAuthentication ,
+.Cm PermitEmptyPasswords ,
+.Cm PermitOpen ,
+.Cm PermitRootLogin ,
+.Cm PubkeyAuthentication ,
+.Cm RhostsRSAAuthentication ,
+.Cm RSAAuthentication ,
+.Cm X11DisplayOffset ,
+.Cm X11Forwarding
 and
-.Cm PermitOpen .
+.Cm X11UseLocalHost .
 .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 MaxSessions
+Specifies the maximum number of open sessions permitted per network connection.
+The default is 10.
 .It Cm MaxStartups
 Specifies the maximum number of concurrent unauthenticated connections to the
 SSH daemon.
@@ -547,9 +685,7 @@ The forwarding specification must be one of the following forms:
 .Sm on
 .El
 .Pp
-Multiple instances of
-.Cm PermitOpen
-are permitted.
+Multiple forwards may be specified by separating them with whitespace.
 An argument of
 .Dq any
 can be used to remove all restrictions and permit any forwarding requests.
@@ -657,7 +793,7 @@ and
 .Sq 2 .
 Multiple versions must be comma-separated.
 The default is
-.Dq 2,1 .
+.Sq 2 .
 Note that the order of the protocol list does not indicate preference,
 because the client selects among multiple protocol versions offered
 by the server.
@@ -683,7 +819,7 @@ The default is
 This option applies to protocol version 1 only.
 .It Cm ServerKeyBits
 Defines the number of bits in the ephemeral protocol version 1 server key.
-The minimum value is 512, and the default is 768.
+The minimum value is 512, and the default is 1024.
 .It Cm StrictModes
 Specifies whether
 .Xr sshd 8
@@ -693,15 +829,29 @@ This is normally desirable because novices sometimes accidentally leave their
 directory or files world-writable.
 The default is
 .Dq yes .
+Note that this does not apply to
+.Cm ChrootDirectory ,
+whose permissions and ownership are checked unconditionally.
 .It Cm Subsystem
 Configures an external subsystem (e.g. file transfer daemon).
 Arguments should be a subsystem name and a command (with optional arguments)
 to execute upon subsystem request.
+.Pp
 The command
 .Xr sftp-server 8
 implements the
 .Dq sftp
 file transfer subsystem.
+.Pp
+Alternately the name
+.Dq internal-sftp
+implements an in-process
+.Dq sftp
+server.
+This may simplify configurations using
+.Cm ChrootDirectory
+to force a different filesystem root on clients.
+.Pp
 By default no subsystems are defined.
 Note that this option applies to protocol version 2 only.
 .It Cm SyslogFacility