1816 lines
51 KiB
Groff
1816 lines
51 KiB
Groff
.\"
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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 1.242 2017/02/27 14:30:33 jmc Exp $
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.\" $FreeBSD$
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.Dd $Mdocdate: February 27 2017 $
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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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|
.Cm 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 usually the one given on the command line
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(see the
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.Cm CanonicalizeHostname
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|
option for exceptions).
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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 file contains keyword-argument pairs, one per line.
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|
Lines starting with
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.Ql #
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|
and empty lines are interpreted as comments.
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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.
|
|
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
|
|
.Nm sftp
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|
.Fl o
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|
option.
|
|
.Pp
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|
The possible
|
|
keywords and their meanings are as follows (note that
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|
keywords are case-insensitive and arguments are case-sensitive):
|
|
.Bl -tag -width Ds
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|
.It Cm Host
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|
Restricts the following declarations (up to the next
|
|
.Cm Host
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|
or
|
|
.Cm Match
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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 whitespace.
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|
A single
|
|
.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 usually the
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|
.Ar hostname
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|
argument given on the command line
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(see the
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|
.Cm CanonicalizeHostname
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|
keyword for exceptions).
|
|
.Pp
|
|
A pattern entry may be negated by prefixing it with an exclamation mark
|
|
.Pq Sq !\& .
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|
If a negated entry is matched, then the
|
|
.Cm Host
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|
entry is ignored, regardless of whether any other patterns on the line
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match.
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|
Negated matches are therefore useful to provide exceptions for wildcard
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|
matches.
|
|
.Pp
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|
See
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.Sx PATTERNS
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|
for more information on patterns.
|
|
.It Cm Match
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|
Restricts the following declarations (up to the next
|
|
.Cm Host
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|
or
|
|
.Cm Match
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|
keyword) to be used only when the conditions following the
|
|
.Cm Match
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|
keyword are satisfied.
|
|
Match conditions are specified using one or more criteria
|
|
or the single token
|
|
.Cm all
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|
which always matches.
|
|
The available criteria keywords are:
|
|
.Cm canonical ,
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|
.Cm exec ,
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|
.Cm host ,
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|
.Cm originalhost ,
|
|
.Cm user ,
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|
and
|
|
.Cm localuser .
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|
The
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.Cm all
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|
criteria must appear alone or immediately after
|
|
.Cm canonical .
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|
Other criteria may be combined arbitrarily.
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|
All criteria but
|
|
.Cm all
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|
and
|
|
.Cm canonical
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|
require an argument.
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|
Criteria may be negated by prepending an exclamation mark
|
|
.Pq Sq !\& .
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|
.Pp
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|
The
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.Cm canonical
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keyword matches only when the configuration file is being re-parsed
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|
after hostname canonicalization (see the
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.Cm CanonicalizeHostname
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option.)
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This may be useful to specify conditions that work with canonical host
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names only.
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|
The
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.Cm exec
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keyword executes the specified command under the user's shell.
|
|
If the command returns a zero exit status then the condition is considered true.
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|
Commands containing whitespace characters must be quoted.
|
|
Arguments to
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|
.Cm exec
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|
accept the tokens described in the
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|
.Sx TOKENS
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section.
|
|
.Pp
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|
The other keywords' criteria must be single entries or comma-separated
|
|
lists and may use the wildcard and negation operators described in the
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|
.Sx PATTERNS
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section.
|
|
The criteria for the
|
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.Cm host
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keyword are matched against the target hostname, after any substitution
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by the
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|
.Cm Hostname
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or
|
|
.Cm CanonicalizeHostname
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|
options.
|
|
The
|
|
.Cm originalhost
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keyword matches against the hostname as it was specified on the command-line.
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The
|
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.Cm user
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|
keyword matches against the target username on the remote host.
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|
The
|
|
.Cm localuser
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|
keyword matches against the name of the local user running
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|
.Xr ssh 1
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|
(this keyword may be useful in system-wide
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|
.Nm
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|
files).
|
|
.It Cm AddKeysToAgent
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|
Specifies whether keys should be automatically added to a running
|
|
.Xr ssh-agent 1 .
|
|
If this option is set to
|
|
.Cm yes
|
|
and a key is loaded from a file, the key and its passphrase are added to
|
|
the agent with the default lifetime, as if by
|
|
.Xr ssh-add 1 .
|
|
If this option is set to
|
|
.Cm ask ,
|
|
.Xr ssh 1
|
|
will require confirmation using the
|
|
.Ev SSH_ASKPASS
|
|
program before adding a key (see
|
|
.Xr ssh-add 1
|
|
for details).
|
|
If this option is set to
|
|
.Cm confirm ,
|
|
each use of the key must be confirmed, as if the
|
|
.Fl c
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|
option was specified to
|
|
.Xr ssh-add 1 .
|
|
If this option is set to
|
|
.Cm no ,
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|
no keys are added to the agent.
|
|
The argument must be
|
|
.Cm yes ,
|
|
.Cm confirm ,
|
|
.Cm ask ,
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|
or
|
|
.Cm no
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|
(the default).
|
|
.It Cm AddressFamily
|
|
Specifies which address family to use when connecting.
|
|
Valid arguments are
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|
.Cm any
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|
(the default),
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|
.Cm inet
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|
(use IPv4 only), or
|
|
.Cm inet6
|
|
(use IPv6 only).
|
|
.It Cm BatchMode
|
|
If set to
|
|
.Cm 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
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
.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
|
|
.Cm yes .
|
|
.It Cm CanonicalDomains
|
|
When
|
|
.Cm CanonicalizeHostname
|
|
is enabled, this option specifies the list of domain suffixes in which to
|
|
search for the specified destination host.
|
|
.It Cm CanonicalizeFallbackLocal
|
|
Specifies whether to fail with an error when hostname canonicalization fails.
|
|
The default,
|
|
.Cm yes ,
|
|
will attempt to look up the unqualified hostname using the system resolver's
|
|
search rules.
|
|
A value of
|
|
.Cm no
|
|
will cause
|
|
.Xr ssh 1
|
|
to fail instantly if
|
|
.Cm CanonicalizeHostname
|
|
is enabled and the target hostname cannot be found in any of the domains
|
|
specified by
|
|
.Cm CanonicalDomains .
|
|
.It Cm CanonicalizeHostname
|
|
Controls whether explicit hostname canonicalization is performed.
|
|
The default,
|
|
.Cm no ,
|
|
is not to perform any name rewriting and let the system resolver handle all
|
|
hostname lookups.
|
|
If set to
|
|
.Cm yes
|
|
then, for connections that do not use a
|
|
.Cm ProxyCommand ,
|
|
.Xr ssh 1
|
|
will attempt to canonicalize the hostname specified on the command line
|
|
using the
|
|
.Cm CanonicalDomains
|
|
suffixes and
|
|
.Cm CanonicalizePermittedCNAMEs
|
|
rules.
|
|
If
|
|
.Cm CanonicalizeHostname
|
|
is set to
|
|
.Cm always ,
|
|
then canonicalization is applied to proxied connections too.
|
|
.Pp
|
|
If this option is enabled, then the configuration files are processed
|
|
again using the new target name to pick up any new configuration in matching
|
|
.Cm Host
|
|
and
|
|
.Cm Match
|
|
stanzas.
|
|
.It Cm CanonicalizeMaxDots
|
|
Specifies the maximum number of dot characters in a hostname before
|
|
canonicalization is disabled.
|
|
The default, 1,
|
|
allows a single dot (i.e. hostname.subdomain).
|
|
.It Cm CanonicalizePermittedCNAMEs
|
|
Specifies rules to determine whether CNAMEs should be followed when
|
|
canonicalizing hostnames.
|
|
The rules consist of one or more arguments of
|
|
.Ar source_domain_list : Ns Ar target_domain_list ,
|
|
where
|
|
.Ar source_domain_list
|
|
is a pattern-list of domains that may follow CNAMEs in canonicalization,
|
|
and
|
|
.Ar target_domain_list
|
|
is a pattern-list of domains that they may resolve to.
|
|
.Pp
|
|
For example,
|
|
.Qq *.a.example.com:*.b.example.com,*.c.example.com
|
|
will allow hostnames matching
|
|
.Qq *.a.example.com
|
|
to be canonicalized to names in the
|
|
.Qq *.b.example.com
|
|
or
|
|
.Qq *.c.example.com
|
|
domains.
|
|
.It Cm CertificateFile
|
|
Specifies a file from which the user's certificate is read.
|
|
A corresponding private key must be provided separately in order
|
|
to use this certificate either
|
|
from an
|
|
.Cm IdentityFile
|
|
directive or
|
|
.Fl i
|
|
flag to
|
|
.Xr ssh 1 ,
|
|
via
|
|
.Xr ssh-agent 1 ,
|
|
or via a
|
|
.Cm PKCS11Provider .
|
|
.Pp
|
|
Arguments to
|
|
.Cm CertificateFile
|
|
may use the tilde syntax to refer to a user's home directory
|
|
or the tokens described in the
|
|
.Sx TOKENS
|
|
section.
|
|
.Pp
|
|
It is possible to have multiple certificate files specified in
|
|
configuration files; these certificates will be tried in sequence.
|
|
Multiple
|
|
.Cm CertificateFile
|
|
directives will add to the list of certificates used for
|
|
authentication.
|
|
.It Cm ChallengeResponseAuthentication
|
|
Specifies whether to use challenge-response authentication.
|
|
The argument to this keyword must be
|
|
.Cm yes
|
|
(the default)
|
|
or
|
|
.Cm no .
|
|
.It Cm CheckHostIP
|
|
If set to
|
|
.Cm yes ,
|
|
.Xr ssh 1
|
|
will additionally check the host IP address in the
|
|
.Pa known_hosts
|
|
file.
|
|
This allows it to detect if a host key changed due to DNS spoofing
|
|
and will add addresses of destination hosts to
|
|
.Pa ~/.ssh/known_hosts
|
|
in the process, regardless of the setting of
|
|
.Cm StrictHostKeyChecking .
|
|
If the option is set to
|
|
.Cm no ,
|
|
the check will not be executed.
|
|
The default is
|
|
.Cm no .
|
|
.It Cm Cipher
|
|
Specifies the cipher to use for encrypting the session
|
|
in protocol version 1.
|
|
Currently,
|
|
.Cm blowfish ,
|
|
.Cm 3des
|
|
(the default),
|
|
and
|
|
.Cm des
|
|
are supported,
|
|
though
|
|
.Cm des
|
|
is only supported in the
|
|
.Xr ssh 1
|
|
client for interoperability with legacy protocol 1 implementations;
|
|
its use is strongly discouraged due to cryptographic weaknesses.
|
|
.It Cm Ciphers
|
|
Specifies the ciphers allowed for protocol version 2
|
|
in order of preference.
|
|
Multiple ciphers must be comma-separated.
|
|
If the specified value begins with a
|
|
.Sq +
|
|
character, then the specified ciphers will be appended to the default set
|
|
instead of replacing them.
|
|
If the specified value begins with a
|
|
.Sq -
|
|
character, then the specified ciphers (including wildcards) will be removed
|
|
from the default set instead of replacing them.
|
|
.Pp
|
|
The supported ciphers are:
|
|
.Bd -literal -offset indent
|
|
3des-cbc
|
|
aes128-cbc
|
|
aes192-cbc
|
|
aes256-cbc
|
|
aes128-ctr
|
|
aes192-ctr
|
|
aes256-ctr
|
|
aes128-gcm@openssh.com
|
|
aes256-gcm@openssh.com
|
|
arcfour
|
|
arcfour128
|
|
arcfour256
|
|
blowfish-cbc
|
|
cast128-cbc
|
|
chacha20-poly1305@openssh.com
|
|
.Ed
|
|
.Pp
|
|
The default is:
|
|
.Bd -literal -offset indent
|
|
chacha20-poly1305@openssh.com,
|
|
aes128-ctr,aes192-ctr,aes256-ctr,
|
|
aes128-gcm@openssh.com,aes256-gcm@openssh.com,
|
|
aes128-cbc,aes192-cbc,aes256-cbc
|
|
.Ed
|
|
.Pp
|
|
The list of available ciphers may also be obtained using
|
|
.Qq ssh -Q cipher .
|
|
.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
|
|
.Xr ssh 1
|
|
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
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
.It Cm Compression
|
|
Specifies whether to use compression.
|
|
The argument must be
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
.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
|
|
.Cm yes ,
|
|
.Xr ssh 1
|
|
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
|
|
.Cm 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
|
|
.Cm ask
|
|
will cause
|
|
.Xr ssh 1
|
|
to listen for control connections, but require confirmation using
|
|
.Xr ssh-askpass 1 .
|
|
If the
|
|
.Cm ControlPath
|
|
cannot be opened,
|
|
.Xr ssh 1
|
|
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:
|
|
.Cm auto
|
|
and
|
|
.Cm autoask .
|
|
The latter requires confirmation like the
|
|
.Cm 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
|
|
.Cm none
|
|
to disable connection sharing.
|
|
Arguments to
|
|
.Cm ControlPath
|
|
may use the tilde syntax to refer to a user's home directory
|
|
or the tokens described in the
|
|
.Sx TOKENS
|
|
section.
|
|
It is recommended that any
|
|
.Cm ControlPath
|
|
used for opportunistic connection sharing include
|
|
at least %h, %p, and %r (or alternatively %C) and be placed in a directory
|
|
that is not writable by other users.
|
|
This ensures that shared connections are uniquely identified.
|
|
.It Cm ControlPersist
|
|
When used in conjunction with
|
|
.Cm ControlMaster ,
|
|
specifies that the master connection should remain open
|
|
in the background (waiting for future client connections)
|
|
after the initial client connection has been closed.
|
|
If set to
|
|
.Cm no ,
|
|
then the master connection will not be placed into the background,
|
|
and will close as soon as the initial client connection is closed.
|
|
If set to
|
|
.Cm yes
|
|
or 0,
|
|
then the master connection will remain in the background indefinitely
|
|
(until killed or closed via a mechanism such as the
|
|
.Qq ssh -O exit ) .
|
|
If set to a time in seconds, or a time in any of the formats documented in
|
|
.Xr sshd_config 5 ,
|
|
then the backgrounded master connection will automatically terminate
|
|
after it has remained idle (with no client connections) for the
|
|
specified time.
|
|
.It Cm DynamicForward
|
|
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.
|
|
.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.
|
|
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
|
|
.Cm 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
|
|
.Xr ssh 1
|
|
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
|
|
.Cm yes
|
|
in the global client configuration file
|
|
.Pa /etc/ssh/ssh_config
|
|
enables the use of the helper program
|
|
.Xr ssh-keysign 8
|
|
during
|
|
.Cm HostbasedAuthentication .
|
|
The argument must be
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
This option should be placed in the non-hostspecific section.
|
|
See
|
|
.Xr ssh-keysign 8
|
|
for more information.
|
|
.It Cm EscapeChar
|
|
Sets the escape character (default:
|
|
.Ql ~ ) .
|
|
The escape character can also
|
|
be set on the command line.
|
|
The argument should be a single character,
|
|
.Ql ^
|
|
followed by a letter, or
|
|
.Cm none
|
|
to disable the escape
|
|
character entirely (making the connection transparent for binary
|
|
data).
|
|
.It Cm ExitOnForwardFailure
|
|
Specifies whether
|
|
.Xr ssh 1
|
|
should terminate the connection if it cannot set up all requested
|
|
dynamic, tunnel, local, and remote port forwardings, (e.g.\&
|
|
if either end is unable to bind and listen on a specified port).
|
|
Note that
|
|
.Cm ExitOnForwardFailure
|
|
does not apply to connections made over port forwardings and will not,
|
|
for example, cause
|
|
.Xr ssh 1
|
|
to exit if TCP connections to the ultimate forwarding destination fail.
|
|
The argument must be
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
.It Cm FingerprintHash
|
|
Specifies the hash algorithm used when displaying key fingerprints.
|
|
Valid options are:
|
|
.Cm md5
|
|
and
|
|
.Cm sha256
|
|
(the default).
|
|
.It Cm ForwardAgent
|
|
Specifies whether the connection to the authentication agent (if any)
|
|
will be forwarded to the remote machine.
|
|
The argument must be
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
.Pp
|
|
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
|
|
authenticate using the identities loaded into the agent.
|
|
.It Cm ForwardX11
|
|
Specifies whether X11 connections will be automatically redirected
|
|
over the secure channel and
|
|
.Ev DISPLAY
|
|
set.
|
|
The argument must be
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
.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
|
|
.Cm ForwardX11Trusted
|
|
option is also enabled.
|
|
.It Cm ForwardX11Timeout
|
|
Specify a timeout for untrusted X11 forwarding
|
|
using the format described in the
|
|
.Sx TIME FORMATS
|
|
section of
|
|
.Xr sshd_config 5 .
|
|
X11 connections received by
|
|
.Xr ssh 1
|
|
after this time will be refused.
|
|
The default is to disable untrusted X11 forwarding after twenty minutes has
|
|
elapsed.
|
|
.It Cm ForwardX11Trusted
|
|
If this option is set to
|
|
.Cm yes ,
|
|
remote X11 clients will have full access to the original X11 display.
|
|
.Pp
|
|
If this option is set to
|
|
.Cm no
|
|
(the default),
|
|
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
|
|
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
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
.It Cm GlobalKnownHostsFile
|
|
Specifies one or more files to use for the global
|
|
host key database, separated by whitespace.
|
|
The default is
|
|
.Pa /etc/ssh/ssh_known_hosts ,
|
|
.Pa /etc/ssh/ssh_known_hosts2 .
|
|
.It Cm GSSAPIAuthentication
|
|
Specifies whether user authentication based on GSSAPI is allowed.
|
|
The default is
|
|
.Cm no .
|
|
.It Cm GSSAPIDelegateCredentials
|
|
Forward (delegate) credentials to the server.
|
|
The default is
|
|
.Cm no .
|
|
.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
|
|
.Cm 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
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
.It Cm HostbasedKeyTypes
|
|
Specifies the key types that will be used for hostbased authentication
|
|
as a comma-separated pattern list.
|
|
Alternately if the specified value begins with a
|
|
.Sq +
|
|
character, then the specified key types will be appended to the default set
|
|
instead of replacing them.
|
|
If the specified value begins with a
|
|
.Sq -
|
|
character, then the specified key types (including wildcards) will be removed
|
|
from the default set instead of replacing them.
|
|
The default for this option is:
|
|
.Bd -literal -offset 3n
|
|
ecdsa-sha2-nistp256-cert-v01@openssh.com,
|
|
ecdsa-sha2-nistp384-cert-v01@openssh.com,
|
|
ecdsa-sha2-nistp521-cert-v01@openssh.com,
|
|
ssh-ed25519-cert-v01@openssh.com,
|
|
ssh-rsa-cert-v01@openssh.com,
|
|
ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
|
|
ssh-ed25519,ssh-rsa
|
|
.Ed
|
|
.Pp
|
|
The
|
|
.Fl Q
|
|
option of
|
|
.Xr ssh 1
|
|
may be used to list supported key types.
|
|
.It Cm HostKeyAlgorithms
|
|
Specifies the host key algorithms
|
|
that the client wants to use in order of preference.
|
|
Alternately if the specified value begins with a
|
|
.Sq +
|
|
character, then the specified key types will be appended to the default set
|
|
instead of replacing them.
|
|
If the specified value begins with a
|
|
.Sq -
|
|
character, then the specified key types (including wildcards) will be removed
|
|
from the default set instead of replacing them.
|
|
The default for this option is:
|
|
.Bd -literal -offset 3n
|
|
ecdsa-sha2-nistp256-cert-v01@openssh.com,
|
|
ecdsa-sha2-nistp384-cert-v01@openssh.com,
|
|
ecdsa-sha2-nistp521-cert-v01@openssh.com,
|
|
ssh-ed25519-cert-v01@openssh.com,
|
|
ssh-rsa-cert-v01@openssh.com,
|
|
ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
|
|
ssh-ed25519,ssh-rsa
|
|
.Ed
|
|
.Pp
|
|
If hostkeys are known for the destination host then this default is modified
|
|
to prefer their algorithms.
|
|
.Pp
|
|
The list of available key types may also be obtained using
|
|
.Qq ssh -Q key .
|
|
.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.
|
|
Arguments to
|
|
.Cm HostName
|
|
accept the tokens described in the
|
|
.Sx TOKENS
|
|
section.
|
|
Numeric IP addresses are also permitted (both on the command line and in
|
|
.Cm HostName
|
|
specifications).
|
|
The default is the name given on the command line.
|
|
.It Cm IdentitiesOnly
|
|
Specifies that
|
|
.Xr ssh 1
|
|
should only use the authentication identity and certificate files explicitly
|
|
configured in the
|
|
.Nm
|
|
files
|
|
or passed on the
|
|
.Xr ssh 1
|
|
command-line,
|
|
even if
|
|
.Xr ssh-agent 1
|
|
or a
|
|
.Cm PKCS11Provider
|
|
offers more identities.
|
|
The argument to this keyword must be
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
This option is intended for situations where ssh-agent
|
|
offers many different identities.
|
|
.It Cm IdentityAgent
|
|
Specifies the
|
|
.Ux Ns -domain
|
|
socket used to communicate with the authentication agent.
|
|
.Pp
|
|
This option overrides the
|
|
.Ev SSH_AUTH_SOCK
|
|
environment variable and can be used to select a specific agent.
|
|
Setting the socket name to
|
|
.Cm none
|
|
disables the use of an authentication agent.
|
|
If the string
|
|
.Qq SSH_AUTH_SOCK
|
|
is specified, the location of the socket will be read from the
|
|
.Ev SSH_AUTH_SOCK
|
|
environment variable.
|
|
.Pp
|
|
Arguments to
|
|
.Cm IdentityAgent
|
|
may use the tilde syntax to refer to a user's home directory
|
|
or the tokens described in the
|
|
.Sx TOKENS
|
|
section.
|
|
.It Cm IdentityFile
|
|
Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA authentication
|
|
identity is read.
|
|
The default is
|
|
.Pa ~/.ssh/identity
|
|
for protocol version 1, and
|
|
.Pa ~/.ssh/id_dsa ,
|
|
.Pa ~/.ssh/id_ecdsa ,
|
|
.Pa ~/.ssh/id_ed25519
|
|
and
|
|
.Pa ~/.ssh/id_rsa
|
|
for protocol version 2.
|
|
Additionally, any identities represented by the authentication agent
|
|
will be used for authentication unless
|
|
.Cm IdentitiesOnly
|
|
is set.
|
|
If no certificates have been explicitly specified by
|
|
.Cm CertificateFile ,
|
|
.Xr ssh 1
|
|
will try to load certificate information from the filename obtained by
|
|
appending
|
|
.Pa -cert.pub
|
|
to the path of a specified
|
|
.Cm IdentityFile .
|
|
.Pp
|
|
Arguments to
|
|
.Cm IdentityFile
|
|
may use the tilde syntax to refer to a user's home directory
|
|
or the tokens described in the
|
|
.Sx TOKENS
|
|
section.
|
|
.Pp
|
|
It is possible to have
|
|
multiple identity files specified in configuration files; all these
|
|
identities will be tried in sequence.
|
|
Multiple
|
|
.Cm IdentityFile
|
|
directives will add to the list of identities tried (this behaviour
|
|
differs from that of other configuration directives).
|
|
.Pp
|
|
.Cm IdentityFile
|
|
may be used in conjunction with
|
|
.Cm IdentitiesOnly
|
|
to select which identities in an agent are offered during authentication.
|
|
.Cm IdentityFile
|
|
may also be used in conjunction with
|
|
.Cm CertificateFile
|
|
in order to provide any certificate also needed for authentication with
|
|
the identity.
|
|
.It Cm IgnoreUnknown
|
|
Specifies a pattern-list of unknown options to be ignored if they are
|
|
encountered in configuration parsing.
|
|
This may be used to suppress errors if
|
|
.Nm
|
|
contains options that are unrecognised by
|
|
.Xr ssh 1 .
|
|
It is recommended that
|
|
.Cm IgnoreUnknown
|
|
be listed early in the configuration file as it will not be applied
|
|
to unknown options that appear before it.
|
|
.It Cm Include
|
|
Include the specified configuration file(s).
|
|
Multiple pathnames may be specified and each pathname may contain
|
|
.Xr glob 3
|
|
wildcards and, for user configurations, shell-like
|
|
.Sq ~
|
|
references to user home directories.
|
|
Files without absolute paths are assumed to be in
|
|
.Pa ~/.ssh
|
|
if included in a user configuration file or
|
|
.Pa /etc/ssh
|
|
if included from the system configuration file.
|
|
.Cm Include
|
|
directive may appear inside a
|
|
.Cm Match
|
|
or
|
|
.Cm Host
|
|
block
|
|
to perform conditional inclusion.
|
|
.It Cm IPQoS
|
|
Specifies the IPv4 type-of-service or DSCP class for connections.
|
|
Accepted values are
|
|
.Cm af11 ,
|
|
.Cm af12 ,
|
|
.Cm af13 ,
|
|
.Cm af21 ,
|
|
.Cm af22 ,
|
|
.Cm af23 ,
|
|
.Cm af31 ,
|
|
.Cm af32 ,
|
|
.Cm af33 ,
|
|
.Cm af41 ,
|
|
.Cm af42 ,
|
|
.Cm af43 ,
|
|
.Cm cs0 ,
|
|
.Cm cs1 ,
|
|
.Cm cs2 ,
|
|
.Cm cs3 ,
|
|
.Cm cs4 ,
|
|
.Cm cs5 ,
|
|
.Cm cs6 ,
|
|
.Cm cs7 ,
|
|
.Cm ef ,
|
|
.Cm lowdelay ,
|
|
.Cm throughput ,
|
|
.Cm reliability ,
|
|
or a numeric value.
|
|
This option may take one or two arguments, separated by whitespace.
|
|
If one argument is specified, it is used as the packet class unconditionally.
|
|
If two values are specified, the first is automatically selected for
|
|
interactive sessions and the second for non-interactive sessions.
|
|
The default is
|
|
.Cm lowdelay
|
|
for interactive sessions and
|
|
.Cm throughput
|
|
for non-interactive sessions.
|
|
.It Cm KbdInteractiveAuthentication
|
|
Specifies whether to use keyboard-interactive authentication.
|
|
The argument to this keyword must be
|
|
.Cm yes
|
|
(the default)
|
|
or
|
|
.Cm no .
|
|
.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:
|
|
.Cm bsdauth ,
|
|
.Cm pam ,
|
|
and
|
|
.Cm skey .
|
|
.It Cm KexAlgorithms
|
|
Specifies the available KEX (Key Exchange) algorithms.
|
|
Multiple algorithms must be comma-separated.
|
|
Alternately if the specified value begins with a
|
|
.Sq +
|
|
character, then the specified methods will be appended to the default set
|
|
instead of replacing them.
|
|
If the specified value begins with a
|
|
.Sq -
|
|
character, then the specified methods (including wildcards) will be removed
|
|
from the default set instead of replacing them.
|
|
The default is:
|
|
.Bd -literal -offset indent
|
|
curve25519-sha256,curve25519-sha256@libssh.org,
|
|
ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
|
|
diffie-hellman-group-exchange-sha256,
|
|
diffie-hellman-group-exchange-sha1,
|
|
diffie-hellman-group14-sha1
|
|
.Ed
|
|
.Pp
|
|
The list of available key exchange algorithms may also be obtained using
|
|
.Qq ssh -Q kex .
|
|
.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.
|
|
Arguments to
|
|
.Cm LocalCommand
|
|
accept the tokens described in the
|
|
.Sx TOKENS
|
|
section.
|
|
.Pp
|
|
The command is run synchronously and does not have access to the
|
|
session of the
|
|
.Xr ssh 1
|
|
that spawned it.
|
|
It should not be used for interactive commands.
|
|
.Pp
|
|
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.
|
|
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
|
|
.Cm 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 for data integrity protection.
|
|
Multiple algorithms must be comma-separated.
|
|
If the specified value begins with a
|
|
.Sq +
|
|
character, then the specified algorithms will be appended to the default set
|
|
instead of replacing them.
|
|
If the specified value begins with a
|
|
.Sq -
|
|
character, then the specified algorithms (including wildcards) will be removed
|
|
from the default set instead of replacing them.
|
|
.Pp
|
|
The algorithms that contain
|
|
.Qq -etm
|
|
calculate the MAC after encryption (encrypt-then-mac).
|
|
These are considered safer and their use recommended.
|
|
.Pp
|
|
The default is:
|
|
.Bd -literal -offset indent
|
|
umac-64-etm@openssh.com,umac-128-etm@openssh.com,
|
|
hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
|
|
hmac-sha1-etm@openssh.com,
|
|
umac-64@openssh.com,umac-128@openssh.com,
|
|
hmac-sha2-256,hmac-sha2-512,hmac-sha1
|
|
.Ed
|
|
.Pp
|
|
The list of available MAC algorithms may also be obtained using
|
|
.Qq ssh -Q mac .
|
|
.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
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
.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
|
|
.Cm yes
|
|
(the default)
|
|
or
|
|
.Cm no .
|
|
.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
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
.It Cm PKCS11Provider
|
|
Specifies which PKCS#11 provider to use.
|
|
The argument to this keyword is the PKCS#11 shared library
|
|
.Xr ssh 1
|
|
should use to communicate with a PKCS#11 token providing the user's
|
|
private RSA key.
|
|
.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 authentication methods.
|
|
This allows a client to prefer one method (e.g.\&
|
|
.Cm keyboard-interactive )
|
|
over another method (e.g.\&
|
|
.Cm password ) .
|
|
The default is:
|
|
.Bd -literal -offset indent
|
|
gssapi-with-mic,hostbased,publickey,
|
|
keyboard-interactive,password
|
|
.Ed
|
|
.It Cm Protocol
|
|
Specifies the protocol versions
|
|
.Xr ssh 1
|
|
should support in order of preference.
|
|
The possible values are 1 and 2.
|
|
Multiple versions must be comma-separated.
|
|
When this option is set to
|
|
.Cm 2,1
|
|
.Nm ssh
|
|
will try version 2 and fall back to version 1
|
|
if version 2 is not available.
|
|
The default is version 2.
|
|
Protocol 1 suffers from a number of cryptographic weaknesses and should
|
|
not be used.
|
|
It is only offered to support legacy devices.
|
|
.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
|
|
using the user's shell
|
|
.Ql exec
|
|
directive to avoid a lingering shell process.
|
|
.Pp
|
|
Arguments to
|
|
.Cm ProxyCommand
|
|
accept the tokens described in the
|
|
.Sx TOKENS
|
|
section.
|
|
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
|
|
.Cm 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 ProxyJump
|
|
Specifies one or more jump proxies as
|
|
.Xo
|
|
.Sm off
|
|
.Op Ar user No @
|
|
.Ar host
|
|
.Op : Ns Ar port
|
|
.Sm on
|
|
.Xc .
|
|
Multiple proxies may be separated by comma characters and will be visited
|
|
sequentially.
|
|
Setting this option will cause
|
|
.Xr ssh 1
|
|
to connect to the target host by first making a
|
|
.Xr ssh 1
|
|
connection to the specified
|
|
.Cm ProxyJump
|
|
host and then establishing a
|
|
TCP forwarding to the ultimate target from there.
|
|
.Pp
|
|
Note that this option will compete with the
|
|
.Cm ProxyCommand
|
|
option - whichever is specified first will prevent later instances of the
|
|
other from taking effect.
|
|
.It Cm ProxyUseFdpass
|
|
Specifies that
|
|
.Cm ProxyCommand
|
|
will pass a connected file descriptor back to
|
|
.Xr ssh 1
|
|
instead of continuing to execute and pass data.
|
|
The default is
|
|
.Cm no .
|
|
.It Cm PubkeyAcceptedKeyTypes
|
|
Specifies the key types that will be used for public key authentication
|
|
as a comma-separated pattern list.
|
|
Alternately if the specified value begins with a
|
|
.Sq +
|
|
character, then the key types after it will be appended to the default
|
|
instead of replacing it.
|
|
If the specified value begins with a
|
|
.Sq -
|
|
character, then the specified key types (including wildcards) will be removed
|
|
from the default set instead of replacing them.
|
|
The default for this option is:
|
|
.Bd -literal -offset 3n
|
|
ecdsa-sha2-nistp256-cert-v01@openssh.com,
|
|
ecdsa-sha2-nistp384-cert-v01@openssh.com,
|
|
ecdsa-sha2-nistp521-cert-v01@openssh.com,
|
|
ssh-ed25519-cert-v01@openssh.com,
|
|
ssh-rsa-cert-v01@openssh.com,
|
|
ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
|
|
ssh-ed25519,ssh-rsa
|
|
.Ed
|
|
.Pp
|
|
The list of available key types may also be obtained using
|
|
.Qq ssh -Q key .
|
|
.It Cm PubkeyAuthentication
|
|
Specifies whether to try public key authentication.
|
|
The argument to this keyword must be
|
|
.Cm yes
|
|
(the default)
|
|
or
|
|
.Cm no .
|
|
.It Cm RekeyLimit
|
|
Specifies the maximum amount of data that may be transmitted before the
|
|
session key is renegotiated, optionally followed a maximum amount of
|
|
time that may pass before the session key is renegotiated.
|
|
The first argument is specified in bytes and may have a 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.
|
|
The optional second value is specified in seconds and may use any of the
|
|
units documented in the
|
|
.Sx TIME FORMATS
|
|
section of
|
|
.Xr sshd_config 5 .
|
|
The default value for
|
|
.Cm RekeyLimit
|
|
is
|
|
.Cm default none ,
|
|
which means that rekeying is performed after the cipher's default amount
|
|
of data has been sent or received and no time based rekeying is done.
|
|
.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.
|
|
Multiple forwardings may be specified, and additional
|
|
forwardings can be given on the command line.
|
|
Privileged ports can be forwarded only when
|
|
logging in as root on the remote machine.
|
|
.Pp
|
|
If the
|
|
.Ar port
|
|
argument is 0,
|
|
the listen port will be dynamically allocated on the server and reported
|
|
to the client at run time.
|
|
.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 RequestTTY
|
|
Specifies whether to request a pseudo-tty for the session.
|
|
The argument may be one of:
|
|
.Cm no
|
|
(never request a TTY),
|
|
.Cm yes
|
|
(always request a TTY when standard input is a TTY),
|
|
.Cm force
|
|
(always request a TTY) or
|
|
.Cm auto
|
|
(request a TTY when opening a login session).
|
|
This option mirrors the
|
|
.Fl t
|
|
and
|
|
.Fl T
|
|
flags for
|
|
.Xr ssh 1 .
|
|
.It Cm RevokedHostKeys
|
|
Specifies revoked host public keys.
|
|
Keys listed in this file will be refused for host authentication.
|
|
Note that if this file does not exist or is not readable,
|
|
then host authentication will be refused for all hosts.
|
|
Keys may be specified as a text file, listing one public key per line, or as
|
|
an OpenSSH Key Revocation List (KRL) as generated by
|
|
.Xr ssh-keygen 1 .
|
|
For more information on KRLs, see the KEY REVOCATION LISTS section in
|
|
.Xr ssh-keygen 1 .
|
|
.It Cm RhostsRSAAuthentication
|
|
Specifies whether to try rhosts based authentication with RSA host
|
|
authentication.
|
|
The argument must be
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
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
|
|
.Cm yes
|
|
(the default)
|
|
or
|
|
.Cm no .
|
|
RSA authentication will only be
|
|
attempted if the identity file exists, or an authentication agent is
|
|
running.
|
|
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.
|
|
The server must also support it, and the server must be configured to
|
|
accept these environment variables.
|
|
Note that the
|
|
.Ev TERM
|
|
environment variable is always sent whenever a
|
|
pseudo-terminal is requested as it is required by the protocol.
|
|
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.
|
|
.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.
|
|
.It Cm StreamLocalBindMask
|
|
Sets the octal file creation mode mask
|
|
.Pq umask
|
|
used when creating a Unix-domain socket file for local or remote
|
|
port forwarding.
|
|
This option is only used for port forwarding to a Unix-domain socket file.
|
|
.Pp
|
|
The default value is 0177, which creates a Unix-domain socket file that is
|
|
readable and writable only by the owner.
|
|
Note that not all operating systems honor the file mode on Unix-domain
|
|
socket files.
|
|
.It Cm StreamLocalBindUnlink
|
|
Specifies whether to remove an existing Unix-domain socket file for local
|
|
or remote port forwarding before creating a new one.
|
|
If the socket file already exists and
|
|
.Cm StreamLocalBindUnlink
|
|
is not enabled,
|
|
.Nm ssh
|
|
will be unable to forward the port to the Unix-domain socket file.
|
|
This option is only used for port forwarding to a Unix-domain socket file.
|
|
.Pp
|
|
The argument must be
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
.It Cm StrictHostKeyChecking
|
|
If this flag is set to
|
|
.Cm 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
|
|
.Cm no ,
|
|
ssh will automatically add new host keys to the
|
|
user known hosts files.
|
|
If this flag is set to
|
|
.Cm ask
|
|
(the default),
|
|
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.
|
|
.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
|
|
.Cm 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
|
|
.Cm no .
|
|
.It Cm Tunnel
|
|
Request
|
|
.Xr tun 4
|
|
device forwarding between the client and the server.
|
|
The argument must be
|
|
.Cm yes ,
|
|
.Cm point-to-point
|
|
(layer 3),
|
|
.Cm ethernet
|
|
(layer 2),
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
Specifying
|
|
.Cm yes
|
|
requests the default tunnel mode, which is
|
|
.Cm point-to-point .
|
|
.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
|
|
.Cm any ,
|
|
which uses the next available tunnel device.
|
|
If
|
|
.Ar remote_tun
|
|
is not specified, it defaults to
|
|
.Cm any .
|
|
The default is
|
|
.Cm any:any .
|
|
.It Cm UpdateHostKeys
|
|
Specifies whether
|
|
.Xr ssh 1
|
|
should accept notifications of additional hostkeys from the server sent
|
|
after authentication has completed and add them to
|
|
.Cm UserKnownHostsFile .
|
|
The argument must be
|
|
.Cm yes ,
|
|
.Cm no
|
|
(the default) or
|
|
.Cm ask .
|
|
Enabling this option allows learning alternate hostkeys for a server
|
|
and supports graceful key rotation by allowing a server to send replacement
|
|
public keys before old ones are removed.
|
|
Additional hostkeys are only accepted if the key used to authenticate the
|
|
host was already trusted or explicitly accepted by the user.
|
|
If
|
|
.Cm UpdateHostKeys
|
|
is set to
|
|
.Cm ask ,
|
|
then the user is asked to confirm the modifications to the known_hosts file.
|
|
Confirmation is currently incompatible with
|
|
.Cm ControlPersist ,
|
|
and will be disabled if it is enabled.
|
|
.Pp
|
|
Presently, only
|
|
.Xr sshd 8
|
|
from OpenSSH 6.8 and greater support the
|
|
.Qq hostkeys@openssh.com
|
|
protocol extension used to inform the client of all the server's hostkeys.
|
|
.It Cm UsePrivilegedPort
|
|
Specifies whether to use a privileged port for outgoing connections.
|
|
The argument must be
|
|
.Cm yes
|
|
or
|
|
.Cm no
|
|
(the default).
|
|
If set to
|
|
.Cm yes ,
|
|
.Xr ssh 1
|
|
must be setuid root.
|
|
Note that this option must be set to
|
|
.Cm 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 one or more files to use for the user
|
|
host key database, separated by whitespace.
|
|
The default is
|
|
.Pa ~/.ssh/known_hosts ,
|
|
.Pa ~/.ssh/known_hosts2 .
|
|
.It Cm VerifyHostKeyDNS
|
|
Specifies whether to verify the remote key using DNS and SSHFP resource
|
|
records.
|
|
If this option is set to
|
|
.Cm 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
|
|
.Cm ask .
|
|
If this option is set to
|
|
.Cm 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 default is
|
|
.Cm yes
|
|
if compiled with LDNS and
|
|
.Cm no
|
|
otherwise.
|
|
.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-20170804 .
|
|
The value
|
|
.Cm none
|
|
may be used to disable this.
|
|
.It Cm VisualHostKey
|
|
If this flag is set to
|
|
.Cm yes ,
|
|
an ASCII art representation of the remote host key fingerprint is
|
|
printed in addition to the fingerprint string at login and
|
|
for unknown host keys.
|
|
If this flag is set to
|
|
.Cm no
|
|
(the default),
|
|
no fingerprint strings are printed at login and
|
|
only the fingerprint string will be printed for unknown host keys.
|
|
.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
|
|
.Qq .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 organization
|
|
except from the
|
|
.Qq dialup
|
|
pool,
|
|
the following entry (in authorized_keys) could be used:
|
|
.Pp
|
|
.Dl from=\&"!*.dialup.example.com,*.example.com\&"
|
|
.Sh TOKENS
|
|
Arguments to some keywords can make use of tokens,
|
|
which are expanded at runtime:
|
|
.Pp
|
|
.Bl -tag -width XXXX -offset indent -compact
|
|
.It %%
|
|
A literal
|
|
.Sq % .
|
|
.It \&%C
|
|
Shorthand for %l%h%p%r.
|
|
.It %d
|
|
Local user's home directory.
|
|
.It %h
|
|
The remote hostname.
|
|
.It %i
|
|
The local user ID.
|
|
.It %L
|
|
The local hostname.
|
|
.It %l
|
|
The local hostname, including the domain name.
|
|
.It %n
|
|
The original remote hostname, as given on the command line.
|
|
.It %p
|
|
The remote port.
|
|
.It %r
|
|
The remote username.
|
|
.It %u
|
|
The local username.
|
|
.El
|
|
.Pp
|
|
.Cm Match exec
|
|
accepts the tokens %%, %h, %L, %l, %n, %p, %r, and %u.
|
|
.Pp
|
|
.Cm CertificateFile
|
|
accepts the tokens %%, %d, %h, %l, %r, and %u.
|
|
.Pp
|
|
.Cm ControlPath
|
|
accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and %u.
|
|
.Pp
|
|
.Cm HostName
|
|
accepts the tokens %% and %h.
|
|
.Pp
|
|
.Cm IdentityAgent
|
|
and
|
|
.Cm IdentityFile
|
|
accept the tokens %%, %d, %h, %l, %r, and %u.
|
|
.Pp
|
|
.Cm LocalCommand
|
|
accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, and %u.
|
|
.Pp
|
|
.Cm ProxyCommand
|
|
accepts the tokens %%, %h, %p, and %r.
|
|
.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
|
|
.An -nosplit
|
|
OpenSSH is a derivative of the original and free
|
|
ssh 1.2.12 release by
|
|
.An Tatu Ylonen .
|
|
.An Aaron Campbell , Bob Beck , Markus Friedl ,
|
|
.An Niels Provos , Theo de Raadt
|
|
and
|
|
.An Dug Song
|
|
removed many bugs, re-added newer features and
|
|
created OpenSSH.
|
|
.An Markus Friedl
|
|
contributed the support for SSH protocol versions 1.5 and 2.0.
|