.\" (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: ssh_config.5,v 1.30 2004/04/19 13:02:40 djm Exp $
+.\" $OpenBSD: ssh_config.5,v 1.75 2006/01/20 00:14:55 dtucker Exp $
.Dd September 25, 1999
.Dt SSH_CONFIG 5
.Os
.Nd OpenSSH SSH client configuration files
.Sh SYNOPSIS
.Bl -tag -width Ds -compact
-.It Pa $HOME/.ssh/config
+.It Pa ~/.ssh/config
.It Pa /etc/ssh/ssh_config
.El
.Sh DESCRIPTION
command-line options
.It
user's configuration file
-.Pq Pa $HOME/.ssh/config
+.Pq Pa ~/.ssh/config
.It
system-wide configuration file
.Pq Pa /etc/ssh/ssh_config
.Pp
For each parameter, the first obtained value
will be used.
-The configuration files contain sections bracketed by
+The configuration files contain sections separated by
.Dq Host
specifications, and that section is only applied for hosts that
match one of the patterns given in the specification.
Valid arguments are
.Dq any ,
.Dq inet
-(Use IPv4 only) or
+(use IPv4 only) or
.Dq inet6
-(Use IPv6 only.)
+(use IPv6 only).
.It Cm BatchMode
If set to
.Dq yes ,
The default is
.Dq no .
.It Cm BindAddress
-Specify the interface to transmit from on machines with multiple
-interfaces or aliased addresses.
+Use the specified address on the local machine as the source address of
+the connection.
+Only useful on systems with more than one address.
Note that this option does not work if
.Cm UsePrivilegedPort
is set to
Specifies the ciphers allowed for protocol version 2
in order of preference.
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
.Bd -literal
- ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
- aes192-cbc,aes256-cbc''
+ ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
+ arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
+ aes192-ctr,aes256-ctr''
.Ed
.It Cm ClearAllForwardings
Specifies that all local, remote and dynamic port forwardings
server, instead of using the default system TCP timeout.
This value is used only when the target is down or really unreachable,
not when it refuses the connection.
+.It Cm ControlMaster
+Enables the sharing of multiple sessions over a single network connection.
+When set to
+.Dq yes
+.Nm ssh
+will listen for connections on a control socket specified using the
+.Cm ControlPath
+argument.
+Additional sessions can connect to this socket using the same
+.Cm ControlPath
+with
+.Cm ControlMaster
+set to
+.Dq no
+(the default).
+These sessions will try to reuse the master instance's network connection
+rather than initiating new ones, but will fall back to connecting normally
+if the control socket does not exist, or is not listening.
+.Pp
+Setting this to
+.Dq ask
+will cause
+.Nm ssh
+to listen for control connections, but require confirmation using the
+.Ev SSH_ASKPASS
+program before they are accepted (see
+.Xr ssh-add 1
+for details).
+If the
+.Cm ControlPath
+can not be opened,
+.Nm ssh
+will continue without connecting to a master instance.
+.Pp
+X11 and
+.Xr ssh-agent 1
+forwarding is supported over these multiplexed connections, however the
+display and agent forwarded will be the one belonging to the master
+connection i.e. it is not possible to forward multiple displays or agents.
+.Pp
+Two additional options allow for opportunistic multiplexing: try to use a
+master connection but fall back to creating a new one if one does not already
+exist.
+These options are:
+.Dq auto
+and
+.Dq autoask .
+The latter requires confirmation like the
+.Dq ask
+option.
+.It Cm ControlPath
+Specify the path to the control socket used for connection sharing as described
+in the
+.Cm ControlMaster
+section above or the string
+.Dq none
+to disable connection sharing.
+In the path,
+.Ql %h
+will be substituted by the target host name,
+.Ql %p
+the port and
+.Ql %r
+by the remote login username.
+It is recommended that any
+.Cm ControlPath
+used for opportunistic connection sharing include
+all three of these escape sequences.
+This ensures that shared connections are uniquely identified.
.It Cm DynamicForward
-Specifies that a TCP/IP port on the local machine be forwarded
+Specifies that a TCP port on the local machine be forwarded
over the secure channel, and the application
protocol is then used to determine where to connect to from the
remote machine.
-The argument must be a port number.
+.Pp
+The argument must be
+.Sm off
+.Oo Ar bind_address : Oc Ar port .
+.Sm on
+IPv6 addresses can be specified by enclosing addresses in square brackets or
+by using an alternative syntax:
+.Oo Ar bind_address Ns / Oc Ns Ar port .
+By default, the local port is bound in accordance with the
+.Cm GatewayPorts
+setting.
+However, an explicit
+.Ar bind_address
+may be used to bind the connection to a specific address.
+The
+.Ar bind_address
+of
+.Dq localhost
+indicates that the listening port be bound for local use only, while an
+empty address or
+.Sq *
+indicates that the port should be available from all interfaces.
+.Pp
Currently the SOCKS4 and SOCKS5 protocols are supported, and
.Nm ssh
will act as a SOCKS server.
.Cm ForwardX11Trusted
option is also enabled.
.It Cm ForwardX11Trusted
-If the this option is set to
+If this option is set to
.Dq yes
then remote X11 clients will have full access to the original X11 display.
+.Pp
If this option is set to
.Dq no
then remote X11 clients will be considered untrusted and prevented
from stealing or tampering with data belonging to trusted X11
clients.
+Furthermore, the
+.Xr xauth 1
+token used for the session will be set to expire after 20 minutes.
+Remote clients will be refused access after this time.
.Pp
The default is
.Dq no .
The default is
.Dq no .
Note that this option applies to protocol version 2 only.
+.It Cm HashKnownHosts
+Indicates that
+.Nm ssh
+should hash host names and addresses when they are added to
+.Pa ~/.ssh/known_hosts .
+These hashed names may be used normally by
+.Nm ssh
+and
+.Nm sshd ,
+but they do not reveal identifying information should the file's contents
+be disclosed.
+The default is
+.Dq no .
+Note that hashing of names and addresses will not be retrospectively applied
+to existing known hosts files, but these may be manually hashed using
+.Xr ssh-keygen 1 .
.It Cm HostbasedAuthentication
Specifies whether to try rhosts based authentication with public key
authentication.
Numeric IP addresses are also permitted (both on the command line and in
.Cm HostName
specifications).
-.It Cm IdentityFile
-Specifies a file from which the user's RSA or DSA authentication identity
-is read.
-The default is
-.Pa $HOME/.ssh/identity
-for protocol version 1, and
-.Pa $HOME/.ssh/id_rsa
-and
-.Pa $HOME/.ssh/id_dsa
-for protocol version 2.
-Additionally, any identities represented by the authentication agent
-will be used for authentication.
-The file name may use the tilde
-syntax to refer to a user's home directory.
-It is possible to have
-multiple identity files specified in configuration files; all these
-identities will be tried in sequence.
.It Cm IdentitiesOnly
Specifies that
.Nm ssh
should only use the authentication identity files configured in the
-.Nm
+.Nm
files,
even if the
.Nm ssh-agent
.Dq yes
or
.Dq no .
-This option is intented for situations where
+This option is intended for situations where
.Nm ssh-agent
offers many different identities.
The default is
.Dq no .
+.It Cm IdentityFile
+Specifies a file from which the user's RSA or DSA authentication identity
+is read.
+The default is
+.Pa ~/.ssh/identity
+for protocol version 1, and
+.Pa ~/.ssh/id_rsa
+and
+.Pa ~/.ssh/id_dsa
+for protocol version 2.
+Additionally, any identities represented by the authentication agent
+will be used for authentication.
+The file name may use the tilde
+syntax to refer to a user's home directory.
+It is possible to have
+multiple identity files specified in configuration files; all these
+identities will be tried in sequence.
+.It Cm KbdInteractiveDevices
+Specifies the list of methods to use in keyboard-interactive authentication.
+Multiple method names must be comma-separated.
+The default is to use the server specified list.
+.It Cm LocalCommand
+Specifies a command to execute on the local machine after successfully
+connecting to the server.
+The command string extends to the end of the line, and is executed with
+.Pa /bin/sh .
+This directive is ignored unless
+.Cm PermitLocalCommand
+has been enabled.
.It Cm LocalForward
-Specifies that a TCP/IP port on the local machine be forwarded over
+Specifies that a TCP port on the local machine be forwarded over
the secure channel to the specified host and port from the remote machine.
-The first argument must be a port number, and the second must be
-.Ar host:port .
-IPv6 addresses can be specified with an alternative syntax:
-.Ar host/port .
-Multiple forwardings may be specified, and additional
-forwardings can be given on the command line.
+The first argument must be
+.Sm off
+.Oo Ar bind_address : Oc Ar port
+.Sm on
+and the second argument must be
+.Ar host : Ns Ar hostport .
+IPv6 addresses can be specified by enclosing addresses in square brackets or
+by using an alternative syntax:
+.Oo Ar bind_address Ns / Oc Ns Ar port
+and
+.Ar host Ns / Ns Ar hostport .
+Multiple forwardings may be specified, and additional forwardings can be
+given on the command line.
Only the superuser can forward privileged ports.
+By default, the local port is bound in accordance with the
+.Cm GatewayPorts
+setting.
+However, an explicit
+.Ar bind_address
+may be used to bind the connection to a specific address.
+The
+.Ar bind_address
+of
+.Dq localhost
+indicates that the listening port be bound for local use only, while an
+empty address or
+.Sq *
+indicates that the port should be available from all interfaces.
.It Cm LogLevel
Gives the verbosity level that is used when logging messages from
.Nm ssh .
.Dq no .
The default is
.Dq yes .
+.It Cm PermitLocalCommand
+Allow local command execution via the
+.Ic LocalCommand
+option or using the
+.Ic !\& Ns Ar command
+escape sequence in
+.Xr ssh 1 .
+The argument must be
+.Dq yes
+or
+.Dq no .
+The default is
+.Dq no .
.It Cm Port
Specifies the port number to connect on the remote host.
Default is 22.
.It Cm PreferredAuthentications
Specifies the order in which the client should try protocol 2
authentication methods.
-This allows a client to prefer one method (e.g.
+This allows a client to prefer one method (e.g.\&
.Cm keyboard-interactive )
-over another method (e.g.
+over another method (e.g.\&
.Cm password )
The default for this option is:
.Dq hostbased,publickey,keyboard-interactive,password .
.Cm CheckHostIP
is not available for connects with a proxy command.
.Pp
+This directive is useful in conjunction with
+.Xr nc 1
+and its proxy support.
+For example, the following directive would connect via an HTTP proxy at
+192.0.2.0:
+.Bd -literal -offset 3n
+ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
+.Ed
.It Cm PubkeyAuthentication
Specifies whether to try public key authentication.
The argument to this keyword must be
The default is
.Dq yes .
This option applies to protocol version 2 only.
+.It Cm RekeyLimit
+Specifies the maximum amount of data that may be transmitted before the
+session key will be renegotiated.
+The argument is the number of bytes, with an optional suffix of
+.Dq K ,
+.Dq M ,
+or
+.Dq G
+to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
+The default is between
+.Dq 1G
+and
+.Dq 4G ,
+depending on the cipher.
+Note that this option applies to protocol version 2 only.
.It Cm RemoteForward
-Specifies that a TCP/IP port on the remote machine be forwarded over
+Specifies that a TCP port on the remote machine be forwarded over
the secure channel to the specified host and port from the local machine.
-The first argument must be a port number, and the second must be
-.Ar host:port .
-IPv6 addresses can be specified with an alternative syntax:
-.Ar host/port .
+The first argument must be
+.Sm off
+.Oo Ar bind_address : Oc Ar port
+.Sm on
+and the second argument must be
+.Ar host : Ns Ar hostport .
+IPv6 addresses can be specified by enclosing addresses in square brackets
+or by using an alternative syntax:
+.Oo Ar bind_address Ns / Oc Ns Ar port
+and
+.Ar host Ns / Ns Ar hostport .
Multiple forwardings may be specified, and additional
forwardings can be given on the command line.
Only the superuser can forward privileged ports.
+.Pp
+If the
+.Ar bind_address
+is not specified, the default is to only bind to loopback addresses.
+If the
+.Ar bind_address
+is
+.Ql *
+or an empty string, then the forwarding is requested to listen on all
+interfaces.
+Specifying a remote
+.Ar bind_address
+will only succeed if the server's
+.Cm GatewayPorts
+option is enabled (see
+.Xr sshd_config 5 ) .
.It Cm RhostsRSAAuthentication
Specifies whether to try rhosts based authentication with RSA host
authentication.
The default is
.Dq yes .
Note that this option applies to protocol version 1 only.
-.It Cm ServerAliveInterval
-Sets a timeout interval in seconds after which if no data has been received
-from the server,
-.Nm ssh
-will send a message through the encrypted
-channel to request a response from the server.
-The default
-is 0, indicating that these messages will not be sent to the server.
-This option applies to protocol version 2 only.
+.It Cm SendEnv
+Specifies what variables from the local
+.Xr environ 7
+should be sent to the server.
+Note that environment passing is only supported for protocol 2, the
+server must also support it, and the server must be configured to
+accept these environment variables.
+Refer to
+.Cm AcceptEnv
+in
+.Xr sshd_config 5
+for how to configure the server.
+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 SendEnv
+directives.
+The default is not to send any environment variables.
.It Cm ServerAliveCountMax
-Sets the number of server alive messages (see above) which may be
+Sets the number of server alive messages (see below) which may be
sent without
.Nm ssh
receiving any messages back from the server.
The default value is 3.
If, for example,
.Cm ServerAliveInterval
-(above) is set to 15, and
+(see below) is set to 15, and
.Cm ServerAliveCountMax
is left at the default, if the server becomes unresponsive ssh
will disconnect after approximately 45 seconds.
+.It Cm ServerAliveInterval
+Sets a timeout interval in seconds after which if no data has been received
+from the server,
+.Nm ssh
+will send a message through the encrypted
+channel to request a response from the server.
+The default
+is 0, indicating that these messages will not be sent to the server.
+This option applies to protocol version 2 only.
.It Cm SmartcardDevice
Specifies which smartcard device to use.
The argument to this keyword is the device
.Dq yes ,
.Nm ssh
will never automatically add host keys to the
-.Pa $HOME/.ssh/known_hosts
+.Pa ~/.ssh/known_hosts
file, and refuses to connect to hosts whose host key has changed.
This provides maximum protection against trojan horse attacks,
however, can be annoying when the
.Pp
To disable TCP keepalive messages, the value should be set to
.Dq no .
+.It Cm Tunnel
+Request starting
+.Xr tun 4
+device forwarding between the client and the server.
+This option also allows requesting layer 2 (ethernet)
+instead of layer 3 (point-to-point) tunneling from the server.
+The argument must be
+.Dq yes ,
+.Dq point-to-point ,
+.Dq ethernet
+or
+.Dq no .
+The default is
+.Dq no .
+.It Cm TunnelDevice
+Force a specified
+.Xr tun 4
+device on the client.
+Without this option, the next available device will be used.
.It Cm UsePrivilegedPort
Specifies whether to use a privileged port for outgoing connections.
The argument must be
.It Cm UserKnownHostsFile
Specifies a file to use for the user
host key database instead of
-.Pa $HOME/.ssh/known_hosts .
+.Pa ~/.ssh/known_hosts .
.It Cm VerifyHostKeyDNS
Specifies whether to verify the remote key using DNS and SSHFP resource
records.
.El
.Sh FILES
.Bl -tag -width Ds
-.It Pa $HOME/.ssh/config
+.It Pa ~/.ssh/config
This is the per-user configuration file.
The format of this file is described above.
This file is used by the
andersk / openssh.git / blobdiff