1147 lines
32 KiB
Groff
1147 lines
32 KiB
Groff
.\" -*- nroff -*-
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.\"
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.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
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.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
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.\" All rights reserved
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.\"
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.\" As far as I am concerned, the code I have written for this software
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.\" can be used freely for any purpose. Any derived versions of this
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.\" software must be clearly marked as such, and if the derived work is
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.\" incompatible with the protocol description in the RFC file, it must be
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.\" called by a name other than "ssh" or "Secure Shell".
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.\"
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.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
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.\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
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.\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $OpenBSD: ssh_config.5,v 1.111 2008/06/26 11:46:31 grunk Exp $
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.\" $FreeBSD$
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.Dd June 26 2008
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.Dt SSH_CONFIG 5
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.Os
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.Sh NAME
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.Nm ssh_config
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.Nd OpenSSH SSH client configuration files
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.Sh SYNOPSIS
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.Nm ~/.ssh/config
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.Nm /etc/ssh/ssh_config
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.Sh DESCRIPTION
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.Xr ssh 1
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obtains configuration data from the following sources in
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the following order:
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.Pp
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.Bl -enum -offset indent -compact
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.It
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command-line options
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.It
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user's configuration file
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.Pq Pa ~/.ssh/config
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.It
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system-wide configuration file
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.Pq Pa /etc/ssh/ssh_config
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.El
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.Pp
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For each parameter, the first obtained value
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will be used.
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The configuration files contain sections separated by
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.Dq Host
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specifications, and that section is only applied for hosts that
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match one of the patterns given in the specification.
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The matched host name is the one given on the command line.
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.Pp
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Since the first obtained value for each parameter is used, more
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host-specific declarations should be given near the beginning of the
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file, and general defaults at the end.
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.Pp
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The configuration file has the following format:
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.Pp
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Empty lines and lines starting with
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.Ql #
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are comments.
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Otherwise a line is of the format
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.Dq keyword arguments .
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Configuration options may be separated by whitespace or
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optional whitespace and exactly one
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.Ql = ;
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the latter format is useful to avoid the need to quote whitespace
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when specifying configuration options using the
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.Nm ssh ,
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.Nm scp ,
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and
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.Nm sftp
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.Fl o
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option.
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Arguments may optionally be enclosed in double quotes
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.Pq \&"
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in order to represent arguments containing spaces.
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.Pp
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The possible
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keywords and their meanings are as follows (note that
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keywords are case-insensitive and arguments are case-sensitive):
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.Bl -tag -width Ds
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.It Cm Host
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Restricts the following declarations (up to the next
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.Cm Host
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keyword) to be only for those hosts that match one of the patterns
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given after the keyword.
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If more than one pattern is provided, they should be separated by whitepsace.
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A single
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.Ql *
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as a pattern can be used to provide global
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defaults for all hosts.
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The host is the
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.Ar hostname
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argument given on the command line (i.e. the name is not converted to
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a canonicalized host name before matching).
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.Pp
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See
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.Sx PATTERNS
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for more information on patterns.
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.It Cm AddressFamily
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Specifies which address family to use when connecting.
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Valid arguments are
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.Dq any ,
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.Dq inet
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(use IPv4 only), or
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.Dq inet6
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(use IPv6 only).
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.It Cm BatchMode
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If set to
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.Dq yes ,
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passphrase/password querying will be disabled.
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This option is useful in scripts and other batch jobs where no user
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is present to supply the password.
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The argument must be
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.Dq yes
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or
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.Dq no .
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The default is
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.Dq no .
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.It Cm BindAddress
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Use the specified address on the local machine as the source address of
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the connection.
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Only useful on systems with more than one address.
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Note that this option does not work if
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.Cm UsePrivilegedPort
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is set to
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.Dq yes .
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.It Cm ChallengeResponseAuthentication
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Specifies whether to use challenge-response authentication.
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The argument to this keyword must be
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.Dq yes
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or
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.Dq no .
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The default is
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.Dq yes .
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.It Cm CheckHostIP
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If this flag is set to
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.Dq yes ,
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.Xr ssh 1
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will additionally check the host IP address in the
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.Pa known_hosts
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file.
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This allows ssh to detect if a host key changed due to DNS spoofing.
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If the option is set to
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.Dq no ,
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the check will not be executed.
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The default is
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.Dq no .
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.It Cm Cipher
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Specifies the cipher to use for encrypting the session
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in protocol version 1.
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Currently,
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.Dq blowfish ,
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.Dq 3des ,
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and
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.Dq des
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are supported.
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.Ar des
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is only supported in the
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.Xr ssh 1
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client for interoperability with legacy protocol 1 implementations
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that do not support the
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.Ar 3des
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cipher.
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Its use is strongly discouraged due to cryptographic weaknesses.
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The default is
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.Dq 3des .
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.It Cm Ciphers
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Specifies the ciphers allowed for protocol version 2
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in order of preference.
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Multiple ciphers must be comma-separated.
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The supported ciphers are
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.Dq 3des-cbc ,
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.Dq aes128-cbc ,
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.Dq aes192-cbc ,
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.Dq aes256-cbc ,
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.Dq aes128-ctr ,
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.Dq aes192-ctr ,
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.Dq aes256-ctr ,
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.Dq arcfour128 ,
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.Dq arcfour256 ,
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.Dq arcfour ,
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.Dq blowfish-cbc ,
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and
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.Dq cast128-cbc .
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The default is:
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.Bd -literal -offset 3n
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aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
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arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
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aes192-ctr,aes256-ctr
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.Ed
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.It Cm ClearAllForwardings
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Specifies that all local, remote, and dynamic port forwardings
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specified in the configuration files or on the command line be
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cleared.
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This option is primarily useful when used from the
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.Xr ssh 1
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command line to clear port forwardings set in
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configuration files, and is automatically set by
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.Xr scp 1
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and
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.Xr sftp 1 .
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The argument must be
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.Dq yes
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or
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.Dq no .
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The default is
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.Dq no .
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.It Cm Compression
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Specifies whether to use compression.
|
|
The argument must be
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.Dq yes
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or
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.Dq no .
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The default is
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.Dq no .
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.It Cm CompressionLevel
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Specifies the compression level to use if compression is enabled.
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The argument must be an integer from 1 (fast) to 9 (slow, best).
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The default level is 6, which is good for most applications.
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The meaning of the values is the same as in
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.Xr gzip 1 .
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Note that this option applies to protocol version 1 only.
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.It Cm ConnectionAttempts
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Specifies the number of tries (one per second) to make before exiting.
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The argument must be an integer.
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This may be useful in scripts if the connection sometimes fails.
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The default is 1.
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.It Cm ConnectTimeout
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Specifies the timeout (in seconds) used when connecting to the
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SSH server, instead of using the default system TCP timeout.
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This value is used only when the target is down or really unreachable,
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not when it refuses the connection.
|
|
.It Cm ControlMaster
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Enables the sharing of multiple sessions over a single network connection.
|
|
When set to
|
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.Dq yes ,
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.Xr ssh 1
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will listen for connections on a control socket specified using the
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.Cm ControlPath
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argument.
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|
Additional sessions can connect to this socket using the same
|
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.Cm ControlPath
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with
|
|
.Cm ControlMaster
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|
set to
|
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.Dq no
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|
(the default).
|
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These sessions will try to reuse the master instance's network connection
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rather than initiating new ones, but will fall back to connecting normally
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if the control socket does not exist, or is not listening.
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.Pp
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Setting this to
|
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.Dq ask
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will cause ssh
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to listen for control connections, but require confirmation using the
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.Ev SSH_ASKPASS
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program before they are accepted (see
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.Xr ssh-add 1
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for details).
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|
If the
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.Cm ControlPath
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cannot be opened,
|
|
ssh will continue without connecting to a master instance.
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.Pp
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|
X11 and
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.Xr ssh-agent 1
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forwarding is supported over these multiplexed connections, however the
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|
display and agent forwarded will be the one belonging to the master
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connection i.e. it is not possible to forward multiple displays or agents.
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.Pp
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Two additional options allow for opportunistic multiplexing: try to use a
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master connection but fall back to creating a new one if one does not already
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exist.
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|
These options are:
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.Dq auto
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and
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.Dq autoask .
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The latter requires confirmation like the
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.Dq ask
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|
option.
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.It Cm ControlPath
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Specify the path to the control socket used for connection sharing as described
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in the
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.Cm ControlMaster
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section above or the string
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.Dq none
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to disable connection sharing.
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|
In the path,
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.Ql %l
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will be substituted by the local host name,
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.Ql %h
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will be substituted by the target host name,
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.Ql %p
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the port, and
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.Ql %r
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by the remote login username.
|
|
It is recommended that any
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.Cm ControlPath
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used for opportunistic connection sharing include
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at least %h, %p, and %r.
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This ensures that shared connections are uniquely identified.
|
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.It Cm DynamicForward
|
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Specifies that a TCP port on the local machine be forwarded
|
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over the secure channel, and the application
|
|
protocol is then used to determine where to connect to from the
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remote machine.
|
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.Pp
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The argument must be
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.Sm off
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.Oo Ar bind_address : Oc Ar port .
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.Sm on
|
|
IPv6 addresses can be specified by enclosing addresses in square brackets or
|
|
by using an alternative syntax:
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|
.Oo Ar bind_address Ns / Oc Ns Ar port .
|
|
By default, the local port is bound in accordance with the
|
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.Cm GatewayPorts
|
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setting.
|
|
However, an explicit
|
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.Ar bind_address
|
|
may be used to bind the connection to a specific address.
|
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The
|
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.Ar bind_address
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of
|
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.Dq localhost
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indicates that the listening port be bound for local use only, while an
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empty address or
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.Sq *
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indicates that the port should be available from all interfaces.
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.Pp
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Currently the SOCKS4 and SOCKS5 protocols are supported, and
|
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.Xr ssh 1
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will act as a SOCKS server.
|
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Multiple forwardings may be specified, and
|
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additional forwardings can be given on the command line.
|
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Only the superuser can forward privileged ports.
|
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.It Cm EnableSSHKeysign
|
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Setting this option to
|
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.Dq yes
|
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in the global client configuration file
|
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.Pa /etc/ssh/ssh_config
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enables the use of the helper program
|
|
.Xr ssh-keysign 8
|
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during
|
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.Cm HostbasedAuthentication .
|
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The argument must be
|
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.Dq yes
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or
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.Dq no .
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The default is
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.Dq no .
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This option should be placed in the non-hostspecific section.
|
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See
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.Xr ssh-keysign 8
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for more information.
|
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.It Cm EscapeChar
|
|
Sets the escape character (default:
|
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.Ql ~ ) .
|
|
The escape character can also
|
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be set on the command line.
|
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The argument should be a single character,
|
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.Ql ^
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followed by a letter, or
|
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.Dq none
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to disable the escape
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character entirely (making the connection transparent for binary
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data).
|
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.It Cm ExitOnForwardFailure
|
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Specifies whether
|
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.Xr ssh 1
|
|
should terminate the connection if it cannot set up all requested
|
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dynamic, tunnel, local, and remote port forwardings.
|
|
The argument must be
|
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.Dq yes
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or
|
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.Dq no .
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The default is
|
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.Dq no .
|
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.It Cm ForwardAgent
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Specifies whether the connection to the authentication agent (if any)
|
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will be forwarded to the remote machine.
|
|
The argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
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The default is
|
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.Dq no .
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.Pp
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Agent forwarding should be enabled with caution.
|
|
Users with the ability to bypass file permissions on the remote host
|
|
(for the agent's Unix-domain socket)
|
|
can access the local agent through the forwarded connection.
|
|
An attacker cannot obtain key material from the agent,
|
|
however they can perform operations on the keys that enable them to
|
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authenticate using the identities loaded into the agent.
|
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.It Cm ForwardX11
|
|
Specifies whether X11 connections will be automatically redirected
|
|
over the secure channel and
|
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.Ev DISPLAY
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set.
|
|
The argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
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The default is
|
|
.Dq no .
|
|
.Pp
|
|
X11 forwarding should be enabled with caution.
|
|
Users with the ability to bypass file permissions on the remote host
|
|
(for the user's X11 authorization database)
|
|
can access the local X11 display through the forwarded connection.
|
|
An attacker may then be able to perform activities such as keystroke monitoring
|
|
if the
|
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.Cm ForwardX11Trusted
|
|
option is also enabled.
|
|
.It Cm ForwardX11Trusted
|
|
If this option is set to
|
|
.Dq yes ,
|
|
remote X11 clients will have full access to the original X11 display.
|
|
.Pp
|
|
If this option is set to
|
|
.Dq no ,
|
|
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 .
|
|
.Pp
|
|
See the X11 SECURITY extension specification for full details on
|
|
the restrictions imposed on untrusted clients.
|
|
.It Cm GatewayPorts
|
|
Specifies whether remote hosts are allowed to connect to local
|
|
forwarded ports.
|
|
By default,
|
|
.Xr ssh 1
|
|
binds local port forwardings to the loopback address.
|
|
This prevents other remote hosts from connecting to forwarded ports.
|
|
.Cm GatewayPorts
|
|
can be used to specify that ssh
|
|
should bind local port forwardings to the wildcard address,
|
|
thus allowing remote hosts to connect to forwarded ports.
|
|
The argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
The default is
|
|
.Dq no .
|
|
.It Cm GlobalKnownHostsFile
|
|
Specifies a file to use for the global
|
|
host key database instead of
|
|
.Pa /etc/ssh/ssh_known_hosts .
|
|
.It Cm GSSAPIAuthentication
|
|
Specifies whether user authentication based on GSSAPI is allowed.
|
|
The default is
|
|
.Dq no .
|
|
Note that this option applies to protocol version 2 only.
|
|
.It Cm GSSAPIDelegateCredentials
|
|
Forward (delegate) credentials to the server.
|
|
The default is
|
|
.Dq no .
|
|
Note that this option applies to protocol version 2 only.
|
|
.It Cm HashKnownHosts
|
|
Indicates that
|
|
.Xr ssh 1
|
|
should hash host names and addresses when they are added to
|
|
.Pa ~/.ssh/known_hosts .
|
|
These hashed names may be used normally by
|
|
.Xr ssh 1
|
|
and
|
|
.Xr sshd 8 ,
|
|
but they do not reveal identifying information should the file's contents
|
|
be disclosed.
|
|
The default is
|
|
.Dq no .
|
|
Note that existing names and addresses in known hosts files
|
|
will not be converted automatically,
|
|
but may be manually hashed using
|
|
.Xr ssh-keygen 1 .
|
|
.It Cm HostbasedAuthentication
|
|
Specifies whether to try rhosts based authentication with public key
|
|
authentication.
|
|
The argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
The default is
|
|
.Dq no .
|
|
This option applies to protocol version 2 only and
|
|
is similar to
|
|
.Cm RhostsRSAAuthentication .
|
|
.It Cm HostKeyAlgorithms
|
|
Specifies the protocol version 2 host key algorithms
|
|
that the client wants to use in order of preference.
|
|
The default for this option is:
|
|
.Dq ssh-rsa,ssh-dss .
|
|
.It Cm HostKeyAlias
|
|
Specifies an alias that should be used instead of the
|
|
real host name when looking up or saving the host key
|
|
in the host key database files.
|
|
This option is useful for tunneling SSH connections
|
|
or for multiple servers running on a single host.
|
|
.It Cm HostName
|
|
Specifies the real host name to log into.
|
|
This can be used to specify nicknames or abbreviations for hosts.
|
|
The default is the name given on the command line.
|
|
Numeric IP addresses are also permitted (both on the command line and in
|
|
.Cm HostName
|
|
specifications).
|
|
.It Cm IdentitiesOnly
|
|
Specifies that
|
|
.Xr ssh 1
|
|
should only use the authentication identity files configured in the
|
|
.Nm
|
|
files,
|
|
even if
|
|
.Xr ssh-agent 1
|
|
offers more identities.
|
|
The argument to this keyword must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
This option is intended for situations where 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.
|
|
.Pp
|
|
The file name may use the tilde
|
|
syntax to refer to a user's home directory or one of the following
|
|
escape characters:
|
|
.Ql %d
|
|
(local user's home directory),
|
|
.Ql %u
|
|
(local user name),
|
|
.Ql %l
|
|
(local host name),
|
|
.Ql %h
|
|
(remote host name) or
|
|
.Ql %r
|
|
(remote user name).
|
|
.Pp
|
|
It is possible to have
|
|
multiple identity files specified in configuration files; all these
|
|
identities will be tried in sequence.
|
|
.It Cm KbdInteractiveAuthentication
|
|
Specifies whether to use keyboard-interactive authentication.
|
|
The argument to this keyword must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
The default is
|
|
.Dq yes .
|
|
.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.
|
|
The methods available vary depending on what the server supports.
|
|
For an OpenSSH server,
|
|
it may be zero or more of:
|
|
.Dq bsdauth ,
|
|
.Dq pam ,
|
|
and
|
|
.Dq skey .
|
|
.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
|
|
the user's shell.
|
|
The following escape character substitutions will be performed:
|
|
.Ql %d
|
|
(local user's home directory),
|
|
.Ql %h
|
|
(remote host name),
|
|
.Ql %l
|
|
(local host name),
|
|
.Ql %n
|
|
(host name as provided on the command line),
|
|
.Ql %p
|
|
(remote port),
|
|
.Ql %r
|
|
(remote user name) or
|
|
.Ql %u
|
|
(local user name).
|
|
This directive is ignored unless
|
|
.Cm PermitLocalCommand
|
|
has been enabled.
|
|
.It Cm LocalForward
|
|
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
|
|
.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
|
|
.Xr ssh 1 .
|
|
The possible values are:
|
|
QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
|
|
The default is INFO.
|
|
DEBUG and DEBUG1 are equivalent.
|
|
DEBUG2 and DEBUG3 each specify higher levels of verbose output.
|
|
.It Cm MACs
|
|
Specifies the MAC (message authentication code) algorithms
|
|
in order of preference.
|
|
The MAC algorithm is used in protocol version 2
|
|
for data integrity protection.
|
|
Multiple algorithms must be comma-separated.
|
|
The default is:
|
|
.Bd -literal -offset indent
|
|
hmac-md5,hmac-sha1,umac-64@openssh.com,
|
|
hmac-ripemd160,hmac-sha1-96,hmac-md5-96
|
|
.Ed
|
|
.It Cm NoHostAuthenticationForLocalhost
|
|
This option can be used if the home directory is shared across machines.
|
|
In this case localhost will refer to a different machine on each of
|
|
the machines and the user will get many warnings about changed host keys.
|
|
However, this option disables host authentication for localhost.
|
|
The argument to this keyword must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
The default is to check the host key for localhost.
|
|
.It Cm NumberOfPasswordPrompts
|
|
Specifies the number of password prompts before giving up.
|
|
The argument to this keyword must be an integer.
|
|
The default is 3.
|
|
.It Cm PasswordAuthentication
|
|
Specifies whether to use password authentication.
|
|
The argument to this keyword must be
|
|
.Dq yes
|
|
or
|
|
.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.
|
|
The 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.\&
|
|
.Cm keyboard-interactive )
|
|
over another method (e.g.\&
|
|
.Cm password )
|
|
The default for this option is:
|
|
.Do gssapi-with-mic ,
|
|
hostbased,
|
|
publickey,
|
|
keyboard-interactive,
|
|
password
|
|
.Dc .
|
|
.It Cm Protocol
|
|
Specifies the protocol versions
|
|
.Xr ssh 1
|
|
should support in order of preference.
|
|
The possible values are
|
|
.Sq 1
|
|
and
|
|
.Sq 2 .
|
|
Multiple versions must be comma-separated.
|
|
The default is
|
|
.Dq 2,1 .
|
|
This means that ssh
|
|
tries version 2 and falls back to version 1
|
|
if version 2 is not available.
|
|
.It Cm ProxyCommand
|
|
Specifies the command to use to connect to the server.
|
|
The command
|
|
string extends to the end of the line, and is executed with
|
|
the user's shell.
|
|
In the command string,
|
|
.Ql %h
|
|
will be substituted by the host name to
|
|
connect and
|
|
.Ql %p
|
|
by the port.
|
|
The command can be basically anything,
|
|
and should read from its standard input and write to its standard output.
|
|
It should eventually connect an
|
|
.Xr sshd 8
|
|
server running on some machine, or execute
|
|
.Ic sshd -i
|
|
somewhere.
|
|
Host key management will be done using the
|
|
HostName of the host being connected (defaulting to the name typed by
|
|
the user).
|
|
Setting the command to
|
|
.Dq none
|
|
disables this option entirely.
|
|
Note that
|
|
.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
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
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 is renegotiated.
|
|
The argument is the number of bytes, with an optional suffix of
|
|
.Sq K ,
|
|
.Sq M ,
|
|
or
|
|
.Sq G
|
|
to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
|
|
The default is between
|
|
.Sq 1G
|
|
and
|
|
.Sq 4G ,
|
|
depending on the cipher.
|
|
This option applies to protocol version 2 only.
|
|
.It Cm RemoteForward
|
|
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
|
|
.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 argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
The default is
|
|
.Dq no .
|
|
This option applies to protocol version 1 only and requires
|
|
.Xr ssh 1
|
|
to be setuid root.
|
|
.It Cm RSAAuthentication
|
|
Specifies whether to try RSA authentication.
|
|
The argument to this keyword must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
RSA authentication will only be
|
|
attempted if the identity file exists, or an authentication agent is
|
|
running.
|
|
The default is
|
|
.Dq yes .
|
|
Note that this option applies to protocol version 1 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 wildcard characters.
|
|
Multiple environment variables may be separated by whitespace or spread
|
|
across multiple
|
|
.Cm SendEnv
|
|
directives.
|
|
The default is not to send any environment variables.
|
|
.Pp
|
|
See
|
|
.Sx PATTERNS
|
|
for more information on patterns.
|
|
.It Cm ServerAliveCountMax
|
|
Sets the number of server alive messages (see below) which may be
|
|
sent without
|
|
.Xr ssh 1
|
|
receiving any messages back from the server.
|
|
If this threshold is reached while server alive messages are being sent,
|
|
ssh will disconnect from the server, terminating the session.
|
|
It is important to note that the use of server alive messages is very
|
|
different from
|
|
.Cm TCPKeepAlive
|
|
(below).
|
|
The server alive messages are sent through the encrypted channel
|
|
and therefore will not be spoofable.
|
|
The TCP keepalive option enabled by
|
|
.Cm TCPKeepAlive
|
|
is spoofable.
|
|
The server alive mechanism is valuable when the client or
|
|
server depend on knowing when a connection has become inactive.
|
|
.Pp
|
|
The default value is 3.
|
|
If, for example,
|
|
.Cm ServerAliveInterval
|
|
(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.
|
|
This option applies to protocol version 2 only.
|
|
.It Cm ServerAliveInterval
|
|
Sets a timeout interval in seconds after which if no data has been received
|
|
from the server,
|
|
.Xr ssh 1
|
|
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
|
|
.Xr ssh 1
|
|
should use to communicate with a smartcard used for storing the user's
|
|
private RSA key.
|
|
By default, no device is specified and smartcard support is not activated.
|
|
.It Cm StrictHostKeyChecking
|
|
If this flag is set to
|
|
.Dq yes ,
|
|
.Xr ssh 1
|
|
will never automatically add host keys to the
|
|
.Pa ~/.ssh/known_hosts
|
|
file, and refuses to connect to hosts whose host key has changed.
|
|
This provides maximum protection against trojan horse attacks,
|
|
though it can be annoying when the
|
|
.Pa /etc/ssh/ssh_known_hosts
|
|
file is poorly maintained or when connections to new hosts are
|
|
frequently made.
|
|
This option forces the user to manually
|
|
add all new hosts.
|
|
If this flag is set to
|
|
.Dq no ,
|
|
ssh will automatically add new host keys to the
|
|
user known hosts files.
|
|
If this flag is set to
|
|
.Dq ask ,
|
|
new host keys
|
|
will be added to the user known host files only after the user
|
|
has confirmed that is what they really want to do, and
|
|
ssh will refuse to connect to hosts whose host key has changed.
|
|
The host keys of
|
|
known hosts will be verified automatically in all cases.
|
|
The argument must be
|
|
.Dq yes ,
|
|
.Dq no ,
|
|
or
|
|
.Dq ask .
|
|
The default is
|
|
.Dq ask .
|
|
.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.
|
|
.Pp
|
|
The default is
|
|
.Dq yes
|
|
(to send TCP keepalive messages), and the client will notice
|
|
if the network goes down or the remote host dies.
|
|
This is important in scripts, and many users want it too.
|
|
.Pp
|
|
To disable TCP keepalive messages, the value should be set to
|
|
.Dq no .
|
|
.It Cm Tunnel
|
|
Request
|
|
.Xr tun 4
|
|
device forwarding between the client and the server.
|
|
The argument must be
|
|
.Dq yes ,
|
|
.Dq point-to-point
|
|
(layer 3),
|
|
.Dq ethernet
|
|
(layer 2),
|
|
or
|
|
.Dq no .
|
|
Specifying
|
|
.Dq yes
|
|
requests the default tunnel mode, which is
|
|
.Dq point-to-point .
|
|
The default is
|
|
.Dq no .
|
|
.It Cm TunnelDevice
|
|
Specifies the
|
|
.Xr tun 4
|
|
devices to open on the client
|
|
.Pq Ar local_tun
|
|
and the server
|
|
.Pq Ar remote_tun .
|
|
.Pp
|
|
The argument must be
|
|
.Sm off
|
|
.Ar local_tun Op : Ar remote_tun .
|
|
.Sm on
|
|
The devices may be specified by numerical ID or the keyword
|
|
.Dq any ,
|
|
which uses the next available tunnel device.
|
|
If
|
|
.Ar remote_tun
|
|
is not specified, it defaults to
|
|
.Dq any .
|
|
The default is
|
|
.Dq any:any .
|
|
.It Cm UsePrivilegedPort
|
|
Specifies whether to use a privileged port for outgoing connections.
|
|
The argument must be
|
|
.Dq yes
|
|
or
|
|
.Dq no .
|
|
The default is
|
|
.Dq no .
|
|
If set to
|
|
.Dq yes ,
|
|
.Xr ssh 1
|
|
must be setuid root.
|
|
Note that this option must be set to
|
|
.Dq yes
|
|
for
|
|
.Cm RhostsRSAAuthentication
|
|
with older servers.
|
|
.It Cm User
|
|
Specifies the user to log in as.
|
|
This can be useful when a different user name is used on different machines.
|
|
This saves the trouble of
|
|
having to remember to give the user name on the command line.
|
|
.It Cm UserKnownHostsFile
|
|
Specifies a file to use for the user
|
|
host key database instead of
|
|
.Pa ~/.ssh/known_hosts .
|
|
.It Cm VerifyHostKeyDNS
|
|
Specifies whether to verify the remote key using DNS and SSHFP resource
|
|
records.
|
|
If this option is set to
|
|
.Dq yes ,
|
|
the client will implicitly trust keys that match a secure fingerprint
|
|
from DNS.
|
|
Insecure fingerprints will be handled as if this option was set to
|
|
.Dq ask .
|
|
If this option is set to
|
|
.Dq ask ,
|
|
information on fingerprint match will be displayed, but the user will still
|
|
need to confirm new host keys according to the
|
|
.Cm StrictHostKeyChecking
|
|
option.
|
|
The argument must be
|
|
.Dq yes ,
|
|
.Dq no ,
|
|
or
|
|
.Dq ask .
|
|
The default is
|
|
.Dq no .
|
|
Note that this option applies to protocol version 2 only.
|
|
.Pp
|
|
See also
|
|
.Sx VERIFYING HOST KEYS
|
|
in
|
|
.Xr ssh 1 .
|
|
.It Cm VersionAddendum
|
|
Specifies a string to append to the regular version string to identify
|
|
OS- or site-specific modifications.
|
|
The default is
|
|
.Dq FreeBSD-20080801 .
|
|
.It Cm VisualHostKey
|
|
If this flag is set to
|
|
.Dq yes ,
|
|
an ASCII art representation of the remote host key fingerprint is
|
|
printed additionally to the hex fingerprint string.
|
|
If this flag is set to
|
|
.Dq no ,
|
|
only the hex fingerprint string will be printed.
|
|
The default is
|
|
.Dq no .
|
|
.It Cm XAuthLocation
|
|
Specifies the full pathname of the
|
|
.Xr xauth 1
|
|
program.
|
|
The default is
|
|
.Pa /usr/local/bin/xauth .
|
|
.El
|
|
.Sh PATTERNS
|
|
A
|
|
.Em pattern
|
|
consists of zero or more non-whitespace characters,
|
|
.Sq *
|
|
(a wildcard that matches zero or more characters),
|
|
or
|
|
.Sq ?\&
|
|
(a wildcard that matches exactly one character).
|
|
For example, to specify a set of declarations for any host in the
|
|
.Dq .co.uk
|
|
set of domains,
|
|
the following pattern could be used:
|
|
.Pp
|
|
.Dl Host *.co.uk
|
|
.Pp
|
|
The following pattern
|
|
would match any host in the 192.168.0.[0-9] network range:
|
|
.Pp
|
|
.Dl Host 192.168.0.?
|
|
.Pp
|
|
A
|
|
.Em pattern-list
|
|
is a comma-separated list of patterns.
|
|
Patterns within pattern-lists may be negated
|
|
by preceding them with an exclamation mark
|
|
.Pq Sq !\& .
|
|
For example,
|
|
to allow a key to be used from anywhere within an organisation
|
|
except from the
|
|
.Dq dialup
|
|
pool,
|
|
the following entry (in authorized_keys) could be used:
|
|
.Pp
|
|
.Dl from=\&"!*.dialup.example.com,*.example.com\&"
|
|
.Sh FILES
|
|
.Bl -tag -width Ds
|
|
.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 SSH client.
|
|
Because of the potential for abuse, this file must have strict permissions:
|
|
read/write for the user, and not accessible by others.
|
|
.It Pa /etc/ssh/ssh_config
|
|
Systemwide configuration file.
|
|
This file provides defaults for those
|
|
values that are not specified in the user's configuration file, and
|
|
for those users who do not have a configuration file.
|
|
This file must be world-readable.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr ssh 1
|
|
.Sh AUTHORS
|
|
OpenSSH is a derivative of the original and free
|
|
ssh 1.2.12 release by Tatu Ylonen.
|
|
Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
|
|
Theo de Raadt and Dug Song
|
|
removed many bugs, re-added newer features and
|
|
created OpenSSH.
|
|
Markus Friedl contributed the support for SSH
|
|
protocol versions 1.5 and 2.0.
|