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Damien Miller32aa1441999-10-29 09:15:49 +10001.\"
Damien Miller32aa1441999-10-29 09:15:49 +10002.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
Damien Miller32aa1441999-10-29 09:15:49 +10003.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4.\" All rights reserved
5.\"
Damien Millere4340be2000-09-16 13:29:08 +11006.\" As far as I am concerned, the code I have written for this software
7.\" can be used freely for any purpose. Any derived versions of this
8.\" software must be clearly marked as such, and if the derived work is
9.\" incompatible with the protocol description in the RFC file, it must be
10.\" called by a name other than "ssh" or "Secure Shell".
Damien Miller32aa1441999-10-29 09:15:49 +100011.\"
Ben Lindstrom92a2e382001-03-05 06:59:27 +000012.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13.\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14.\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
Damien Millere4340be2000-09-16 13:29:08 +110015.\"
16.\" Redistribution and use in source and binary forms, with or without
17.\" modification, are permitted provided that the following conditions
18.\" are met:
19.\" 1. Redistributions of source code must retain the above copyright
20.\" notice, this list of conditions and the following disclaimer.
21.\" 2. Redistributions in binary form must reproduce the above copyright
22.\" notice, this list of conditions and the following disclaimer in the
23.\" documentation and/or other materials provided with the distribution.
24.\"
25.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
31.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
32.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
34.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Damien Miller32aa1441999-10-29 09:15:49 +100035.\"
Damien Millerbdb352a2013-12-05 10:20:52 +110036.\" $OpenBSD: ssh.1,v 1.342 2013/11/26 12:14:54 jmc Exp $
37.Dd $Mdocdate: November 26 2013 $
Damien Miller32aa1441999-10-29 09:15:49 +100038.Dt SSH 1
39.Os
40.Sh NAME
41.Nm ssh
Ben Lindstromd58eb5f2001-03-07 06:07:22 +000042.Nd OpenSSH SSH client (remote login program)
Damien Miller32aa1441999-10-29 09:15:49 +100043.Sh SYNOPSIS
44.Nm ssh
Damien Millerbcfbc482010-07-16 13:59:11 +100045.Bk -words
Damien Millere272a5b2008-11-03 19:22:37 +110046.Op Fl 1246AaCfgKkMNnqsTtVvXxYy
Ben Lindstrome0f88042001-04-30 13:06:24 +000047.Op Fl b Ar bind_address
Damien Miller30c3d422000-05-09 11:02:59 +100048.Op Fl c Ar cipher_spec
Damien Millerbcfbc482010-07-16 13:59:11 +100049.Op Fl D Oo Ar bind_address : Oc Ns Ar port
Damien Miller03d4d7e2013-04-23 15:21:06 +100050.Op Fl E Ar log_file
Damien Miller32aa1441999-10-29 09:15:49 +100051.Op Fl e Ar escape_char
Ben Lindstrom14f31ab2001-09-12 17:48:04 +000052.Op Fl F Ar configfile
Damien Miller048dc932010-02-12 09:22:04 +110053.Op Fl I Ar pkcs11
Darren Tucker61776952003-10-02 16:19:47 +100054.Op Fl i Ar identity_file
Damien Millerbcfbc482010-07-16 13:59:11 +100055.Op Fl L Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport
Darren Tucker61776952003-10-02 16:19:47 +100056.Op Fl l Ar login_name
57.Op Fl m Ar mac_spec
Darren Tucker7ebfc102004-11-07 20:06:19 +110058.Op Fl O Ar ctl_cmd
Darren Tucker61776952003-10-02 16:19:47 +100059.Op Fl o Ar option
Darren Tucker61776952003-10-02 16:19:47 +100060.Op Fl p Ar port
Damien Millerbdb352a2013-12-05 10:20:52 +110061.Op Fl Q Cm cipher | cipher-auth | mac | kex | key
Damien Millerbcfbc482010-07-16 13:59:11 +100062.Op Fl R Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport
Darren Tucker7ebfc102004-11-07 20:06:19 +110063.Op Fl S Ar ctl_path
Darren Tucker7ad8dd22010-01-12 19:40:27 +110064.Op Fl W Ar host : Ns Ar port
Damien Millerbcfbc482010-07-16 13:59:11 +100065.Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun
Darren Tucker61776952003-10-02 16:19:47 +100066.Oo Ar user Ns @ Oc Ns Ar hostname
Damien Miller32aa1441999-10-29 09:15:49 +100067.Op Ar command
Damien Millerbcfbc482010-07-16 13:59:11 +100068.Ek
Damien Miller22c77262000-04-13 12:26:34 +100069.Sh DESCRIPTION
Damien Miller32aa1441999-10-29 09:15:49 +100070.Nm
Ben Lindstromd58eb5f2001-03-07 06:07:22 +000071(SSH client) is a program for logging into a remote machine and for
Damien Miller7684ee12000-03-17 23:40:15 +110072executing commands on a remote machine.
Darren Tucker61776952003-10-02 16:19:47 +100073It is intended to replace rlogin and rsh,
74and provide secure encrypted communications between
Damien Miller7684ee12000-03-17 23:40:15 +110075two untrusted hosts over an insecure network.
Damien Miller8bfaf932006-01-14 10:09:30 +110076X11 connections and arbitrary TCP ports
Darren Tucker61776952003-10-02 16:19:47 +100077can also be forwarded over the secure channel.
Damien Miller32aa1441999-10-29 09:15:49 +100078.Pp
79.Nm
Damien Miller22c77262000-04-13 12:26:34 +100080connects and logs into the specified
Darren Tucker61776952003-10-02 16:19:47 +100081.Ar hostname
82(with optional
83.Ar user
84name).
Damien Miller32aa1441999-10-29 09:15:49 +100085The user must prove
Damien Millere247cc42000-05-07 12:03:14 +100086his/her identity to the remote machine using one of several methods
Darren Tucker5434cfe2005-12-20 16:11:35 +110087depending on the protocol version used (see below).
Damien Millere247cc42000-05-07 12:03:14 +100088.Pp
Darren Tucker61776952003-10-02 16:19:47 +100089If
90.Ar command
91is specified,
Darren Tuckerb18c8672005-12-20 16:10:09 +110092it is executed on the remote host instead of a login shell.
Darren Tucker0b42e6d2004-08-13 21:22:40 +100093.Pp
Damien Miller0bc1bd82000-11-13 22:57:25 +110094The options are as follows:
Damien Miller32aa1441999-10-29 09:15:49 +100095.Bl -tag -width Ds
Darren Tucker61776952003-10-02 16:19:47 +100096.It Fl 1
97Forces
98.Nm
99to try protocol version 1 only.
100.It Fl 2
101Forces
102.Nm
103to try protocol version 2 only.
104.It Fl 4
105Forces
106.Nm
107to use IPv4 addresses only.
108.It Fl 6
109Forces
110.Nm
111to use IPv6 addresses only.
Damien Millerb1715dc2000-05-30 13:44:51 +1000112.It Fl A
113Enables forwarding of the authentication agent connection.
114This can also be specified on a per-host basis in a configuration file.
Damien Millerb5fdfaa2002-09-12 09:52:03 +1000115.Pp
Damien Miller495dca32003-04-01 21:42:14 +1000116Agent forwarding should be enabled with caution.
117Users with the ability to bypass file permissions on the remote host
Darren Tuckerae69e1d2009-10-24 11:41:34 +1100118(for the agent's
Darren Tucker98c9aec2009-10-24 11:42:44 +1100119.Ux Ns -domain
120socket) can access the local agent through the forwarded connection.
Damien Miller495dca32003-04-01 21:42:14 +1000121An attacker cannot obtain key material from the agent,
Damien Millerb5fdfaa2002-09-12 09:52:03 +1000122however they can perform operations on the keys that enable them to
123authenticate using the identities loaded into the agent.
Darren Tucker61776952003-10-02 16:19:47 +1000124.It Fl a
125Disables forwarding of the authentication agent connection.
Ben Lindstrome0f88042001-04-30 13:06:24 +0000126.It Fl b Ar bind_address
Darren Tuckera5cf8552005-07-14 17:04:18 +1000127Use
128.Ar bind_address
129on the local machine as the source address
130of the connection.
131Only useful on systems with more than one address.
Darren Tucker61776952003-10-02 16:19:47 +1000132.It Fl C
133Requests compression of all data (including stdin, stdout, stderr, and
Damien Miller8bfaf932006-01-14 10:09:30 +1100134data for forwarded X11 and TCP connections).
Darren Tucker61776952003-10-02 16:19:47 +1000135The compression algorithm is the same used by
136.Xr gzip 1 ,
137and the
138.Dq level
139can be controlled by the
140.Cm CompressionLevel
141option for protocol version 1.
142Compression is desirable on modem lines and other
143slow connections, but will only slow down things on fast networks.
144The default value can be set on a host-by-host basis in the
145configuration files; see the
146.Cm Compression
147option.
Damien Miller05202ff2004-06-15 10:30:39 +1000148.It Fl c Ar cipher_spec
149Selects the cipher specification for encrypting the session.
150.Pp
151Protocol version 1 allows specification of a single cipher.
Darren Tucker1e4308e2005-10-03 18:18:40 +1000152The supported values are
Damien Miller05202ff2004-06-15 10:30:39 +1000153.Dq 3des ,
Darren Tuckerff9f4842005-12-20 16:10:45 +1100154.Dq blowfish ,
Damien Miller05202ff2004-06-15 10:30:39 +1000155and
156.Dq des .
Damien Miller32aa1441999-10-29 09:15:49 +1000157.Ar 3des
158(triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
Damien Miller05202ff2004-06-15 10:30:39 +1000159It is believed to be secure.
Damien Miller32aa1441999-10-29 09:15:49 +1000160.Ar blowfish
Darren Tucker61776952003-10-02 16:19:47 +1000161is a fast block cipher; it appears very secure and is much faster than
Damien Miller7684ee12000-03-17 23:40:15 +1100162.Ar 3des .
Ben Lindstromffa1dd62001-09-12 16:52:28 +0000163.Ar des
164is only supported in the
165.Nm
166client for interoperability with legacy protocol 1 implementations
167that do not support the
168.Ar 3des
Damien Miller495dca32003-04-01 21:42:14 +1000169cipher.
170Its use is strongly discouraged due to cryptographic weaknesses.
Damien Miller05202ff2004-06-15 10:30:39 +1000171The default is
172.Dq 3des .
173.Pp
Damien Miller35978212005-12-24 14:56:47 +1100174For protocol version 2,
Damien Miller05202ff2004-06-15 10:30:39 +1000175.Ar cipher_spec
176is a comma-separated list of ciphers
177listed in order of preference.
Darren Tucker3a6a51f2009-06-21 17:48:52 +1000178See the
179.Cm Ciphers
Damien Miller081f3c72010-08-03 16:05:25 +1000180keyword in
181.Xr ssh_config 5
182for more information.
Darren Tuckerc8d64212005-10-03 18:13:42 +1000183.It Fl D Xo
184.Sm off
185.Oo Ar bind_address : Oc
186.Ar port
187.Sm on
188.Xc
Darren Tucker61776952003-10-02 16:19:47 +1000189Specifies a local
190.Dq dynamic
191application-level port forwarding.
192This works by allocating a socket to listen to
193.Ar port
Darren Tuckerc8d64212005-10-03 18:13:42 +1000194on the local side, optionally bound to the specified
195.Ar bind_address .
196Whenever a connection is made to this port, the
Darren Tucker61776952003-10-02 16:19:47 +1000197connection is forwarded over the secure channel, and the application
198protocol is then used to determine where to connect to from the
199remote machine.
200Currently the SOCKS4 and SOCKS5 protocols are supported, and
201.Nm
202will act as a SOCKS server.
203Only root can forward privileged ports.
204Dynamic port forwardings can also be specified in the configuration file.
Darren Tuckerc8d64212005-10-03 18:13:42 +1000205.Pp
Damien Miller7fa96602010-08-05 13:03:13 +1000206IPv6 addresses can be specified by enclosing the address in square brackets.
Darren Tuckerc8d64212005-10-03 18:13:42 +1000207Only the superuser can forward privileged ports.
208By default, the local port is bound in accordance with the
209.Cm GatewayPorts
210setting.
211However, an explicit
212.Ar bind_address
213may be used to bind the connection to a specific address.
214The
215.Ar bind_address
216of
217.Dq localhost
218indicates that the listening port be bound for local use only, while an
219empty address or
220.Sq *
221indicates that the port should be available from all interfaces.
Damien Miller03d4d7e2013-04-23 15:21:06 +1000222.It Fl E Ar log_file
223Append debug logs to
224.Ar log_file
225instead of standard error.
Damien Miller2142ba02005-12-24 14:56:29 +1100226.It Fl e Ar escape_char
Damien Miller32aa1441999-10-29 09:15:49 +1000227Sets the escape character for sessions with a pty (default:
228.Ql ~ ) .
Damien Miller7684ee12000-03-17 23:40:15 +1100229The escape character is only recognized at the beginning of a line.
230The escape character followed by a dot
Damien Miller32aa1441999-10-29 09:15:49 +1000231.Pq Ql \&.
Darren Tucker61776952003-10-02 16:19:47 +1000232closes the connection;
233followed by control-Z suspends the connection;
234and followed by itself sends the escape character once.
Damien Miller7684ee12000-03-17 23:40:15 +1100235Setting the character to
Damien Miller32aa1441999-10-29 09:15:49 +1000236.Dq none
237disables any escapes and makes the session fully transparent.
Darren Tucker61776952003-10-02 16:19:47 +1000238.It Fl F Ar configfile
239Specifies an alternative per-user configuration file.
240If a configuration file is given on the command line,
241the system-wide configuration file
242.Pq Pa /etc/ssh/ssh_config
243will be ignored.
244The default for the per-user configuration file is
Damien Miller167ea5d2005-05-26 12:04:02 +1000245.Pa ~/.ssh/config .
Damien Miller32aa1441999-10-29 09:15:49 +1000246.It Fl f
247Requests
248.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100249to go to background just before command execution.
250This is useful if
Damien Miller32aa1441999-10-29 09:15:49 +1000251.Nm
252is going to ask for passwords or passphrases, but the user
Damien Miller7684ee12000-03-17 23:40:15 +1100253wants it in the background.
Damien Miller22c77262000-04-13 12:26:34 +1000254This implies
Damien Miller32aa1441999-10-29 09:15:49 +1000255.Fl n .
256The recommended way to start X11 programs at a remote site is with
257something like
258.Ic ssh -f host xterm .
Darren Tucker9a2a6092008-07-04 12:53:50 +1000259.Pp
260If the
261.Cm ExitOnForwardFailure
262configuration option is set to
263.Dq yes ,
264then a client started with
265.Fl f
266will wait for all remote port forwards to be successfully established
267before placing itself in the background.
Damien Miller396691a2000-01-20 22:44:08 +1100268.It Fl g
269Allows remote hosts to connect to local forwarded ports.
Damien Miller7ea845e2010-02-12 09:21:02 +1100270.It Fl I Ar pkcs11
Damien Millerd400da52010-02-12 09:26:23 +1100271Specify the PKCS#11 shared library
Darren Tucker61776952003-10-02 16:19:47 +1000272.Nm
Damien Millera7618442010-02-12 09:26:02 +1100273should use to communicate with a PKCS#11 token providing the user's
Darren Tucker61776952003-10-02 16:19:47 +1000274private RSA key.
Damien Miller32aa1441999-10-29 09:15:49 +1000275.It Fl i Ar identity_file
Damien Millerfae23862002-01-22 23:32:26 +1100276Selects a file from which the identity (private key) for
Damien Millereb8b60e2010-08-31 22:41:14 +1000277public key authentication is read.
Damien Millerfae23862002-01-22 23:32:26 +1100278The default is
Damien Miller167ea5d2005-05-26 12:04:02 +1000279.Pa ~/.ssh/identity
Damien Millerfae23862002-01-22 23:32:26 +1100280for protocol version 1, and
Damien Millereb8b60e2010-08-31 22:41:14 +1000281.Pa ~/.ssh/id_dsa ,
282.Pa ~/.ssh/id_ecdsa
Damien Millerfae23862002-01-22 23:32:26 +1100283and
Damien Millereb8b60e2010-08-31 22:41:14 +1000284.Pa ~/.ssh/id_rsa
Damien Millerfae23862002-01-22 23:32:26 +1100285for protocol version 2.
Damien Miller7684ee12000-03-17 23:40:15 +1100286Identity files may also be specified on
287a per-host basis in the configuration file.
288It is possible to have multiple
Damien Miller32aa1441999-10-29 09:15:49 +1000289.Fl i
290options (and multiple identities specified in
291configuration files).
Damien Miller5059d8d2010-03-05 21:31:11 +1100292.Nm
293will also try to load certificate information from the filename obtained
294by appending
295.Pa -cert.pub
296to identity filenames.
Darren Tucker415bddc2007-06-12 23:43:16 +1000297.It Fl K
298Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
299credentials to the server.
Damien Miller32aa1441999-10-29 09:15:49 +1000300.It Fl k
Damien Millere0113cc2003-11-24 13:10:09 +1100301Disables forwarding (delegation) of GSSAPI credentials to the server.
Darren Tucker61776952003-10-02 16:19:47 +1000302.It Fl L Xo
303.Sm off
Damien Millerf91ee4c2005-03-01 21:24:33 +1100304.Oo Ar bind_address : Oc
Darren Tucker61776952003-10-02 16:19:47 +1000305.Ar port : host : hostport
306.Sm on
307.Xc
308Specifies that the given port on the local (client) host is to be
309forwarded to the given host and port on the remote side.
310This works by allocating a socket to listen to
311.Ar port
Damien Millerf91ee4c2005-03-01 21:24:33 +1100312on the local side, optionally bound to the specified
313.Ar bind_address .
314Whenever a connection is made to this port, the
Darren Tucker61776952003-10-02 16:19:47 +1000315connection is forwarded over the secure channel, and a connection is
316made to
317.Ar host
318port
319.Ar hostport
320from the remote machine.
321Port forwardings can also be specified in the configuration file.
Damien Miller7fa96602010-08-05 13:03:13 +1000322IPv6 addresses can be specified by enclosing the address in square brackets.
Damien Millerf91ee4c2005-03-01 21:24:33 +1100323Only the superuser can forward privileged ports.
324By default, the local port is bound in accordance with the
325.Cm GatewayPorts
326setting.
327However, an explicit
328.Ar bind_address
329may be used to bind the connection to a specific address.
330The
331.Ar bind_address
332of
333.Dq localhost
Damien Miller36bf7dd2005-03-02 12:02:47 +1100334indicates that the listening port be bound for local use only, while an
335empty address or
336.Sq *
Damien Millerf91ee4c2005-03-01 21:24:33 +1100337indicates that the port should be available from all interfaces.
Damien Miller32aa1441999-10-29 09:15:49 +1000338.It Fl l Ar login_name
Damien Miller7684ee12000-03-17 23:40:15 +1100339Specifies the user to log in as on the remote machine.
340This also may be specified on a per-host basis in the configuration file.
Damien Miller0e220db2004-06-15 10:34:08 +1000341.It Fl M
342Places the
343.Nm
344client into
345.Dq master
346mode for connection sharing.
Damien Miller88b25522005-12-31 16:23:15 +1100347Multiple
348.Fl M
349options places
350.Nm
351into
352.Dq master
353mode with confirmation required before slave connections are accepted.
Damien Miller0e220db2004-06-15 10:34:08 +1000354Refer to the description of
355.Cm ControlMaster
356in
357.Xr ssh_config 5
358for details.
Damien Miller5d1eceb2004-06-30 22:37:57 +1000359.It Fl m Ar mac_spec
360Additionally, for protocol version 2 a comma-separated list of MAC
361(message authentication code) algorithms can
362be specified in order of preference.
363See the
364.Cm MACs
365keyword for more information.
Darren Tucker61776952003-10-02 16:19:47 +1000366.It Fl N
367Do not execute a remote command.
368This is useful for just forwarding ports
369(protocol version 2 only).
Damien Miller32aa1441999-10-29 09:15:49 +1000370.It Fl n
371Redirects stdin from
372.Pa /dev/null
373(actually, prevents reading from stdin).
374This must be used when
375.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100376is run in the background.
377A common trick is to use this to run X11 programs on a remote machine.
378For example,
Damien Miller32aa1441999-10-29 09:15:49 +1000379.Ic ssh -n shadows.cs.hut.fi emacs &
380will start an emacs on shadows.cs.hut.fi, and the X11
381connection will be automatically forwarded over an encrypted channel.
382The
383.Nm
384program will be put in the background.
385(This does not work if
386.Nm
387needs to ask for a password or passphrase; see also the
388.Fl f
389option.)
Darren Tuckere04644c2004-12-03 14:08:45 +1100390.It Fl O Ar ctl_cmd
391Control an active connection multiplexing master process.
392When the
393.Fl O
394option is specified, the
395.Ar ctl_cmd
396argument is interpreted and passed to the master process.
397Valid commands are:
398.Dq check
Damien Miller388f6fc2010-05-21 14:57:35 +1000399(check that the master process is running),
400.Dq forward
Damien Miller8cb1cda2011-05-05 14:16:56 +1000401(request forwardings without command execution),
Damien Miller1bcbd0a2011-09-22 21:40:45 +1000402.Dq cancel
403(cancel forwardings),
Darren Tuckere04644c2004-12-03 14:08:45 +1100404.Dq exit
Damien Miller8cb1cda2011-05-05 14:16:56 +1000405(request the master to exit), and
Damien Miller6c3eec72011-05-05 14:16:22 +1000406.Dq stop
407(request the master to stop accepting further multiplexing requests).
Damien Miller32aa1441999-10-29 09:15:49 +1000408.It Fl o Ar option
Ben Lindstrom14c62eb2001-08-15 23:25:46 +0000409Can be used to give options in the format used in the configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000410This is useful for specifying options for which there is no separate
Damien Miller7684ee12000-03-17 23:40:15 +1100411command-line flag.
Darren Tucker61776952003-10-02 16:19:47 +1000412For full details of the options listed below, and their possible values, see
413.Xr ssh_config 5 .
414.Pp
415.Bl -tag -width Ds -offset indent -compact
416.It AddressFamily
417.It BatchMode
418.It BindAddress
Damien Miller0faf7472013-10-17 11:47:23 +1100419.It CanonicalDomains
Damien Miller38505592013-10-17 11:48:13 +1100420.It CanonicalizeFallbackLocal
421.It CanonicalizeHostname
422.It CanonicalizeMaxDots
423.It CanonicalizePermittedCNAMEs
Darren Tucker61776952003-10-02 16:19:47 +1000424.It ChallengeResponseAuthentication
425.It CheckHostIP
426.It Cipher
427.It Ciphers
428.It ClearAllForwardings
429.It Compression
430.It CompressionLevel
431.It ConnectionAttempts
Darren Tuckeredae0ec2004-05-02 22:15:52 +1000432.It ConnectTimeout
Damien Miller0e220db2004-06-15 10:34:08 +1000433.It ControlMaster
434.It ControlPath
Damien Millerefad7272011-09-22 21:33:53 +1000435.It ControlPersist
Darren Tucker61776952003-10-02 16:19:47 +1000436.It DynamicForward
Darren Tucker61776952003-10-02 16:19:47 +1000437.It EscapeChar
Darren Tuckere7d4b192006-07-12 22:17:10 +1000438.It ExitOnForwardFailure
Darren Tucker61776952003-10-02 16:19:47 +1000439.It ForwardAgent
440.It ForwardX11
Damien Millerefad7272011-09-22 21:33:53 +1000441.It ForwardX11Timeout
Darren Tucker0a118da2003-10-15 15:54:32 +1000442.It ForwardX11Trusted
Darren Tucker61776952003-10-02 16:19:47 +1000443.It GatewayPorts
444.It GlobalKnownHostsFile
445.It GSSAPIAuthentication
446.It GSSAPIDelegateCredentials
Damien Millere1776152005-03-01 21:47:37 +1100447.It HashKnownHosts
Darren Tucker61776952003-10-02 16:19:47 +1000448.It Host
449.It HostbasedAuthentication
450.It HostKeyAlgorithms
451.It HostKeyAlias
452.It HostName
453.It IdentityFile
Damien Millerbd394c32004-03-08 23:12:36 +1100454.It IdentitiesOnly
Damien Miller0a184732010-11-20 15:21:03 +1100455.It IPQoS
Damien Millerefad7272011-09-22 21:33:53 +1000456.It KbdInteractiveAuthentication
Darren Tucker636ca902004-11-05 20:22:00 +1100457.It KbdInteractiveDevices
Damien Miller7fe2b1f2010-09-24 22:11:53 +1000458.It KexAlgorithms
Damien Millerd27b9472005-12-13 19:29:02 +1100459.It LocalCommand
Darren Tucker61776952003-10-02 16:19:47 +1000460.It LocalForward
461.It LogLevel
462.It MACs
Damien Millerd77b81f2013-10-17 11:39:00 +1100463.It Match
Darren Tucker61776952003-10-02 16:19:47 +1000464.It NoHostAuthenticationForLocalhost
465.It NumberOfPasswordPrompts
466.It PasswordAuthentication
Damien Millerd27b9472005-12-13 19:29:02 +1100467.It PermitLocalCommand
Damien Miller7ea845e2010-02-12 09:21:02 +1100468.It PKCS11Provider
Darren Tucker61776952003-10-02 16:19:47 +1000469.It Port
470.It PreferredAuthentications
471.It Protocol
472.It ProxyCommand
Damien Millerf2f6c312013-08-21 02:44:58 +1000473.It ProxyUseFdpass
Darren Tucker61776952003-10-02 16:19:47 +1000474.It PubkeyAuthentication
Darren Tucker62388b22006-01-20 11:31:47 +1100475.It RekeyLimit
Darren Tucker61776952003-10-02 16:19:47 +1000476.It RemoteForward
Damien Millerf4b32aa2011-05-15 08:47:43 +1000477.It RequestTTY
Darren Tucker61776952003-10-02 16:19:47 +1000478.It RhostsRSAAuthentication
479.It RSAAuthentication
Darren Tucker7a6c0662004-05-02 22:14:03 +1000480.It SendEnv
Damien Miller509b0102003-12-17 16:33:10 +1100481.It ServerAliveInterval
482.It ServerAliveCountMax
Darren Tucker61776952003-10-02 16:19:47 +1000483.It StrictHostKeyChecking
Damien Miller12c150e2003-12-17 16:31:10 +1100484.It TCPKeepAlive
Damien Millerd27b9472005-12-13 19:29:02 +1100485.It Tunnel
486.It TunnelDevice
Darren Tucker61776952003-10-02 16:19:47 +1000487.It UsePrivilegedPort
488.It User
489.It UserKnownHostsFile
490.It VerifyHostKeyDNS
Damien Miller86399202008-06-30 00:04:31 +1000491.It VisualHostKey
Darren Tucker61776952003-10-02 16:19:47 +1000492.It XAuthLocation
493.El
Damien Miller32aa1441999-10-29 09:15:49 +1000494.It Fl p Ar port
Damien Miller7684ee12000-03-17 23:40:15 +1100495Port to connect to on the remote host.
496This can be specified on a
Damien Miller32aa1441999-10-29 09:15:49 +1000497per-host basis in the configuration file.
Damien Millerbdb352a2013-12-05 10:20:52 +1100498.It Fl Q Cm cipher | cipher-auth | mac | kex | key
Damien Millerea111192013-04-23 19:24:32 +1000499Queries
500.Nm
Damien Millerd937dc02013-12-05 10:19:54 +1100501for the algorithms supported for the specified version 2.
502The available features are:
503.Ar cipher
Damien Millerea111192013-04-23 19:24:32 +1000504(supported symmetric ciphers),
Damien Millerd937dc02013-12-05 10:19:54 +1100505.Ar cipher-auth
Damien Miller0fde8ac2013-11-21 14:12:23 +1100506(supported symmetric ciphers that support authenticated encryption),
Damien Millerd937dc02013-12-05 10:19:54 +1100507.Ar mac
Damien Millerea111192013-04-23 19:24:32 +1000508(supported message integrity codes),
Damien Millerd937dc02013-12-05 10:19:54 +1100509.Ar kex
Damien Millerea111192013-04-23 19:24:32 +1000510(key exchange algorithms),
Damien Millerd937dc02013-12-05 10:19:54 +1100511.Ar key
Damien Millerea111192013-04-23 19:24:32 +1000512(key types).
Damien Miller32aa1441999-10-29 09:15:49 +1000513.It Fl q
Damien Miller7684ee12000-03-17 23:40:15 +1100514Quiet mode.
Damien Millereb602472008-02-10 22:21:28 +1100515Causes most warning and diagnostic messages to be suppressed.
Darren Tucker61776952003-10-02 16:19:47 +1000516.It Fl R Xo
517.Sm off
Damien Millerf91ee4c2005-03-01 21:24:33 +1100518.Oo Ar bind_address : Oc
Darren Tucker61776952003-10-02 16:19:47 +1000519.Ar port : host : hostport
520.Sm on
521.Xc
Damien Miller32aa1441999-10-29 09:15:49 +1000522Specifies that the given port on the remote (server) host is to be
Damien Miller7684ee12000-03-17 23:40:15 +1100523forwarded to the given host and port on the local side.
524This works by allocating a socket to listen to
Damien Miller32aa1441999-10-29 09:15:49 +1000525.Ar port
526on the remote side, and whenever a connection is made to this port, the
527connection is forwarded over the secure channel, and a connection is
528made to
Damien Miller34132e52000-01-14 15:45:46 +1100529.Ar host
530port
531.Ar hostport
Damien Miller7684ee12000-03-17 23:40:15 +1100532from the local machine.
Damien Millerf91ee4c2005-03-01 21:24:33 +1100533.Pp
Damien Miller7684ee12000-03-17 23:40:15 +1100534Port forwardings can also be specified in the configuration file.
535Privileged ports can be forwarded only when
Damien Miller32aa1441999-10-29 09:15:49 +1000536logging in as root on the remote machine.
Damien Miller70b2d552012-04-22 11:26:10 +1000537IPv6 addresses can be specified by enclosing the address in square brackets.
Damien Millerf91ee4c2005-03-01 21:24:33 +1100538.Pp
539By default, the listening socket on the server will be bound to the loopback
540interface only.
Darren Tucker63917bd2008-11-11 16:33:48 +1100541This may be overridden by specifying a
Damien Millerf91ee4c2005-03-01 21:24:33 +1100542.Ar bind_address .
Damien Miller36bf7dd2005-03-02 12:02:47 +1100543An empty
544.Ar bind_address ,
Damien Millerf91ee4c2005-03-01 21:24:33 +1100545or the address
Damien Miller36bf7dd2005-03-02 12:02:47 +1100546.Ql * ,
Damien Millerf91ee4c2005-03-01 21:24:33 +1100547indicates that the remote socket should listen on all interfaces.
548Specifying a remote
549.Ar bind_address
Damien Miller36bf7dd2005-03-02 12:02:47 +1100550will only succeed if the server's
551.Cm GatewayPorts
Damien Millerf91ee4c2005-03-01 21:24:33 +1100552option is enabled (see
Damien Miller36bf7dd2005-03-02 12:02:47 +1100553.Xr sshd_config 5 ) .
Damien Millere2f4cc52009-02-14 16:33:49 +1100554.Pp
555If the
556.Ar port
557argument is
Damien Miller65fa4ca2009-02-14 16:34:05 +1100558.Ql 0 ,
Damien Millere2f4cc52009-02-14 16:33:49 +1100559the listen port will be dynamically allocated on the server and reported
560to the client at run time.
Damien Miller388f6fc2010-05-21 14:57:35 +1000561When used together with
562.Ic -O forward
563the allocated port will be printed to the standard output.
Darren Tucker7ebfc102004-11-07 20:06:19 +1100564.It Fl S Ar ctl_path
Damien Miller67f30d72010-04-16 15:52:03 +1000565Specifies the location of a control socket for connection sharing,
Damien Miller9c60f242010-03-26 11:28:35 +1100566or the string
567.Dq none
568to disable connection sharing.
Damien Miller0e220db2004-06-15 10:34:08 +1000569Refer to the description of
Darren Tuckerba5c5922004-06-18 16:22:39 +1000570.Cm ControlPath
571and
Damien Miller0e220db2004-06-15 10:34:08 +1000572.Cm ControlMaster
573in
574.Xr ssh_config 5
575for details.
Darren Tucker61776952003-10-02 16:19:47 +1000576.It Fl s
577May be used to request invocation of a subsystem on the remote system.
578Subsystems are a feature of the SSH2 protocol which facilitate the use
579of SSH as a secure transport for other applications (eg.\&
580.Xr sftp 1 ) .
581The subsystem is specified as the remote command.
582.It Fl T
583Disable pseudo-tty allocation.
584.It Fl t
585Force pseudo-tty allocation.
586This can be used to execute arbitrary
587screen-based programs on a remote machine, which can be very useful,
Damien Miller208f1ed2006-03-15 11:56:03 +1100588e.g. when implementing menu services.
Darren Tucker61776952003-10-02 16:19:47 +1000589Multiple
590.Fl t
591options force tty allocation, even if
Ben Lindstrom19ceb172001-09-12 17:54:24 +0000592.Nm
Darren Tucker61776952003-10-02 16:19:47 +1000593has no local tty.
594.It Fl V
595Display the version number and exit.
596.It Fl v
597Verbose mode.
598Causes
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000599.Nm
Darren Tucker61776952003-10-02 16:19:47 +1000600to print debugging messages about its progress.
601This is helpful in
602debugging connection, authentication, and configuration problems.
603Multiple
604.Fl v
605options increase the verbosity.
606The maximum is 3.
Darren Tucker7ad8dd22010-01-12 19:40:27 +1100607.It Fl W Ar host : Ns Ar port
608Requests that standard input and output on the client be forwarded to
609.Ar host
610on
611.Ar port
612over the secure channel.
613Implies
614.Fl N ,
615.Fl T ,
616.Cm ExitOnForwardFailure
617and
Damien Miller36378c62012-06-20 21:53:25 +1000618.Cm ClearAllForwardings .
619Works with Protocol version 2 only.
Damien Miller991dba42006-07-10 20:16:27 +1000620.It Fl w Xo
621.Ar local_tun Ns Op : Ns Ar remote_tun
622.Xc
623Requests
624tunnel
625device forwarding with the specified
Damien Millerd27b9472005-12-13 19:29:02 +1100626.Xr tun 4
Damien Miller991dba42006-07-10 20:16:27 +1000627devices between the client
628.Pq Ar local_tun
629and the server
630.Pq Ar remote_tun .
631.Pp
Damien Millercf1e3422005-12-24 14:56:04 +1100632The devices may be specified by numerical ID or the keyword
633.Dq any ,
634which uses the next available tunnel device.
Damien Miller991dba42006-07-10 20:16:27 +1000635If
636.Ar remote_tun
637is not specified, it defaults to
638.Dq any .
Damien Millercf1e3422005-12-24 14:56:04 +1100639See also the
Damien Millerd27b9472005-12-13 19:29:02 +1100640.Cm Tunnel
Damien Miller991dba42006-07-10 20:16:27 +1000641and
642.Cm TunnelDevice
643directives in
Damien Millerd27b9472005-12-13 19:29:02 +1100644.Xr ssh_config 5 .
Damien Miller991dba42006-07-10 20:16:27 +1000645If the
646.Cm Tunnel
647directive is unset, it is set to the default tunnel mode, which is
648.Dq point-to-point .
Darren Tucker61776952003-10-02 16:19:47 +1000649.It Fl X
650Enables X11 forwarding.
651This can also be specified on a per-host basis in a configuration file.
652.Pp
653X11 forwarding should be enabled with caution.
654Users with the ability to bypass file permissions on the remote host
655(for the user's X authorization database)
656can access the local X11 display through the forwarded connection.
657An attacker may then be able to perform activities such as keystroke monitoring.
Damien Miller947219e2005-03-02 13:22:30 +1100658.Pp
Damien Millerb022b232005-03-05 11:22:36 +1100659For this reason, X11 forwarding is subjected to X11 SECURITY extension
Damien Miller947219e2005-03-02 13:22:30 +1100660restrictions by default.
661Please refer to the
662.Nm
663.Fl Y
664option and the
665.Cm ForwardX11Trusted
666directive in
667.Xr ssh_config 5
668for more information.
Darren Tucker61776952003-10-02 16:19:47 +1000669.It Fl x
670Disables X11 forwarding.
Darren Tucker0a118da2003-10-15 15:54:32 +1000671.It Fl Y
672Enables trusted X11 forwarding.
Damien Miller947219e2005-03-02 13:22:30 +1100673Trusted X11 forwardings are not subjected to the X11 SECURITY extension
674controls.
Damien Millere272a5b2008-11-03 19:22:37 +1100675.It Fl y
676Send log information using the
677.Xr syslog 3
678system module.
679By default this information is sent to stderr.
Damien Miller32aa1441999-10-29 09:15:49 +1000680.El
Damien Millere9b333a2005-12-24 14:53:04 +1100681.Pp
682.Nm
683may additionally obtain configuration data from
684a per-user configuration file and a system-wide configuration file.
685The file format and configuration options are described in
686.Xr ssh_config 5 .
Damien Millerc93a8132005-12-24 14:52:13 +1100687.Sh AUTHENTICATION
Darren Tucker94299ec2006-01-20 11:30:14 +1100688The OpenSSH SSH client supports SSH protocols 1 and 2.
Darren Tucker7a4a7652009-10-11 21:51:40 +1100689The default is to use protocol 2 only,
690though this can be changed via the
Damien Millerc93a8132005-12-24 14:52:13 +1100691.Cm Protocol
692option in
Darren Tucker7a4a7652009-10-11 21:51:40 +1100693.Xr ssh_config 5
694or the
Damien Millerc93a8132005-12-24 14:52:13 +1100695.Fl 1
696and
697.Fl 2
698options (see above).
699Both protocols support similar authentication methods,
Darren Tucker7a4a7652009-10-11 21:51:40 +1100700but protocol 2 is the default since
Damien Millerc93a8132005-12-24 14:52:13 +1100701it provides additional mechanisms for confidentiality
702(the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
Damien Miller20bd4532011-08-06 06:17:30 +1000703and integrity (hmac-md5, hmac-sha1,
704hmac-sha2-256, hmac-sha2-512,
Darren Tucker427e4092012-10-05 11:02:39 +1000705umac-64, umac-128, hmac-ripemd160).
Damien Millerc93a8132005-12-24 14:52:13 +1100706Protocol 1 lacks a strong mechanism for ensuring the
707integrity of the connection.
708.Pp
709The methods available for authentication are:
Damien Millerfbc94c82006-06-13 13:03:16 +1000710GSSAPI-based authentication,
Damien Millerc93a8132005-12-24 14:52:13 +1100711host-based authentication,
712public key authentication,
713challenge-response authentication,
714and password authentication.
715Authentication methods are tried in the order specified above,
716though protocol 2 has a configuration option to change the default order:
717.Cm PreferredAuthentications .
718.Pp
719Host-based authentication works as follows:
Darren Tuckerd3877b92005-12-20 16:09:36 +1100720If the machine the user logs in from is listed in
721.Pa /etc/hosts.equiv
722or
723.Pa /etc/shosts.equiv
724on the remote machine, and the user names are
725the same on both sides, or if the files
726.Pa ~/.rhosts
727or
728.Pa ~/.shosts
729exist in the user's home directory on the
730remote machine and contain a line containing the name of the client
731machine and the name of the user on that machine, the user is
Damien Millerc93a8132005-12-24 14:52:13 +1100732considered for login.
733Additionally, the server
734.Em must
735be able to verify the client's
736host key (see the description of
Darren Tuckerd3877b92005-12-20 16:09:36 +1100737.Pa /etc/ssh/ssh_known_hosts
738and
Damien Millerc93a8132005-12-24 14:52:13 +1100739.Pa ~/.ssh/known_hosts ,
740below)
741for login to be permitted.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100742This authentication method closes security holes due to IP
Damien Millerc93a8132005-12-24 14:52:13 +1100743spoofing, DNS spoofing, and routing spoofing.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100744[Note to the administrator:
745.Pa /etc/hosts.equiv ,
746.Pa ~/.rhosts ,
747and the rlogin/rsh protocol in general, are inherently insecure and should be
748disabled if security is desired.]
749.Pp
Damien Millerc93a8132005-12-24 14:52:13 +1100750Public key authentication works as follows:
751The scheme is based on public-key cryptography,
752using cryptosystems
753where encryption and decryption are done using separate keys,
754and it is unfeasible to derive the decryption key from the encryption key.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100755The idea is that each user creates a public/private
756key pair for authentication purposes.
757The server knows the public key, and only the user knows the private key.
Damien Millerc93a8132005-12-24 14:52:13 +1100758.Nm
759implements public key authentication protocol automatically,
Damien Millereb8b60e2010-08-31 22:41:14 +1000760using one of the DSA, ECDSA or RSA algorithms.
Damien Millerc93a8132005-12-24 14:52:13 +1100761Protocol 1 is restricted to using only RSA keys,
Damien Millereb8b60e2010-08-31 22:41:14 +1000762but protocol 2 may use any.
Damien Millerfecfd112013-07-18 16:11:50 +1000763The HISTORY section of
Damien Millerc93a8132005-12-24 14:52:13 +1100764.Xr ssl 8
Damien Millerd4427902010-09-10 11:15:10 +1000765contains a brief discussion of the DSA and RSA algorithms.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100766.Pp
767The file
768.Pa ~/.ssh/authorized_keys
769lists the public keys that are permitted for logging in.
770When the user logs in, the
771.Nm
772program tells the server which key pair it would like to use for
773authentication.
Damien Millerc93a8132005-12-24 14:52:13 +1100774The client proves that it has access to the private key
775and the server checks that the corresponding public key
776is authorized to accept the account.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100777.Pp
Damien Millerc93a8132005-12-24 14:52:13 +1100778The user creates his/her key pair by running
Darren Tuckerd3877b92005-12-20 16:09:36 +1100779.Xr ssh-keygen 1 .
780This stores the private key in
781.Pa ~/.ssh/identity
Damien Millerc93a8132005-12-24 14:52:13 +1100782(protocol 1),
783.Pa ~/.ssh/id_dsa
784(protocol 2 DSA),
Damien Millereb8b60e2010-08-31 22:41:14 +1000785.Pa ~/.ssh/id_ecdsa
786(protocol 2 ECDSA),
Damien Millerc93a8132005-12-24 14:52:13 +1100787or
788.Pa ~/.ssh/id_rsa
789(protocol 2 RSA)
Darren Tuckerd3877b92005-12-20 16:09:36 +1100790and stores the public key in
791.Pa ~/.ssh/identity.pub
Damien Millerc93a8132005-12-24 14:52:13 +1100792(protocol 1),
793.Pa ~/.ssh/id_dsa.pub
794(protocol 2 DSA),
Damien Millereb8b60e2010-08-31 22:41:14 +1000795.Pa ~/.ssh/id_ecdsa.pub
796(protocol 2 ECDSA),
Damien Millerc93a8132005-12-24 14:52:13 +1100797or
798.Pa ~/.ssh/id_rsa.pub
799(protocol 2 RSA)
Darren Tuckerd3877b92005-12-20 16:09:36 +1100800in the user's home directory.
Damien Millerc93a8132005-12-24 14:52:13 +1100801The user should then copy the public key
Darren Tuckerd3877b92005-12-20 16:09:36 +1100802to
803.Pa ~/.ssh/authorized_keys
Damien Millerc93a8132005-12-24 14:52:13 +1100804in his/her home directory on the remote machine.
805The
Darren Tuckerd3877b92005-12-20 16:09:36 +1100806.Pa authorized_keys
807file corresponds to the conventional
808.Pa ~/.rhosts
809file, and has one key
Damien Millerc93a8132005-12-24 14:52:13 +1100810per line, though the lines can be very long.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100811After this, the user can log in without giving the password.
812.Pp
Damien Miller922b5412010-03-05 21:30:54 +1100813A variation on public key authentication
814is available in the form of certificate authentication:
815instead of a set of public/private keys,
816signed certificates are used.
817This has the advantage that a single trusted certification authority
818can be used in place of many public/private keys.
Damien Millerfecfd112013-07-18 16:11:50 +1000819See the CERTIFICATES section of
Damien Miller922b5412010-03-05 21:30:54 +1100820.Xr ssh-keygen 1
821for more information.
822.Pp
823The most convenient way to use public key or certificate authentication
824may be with an authentication agent.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100825See
826.Xr ssh-agent 1
827for more information.
828.Pp
Damien Millerc93a8132005-12-24 14:52:13 +1100829Challenge-response authentication works as follows:
830The server sends an arbitrary
831.Qq challenge
832text, and prompts for a response.
833Protocol 2 allows multiple challenges and responses;
834protocol 1 is restricted to just one challenge/response.
835Examples of challenge-response authentication include
Damien Millerb7727df2013-08-21 02:43:49 +1000836.Bx
837Authentication (see
Damien Millerc93a8132005-12-24 14:52:13 +1100838.Xr login.conf 5 )
Damien Millerb7727df2013-08-21 02:43:49 +1000839and PAM (some
840.Pf non- Ox
841systems).
Damien Millerc93a8132005-12-24 14:52:13 +1100842.Pp
843Finally, if other authentication methods fail,
Darren Tuckerd3877b92005-12-20 16:09:36 +1100844.Nm
845prompts the user for a password.
846The password is sent to the remote
847host for checking; however, since all communications are encrypted,
848the password cannot be seen by someone listening on the network.
Damien Miller48c94ab2006-01-02 23:38:00 +1100849.Pp
850.Nm
851automatically maintains and checks a database containing
852identification for all hosts it has ever been used with.
853Host keys are stored in
854.Pa ~/.ssh/known_hosts
855in the user's home directory.
856Additionally, the file
857.Pa /etc/ssh/ssh_known_hosts
858is automatically checked for known hosts.
859Any new hosts are automatically added to the user's file.
860If a host's identification ever changes,
861.Nm
862warns about this and disables password authentication to prevent
863server spoofing or man-in-the-middle attacks,
864which could otherwise be used to circumvent the encryption.
865The
866.Cm StrictHostKeyChecking
867option can be used to control logins to machines whose
868host key is not known or has changed.
869.Pp
Darren Tuckerd3877b92005-12-20 16:09:36 +1100870When the user's identity has been accepted by the server, the server
871either executes the given command, or logs into the machine and gives
872the user a normal shell on the remote machine.
873All communication with
874the remote command or shell will be automatically encrypted.
875.Pp
876If a pseudo-terminal has been allocated (normal login session), the
877user may use the escape characters noted below.
878.Pp
879If no pseudo-tty has been allocated,
880the session is transparent and can be used to reliably transfer binary data.
881On most systems, setting the escape character to
882.Dq none
883will also make the session transparent even if a tty is used.
884.Pp
885The session terminates when the command or shell on the remote
Damien Miller8bfaf932006-01-14 10:09:30 +1100886machine exits and all X11 and TCP connections have been closed.
Damien Miller52d20612005-12-24 14:52:36 +1100887.Sh ESCAPE CHARACTERS
Darren Tuckerd3877b92005-12-20 16:09:36 +1100888When a pseudo-terminal has been requested,
889.Nm
890supports a number of functions through the use of an escape character.
891.Pp
892A single tilde character can be sent as
893.Ic ~~
894or by following the tilde by a character other than those described below.
895The escape character must always follow a newline to be interpreted as
896special.
897The escape character can be changed in configuration files using the
898.Cm EscapeChar
899configuration directive or on the command line by the
900.Fl e
901option.
902.Pp
903The supported escapes (assuming the default
904.Ql ~ )
905are:
906.Bl -tag -width Ds
907.It Cm ~.
908Disconnect.
909.It Cm ~^Z
910Background
Damien Miller1164c292006-01-02 23:38:37 +1100911.Nm .
Darren Tuckerd3877b92005-12-20 16:09:36 +1100912.It Cm ~#
913List forwarded connections.
914.It Cm ~&
915Background
916.Nm
917at logout when waiting for forwarded connection / X11 sessions to terminate.
918.It Cm ~?
919Display a list of escape characters.
920.It Cm ~B
921Send a BREAK to the remote system
922(only useful for SSH protocol version 2 and if the peer supports it).
923.It Cm ~C
924Open command line.
925Currently this allows the addition of port forwardings using the
Damien Miller0164cb82008-11-05 16:30:31 +1100926.Fl L ,
Darren Tuckerd3877b92005-12-20 16:09:36 +1100927.Fl R
Damien Miller0164cb82008-11-05 16:30:31 +1100928and
929.Fl D
Damien Miller329cb012005-12-24 14:53:23 +1100930options (see above).
Damien Millerff773642011-09-22 21:39:48 +1000931It also allows the cancellation of existing port-forwardings
932with
Damien Miller57e8ad32006-07-10 20:20:52 +1000933.Sm off
Damien Millerff773642011-09-22 21:39:48 +1000934.Fl KL Oo Ar bind_address : Oc Ar port
Damien Miller57e8ad32006-07-10 20:20:52 +1000935.Sm on
Damien Millerff773642011-09-22 21:39:48 +1000936for local,
937.Sm off
938.Fl KR Oo Ar bind_address : Oc Ar port
939.Sm on
940for remote and
941.Sm off
942.Fl KD Oo Ar bind_address : Oc Ar port
943.Sm on
944for dynamic port-forwardings.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100945.Ic !\& Ns Ar command
946allows the user to execute a local command if the
947.Ic PermitLocalCommand
948option is enabled in
949.Xr ssh_config 5 .
950Basic help is available, using the
951.Fl h
952option.
953.It Cm ~R
954Request rekeying of the connection
955(only useful for SSH protocol version 2 and if the peer supports it).
Darren Tucker50a48d02012-09-06 21:25:37 +1000956.It Cm ~V
957Decrease the verbosity
958.Pq Ic LogLevel
959when errors are being written to stderr.
960.It Cm ~v
Darren Tucker83d0af62012-09-07 11:21:03 +1000961Increase the verbosity
Darren Tucker50a48d02012-09-06 21:25:37 +1000962.Pq Ic LogLevel
963when errors are being written to stderr.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100964.El
Damien Millerf3177182006-01-14 10:09:13 +1100965.Sh TCP FORWARDING
966Forwarding of arbitrary TCP connections over the secure channel can
967be specified either on the command line or in a configuration file.
968One possible application of TCP forwarding is a secure connection to a
969mail server; another is going through firewalls.
970.Pp
971In the example below, we look at encrypting communication between
972an IRC client and server, even though the IRC server does not directly
973support encrypted communications.
974This works as follows:
975the user connects to the remote host using
976.Nm ,
977specifying a port to be used to forward connections
978to the remote server.
979After that it is possible to start the service which is to be encrypted
980on the client machine,
981connecting to the same local port,
982and
983.Nm
984will encrypt and forward the connection.
985.Pp
986The following example tunnels an IRC session from client machine
987.Dq 127.0.0.1
988(localhost)
989to remote server
990.Dq server.example.com :
991.Bd -literal -offset 4n
992$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
993$ irc -c '#users' -p 1234 pinky 127.0.0.1
994.Ed
995.Pp
996This tunnels a connection to IRC server
997.Dq server.example.com ,
998joining channel
999.Dq #users ,
1000nickname
1001.Dq pinky ,
1002using port 1234.
1003It doesn't matter which port is used,
1004as long as it's greater than 1023
1005(remember, only root can open sockets on privileged ports)
1006and doesn't conflict with any ports already in use.
1007The connection is forwarded to port 6667 on the remote server,
1008since that's the standard port for IRC services.
1009.Pp
1010The
1011.Fl f
1012option backgrounds
1013.Nm
1014and the remote command
1015.Dq sleep 10
1016is specified to allow an amount of time
1017(10 seconds, in the example)
1018to start the service which is to be tunnelled.
1019If no connections are made within the time specified,
1020.Nm
1021will exit.
Damien Millerf3177182006-01-14 10:09:13 +11001022.Sh X11 FORWARDING
Darren Tuckerd3877b92005-12-20 16:09:36 +11001023If the
1024.Cm ForwardX11
1025variable is set to
1026.Dq yes
1027(or see the description of the
Damien Millerd7f308f2005-12-24 14:55:16 +11001028.Fl X ,
1029.Fl x ,
Darren Tuckerd3877b92005-12-20 16:09:36 +11001030and
Damien Millerd7f308f2005-12-24 14:55:16 +11001031.Fl Y
Damien Miller9a765b22005-12-24 14:53:44 +11001032options above)
Darren Tuckerd3877b92005-12-20 16:09:36 +11001033and the user is using X11 (the
1034.Ev DISPLAY
1035environment variable is set), the connection to the X11 display is
1036automatically forwarded to the remote side in such a way that any X11
1037programs started from the shell (or command) will go through the
1038encrypted channel, and the connection to the real X server will be made
1039from the local machine.
1040The user should not manually set
1041.Ev DISPLAY .
1042Forwarding of X11 connections can be
1043configured on the command line or in configuration files.
1044.Pp
1045The
1046.Ev DISPLAY
1047value set by
1048.Nm
1049will point to the server machine, but with a display number greater than zero.
1050This is normal, and happens because
1051.Nm
1052creates a
1053.Dq proxy
1054X server on the server machine for forwarding the
1055connections over the encrypted channel.
1056.Pp
1057.Nm
1058will also automatically set up Xauthority data on the server machine.
1059For this purpose, it will generate a random authorization cookie,
1060store it in Xauthority on the server, and verify that any forwarded
1061connections carry this cookie and replace it by the real cookie when
1062the connection is opened.
1063The real authentication cookie is never
1064sent to the server machine (and no cookies are sent in the plain).
1065.Pp
1066If the
1067.Cm ForwardAgent
1068variable is set to
1069.Dq yes
1070(or see the description of the
1071.Fl A
1072and
1073.Fl a
Damien Miller9a765b22005-12-24 14:53:44 +11001074options above) and
Darren Tuckerd3877b92005-12-20 16:09:36 +11001075the user is using an authentication agent, the connection to the agent
1076is automatically forwarded to the remote side.
Damien Millerbbc59092006-01-31 21:46:51 +11001077.Sh VERIFYING HOST KEYS
1078When connecting to a server for the first time,
1079a fingerprint of the server's public key is presented to the user
1080(unless the option
1081.Cm StrictHostKeyChecking
1082has been disabled).
1083Fingerprints can be determined using
1084.Xr ssh-keygen 1 :
1085.Pp
1086.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1087.Pp
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001088If the fingerprint is already known, it can be matched
1089and the key can be accepted or rejected.
1090Because of the difficulty of comparing host keys
1091just by looking at hex strings,
1092there is also support to compare host keys visually,
1093using
1094.Em random art .
1095By setting the
Damien Miller10288242008-06-30 00:04:03 +10001096.Cm VisualHostKey
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001097option to
Damien Miller10288242008-06-30 00:04:03 +10001098.Dq yes ,
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001099a small ASCII graphic gets displayed on every login to a server, no matter
1100if the session itself is interactive or not.
1101By learning the pattern a known server produces, a user can easily
1102find out that the host key has changed when a completely different pattern
1103is displayed.
1104Because these patterns are not unambiguous however, a pattern that looks
1105similar to the pattern remembered only gives a good probability that the
1106host key is the same, not guaranteed proof.
1107.Pp
1108To get a listing of the fingerprints along with their random art for
1109all known hosts, the following command line can be used:
1110.Pp
1111.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1112.Pp
Damien Millerbbc59092006-01-31 21:46:51 +11001113If the fingerprint is unknown,
1114an alternative method of verification is available:
1115SSH fingerprints verified by DNS.
1116An additional resource record (RR),
1117SSHFP,
1118is added to a zonefile
1119and the connecting client is able to match the fingerprint
1120with that of the key presented.
1121.Pp
1122In this example, we are connecting a client to a server,
1123.Dq host.example.com .
1124The SSHFP resource records should first be added to the zonefile for
1125host.example.com:
1126.Bd -literal -offset indent
Damien Millera1b3d632006-03-26 00:07:02 +11001127$ ssh-keygen -r host.example.com.
Damien Millerbbc59092006-01-31 21:46:51 +11001128.Ed
1129.Pp
1130The output lines will have to be added to the zonefile.
1131To check that the zone is answering fingerprint queries:
1132.Pp
1133.Dl $ dig -t SSHFP host.example.com
1134.Pp
1135Finally the client connects:
1136.Bd -literal -offset indent
1137$ ssh -o "VerifyHostKeyDNS ask" host.example.com
1138[...]
1139Matching host key fingerprint found in DNS.
1140Are you sure you want to continue connecting (yes/no)?
1141.Ed
1142.Pp
1143See the
1144.Cm VerifyHostKeyDNS
1145option in
1146.Xr ssh_config 5
1147for more information.
Darren Tucker248dd132006-01-20 11:30:58 +11001148.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1149.Nm
1150contains support for Virtual Private Network (VPN) tunnelling
1151using the
1152.Xr tun 4
1153network pseudo-device,
1154allowing two networks to be joined securely.
1155The
1156.Xr sshd_config 5
1157configuration option
1158.Cm PermitTunnel
1159controls whether the server supports this,
1160and at what level (layer 2 or 3 traffic).
1161.Pp
1162The following example would connect client network 10.0.50.0/24
Damien Miller3975ee22006-11-05 05:31:33 +11001163with remote network 10.0.99.0/24 using a point-to-point connection
1164from 10.1.1.1 to 10.1.1.2,
1165provided that the SSH server running on the gateway to the remote network,
1166at 192.168.1.15, allows it.
1167.Pp
1168On the client:
Darren Tucker248dd132006-01-20 11:30:58 +11001169.Bd -literal -offset indent
1170# ssh -f -w 0:1 192.168.1.15 true
Damien Miller3975ee22006-11-05 05:31:33 +11001171# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1172# route add 10.0.99.0/24 10.1.1.2
1173.Ed
1174.Pp
1175On the server:
1176.Bd -literal -offset indent
1177# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1178# route add 10.0.50.0/24 10.1.1.1
Darren Tucker248dd132006-01-20 11:30:58 +11001179.Ed
1180.Pp
1181Client access may be more finely tuned via the
1182.Pa /root/.ssh/authorized_keys
1183file (see below) and the
1184.Cm PermitRootLogin
1185server option.
Damien Millere93eaaa2006-03-15 11:05:59 +11001186The following entry would permit connections on
Darren Tucker248dd132006-01-20 11:30:58 +11001187.Xr tun 4
Damien Millere93eaaa2006-03-15 11:05:59 +11001188device 1 from user
Darren Tucker248dd132006-01-20 11:30:58 +11001189.Dq jane
Damien Millere93eaaa2006-03-15 11:05:59 +11001190and on tun device 2 from user
Darren Tucker248dd132006-01-20 11:30:58 +11001191.Dq john ,
1192if
1193.Cm PermitRootLogin
1194is set to
1195.Dq forced-commands-only :
1196.Bd -literal -offset 2n
1197tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
Damien Miller9f67a212006-03-15 11:05:35 +11001198tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
Darren Tucker248dd132006-01-20 11:30:58 +11001199.Ed
1200.Pp
Darren Tuckerffe88e12006-10-18 07:53:06 +10001201Since an SSH-based setup entails a fair amount of overhead,
Darren Tucker248dd132006-01-20 11:30:58 +11001202it may be more suited to temporary setups,
1203such as for wireless VPNs.
1204More permanent VPNs are better provided by tools such as
1205.Xr ipsecctl 8
1206and
1207.Xr isakmpd 8 .
Damien Miller32aa1441999-10-29 09:15:49 +10001208.Sh ENVIRONMENT
1209.Nm
1210will normally set the following environment variables:
Damien Miller6aa22902006-01-06 14:48:34 +11001211.Bl -tag -width "SSH_ORIGINAL_COMMAND"
Damien Miller32aa1441999-10-29 09:15:49 +10001212.It Ev DISPLAY
1213The
1214.Ev DISPLAY
Damien Miller7684ee12000-03-17 23:40:15 +11001215variable indicates the location of the X11 server.
Damien Miller22c77262000-04-13 12:26:34 +10001216It is automatically set by
Damien Miller32aa1441999-10-29 09:15:49 +10001217.Nm
1218to point to a value of the form
Damien Miller14af93e2006-01-02 23:38:21 +11001219.Dq hostname:n ,
1220where
1221.Dq hostname
1222indicates the host where the shell runs, and
1223.Sq n
1224is an integer \*(Ge 1.
Damien Miller7684ee12000-03-17 23:40:15 +11001225.Nm
1226uses this special value to forward X11 connections over the secure
1227channel.
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001228The user should normally not set
1229.Ev DISPLAY
1230explicitly, as that
Damien Miller32aa1441999-10-29 09:15:49 +10001231will render the X11 connection insecure (and will require the user to
1232manually copy any required authorization cookies).
1233.It Ev HOME
1234Set to the path of the user's home directory.
1235.It Ev LOGNAME
1236Synonym for
1237.Ev USER ;
1238set for compatibility with systems that use this variable.
1239.It Ev MAIL
Ben Lindstrome59433d2001-09-12 16:41:37 +00001240Set to the path of the user's mailbox.
Damien Miller7684ee12000-03-17 23:40:15 +11001241.It Ev PATH
Damien Miller32aa1441999-10-29 09:15:49 +10001242Set to the default
1243.Ev PATH ,
1244as specified when compiling
Damien Miller1164c292006-01-02 23:38:37 +11001245.Nm .
Ben Lindstrom5bf5d672001-07-04 04:31:38 +00001246.It Ev SSH_ASKPASS
1247If
1248.Nm
1249needs a passphrase, it will read the passphrase from the current
1250terminal if it was run from a terminal.
1251If
1252.Nm
1253does not have a terminal associated with it but
1254.Ev DISPLAY
1255and
1256.Ev SSH_ASKPASS
1257are set, it will execute the program specified by
1258.Ev SSH_ASKPASS
1259and open an X11 window to read the passphrase.
1260This is particularly useful when calling
1261.Nm
1262from a
Darren Tucker4e4fe002004-11-05 20:01:03 +11001263.Pa .xsession
Ben Lindstrom5bf5d672001-07-04 04:31:38 +00001264or related script.
1265(Note that on some machines it
1266may be necessary to redirect the input from
1267.Pa /dev/null
1268to make this work.)
Damien Miller32aa1441999-10-29 09:15:49 +10001269.It Ev SSH_AUTH_SOCK
Damien Miller14af93e2006-01-02 23:38:21 +11001270Identifies the path of a
1271.Ux Ns -domain
1272socket used to communicate with the agent.
Damien Millerf37e2462002-09-19 11:47:55 +10001273.It Ev SSH_CONNECTION
1274Identifies the client and server ends of the connection.
Damien Miller7684ee12000-03-17 23:40:15 +11001275The variable contains
Damien Miller14af93e2006-01-02 23:38:21 +11001276four space-separated values: client IP address, client port number,
1277server IP address, and server port number.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001278.It Ev SSH_ORIGINAL_COMMAND
Damien Miller14af93e2006-01-02 23:38:21 +11001279This variable contains the original command line if a forced command
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001280is executed.
1281It can be used to extract the original arguments.
Damien Miller32aa1441999-10-29 09:15:49 +10001282.It Ev SSH_TTY
1283This is set to the name of the tty (path to the device) associated
Damien Miller7684ee12000-03-17 23:40:15 +11001284with the current shell or command.
1285If the current session has no tty,
Damien Miller32aa1441999-10-29 09:15:49 +10001286this variable is not set.
1287.It Ev TZ
Damien Miller6dbdb6a2005-12-13 19:25:43 +11001288This variable is set to indicate the present time zone if it
Damien Miller208f1ed2006-03-15 11:56:03 +11001289was set when the daemon was started (i.e. the daemon passes the value
Damien Miller32aa1441999-10-29 09:15:49 +10001290on to new connections).
1291.It Ev USER
1292Set to the name of the user logging in.
1293.El
1294.Pp
Damien Miller22c77262000-04-13 12:26:34 +10001295Additionally,
Damien Miller32aa1441999-10-29 09:15:49 +10001296.Nm
Damien Miller22c77262000-04-13 12:26:34 +10001297reads
Damien Miller167ea5d2005-05-26 12:04:02 +10001298.Pa ~/.ssh/environment ,
Damien Miller32aa1441999-10-29 09:15:49 +10001299and adds lines of the format
1300.Dq VARNAME=value
Damien Miller14af93e2006-01-02 23:38:21 +11001301to the environment if the file exists and users are allowed to
Ben Lindstromdc7adf22002-08-20 18:38:02 +00001302change their environment.
Darren Tucker61776952003-10-02 16:19:47 +10001303For more information, see the
Ben Lindstromdc7adf22002-08-20 18:38:02 +00001304.Cm PermitUserEnvironment
Ben Lindstrombd9bf382002-08-20 18:54:20 +00001305option in
Ben Lindstromdc7adf22002-08-20 18:38:02 +00001306.Xr sshd_config 5 .
Damien Miller32aa1441999-10-29 09:15:49 +10001307.Sh FILES
Damien Miller7655f5c2006-01-06 14:48:18 +11001308.Bl -tag -width Ds -compact
Damien Millerafdae612010-08-31 22:31:14 +10001309.It Pa ~/.rhosts
Damien Miller1bcdb502006-01-06 14:49:38 +11001310This file is used for host-based authentication (see above).
Ben Lindstromebd888d2001-03-05 05:49:29 +00001311On some machines this file may need to be
Damien Miller1bcdb502006-01-06 14:49:38 +11001312world-readable if the user's home directory is on an NFS partition,
Damien Miller32aa1441999-10-29 09:15:49 +10001313because
1314.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001315reads it as root.
1316Additionally, this file must be owned by the user,
1317and must not have write permissions for anyone else.
1318The recommended
Damien Miller32aa1441999-10-29 09:15:49 +10001319permission for most machines is read/write for the user, and not
1320accessible by others.
1321.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001322.It Pa ~/.shosts
Damien Miller1bcdb502006-01-06 14:49:38 +11001323This file is used in exactly the same way as
1324.Pa .rhosts ,
1325but allows host-based authentication without permitting login with
1326rlogin/rsh.
Damien Miller7655f5c2006-01-06 14:48:18 +11001327.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001328.It Pa ~/.ssh/
Damien Miller520e6152008-02-10 22:46:22 +11001329This directory is the default location for all user-specific configuration
1330and authentication information.
1331There is no general requirement to keep the entire contents of this directory
1332secret, but the recommended permissions are read/write/execute for the user,
1333and not accessible by others.
1334.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001335.It Pa ~/.ssh/authorized_keys
Damien Millereb8b60e2010-08-31 22:41:14 +10001336Lists the public keys (DSA/ECDSA/RSA) that can be used for logging in as
1337this user.
Damien Millerfb8ea742006-01-06 14:48:52 +11001338The format of this file is described in the
1339.Xr sshd 8
1340manual page.
Damien Millerfb8ea742006-01-06 14:48:52 +11001341This file is not highly sensitive, but the recommended
1342permissions are read/write for the user, and not accessible by others.
1343.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001344.It Pa ~/.ssh/config
Damien Millerfb8ea742006-01-06 14:48:52 +11001345This is the per-user configuration file.
1346The file format and configuration options are described in
1347.Xr ssh_config 5 .
1348Because of the potential for abuse, this file must have strict permissions:
Damien Millerd93340c2013-07-18 16:14:34 +10001349read/write for the user, and not writable by others.
Damien Millerfb8ea742006-01-06 14:48:52 +11001350.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001351.It Pa ~/.ssh/environment
Damien Miller4c102ee2006-01-06 14:49:17 +11001352Contains additional definitions for environment variables; see
1353.Sx ENVIRONMENT ,
Damien Millerfb8ea742006-01-06 14:48:52 +11001354above.
1355.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001356.It Pa ~/.ssh/identity
1357.It Pa ~/.ssh/id_dsa
Damien Millereb8b60e2010-08-31 22:41:14 +10001358.It Pa ~/.ssh/id_ecdsa
Damien Millerafdae612010-08-31 22:31:14 +10001359.It Pa ~/.ssh/id_rsa
Damien Millerfb8ea742006-01-06 14:48:52 +11001360Contains the private key for authentication.
1361These files
1362contain sensitive data and should be readable by the user but not
1363accessible by others (read/write/execute).
1364.Nm
1365will simply ignore a private key file if it is accessible by others.
1366It is possible to specify a passphrase when
1367generating the key which will be used to encrypt the
1368sensitive part of this file using 3DES.
1369.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001370.It Pa ~/.ssh/identity.pub
1371.It Pa ~/.ssh/id_dsa.pub
Damien Millereb8b60e2010-08-31 22:41:14 +10001372.It Pa ~/.ssh/id_ecdsa.pub
Damien Millerafdae612010-08-31 22:31:14 +10001373.It Pa ~/.ssh/id_rsa.pub
Damien Millerfb8ea742006-01-06 14:48:52 +11001374Contains the public key for authentication.
1375These files are not
1376sensitive and can (but need not) be readable by anyone.
Damien Millerfb8ea742006-01-06 14:48:52 +11001377.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001378.It Pa ~/.ssh/known_hosts
Damien Millere87eb4c2006-01-14 10:08:36 +11001379Contains a list of host keys for all hosts the user has logged into
1380that are not already in the systemwide list of known host keys.
Damien Millerfb8ea742006-01-06 14:48:52 +11001381See
Damien Millere87eb4c2006-01-14 10:08:36 +11001382.Xr sshd 8
1383for further details of the format of this file.
Damien Millerfb8ea742006-01-06 14:48:52 +11001384.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001385.It Pa ~/.ssh/rc
Damien Millerfb8ea742006-01-06 14:48:52 +11001386Commands in this file are executed by
1387.Nm
Damien Miller7e76e1f2006-01-14 10:08:57 +11001388when the user logs in, just before the user's shell (or command) is
Damien Millerfb8ea742006-01-06 14:48:52 +11001389started.
1390See the
1391.Xr sshd 8
1392manual page for more information.
1393.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001394.It Pa /etc/hosts.equiv
Damien Miller1bcdb502006-01-06 14:49:38 +11001395This file is for host-based authentication (see above).
1396It should only be writable by root.
Damien Miller7655f5c2006-01-06 14:48:18 +11001397.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001398.It Pa /etc/shosts.equiv
Damien Miller1bcdb502006-01-06 14:49:38 +11001399This file is used in exactly the same way as
1400.Pa hosts.equiv ,
1401but allows host-based authentication without permitting login with
1402rlogin/rsh.
Damien Miller7655f5c2006-01-06 14:48:18 +11001403.Pp
Damien Millerfb8ea742006-01-06 14:48:52 +11001404.It Pa /etc/ssh/ssh_config
1405Systemwide configuration file.
1406The file format and configuration options are described in
1407.Xr ssh_config 5 .
1408.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001409.It Pa /etc/ssh/ssh_host_key
1410.It Pa /etc/ssh/ssh_host_dsa_key
Damien Millereb8b60e2010-08-31 22:41:14 +10001411.It Pa /etc/ssh/ssh_host_ecdsa_key
Damien Millerafdae612010-08-31 22:31:14 +10001412.It Pa /etc/ssh/ssh_host_rsa_key
Damien Millerb9902cf2012-06-20 21:52:58 +10001413These files contain the private parts of the host keys
Damien Miller7e76e1f2006-01-14 10:08:57 +11001414and are used for host-based authentication.
1415If protocol version 1 is used,
Damien Millerfb8ea742006-01-06 14:48:52 +11001416.Nm
1417must be setuid root, since the host key is readable only by root.
1418For protocol version 2,
1419.Nm
1420uses
1421.Xr ssh-keysign 8
Damien Miller7e76e1f2006-01-14 10:08:57 +11001422to access the host keys,
1423eliminating the requirement that
Damien Millerfb8ea742006-01-06 14:48:52 +11001424.Nm
Damien Miller7e76e1f2006-01-14 10:08:57 +11001425be setuid root when host-based authentication is used.
Damien Millerfb8ea742006-01-06 14:48:52 +11001426By default
1427.Nm
1428is not setuid root.
1429.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001430.It Pa /etc/ssh/ssh_known_hosts
Damien Millerfb8ea742006-01-06 14:48:52 +11001431Systemwide list of known host keys.
1432This file should be prepared by the
1433system administrator to contain the public host keys of all machines in the
1434organization.
Damien Millere87eb4c2006-01-14 10:08:36 +11001435It should be world-readable.
1436See
Damien Millerfb8ea742006-01-06 14:48:52 +11001437.Xr sshd 8
Damien Millere87eb4c2006-01-14 10:08:36 +11001438for further details of the format of this file.
Damien Millerfb8ea742006-01-06 14:48:52 +11001439.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001440.It Pa /etc/ssh/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +10001441Commands in this file are executed by
1442.Nm
Damien Miller7e76e1f2006-01-14 10:08:57 +11001443when the user logs in, just before the user's shell (or command) is started.
Damien Miller32aa1441999-10-29 09:15:49 +10001444See the
1445.Xr sshd 8
1446manual page for more information.
Damien Miller7b28dc52000-09-05 13:34:53 +11001447.El
Damien Millerdaa7b222010-09-10 11:19:33 +10001448.Sh EXIT STATUS
1449.Nm
1450exits with the exit status of the remote command or with 255
1451if an error occurred.
Damien Miller32aa1441999-10-29 09:15:49 +10001452.Sh SEE ALSO
Damien Miller32aa1441999-10-29 09:15:49 +10001453.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +11001454.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +10001455.Xr ssh-add 1 ,
1456.Xr ssh-agent 1 ,
1457.Xr ssh-keygen 1 ,
Damien Miller128a0f12006-01-06 14:50:11 +11001458.Xr ssh-keyscan 1 ,
Darren Tucker248dd132006-01-20 11:30:58 +11001459.Xr tun 4 ,
Darren Tucker61776952003-10-02 16:19:47 +10001460.Xr hosts.equiv 5 ,
Ben Lindstrombf69e3b2002-06-23 00:31:24 +00001461.Xr ssh_config 5 ,
Ben Lindstromc001cd32002-06-23 00:32:11 +00001462.Xr ssh-keysign 8 ,
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +00001463.Xr sshd 8
Darren Tucker628a3fd2012-10-05 10:50:15 +10001464.Sh STANDARDS
Ben Lindstrom160ec622001-04-22 17:17:46 +00001465.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001466.%A S. Lehtinen
1467.%A C. Lonvick
1468.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001469.%R RFC 4250
Darren Tucker628a3fd2012-10-05 10:50:15 +10001470.%T The Secure Shell (SSH) Protocol Assigned Numbers
Damien Miller39a93a32006-03-15 11:34:45 +11001471.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001472.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001473.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001474.%A T. Ylonen
1475.%A C. Lonvick
1476.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001477.%R RFC 4251
Darren Tucker628a3fd2012-10-05 10:50:15 +10001478.%T The Secure Shell (SSH) Protocol Architecture
Damien Miller39a93a32006-03-15 11:34:45 +11001479.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001480.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001481.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001482.%A T. Ylonen
1483.%A C. Lonvick
1484.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001485.%R RFC 4252
Darren Tucker628a3fd2012-10-05 10:50:15 +10001486.%T The Secure Shell (SSH) Authentication Protocol
Damien Miller39a93a32006-03-15 11:34:45 +11001487.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001488.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001489.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001490.%A T. Ylonen
1491.%A C. Lonvick
1492.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001493.%R RFC 4253
Darren Tucker628a3fd2012-10-05 10:50:15 +10001494.%T The Secure Shell (SSH) Transport Layer Protocol
Damien Miller39a93a32006-03-15 11:34:45 +11001495.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001496.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001497.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001498.%A T. Ylonen
1499.%A C. Lonvick
1500.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001501.%R RFC 4254
Darren Tucker628a3fd2012-10-05 10:50:15 +10001502.%T The Secure Shell (SSH) Connection Protocol
Damien Miller39a93a32006-03-15 11:34:45 +11001503.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001504.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001505.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001506.%A J. Schlyter
1507.%A W. Griffin
1508.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001509.%R RFC 4255
Darren Tucker628a3fd2012-10-05 10:50:15 +10001510.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
Damien Miller39a93a32006-03-15 11:34:45 +11001511.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001512.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001513.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001514.%A F. Cusack
1515.%A M. Forssen
1516.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001517.%R RFC 4256
Darren Tucker628a3fd2012-10-05 10:50:15 +10001518.%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)
Damien Miller39a93a32006-03-15 11:34:45 +11001519.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001520.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001521.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001522.%A J. Galbraith
1523.%A P. Remaker
1524.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001525.%R RFC 4335
Darren Tucker628a3fd2012-10-05 10:50:15 +10001526.%T The Secure Shell (SSH) Session Channel Break Extension
Damien Miller39a93a32006-03-15 11:34:45 +11001527.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001528.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001529.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001530.%A M. Bellare
1531.%A T. Kohno
1532.%A C. Namprempre
1533.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001534.%R RFC 4344
Darren Tucker628a3fd2012-10-05 10:50:15 +10001535.%T The Secure Shell (SSH) Transport Layer Encryption Modes
Damien Miller39a93a32006-03-15 11:34:45 +11001536.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001537.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001538.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001539.%A B. Harris
1540.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001541.%R RFC 4345
Darren Tucker628a3fd2012-10-05 10:50:15 +10001542.%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol
Ben Lindstrom160ec622001-04-22 17:17:46 +00001543.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001544.Pp
Damien Miller3e96d742006-03-25 23:39:29 +11001545.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001546.%A M. Friedl
1547.%A N. Provos
1548.%A W. Simpson
1549.%D March 2006
Damien Miller3e96d742006-03-25 23:39:29 +11001550.%R RFC 4419
Darren Tucker628a3fd2012-10-05 10:50:15 +10001551.%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol
Damien Miller3e96d742006-03-25 23:39:29 +11001552.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001553.Pp
Damien Millerc0367fb2007-01-05 16:25:46 +11001554.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001555.%A J. Galbraith
1556.%A R. Thayer
1557.%D November 2006
Damien Millerc0367fb2007-01-05 16:25:46 +11001558.%R RFC 4716
Darren Tucker628a3fd2012-10-05 10:50:15 +10001559.%T The Secure Shell (SSH) Public Key File Format
Damien Millerc0367fb2007-01-05 16:25:46 +11001560.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001561.Pp
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001562.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001563.%A D. Stebila
1564.%A J. Green
1565.%D December 2009
Damien Miller1ca94692010-09-24 22:01:22 +10001566.%R RFC 5656
Darren Tucker628a3fd2012-10-05 10:50:15 +10001567.%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
Damien Miller1ca94692010-09-24 22:01:22 +10001568.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001569.Pp
Damien Miller1ca94692010-09-24 22:01:22 +10001570.Rs
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001571.%A A. Perrig
1572.%A D. Song
1573.%D 1999
Darren Tucker628a3fd2012-10-05 10:50:15 +10001574.%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)
1575.%T Hash Visualization: a New Technique to improve Real-World Security
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001576.Re
Damien Millerf1ce5052003-06-11 22:04:39 +10001577.Sh AUTHORS
1578OpenSSH is a derivative of the original and free
1579ssh 1.2.12 release by Tatu Ylonen.
1580Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1581Theo de Raadt and Dug Song
1582removed many bugs, re-added newer features and
1583created OpenSSH.
1584Markus Friedl contributed the support for SSH
1585protocol versions 1.5 and 2.0.