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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.\"
djm@openbsd.orgf9487372015-05-22 05:28:45 +000036.\" $OpenBSD: ssh.1,v 1.358 2015/05/22 05:28:45 djm Exp $
37.Dd $Mdocdate: May 22 2015 $
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
jmc@openbsd.orgb1ba15f2014-10-09 06:21:31 +000046.Op Fl 1246AaCfGgKkMNnqsTtVvXxYy
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
djm@openbsd.org68d2dfc2015-03-03 06:48:58 +000061.Op Fl Q Cm cipher | cipher-auth | mac | kex | key | protocol-version
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 Millera8a0f652014-07-30 12:32:28 +100076X11 connections, arbitrary TCP ports and
77.Ux Ns -domain
78sockets can also be forwarded over the secure channel.
Damien Miller32aa1441999-10-29 09:15:49 +100079.Pp
80.Nm
Damien Miller22c77262000-04-13 12:26:34 +100081connects and logs into the specified
Darren Tucker61776952003-10-02 16:19:47 +100082.Ar hostname
83(with optional
84.Ar user
85name).
Damien Miller32aa1441999-10-29 09:15:49 +100086The user must prove
Damien Millere247cc42000-05-07 12:03:14 +100087his/her identity to the remote machine using one of several methods
Darren Tucker5434cfe2005-12-20 16:11:35 +110088depending on the protocol version used (see below).
Damien Millere247cc42000-05-07 12:03:14 +100089.Pp
Darren Tucker61776952003-10-02 16:19:47 +100090If
91.Ar command
92is specified,
Darren Tuckerb18c8672005-12-20 16:10:09 +110093it is executed on the remote host instead of a login shell.
Darren Tucker0b42e6d2004-08-13 21:22:40 +100094.Pp
Damien Miller0bc1bd82000-11-13 22:57:25 +110095The options are as follows:
Damien Miller32aa1441999-10-29 09:15:49 +100096.Bl -tag -width Ds
Darren Tucker61776952003-10-02 16:19:47 +100097.It Fl 1
98Forces
99.Nm
100to try protocol version 1 only.
101.It Fl 2
102Forces
103.Nm
104to try protocol version 2 only.
105.It Fl 4
106Forces
107.Nm
108to use IPv4 addresses only.
109.It Fl 6
110Forces
111.Nm
112to use IPv6 addresses only.
Damien Millerb1715dc2000-05-30 13:44:51 +1000113.It Fl A
114Enables forwarding of the authentication agent connection.
115This can also be specified on a per-host basis in a configuration file.
Damien Millerb5fdfaa2002-09-12 09:52:03 +1000116.Pp
Damien Miller495dca32003-04-01 21:42:14 +1000117Agent forwarding should be enabled with caution.
118Users with the ability to bypass file permissions on the remote host
Darren Tuckerae69e1d2009-10-24 11:41:34 +1100119(for the agent's
Darren Tucker98c9aec2009-10-24 11:42:44 +1100120.Ux Ns -domain
121socket) can access the local agent through the forwarded connection.
Damien Miller495dca32003-04-01 21:42:14 +1000122An attacker cannot obtain key material from the agent,
Damien Millerb5fdfaa2002-09-12 09:52:03 +1000123however they can perform operations on the keys that enable them to
124authenticate using the identities loaded into the agent.
Darren Tucker61776952003-10-02 16:19:47 +1000125.It Fl a
126Disables forwarding of the authentication agent connection.
Ben Lindstrome0f88042001-04-30 13:06:24 +0000127.It Fl b Ar bind_address
Darren Tuckera5cf8552005-07-14 17:04:18 +1000128Use
129.Ar bind_address
130on the local machine as the source address
131of the connection.
132Only useful on systems with more than one address.
Darren Tucker61776952003-10-02 16:19:47 +1000133.It Fl C
134Requests compression of all data (including stdin, stdout, stderr, and
Damien Millera8a0f652014-07-30 12:32:28 +1000135data for forwarded X11, TCP and
136.Ux Ns -domain
137connections).
Darren Tucker61776952003-10-02 16:19:47 +1000138The compression algorithm is the same used by
139.Xr gzip 1 ,
140and the
141.Dq level
142can be controlled by the
143.Cm CompressionLevel
144option for protocol version 1.
145Compression is desirable on modem lines and other
146slow connections, but will only slow down things on fast networks.
147The default value can be set on a host-by-host basis in the
148configuration files; see the
149.Cm Compression
150option.
Damien Miller05202ff2004-06-15 10:30:39 +1000151.It Fl c Ar cipher_spec
152Selects the cipher specification for encrypting the session.
153.Pp
154Protocol version 1 allows specification of a single cipher.
Darren Tucker1e4308e2005-10-03 18:18:40 +1000155The supported values are
Damien Miller05202ff2004-06-15 10:30:39 +1000156.Dq 3des ,
Darren Tuckerff9f4842005-12-20 16:10:45 +1100157.Dq blowfish ,
Damien Miller05202ff2004-06-15 10:30:39 +1000158and
159.Dq des .
Damien Miller35978212005-12-24 14:56:47 +1100160For protocol version 2,
Damien Miller05202ff2004-06-15 10:30:39 +1000161.Ar cipher_spec
162is a comma-separated list of ciphers
163listed in order of preference.
Darren Tucker3a6a51f2009-06-21 17:48:52 +1000164See the
165.Cm Ciphers
Damien Miller081f3c72010-08-03 16:05:25 +1000166keyword in
167.Xr ssh_config 5
168for more information.
Darren Tuckerc8d64212005-10-03 18:13:42 +1000169.It Fl D Xo
170.Sm off
171.Oo Ar bind_address : Oc
172.Ar port
173.Sm on
174.Xc
Darren Tucker61776952003-10-02 16:19:47 +1000175Specifies a local
176.Dq dynamic
177application-level port forwarding.
178This works by allocating a socket to listen to
179.Ar port
Darren Tuckerc8d64212005-10-03 18:13:42 +1000180on the local side, optionally bound to the specified
181.Ar bind_address .
182Whenever a connection is made to this port, the
Darren Tucker61776952003-10-02 16:19:47 +1000183connection is forwarded over the secure channel, and the application
184protocol is then used to determine where to connect to from the
185remote machine.
186Currently the SOCKS4 and SOCKS5 protocols are supported, and
187.Nm
188will act as a SOCKS server.
189Only root can forward privileged ports.
190Dynamic port forwardings can also be specified in the configuration file.
Darren Tuckerc8d64212005-10-03 18:13:42 +1000191.Pp
Damien Miller7fa96602010-08-05 13:03:13 +1000192IPv6 addresses can be specified by enclosing the address in square brackets.
Darren Tuckerc8d64212005-10-03 18:13:42 +1000193Only the superuser can forward privileged ports.
194By default, the local port is bound in accordance with the
195.Cm GatewayPorts
196setting.
197However, an explicit
198.Ar bind_address
199may be used to bind the connection to a specific address.
200The
201.Ar bind_address
202of
203.Dq localhost
204indicates that the listening port be bound for local use only, while an
205empty address or
206.Sq *
207indicates that the port should be available from all interfaces.
Damien Miller03d4d7e2013-04-23 15:21:06 +1000208.It Fl E Ar log_file
209Append debug logs to
210.Ar log_file
211instead of standard error.
Damien Miller2142ba02005-12-24 14:56:29 +1100212.It Fl e Ar escape_char
Damien Miller32aa1441999-10-29 09:15:49 +1000213Sets the escape character for sessions with a pty (default:
214.Ql ~ ) .
Damien Miller7684ee12000-03-17 23:40:15 +1100215The escape character is only recognized at the beginning of a line.
216The escape character followed by a dot
Damien Miller32aa1441999-10-29 09:15:49 +1000217.Pq Ql \&.
Darren Tucker61776952003-10-02 16:19:47 +1000218closes the connection;
219followed by control-Z suspends the connection;
220and followed by itself sends the escape character once.
Damien Miller7684ee12000-03-17 23:40:15 +1100221Setting the character to
Damien Miller32aa1441999-10-29 09:15:49 +1000222.Dq none
223disables any escapes and makes the session fully transparent.
Darren Tucker61776952003-10-02 16:19:47 +1000224.It Fl F Ar configfile
225Specifies an alternative per-user configuration file.
226If a configuration file is given on the command line,
227the system-wide configuration file
228.Pq Pa /etc/ssh/ssh_config
229will be ignored.
230The default for the per-user configuration file is
Damien Miller167ea5d2005-05-26 12:04:02 +1000231.Pa ~/.ssh/config .
Damien Miller32aa1441999-10-29 09:15:49 +1000232.It Fl f
233Requests
234.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100235to go to background just before command execution.
236This is useful if
Damien Miller32aa1441999-10-29 09:15:49 +1000237.Nm
238is going to ask for passwords or passphrases, but the user
Damien Miller7684ee12000-03-17 23:40:15 +1100239wants it in the background.
Damien Miller22c77262000-04-13 12:26:34 +1000240This implies
Damien Miller32aa1441999-10-29 09:15:49 +1000241.Fl n .
242The recommended way to start X11 programs at a remote site is with
243something like
244.Ic ssh -f host xterm .
Darren Tucker9a2a6092008-07-04 12:53:50 +1000245.Pp
246If the
247.Cm ExitOnForwardFailure
248configuration option is set to
249.Dq yes ,
250then a client started with
251.Fl f
252will wait for all remote port forwards to be successfully established
253before placing itself in the background.
djm@openbsd.org957fbce2014-10-08 22:20:25 +0000254.It Fl G
255Causes
256.Nm
257to print its configuration after evaluating
258.Cm Host
259and
260.Cm Match
261blocks and exit.
Damien Miller396691a2000-01-20 22:44:08 +1100262.It Fl g
263Allows remote hosts to connect to local forwarded ports.
Damien Miller49d9bfe2014-07-03 21:26:42 +1000264If used on a multiplexed connection, then this option must be specified
265on the master process.
Damien Miller7ea845e2010-02-12 09:21:02 +1100266.It Fl I Ar pkcs11
Damien Millerd400da52010-02-12 09:26:23 +1100267Specify the PKCS#11 shared library
Darren Tucker61776952003-10-02 16:19:47 +1000268.Nm
Damien Millera7618442010-02-12 09:26:02 +1100269should use to communicate with a PKCS#11 token providing the user's
Darren Tucker61776952003-10-02 16:19:47 +1000270private RSA key.
Damien Miller32aa1441999-10-29 09:15:49 +1000271.It Fl i Ar identity_file
Damien Millerfae23862002-01-22 23:32:26 +1100272Selects a file from which the identity (private key) for
Damien Millereb8b60e2010-08-31 22:41:14 +1000273public key authentication is read.
Damien Millerfae23862002-01-22 23:32:26 +1100274The default is
Damien Miller167ea5d2005-05-26 12:04:02 +1000275.Pa ~/.ssh/identity
Damien Millerfae23862002-01-22 23:32:26 +1100276for protocol version 1, and
Damien Millereb8b60e2010-08-31 22:41:14 +1000277.Pa ~/.ssh/id_dsa ,
Damien Miller8ba0ead2013-12-18 17:46:27 +1100278.Pa ~/.ssh/id_ecdsa ,
279.Pa ~/.ssh/id_ed25519
Damien Millerfae23862002-01-22 23:32:26 +1100280and
Damien Millereb8b60e2010-08-31 22:41:14 +1000281.Pa ~/.ssh/id_rsa
Damien Millerfae23862002-01-22 23:32:26 +1100282for protocol version 2.
Damien Miller7684ee12000-03-17 23:40:15 +1100283Identity files may also be specified on
284a per-host basis in the configuration file.
285It is possible to have multiple
Damien Miller32aa1441999-10-29 09:15:49 +1000286.Fl i
287options (and multiple identities specified in
288configuration files).
Damien Miller5059d8d2010-03-05 21:31:11 +1100289.Nm
290will also try to load certificate information from the filename obtained
291by appending
292.Pa -cert.pub
293to identity filenames.
Darren Tucker415bddc2007-06-12 23:43:16 +1000294.It Fl K
295Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
296credentials to the server.
Damien Miller32aa1441999-10-29 09:15:49 +1000297.It Fl k
Damien Millere0113cc2003-11-24 13:10:09 +1100298Disables forwarding (delegation) of GSSAPI credentials to the server.
Darren Tucker61776952003-10-02 16:19:47 +1000299.It Fl L Xo
300.Sm off
Damien Millerf91ee4c2005-03-01 21:24:33 +1100301.Oo Ar bind_address : Oc
Darren Tucker61776952003-10-02 16:19:47 +1000302.Ar port : host : hostport
303.Sm on
304.Xc
305Specifies that the given port on the local (client) host is to be
306forwarded to the given host and port on the remote side.
307This works by allocating a socket to listen to
308.Ar port
Damien Millerf91ee4c2005-03-01 21:24:33 +1100309on the local side, optionally bound to the specified
310.Ar bind_address .
311Whenever a connection is made to this port, the
Darren Tucker61776952003-10-02 16:19:47 +1000312connection is forwarded over the secure channel, and a connection is
313made to
314.Ar host
315port
316.Ar hostport
317from the remote machine.
318Port forwardings can also be specified in the configuration file.
Damien Miller7fa96602010-08-05 13:03:13 +1000319IPv6 addresses can be specified by enclosing the address in square brackets.
Damien Millerf91ee4c2005-03-01 21:24:33 +1100320Only the superuser can forward privileged ports.
321By default, the local port is bound in accordance with the
322.Cm GatewayPorts
323setting.
324However, an explicit
325.Ar bind_address
326may be used to bind the connection to a specific address.
327The
328.Ar bind_address
329of
330.Dq localhost
Damien Miller36bf7dd2005-03-02 12:02:47 +1100331indicates that the listening port be bound for local use only, while an
332empty address or
333.Sq *
Damien Millerf91ee4c2005-03-01 21:24:33 +1100334indicates that the port should be available from all interfaces.
Damien Miller32aa1441999-10-29 09:15:49 +1000335.It Fl l Ar login_name
Damien Miller7684ee12000-03-17 23:40:15 +1100336Specifies the user to log in as on the remote machine.
337This also may be specified on a per-host basis in the configuration file.
Damien Miller0e220db2004-06-15 10:34:08 +1000338.It Fl M
339Places the
340.Nm
341client into
342.Dq master
343mode for connection sharing.
Damien Miller88b25522005-12-31 16:23:15 +1100344Multiple
345.Fl M
346options places
347.Nm
348into
349.Dq master
350mode with confirmation required before slave connections are accepted.
Damien Miller0e220db2004-06-15 10:34:08 +1000351Refer to the description of
352.Cm ControlMaster
353in
354.Xr ssh_config 5
355for details.
Damien Miller5d1eceb2004-06-30 22:37:57 +1000356.It Fl m Ar mac_spec
357Additionally, for protocol version 2 a comma-separated list of MAC
358(message authentication code) algorithms can
359be specified in order of preference.
360See the
361.Cm MACs
362keyword for more information.
Darren Tucker61776952003-10-02 16:19:47 +1000363.It Fl N
364Do not execute a remote command.
365This is useful for just forwarding ports
366(protocol version 2 only).
Damien Miller32aa1441999-10-29 09:15:49 +1000367.It Fl n
368Redirects stdin from
369.Pa /dev/null
370(actually, prevents reading from stdin).
371This must be used when
372.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100373is run in the background.
374A common trick is to use this to run X11 programs on a remote machine.
375For example,
Damien Miller32aa1441999-10-29 09:15:49 +1000376.Ic ssh -n shadows.cs.hut.fi emacs &
377will start an emacs on shadows.cs.hut.fi, and the X11
378connection will be automatically forwarded over an encrypted channel.
379The
380.Nm
381program will be put in the background.
382(This does not work if
383.Nm
384needs to ask for a password or passphrase; see also the
385.Fl f
386option.)
Darren Tuckere04644c2004-12-03 14:08:45 +1100387.It Fl O Ar ctl_cmd
388Control an active connection multiplexing master process.
389When the
390.Fl O
391option is specified, the
392.Ar ctl_cmd
393argument is interpreted and passed to the master process.
394Valid commands are:
395.Dq check
Damien Miller388f6fc2010-05-21 14:57:35 +1000396(check that the master process is running),
397.Dq forward
Damien Miller8cb1cda2011-05-05 14:16:56 +1000398(request forwardings without command execution),
Damien Miller1bcbd0a2011-09-22 21:40:45 +1000399.Dq cancel
400(cancel forwardings),
Darren Tuckere04644c2004-12-03 14:08:45 +1100401.Dq exit
Damien Miller8cb1cda2011-05-05 14:16:56 +1000402(request the master to exit), and
Damien Miller6c3eec72011-05-05 14:16:22 +1000403.Dq stop
404(request the master to stop accepting further multiplexing requests).
Damien Miller32aa1441999-10-29 09:15:49 +1000405.It Fl o Ar option
Ben Lindstrom14c62eb2001-08-15 23:25:46 +0000406Can be used to give options in the format used in the configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000407This is useful for specifying options for which there is no separate
Damien Miller7684ee12000-03-17 23:40:15 +1100408command-line flag.
Darren Tucker61776952003-10-02 16:19:47 +1000409For full details of the options listed below, and their possible values, see
410.Xr ssh_config 5 .
411.Pp
412.Bl -tag -width Ds -offset indent -compact
413.It AddressFamily
414.It BatchMode
415.It BindAddress
Damien Miller0faf7472013-10-17 11:47:23 +1100416.It CanonicalDomains
Damien Miller38505592013-10-17 11:48:13 +1100417.It CanonicalizeFallbackLocal
418.It CanonicalizeHostname
419.It CanonicalizeMaxDots
420.It CanonicalizePermittedCNAMEs
Darren Tucker61776952003-10-02 16:19:47 +1000421.It ChallengeResponseAuthentication
422.It CheckHostIP
423.It Cipher
424.It Ciphers
425.It ClearAllForwardings
426.It Compression
427.It CompressionLevel
428.It ConnectionAttempts
Darren Tuckeredae0ec2004-05-02 22:15:52 +1000429.It ConnectTimeout
Damien Miller0e220db2004-06-15 10:34:08 +1000430.It ControlMaster
431.It ControlPath
Damien Millerefad7272011-09-22 21:33:53 +1000432.It ControlPersist
Darren Tucker61776952003-10-02 16:19:47 +1000433.It DynamicForward
Darren Tucker61776952003-10-02 16:19:47 +1000434.It EscapeChar
Darren Tuckere7d4b192006-07-12 22:17:10 +1000435.It ExitOnForwardFailure
jmc@openbsd.org8abd8032014-12-22 09:26:31 +0000436.It FingerprintHash
Darren Tucker61776952003-10-02 16:19:47 +1000437.It ForwardAgent
438.It ForwardX11
Damien Millerefad7272011-09-22 21:33:53 +1000439.It ForwardX11Timeout
Darren Tucker0a118da2003-10-15 15:54:32 +1000440.It ForwardX11Trusted
Darren Tucker61776952003-10-02 16:19:47 +1000441.It GatewayPorts
442.It GlobalKnownHostsFile
443.It GSSAPIAuthentication
444.It GSSAPIDelegateCredentials
Damien Millere1776152005-03-01 21:47:37 +1100445.It HashKnownHosts
Darren Tucker61776952003-10-02 16:19:47 +1000446.It Host
447.It HostbasedAuthentication
djm@openbsd.org46347ed2015-01-30 11:43:14 +0000448.It HostbasedKeyTypes
Darren Tucker61776952003-10-02 16:19:47 +1000449.It HostKeyAlgorithms
450.It HostKeyAlias
451.It HostName
452.It IdentityFile
Damien Millerbd394c32004-03-08 23:12:36 +1100453.It IdentitiesOnly
Damien Miller0a184732010-11-20 15:21:03 +1100454.It IPQoS
Damien Millerefad7272011-09-22 21:33:53 +1000455.It KbdInteractiveAuthentication
Darren Tucker636ca902004-11-05 20:22:00 +1100456.It KbdInteractiveDevices
Damien Miller7fe2b1f2010-09-24 22:11:53 +1000457.It KexAlgorithms
Damien Millerd27b9472005-12-13 19:29:02 +1100458.It LocalCommand
Darren Tucker61776952003-10-02 16:19:47 +1000459.It LocalForward
460.It LogLevel
461.It MACs
Damien Millerd77b81f2013-10-17 11:39:00 +1100462.It Match
Darren Tucker61776952003-10-02 16:19:47 +1000463.It NoHostAuthenticationForLocalhost
464.It NumberOfPasswordPrompts
465.It PasswordAuthentication
Damien Millerd27b9472005-12-13 19:29:02 +1100466.It PermitLocalCommand
Damien Miller7ea845e2010-02-12 09:21:02 +1100467.It PKCS11Provider
Darren Tucker61776952003-10-02 16:19:47 +1000468.It Port
469.It PreferredAuthentications
470.It Protocol
471.It ProxyCommand
Damien Millerf2f6c312013-08-21 02:44:58 +1000472.It ProxyUseFdpass
Darren Tucker61776952003-10-02 16:19:47 +1000473.It PubkeyAuthentication
Darren Tucker62388b22006-01-20 11:31:47 +1100474.It RekeyLimit
Darren Tucker61776952003-10-02 16:19:47 +1000475.It RemoteForward
Damien Millerf4b32aa2011-05-15 08:47:43 +1000476.It RequestTTY
Darren Tucker61776952003-10-02 16:19:47 +1000477.It RhostsRSAAuthentication
478.It RSAAuthentication
Darren Tucker7a6c0662004-05-02 22:14:03 +1000479.It SendEnv
Damien Miller509b0102003-12-17 16:33:10 +1100480.It ServerAliveInterval
481.It ServerAliveCountMax
Damien Miller6d576562014-07-18 15:02:06 +1000482.It StreamLocalBindMask
483.It StreamLocalBindUnlink
Darren Tucker61776952003-10-02 16:19:47 +1000484.It StrictHostKeyChecking
Damien Miller12c150e2003-12-17 16:31:10 +1100485.It TCPKeepAlive
Damien Millerd27b9472005-12-13 19:29:02 +1100486.It Tunnel
487.It TunnelDevice
djm@openbsd.org1d1092b2015-01-26 12:16:36 +0000488.It UpdateHostKeys
Darren Tucker61776952003-10-02 16:19:47 +1000489.It UsePrivilegedPort
490.It User
491.It UserKnownHostsFile
492.It VerifyHostKeyDNS
Damien Miller86399202008-06-30 00:04:31 +1000493.It VisualHostKey
Darren Tucker61776952003-10-02 16:19:47 +1000494.It XAuthLocation
495.El
Damien Miller32aa1441999-10-29 09:15:49 +1000496.It Fl p Ar port
Damien Miller7684ee12000-03-17 23:40:15 +1100497Port to connect to on the remote host.
498This can be specified on a
Damien Miller32aa1441999-10-29 09:15:49 +1000499per-host basis in the configuration file.
djm@openbsd.org68d2dfc2015-03-03 06:48:58 +0000500.It Fl Q Cm cipher | cipher-auth | mac | kex | key | protocol-version
Damien Millerea111192013-04-23 19:24:32 +1000501Queries
502.Nm
Damien Millerd937dc02013-12-05 10:19:54 +1100503for the algorithms supported for the specified version 2.
504The available features are:
505.Ar cipher
Damien Millerea111192013-04-23 19:24:32 +1000506(supported symmetric ciphers),
Damien Millerd937dc02013-12-05 10:19:54 +1100507.Ar cipher-auth
Damien Miller0fde8ac2013-11-21 14:12:23 +1100508(supported symmetric ciphers that support authenticated encryption),
Damien Millerd937dc02013-12-05 10:19:54 +1100509.Ar mac
Damien Millerea111192013-04-23 19:24:32 +1000510(supported message integrity codes),
Damien Millerd937dc02013-12-05 10:19:54 +1100511.Ar kex
Damien Millerea111192013-04-23 19:24:32 +1000512(key exchange algorithms),
Damien Millerd937dc02013-12-05 10:19:54 +1100513.Ar key
djm@openbsd.org68d2dfc2015-03-03 06:48:58 +0000514(key types) and
515.Ar protocol-version
516(supported SSH protocol versions).
Damien Miller32aa1441999-10-29 09:15:49 +1000517.It Fl q
Damien Miller7684ee12000-03-17 23:40:15 +1100518Quiet mode.
Damien Millereb602472008-02-10 22:21:28 +1100519Causes most warning and diagnostic messages to be suppressed.
Darren Tucker61776952003-10-02 16:19:47 +1000520.It Fl R Xo
521.Sm off
Damien Millerf91ee4c2005-03-01 21:24:33 +1100522.Oo Ar bind_address : Oc
Darren Tucker61776952003-10-02 16:19:47 +1000523.Ar port : host : hostport
524.Sm on
525.Xc
Damien Miller32aa1441999-10-29 09:15:49 +1000526Specifies that the given port on the remote (server) host is to be
Damien Miller7684ee12000-03-17 23:40:15 +1100527forwarded to the given host and port on the local side.
528This works by allocating a socket to listen to
Damien Miller32aa1441999-10-29 09:15:49 +1000529.Ar port
530on the remote side, and whenever a connection is made to this port, the
531connection is forwarded over the secure channel, and a connection is
532made to
Damien Miller34132e52000-01-14 15:45:46 +1100533.Ar host
534port
535.Ar hostport
Damien Miller7684ee12000-03-17 23:40:15 +1100536from the local machine.
Damien Millerf91ee4c2005-03-01 21:24:33 +1100537.Pp
Damien Miller7684ee12000-03-17 23:40:15 +1100538Port forwardings can also be specified in the configuration file.
539Privileged ports can be forwarded only when
Damien Miller32aa1441999-10-29 09:15:49 +1000540logging in as root on the remote machine.
Damien Miller70b2d552012-04-22 11:26:10 +1000541IPv6 addresses can be specified by enclosing the address in square brackets.
Damien Millerf91ee4c2005-03-01 21:24:33 +1100542.Pp
543By default, the listening socket on the server will be bound to the loopback
544interface only.
Darren Tucker63917bd2008-11-11 16:33:48 +1100545This may be overridden by specifying a
Damien Millerf91ee4c2005-03-01 21:24:33 +1100546.Ar bind_address .
Damien Miller36bf7dd2005-03-02 12:02:47 +1100547An empty
548.Ar bind_address ,
Damien Millerf91ee4c2005-03-01 21:24:33 +1100549or the address
Damien Miller36bf7dd2005-03-02 12:02:47 +1100550.Ql * ,
Damien Millerf91ee4c2005-03-01 21:24:33 +1100551indicates that the remote socket should listen on all interfaces.
552Specifying a remote
553.Ar bind_address
Damien Miller36bf7dd2005-03-02 12:02:47 +1100554will only succeed if the server's
555.Cm GatewayPorts
Damien Millerf91ee4c2005-03-01 21:24:33 +1100556option is enabled (see
Damien Miller36bf7dd2005-03-02 12:02:47 +1100557.Xr sshd_config 5 ) .
Damien Millere2f4cc52009-02-14 16:33:49 +1100558.Pp
559If the
560.Ar port
561argument is
Damien Miller65fa4ca2009-02-14 16:34:05 +1100562.Ql 0 ,
Damien Millere2f4cc52009-02-14 16:33:49 +1100563the listen port will be dynamically allocated on the server and reported
564to the client at run time.
Damien Miller388f6fc2010-05-21 14:57:35 +1000565When used together with
566.Ic -O forward
567the allocated port will be printed to the standard output.
Darren Tucker7ebfc102004-11-07 20:06:19 +1100568.It Fl S Ar ctl_path
Damien Miller67f30d72010-04-16 15:52:03 +1000569Specifies the location of a control socket for connection sharing,
Damien Miller9c60f242010-03-26 11:28:35 +1100570or the string
571.Dq none
572to disable connection sharing.
Damien Miller0e220db2004-06-15 10:34:08 +1000573Refer to the description of
Darren Tuckerba5c5922004-06-18 16:22:39 +1000574.Cm ControlPath
575and
Damien Miller0e220db2004-06-15 10:34:08 +1000576.Cm ControlMaster
577in
578.Xr ssh_config 5
579for details.
Darren Tucker61776952003-10-02 16:19:47 +1000580.It Fl s
581May be used to request invocation of a subsystem on the remote system.
582Subsystems are a feature of the SSH2 protocol which facilitate the use
583of SSH as a secure transport for other applications (eg.\&
584.Xr sftp 1 ) .
585The subsystem is specified as the remote command.
586.It Fl T
dtucker@openbsd.orgf8484da2015-05-06 05:45:17 +0000587Disable pseudo-terminal allocation.
Darren Tucker61776952003-10-02 16:19:47 +1000588.It Fl t
dtucker@openbsd.orgf8484da2015-05-06 05:45:17 +0000589Force pseudo-terminal allocation.
Darren Tucker61776952003-10-02 16:19:47 +1000590This can be used to execute arbitrary
591screen-based programs on a remote machine, which can be very useful,
Damien Miller208f1ed2006-03-15 11:56:03 +1100592e.g. when implementing menu services.
Darren Tucker61776952003-10-02 16:19:47 +1000593Multiple
594.Fl t
595options force tty allocation, even if
Ben Lindstrom19ceb172001-09-12 17:54:24 +0000596.Nm
Darren Tucker61776952003-10-02 16:19:47 +1000597has no local tty.
598.It Fl V
599Display the version number and exit.
600.It Fl v
601Verbose mode.
602Causes
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000603.Nm
Darren Tucker61776952003-10-02 16:19:47 +1000604to print debugging messages about its progress.
605This is helpful in
606debugging connection, authentication, and configuration problems.
607Multiple
608.Fl v
609options increase the verbosity.
610The maximum is 3.
Darren Tucker7ad8dd22010-01-12 19:40:27 +1100611.It Fl W Ar host : Ns Ar port
612Requests that standard input and output on the client be forwarded to
613.Ar host
614on
615.Ar port
616over the secure channel.
617Implies
618.Fl N ,
619.Fl T ,
620.Cm ExitOnForwardFailure
621and
Damien Miller36378c62012-06-20 21:53:25 +1000622.Cm ClearAllForwardings .
623Works with Protocol version 2 only.
Damien Miller991dba42006-07-10 20:16:27 +1000624.It Fl w Xo
625.Ar local_tun Ns Op : Ns Ar remote_tun
626.Xc
627Requests
628tunnel
629device forwarding with the specified
Damien Millerd27b9472005-12-13 19:29:02 +1100630.Xr tun 4
Damien Miller991dba42006-07-10 20:16:27 +1000631devices between the client
632.Pq Ar local_tun
633and the server
634.Pq Ar remote_tun .
635.Pp
Damien Millercf1e3422005-12-24 14:56:04 +1100636The devices may be specified by numerical ID or the keyword
637.Dq any ,
638which uses the next available tunnel device.
Damien Miller991dba42006-07-10 20:16:27 +1000639If
640.Ar remote_tun
641is not specified, it defaults to
642.Dq any .
Damien Millercf1e3422005-12-24 14:56:04 +1100643See also the
Damien Millerd27b9472005-12-13 19:29:02 +1100644.Cm Tunnel
Damien Miller991dba42006-07-10 20:16:27 +1000645and
646.Cm TunnelDevice
647directives in
Damien Millerd27b9472005-12-13 19:29:02 +1100648.Xr ssh_config 5 .
Damien Miller991dba42006-07-10 20:16:27 +1000649If the
650.Cm Tunnel
651directive is unset, it is set to the default tunnel mode, which is
652.Dq point-to-point .
Darren Tucker61776952003-10-02 16:19:47 +1000653.It Fl X
654Enables X11 forwarding.
655This can also be specified on a per-host basis in a configuration file.
656.Pp
657X11 forwarding should be enabled with caution.
658Users with the ability to bypass file permissions on the remote host
659(for the user's X authorization database)
660can access the local X11 display through the forwarded connection.
661An attacker may then be able to perform activities such as keystroke monitoring.
Damien Miller947219e2005-03-02 13:22:30 +1100662.Pp
Damien Millerb022b232005-03-05 11:22:36 +1100663For this reason, X11 forwarding is subjected to X11 SECURITY extension
Damien Miller947219e2005-03-02 13:22:30 +1100664restrictions by default.
665Please refer to the
666.Nm
667.Fl Y
668option and the
669.Cm ForwardX11Trusted
670directive in
671.Xr ssh_config 5
672for more information.
Darren Tucker61776952003-10-02 16:19:47 +1000673.It Fl x
674Disables X11 forwarding.
Darren Tucker0a118da2003-10-15 15:54:32 +1000675.It Fl Y
676Enables trusted X11 forwarding.
Damien Miller947219e2005-03-02 13:22:30 +1100677Trusted X11 forwardings are not subjected to the X11 SECURITY extension
678controls.
Damien Millere272a5b2008-11-03 19:22:37 +1100679.It Fl y
680Send log information using the
681.Xr syslog 3
682system module.
683By default this information is sent to stderr.
Damien Miller32aa1441999-10-29 09:15:49 +1000684.El
Damien Millere9b333a2005-12-24 14:53:04 +1100685.Pp
686.Nm
687may additionally obtain configuration data from
688a per-user configuration file and a system-wide configuration file.
689The file format and configuration options are described in
690.Xr ssh_config 5 .
Damien Millerc93a8132005-12-24 14:52:13 +1100691.Sh AUTHENTICATION
Darren Tucker94299ec2006-01-20 11:30:14 +1100692The OpenSSH SSH client supports SSH protocols 1 and 2.
Darren Tucker7a4a7652009-10-11 21:51:40 +1100693The default is to use protocol 2 only,
694though this can be changed via the
Damien Millerc93a8132005-12-24 14:52:13 +1100695.Cm Protocol
696option in
Darren Tucker7a4a7652009-10-11 21:51:40 +1100697.Xr ssh_config 5
698or the
Damien Millerc93a8132005-12-24 14:52:13 +1100699.Fl 1
700and
701.Fl 2
702options (see above).
703Both protocols support similar authentication methods,
Darren Tucker7a4a7652009-10-11 21:51:40 +1100704but protocol 2 is the default since
Damien Millerc93a8132005-12-24 14:52:13 +1100705it provides additional mechanisms for confidentiality
706(the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
Damien Miller20bd4532011-08-06 06:17:30 +1000707and integrity (hmac-md5, hmac-sha1,
708hmac-sha2-256, hmac-sha2-512,
Darren Tucker427e4092012-10-05 11:02:39 +1000709umac-64, umac-128, hmac-ripemd160).
Damien Millerc93a8132005-12-24 14:52:13 +1100710Protocol 1 lacks a strong mechanism for ensuring the
711integrity of the connection.
712.Pp
713The methods available for authentication are:
Damien Millerfbc94c82006-06-13 13:03:16 +1000714GSSAPI-based authentication,
Damien Millerc93a8132005-12-24 14:52:13 +1100715host-based authentication,
716public key authentication,
717challenge-response authentication,
718and password authentication.
719Authentication methods are tried in the order specified above,
720though protocol 2 has a configuration option to change the default order:
721.Cm PreferredAuthentications .
722.Pp
723Host-based authentication works as follows:
Darren Tuckerd3877b92005-12-20 16:09:36 +1100724If the machine the user logs in from is listed in
725.Pa /etc/hosts.equiv
726or
727.Pa /etc/shosts.equiv
728on the remote machine, and the user names are
729the same on both sides, or if the files
730.Pa ~/.rhosts
731or
732.Pa ~/.shosts
733exist in the user's home directory on the
734remote machine and contain a line containing the name of the client
735machine and the name of the user on that machine, the user is
Damien Millerc93a8132005-12-24 14:52:13 +1100736considered for login.
737Additionally, the server
738.Em must
739be able to verify the client's
740host key (see the description of
Darren Tuckerd3877b92005-12-20 16:09:36 +1100741.Pa /etc/ssh/ssh_known_hosts
742and
Damien Millerc93a8132005-12-24 14:52:13 +1100743.Pa ~/.ssh/known_hosts ,
744below)
745for login to be permitted.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100746This authentication method closes security holes due to IP
Damien Millerc93a8132005-12-24 14:52:13 +1100747spoofing, DNS spoofing, and routing spoofing.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100748[Note to the administrator:
749.Pa /etc/hosts.equiv ,
750.Pa ~/.rhosts ,
751and the rlogin/rsh protocol in general, are inherently insecure and should be
752disabled if security is desired.]
753.Pp
Damien Millerc93a8132005-12-24 14:52:13 +1100754Public key authentication works as follows:
755The scheme is based on public-key cryptography,
756using cryptosystems
757where encryption and decryption are done using separate keys,
758and it is unfeasible to derive the decryption key from the encryption key.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100759The idea is that each user creates a public/private
760key pair for authentication purposes.
761The server knows the public key, and only the user knows the private key.
Damien Millerc93a8132005-12-24 14:52:13 +1100762.Nm
763implements public key authentication protocol automatically,
sobrado@openbsd.orgf70b22b2014-08-30 15:33:50 +0000764using one of the DSA, ECDSA, Ed25519 or RSA algorithms.
Damien Millerc93a8132005-12-24 14:52:13 +1100765Protocol 1 is restricted to using only RSA keys,
Damien Millereb8b60e2010-08-31 22:41:14 +1000766but protocol 2 may use any.
Damien Millerfecfd112013-07-18 16:11:50 +1000767The HISTORY section of
Damien Millerc93a8132005-12-24 14:52:13 +1100768.Xr ssl 8
Damien Millerd4427902010-09-10 11:15:10 +1000769contains a brief discussion of the DSA and RSA algorithms.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100770.Pp
771The file
772.Pa ~/.ssh/authorized_keys
773lists the public keys that are permitted for logging in.
774When the user logs in, the
775.Nm
776program tells the server which key pair it would like to use for
777authentication.
Damien Millerc93a8132005-12-24 14:52:13 +1100778The client proves that it has access to the private key
779and the server checks that the corresponding public key
780is authorized to accept the account.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100781.Pp
Damien Millerc93a8132005-12-24 14:52:13 +1100782The user creates his/her key pair by running
Darren Tuckerd3877b92005-12-20 16:09:36 +1100783.Xr ssh-keygen 1 .
784This stores the private key in
785.Pa ~/.ssh/identity
Damien Millerc93a8132005-12-24 14:52:13 +1100786(protocol 1),
787.Pa ~/.ssh/id_dsa
788(protocol 2 DSA),
Damien Millereb8b60e2010-08-31 22:41:14 +1000789.Pa ~/.ssh/id_ecdsa
790(protocol 2 ECDSA),
Damien Miller8ba0ead2013-12-18 17:46:27 +1100791.Pa ~/.ssh/id_ed25519
sobrado@openbsd.orgf70b22b2014-08-30 15:33:50 +0000792(protocol 2 Ed25519),
Damien Millerc93a8132005-12-24 14:52:13 +1100793or
794.Pa ~/.ssh/id_rsa
795(protocol 2 RSA)
Darren Tuckerd3877b92005-12-20 16:09:36 +1100796and stores the public key in
797.Pa ~/.ssh/identity.pub
Damien Millerc93a8132005-12-24 14:52:13 +1100798(protocol 1),
799.Pa ~/.ssh/id_dsa.pub
800(protocol 2 DSA),
Damien Millereb8b60e2010-08-31 22:41:14 +1000801.Pa ~/.ssh/id_ecdsa.pub
802(protocol 2 ECDSA),
Damien Miller8ba0ead2013-12-18 17:46:27 +1100803.Pa ~/.ssh/id_ed25519.pub
sobrado@openbsd.orgf70b22b2014-08-30 15:33:50 +0000804(protocol 2 Ed25519),
Damien Millerc93a8132005-12-24 14:52:13 +1100805or
806.Pa ~/.ssh/id_rsa.pub
807(protocol 2 RSA)
Darren Tuckerd3877b92005-12-20 16:09:36 +1100808in the user's home directory.
Damien Millerc93a8132005-12-24 14:52:13 +1100809The user should then copy the public key
Darren Tuckerd3877b92005-12-20 16:09:36 +1100810to
811.Pa ~/.ssh/authorized_keys
Damien Millerc93a8132005-12-24 14:52:13 +1100812in his/her home directory on the remote machine.
813The
Darren Tuckerd3877b92005-12-20 16:09:36 +1100814.Pa authorized_keys
815file corresponds to the conventional
816.Pa ~/.rhosts
817file, and has one key
Damien Millerc93a8132005-12-24 14:52:13 +1100818per line, though the lines can be very long.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100819After this, the user can log in without giving the password.
820.Pp
Damien Miller922b5412010-03-05 21:30:54 +1100821A variation on public key authentication
822is available in the form of certificate authentication:
823instead of a set of public/private keys,
824signed certificates are used.
825This has the advantage that a single trusted certification authority
826can be used in place of many public/private keys.
Damien Millerfecfd112013-07-18 16:11:50 +1000827See the CERTIFICATES section of
Damien Miller922b5412010-03-05 21:30:54 +1100828.Xr ssh-keygen 1
829for more information.
830.Pp
831The most convenient way to use public key or certificate authentication
832may be with an authentication agent.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100833See
834.Xr ssh-agent 1
835for more information.
836.Pp
Damien Millerc93a8132005-12-24 14:52:13 +1100837Challenge-response authentication works as follows:
838The server sends an arbitrary
839.Qq challenge
840text, and prompts for a response.
841Protocol 2 allows multiple challenges and responses;
842protocol 1 is restricted to just one challenge/response.
843Examples of challenge-response authentication include
Damien Millerb7727df2013-08-21 02:43:49 +1000844.Bx
845Authentication (see
Damien Millerc93a8132005-12-24 14:52:13 +1100846.Xr login.conf 5 )
Damien Millerb7727df2013-08-21 02:43:49 +1000847and PAM (some
848.Pf non- Ox
849systems).
Damien Millerc93a8132005-12-24 14:52:13 +1100850.Pp
851Finally, if other authentication methods fail,
Darren Tuckerd3877b92005-12-20 16:09:36 +1100852.Nm
853prompts the user for a password.
854The password is sent to the remote
855host for checking; however, since all communications are encrypted,
856the password cannot be seen by someone listening on the network.
Damien Miller48c94ab2006-01-02 23:38:00 +1100857.Pp
858.Nm
859automatically maintains and checks a database containing
860identification for all hosts it has ever been used with.
861Host keys are stored in
862.Pa ~/.ssh/known_hosts
863in the user's home directory.
864Additionally, the file
865.Pa /etc/ssh/ssh_known_hosts
866is automatically checked for known hosts.
867Any new hosts are automatically added to the user's file.
868If a host's identification ever changes,
869.Nm
870warns about this and disables password authentication to prevent
871server spoofing or man-in-the-middle attacks,
872which could otherwise be used to circumvent the encryption.
873The
874.Cm StrictHostKeyChecking
875option can be used to control logins to machines whose
876host key is not known or has changed.
877.Pp
Darren Tuckerd3877b92005-12-20 16:09:36 +1100878When the user's identity has been accepted by the server, the server
dtucker@openbsd.orgf8484da2015-05-06 05:45:17 +0000879either executes the given command in a non-interactive session or,
880if no command has been specified, logs into the machine and gives
881the user a normal shell as an interactive session.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100882All communication with
883the remote command or shell will be automatically encrypted.
884.Pp
dtucker@openbsd.orgf8484da2015-05-06 05:45:17 +0000885If an interactive session is requested
886.Nm
887by default will only request a pseudo-terminal (pty) for interactive
888sessions when the client has one.
889The flags
890.Fl T
891and
892.Fl t
893can be used to override this behaviour.
894.Pp
895If a pseudo-terminal has been allocated the
Darren Tuckerd3877b92005-12-20 16:09:36 +1100896user may use the escape characters noted below.
897.Pp
dtucker@openbsd.orgf8484da2015-05-06 05:45:17 +0000898If no pseudo-terminal has been allocated,
Darren Tuckerd3877b92005-12-20 16:09:36 +1100899the session is transparent and can be used to reliably transfer binary data.
900On most systems, setting the escape character to
901.Dq none
902will also make the session transparent even if a tty is used.
903.Pp
904The session terminates when the command or shell on the remote
Damien Miller8bfaf932006-01-14 10:09:30 +1100905machine exits and all X11 and TCP connections have been closed.
Damien Miller52d20612005-12-24 14:52:36 +1100906.Sh ESCAPE CHARACTERS
Darren Tuckerd3877b92005-12-20 16:09:36 +1100907When a pseudo-terminal has been requested,
908.Nm
909supports a number of functions through the use of an escape character.
910.Pp
911A single tilde character can be sent as
912.Ic ~~
913or by following the tilde by a character other than those described below.
914The escape character must always follow a newline to be interpreted as
915special.
916The escape character can be changed in configuration files using the
917.Cm EscapeChar
918configuration directive or on the command line by the
919.Fl e
920option.
921.Pp
922The supported escapes (assuming the default
923.Ql ~ )
924are:
925.Bl -tag -width Ds
926.It Cm ~.
927Disconnect.
928.It Cm ~^Z
929Background
Damien Miller1164c292006-01-02 23:38:37 +1100930.Nm .
Darren Tuckerd3877b92005-12-20 16:09:36 +1100931.It Cm ~#
932List forwarded connections.
933.It Cm ~&
934Background
935.Nm
936at logout when waiting for forwarded connection / X11 sessions to terminate.
937.It Cm ~?
938Display a list of escape characters.
939.It Cm ~B
940Send a BREAK to the remote system
941(only useful for SSH protocol version 2 and if the peer supports it).
942.It Cm ~C
943Open command line.
944Currently this allows the addition of port forwardings using the
Damien Miller0164cb82008-11-05 16:30:31 +1100945.Fl L ,
Darren Tuckerd3877b92005-12-20 16:09:36 +1100946.Fl R
Damien Miller0164cb82008-11-05 16:30:31 +1100947and
948.Fl D
Damien Miller329cb012005-12-24 14:53:23 +1100949options (see above).
Damien Millerff773642011-09-22 21:39:48 +1000950It also allows the cancellation of existing port-forwardings
951with
Damien Miller57e8ad32006-07-10 20:20:52 +1000952.Sm off
Damien Millerff773642011-09-22 21:39:48 +1000953.Fl KL Oo Ar bind_address : Oc Ar port
Damien Miller57e8ad32006-07-10 20:20:52 +1000954.Sm on
Damien Millerff773642011-09-22 21:39:48 +1000955for local,
956.Sm off
957.Fl KR Oo Ar bind_address : Oc Ar port
958.Sm on
959for remote and
960.Sm off
961.Fl KD Oo Ar bind_address : Oc Ar port
962.Sm on
963for dynamic port-forwardings.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100964.Ic !\& Ns Ar command
965allows the user to execute a local command if the
966.Ic PermitLocalCommand
967option is enabled in
968.Xr ssh_config 5 .
969Basic help is available, using the
970.Fl h
971option.
972.It Cm ~R
973Request rekeying of the connection
974(only useful for SSH protocol version 2 and if the peer supports it).
Darren Tucker50a48d02012-09-06 21:25:37 +1000975.It Cm ~V
976Decrease the verbosity
977.Pq Ic LogLevel
978when errors are being written to stderr.
979.It Cm ~v
Darren Tucker83d0af62012-09-07 11:21:03 +1000980Increase the verbosity
Darren Tucker50a48d02012-09-06 21:25:37 +1000981.Pq Ic LogLevel
982when errors are being written to stderr.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100983.El
Damien Millerf3177182006-01-14 10:09:13 +1100984.Sh TCP FORWARDING
985Forwarding of arbitrary TCP connections over the secure channel can
986be specified either on the command line or in a configuration file.
987One possible application of TCP forwarding is a secure connection to a
988mail server; another is going through firewalls.
989.Pp
990In the example below, we look at encrypting communication between
991an IRC client and server, even though the IRC server does not directly
992support encrypted communications.
993This works as follows:
994the user connects to the remote host using
995.Nm ,
996specifying a port to be used to forward connections
997to the remote server.
998After that it is possible to start the service which is to be encrypted
999on the client machine,
1000connecting to the same local port,
1001and
1002.Nm
1003will encrypt and forward the connection.
1004.Pp
1005The following example tunnels an IRC session from client machine
1006.Dq 127.0.0.1
1007(localhost)
1008to remote server
1009.Dq server.example.com :
1010.Bd -literal -offset 4n
1011$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
1012$ irc -c '#users' -p 1234 pinky 127.0.0.1
1013.Ed
1014.Pp
1015This tunnels a connection to IRC server
1016.Dq server.example.com ,
1017joining channel
1018.Dq #users ,
1019nickname
1020.Dq pinky ,
1021using port 1234.
1022It doesn't matter which port is used,
1023as long as it's greater than 1023
1024(remember, only root can open sockets on privileged ports)
1025and doesn't conflict with any ports already in use.
1026The connection is forwarded to port 6667 on the remote server,
1027since that's the standard port for IRC services.
1028.Pp
1029The
1030.Fl f
1031option backgrounds
1032.Nm
1033and the remote command
1034.Dq sleep 10
1035is specified to allow an amount of time
1036(10 seconds, in the example)
1037to start the service which is to be tunnelled.
1038If no connections are made within the time specified,
1039.Nm
1040will exit.
Damien Millerf3177182006-01-14 10:09:13 +11001041.Sh X11 FORWARDING
Darren Tuckerd3877b92005-12-20 16:09:36 +11001042If the
1043.Cm ForwardX11
1044variable is set to
1045.Dq yes
1046(or see the description of the
Damien Millerd7f308f2005-12-24 14:55:16 +11001047.Fl X ,
1048.Fl x ,
Darren Tuckerd3877b92005-12-20 16:09:36 +11001049and
Damien Millerd7f308f2005-12-24 14:55:16 +11001050.Fl Y
Damien Miller9a765b22005-12-24 14:53:44 +11001051options above)
Darren Tuckerd3877b92005-12-20 16:09:36 +11001052and the user is using X11 (the
1053.Ev DISPLAY
1054environment variable is set), the connection to the X11 display is
1055automatically forwarded to the remote side in such a way that any X11
1056programs started from the shell (or command) will go through the
1057encrypted channel, and the connection to the real X server will be made
1058from the local machine.
1059The user should not manually set
1060.Ev DISPLAY .
1061Forwarding of X11 connections can be
1062configured on the command line or in configuration files.
1063.Pp
1064The
1065.Ev DISPLAY
1066value set by
1067.Nm
1068will point to the server machine, but with a display number greater than zero.
1069This is normal, and happens because
1070.Nm
1071creates a
1072.Dq proxy
1073X server on the server machine for forwarding the
1074connections over the encrypted channel.
1075.Pp
1076.Nm
1077will also automatically set up Xauthority data on the server machine.
1078For this purpose, it will generate a random authorization cookie,
1079store it in Xauthority on the server, and verify that any forwarded
1080connections carry this cookie and replace it by the real cookie when
1081the connection is opened.
1082The real authentication cookie is never
1083sent to the server machine (and no cookies are sent in the plain).
1084.Pp
1085If the
1086.Cm ForwardAgent
1087variable is set to
1088.Dq yes
1089(or see the description of the
1090.Fl A
1091and
1092.Fl a
Damien Miller9a765b22005-12-24 14:53:44 +11001093options above) and
Darren Tuckerd3877b92005-12-20 16:09:36 +11001094the user is using an authentication agent, the connection to the agent
1095is automatically forwarded to the remote side.
Damien Millerbbc59092006-01-31 21:46:51 +11001096.Sh VERIFYING HOST KEYS
1097When connecting to a server for the first time,
1098a fingerprint of the server's public key is presented to the user
1099(unless the option
1100.Cm StrictHostKeyChecking
1101has been disabled).
1102Fingerprints can be determined using
1103.Xr ssh-keygen 1 :
1104.Pp
1105.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1106.Pp
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001107If the fingerprint is already known, it can be matched
1108and the key can be accepted or rejected.
djm@openbsd.orgf9487372015-05-22 05:28:45 +00001109If only legacy (MD5) fingerprints for the server are available, the
1110.Xr ssh-keygen 1
1111.Fl E
1112option may be used to downgrade the fingerprint algorithm to match.
1113.Pp
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001114Because of the difficulty of comparing host keys
djm@openbsd.org56d1c832014-12-21 22:27:55 +00001115just by looking at fingerprint strings,
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001116there is also support to compare host keys visually,
1117using
1118.Em random art .
1119By setting the
Damien Miller10288242008-06-30 00:04:03 +10001120.Cm VisualHostKey
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001121option to
Damien Miller10288242008-06-30 00:04:03 +10001122.Dq yes ,
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001123a small ASCII graphic gets displayed on every login to a server, no matter
1124if the session itself is interactive or not.
1125By learning the pattern a known server produces, a user can easily
1126find out that the host key has changed when a completely different pattern
1127is displayed.
1128Because these patterns are not unambiguous however, a pattern that looks
1129similar to the pattern remembered only gives a good probability that the
1130host key is the same, not guaranteed proof.
1131.Pp
1132To get a listing of the fingerprints along with their random art for
1133all known hosts, the following command line can be used:
1134.Pp
1135.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1136.Pp
Damien Millerbbc59092006-01-31 21:46:51 +11001137If the fingerprint is unknown,
1138an alternative method of verification is available:
1139SSH fingerprints verified by DNS.
1140An additional resource record (RR),
1141SSHFP,
1142is added to a zonefile
1143and the connecting client is able to match the fingerprint
1144with that of the key presented.
1145.Pp
1146In this example, we are connecting a client to a server,
1147.Dq host.example.com .
1148The SSHFP resource records should first be added to the zonefile for
1149host.example.com:
1150.Bd -literal -offset indent
Damien Millera1b3d632006-03-26 00:07:02 +11001151$ ssh-keygen -r host.example.com.
Damien Millerbbc59092006-01-31 21:46:51 +11001152.Ed
1153.Pp
1154The output lines will have to be added to the zonefile.
1155To check that the zone is answering fingerprint queries:
1156.Pp
1157.Dl $ dig -t SSHFP host.example.com
1158.Pp
1159Finally the client connects:
1160.Bd -literal -offset indent
1161$ ssh -o "VerifyHostKeyDNS ask" host.example.com
1162[...]
1163Matching host key fingerprint found in DNS.
1164Are you sure you want to continue connecting (yes/no)?
1165.Ed
1166.Pp
1167See the
1168.Cm VerifyHostKeyDNS
1169option in
1170.Xr ssh_config 5
1171for more information.
Darren Tucker248dd132006-01-20 11:30:58 +11001172.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1173.Nm
1174contains support for Virtual Private Network (VPN) tunnelling
1175using the
1176.Xr tun 4
1177network pseudo-device,
1178allowing two networks to be joined securely.
1179The
1180.Xr sshd_config 5
1181configuration option
1182.Cm PermitTunnel
1183controls whether the server supports this,
1184and at what level (layer 2 or 3 traffic).
1185.Pp
1186The following example would connect client network 10.0.50.0/24
Damien Miller3975ee22006-11-05 05:31:33 +11001187with remote network 10.0.99.0/24 using a point-to-point connection
1188from 10.1.1.1 to 10.1.1.2,
1189provided that the SSH server running on the gateway to the remote network,
1190at 192.168.1.15, allows it.
1191.Pp
1192On the client:
Darren Tucker248dd132006-01-20 11:30:58 +11001193.Bd -literal -offset indent
1194# ssh -f -w 0:1 192.168.1.15 true
Damien Miller3975ee22006-11-05 05:31:33 +11001195# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1196# route add 10.0.99.0/24 10.1.1.2
1197.Ed
1198.Pp
1199On the server:
1200.Bd -literal -offset indent
1201# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1202# route add 10.0.50.0/24 10.1.1.1
Darren Tucker248dd132006-01-20 11:30:58 +11001203.Ed
1204.Pp
1205Client access may be more finely tuned via the
1206.Pa /root/.ssh/authorized_keys
1207file (see below) and the
1208.Cm PermitRootLogin
1209server option.
Damien Millere93eaaa2006-03-15 11:05:59 +11001210The following entry would permit connections on
Darren Tucker248dd132006-01-20 11:30:58 +11001211.Xr tun 4
Damien Millere93eaaa2006-03-15 11:05:59 +11001212device 1 from user
Darren Tucker248dd132006-01-20 11:30:58 +11001213.Dq jane
Damien Millere93eaaa2006-03-15 11:05:59 +11001214and on tun device 2 from user
Darren Tucker248dd132006-01-20 11:30:58 +11001215.Dq john ,
1216if
1217.Cm PermitRootLogin
1218is set to
1219.Dq forced-commands-only :
1220.Bd -literal -offset 2n
1221tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
Damien Miller9f67a212006-03-15 11:05:35 +11001222tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
Darren Tucker248dd132006-01-20 11:30:58 +11001223.Ed
1224.Pp
Darren Tuckerffe88e12006-10-18 07:53:06 +10001225Since an SSH-based setup entails a fair amount of overhead,
Darren Tucker248dd132006-01-20 11:30:58 +11001226it may be more suited to temporary setups,
1227such as for wireless VPNs.
1228More permanent VPNs are better provided by tools such as
1229.Xr ipsecctl 8
1230and
1231.Xr isakmpd 8 .
Damien Miller32aa1441999-10-29 09:15:49 +10001232.Sh ENVIRONMENT
1233.Nm
1234will normally set the following environment variables:
Damien Miller6aa22902006-01-06 14:48:34 +11001235.Bl -tag -width "SSH_ORIGINAL_COMMAND"
Damien Miller32aa1441999-10-29 09:15:49 +10001236.It Ev DISPLAY
1237The
1238.Ev DISPLAY
Damien Miller7684ee12000-03-17 23:40:15 +11001239variable indicates the location of the X11 server.
Damien Miller22c77262000-04-13 12:26:34 +10001240It is automatically set by
Damien Miller32aa1441999-10-29 09:15:49 +10001241.Nm
1242to point to a value of the form
Damien Miller14af93e2006-01-02 23:38:21 +11001243.Dq hostname:n ,
1244where
1245.Dq hostname
1246indicates the host where the shell runs, and
1247.Sq n
1248is an integer \*(Ge 1.
Damien Miller7684ee12000-03-17 23:40:15 +11001249.Nm
1250uses this special value to forward X11 connections over the secure
1251channel.
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001252The user should normally not set
1253.Ev DISPLAY
1254explicitly, as that
Damien Miller32aa1441999-10-29 09:15:49 +10001255will render the X11 connection insecure (and will require the user to
1256manually copy any required authorization cookies).
1257.It Ev HOME
1258Set to the path of the user's home directory.
1259.It Ev LOGNAME
1260Synonym for
1261.Ev USER ;
1262set for compatibility with systems that use this variable.
1263.It Ev MAIL
Ben Lindstrome59433d2001-09-12 16:41:37 +00001264Set to the path of the user's mailbox.
Damien Miller7684ee12000-03-17 23:40:15 +11001265.It Ev PATH
Damien Miller32aa1441999-10-29 09:15:49 +10001266Set to the default
1267.Ev PATH ,
1268as specified when compiling
Damien Miller1164c292006-01-02 23:38:37 +11001269.Nm .
Ben Lindstrom5bf5d672001-07-04 04:31:38 +00001270.It Ev SSH_ASKPASS
1271If
1272.Nm
1273needs a passphrase, it will read the passphrase from the current
1274terminal if it was run from a terminal.
1275If
1276.Nm
1277does not have a terminal associated with it but
1278.Ev DISPLAY
1279and
1280.Ev SSH_ASKPASS
1281are set, it will execute the program specified by
1282.Ev SSH_ASKPASS
1283and open an X11 window to read the passphrase.
1284This is particularly useful when calling
1285.Nm
1286from a
Darren Tucker4e4fe002004-11-05 20:01:03 +11001287.Pa .xsession
Ben Lindstrom5bf5d672001-07-04 04:31:38 +00001288or related script.
1289(Note that on some machines it
1290may be necessary to redirect the input from
1291.Pa /dev/null
1292to make this work.)
Damien Miller32aa1441999-10-29 09:15:49 +10001293.It Ev SSH_AUTH_SOCK
Damien Miller14af93e2006-01-02 23:38:21 +11001294Identifies the path of a
1295.Ux Ns -domain
1296socket used to communicate with the agent.
Damien Millerf37e2462002-09-19 11:47:55 +10001297.It Ev SSH_CONNECTION
1298Identifies the client and server ends of the connection.
Damien Miller7684ee12000-03-17 23:40:15 +11001299The variable contains
Damien Miller14af93e2006-01-02 23:38:21 +11001300four space-separated values: client IP address, client port number,
1301server IP address, and server port number.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001302.It Ev SSH_ORIGINAL_COMMAND
Damien Miller14af93e2006-01-02 23:38:21 +11001303This variable contains the original command line if a forced command
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001304is executed.
1305It can be used to extract the original arguments.
Damien Miller32aa1441999-10-29 09:15:49 +10001306.It Ev SSH_TTY
1307This is set to the name of the tty (path to the device) associated
Damien Miller7684ee12000-03-17 23:40:15 +11001308with the current shell or command.
1309If the current session has no tty,
Damien Miller32aa1441999-10-29 09:15:49 +10001310this variable is not set.
1311.It Ev TZ
Damien Miller6dbdb6a2005-12-13 19:25:43 +11001312This variable is set to indicate the present time zone if it
Damien Miller208f1ed2006-03-15 11:56:03 +11001313was set when the daemon was started (i.e. the daemon passes the value
Damien Miller32aa1441999-10-29 09:15:49 +10001314on to new connections).
1315.It Ev USER
1316Set to the name of the user logging in.
1317.El
1318.Pp
Damien Miller22c77262000-04-13 12:26:34 +10001319Additionally,
Damien Miller32aa1441999-10-29 09:15:49 +10001320.Nm
Damien Miller22c77262000-04-13 12:26:34 +10001321reads
Damien Miller167ea5d2005-05-26 12:04:02 +10001322.Pa ~/.ssh/environment ,
Damien Miller32aa1441999-10-29 09:15:49 +10001323and adds lines of the format
1324.Dq VARNAME=value
Damien Miller14af93e2006-01-02 23:38:21 +11001325to the environment if the file exists and users are allowed to
Ben Lindstromdc7adf22002-08-20 18:38:02 +00001326change their environment.
Darren Tucker61776952003-10-02 16:19:47 +10001327For more information, see the
Ben Lindstromdc7adf22002-08-20 18:38:02 +00001328.Cm PermitUserEnvironment
Ben Lindstrombd9bf382002-08-20 18:54:20 +00001329option in
Ben Lindstromdc7adf22002-08-20 18:38:02 +00001330.Xr sshd_config 5 .
Damien Miller32aa1441999-10-29 09:15:49 +10001331.Sh FILES
Damien Miller7655f5c2006-01-06 14:48:18 +11001332.Bl -tag -width Ds -compact
Damien Millerafdae612010-08-31 22:31:14 +10001333.It Pa ~/.rhosts
Damien Miller1bcdb502006-01-06 14:49:38 +11001334This file is used for host-based authentication (see above).
Ben Lindstromebd888d2001-03-05 05:49:29 +00001335On some machines this file may need to be
Damien Miller1bcdb502006-01-06 14:49:38 +11001336world-readable if the user's home directory is on an NFS partition,
Damien Miller32aa1441999-10-29 09:15:49 +10001337because
1338.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001339reads it as root.
1340Additionally, this file must be owned by the user,
1341and must not have write permissions for anyone else.
1342The recommended
Damien Miller32aa1441999-10-29 09:15:49 +10001343permission for most machines is read/write for the user, and not
1344accessible by others.
1345.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001346.It Pa ~/.shosts
Damien Miller1bcdb502006-01-06 14:49:38 +11001347This file is used in exactly the same way as
1348.Pa .rhosts ,
1349but allows host-based authentication without permitting login with
1350rlogin/rsh.
Damien Miller7655f5c2006-01-06 14:48:18 +11001351.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001352.It Pa ~/.ssh/
Damien Miller520e6152008-02-10 22:46:22 +11001353This directory is the default location for all user-specific configuration
1354and authentication information.
1355There is no general requirement to keep the entire contents of this directory
1356secret, but the recommended permissions are read/write/execute for the user,
1357and not accessible by others.
1358.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001359.It Pa ~/.ssh/authorized_keys
sobrado@openbsd.orgf70b22b2014-08-30 15:33:50 +00001360Lists the public keys (DSA, ECDSA, Ed25519, RSA)
Damien Miller8ba0ead2013-12-18 17:46:27 +11001361that can be used for logging in as this user.
Damien Millerfb8ea742006-01-06 14:48:52 +11001362The format of this file is described in the
1363.Xr sshd 8
1364manual page.
Damien Millerfb8ea742006-01-06 14:48:52 +11001365This file is not highly sensitive, but the recommended
1366permissions are read/write for the user, and not accessible by others.
1367.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001368.It Pa ~/.ssh/config
Damien Millerfb8ea742006-01-06 14:48:52 +11001369This is the per-user configuration file.
1370The file format and configuration options are described in
1371.Xr ssh_config 5 .
1372Because of the potential for abuse, this file must have strict permissions:
Damien Millerd93340c2013-07-18 16:14:34 +10001373read/write for the user, and not writable by others.
Damien Millerfb8ea742006-01-06 14:48:52 +11001374.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001375.It Pa ~/.ssh/environment
Damien Miller4c102ee2006-01-06 14:49:17 +11001376Contains additional definitions for environment variables; see
1377.Sx ENVIRONMENT ,
Damien Millerfb8ea742006-01-06 14:48:52 +11001378above.
1379.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001380.It Pa ~/.ssh/identity
1381.It Pa ~/.ssh/id_dsa
Damien Millereb8b60e2010-08-31 22:41:14 +10001382.It Pa ~/.ssh/id_ecdsa
Damien Miller8ba0ead2013-12-18 17:46:27 +11001383.It Pa ~/.ssh/id_ed25519
Damien Millerafdae612010-08-31 22:31:14 +10001384.It Pa ~/.ssh/id_rsa
Damien Millerfb8ea742006-01-06 14:48:52 +11001385Contains the private key for authentication.
1386These files
1387contain sensitive data and should be readable by the user but not
1388accessible by others (read/write/execute).
1389.Nm
1390will simply ignore a private key file if it is accessible by others.
1391It is possible to specify a passphrase when
1392generating the key which will be used to encrypt the
1393sensitive part of this file using 3DES.
1394.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001395.It Pa ~/.ssh/identity.pub
1396.It Pa ~/.ssh/id_dsa.pub
Damien Millereb8b60e2010-08-31 22:41:14 +10001397.It Pa ~/.ssh/id_ecdsa.pub
Damien Miller8ba0ead2013-12-18 17:46:27 +11001398.It Pa ~/.ssh/id_ed25519.pub
Damien Millerafdae612010-08-31 22:31:14 +10001399.It Pa ~/.ssh/id_rsa.pub
Damien Millerfb8ea742006-01-06 14:48:52 +11001400Contains the public key for authentication.
1401These files are not
1402sensitive and can (but need not) be readable by anyone.
Damien Millerfb8ea742006-01-06 14:48:52 +11001403.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001404.It Pa ~/.ssh/known_hosts
Damien Millere87eb4c2006-01-14 10:08:36 +11001405Contains a list of host keys for all hosts the user has logged into
1406that are not already in the systemwide list of known host keys.
Damien Millerfb8ea742006-01-06 14:48:52 +11001407See
Damien Millere87eb4c2006-01-14 10:08:36 +11001408.Xr sshd 8
1409for further details of the format of this file.
Damien Millerfb8ea742006-01-06 14:48:52 +11001410.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001411.It Pa ~/.ssh/rc
Damien Millerfb8ea742006-01-06 14:48:52 +11001412Commands in this file are executed by
1413.Nm
Damien Miller7e76e1f2006-01-14 10:08:57 +11001414when the user logs in, just before the user's shell (or command) is
Damien Millerfb8ea742006-01-06 14:48:52 +11001415started.
1416See the
1417.Xr sshd 8
1418manual page for more information.
1419.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001420.It Pa /etc/hosts.equiv
Damien Miller1bcdb502006-01-06 14:49:38 +11001421This file is for host-based authentication (see above).
1422It should only be writable by root.
Damien Miller7655f5c2006-01-06 14:48:18 +11001423.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001424.It Pa /etc/shosts.equiv
Damien Miller1bcdb502006-01-06 14:49:38 +11001425This file is used in exactly the same way as
1426.Pa hosts.equiv ,
1427but allows host-based authentication without permitting login with
1428rlogin/rsh.
Damien Miller7655f5c2006-01-06 14:48:18 +11001429.Pp
Damien Millerfb8ea742006-01-06 14:48:52 +11001430.It Pa /etc/ssh/ssh_config
1431Systemwide configuration file.
1432The file format and configuration options are described in
1433.Xr ssh_config 5 .
1434.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001435.It Pa /etc/ssh/ssh_host_key
1436.It Pa /etc/ssh/ssh_host_dsa_key
Damien Millereb8b60e2010-08-31 22:41:14 +10001437.It Pa /etc/ssh/ssh_host_ecdsa_key
Damien Miller8ba0ead2013-12-18 17:46:27 +11001438.It Pa /etc/ssh/ssh_host_ed25519_key
Damien Millerafdae612010-08-31 22:31:14 +10001439.It Pa /etc/ssh/ssh_host_rsa_key
Damien Millerb9902cf2012-06-20 21:52:58 +10001440These files contain the private parts of the host keys
Damien Miller7e76e1f2006-01-14 10:08:57 +11001441and are used for host-based authentication.
1442If protocol version 1 is used,
Damien Millerfb8ea742006-01-06 14:48:52 +11001443.Nm
1444must be setuid root, since the host key is readable only by root.
1445For protocol version 2,
1446.Nm
1447uses
1448.Xr ssh-keysign 8
Damien Miller7e76e1f2006-01-14 10:08:57 +11001449to access the host keys,
1450eliminating the requirement that
Damien Millerfb8ea742006-01-06 14:48:52 +11001451.Nm
Damien Miller7e76e1f2006-01-14 10:08:57 +11001452be setuid root when host-based authentication is used.
Damien Millerfb8ea742006-01-06 14:48:52 +11001453By default
1454.Nm
1455is not setuid root.
1456.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001457.It Pa /etc/ssh/ssh_known_hosts
Damien Millerfb8ea742006-01-06 14:48:52 +11001458Systemwide list of known host keys.
1459This file should be prepared by the
1460system administrator to contain the public host keys of all machines in the
1461organization.
Damien Millere87eb4c2006-01-14 10:08:36 +11001462It should be world-readable.
1463See
Damien Millerfb8ea742006-01-06 14:48:52 +11001464.Xr sshd 8
Damien Millere87eb4c2006-01-14 10:08:36 +11001465for further details of the format of this file.
Damien Millerfb8ea742006-01-06 14:48:52 +11001466.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001467.It Pa /etc/ssh/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +10001468Commands in this file are executed by
1469.Nm
Damien Miller7e76e1f2006-01-14 10:08:57 +11001470when the user logs in, just before the user's shell (or command) is started.
Damien Miller32aa1441999-10-29 09:15:49 +10001471See the
1472.Xr sshd 8
1473manual page for more information.
Damien Miller7b28dc52000-09-05 13:34:53 +11001474.El
Damien Millerdaa7b222010-09-10 11:19:33 +10001475.Sh EXIT STATUS
1476.Nm
1477exits with the exit status of the remote command or with 255
1478if an error occurred.
Damien Miller32aa1441999-10-29 09:15:49 +10001479.Sh SEE ALSO
Damien Miller32aa1441999-10-29 09:15:49 +10001480.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +11001481.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +10001482.Xr ssh-add 1 ,
1483.Xr ssh-agent 1 ,
1484.Xr ssh-keygen 1 ,
Damien Miller128a0f12006-01-06 14:50:11 +11001485.Xr ssh-keyscan 1 ,
Darren Tucker248dd132006-01-20 11:30:58 +11001486.Xr tun 4 ,
Ben Lindstrombf69e3b2002-06-23 00:31:24 +00001487.Xr ssh_config 5 ,
Ben Lindstromc001cd32002-06-23 00:32:11 +00001488.Xr ssh-keysign 8 ,
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +00001489.Xr sshd 8
Darren Tucker628a3fd2012-10-05 10:50:15 +10001490.Sh STANDARDS
Ben Lindstrom160ec622001-04-22 17:17:46 +00001491.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001492.%A S. Lehtinen
1493.%A C. Lonvick
1494.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001495.%R RFC 4250
Darren Tucker628a3fd2012-10-05 10:50:15 +10001496.%T The Secure Shell (SSH) Protocol Assigned Numbers
Damien Miller39a93a32006-03-15 11:34:45 +11001497.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001498.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001499.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001500.%A T. Ylonen
1501.%A C. Lonvick
1502.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001503.%R RFC 4251
Darren Tucker628a3fd2012-10-05 10:50:15 +10001504.%T The Secure Shell (SSH) Protocol Architecture
Damien Miller39a93a32006-03-15 11:34:45 +11001505.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001506.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001507.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001508.%A T. Ylonen
1509.%A C. Lonvick
1510.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001511.%R RFC 4252
Darren Tucker628a3fd2012-10-05 10:50:15 +10001512.%T The Secure Shell (SSH) Authentication Protocol
Damien Miller39a93a32006-03-15 11:34:45 +11001513.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001514.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001515.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001516.%A T. Ylonen
1517.%A C. Lonvick
1518.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001519.%R RFC 4253
Darren Tucker628a3fd2012-10-05 10:50:15 +10001520.%T The Secure Shell (SSH) Transport Layer Protocol
Damien Miller39a93a32006-03-15 11:34:45 +11001521.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001522.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001523.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001524.%A T. Ylonen
1525.%A C. Lonvick
1526.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001527.%R RFC 4254
Darren Tucker628a3fd2012-10-05 10:50:15 +10001528.%T The Secure Shell (SSH) Connection Protocol
Damien Miller39a93a32006-03-15 11:34:45 +11001529.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001530.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001531.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001532.%A J. Schlyter
1533.%A W. Griffin
1534.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001535.%R RFC 4255
Darren Tucker628a3fd2012-10-05 10:50:15 +10001536.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
Damien Miller39a93a32006-03-15 11:34:45 +11001537.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001538.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001539.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001540.%A F. Cusack
1541.%A M. Forssen
1542.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001543.%R RFC 4256
Darren Tucker628a3fd2012-10-05 10:50:15 +10001544.%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)
Damien Miller39a93a32006-03-15 11:34:45 +11001545.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001546.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001547.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001548.%A J. Galbraith
1549.%A P. Remaker
1550.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001551.%R RFC 4335
Darren Tucker628a3fd2012-10-05 10:50:15 +10001552.%T The Secure Shell (SSH) Session Channel Break Extension
Damien Miller39a93a32006-03-15 11:34:45 +11001553.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001554.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001555.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001556.%A M. Bellare
1557.%A T. Kohno
1558.%A C. Namprempre
1559.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001560.%R RFC 4344
Darren Tucker628a3fd2012-10-05 10:50:15 +10001561.%T The Secure Shell (SSH) Transport Layer Encryption Modes
Damien Miller39a93a32006-03-15 11:34:45 +11001562.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001563.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001564.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001565.%A B. Harris
1566.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001567.%R RFC 4345
Darren Tucker628a3fd2012-10-05 10:50:15 +10001568.%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol
Ben Lindstrom160ec622001-04-22 17:17:46 +00001569.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001570.Pp
Damien Miller3e96d742006-03-25 23:39:29 +11001571.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001572.%A M. Friedl
1573.%A N. Provos
1574.%A W. Simpson
1575.%D March 2006
Damien Miller3e96d742006-03-25 23:39:29 +11001576.%R RFC 4419
Darren Tucker628a3fd2012-10-05 10:50:15 +10001577.%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol
Damien Miller3e96d742006-03-25 23:39:29 +11001578.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001579.Pp
Damien Millerc0367fb2007-01-05 16:25:46 +11001580.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001581.%A J. Galbraith
1582.%A R. Thayer
1583.%D November 2006
Damien Millerc0367fb2007-01-05 16:25:46 +11001584.%R RFC 4716
Darren Tucker628a3fd2012-10-05 10:50:15 +10001585.%T The Secure Shell (SSH) Public Key File Format
Damien Millerc0367fb2007-01-05 16:25:46 +11001586.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001587.Pp
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001588.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001589.%A D. Stebila
1590.%A J. Green
1591.%D December 2009
Damien Miller1ca94692010-09-24 22:01:22 +10001592.%R RFC 5656
Darren Tucker628a3fd2012-10-05 10:50:15 +10001593.%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
Damien Miller1ca94692010-09-24 22:01:22 +10001594.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001595.Pp
Damien Miller1ca94692010-09-24 22:01:22 +10001596.Rs
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001597.%A A. Perrig
1598.%A D. Song
1599.%D 1999
Darren Tucker628a3fd2012-10-05 10:50:15 +10001600.%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)
1601.%T Hash Visualization: a New Technique to improve Real-World Security
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001602.Re
Damien Millerf1ce5052003-06-11 22:04:39 +10001603.Sh AUTHORS
1604OpenSSH is a derivative of the original and free
1605ssh 1.2.12 release by Tatu Ylonen.
1606Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1607Theo de Raadt and Dug Song
1608removed many bugs, re-added newer features and
1609created OpenSSH.
1610Markus Friedl contributed the support for SSH
1611protocol versions 1.5 and 2.0.