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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 Millerea111192013-04-23 19:24:32 +100036.\" $OpenBSD: ssh.1,v 1.332 2013/04/19 01:06:50 djm Exp $
37.Dd $Mdocdate: April 19 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 Millerbcfbc482010-07-16 13:59:11 +100061.Op Fl R Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport
Darren Tucker7ebfc102004-11-07 20:06:19 +110062.Op Fl S Ar ctl_path
Darren Tucker7ad8dd22010-01-12 19:40:27 +110063.Op Fl W Ar host : Ns Ar port
Damien Millerbcfbc482010-07-16 13:59:11 +100064.Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun
Darren Tucker61776952003-10-02 16:19:47 +100065.Oo Ar user Ns @ Oc Ns Ar hostname
Damien Miller32aa1441999-10-29 09:15:49 +100066.Op Ar command
Damien Millerbcfbc482010-07-16 13:59:11 +100067.Ek
Damien Millerea111192013-04-23 19:24:32 +100068.Nm
69.Fl Q Ar protocol_feature
Damien Miller22c77262000-04-13 12:26:34 +100070.Sh DESCRIPTION
Damien Miller32aa1441999-10-29 09:15:49 +100071.Nm
Ben Lindstromd58eb5f2001-03-07 06:07:22 +000072(SSH client) is a program for logging into a remote machine and for
Damien Miller7684ee12000-03-17 23:40:15 +110073executing commands on a remote machine.
Darren Tucker61776952003-10-02 16:19:47 +100074It is intended to replace rlogin and rsh,
75and provide secure encrypted communications between
Damien Miller7684ee12000-03-17 23:40:15 +110076two untrusted hosts over an insecure network.
Damien Miller8bfaf932006-01-14 10:09:30 +110077X11 connections and arbitrary TCP ports
Darren Tucker61776952003-10-02 16:19:47 +100078can 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 Miller8bfaf932006-01-14 10:09:30 +1100135data for forwarded X11 and TCP connections).
Darren Tucker61776952003-10-02 16:19:47 +1000136The compression algorithm is the same used by
137.Xr gzip 1 ,
138and the
139.Dq level
140can be controlled by the
141.Cm CompressionLevel
142option for protocol version 1.
143Compression is desirable on modem lines and other
144slow connections, but will only slow down things on fast networks.
145The default value can be set on a host-by-host basis in the
146configuration files; see the
147.Cm Compression
148option.
Damien Miller05202ff2004-06-15 10:30:39 +1000149.It Fl c Ar cipher_spec
150Selects the cipher specification for encrypting the session.
151.Pp
152Protocol version 1 allows specification of a single cipher.
Darren Tucker1e4308e2005-10-03 18:18:40 +1000153The supported values are
Damien Miller05202ff2004-06-15 10:30:39 +1000154.Dq 3des ,
Darren Tuckerff9f4842005-12-20 16:10:45 +1100155.Dq blowfish ,
Damien Miller05202ff2004-06-15 10:30:39 +1000156and
157.Dq des .
Damien Miller32aa1441999-10-29 09:15:49 +1000158.Ar 3des
159(triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
Damien Miller05202ff2004-06-15 10:30:39 +1000160It is believed to be secure.
Damien Miller32aa1441999-10-29 09:15:49 +1000161.Ar blowfish
Darren Tucker61776952003-10-02 16:19:47 +1000162is a fast block cipher; it appears very secure and is much faster than
Damien Miller7684ee12000-03-17 23:40:15 +1100163.Ar 3des .
Ben Lindstromffa1dd62001-09-12 16:52:28 +0000164.Ar des
165is only supported in the
166.Nm
167client for interoperability with legacy protocol 1 implementations
168that do not support the
169.Ar 3des
Damien Miller495dca32003-04-01 21:42:14 +1000170cipher.
171Its use is strongly discouraged due to cryptographic weaknesses.
Damien Miller05202ff2004-06-15 10:30:39 +1000172The default is
173.Dq 3des .
174.Pp
Damien Miller35978212005-12-24 14:56:47 +1100175For protocol version 2,
Damien Miller05202ff2004-06-15 10:30:39 +1000176.Ar cipher_spec
177is a comma-separated list of ciphers
178listed in order of preference.
Darren Tucker3a6a51f2009-06-21 17:48:52 +1000179See the
180.Cm Ciphers
Damien Miller081f3c72010-08-03 16:05:25 +1000181keyword in
182.Xr ssh_config 5
183for more information.
Darren Tuckerc8d64212005-10-03 18:13:42 +1000184.It Fl D Xo
185.Sm off
186.Oo Ar bind_address : Oc
187.Ar port
188.Sm on
189.Xc
Darren Tucker61776952003-10-02 16:19:47 +1000190Specifies a local
191.Dq dynamic
192application-level port forwarding.
193This works by allocating a socket to listen to
194.Ar port
Darren Tuckerc8d64212005-10-03 18:13:42 +1000195on the local side, optionally bound to the specified
196.Ar bind_address .
197Whenever a connection is made to this port, the
Darren Tucker61776952003-10-02 16:19:47 +1000198connection is forwarded over the secure channel, and the application
199protocol is then used to determine where to connect to from the
200remote machine.
201Currently the SOCKS4 and SOCKS5 protocols are supported, and
202.Nm
203will act as a SOCKS server.
204Only root can forward privileged ports.
205Dynamic port forwardings can also be specified in the configuration file.
Darren Tuckerc8d64212005-10-03 18:13:42 +1000206.Pp
Damien Miller7fa96602010-08-05 13:03:13 +1000207IPv6 addresses can be specified by enclosing the address in square brackets.
Darren Tuckerc8d64212005-10-03 18:13:42 +1000208Only the superuser can forward privileged ports.
209By default, the local port is bound in accordance with the
210.Cm GatewayPorts
211setting.
212However, an explicit
213.Ar bind_address
214may be used to bind the connection to a specific address.
215The
216.Ar bind_address
217of
218.Dq localhost
219indicates that the listening port be bound for local use only, while an
220empty address or
221.Sq *
222indicates that the port should be available from all interfaces.
Damien Miller03d4d7e2013-04-23 15:21:06 +1000223.It Fl E Ar log_file
224Append debug logs to
225.Ar log_file
226instead of standard error.
Damien Miller2142ba02005-12-24 14:56:29 +1100227.It Fl e Ar escape_char
Damien Miller32aa1441999-10-29 09:15:49 +1000228Sets the escape character for sessions with a pty (default:
229.Ql ~ ) .
Damien Miller7684ee12000-03-17 23:40:15 +1100230The escape character is only recognized at the beginning of a line.
231The escape character followed by a dot
Damien Miller32aa1441999-10-29 09:15:49 +1000232.Pq Ql \&.
Darren Tucker61776952003-10-02 16:19:47 +1000233closes the connection;
234followed by control-Z suspends the connection;
235and followed by itself sends the escape character once.
Damien Miller7684ee12000-03-17 23:40:15 +1100236Setting the character to
Damien Miller32aa1441999-10-29 09:15:49 +1000237.Dq none
238disables any escapes and makes the session fully transparent.
Darren Tucker61776952003-10-02 16:19:47 +1000239.It Fl F Ar configfile
240Specifies an alternative per-user configuration file.
241If a configuration file is given on the command line,
242the system-wide configuration file
243.Pq Pa /etc/ssh/ssh_config
244will be ignored.
245The default for the per-user configuration file is
Damien Miller167ea5d2005-05-26 12:04:02 +1000246.Pa ~/.ssh/config .
Damien Miller32aa1441999-10-29 09:15:49 +1000247.It Fl f
248Requests
249.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100250to go to background just before command execution.
251This is useful if
Damien Miller32aa1441999-10-29 09:15:49 +1000252.Nm
253is going to ask for passwords or passphrases, but the user
Damien Miller7684ee12000-03-17 23:40:15 +1100254wants it in the background.
Damien Miller22c77262000-04-13 12:26:34 +1000255This implies
Damien Miller32aa1441999-10-29 09:15:49 +1000256.Fl n .
257The recommended way to start X11 programs at a remote site is with
258something like
259.Ic ssh -f host xterm .
Darren Tucker9a2a6092008-07-04 12:53:50 +1000260.Pp
261If the
262.Cm ExitOnForwardFailure
263configuration option is set to
264.Dq yes ,
265then a client started with
266.Fl f
267will wait for all remote port forwards to be successfully established
268before placing itself in the background.
Damien Miller396691a2000-01-20 22:44:08 +1100269.It Fl g
270Allows remote hosts to connect to local forwarded ports.
Damien Miller7ea845e2010-02-12 09:21:02 +1100271.It Fl I Ar pkcs11
Damien Millerd400da52010-02-12 09:26:23 +1100272Specify the PKCS#11 shared library
Darren Tucker61776952003-10-02 16:19:47 +1000273.Nm
Damien Millera7618442010-02-12 09:26:02 +1100274should use to communicate with a PKCS#11 token providing the user's
Darren Tucker61776952003-10-02 16:19:47 +1000275private RSA key.
Damien Miller32aa1441999-10-29 09:15:49 +1000276.It Fl i Ar identity_file
Damien Millerfae23862002-01-22 23:32:26 +1100277Selects a file from which the identity (private key) for
Damien Millereb8b60e2010-08-31 22:41:14 +1000278public key authentication is read.
Damien Millerfae23862002-01-22 23:32:26 +1100279The default is
Damien Miller167ea5d2005-05-26 12:04:02 +1000280.Pa ~/.ssh/identity
Damien Millerfae23862002-01-22 23:32:26 +1100281for protocol version 1, and
Damien Millereb8b60e2010-08-31 22:41:14 +1000282.Pa ~/.ssh/id_dsa ,
283.Pa ~/.ssh/id_ecdsa
Damien Millerfae23862002-01-22 23:32:26 +1100284and
Damien Millereb8b60e2010-08-31 22:41:14 +1000285.Pa ~/.ssh/id_rsa
Damien Millerfae23862002-01-22 23:32:26 +1100286for protocol version 2.
Damien Miller7684ee12000-03-17 23:40:15 +1100287Identity files may also be specified on
288a per-host basis in the configuration file.
289It is possible to have multiple
Damien Miller32aa1441999-10-29 09:15:49 +1000290.Fl i
291options (and multiple identities specified in
292configuration files).
Damien Miller5059d8d2010-03-05 21:31:11 +1100293.Nm
294will also try to load certificate information from the filename obtained
295by appending
296.Pa -cert.pub
297to identity filenames.
Darren Tucker415bddc2007-06-12 23:43:16 +1000298.It Fl K
299Enables GSSAPI-based authentication and forwarding (delegation) of GSSAPI
300credentials to the server.
Damien Miller32aa1441999-10-29 09:15:49 +1000301.It Fl k
Damien Millere0113cc2003-11-24 13:10:09 +1100302Disables forwarding (delegation) of GSSAPI credentials to the server.
Darren Tucker61776952003-10-02 16:19:47 +1000303.It Fl L Xo
304.Sm off
Damien Millerf91ee4c2005-03-01 21:24:33 +1100305.Oo Ar bind_address : Oc
Darren Tucker61776952003-10-02 16:19:47 +1000306.Ar port : host : hostport
307.Sm on
308.Xc
309Specifies that the given port on the local (client) host is to be
310forwarded to the given host and port on the remote side.
311This works by allocating a socket to listen to
312.Ar port
Damien Millerf91ee4c2005-03-01 21:24:33 +1100313on the local side, optionally bound to the specified
314.Ar bind_address .
315Whenever a connection is made to this port, the
Darren Tucker61776952003-10-02 16:19:47 +1000316connection is forwarded over the secure channel, and a connection is
317made to
318.Ar host
319port
320.Ar hostport
321from the remote machine.
322Port forwardings can also be specified in the configuration file.
Damien Miller7fa96602010-08-05 13:03:13 +1000323IPv6 addresses can be specified by enclosing the address in square brackets.
Damien Millerf91ee4c2005-03-01 21:24:33 +1100324Only the superuser can forward privileged ports.
325By default, the local port is bound in accordance with the
326.Cm GatewayPorts
327setting.
328However, an explicit
329.Ar bind_address
330may be used to bind the connection to a specific address.
331The
332.Ar bind_address
333of
334.Dq localhost
Damien Miller36bf7dd2005-03-02 12:02:47 +1100335indicates that the listening port be bound for local use only, while an
336empty address or
337.Sq *
Damien Millerf91ee4c2005-03-01 21:24:33 +1100338indicates that the port should be available from all interfaces.
Damien Miller32aa1441999-10-29 09:15:49 +1000339.It Fl l Ar login_name
Damien Miller7684ee12000-03-17 23:40:15 +1100340Specifies the user to log in as on the remote machine.
341This also may be specified on a per-host basis in the configuration file.
Damien Miller0e220db2004-06-15 10:34:08 +1000342.It Fl M
343Places the
344.Nm
345client into
346.Dq master
347mode for connection sharing.
Damien Miller88b25522005-12-31 16:23:15 +1100348Multiple
349.Fl M
350options places
351.Nm
352into
353.Dq master
354mode with confirmation required before slave connections are accepted.
Damien Miller0e220db2004-06-15 10:34:08 +1000355Refer to the description of
356.Cm ControlMaster
357in
358.Xr ssh_config 5
359for details.
Damien Miller5d1eceb2004-06-30 22:37:57 +1000360.It Fl m Ar mac_spec
361Additionally, for protocol version 2 a comma-separated list of MAC
362(message authentication code) algorithms can
363be specified in order of preference.
364See the
365.Cm MACs
366keyword for more information.
Darren Tucker61776952003-10-02 16:19:47 +1000367.It Fl N
368Do not execute a remote command.
369This is useful for just forwarding ports
370(protocol version 2 only).
Damien Miller32aa1441999-10-29 09:15:49 +1000371.It Fl n
372Redirects stdin from
373.Pa /dev/null
374(actually, prevents reading from stdin).
375This must be used when
376.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100377is run in the background.
378A common trick is to use this to run X11 programs on a remote machine.
379For example,
Damien Miller32aa1441999-10-29 09:15:49 +1000380.Ic ssh -n shadows.cs.hut.fi emacs &
381will start an emacs on shadows.cs.hut.fi, and the X11
382connection will be automatically forwarded over an encrypted channel.
383The
384.Nm
385program will be put in the background.
386(This does not work if
387.Nm
388needs to ask for a password or passphrase; see also the
389.Fl f
390option.)
Darren Tuckere04644c2004-12-03 14:08:45 +1100391.It Fl O Ar ctl_cmd
392Control an active connection multiplexing master process.
393When the
394.Fl O
395option is specified, the
396.Ar ctl_cmd
397argument is interpreted and passed to the master process.
398Valid commands are:
399.Dq check
Damien Miller388f6fc2010-05-21 14:57:35 +1000400(check that the master process is running),
401.Dq forward
Damien Miller8cb1cda2011-05-05 14:16:56 +1000402(request forwardings without command execution),
Damien Miller1bcbd0a2011-09-22 21:40:45 +1000403.Dq cancel
404(cancel forwardings),
Darren Tuckere04644c2004-12-03 14:08:45 +1100405.Dq exit
Damien Miller8cb1cda2011-05-05 14:16:56 +1000406(request the master to exit), and
Damien Miller6c3eec72011-05-05 14:16:22 +1000407.Dq stop
408(request the master to stop accepting further multiplexing requests).
Damien Miller32aa1441999-10-29 09:15:49 +1000409.It Fl o Ar option
Ben Lindstrom14c62eb2001-08-15 23:25:46 +0000410Can be used to give options in the format used in the configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000411This is useful for specifying options for which there is no separate
Damien Miller7684ee12000-03-17 23:40:15 +1100412command-line flag.
Darren Tucker61776952003-10-02 16:19:47 +1000413For full details of the options listed below, and their possible values, see
414.Xr ssh_config 5 .
415.Pp
416.Bl -tag -width Ds -offset indent -compact
417.It AddressFamily
418.It BatchMode
419.It BindAddress
420.It ChallengeResponseAuthentication
421.It CheckHostIP
422.It Cipher
423.It Ciphers
424.It ClearAllForwardings
425.It Compression
426.It CompressionLevel
427.It ConnectionAttempts
Darren Tuckeredae0ec2004-05-02 22:15:52 +1000428.It ConnectTimeout
Damien Miller0e220db2004-06-15 10:34:08 +1000429.It ControlMaster
430.It ControlPath
Damien Millerefad7272011-09-22 21:33:53 +1000431.It ControlPersist
Darren Tucker61776952003-10-02 16:19:47 +1000432.It DynamicForward
Darren Tucker61776952003-10-02 16:19:47 +1000433.It EscapeChar
Darren Tuckere7d4b192006-07-12 22:17:10 +1000434.It ExitOnForwardFailure
Darren Tucker61776952003-10-02 16:19:47 +1000435.It ForwardAgent
436.It ForwardX11
Damien Millerefad7272011-09-22 21:33:53 +1000437.It ForwardX11Timeout
Darren Tucker0a118da2003-10-15 15:54:32 +1000438.It ForwardX11Trusted
Darren Tucker61776952003-10-02 16:19:47 +1000439.It GatewayPorts
440.It GlobalKnownHostsFile
441.It GSSAPIAuthentication
442.It GSSAPIDelegateCredentials
Damien Millere1776152005-03-01 21:47:37 +1100443.It HashKnownHosts
Darren Tucker61776952003-10-02 16:19:47 +1000444.It Host
445.It HostbasedAuthentication
446.It HostKeyAlgorithms
447.It HostKeyAlias
448.It HostName
449.It IdentityFile
Damien Millerbd394c32004-03-08 23:12:36 +1100450.It IdentitiesOnly
Damien Miller0a184732010-11-20 15:21:03 +1100451.It IPQoS
Damien Millerefad7272011-09-22 21:33:53 +1000452.It KbdInteractiveAuthentication
Darren Tucker636ca902004-11-05 20:22:00 +1100453.It KbdInteractiveDevices
Damien Miller7fe2b1f2010-09-24 22:11:53 +1000454.It KexAlgorithms
Damien Millerd27b9472005-12-13 19:29:02 +1100455.It LocalCommand
Darren Tucker61776952003-10-02 16:19:47 +1000456.It LocalForward
457.It LogLevel
458.It MACs
459.It NoHostAuthenticationForLocalhost
460.It NumberOfPasswordPrompts
461.It PasswordAuthentication
Damien Millerd27b9472005-12-13 19:29:02 +1100462.It PermitLocalCommand
Damien Miller7ea845e2010-02-12 09:21:02 +1100463.It PKCS11Provider
Darren Tucker61776952003-10-02 16:19:47 +1000464.It Port
465.It PreferredAuthentications
466.It Protocol
467.It ProxyCommand
468.It PubkeyAuthentication
Darren Tucker62388b22006-01-20 11:31:47 +1100469.It RekeyLimit
Darren Tucker61776952003-10-02 16:19:47 +1000470.It RemoteForward
Damien Millerf4b32aa2011-05-15 08:47:43 +1000471.It RequestTTY
Darren Tucker61776952003-10-02 16:19:47 +1000472.It RhostsRSAAuthentication
473.It RSAAuthentication
Darren Tucker7a6c0662004-05-02 22:14:03 +1000474.It SendEnv
Damien Miller509b0102003-12-17 16:33:10 +1100475.It ServerAliveInterval
476.It ServerAliveCountMax
Darren Tucker61776952003-10-02 16:19:47 +1000477.It StrictHostKeyChecking
Damien Miller12c150e2003-12-17 16:31:10 +1100478.It TCPKeepAlive
Damien Millerd27b9472005-12-13 19:29:02 +1100479.It Tunnel
480.It TunnelDevice
Darren Tucker61776952003-10-02 16:19:47 +1000481.It UsePrivilegedPort
482.It User
483.It UserKnownHostsFile
484.It VerifyHostKeyDNS
Damien Miller86399202008-06-30 00:04:31 +1000485.It VisualHostKey
Darren Tucker61776952003-10-02 16:19:47 +1000486.It XAuthLocation
487.El
Damien Miller32aa1441999-10-29 09:15:49 +1000488.It Fl p Ar port
Damien Miller7684ee12000-03-17 23:40:15 +1100489Port to connect to on the remote host.
490This can be specified on a
Damien Miller32aa1441999-10-29 09:15:49 +1000491per-host basis in the configuration file.
Damien Millerea111192013-04-23 19:24:32 +1000492.It Fl Q Ar protocol_feature
493Queries
494.Nm
495for the algorithms supported for the specified version 2
496.Ar protocol_feature .
497The queriable features are:
498.Dq cipher
499(supported symmetric ciphers),
500.Dq MAC
501(supported message integrity codes),
502.Dq KEX
503(key exchange algorithms),
504.Dq key
505(key types).
506Protocol features are treated case-insensitively.
Damien Miller32aa1441999-10-29 09:15:49 +1000507.It Fl q
Damien Miller7684ee12000-03-17 23:40:15 +1100508Quiet mode.
Damien Millereb602472008-02-10 22:21:28 +1100509Causes most warning and diagnostic messages to be suppressed.
Darren Tucker61776952003-10-02 16:19:47 +1000510.It Fl R Xo
511.Sm off
Damien Millerf91ee4c2005-03-01 21:24:33 +1100512.Oo Ar bind_address : Oc
Darren Tucker61776952003-10-02 16:19:47 +1000513.Ar port : host : hostport
514.Sm on
515.Xc
Damien Miller32aa1441999-10-29 09:15:49 +1000516Specifies that the given port on the remote (server) host is to be
Damien Miller7684ee12000-03-17 23:40:15 +1100517forwarded to the given host and port on the local side.
518This works by allocating a socket to listen to
Damien Miller32aa1441999-10-29 09:15:49 +1000519.Ar port
520on the remote side, and whenever a connection is made to this port, the
521connection is forwarded over the secure channel, and a connection is
522made to
Damien Miller34132e52000-01-14 15:45:46 +1100523.Ar host
524port
525.Ar hostport
Damien Miller7684ee12000-03-17 23:40:15 +1100526from the local machine.
Damien Millerf91ee4c2005-03-01 21:24:33 +1100527.Pp
Damien Miller7684ee12000-03-17 23:40:15 +1100528Port forwardings can also be specified in the configuration file.
529Privileged ports can be forwarded only when
Damien Miller32aa1441999-10-29 09:15:49 +1000530logging in as root on the remote machine.
Damien Miller70b2d552012-04-22 11:26:10 +1000531IPv6 addresses can be specified by enclosing the address in square brackets.
Damien Millerf91ee4c2005-03-01 21:24:33 +1100532.Pp
533By default, the listening socket on the server will be bound to the loopback
534interface only.
Darren Tucker63917bd2008-11-11 16:33:48 +1100535This may be overridden by specifying a
Damien Millerf91ee4c2005-03-01 21:24:33 +1100536.Ar bind_address .
Damien Miller36bf7dd2005-03-02 12:02:47 +1100537An empty
538.Ar bind_address ,
Damien Millerf91ee4c2005-03-01 21:24:33 +1100539or the address
Damien Miller36bf7dd2005-03-02 12:02:47 +1100540.Ql * ,
Damien Millerf91ee4c2005-03-01 21:24:33 +1100541indicates that the remote socket should listen on all interfaces.
542Specifying a remote
543.Ar bind_address
Damien Miller36bf7dd2005-03-02 12:02:47 +1100544will only succeed if the server's
545.Cm GatewayPorts
Damien Millerf91ee4c2005-03-01 21:24:33 +1100546option is enabled (see
Damien Miller36bf7dd2005-03-02 12:02:47 +1100547.Xr sshd_config 5 ) .
Damien Millere2f4cc52009-02-14 16:33:49 +1100548.Pp
549If the
550.Ar port
551argument is
Damien Miller65fa4ca2009-02-14 16:34:05 +1100552.Ql 0 ,
Damien Millere2f4cc52009-02-14 16:33:49 +1100553the listen port will be dynamically allocated on the server and reported
554to the client at run time.
Damien Miller388f6fc2010-05-21 14:57:35 +1000555When used together with
556.Ic -O forward
557the allocated port will be printed to the standard output.
Darren Tucker7ebfc102004-11-07 20:06:19 +1100558.It Fl S Ar ctl_path
Damien Miller67f30d72010-04-16 15:52:03 +1000559Specifies the location of a control socket for connection sharing,
Damien Miller9c60f242010-03-26 11:28:35 +1100560or the string
561.Dq none
562to disable connection sharing.
Damien Miller0e220db2004-06-15 10:34:08 +1000563Refer to the description of
Darren Tuckerba5c5922004-06-18 16:22:39 +1000564.Cm ControlPath
565and
Damien Miller0e220db2004-06-15 10:34:08 +1000566.Cm ControlMaster
567in
568.Xr ssh_config 5
569for details.
Darren Tucker61776952003-10-02 16:19:47 +1000570.It Fl s
571May be used to request invocation of a subsystem on the remote system.
572Subsystems are a feature of the SSH2 protocol which facilitate the use
573of SSH as a secure transport for other applications (eg.\&
574.Xr sftp 1 ) .
575The subsystem is specified as the remote command.
576.It Fl T
577Disable pseudo-tty allocation.
578.It Fl t
579Force pseudo-tty allocation.
580This can be used to execute arbitrary
581screen-based programs on a remote machine, which can be very useful,
Damien Miller208f1ed2006-03-15 11:56:03 +1100582e.g. when implementing menu services.
Darren Tucker61776952003-10-02 16:19:47 +1000583Multiple
584.Fl t
585options force tty allocation, even if
Ben Lindstrom19ceb172001-09-12 17:54:24 +0000586.Nm
Darren Tucker61776952003-10-02 16:19:47 +1000587has no local tty.
588.It Fl V
589Display the version number and exit.
590.It Fl v
591Verbose mode.
592Causes
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000593.Nm
Darren Tucker61776952003-10-02 16:19:47 +1000594to print debugging messages about its progress.
595This is helpful in
596debugging connection, authentication, and configuration problems.
597Multiple
598.Fl v
599options increase the verbosity.
600The maximum is 3.
Darren Tucker7ad8dd22010-01-12 19:40:27 +1100601.It Fl W Ar host : Ns Ar port
602Requests that standard input and output on the client be forwarded to
603.Ar host
604on
605.Ar port
606over the secure channel.
607Implies
608.Fl N ,
609.Fl T ,
610.Cm ExitOnForwardFailure
611and
Damien Miller36378c62012-06-20 21:53:25 +1000612.Cm ClearAllForwardings .
613Works with Protocol version 2 only.
Damien Miller991dba42006-07-10 20:16:27 +1000614.It Fl w Xo
615.Ar local_tun Ns Op : Ns Ar remote_tun
616.Xc
617Requests
618tunnel
619device forwarding with the specified
Damien Millerd27b9472005-12-13 19:29:02 +1100620.Xr tun 4
Damien Miller991dba42006-07-10 20:16:27 +1000621devices between the client
622.Pq Ar local_tun
623and the server
624.Pq Ar remote_tun .
625.Pp
Damien Millercf1e3422005-12-24 14:56:04 +1100626The devices may be specified by numerical ID or the keyword
627.Dq any ,
628which uses the next available tunnel device.
Damien Miller991dba42006-07-10 20:16:27 +1000629If
630.Ar remote_tun
631is not specified, it defaults to
632.Dq any .
Damien Millercf1e3422005-12-24 14:56:04 +1100633See also the
Damien Millerd27b9472005-12-13 19:29:02 +1100634.Cm Tunnel
Damien Miller991dba42006-07-10 20:16:27 +1000635and
636.Cm TunnelDevice
637directives in
Damien Millerd27b9472005-12-13 19:29:02 +1100638.Xr ssh_config 5 .
Damien Miller991dba42006-07-10 20:16:27 +1000639If the
640.Cm Tunnel
641directive is unset, it is set to the default tunnel mode, which is
642.Dq point-to-point .
Darren Tucker61776952003-10-02 16:19:47 +1000643.It Fl X
644Enables X11 forwarding.
645This can also be specified on a per-host basis in a configuration file.
646.Pp
647X11 forwarding should be enabled with caution.
648Users with the ability to bypass file permissions on the remote host
649(for the user's X authorization database)
650can access the local X11 display through the forwarded connection.
651An attacker may then be able to perform activities such as keystroke monitoring.
Damien Miller947219e2005-03-02 13:22:30 +1100652.Pp
Damien Millerb022b232005-03-05 11:22:36 +1100653For this reason, X11 forwarding is subjected to X11 SECURITY extension
Damien Miller947219e2005-03-02 13:22:30 +1100654restrictions by default.
655Please refer to the
656.Nm
657.Fl Y
658option and the
659.Cm ForwardX11Trusted
660directive in
661.Xr ssh_config 5
662for more information.
Darren Tucker61776952003-10-02 16:19:47 +1000663.It Fl x
664Disables X11 forwarding.
Darren Tucker0a118da2003-10-15 15:54:32 +1000665.It Fl Y
666Enables trusted X11 forwarding.
Damien Miller947219e2005-03-02 13:22:30 +1100667Trusted X11 forwardings are not subjected to the X11 SECURITY extension
668controls.
Damien Millere272a5b2008-11-03 19:22:37 +1100669.It Fl y
670Send log information using the
671.Xr syslog 3
672system module.
673By default this information is sent to stderr.
Damien Miller32aa1441999-10-29 09:15:49 +1000674.El
Damien Millere9b333a2005-12-24 14:53:04 +1100675.Pp
676.Nm
677may additionally obtain configuration data from
678a per-user configuration file and a system-wide configuration file.
679The file format and configuration options are described in
680.Xr ssh_config 5 .
Damien Millerc93a8132005-12-24 14:52:13 +1100681.Sh AUTHENTICATION
Darren Tucker94299ec2006-01-20 11:30:14 +1100682The OpenSSH SSH client supports SSH protocols 1 and 2.
Darren Tucker7a4a7652009-10-11 21:51:40 +1100683The default is to use protocol 2 only,
684though this can be changed via the
Damien Millerc93a8132005-12-24 14:52:13 +1100685.Cm Protocol
686option in
Darren Tucker7a4a7652009-10-11 21:51:40 +1100687.Xr ssh_config 5
688or the
Damien Millerc93a8132005-12-24 14:52:13 +1100689.Fl 1
690and
691.Fl 2
692options (see above).
693Both protocols support similar authentication methods,
Darren Tucker7a4a7652009-10-11 21:51:40 +1100694but protocol 2 is the default since
Damien Millerc93a8132005-12-24 14:52:13 +1100695it provides additional mechanisms for confidentiality
696(the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
Damien Miller20bd4532011-08-06 06:17:30 +1000697and integrity (hmac-md5, hmac-sha1,
698hmac-sha2-256, hmac-sha2-512,
Darren Tucker427e4092012-10-05 11:02:39 +1000699umac-64, umac-128, hmac-ripemd160).
Damien Millerc93a8132005-12-24 14:52:13 +1100700Protocol 1 lacks a strong mechanism for ensuring the
701integrity of the connection.
702.Pp
703The methods available for authentication are:
Damien Millerfbc94c82006-06-13 13:03:16 +1000704GSSAPI-based authentication,
Damien Millerc93a8132005-12-24 14:52:13 +1100705host-based authentication,
706public key authentication,
707challenge-response authentication,
708and password authentication.
709Authentication methods are tried in the order specified above,
710though protocol 2 has a configuration option to change the default order:
711.Cm PreferredAuthentications .
712.Pp
713Host-based authentication works as follows:
Darren Tuckerd3877b92005-12-20 16:09:36 +1100714If the machine the user logs in from is listed in
715.Pa /etc/hosts.equiv
716or
717.Pa /etc/shosts.equiv
718on the remote machine, and the user names are
719the same on both sides, or if the files
720.Pa ~/.rhosts
721or
722.Pa ~/.shosts
723exist in the user's home directory on the
724remote machine and contain a line containing the name of the client
725machine and the name of the user on that machine, the user is
Damien Millerc93a8132005-12-24 14:52:13 +1100726considered for login.
727Additionally, the server
728.Em must
729be able to verify the client's
730host key (see the description of
Darren Tuckerd3877b92005-12-20 16:09:36 +1100731.Pa /etc/ssh/ssh_known_hosts
732and
Damien Millerc93a8132005-12-24 14:52:13 +1100733.Pa ~/.ssh/known_hosts ,
734below)
735for login to be permitted.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100736This authentication method closes security holes due to IP
Damien Millerc93a8132005-12-24 14:52:13 +1100737spoofing, DNS spoofing, and routing spoofing.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100738[Note to the administrator:
739.Pa /etc/hosts.equiv ,
740.Pa ~/.rhosts ,
741and the rlogin/rsh protocol in general, are inherently insecure and should be
742disabled if security is desired.]
743.Pp
Damien Millerc93a8132005-12-24 14:52:13 +1100744Public key authentication works as follows:
745The scheme is based on public-key cryptography,
746using cryptosystems
747where encryption and decryption are done using separate keys,
748and it is unfeasible to derive the decryption key from the encryption key.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100749The idea is that each user creates a public/private
750key pair for authentication purposes.
751The server knows the public key, and only the user knows the private key.
Damien Millerc93a8132005-12-24 14:52:13 +1100752.Nm
753implements public key authentication protocol automatically,
Damien Millereb8b60e2010-08-31 22:41:14 +1000754using one of the DSA, ECDSA or RSA algorithms.
Damien Millerc93a8132005-12-24 14:52:13 +1100755Protocol 1 is restricted to using only RSA keys,
Damien Millereb8b60e2010-08-31 22:41:14 +1000756but protocol 2 may use any.
Damien Millerc93a8132005-12-24 14:52:13 +1100757The
758.Sx HISTORY
759section of
760.Xr ssl 8
Damien Millerd4427902010-09-10 11:15:10 +1000761contains a brief discussion of the DSA and RSA algorithms.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100762.Pp
763The file
764.Pa ~/.ssh/authorized_keys
765lists the public keys that are permitted for logging in.
766When the user logs in, the
767.Nm
768program tells the server which key pair it would like to use for
769authentication.
Damien Millerc93a8132005-12-24 14:52:13 +1100770The client proves that it has access to the private key
771and the server checks that the corresponding public key
772is authorized to accept the account.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100773.Pp
Damien Millerc93a8132005-12-24 14:52:13 +1100774The user creates his/her key pair by running
Darren Tuckerd3877b92005-12-20 16:09:36 +1100775.Xr ssh-keygen 1 .
776This stores the private key in
777.Pa ~/.ssh/identity
Damien Millerc93a8132005-12-24 14:52:13 +1100778(protocol 1),
779.Pa ~/.ssh/id_dsa
780(protocol 2 DSA),
Damien Millereb8b60e2010-08-31 22:41:14 +1000781.Pa ~/.ssh/id_ecdsa
782(protocol 2 ECDSA),
Damien Millerc93a8132005-12-24 14:52:13 +1100783or
784.Pa ~/.ssh/id_rsa
785(protocol 2 RSA)
Darren Tuckerd3877b92005-12-20 16:09:36 +1100786and stores the public key in
787.Pa ~/.ssh/identity.pub
Damien Millerc93a8132005-12-24 14:52:13 +1100788(protocol 1),
789.Pa ~/.ssh/id_dsa.pub
790(protocol 2 DSA),
Damien Millereb8b60e2010-08-31 22:41:14 +1000791.Pa ~/.ssh/id_ecdsa.pub
792(protocol 2 ECDSA),
Damien Millerc93a8132005-12-24 14:52:13 +1100793or
794.Pa ~/.ssh/id_rsa.pub
795(protocol 2 RSA)
Darren Tuckerd3877b92005-12-20 16:09:36 +1100796in the user's home directory.
Damien Millerc93a8132005-12-24 14:52:13 +1100797The user should then copy the public key
Darren Tuckerd3877b92005-12-20 16:09:36 +1100798to
799.Pa ~/.ssh/authorized_keys
Damien Millerc93a8132005-12-24 14:52:13 +1100800in his/her home directory on the remote machine.
801The
Darren Tuckerd3877b92005-12-20 16:09:36 +1100802.Pa authorized_keys
803file corresponds to the conventional
804.Pa ~/.rhosts
805file, and has one key
Damien Millerc93a8132005-12-24 14:52:13 +1100806per line, though the lines can be very long.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100807After this, the user can log in without giving the password.
808.Pp
Damien Miller922b5412010-03-05 21:30:54 +1100809A variation on public key authentication
810is available in the form of certificate authentication:
811instead of a set of public/private keys,
812signed certificates are used.
813This has the advantage that a single trusted certification authority
814can be used in place of many public/private keys.
815See the
816.Sx CERTIFICATES
817section of
818.Xr ssh-keygen 1
819for more information.
820.Pp
821The most convenient way to use public key or certificate authentication
822may be with an authentication agent.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100823See
824.Xr ssh-agent 1
825for more information.
826.Pp
Damien Millerc93a8132005-12-24 14:52:13 +1100827Challenge-response authentication works as follows:
828The server sends an arbitrary
829.Qq challenge
830text, and prompts for a response.
831Protocol 2 allows multiple challenges and responses;
832protocol 1 is restricted to just one challenge/response.
833Examples of challenge-response authentication include
834BSD Authentication (see
835.Xr login.conf 5 )
836and PAM (some non-OpenBSD systems).
837.Pp
838Finally, if other authentication methods fail,
Darren Tuckerd3877b92005-12-20 16:09:36 +1100839.Nm
840prompts the user for a password.
841The password is sent to the remote
842host for checking; however, since all communications are encrypted,
843the password cannot be seen by someone listening on the network.
Damien Miller48c94ab2006-01-02 23:38:00 +1100844.Pp
845.Nm
846automatically maintains and checks a database containing
847identification for all hosts it has ever been used with.
848Host keys are stored in
849.Pa ~/.ssh/known_hosts
850in the user's home directory.
851Additionally, the file
852.Pa /etc/ssh/ssh_known_hosts
853is automatically checked for known hosts.
854Any new hosts are automatically added to the user's file.
855If a host's identification ever changes,
856.Nm
857warns about this and disables password authentication to prevent
858server spoofing or man-in-the-middle attacks,
859which could otherwise be used to circumvent the encryption.
860The
861.Cm StrictHostKeyChecking
862option can be used to control logins to machines whose
863host key is not known or has changed.
864.Pp
Darren Tuckerd3877b92005-12-20 16:09:36 +1100865When the user's identity has been accepted by the server, the server
866either executes the given command, or logs into the machine and gives
867the user a normal shell on the remote machine.
868All communication with
869the remote command or shell will be automatically encrypted.
870.Pp
871If a pseudo-terminal has been allocated (normal login session), the
872user may use the escape characters noted below.
873.Pp
874If no pseudo-tty has been allocated,
875the session is transparent and can be used to reliably transfer binary data.
876On most systems, setting the escape character to
877.Dq none
878will also make the session transparent even if a tty is used.
879.Pp
880The session terminates when the command or shell on the remote
Damien Miller8bfaf932006-01-14 10:09:30 +1100881machine exits and all X11 and TCP connections have been closed.
Damien Miller52d20612005-12-24 14:52:36 +1100882.Sh ESCAPE CHARACTERS
Darren Tuckerd3877b92005-12-20 16:09:36 +1100883When a pseudo-terminal has been requested,
884.Nm
885supports a number of functions through the use of an escape character.
886.Pp
887A single tilde character can be sent as
888.Ic ~~
889or by following the tilde by a character other than those described below.
890The escape character must always follow a newline to be interpreted as
891special.
892The escape character can be changed in configuration files using the
893.Cm EscapeChar
894configuration directive or on the command line by the
895.Fl e
896option.
897.Pp
898The supported escapes (assuming the default
899.Ql ~ )
900are:
901.Bl -tag -width Ds
902.It Cm ~.
903Disconnect.
904.It Cm ~^Z
905Background
Damien Miller1164c292006-01-02 23:38:37 +1100906.Nm .
Darren Tuckerd3877b92005-12-20 16:09:36 +1100907.It Cm ~#
908List forwarded connections.
909.It Cm ~&
910Background
911.Nm
912at logout when waiting for forwarded connection / X11 sessions to terminate.
913.It Cm ~?
914Display a list of escape characters.
915.It Cm ~B
916Send a BREAK to the remote system
917(only useful for SSH protocol version 2 and if the peer supports it).
918.It Cm ~C
919Open command line.
920Currently this allows the addition of port forwardings using the
Damien Miller0164cb82008-11-05 16:30:31 +1100921.Fl L ,
Darren Tuckerd3877b92005-12-20 16:09:36 +1100922.Fl R
Damien Miller0164cb82008-11-05 16:30:31 +1100923and
924.Fl D
Damien Miller329cb012005-12-24 14:53:23 +1100925options (see above).
Damien Millerff773642011-09-22 21:39:48 +1000926It also allows the cancellation of existing port-forwardings
927with
Damien Miller57e8ad32006-07-10 20:20:52 +1000928.Sm off
Damien Millerff773642011-09-22 21:39:48 +1000929.Fl KL Oo Ar bind_address : Oc Ar port
Damien Miller57e8ad32006-07-10 20:20:52 +1000930.Sm on
Damien Millerff773642011-09-22 21:39:48 +1000931for local,
932.Sm off
933.Fl KR Oo Ar bind_address : Oc Ar port
934.Sm on
935for remote and
936.Sm off
937.Fl KD Oo Ar bind_address : Oc Ar port
938.Sm on
939for dynamic port-forwardings.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100940.Ic !\& Ns Ar command
941allows the user to execute a local command if the
942.Ic PermitLocalCommand
943option is enabled in
944.Xr ssh_config 5 .
945Basic help is available, using the
946.Fl h
947option.
948.It Cm ~R
949Request rekeying of the connection
950(only useful for SSH protocol version 2 and if the peer supports it).
Darren Tucker50a48d02012-09-06 21:25:37 +1000951.It Cm ~V
952Decrease the verbosity
953.Pq Ic LogLevel
954when errors are being written to stderr.
955.It Cm ~v
Darren Tucker83d0af62012-09-07 11:21:03 +1000956Increase the verbosity
Darren Tucker50a48d02012-09-06 21:25:37 +1000957.Pq Ic LogLevel
958when errors are being written to stderr.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100959.El
Damien Millerf3177182006-01-14 10:09:13 +1100960.Sh TCP FORWARDING
961Forwarding of arbitrary TCP connections over the secure channel can
962be specified either on the command line or in a configuration file.
963One possible application of TCP forwarding is a secure connection to a
964mail server; another is going through firewalls.
965.Pp
966In the example below, we look at encrypting communication between
967an IRC client and server, even though the IRC server does not directly
968support encrypted communications.
969This works as follows:
970the user connects to the remote host using
971.Nm ,
972specifying a port to be used to forward connections
973to the remote server.
974After that it is possible to start the service which is to be encrypted
975on the client machine,
976connecting to the same local port,
977and
978.Nm
979will encrypt and forward the connection.
980.Pp
981The following example tunnels an IRC session from client machine
982.Dq 127.0.0.1
983(localhost)
984to remote server
985.Dq server.example.com :
986.Bd -literal -offset 4n
987$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
988$ irc -c '#users' -p 1234 pinky 127.0.0.1
989.Ed
990.Pp
991This tunnels a connection to IRC server
992.Dq server.example.com ,
993joining channel
994.Dq #users ,
995nickname
996.Dq pinky ,
997using port 1234.
998It doesn't matter which port is used,
999as long as it's greater than 1023
1000(remember, only root can open sockets on privileged ports)
1001and doesn't conflict with any ports already in use.
1002The connection is forwarded to port 6667 on the remote server,
1003since that's the standard port for IRC services.
1004.Pp
1005The
1006.Fl f
1007option backgrounds
1008.Nm
1009and the remote command
1010.Dq sleep 10
1011is specified to allow an amount of time
1012(10 seconds, in the example)
1013to start the service which is to be tunnelled.
1014If no connections are made within the time specified,
1015.Nm
1016will exit.
Damien Millerf3177182006-01-14 10:09:13 +11001017.Sh X11 FORWARDING
Darren Tuckerd3877b92005-12-20 16:09:36 +11001018If the
1019.Cm ForwardX11
1020variable is set to
1021.Dq yes
1022(or see the description of the
Damien Millerd7f308f2005-12-24 14:55:16 +11001023.Fl X ,
1024.Fl x ,
Darren Tuckerd3877b92005-12-20 16:09:36 +11001025and
Damien Millerd7f308f2005-12-24 14:55:16 +11001026.Fl Y
Damien Miller9a765b22005-12-24 14:53:44 +11001027options above)
Darren Tuckerd3877b92005-12-20 16:09:36 +11001028and the user is using X11 (the
1029.Ev DISPLAY
1030environment variable is set), the connection to the X11 display is
1031automatically forwarded to the remote side in such a way that any X11
1032programs started from the shell (or command) will go through the
1033encrypted channel, and the connection to the real X server will be made
1034from the local machine.
1035The user should not manually set
1036.Ev DISPLAY .
1037Forwarding of X11 connections can be
1038configured on the command line or in configuration files.
1039.Pp
1040The
1041.Ev DISPLAY
1042value set by
1043.Nm
1044will point to the server machine, but with a display number greater than zero.
1045This is normal, and happens because
1046.Nm
1047creates a
1048.Dq proxy
1049X server on the server machine for forwarding the
1050connections over the encrypted channel.
1051.Pp
1052.Nm
1053will also automatically set up Xauthority data on the server machine.
1054For this purpose, it will generate a random authorization cookie,
1055store it in Xauthority on the server, and verify that any forwarded
1056connections carry this cookie and replace it by the real cookie when
1057the connection is opened.
1058The real authentication cookie is never
1059sent to the server machine (and no cookies are sent in the plain).
1060.Pp
1061If the
1062.Cm ForwardAgent
1063variable is set to
1064.Dq yes
1065(or see the description of the
1066.Fl A
1067and
1068.Fl a
Damien Miller9a765b22005-12-24 14:53:44 +11001069options above) and
Darren Tuckerd3877b92005-12-20 16:09:36 +11001070the user is using an authentication agent, the connection to the agent
1071is automatically forwarded to the remote side.
Damien Millerbbc59092006-01-31 21:46:51 +11001072.Sh VERIFYING HOST KEYS
1073When connecting to a server for the first time,
1074a fingerprint of the server's public key is presented to the user
1075(unless the option
1076.Cm StrictHostKeyChecking
1077has been disabled).
1078Fingerprints can be determined using
1079.Xr ssh-keygen 1 :
1080.Pp
1081.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1082.Pp
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001083If the fingerprint is already known, it can be matched
1084and the key can be accepted or rejected.
1085Because of the difficulty of comparing host keys
1086just by looking at hex strings,
1087there is also support to compare host keys visually,
1088using
1089.Em random art .
1090By setting the
Damien Miller10288242008-06-30 00:04:03 +10001091.Cm VisualHostKey
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001092option to
Damien Miller10288242008-06-30 00:04:03 +10001093.Dq yes ,
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001094a small ASCII graphic gets displayed on every login to a server, no matter
1095if the session itself is interactive or not.
1096By learning the pattern a known server produces, a user can easily
1097find out that the host key has changed when a completely different pattern
1098is displayed.
1099Because these patterns are not unambiguous however, a pattern that looks
1100similar to the pattern remembered only gives a good probability that the
1101host key is the same, not guaranteed proof.
1102.Pp
1103To get a listing of the fingerprints along with their random art for
1104all known hosts, the following command line can be used:
1105.Pp
1106.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1107.Pp
Damien Millerbbc59092006-01-31 21:46:51 +11001108If the fingerprint is unknown,
1109an alternative method of verification is available:
1110SSH fingerprints verified by DNS.
1111An additional resource record (RR),
1112SSHFP,
1113is added to a zonefile
1114and the connecting client is able to match the fingerprint
1115with that of the key presented.
1116.Pp
1117In this example, we are connecting a client to a server,
1118.Dq host.example.com .
1119The SSHFP resource records should first be added to the zonefile for
1120host.example.com:
1121.Bd -literal -offset indent
Damien Millera1b3d632006-03-26 00:07:02 +11001122$ ssh-keygen -r host.example.com.
Damien Millerbbc59092006-01-31 21:46:51 +11001123.Ed
1124.Pp
1125The output lines will have to be added to the zonefile.
1126To check that the zone is answering fingerprint queries:
1127.Pp
1128.Dl $ dig -t SSHFP host.example.com
1129.Pp
1130Finally the client connects:
1131.Bd -literal -offset indent
1132$ ssh -o "VerifyHostKeyDNS ask" host.example.com
1133[...]
1134Matching host key fingerprint found in DNS.
1135Are you sure you want to continue connecting (yes/no)?
1136.Ed
1137.Pp
1138See the
1139.Cm VerifyHostKeyDNS
1140option in
1141.Xr ssh_config 5
1142for more information.
Darren Tucker248dd132006-01-20 11:30:58 +11001143.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1144.Nm
1145contains support for Virtual Private Network (VPN) tunnelling
1146using the
1147.Xr tun 4
1148network pseudo-device,
1149allowing two networks to be joined securely.
1150The
1151.Xr sshd_config 5
1152configuration option
1153.Cm PermitTunnel
1154controls whether the server supports this,
1155and at what level (layer 2 or 3 traffic).
1156.Pp
1157The following example would connect client network 10.0.50.0/24
Damien Miller3975ee22006-11-05 05:31:33 +11001158with remote network 10.0.99.0/24 using a point-to-point connection
1159from 10.1.1.1 to 10.1.1.2,
1160provided that the SSH server running on the gateway to the remote network,
1161at 192.168.1.15, allows it.
1162.Pp
1163On the client:
Darren Tucker248dd132006-01-20 11:30:58 +11001164.Bd -literal -offset indent
1165# ssh -f -w 0:1 192.168.1.15 true
Damien Miller3975ee22006-11-05 05:31:33 +11001166# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1167# route add 10.0.99.0/24 10.1.1.2
1168.Ed
1169.Pp
1170On the server:
1171.Bd -literal -offset indent
1172# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1173# route add 10.0.50.0/24 10.1.1.1
Darren Tucker248dd132006-01-20 11:30:58 +11001174.Ed
1175.Pp
1176Client access may be more finely tuned via the
1177.Pa /root/.ssh/authorized_keys
1178file (see below) and the
1179.Cm PermitRootLogin
1180server option.
Damien Millere93eaaa2006-03-15 11:05:59 +11001181The following entry would permit connections on
Darren Tucker248dd132006-01-20 11:30:58 +11001182.Xr tun 4
Damien Millere93eaaa2006-03-15 11:05:59 +11001183device 1 from user
Darren Tucker248dd132006-01-20 11:30:58 +11001184.Dq jane
Damien Millere93eaaa2006-03-15 11:05:59 +11001185and on tun device 2 from user
Darren Tucker248dd132006-01-20 11:30:58 +11001186.Dq john ,
1187if
1188.Cm PermitRootLogin
1189is set to
1190.Dq forced-commands-only :
1191.Bd -literal -offset 2n
1192tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
Damien Miller9f67a212006-03-15 11:05:35 +11001193tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
Darren Tucker248dd132006-01-20 11:30:58 +11001194.Ed
1195.Pp
Darren Tuckerffe88e12006-10-18 07:53:06 +10001196Since an SSH-based setup entails a fair amount of overhead,
Darren Tucker248dd132006-01-20 11:30:58 +11001197it may be more suited to temporary setups,
1198such as for wireless VPNs.
1199More permanent VPNs are better provided by tools such as
1200.Xr ipsecctl 8
1201and
1202.Xr isakmpd 8 .
Damien Miller32aa1441999-10-29 09:15:49 +10001203.Sh ENVIRONMENT
1204.Nm
1205will normally set the following environment variables:
Damien Miller6aa22902006-01-06 14:48:34 +11001206.Bl -tag -width "SSH_ORIGINAL_COMMAND"
Damien Miller32aa1441999-10-29 09:15:49 +10001207.It Ev DISPLAY
1208The
1209.Ev DISPLAY
Damien Miller7684ee12000-03-17 23:40:15 +11001210variable indicates the location of the X11 server.
Damien Miller22c77262000-04-13 12:26:34 +10001211It is automatically set by
Damien Miller32aa1441999-10-29 09:15:49 +10001212.Nm
1213to point to a value of the form
Damien Miller14af93e2006-01-02 23:38:21 +11001214.Dq hostname:n ,
1215where
1216.Dq hostname
1217indicates the host where the shell runs, and
1218.Sq n
1219is an integer \*(Ge 1.
Damien Miller7684ee12000-03-17 23:40:15 +11001220.Nm
1221uses this special value to forward X11 connections over the secure
1222channel.
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001223The user should normally not set
1224.Ev DISPLAY
1225explicitly, as that
Damien Miller32aa1441999-10-29 09:15:49 +10001226will render the X11 connection insecure (and will require the user to
1227manually copy any required authorization cookies).
1228.It Ev HOME
1229Set to the path of the user's home directory.
1230.It Ev LOGNAME
1231Synonym for
1232.Ev USER ;
1233set for compatibility with systems that use this variable.
1234.It Ev MAIL
Ben Lindstrome59433d2001-09-12 16:41:37 +00001235Set to the path of the user's mailbox.
Damien Miller7684ee12000-03-17 23:40:15 +11001236.It Ev PATH
Damien Miller32aa1441999-10-29 09:15:49 +10001237Set to the default
1238.Ev PATH ,
1239as specified when compiling
Damien Miller1164c292006-01-02 23:38:37 +11001240.Nm .
Ben Lindstrom5bf5d672001-07-04 04:31:38 +00001241.It Ev SSH_ASKPASS
1242If
1243.Nm
1244needs a passphrase, it will read the passphrase from the current
1245terminal if it was run from a terminal.
1246If
1247.Nm
1248does not have a terminal associated with it but
1249.Ev DISPLAY
1250and
1251.Ev SSH_ASKPASS
1252are set, it will execute the program specified by
1253.Ev SSH_ASKPASS
1254and open an X11 window to read the passphrase.
1255This is particularly useful when calling
1256.Nm
1257from a
Darren Tucker4e4fe002004-11-05 20:01:03 +11001258.Pa .xsession
Ben Lindstrom5bf5d672001-07-04 04:31:38 +00001259or related script.
1260(Note that on some machines it
1261may be necessary to redirect the input from
1262.Pa /dev/null
1263to make this work.)
Damien Miller32aa1441999-10-29 09:15:49 +10001264.It Ev SSH_AUTH_SOCK
Damien Miller14af93e2006-01-02 23:38:21 +11001265Identifies the path of a
1266.Ux Ns -domain
1267socket used to communicate with the agent.
Damien Millerf37e2462002-09-19 11:47:55 +10001268.It Ev SSH_CONNECTION
1269Identifies the client and server ends of the connection.
Damien Miller7684ee12000-03-17 23:40:15 +11001270The variable contains
Damien Miller14af93e2006-01-02 23:38:21 +11001271four space-separated values: client IP address, client port number,
1272server IP address, and server port number.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001273.It Ev SSH_ORIGINAL_COMMAND
Damien Miller14af93e2006-01-02 23:38:21 +11001274This variable contains the original command line if a forced command
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001275is executed.
1276It can be used to extract the original arguments.
Damien Miller32aa1441999-10-29 09:15:49 +10001277.It Ev SSH_TTY
1278This is set to the name of the tty (path to the device) associated
Damien Miller7684ee12000-03-17 23:40:15 +11001279with the current shell or command.
1280If the current session has no tty,
Damien Miller32aa1441999-10-29 09:15:49 +10001281this variable is not set.
1282.It Ev TZ
Damien Miller6dbdb6a2005-12-13 19:25:43 +11001283This variable is set to indicate the present time zone if it
Damien Miller208f1ed2006-03-15 11:56:03 +11001284was set when the daemon was started (i.e. the daemon passes the value
Damien Miller32aa1441999-10-29 09:15:49 +10001285on to new connections).
1286.It Ev USER
1287Set to the name of the user logging in.
1288.El
1289.Pp
Damien Miller22c77262000-04-13 12:26:34 +10001290Additionally,
Damien Miller32aa1441999-10-29 09:15:49 +10001291.Nm
Damien Miller22c77262000-04-13 12:26:34 +10001292reads
Damien Miller167ea5d2005-05-26 12:04:02 +10001293.Pa ~/.ssh/environment ,
Damien Miller32aa1441999-10-29 09:15:49 +10001294and adds lines of the format
1295.Dq VARNAME=value
Damien Miller14af93e2006-01-02 23:38:21 +11001296to the environment if the file exists and users are allowed to
Ben Lindstromdc7adf22002-08-20 18:38:02 +00001297change their environment.
Darren Tucker61776952003-10-02 16:19:47 +10001298For more information, see the
Ben Lindstromdc7adf22002-08-20 18:38:02 +00001299.Cm PermitUserEnvironment
Ben Lindstrombd9bf382002-08-20 18:54:20 +00001300option in
Ben Lindstromdc7adf22002-08-20 18:38:02 +00001301.Xr sshd_config 5 .
Damien Miller32aa1441999-10-29 09:15:49 +10001302.Sh FILES
Damien Miller7655f5c2006-01-06 14:48:18 +11001303.Bl -tag -width Ds -compact
Damien Millerafdae612010-08-31 22:31:14 +10001304.It Pa ~/.rhosts
Damien Miller1bcdb502006-01-06 14:49:38 +11001305This file is used for host-based authentication (see above).
Ben Lindstromebd888d2001-03-05 05:49:29 +00001306On some machines this file may need to be
Damien Miller1bcdb502006-01-06 14:49:38 +11001307world-readable if the user's home directory is on an NFS partition,
Damien Miller32aa1441999-10-29 09:15:49 +10001308because
1309.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001310reads it as root.
1311Additionally, this file must be owned by the user,
1312and must not have write permissions for anyone else.
1313The recommended
Damien Miller32aa1441999-10-29 09:15:49 +10001314permission for most machines is read/write for the user, and not
1315accessible by others.
1316.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001317.It Pa ~/.shosts
Damien Miller1bcdb502006-01-06 14:49:38 +11001318This file is used in exactly the same way as
1319.Pa .rhosts ,
1320but allows host-based authentication without permitting login with
1321rlogin/rsh.
Damien Miller7655f5c2006-01-06 14:48:18 +11001322.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001323.It Pa ~/.ssh/
Damien Miller520e6152008-02-10 22:46:22 +11001324This directory is the default location for all user-specific configuration
1325and authentication information.
1326There is no general requirement to keep the entire contents of this directory
1327secret, but the recommended permissions are read/write/execute for the user,
1328and not accessible by others.
1329.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001330.It Pa ~/.ssh/authorized_keys
Damien Millereb8b60e2010-08-31 22:41:14 +10001331Lists the public keys (DSA/ECDSA/RSA) that can be used for logging in as
1332this user.
Damien Millerfb8ea742006-01-06 14:48:52 +11001333The format of this file is described in the
1334.Xr sshd 8
1335manual page.
Damien Millerfb8ea742006-01-06 14:48:52 +11001336This file is not highly sensitive, but the recommended
1337permissions are read/write for the user, and not accessible by others.
1338.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001339.It Pa ~/.ssh/config
Damien Millerfb8ea742006-01-06 14:48:52 +11001340This is the per-user configuration file.
1341The file format and configuration options are described in
1342.Xr ssh_config 5 .
1343Because of the potential for abuse, this file must have strict permissions:
1344read/write for the user, and not accessible by others.
1345.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001346.It Pa ~/.ssh/environment
Damien Miller4c102ee2006-01-06 14:49:17 +11001347Contains additional definitions for environment variables; see
1348.Sx ENVIRONMENT ,
Damien Millerfb8ea742006-01-06 14:48:52 +11001349above.
1350.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001351.It Pa ~/.ssh/identity
1352.It Pa ~/.ssh/id_dsa
Damien Millereb8b60e2010-08-31 22:41:14 +10001353.It Pa ~/.ssh/id_ecdsa
Damien Millerafdae612010-08-31 22:31:14 +10001354.It Pa ~/.ssh/id_rsa
Damien Millerfb8ea742006-01-06 14:48:52 +11001355Contains the private key for authentication.
1356These files
1357contain sensitive data and should be readable by the user but not
1358accessible by others (read/write/execute).
1359.Nm
1360will simply ignore a private key file if it is accessible by others.
1361It is possible to specify a passphrase when
1362generating the key which will be used to encrypt the
1363sensitive part of this file using 3DES.
1364.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001365.It Pa ~/.ssh/identity.pub
1366.It Pa ~/.ssh/id_dsa.pub
Damien Millereb8b60e2010-08-31 22:41:14 +10001367.It Pa ~/.ssh/id_ecdsa.pub
Damien Millerafdae612010-08-31 22:31:14 +10001368.It Pa ~/.ssh/id_rsa.pub
Damien Millerfb8ea742006-01-06 14:48:52 +11001369Contains the public key for authentication.
1370These files are not
1371sensitive and can (but need not) be readable by anyone.
Damien Millerfb8ea742006-01-06 14:48:52 +11001372.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001373.It Pa ~/.ssh/known_hosts
Damien Millere87eb4c2006-01-14 10:08:36 +11001374Contains a list of host keys for all hosts the user has logged into
1375that are not already in the systemwide list of known host keys.
Damien Millerfb8ea742006-01-06 14:48:52 +11001376See
Damien Millere87eb4c2006-01-14 10:08:36 +11001377.Xr sshd 8
1378for further details of the format of this file.
Damien Millerfb8ea742006-01-06 14:48:52 +11001379.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001380.It Pa ~/.ssh/rc
Damien Millerfb8ea742006-01-06 14:48:52 +11001381Commands in this file are executed by
1382.Nm
Damien Miller7e76e1f2006-01-14 10:08:57 +11001383when the user logs in, just before the user's shell (or command) is
Damien Millerfb8ea742006-01-06 14:48:52 +11001384started.
1385See the
1386.Xr sshd 8
1387manual page for more information.
1388.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001389.It Pa /etc/hosts.equiv
Damien Miller1bcdb502006-01-06 14:49:38 +11001390This file is for host-based authentication (see above).
1391It should only be writable by root.
Damien Miller7655f5c2006-01-06 14:48:18 +11001392.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001393.It Pa /etc/shosts.equiv
Damien Miller1bcdb502006-01-06 14:49:38 +11001394This file is used in exactly the same way as
1395.Pa hosts.equiv ,
1396but allows host-based authentication without permitting login with
1397rlogin/rsh.
Damien Miller7655f5c2006-01-06 14:48:18 +11001398.Pp
Damien Millerfb8ea742006-01-06 14:48:52 +11001399.It Pa /etc/ssh/ssh_config
1400Systemwide configuration file.
1401The file format and configuration options are described in
1402.Xr ssh_config 5 .
1403.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001404.It Pa /etc/ssh/ssh_host_key
1405.It Pa /etc/ssh/ssh_host_dsa_key
Damien Millereb8b60e2010-08-31 22:41:14 +10001406.It Pa /etc/ssh/ssh_host_ecdsa_key
Damien Millerafdae612010-08-31 22:31:14 +10001407.It Pa /etc/ssh/ssh_host_rsa_key
Damien Millerb9902cf2012-06-20 21:52:58 +10001408These files contain the private parts of the host keys
Damien Miller7e76e1f2006-01-14 10:08:57 +11001409and are used for host-based authentication.
1410If protocol version 1 is used,
Damien Millerfb8ea742006-01-06 14:48:52 +11001411.Nm
1412must be setuid root, since the host key is readable only by root.
1413For protocol version 2,
1414.Nm
1415uses
1416.Xr ssh-keysign 8
Damien Miller7e76e1f2006-01-14 10:08:57 +11001417to access the host keys,
1418eliminating the requirement that
Damien Millerfb8ea742006-01-06 14:48:52 +11001419.Nm
Damien Miller7e76e1f2006-01-14 10:08:57 +11001420be setuid root when host-based authentication is used.
Damien Millerfb8ea742006-01-06 14:48:52 +11001421By default
1422.Nm
1423is not setuid root.
1424.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001425.It Pa /etc/ssh/ssh_known_hosts
Damien Millerfb8ea742006-01-06 14:48:52 +11001426Systemwide list of known host keys.
1427This file should be prepared by the
1428system administrator to contain the public host keys of all machines in the
1429organization.
Damien Millere87eb4c2006-01-14 10:08:36 +11001430It should be world-readable.
1431See
Damien Millerfb8ea742006-01-06 14:48:52 +11001432.Xr sshd 8
Damien Millere87eb4c2006-01-14 10:08:36 +11001433for further details of the format of this file.
Damien Millerfb8ea742006-01-06 14:48:52 +11001434.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001435.It Pa /etc/ssh/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +10001436Commands in this file are executed by
1437.Nm
Damien Miller7e76e1f2006-01-14 10:08:57 +11001438when the user logs in, just before the user's shell (or command) is started.
Damien Miller32aa1441999-10-29 09:15:49 +10001439See the
1440.Xr sshd 8
1441manual page for more information.
Damien Miller7b28dc52000-09-05 13:34:53 +11001442.El
Damien Millerdaa7b222010-09-10 11:19:33 +10001443.Sh EXIT STATUS
1444.Nm
1445exits with the exit status of the remote command or with 255
1446if an error occurred.
Damien Miller32aa1441999-10-29 09:15:49 +10001447.Sh SEE ALSO
Damien Miller32aa1441999-10-29 09:15:49 +10001448.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +11001449.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +10001450.Xr ssh-add 1 ,
1451.Xr ssh-agent 1 ,
1452.Xr ssh-keygen 1 ,
Damien Miller128a0f12006-01-06 14:50:11 +11001453.Xr ssh-keyscan 1 ,
Darren Tucker248dd132006-01-20 11:30:58 +11001454.Xr tun 4 ,
Darren Tucker61776952003-10-02 16:19:47 +10001455.Xr hosts.equiv 5 ,
Ben Lindstrombf69e3b2002-06-23 00:31:24 +00001456.Xr ssh_config 5 ,
Ben Lindstromc001cd32002-06-23 00:32:11 +00001457.Xr ssh-keysign 8 ,
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +00001458.Xr sshd 8
Darren Tucker628a3fd2012-10-05 10:50:15 +10001459.Sh STANDARDS
Ben Lindstrom160ec622001-04-22 17:17:46 +00001460.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001461.%A S. Lehtinen
1462.%A C. Lonvick
1463.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001464.%R RFC 4250
Darren Tucker628a3fd2012-10-05 10:50:15 +10001465.%T The Secure Shell (SSH) Protocol Assigned Numbers
Damien Miller39a93a32006-03-15 11:34:45 +11001466.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001467.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001468.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001469.%A T. Ylonen
1470.%A C. Lonvick
1471.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001472.%R RFC 4251
Darren Tucker628a3fd2012-10-05 10:50:15 +10001473.%T The Secure Shell (SSH) Protocol Architecture
Damien Miller39a93a32006-03-15 11:34:45 +11001474.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001475.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001476.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001477.%A T. Ylonen
1478.%A C. Lonvick
1479.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001480.%R RFC 4252
Darren Tucker628a3fd2012-10-05 10:50:15 +10001481.%T The Secure Shell (SSH) Authentication Protocol
Damien Miller39a93a32006-03-15 11:34:45 +11001482.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001483.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001484.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001485.%A T. Ylonen
1486.%A C. Lonvick
1487.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001488.%R RFC 4253
Darren Tucker628a3fd2012-10-05 10:50:15 +10001489.%T The Secure Shell (SSH) Transport Layer Protocol
Damien Miller39a93a32006-03-15 11:34:45 +11001490.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001491.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001492.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001493.%A T. Ylonen
1494.%A C. Lonvick
1495.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001496.%R RFC 4254
Darren Tucker628a3fd2012-10-05 10:50:15 +10001497.%T The Secure Shell (SSH) Connection Protocol
Damien Miller39a93a32006-03-15 11:34:45 +11001498.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001499.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001500.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001501.%A J. Schlyter
1502.%A W. Griffin
1503.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001504.%R RFC 4255
Darren Tucker628a3fd2012-10-05 10:50:15 +10001505.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
Damien Miller39a93a32006-03-15 11:34:45 +11001506.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001507.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001508.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001509.%A F. Cusack
1510.%A M. Forssen
1511.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001512.%R RFC 4256
Darren Tucker628a3fd2012-10-05 10:50:15 +10001513.%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)
Damien Miller39a93a32006-03-15 11:34:45 +11001514.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001515.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001516.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001517.%A J. Galbraith
1518.%A P. Remaker
1519.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001520.%R RFC 4335
Darren Tucker628a3fd2012-10-05 10:50:15 +10001521.%T The Secure Shell (SSH) Session Channel Break Extension
Damien Miller39a93a32006-03-15 11:34:45 +11001522.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001523.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001524.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001525.%A M. Bellare
1526.%A T. Kohno
1527.%A C. Namprempre
1528.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001529.%R RFC 4344
Darren Tucker628a3fd2012-10-05 10:50:15 +10001530.%T The Secure Shell (SSH) Transport Layer Encryption Modes
Damien Miller39a93a32006-03-15 11:34:45 +11001531.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001532.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001533.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001534.%A B. Harris
1535.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001536.%R RFC 4345
Darren Tucker628a3fd2012-10-05 10:50:15 +10001537.%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol
Ben Lindstrom160ec622001-04-22 17:17:46 +00001538.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001539.Pp
Damien Miller3e96d742006-03-25 23:39:29 +11001540.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001541.%A M. Friedl
1542.%A N. Provos
1543.%A W. Simpson
1544.%D March 2006
Damien Miller3e96d742006-03-25 23:39:29 +11001545.%R RFC 4419
Darren Tucker628a3fd2012-10-05 10:50:15 +10001546.%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol
Damien Miller3e96d742006-03-25 23:39:29 +11001547.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001548.Pp
Damien Millerc0367fb2007-01-05 16:25:46 +11001549.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001550.%A J. Galbraith
1551.%A R. Thayer
1552.%D November 2006
Damien Millerc0367fb2007-01-05 16:25:46 +11001553.%R RFC 4716
Darren Tucker628a3fd2012-10-05 10:50:15 +10001554.%T The Secure Shell (SSH) Public Key File Format
Damien Millerc0367fb2007-01-05 16:25:46 +11001555.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001556.Pp
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001557.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001558.%A D. Stebila
1559.%A J. Green
1560.%D December 2009
Damien Miller1ca94692010-09-24 22:01:22 +10001561.%R RFC 5656
Darren Tucker628a3fd2012-10-05 10:50:15 +10001562.%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
Damien Miller1ca94692010-09-24 22:01:22 +10001563.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001564.Pp
Damien Miller1ca94692010-09-24 22:01:22 +10001565.Rs
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001566.%A A. Perrig
1567.%A D. Song
1568.%D 1999
Darren Tucker628a3fd2012-10-05 10:50:15 +10001569.%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)
1570.%T Hash Visualization: a New Technique to improve Real-World Security
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001571.Re
Damien Millerf1ce5052003-06-11 22:04:39 +10001572.Sh AUTHORS
1573OpenSSH is a derivative of the original and free
1574ssh 1.2.12 release by Tatu Ylonen.
1575Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1576Theo de Raadt and Dug Song
1577removed many bugs, re-added newer features and
1578created OpenSSH.
1579Markus Friedl contributed the support for SSH
1580protocol versions 1.5 and 2.0.