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|
.\" -*- nroff -*-
.\"
.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
.\" All rights reserved
.\"
.\" As far as I am concerned, the code I have written for this software
.\" can be used freely for any purpose. Any derived versions of this
.\" software must be clearly marked as such, and if the derived work is
.\" incompatible with the protocol description in the RFC file, it must be
.\" called by a name other than "ssh" or "Secure Shell".
.\"
.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
.\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
.\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (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 1.68 2005/12/08 18:34:11 reyk Exp $
.Dd September 25, 1999
.Dt SSH_CONFIG 5
.Os
.Sh NAME
.Nm ssh_config
.Nd OpenSSH SSH client configuration files
.Sh SYNOPSIS
.Bl -tag -width Ds -compact
.It Pa ~/.ssh/config
.It Pa /etc/ssh/ssh_config
.El
.Sh DESCRIPTION
.Nm ssh
obtains configuration data from the following sources in
the following order:
.Bl -enum -offset indent -compact
.It
command-line options
.It
user's configuration file
.Pq Pa ~/.ssh/config
.It
system-wide configuration file
.Pq Pa /etc/ssh/ssh_config
.El
.Pp
For each parameter, the first obtained value
will be used.
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.
The matched host name is the one given on the command line.
.Pp
Since the first obtained value for each parameter is used, more
host-specific declarations should be given near the beginning of the
file, and general defaults at the end.
.Pp
The configuration file has the following format:
.Pp
Empty lines and lines starting with
.Ql #
are comments.
.Pp
Otherwise a line is of the format
.Dq keyword arguments .
Configuration options may be separated by whitespace or
optional whitespace and exactly one
.Ql = ;
the latter format is useful to avoid the need to quote whitespace
when specifying configuration options using the
.Nm ssh ,
.Nm scp
and
.Nm sftp
.Fl o
option.
.Pp
The possible
keywords and their meanings are as follows (note that
keywords are case-insensitive and arguments are case-sensitive):
.Bl -tag -width Ds
.It Cm Host
Restricts the following declarations (up to the next
.Cm Host
keyword) to be only for those hosts that match one of the patterns
given after the keyword.
.Ql \&*
and
.Ql \&?
can be used as wildcards in the
patterns.
A single
.Ql \&*
as a pattern can be used to provide global
defaults for all hosts.
The host is the
.Ar hostname
argument given on the command line (i.e., the name is not converted to
a canonicalized host name before matching).
.It Cm AddressFamily
Specifies which address family to use when connecting.
Valid arguments are
.Dq any ,
.Dq inet
(use IPv4 only) or
.Dq inet6
(use IPv6 only).
.It Cm BatchMode
If set to
.Dq yes ,
passphrase/password querying will be disabled.
This option is useful in scripts and other batch jobs where no user
is present to supply the password.
The argument must be
.Dq yes
or
.Dq no .
The default is
.Dq no .
.It Cm BindAddress
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
.Dq yes .
.It Cm ChallengeResponseAuthentication
Specifies whether to use challenge response authentication.
The argument to this keyword must be
.Dq yes
or
.Dq no .
The default is
.Dq yes .
.It Cm CheckHostIP
If this flag is set to
.Dq yes ,
ssh will additionally check the host IP address in the
.Pa known_hosts
file.
This allows ssh to detect if a host key changed due to DNS spoofing.
If the option is set to
.Dq no ,
the check will not be executed.
The default is
.Dq yes .
.It Cm Cipher
Specifies the cipher to use for encrypting the session
in protocol version 1.
Currently,
.Dq blowfish ,
.Dq 3des ,
and
.Dq des
are supported.
.Ar des
is only supported in the
.Nm ssh
client for interoperability with legacy protocol 1 implementations
that do not support the
.Ar 3des
cipher.
Its use is strongly discouraged due to cryptographic weaknesses.
The default is
.Dq 3des .
.It Cm Ciphers
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,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
specified in the configuration files or on the command line be
cleared.
This option is primarily useful when used from the
.Nm ssh
command line to clear port forwardings set in
configuration files, and is automatically set by
.Xr scp 1
and
.Xr sftp 1 .
The argument must be
.Dq yes
or
.Dq no .
The default is
.Dq no .
.It Cm Compression
Specifies whether to use compression.
The argument must be
.Dq yes
or
.Dq no .
The default is
.Dq no .
.It Cm CompressionLevel
Specifies the compression level to use if compression is enabled.
The argument must be an integer from 1 (fast) to 9 (slow, best).
The default level is 6, which is good for most applications.
The meaning of the values is the same as in
.Xr gzip 1 .
Note that this option applies to protocol version 1 only.
.It Cm ConnectionAttempts
Specifies the number of tries (one per second) to make before exiting.
The argument must be an integer.
This may be useful in scripts if the connection sometimes fails.
The default is 1.
.It Cm ConnectTimeout
Specifies the timeout (in seconds) used when connecting to the ssh
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 fowarded 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
over the secure channel, and the application
protocol is then used to determine where to connect to from the
remote machine.
.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.
Multiple forwardings may be specified, and
additional forwardings can be given on the command line.
Only the superuser can forward privileged ports.
.It Cm EnableSSHKeysign
Setting this option to
.Dq
|