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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 Miller8ba0ead2013-12-18 17:46:27 +110036.\" $OpenBSD: ssh.1,v 1.343 2013/12/07 11:58:46 naddy Exp $
37.Dd $Mdocdate: December 7 2013 $
Damien Miller32aa1441999-10-29 09:15:49 +100038.Dt SSH 1
39.Os
40.Sh NAME
41.Nm ssh
Ben Lindstromd58eb5f2001-03-07 06:07:22 +000042.Nd OpenSSH SSH client (remote login program)
Damien Miller32aa1441999-10-29 09:15:49 +100043.Sh SYNOPSIS
44.Nm ssh
Damien Millerbcfbc482010-07-16 13:59:11 +100045.Bk -words
Damien Millere272a5b2008-11-03 19:22:37 +110046.Op Fl 1246AaCfgKkMNnqsTtVvXxYy
Ben Lindstrome0f88042001-04-30 13:06:24 +000047.Op Fl b Ar bind_address
Damien Miller30c3d422000-05-09 11:02:59 +100048.Op Fl c Ar cipher_spec
Damien Millerbcfbc482010-07-16 13:59:11 +100049.Op Fl D Oo Ar bind_address : Oc Ns Ar port
Damien Miller03d4d7e2013-04-23 15:21:06 +100050.Op Fl E Ar log_file
Damien Miller32aa1441999-10-29 09:15:49 +100051.Op Fl e Ar escape_char
Ben Lindstrom14f31ab2001-09-12 17:48:04 +000052.Op Fl F Ar configfile
Damien Miller048dc932010-02-12 09:22:04 +110053.Op Fl I Ar pkcs11
Darren Tucker61776952003-10-02 16:19:47 +100054.Op Fl i Ar identity_file
Damien Millerbcfbc482010-07-16 13:59:11 +100055.Op Fl L Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport
Darren Tucker61776952003-10-02 16:19:47 +100056.Op Fl l Ar login_name
57.Op Fl m Ar mac_spec
Darren Tucker7ebfc102004-11-07 20:06:19 +110058.Op Fl O Ar ctl_cmd
Darren Tucker61776952003-10-02 16:19:47 +100059.Op Fl o Ar option
Darren Tucker61776952003-10-02 16:19:47 +100060.Op Fl p Ar port
Damien Millerbdb352a2013-12-05 10:20:52 +110061.Op Fl Q Cm cipher | cipher-auth | mac | kex | key
Damien Millerbcfbc482010-07-16 13:59:11 +100062.Op Fl R Oo Ar bind_address : Oc Ns Ar port : Ns Ar host : Ns Ar hostport
Darren Tucker7ebfc102004-11-07 20:06:19 +110063.Op Fl S Ar ctl_path
Darren Tucker7ad8dd22010-01-12 19:40:27 +110064.Op Fl W Ar host : Ns Ar port
Damien Millerbcfbc482010-07-16 13:59:11 +100065.Op Fl w Ar local_tun Ns Op : Ns Ar remote_tun
Darren Tucker61776952003-10-02 16:19:47 +100066.Oo Ar user Ns @ Oc Ns Ar hostname
Damien Miller32aa1441999-10-29 09:15:49 +100067.Op Ar command
Damien Millerbcfbc482010-07-16 13:59:11 +100068.Ek
Damien Miller22c77262000-04-13 12:26:34 +100069.Sh DESCRIPTION
Damien Miller32aa1441999-10-29 09:15:49 +100070.Nm
Ben Lindstromd58eb5f2001-03-07 06:07:22 +000071(SSH client) is a program for logging into a remote machine and for
Damien Miller7684ee12000-03-17 23:40:15 +110072executing commands on a remote machine.
Darren Tucker61776952003-10-02 16:19:47 +100073It is intended to replace rlogin and rsh,
74and provide secure encrypted communications between
Damien Miller7684ee12000-03-17 23:40:15 +110075two untrusted hosts over an insecure network.
Damien Miller8bfaf932006-01-14 10:09:30 +110076X11 connections and arbitrary TCP ports
Darren Tucker61776952003-10-02 16:19:47 +100077can also be forwarded over the secure channel.
Damien Miller32aa1441999-10-29 09:15:49 +100078.Pp
79.Nm
Damien Miller22c77262000-04-13 12:26:34 +100080connects and logs into the specified
Darren Tucker61776952003-10-02 16:19:47 +100081.Ar hostname
82(with optional
83.Ar user
84name).
Damien Miller32aa1441999-10-29 09:15:49 +100085The user must prove
Damien Millere247cc42000-05-07 12:03:14 +100086his/her identity to the remote machine using one of several methods
Darren Tucker5434cfe2005-12-20 16:11:35 +110087depending on the protocol version used (see below).
Damien Millere247cc42000-05-07 12:03:14 +100088.Pp
Darren Tucker61776952003-10-02 16:19:47 +100089If
90.Ar command
91is specified,
Darren Tuckerb18c8672005-12-20 16:10:09 +110092it is executed on the remote host instead of a login shell.
Darren Tucker0b42e6d2004-08-13 21:22:40 +100093.Pp
Damien Miller0bc1bd82000-11-13 22:57:25 +110094The options are as follows:
Damien Miller32aa1441999-10-29 09:15:49 +100095.Bl -tag -width Ds
Darren Tucker61776952003-10-02 16:19:47 +100096.It Fl 1
97Forces
98.Nm
99to try protocol version 1 only.
100.It Fl 2
101Forces
102.Nm
103to try protocol version 2 only.
104.It Fl 4
105Forces
106.Nm
107to use IPv4 addresses only.
108.It Fl 6
109Forces
110.Nm
111to use IPv6 addresses only.
Damien Millerb1715dc2000-05-30 13:44:51 +1000112.It Fl A
113Enables forwarding of the authentication agent connection.
114This can also be specified on a per-host basis in a configuration file.
Damien Millerb5fdfaa2002-09-12 09:52:03 +1000115.Pp
Damien Miller495dca32003-04-01 21:42:14 +1000116Agent forwarding should be enabled with caution.
117Users with the ability to bypass file permissions on the remote host
Darren Tuckerae69e1d2009-10-24 11:41:34 +1100118(for the agent's
Darren Tucker98c9aec2009-10-24 11:42:44 +1100119.Ux Ns -domain
120socket) can access the local agent through the forwarded connection.
Damien Miller495dca32003-04-01 21:42:14 +1000121An attacker cannot obtain key material from the agent,
Damien Millerb5fdfaa2002-09-12 09:52:03 +1000122however they can perform operations on the keys that enable them to
123authenticate using the identities loaded into the agent.
Darren Tucker61776952003-10-02 16:19:47 +1000124.It Fl a
125Disables forwarding of the authentication agent connection.
Ben Lindstrome0f88042001-04-30 13:06:24 +0000126.It Fl b Ar bind_address
Darren Tuckera5cf8552005-07-14 17:04:18 +1000127Use
128.Ar bind_address
129on the local machine as the source address
130of the connection.
131Only useful on systems with more than one address.
Darren Tucker61776952003-10-02 16:19:47 +1000132.It Fl C
133Requests compression of all data (including stdin, stdout, stderr, and
Damien Miller8bfaf932006-01-14 10:09:30 +1100134data for forwarded X11 and TCP connections).
Darren Tucker61776952003-10-02 16:19:47 +1000135The compression algorithm is the same used by
136.Xr gzip 1 ,
137and the
138.Dq level
139can be controlled by the
140.Cm CompressionLevel
141option for protocol version 1.
142Compression is desirable on modem lines and other
143slow connections, but will only slow down things on fast networks.
144The default value can be set on a host-by-host basis in the
145configuration files; see the
146.Cm Compression
147option.
Damien Miller05202ff2004-06-15 10:30:39 +1000148.It Fl c Ar cipher_spec
149Selects the cipher specification for encrypting the session.
150.Pp
151Protocol version 1 allows specification of a single cipher.
Darren Tucker1e4308e2005-10-03 18:18:40 +1000152The supported values are
Damien Miller05202ff2004-06-15 10:30:39 +1000153.Dq 3des ,
Darren Tuckerff9f4842005-12-20 16:10:45 +1100154.Dq blowfish ,
Damien Miller05202ff2004-06-15 10:30:39 +1000155and
156.Dq des .
Damien Miller32aa1441999-10-29 09:15:49 +1000157.Ar 3des
158(triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
Damien Miller05202ff2004-06-15 10:30:39 +1000159It is believed to be secure.
Damien Miller32aa1441999-10-29 09:15:49 +1000160.Ar blowfish
Darren Tucker61776952003-10-02 16:19:47 +1000161is a fast block cipher; it appears very secure and is much faster than
Damien Miller7684ee12000-03-17 23:40:15 +1100162.Ar 3des .
Ben Lindstromffa1dd62001-09-12 16:52:28 +0000163.Ar des
164is only supported in the
165.Nm
166client for interoperability with legacy protocol 1 implementations
167that do not support the
168.Ar 3des
Damien Miller495dca32003-04-01 21:42:14 +1000169cipher.
170Its use is strongly discouraged due to cryptographic weaknesses.
Damien Miller05202ff2004-06-15 10:30:39 +1000171The default is
172.Dq 3des .
173.Pp
Damien Miller35978212005-12-24 14:56:47 +1100174For protocol version 2,
Damien Miller05202ff2004-06-15 10:30:39 +1000175.Ar cipher_spec
176is a comma-separated list of ciphers
177listed in order of preference.
Darren Tucker3a6a51f2009-06-21 17:48:52 +1000178See the
179.Cm Ciphers
Damien Miller081f3c72010-08-03 16:05:25 +1000180keyword in
181.Xr ssh_config 5
182for more information.
Darren Tuckerc8d64212005-10-03 18:13:42 +1000183.It Fl D Xo
184.Sm off
185.Oo Ar bind_address : Oc
186.Ar port
187.Sm on
188.Xc
Darren Tucker61776952003-10-02 16:19:47 +1000189Specifies a local
190.Dq dynamic
191application-level port forwarding.
192This works by allocating a socket to listen to
193.Ar port
Darren Tuckerc8d64212005-10-03 18:13:42 +1000194on the local side, optionally bound to the specified
195.Ar bind_address .
196Whenever a connection is made to this port, the
Darren Tucker61776952003-10-02 16:19:47 +1000197connection is forwarded over the secure channel, and the application
198protocol is then used to determine where to connect to from the
199remote machine.
200Currently the SOCKS4 and SOCKS5 protocols are supported, and
201.Nm
202will act as a SOCKS server.
203Only root can forward privileged ports.
204Dynamic port forwardings can also be specified in the configuration file.
Darren Tuckerc8d64212005-10-03 18:13:42 +1000205.Pp
Damien Miller7fa96602010-08-05 13:03:13 +1000206IPv6 addresses can be specified by enclosing the address in square brackets.
Darren Tuckerc8d64212005-10-03 18:13:42 +1000207Only the superuser can forward privileged ports.
208By default, the local port is bound in accordance with the
209.Cm GatewayPorts
210setting.
211However, an explicit
212.Ar bind_address
213may be used to bind the connection to a specific address.
214The
215.Ar bind_address
216of
217.Dq localhost
218indicates that the listening port be bound for local use only, while an
219empty address or
220.Sq *
221indicates that the port should be available from all interfaces.
Damien Miller03d4d7e2013-04-23 15:21:06 +1000222.It Fl E Ar log_file
223Append debug logs to
224.Ar log_file
225instead of standard error.
Damien Miller2142ba02005-12-24 14:56:29 +1100226.It Fl e Ar escape_char
Damien Miller32aa1441999-10-29 09:15:49 +1000227Sets the escape character for sessions with a pty (default:
228.Ql ~ ) .
Damien Miller7684ee12000-03-17 23:40:15 +1100229The escape character is only recognized at the beginning of a line.
230The escape character followed by a dot
Damien Miller32aa1441999-10-29 09:15:49 +1000231.Pq Ql \&.
Darren Tucker61776952003-10-02 16:19:47 +1000232closes the connection;
233followed by control-Z suspends the connection;
234and followed by itself sends the escape character once.
Damien Miller7684ee12000-03-17 23:40:15 +1100235Setting the character to
Damien Miller32aa1441999-10-29 09:15:49 +1000236.Dq none
237disables any escapes and makes the session fully transparent.
Darren Tucker61776952003-10-02 16:19:47 +1000238.It Fl F Ar configfile
239Specifies an alternative per-user configuration file.
240If a configuration file is given on the command line,
241the system-wide configuration file
242.Pq Pa /etc/ssh/ssh_config
243will be ignored.
244The default for the per-user configuration file is
Damien Miller167ea5d2005-05-26 12:04:02 +1000245.Pa ~/.ssh/config .
Damien Miller32aa1441999-10-29 09:15:49 +1000246.It Fl f
247Requests
248.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100249to go to background just before command execution.
250This is useful if
Damien Miller32aa1441999-10-29 09:15:49 +1000251.Nm
252is going to ask for passwords or passphrases, but the user
Damien Miller7684ee12000-03-17 23:40:15 +1100253wants it in the background.
Damien Miller22c77262000-04-13 12:26:34 +1000254This implies
Damien Miller32aa1441999-10-29 09:15:49 +1000255.Fl n .
256The recommended way to start X11 programs at a remote site is with
257something like
258.Ic ssh -f host xterm .
Darren Tucker9a2a6092008-07-04 12:53:50 +1000259.Pp
260If the
261.Cm ExitOnForwardFailure
262configuration option is set to
263.Dq yes ,
264then a client started with
265.Fl f
266will wait for all remote port forwards to be successfully established
267before placing itself in the background.
Damien Miller396691a2000-01-20 22:44:08 +1100268.It Fl g
269Allows remote hosts to connect to local forwarded ports.
Damien Miller7ea845e2010-02-12 09:21:02 +1100270.It Fl I Ar pkcs11
Damien Millerd400da52010-02-12 09:26:23 +1100271Specify the PKCS#11 shared library
Darren Tucker61776952003-10-02 16:19:47 +1000272.Nm
Damien Millera7618442010-02-12 09:26:02 +1100273should use to communicate with a PKCS#11 token providing the user's
Darren Tucker61776952003-10-02 16:19:47 +1000274private RSA key.
Damien Miller32aa1441999-10-29 09:15:49 +1000275.It Fl i Ar identity_file
Damien Millerfae23862002-01-22 23:32:26 +1100276Selects a file from which the identity (private key) for
Damien Millereb8b60e2010-08-31 22:41:14 +1000277public key authentication is read.
Damien Millerfae23862002-01-22 23:32:26 +1100278The default is
Damien Miller167ea5d2005-05-26 12:04:02 +1000279.Pa ~/.ssh/identity
Damien Millerfae23862002-01-22 23:32:26 +1100280for protocol version 1, and
Damien Millereb8b60e2010-08-31 22:41:14 +1000281.Pa ~/.ssh/id_dsa ,
Damien Miller8ba0ead2013-12-18 17:46:27 +1100282.Pa ~/.ssh/id_ecdsa ,
283.Pa ~/.ssh/id_ed25519
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
Damien Miller0faf7472013-10-17 11:47:23 +1100420.It CanonicalDomains
Damien Miller38505592013-10-17 11:48:13 +1100421.It CanonicalizeFallbackLocal
422.It CanonicalizeHostname
423.It CanonicalizeMaxDots
424.It CanonicalizePermittedCNAMEs
Darren Tucker61776952003-10-02 16:19:47 +1000425.It ChallengeResponseAuthentication
426.It CheckHostIP
427.It Cipher
428.It Ciphers
429.It ClearAllForwardings
430.It Compression
431.It CompressionLevel
432.It ConnectionAttempts
Darren Tuckeredae0ec2004-05-02 22:15:52 +1000433.It ConnectTimeout
Damien Miller0e220db2004-06-15 10:34:08 +1000434.It ControlMaster
435.It ControlPath
Damien Millerefad7272011-09-22 21:33:53 +1000436.It ControlPersist
Darren Tucker61776952003-10-02 16:19:47 +1000437.It DynamicForward
Darren Tucker61776952003-10-02 16:19:47 +1000438.It EscapeChar
Darren Tuckere7d4b192006-07-12 22:17:10 +1000439.It ExitOnForwardFailure
Darren Tucker61776952003-10-02 16:19:47 +1000440.It ForwardAgent
441.It ForwardX11
Damien Millerefad7272011-09-22 21:33:53 +1000442.It ForwardX11Timeout
Darren Tucker0a118da2003-10-15 15:54:32 +1000443.It ForwardX11Trusted
Darren Tucker61776952003-10-02 16:19:47 +1000444.It GatewayPorts
445.It GlobalKnownHostsFile
446.It GSSAPIAuthentication
447.It GSSAPIDelegateCredentials
Damien Millere1776152005-03-01 21:47:37 +1100448.It HashKnownHosts
Darren Tucker61776952003-10-02 16:19:47 +1000449.It Host
450.It HostbasedAuthentication
451.It HostKeyAlgorithms
452.It HostKeyAlias
453.It HostName
454.It IdentityFile
Damien Millerbd394c32004-03-08 23:12:36 +1100455.It IdentitiesOnly
Damien Miller0a184732010-11-20 15:21:03 +1100456.It IPQoS
Damien Millerefad7272011-09-22 21:33:53 +1000457.It KbdInteractiveAuthentication
Darren Tucker636ca902004-11-05 20:22:00 +1100458.It KbdInteractiveDevices
Damien Miller7fe2b1f2010-09-24 22:11:53 +1000459.It KexAlgorithms
Damien Millerd27b9472005-12-13 19:29:02 +1100460.It LocalCommand
Darren Tucker61776952003-10-02 16:19:47 +1000461.It LocalForward
462.It LogLevel
463.It MACs
Damien Millerd77b81f2013-10-17 11:39:00 +1100464.It Match
Darren Tucker61776952003-10-02 16:19:47 +1000465.It NoHostAuthenticationForLocalhost
466.It NumberOfPasswordPrompts
467.It PasswordAuthentication
Damien Millerd27b9472005-12-13 19:29:02 +1100468.It PermitLocalCommand
Damien Miller7ea845e2010-02-12 09:21:02 +1100469.It PKCS11Provider
Darren Tucker61776952003-10-02 16:19:47 +1000470.It Port
471.It PreferredAuthentications
472.It Protocol
473.It ProxyCommand
Damien Millerf2f6c312013-08-21 02:44:58 +1000474.It ProxyUseFdpass
Darren Tucker61776952003-10-02 16:19:47 +1000475.It PubkeyAuthentication
Darren Tucker62388b22006-01-20 11:31:47 +1100476.It RekeyLimit
Darren Tucker61776952003-10-02 16:19:47 +1000477.It RemoteForward
Damien Millerf4b32aa2011-05-15 08:47:43 +1000478.It RequestTTY
Darren Tucker61776952003-10-02 16:19:47 +1000479.It RhostsRSAAuthentication
480.It RSAAuthentication
Darren Tucker7a6c0662004-05-02 22:14:03 +1000481.It SendEnv
Damien Miller509b0102003-12-17 16:33:10 +1100482.It ServerAliveInterval
483.It ServerAliveCountMax
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
Darren Tucker61776952003-10-02 16:19:47 +1000488.It UsePrivilegedPort
489.It User
490.It UserKnownHostsFile
491.It VerifyHostKeyDNS
Damien Miller86399202008-06-30 00:04:31 +1000492.It VisualHostKey
Darren Tucker61776952003-10-02 16:19:47 +1000493.It XAuthLocation
494.El
Damien Miller32aa1441999-10-29 09:15:49 +1000495.It Fl p Ar port
Damien Miller7684ee12000-03-17 23:40:15 +1100496Port to connect to on the remote host.
497This can be specified on a
Damien Miller32aa1441999-10-29 09:15:49 +1000498per-host basis in the configuration file.
Damien Millerbdb352a2013-12-05 10:20:52 +1100499.It Fl Q Cm cipher | cipher-auth | mac | kex | key
Damien Millerea111192013-04-23 19:24:32 +1000500Queries
501.Nm
Damien Millerd937dc02013-12-05 10:19:54 +1100502for the algorithms supported for the specified version 2.
503The available features are:
504.Ar cipher
Damien Millerea111192013-04-23 19:24:32 +1000505(supported symmetric ciphers),
Damien Millerd937dc02013-12-05 10:19:54 +1100506.Ar cipher-auth
Damien Miller0fde8ac2013-11-21 14:12:23 +1100507(supported symmetric ciphers that support authenticated encryption),
Damien Millerd937dc02013-12-05 10:19:54 +1100508.Ar mac
Damien Millerea111192013-04-23 19:24:32 +1000509(supported message integrity codes),
Damien Millerd937dc02013-12-05 10:19:54 +1100510.Ar kex
Damien Millerea111192013-04-23 19:24:32 +1000511(key exchange algorithms),
Damien Millerd937dc02013-12-05 10:19:54 +1100512.Ar key
Damien Millerea111192013-04-23 19:24:32 +1000513(key types).
Damien Miller32aa1441999-10-29 09:15:49 +1000514.It Fl q
Damien Miller7684ee12000-03-17 23:40:15 +1100515Quiet mode.
Damien Millereb602472008-02-10 22:21:28 +1100516Causes most warning and diagnostic messages to be suppressed.
Darren Tucker61776952003-10-02 16:19:47 +1000517.It Fl R Xo
518.Sm off
Damien Millerf91ee4c2005-03-01 21:24:33 +1100519.Oo Ar bind_address : Oc
Darren Tucker61776952003-10-02 16:19:47 +1000520.Ar port : host : hostport
521.Sm on
522.Xc
Damien Miller32aa1441999-10-29 09:15:49 +1000523Specifies that the given port on the remote (server) host is to be
Damien Miller7684ee12000-03-17 23:40:15 +1100524forwarded to the given host and port on the local side.
525This works by allocating a socket to listen to
Damien Miller32aa1441999-10-29 09:15:49 +1000526.Ar port
527on the remote side, and whenever a connection is made to this port, the
528connection is forwarded over the secure channel, and a connection is
529made to
Damien Miller34132e52000-01-14 15:45:46 +1100530.Ar host
531port
532.Ar hostport
Damien Miller7684ee12000-03-17 23:40:15 +1100533from the local machine.
Damien Millerf91ee4c2005-03-01 21:24:33 +1100534.Pp
Damien Miller7684ee12000-03-17 23:40:15 +1100535Port forwardings can also be specified in the configuration file.
536Privileged ports can be forwarded only when
Damien Miller32aa1441999-10-29 09:15:49 +1000537logging in as root on the remote machine.
Damien Miller70b2d552012-04-22 11:26:10 +1000538IPv6 addresses can be specified by enclosing the address in square brackets.
Damien Millerf91ee4c2005-03-01 21:24:33 +1100539.Pp
540By default, the listening socket on the server will be bound to the loopback
541interface only.
Darren Tucker63917bd2008-11-11 16:33:48 +1100542This may be overridden by specifying a
Damien Millerf91ee4c2005-03-01 21:24:33 +1100543.Ar bind_address .
Damien Miller36bf7dd2005-03-02 12:02:47 +1100544An empty
545.Ar bind_address ,
Damien Millerf91ee4c2005-03-01 21:24:33 +1100546or the address
Damien Miller36bf7dd2005-03-02 12:02:47 +1100547.Ql * ,
Damien Millerf91ee4c2005-03-01 21:24:33 +1100548indicates that the remote socket should listen on all interfaces.
549Specifying a remote
550.Ar bind_address
Damien Miller36bf7dd2005-03-02 12:02:47 +1100551will only succeed if the server's
552.Cm GatewayPorts
Damien Millerf91ee4c2005-03-01 21:24:33 +1100553option is enabled (see
Damien Miller36bf7dd2005-03-02 12:02:47 +1100554.Xr sshd_config 5 ) .
Damien Millere2f4cc52009-02-14 16:33:49 +1100555.Pp
556If the
557.Ar port
558argument is
Damien Miller65fa4ca2009-02-14 16:34:05 +1100559.Ql 0 ,
Damien Millere2f4cc52009-02-14 16:33:49 +1100560the listen port will be dynamically allocated on the server and reported
561to the client at run time.
Damien Miller388f6fc2010-05-21 14:57:35 +1000562When used together with
563.Ic -O forward
564the allocated port will be printed to the standard output.
Darren Tucker7ebfc102004-11-07 20:06:19 +1100565.It Fl S Ar ctl_path
Damien Miller67f30d72010-04-16 15:52:03 +1000566Specifies the location of a control socket for connection sharing,
Damien Miller9c60f242010-03-26 11:28:35 +1100567or the string
568.Dq none
569to disable connection sharing.
Damien Miller0e220db2004-06-15 10:34:08 +1000570Refer to the description of
Darren Tuckerba5c5922004-06-18 16:22:39 +1000571.Cm ControlPath
572and
Damien Miller0e220db2004-06-15 10:34:08 +1000573.Cm ControlMaster
574in
575.Xr ssh_config 5
576for details.
Darren Tucker61776952003-10-02 16:19:47 +1000577.It Fl s
578May be used to request invocation of a subsystem on the remote system.
579Subsystems are a feature of the SSH2 protocol which facilitate the use
580of SSH as a secure transport for other applications (eg.\&
581.Xr sftp 1 ) .
582The subsystem is specified as the remote command.
583.It Fl T
584Disable pseudo-tty allocation.
585.It Fl t
586Force pseudo-tty allocation.
587This can be used to execute arbitrary
588screen-based programs on a remote machine, which can be very useful,
Damien Miller208f1ed2006-03-15 11:56:03 +1100589e.g. when implementing menu services.
Darren Tucker61776952003-10-02 16:19:47 +1000590Multiple
591.Fl t
592options force tty allocation, even if
Ben Lindstrom19ceb172001-09-12 17:54:24 +0000593.Nm
Darren Tucker61776952003-10-02 16:19:47 +1000594has no local tty.
595.It Fl V
596Display the version number and exit.
597.It Fl v
598Verbose mode.
599Causes
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000600.Nm
Darren Tucker61776952003-10-02 16:19:47 +1000601to print debugging messages about its progress.
602This is helpful in
603debugging connection, authentication, and configuration problems.
604Multiple
605.Fl v
606options increase the verbosity.
607The maximum is 3.
Darren Tucker7ad8dd22010-01-12 19:40:27 +1100608.It Fl W Ar host : Ns Ar port
609Requests that standard input and output on the client be forwarded to
610.Ar host
611on
612.Ar port
613over the secure channel.
614Implies
615.Fl N ,
616.Fl T ,
617.Cm ExitOnForwardFailure
618and
Damien Miller36378c62012-06-20 21:53:25 +1000619.Cm ClearAllForwardings .
620Works with Protocol version 2 only.
Damien Miller991dba42006-07-10 20:16:27 +1000621.It Fl w Xo
622.Ar local_tun Ns Op : Ns Ar remote_tun
623.Xc
624Requests
625tunnel
626device forwarding with the specified
Damien Millerd27b9472005-12-13 19:29:02 +1100627.Xr tun 4
Damien Miller991dba42006-07-10 20:16:27 +1000628devices between the client
629.Pq Ar local_tun
630and the server
631.Pq Ar remote_tun .
632.Pp
Damien Millercf1e3422005-12-24 14:56:04 +1100633The devices may be specified by numerical ID or the keyword
634.Dq any ,
635which uses the next available tunnel device.
Damien Miller991dba42006-07-10 20:16:27 +1000636If
637.Ar remote_tun
638is not specified, it defaults to
639.Dq any .
Damien Millercf1e3422005-12-24 14:56:04 +1100640See also the
Damien Millerd27b9472005-12-13 19:29:02 +1100641.Cm Tunnel
Damien Miller991dba42006-07-10 20:16:27 +1000642and
643.Cm TunnelDevice
644directives in
Damien Millerd27b9472005-12-13 19:29:02 +1100645.Xr ssh_config 5 .
Damien Miller991dba42006-07-10 20:16:27 +1000646If the
647.Cm Tunnel
648directive is unset, it is set to the default tunnel mode, which is
649.Dq point-to-point .
Darren Tucker61776952003-10-02 16:19:47 +1000650.It Fl X
651Enables X11 forwarding.
652This can also be specified on a per-host basis in a configuration file.
653.Pp
654X11 forwarding should be enabled with caution.
655Users with the ability to bypass file permissions on the remote host
656(for the user's X authorization database)
657can access the local X11 display through the forwarded connection.
658An attacker may then be able to perform activities such as keystroke monitoring.
Damien Miller947219e2005-03-02 13:22:30 +1100659.Pp
Damien Millerb022b232005-03-05 11:22:36 +1100660For this reason, X11 forwarding is subjected to X11 SECURITY extension
Damien Miller947219e2005-03-02 13:22:30 +1100661restrictions by default.
662Please refer to the
663.Nm
664.Fl Y
665option and the
666.Cm ForwardX11Trusted
667directive in
668.Xr ssh_config 5
669for more information.
Darren Tucker61776952003-10-02 16:19:47 +1000670.It Fl x
671Disables X11 forwarding.
Darren Tucker0a118da2003-10-15 15:54:32 +1000672.It Fl Y
673Enables trusted X11 forwarding.
Damien Miller947219e2005-03-02 13:22:30 +1100674Trusted X11 forwardings are not subjected to the X11 SECURITY extension
675controls.
Damien Millere272a5b2008-11-03 19:22:37 +1100676.It Fl y
677Send log information using the
678.Xr syslog 3
679system module.
680By default this information is sent to stderr.
Damien Miller32aa1441999-10-29 09:15:49 +1000681.El
Damien Millere9b333a2005-12-24 14:53:04 +1100682.Pp
683.Nm
684may additionally obtain configuration data from
685a per-user configuration file and a system-wide configuration file.
686The file format and configuration options are described in
687.Xr ssh_config 5 .
Damien Millerc93a8132005-12-24 14:52:13 +1100688.Sh AUTHENTICATION
Darren Tucker94299ec2006-01-20 11:30:14 +1100689The OpenSSH SSH client supports SSH protocols 1 and 2.
Darren Tucker7a4a7652009-10-11 21:51:40 +1100690The default is to use protocol 2 only,
691though this can be changed via the
Damien Millerc93a8132005-12-24 14:52:13 +1100692.Cm Protocol
693option in
Darren Tucker7a4a7652009-10-11 21:51:40 +1100694.Xr ssh_config 5
695or the
Damien Millerc93a8132005-12-24 14:52:13 +1100696.Fl 1
697and
698.Fl 2
699options (see above).
700Both protocols support similar authentication methods,
Darren Tucker7a4a7652009-10-11 21:51:40 +1100701but protocol 2 is the default since
Damien Millerc93a8132005-12-24 14:52:13 +1100702it provides additional mechanisms for confidentiality
703(the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour)
Damien Miller20bd4532011-08-06 06:17:30 +1000704and integrity (hmac-md5, hmac-sha1,
705hmac-sha2-256, hmac-sha2-512,
Darren Tucker427e4092012-10-05 11:02:39 +1000706umac-64, umac-128, hmac-ripemd160).
Damien Millerc93a8132005-12-24 14:52:13 +1100707Protocol 1 lacks a strong mechanism for ensuring the
708integrity of the connection.
709.Pp
710The methods available for authentication are:
Damien Millerfbc94c82006-06-13 13:03:16 +1000711GSSAPI-based authentication,
Damien Millerc93a8132005-12-24 14:52:13 +1100712host-based authentication,
713public key authentication,
714challenge-response authentication,
715and password authentication.
716Authentication methods are tried in the order specified above,
717though protocol 2 has a configuration option to change the default order:
718.Cm PreferredAuthentications .
719.Pp
720Host-based authentication works as follows:
Darren Tuckerd3877b92005-12-20 16:09:36 +1100721If the machine the user logs in from is listed in
722.Pa /etc/hosts.equiv
723or
724.Pa /etc/shosts.equiv
725on the remote machine, and the user names are
726the same on both sides, or if the files
727.Pa ~/.rhosts
728or
729.Pa ~/.shosts
730exist in the user's home directory on the
731remote machine and contain a line containing the name of the client
732machine and the name of the user on that machine, the user is
Damien Millerc93a8132005-12-24 14:52:13 +1100733considered for login.
734Additionally, the server
735.Em must
736be able to verify the client's
737host key (see the description of
Darren Tuckerd3877b92005-12-20 16:09:36 +1100738.Pa /etc/ssh/ssh_known_hosts
739and
Damien Millerc93a8132005-12-24 14:52:13 +1100740.Pa ~/.ssh/known_hosts ,
741below)
742for login to be permitted.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100743This authentication method closes security holes due to IP
Damien Millerc93a8132005-12-24 14:52:13 +1100744spoofing, DNS spoofing, and routing spoofing.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100745[Note to the administrator:
746.Pa /etc/hosts.equiv ,
747.Pa ~/.rhosts ,
748and the rlogin/rsh protocol in general, are inherently insecure and should be
749disabled if security is desired.]
750.Pp
Damien Millerc93a8132005-12-24 14:52:13 +1100751Public key authentication works as follows:
752The scheme is based on public-key cryptography,
753using cryptosystems
754where encryption and decryption are done using separate keys,
755and it is unfeasible to derive the decryption key from the encryption key.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100756The idea is that each user creates a public/private
757key pair for authentication purposes.
758The server knows the public key, and only the user knows the private key.
Damien Millerc93a8132005-12-24 14:52:13 +1100759.Nm
760implements public key authentication protocol automatically,
Damien Miller8ba0ead2013-12-18 17:46:27 +1100761using one of the DSA, ECDSA, ED25519 or RSA algorithms.
Damien Millerc93a8132005-12-24 14:52:13 +1100762Protocol 1 is restricted to using only RSA keys,
Damien Millereb8b60e2010-08-31 22:41:14 +1000763but protocol 2 may use any.
Damien Millerfecfd112013-07-18 16:11:50 +1000764The HISTORY section of
Damien Millerc93a8132005-12-24 14:52:13 +1100765.Xr ssl 8
Damien Millerd4427902010-09-10 11:15:10 +1000766contains a brief discussion of the DSA and RSA algorithms.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100767.Pp
768The file
769.Pa ~/.ssh/authorized_keys
770lists the public keys that are permitted for logging in.
771When the user logs in, the
772.Nm
773program tells the server which key pair it would like to use for
774authentication.
Damien Millerc93a8132005-12-24 14:52:13 +1100775The client proves that it has access to the private key
776and the server checks that the corresponding public key
777is authorized to accept the account.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100778.Pp
Damien Millerc93a8132005-12-24 14:52:13 +1100779The user creates his/her key pair by running
Darren Tuckerd3877b92005-12-20 16:09:36 +1100780.Xr ssh-keygen 1 .
781This stores the private key in
782.Pa ~/.ssh/identity
Damien Millerc93a8132005-12-24 14:52:13 +1100783(protocol 1),
784.Pa ~/.ssh/id_dsa
785(protocol 2 DSA),
Damien Millereb8b60e2010-08-31 22:41:14 +1000786.Pa ~/.ssh/id_ecdsa
787(protocol 2 ECDSA),
Damien Miller8ba0ead2013-12-18 17:46:27 +1100788.Pa ~/.ssh/id_ed25519
789(protocol 2 ED25519),
Damien Millerc93a8132005-12-24 14:52:13 +1100790or
791.Pa ~/.ssh/id_rsa
792(protocol 2 RSA)
Darren Tuckerd3877b92005-12-20 16:09:36 +1100793and stores the public key in
794.Pa ~/.ssh/identity.pub
Damien Millerc93a8132005-12-24 14:52:13 +1100795(protocol 1),
796.Pa ~/.ssh/id_dsa.pub
797(protocol 2 DSA),
Damien Millereb8b60e2010-08-31 22:41:14 +1000798.Pa ~/.ssh/id_ecdsa.pub
799(protocol 2 ECDSA),
Damien Miller8ba0ead2013-12-18 17:46:27 +1100800.Pa ~/.ssh/id_ed25519.pub
801(protocol 2 ED25519),
Damien Millerc93a8132005-12-24 14:52:13 +1100802or
803.Pa ~/.ssh/id_rsa.pub
804(protocol 2 RSA)
Darren Tuckerd3877b92005-12-20 16:09:36 +1100805in the user's home directory.
Damien Millerc93a8132005-12-24 14:52:13 +1100806The user should then copy the public key
Darren Tuckerd3877b92005-12-20 16:09:36 +1100807to
808.Pa ~/.ssh/authorized_keys
Damien Millerc93a8132005-12-24 14:52:13 +1100809in his/her home directory on the remote machine.
810The
Darren Tuckerd3877b92005-12-20 16:09:36 +1100811.Pa authorized_keys
812file corresponds to the conventional
813.Pa ~/.rhosts
814file, and has one key
Damien Millerc93a8132005-12-24 14:52:13 +1100815per line, though the lines can be very long.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100816After this, the user can log in without giving the password.
817.Pp
Damien Miller922b5412010-03-05 21:30:54 +1100818A variation on public key authentication
819is available in the form of certificate authentication:
820instead of a set of public/private keys,
821signed certificates are used.
822This has the advantage that a single trusted certification authority
823can be used in place of many public/private keys.
Damien Millerfecfd112013-07-18 16:11:50 +1000824See the CERTIFICATES section of
Damien Miller922b5412010-03-05 21:30:54 +1100825.Xr ssh-keygen 1
826for more information.
827.Pp
828The most convenient way to use public key or certificate authentication
829may be with an authentication agent.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100830See
831.Xr ssh-agent 1
832for more information.
833.Pp
Damien Millerc93a8132005-12-24 14:52:13 +1100834Challenge-response authentication works as follows:
835The server sends an arbitrary
836.Qq challenge
837text, and prompts for a response.
838Protocol 2 allows multiple challenges and responses;
839protocol 1 is restricted to just one challenge/response.
840Examples of challenge-response authentication include
Damien Millerb7727df2013-08-21 02:43:49 +1000841.Bx
842Authentication (see
Damien Millerc93a8132005-12-24 14:52:13 +1100843.Xr login.conf 5 )
Damien Millerb7727df2013-08-21 02:43:49 +1000844and PAM (some
845.Pf non- Ox
846systems).
Damien Millerc93a8132005-12-24 14:52:13 +1100847.Pp
848Finally, if other authentication methods fail,
Darren Tuckerd3877b92005-12-20 16:09:36 +1100849.Nm
850prompts the user for a password.
851The password is sent to the remote
852host for checking; however, since all communications are encrypted,
853the password cannot be seen by someone listening on the network.
Damien Miller48c94ab2006-01-02 23:38:00 +1100854.Pp
855.Nm
856automatically maintains and checks a database containing
857identification for all hosts it has ever been used with.
858Host keys are stored in
859.Pa ~/.ssh/known_hosts
860in the user's home directory.
861Additionally, the file
862.Pa /etc/ssh/ssh_known_hosts
863is automatically checked for known hosts.
864Any new hosts are automatically added to the user's file.
865If a host's identification ever changes,
866.Nm
867warns about this and disables password authentication to prevent
868server spoofing or man-in-the-middle attacks,
869which could otherwise be used to circumvent the encryption.
870The
871.Cm StrictHostKeyChecking
872option can be used to control logins to machines whose
873host key is not known or has changed.
874.Pp
Darren Tuckerd3877b92005-12-20 16:09:36 +1100875When the user's identity has been accepted by the server, the server
876either executes the given command, or logs into the machine and gives
877the user a normal shell on the remote machine.
878All communication with
879the remote command or shell will be automatically encrypted.
880.Pp
881If a pseudo-terminal has been allocated (normal login session), the
882user may use the escape characters noted below.
883.Pp
884If no pseudo-tty has been allocated,
885the session is transparent and can be used to reliably transfer binary data.
886On most systems, setting the escape character to
887.Dq none
888will also make the session transparent even if a tty is used.
889.Pp
890The session terminates when the command or shell on the remote
Damien Miller8bfaf932006-01-14 10:09:30 +1100891machine exits and all X11 and TCP connections have been closed.
Damien Miller52d20612005-12-24 14:52:36 +1100892.Sh ESCAPE CHARACTERS
Darren Tuckerd3877b92005-12-20 16:09:36 +1100893When a pseudo-terminal has been requested,
894.Nm
895supports a number of functions through the use of an escape character.
896.Pp
897A single tilde character can be sent as
898.Ic ~~
899or by following the tilde by a character other than those described below.
900The escape character must always follow a newline to be interpreted as
901special.
902The escape character can be changed in configuration files using the
903.Cm EscapeChar
904configuration directive or on the command line by the
905.Fl e
906option.
907.Pp
908The supported escapes (assuming the default
909.Ql ~ )
910are:
911.Bl -tag -width Ds
912.It Cm ~.
913Disconnect.
914.It Cm ~^Z
915Background
Damien Miller1164c292006-01-02 23:38:37 +1100916.Nm .
Darren Tuckerd3877b92005-12-20 16:09:36 +1100917.It Cm ~#
918List forwarded connections.
919.It Cm ~&
920Background
921.Nm
922at logout when waiting for forwarded connection / X11 sessions to terminate.
923.It Cm ~?
924Display a list of escape characters.
925.It Cm ~B
926Send a BREAK to the remote system
927(only useful for SSH protocol version 2 and if the peer supports it).
928.It Cm ~C
929Open command line.
930Currently this allows the addition of port forwardings using the
Damien Miller0164cb82008-11-05 16:30:31 +1100931.Fl L ,
Darren Tuckerd3877b92005-12-20 16:09:36 +1100932.Fl R
Damien Miller0164cb82008-11-05 16:30:31 +1100933and
934.Fl D
Damien Miller329cb012005-12-24 14:53:23 +1100935options (see above).
Damien Millerff773642011-09-22 21:39:48 +1000936It also allows the cancellation of existing port-forwardings
937with
Damien Miller57e8ad32006-07-10 20:20:52 +1000938.Sm off
Damien Millerff773642011-09-22 21:39:48 +1000939.Fl KL Oo Ar bind_address : Oc Ar port
Damien Miller57e8ad32006-07-10 20:20:52 +1000940.Sm on
Damien Millerff773642011-09-22 21:39:48 +1000941for local,
942.Sm off
943.Fl KR Oo Ar bind_address : Oc Ar port
944.Sm on
945for remote and
946.Sm off
947.Fl KD Oo Ar bind_address : Oc Ar port
948.Sm on
949for dynamic port-forwardings.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100950.Ic !\& Ns Ar command
951allows the user to execute a local command if the
952.Ic PermitLocalCommand
953option is enabled in
954.Xr ssh_config 5 .
955Basic help is available, using the
956.Fl h
957option.
958.It Cm ~R
959Request rekeying of the connection
960(only useful for SSH protocol version 2 and if the peer supports it).
Darren Tucker50a48d02012-09-06 21:25:37 +1000961.It Cm ~V
962Decrease the verbosity
963.Pq Ic LogLevel
964when errors are being written to stderr.
965.It Cm ~v
Darren Tucker83d0af62012-09-07 11:21:03 +1000966Increase the verbosity
Darren Tucker50a48d02012-09-06 21:25:37 +1000967.Pq Ic LogLevel
968when errors are being written to stderr.
Darren Tuckerd3877b92005-12-20 16:09:36 +1100969.El
Damien Millerf3177182006-01-14 10:09:13 +1100970.Sh TCP FORWARDING
971Forwarding of arbitrary TCP connections over the secure channel can
972be specified either on the command line or in a configuration file.
973One possible application of TCP forwarding is a secure connection to a
974mail server; another is going through firewalls.
975.Pp
976In the example below, we look at encrypting communication between
977an IRC client and server, even though the IRC server does not directly
978support encrypted communications.
979This works as follows:
980the user connects to the remote host using
981.Nm ,
982specifying a port to be used to forward connections
983to the remote server.
984After that it is possible to start the service which is to be encrypted
985on the client machine,
986connecting to the same local port,
987and
988.Nm
989will encrypt and forward the connection.
990.Pp
991The following example tunnels an IRC session from client machine
992.Dq 127.0.0.1
993(localhost)
994to remote server
995.Dq server.example.com :
996.Bd -literal -offset 4n
997$ ssh -f -L 1234:localhost:6667 server.example.com sleep 10
998$ irc -c '#users' -p 1234 pinky 127.0.0.1
999.Ed
1000.Pp
1001This tunnels a connection to IRC server
1002.Dq server.example.com ,
1003joining channel
1004.Dq #users ,
1005nickname
1006.Dq pinky ,
1007using port 1234.
1008It doesn't matter which port is used,
1009as long as it's greater than 1023
1010(remember, only root can open sockets on privileged ports)
1011and doesn't conflict with any ports already in use.
1012The connection is forwarded to port 6667 on the remote server,
1013since that's the standard port for IRC services.
1014.Pp
1015The
1016.Fl f
1017option backgrounds
1018.Nm
1019and the remote command
1020.Dq sleep 10
1021is specified to allow an amount of time
1022(10 seconds, in the example)
1023to start the service which is to be tunnelled.
1024If no connections are made within the time specified,
1025.Nm
1026will exit.
Damien Millerf3177182006-01-14 10:09:13 +11001027.Sh X11 FORWARDING
Darren Tuckerd3877b92005-12-20 16:09:36 +11001028If the
1029.Cm ForwardX11
1030variable is set to
1031.Dq yes
1032(or see the description of the
Damien Millerd7f308f2005-12-24 14:55:16 +11001033.Fl X ,
1034.Fl x ,
Darren Tuckerd3877b92005-12-20 16:09:36 +11001035and
Damien Millerd7f308f2005-12-24 14:55:16 +11001036.Fl Y
Damien Miller9a765b22005-12-24 14:53:44 +11001037options above)
Darren Tuckerd3877b92005-12-20 16:09:36 +11001038and the user is using X11 (the
1039.Ev DISPLAY
1040environment variable is set), the connection to the X11 display is
1041automatically forwarded to the remote side in such a way that any X11
1042programs started from the shell (or command) will go through the
1043encrypted channel, and the connection to the real X server will be made
1044from the local machine.
1045The user should not manually set
1046.Ev DISPLAY .
1047Forwarding of X11 connections can be
1048configured on the command line or in configuration files.
1049.Pp
1050The
1051.Ev DISPLAY
1052value set by
1053.Nm
1054will point to the server machine, but with a display number greater than zero.
1055This is normal, and happens because
1056.Nm
1057creates a
1058.Dq proxy
1059X server on the server machine for forwarding the
1060connections over the encrypted channel.
1061.Pp
1062.Nm
1063will also automatically set up Xauthority data on the server machine.
1064For this purpose, it will generate a random authorization cookie,
1065store it in Xauthority on the server, and verify that any forwarded
1066connections carry this cookie and replace it by the real cookie when
1067the connection is opened.
1068The real authentication cookie is never
1069sent to the server machine (and no cookies are sent in the plain).
1070.Pp
1071If the
1072.Cm ForwardAgent
1073variable is set to
1074.Dq yes
1075(or see the description of the
1076.Fl A
1077and
1078.Fl a
Damien Miller9a765b22005-12-24 14:53:44 +11001079options above) and
Darren Tuckerd3877b92005-12-20 16:09:36 +11001080the user is using an authentication agent, the connection to the agent
1081is automatically forwarded to the remote side.
Damien Millerbbc59092006-01-31 21:46:51 +11001082.Sh VERIFYING HOST KEYS
1083When connecting to a server for the first time,
1084a fingerprint of the server's public key is presented to the user
1085(unless the option
1086.Cm StrictHostKeyChecking
1087has been disabled).
1088Fingerprints can be determined using
1089.Xr ssh-keygen 1 :
1090.Pp
1091.Dl $ ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
1092.Pp
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001093If the fingerprint is already known, it can be matched
1094and the key can be accepted or rejected.
1095Because of the difficulty of comparing host keys
1096just by looking at hex strings,
1097there is also support to compare host keys visually,
1098using
1099.Em random art .
1100By setting the
Damien Miller10288242008-06-30 00:04:03 +10001101.Cm VisualHostKey
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001102option to
Damien Miller10288242008-06-30 00:04:03 +10001103.Dq yes ,
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001104a small ASCII graphic gets displayed on every login to a server, no matter
1105if the session itself is interactive or not.
1106By learning the pattern a known server produces, a user can easily
1107find out that the host key has changed when a completely different pattern
1108is displayed.
1109Because these patterns are not unambiguous however, a pattern that looks
1110similar to the pattern remembered only gives a good probability that the
1111host key is the same, not guaranteed proof.
1112.Pp
1113To get a listing of the fingerprints along with their random art for
1114all known hosts, the following command line can be used:
1115.Pp
1116.Dl $ ssh-keygen -lv -f ~/.ssh/known_hosts
1117.Pp
Damien Millerbbc59092006-01-31 21:46:51 +11001118If the fingerprint is unknown,
1119an alternative method of verification is available:
1120SSH fingerprints verified by DNS.
1121An additional resource record (RR),
1122SSHFP,
1123is added to a zonefile
1124and the connecting client is able to match the fingerprint
1125with that of the key presented.
1126.Pp
1127In this example, we are connecting a client to a server,
1128.Dq host.example.com .
1129The SSHFP resource records should first be added to the zonefile for
1130host.example.com:
1131.Bd -literal -offset indent
Damien Millera1b3d632006-03-26 00:07:02 +11001132$ ssh-keygen -r host.example.com.
Damien Millerbbc59092006-01-31 21:46:51 +11001133.Ed
1134.Pp
1135The output lines will have to be added to the zonefile.
1136To check that the zone is answering fingerprint queries:
1137.Pp
1138.Dl $ dig -t SSHFP host.example.com
1139.Pp
1140Finally the client connects:
1141.Bd -literal -offset indent
1142$ ssh -o "VerifyHostKeyDNS ask" host.example.com
1143[...]
1144Matching host key fingerprint found in DNS.
1145Are you sure you want to continue connecting (yes/no)?
1146.Ed
1147.Pp
1148See the
1149.Cm VerifyHostKeyDNS
1150option in
1151.Xr ssh_config 5
1152for more information.
Darren Tucker248dd132006-01-20 11:30:58 +11001153.Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
1154.Nm
1155contains support for Virtual Private Network (VPN) tunnelling
1156using the
1157.Xr tun 4
1158network pseudo-device,
1159allowing two networks to be joined securely.
1160The
1161.Xr sshd_config 5
1162configuration option
1163.Cm PermitTunnel
1164controls whether the server supports this,
1165and at what level (layer 2 or 3 traffic).
1166.Pp
1167The following example would connect client network 10.0.50.0/24
Damien Miller3975ee22006-11-05 05:31:33 +11001168with remote network 10.0.99.0/24 using a point-to-point connection
1169from 10.1.1.1 to 10.1.1.2,
1170provided that the SSH server running on the gateway to the remote network,
1171at 192.168.1.15, allows it.
1172.Pp
1173On the client:
Darren Tucker248dd132006-01-20 11:30:58 +11001174.Bd -literal -offset indent
1175# ssh -f -w 0:1 192.168.1.15 true
Damien Miller3975ee22006-11-05 05:31:33 +11001176# ifconfig tun0 10.1.1.1 10.1.1.2 netmask 255.255.255.252
1177# route add 10.0.99.0/24 10.1.1.2
1178.Ed
1179.Pp
1180On the server:
1181.Bd -literal -offset indent
1182# ifconfig tun1 10.1.1.2 10.1.1.1 netmask 255.255.255.252
1183# route add 10.0.50.0/24 10.1.1.1
Darren Tucker248dd132006-01-20 11:30:58 +11001184.Ed
1185.Pp
1186Client access may be more finely tuned via the
1187.Pa /root/.ssh/authorized_keys
1188file (see below) and the
1189.Cm PermitRootLogin
1190server option.
Damien Millere93eaaa2006-03-15 11:05:59 +11001191The following entry would permit connections on
Darren Tucker248dd132006-01-20 11:30:58 +11001192.Xr tun 4
Damien Millere93eaaa2006-03-15 11:05:59 +11001193device 1 from user
Darren Tucker248dd132006-01-20 11:30:58 +11001194.Dq jane
Damien Millere93eaaa2006-03-15 11:05:59 +11001195and on tun device 2 from user
Darren Tucker248dd132006-01-20 11:30:58 +11001196.Dq john ,
1197if
1198.Cm PermitRootLogin
1199is set to
1200.Dq forced-commands-only :
1201.Bd -literal -offset 2n
1202tunnel="1",command="sh /etc/netstart tun1" ssh-rsa ... jane
Damien Miller9f67a212006-03-15 11:05:35 +11001203tunnel="2",command="sh /etc/netstart tun2" ssh-rsa ... john
Darren Tucker248dd132006-01-20 11:30:58 +11001204.Ed
1205.Pp
Darren Tuckerffe88e12006-10-18 07:53:06 +10001206Since an SSH-based setup entails a fair amount of overhead,
Darren Tucker248dd132006-01-20 11:30:58 +11001207it may be more suited to temporary setups,
1208such as for wireless VPNs.
1209More permanent VPNs are better provided by tools such as
1210.Xr ipsecctl 8
1211and
1212.Xr isakmpd 8 .
Damien Miller32aa1441999-10-29 09:15:49 +10001213.Sh ENVIRONMENT
1214.Nm
1215will normally set the following environment variables:
Damien Miller6aa22902006-01-06 14:48:34 +11001216.Bl -tag -width "SSH_ORIGINAL_COMMAND"
Damien Miller32aa1441999-10-29 09:15:49 +10001217.It Ev DISPLAY
1218The
1219.Ev DISPLAY
Damien Miller7684ee12000-03-17 23:40:15 +11001220variable indicates the location of the X11 server.
Damien Miller22c77262000-04-13 12:26:34 +10001221It is automatically set by
Damien Miller32aa1441999-10-29 09:15:49 +10001222.Nm
1223to point to a value of the form
Damien Miller14af93e2006-01-02 23:38:21 +11001224.Dq hostname:n ,
1225where
1226.Dq hostname
1227indicates the host where the shell runs, and
1228.Sq n
1229is an integer \*(Ge 1.
Damien Miller7684ee12000-03-17 23:40:15 +11001230.Nm
1231uses this special value to forward X11 connections over the secure
1232channel.
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001233The user should normally not set
1234.Ev DISPLAY
1235explicitly, as that
Damien Miller32aa1441999-10-29 09:15:49 +10001236will render the X11 connection insecure (and will require the user to
1237manually copy any required authorization cookies).
1238.It Ev HOME
1239Set to the path of the user's home directory.
1240.It Ev LOGNAME
1241Synonym for
1242.Ev USER ;
1243set for compatibility with systems that use this variable.
1244.It Ev MAIL
Ben Lindstrome59433d2001-09-12 16:41:37 +00001245Set to the path of the user's mailbox.
Damien Miller7684ee12000-03-17 23:40:15 +11001246.It Ev PATH
Damien Miller32aa1441999-10-29 09:15:49 +10001247Set to the default
1248.Ev PATH ,
1249as specified when compiling
Damien Miller1164c292006-01-02 23:38:37 +11001250.Nm .
Ben Lindstrom5bf5d672001-07-04 04:31:38 +00001251.It Ev SSH_ASKPASS
1252If
1253.Nm
1254needs a passphrase, it will read the passphrase from the current
1255terminal if it was run from a terminal.
1256If
1257.Nm
1258does not have a terminal associated with it but
1259.Ev DISPLAY
1260and
1261.Ev SSH_ASKPASS
1262are set, it will execute the program specified by
1263.Ev SSH_ASKPASS
1264and open an X11 window to read the passphrase.
1265This is particularly useful when calling
1266.Nm
1267from a
Darren Tucker4e4fe002004-11-05 20:01:03 +11001268.Pa .xsession
Ben Lindstrom5bf5d672001-07-04 04:31:38 +00001269or related script.
1270(Note that on some machines it
1271may be necessary to redirect the input from
1272.Pa /dev/null
1273to make this work.)
Damien Miller32aa1441999-10-29 09:15:49 +10001274.It Ev SSH_AUTH_SOCK
Damien Miller14af93e2006-01-02 23:38:21 +11001275Identifies the path of a
1276.Ux Ns -domain
1277socket used to communicate with the agent.
Damien Millerf37e2462002-09-19 11:47:55 +10001278.It Ev SSH_CONNECTION
1279Identifies the client and server ends of the connection.
Damien Miller7684ee12000-03-17 23:40:15 +11001280The variable contains
Damien Miller14af93e2006-01-02 23:38:21 +11001281four space-separated values: client IP address, client port number,
1282server IP address, and server port number.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001283.It Ev SSH_ORIGINAL_COMMAND
Damien Miller14af93e2006-01-02 23:38:21 +11001284This variable contains the original command line if a forced command
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001285is executed.
1286It can be used to extract the original arguments.
Damien Miller32aa1441999-10-29 09:15:49 +10001287.It Ev SSH_TTY
1288This is set to the name of the tty (path to the device) associated
Damien Miller7684ee12000-03-17 23:40:15 +11001289with the current shell or command.
1290If the current session has no tty,
Damien Miller32aa1441999-10-29 09:15:49 +10001291this variable is not set.
1292.It Ev TZ
Damien Miller6dbdb6a2005-12-13 19:25:43 +11001293This variable is set to indicate the present time zone if it
Damien Miller208f1ed2006-03-15 11:56:03 +11001294was set when the daemon was started (i.e. the daemon passes the value
Damien Miller32aa1441999-10-29 09:15:49 +10001295on to new connections).
1296.It Ev USER
1297Set to the name of the user logging in.
1298.El
1299.Pp
Damien Miller22c77262000-04-13 12:26:34 +10001300Additionally,
Damien Miller32aa1441999-10-29 09:15:49 +10001301.Nm
Damien Miller22c77262000-04-13 12:26:34 +10001302reads
Damien Miller167ea5d2005-05-26 12:04:02 +10001303.Pa ~/.ssh/environment ,
Damien Miller32aa1441999-10-29 09:15:49 +10001304and adds lines of the format
1305.Dq VARNAME=value
Damien Miller14af93e2006-01-02 23:38:21 +11001306to the environment if the file exists and users are allowed to
Ben Lindstromdc7adf22002-08-20 18:38:02 +00001307change their environment.
Darren Tucker61776952003-10-02 16:19:47 +10001308For more information, see the
Ben Lindstromdc7adf22002-08-20 18:38:02 +00001309.Cm PermitUserEnvironment
Ben Lindstrombd9bf382002-08-20 18:54:20 +00001310option in
Ben Lindstromdc7adf22002-08-20 18:38:02 +00001311.Xr sshd_config 5 .
Damien Miller32aa1441999-10-29 09:15:49 +10001312.Sh FILES
Damien Miller7655f5c2006-01-06 14:48:18 +11001313.Bl -tag -width Ds -compact
Damien Millerafdae612010-08-31 22:31:14 +10001314.It Pa ~/.rhosts
Damien Miller1bcdb502006-01-06 14:49:38 +11001315This file is used for host-based authentication (see above).
Ben Lindstromebd888d2001-03-05 05:49:29 +00001316On some machines this file may need to be
Damien Miller1bcdb502006-01-06 14:49:38 +11001317world-readable if the user's home directory is on an NFS partition,
Damien Miller32aa1441999-10-29 09:15:49 +10001318because
1319.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001320reads it as root.
1321Additionally, this file must be owned by the user,
1322and must not have write permissions for anyone else.
1323The recommended
Damien Miller32aa1441999-10-29 09:15:49 +10001324permission for most machines is read/write for the user, and not
1325accessible by others.
1326.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001327.It Pa ~/.shosts
Damien Miller1bcdb502006-01-06 14:49:38 +11001328This file is used in exactly the same way as
1329.Pa .rhosts ,
1330but allows host-based authentication without permitting login with
1331rlogin/rsh.
Damien Miller7655f5c2006-01-06 14:48:18 +11001332.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001333.It Pa ~/.ssh/
Damien Miller520e6152008-02-10 22:46:22 +11001334This directory is the default location for all user-specific configuration
1335and authentication information.
1336There is no general requirement to keep the entire contents of this directory
1337secret, but the recommended permissions are read/write/execute for the user,
1338and not accessible by others.
1339.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001340.It Pa ~/.ssh/authorized_keys
Damien Miller8ba0ead2013-12-18 17:46:27 +11001341Lists the public keys (DSA, ECDSA, ED25519, RSA)
1342that can be used for logging in as this user.
Damien Millerfb8ea742006-01-06 14:48:52 +11001343The format of this file is described in the
1344.Xr sshd 8
1345manual page.
Damien Millerfb8ea742006-01-06 14:48:52 +11001346This file is not highly sensitive, but the recommended
1347permissions are read/write for the user, and not accessible by others.
1348.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001349.It Pa ~/.ssh/config
Damien Millerfb8ea742006-01-06 14:48:52 +11001350This is the per-user configuration file.
1351The file format and configuration options are described in
1352.Xr ssh_config 5 .
1353Because of the potential for abuse, this file must have strict permissions:
Damien Millerd93340c2013-07-18 16:14:34 +10001354read/write for the user, and not writable by others.
Damien Millerfb8ea742006-01-06 14:48:52 +11001355.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001356.It Pa ~/.ssh/environment
Damien Miller4c102ee2006-01-06 14:49:17 +11001357Contains additional definitions for environment variables; see
1358.Sx ENVIRONMENT ,
Damien Millerfb8ea742006-01-06 14:48:52 +11001359above.
1360.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001361.It Pa ~/.ssh/identity
1362.It Pa ~/.ssh/id_dsa
Damien Millereb8b60e2010-08-31 22:41:14 +10001363.It Pa ~/.ssh/id_ecdsa
Damien Miller8ba0ead2013-12-18 17:46:27 +11001364.It Pa ~/.ssh/id_ed25519
Damien Millerafdae612010-08-31 22:31:14 +10001365.It Pa ~/.ssh/id_rsa
Damien Millerfb8ea742006-01-06 14:48:52 +11001366Contains the private key for authentication.
1367These files
1368contain sensitive data and should be readable by the user but not
1369accessible by others (read/write/execute).
1370.Nm
1371will simply ignore a private key file if it is accessible by others.
1372It is possible to specify a passphrase when
1373generating the key which will be used to encrypt the
1374sensitive part of this file using 3DES.
1375.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001376.It Pa ~/.ssh/identity.pub
1377.It Pa ~/.ssh/id_dsa.pub
Damien Millereb8b60e2010-08-31 22:41:14 +10001378.It Pa ~/.ssh/id_ecdsa.pub
Damien Miller8ba0ead2013-12-18 17:46:27 +11001379.It Pa ~/.ssh/id_ed25519.pub
Damien Millerafdae612010-08-31 22:31:14 +10001380.It Pa ~/.ssh/id_rsa.pub
Damien Millerfb8ea742006-01-06 14:48:52 +11001381Contains the public key for authentication.
1382These files are not
1383sensitive and can (but need not) be readable by anyone.
Damien Millerfb8ea742006-01-06 14:48:52 +11001384.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001385.It Pa ~/.ssh/known_hosts
Damien Millere87eb4c2006-01-14 10:08:36 +11001386Contains a list of host keys for all hosts the user has logged into
1387that are not already in the systemwide list of known host keys.
Damien Millerfb8ea742006-01-06 14:48:52 +11001388See
Damien Millere87eb4c2006-01-14 10:08:36 +11001389.Xr sshd 8
1390for further details of the format of this file.
Damien Millerfb8ea742006-01-06 14:48:52 +11001391.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001392.It Pa ~/.ssh/rc
Damien Millerfb8ea742006-01-06 14:48:52 +11001393Commands in this file are executed by
1394.Nm
Damien Miller7e76e1f2006-01-14 10:08:57 +11001395when the user logs in, just before the user's shell (or command) is
Damien Millerfb8ea742006-01-06 14:48:52 +11001396started.
1397See the
1398.Xr sshd 8
1399manual page for more information.
1400.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001401.It Pa /etc/hosts.equiv
Damien Miller1bcdb502006-01-06 14:49:38 +11001402This file is for host-based authentication (see above).
1403It should only be writable by root.
Damien Miller7655f5c2006-01-06 14:48:18 +11001404.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001405.It Pa /etc/shosts.equiv
Damien Miller1bcdb502006-01-06 14:49:38 +11001406This file is used in exactly the same way as
1407.Pa hosts.equiv ,
1408but allows host-based authentication without permitting login with
1409rlogin/rsh.
Damien Miller7655f5c2006-01-06 14:48:18 +11001410.Pp
Damien Millerfb8ea742006-01-06 14:48:52 +11001411.It Pa /etc/ssh/ssh_config
1412Systemwide configuration file.
1413The file format and configuration options are described in
1414.Xr ssh_config 5 .
1415.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001416.It Pa /etc/ssh/ssh_host_key
1417.It Pa /etc/ssh/ssh_host_dsa_key
Damien Millereb8b60e2010-08-31 22:41:14 +10001418.It Pa /etc/ssh/ssh_host_ecdsa_key
Damien Miller8ba0ead2013-12-18 17:46:27 +11001419.It Pa /etc/ssh/ssh_host_ed25519_key
Damien Millerafdae612010-08-31 22:31:14 +10001420.It Pa /etc/ssh/ssh_host_rsa_key
Damien Millerb9902cf2012-06-20 21:52:58 +10001421These files contain the private parts of the host keys
Damien Miller7e76e1f2006-01-14 10:08:57 +11001422and are used for host-based authentication.
1423If protocol version 1 is used,
Damien Millerfb8ea742006-01-06 14:48:52 +11001424.Nm
1425must be setuid root, since the host key is readable only by root.
1426For protocol version 2,
1427.Nm
1428uses
1429.Xr ssh-keysign 8
Damien Miller7e76e1f2006-01-14 10:08:57 +11001430to access the host keys,
1431eliminating the requirement that
Damien Millerfb8ea742006-01-06 14:48:52 +11001432.Nm
Damien Miller7e76e1f2006-01-14 10:08:57 +11001433be setuid root when host-based authentication is used.
Damien Millerfb8ea742006-01-06 14:48:52 +11001434By default
1435.Nm
1436is not setuid root.
1437.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001438.It Pa /etc/ssh/ssh_known_hosts
Damien Millerfb8ea742006-01-06 14:48:52 +11001439Systemwide list of known host keys.
1440This file should be prepared by the
1441system administrator to contain the public host keys of all machines in the
1442organization.
Damien Millere87eb4c2006-01-14 10:08:36 +11001443It should be world-readable.
1444See
Damien Millerfb8ea742006-01-06 14:48:52 +11001445.Xr sshd 8
Damien Millere87eb4c2006-01-14 10:08:36 +11001446for further details of the format of this file.
Damien Millerfb8ea742006-01-06 14:48:52 +11001447.Pp
Damien Millerafdae612010-08-31 22:31:14 +10001448.It Pa /etc/ssh/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +10001449Commands in this file are executed by
1450.Nm
Damien Miller7e76e1f2006-01-14 10:08:57 +11001451when the user logs in, just before the user's shell (or command) is started.
Damien Miller32aa1441999-10-29 09:15:49 +10001452See the
1453.Xr sshd 8
1454manual page for more information.
Damien Miller7b28dc52000-09-05 13:34:53 +11001455.El
Damien Millerdaa7b222010-09-10 11:19:33 +10001456.Sh EXIT STATUS
1457.Nm
1458exits with the exit status of the remote command or with 255
1459if an error occurred.
Damien Miller32aa1441999-10-29 09:15:49 +10001460.Sh SEE ALSO
Damien Miller32aa1441999-10-29 09:15:49 +10001461.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +11001462.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +10001463.Xr ssh-add 1 ,
1464.Xr ssh-agent 1 ,
1465.Xr ssh-keygen 1 ,
Damien Miller128a0f12006-01-06 14:50:11 +11001466.Xr ssh-keyscan 1 ,
Darren Tucker248dd132006-01-20 11:30:58 +11001467.Xr tun 4 ,
Darren Tucker61776952003-10-02 16:19:47 +10001468.Xr hosts.equiv 5 ,
Ben Lindstrombf69e3b2002-06-23 00:31:24 +00001469.Xr ssh_config 5 ,
Ben Lindstromc001cd32002-06-23 00:32:11 +00001470.Xr ssh-keysign 8 ,
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +00001471.Xr sshd 8
Darren Tucker628a3fd2012-10-05 10:50:15 +10001472.Sh STANDARDS
Ben Lindstrom160ec622001-04-22 17:17:46 +00001473.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001474.%A S. Lehtinen
1475.%A C. Lonvick
1476.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001477.%R RFC 4250
Darren Tucker628a3fd2012-10-05 10:50:15 +10001478.%T The Secure Shell (SSH) Protocol Assigned Numbers
Damien Miller39a93a32006-03-15 11:34:45 +11001479.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001480.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001481.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001482.%A T. Ylonen
1483.%A C. Lonvick
1484.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001485.%R RFC 4251
Darren Tucker628a3fd2012-10-05 10:50:15 +10001486.%T The Secure Shell (SSH) Protocol Architecture
Damien Miller39a93a32006-03-15 11:34:45 +11001487.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001488.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001489.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001490.%A T. Ylonen
1491.%A C. Lonvick
1492.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001493.%R RFC 4252
Darren Tucker628a3fd2012-10-05 10:50:15 +10001494.%T The Secure Shell (SSH) Authentication Protocol
Damien Miller39a93a32006-03-15 11:34:45 +11001495.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001496.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001497.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001498.%A T. Ylonen
1499.%A C. Lonvick
1500.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001501.%R RFC 4253
Darren Tucker628a3fd2012-10-05 10:50:15 +10001502.%T The Secure Shell (SSH) Transport Layer Protocol
Damien Miller39a93a32006-03-15 11:34:45 +11001503.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001504.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001505.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001506.%A T. Ylonen
1507.%A C. Lonvick
1508.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001509.%R RFC 4254
Darren Tucker628a3fd2012-10-05 10:50:15 +10001510.%T The Secure Shell (SSH) Connection Protocol
Damien Miller39a93a32006-03-15 11:34:45 +11001511.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001512.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001513.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001514.%A J. Schlyter
1515.%A W. Griffin
1516.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001517.%R RFC 4255
Darren Tucker628a3fd2012-10-05 10:50:15 +10001518.%T Using DNS to Securely Publish Secure Shell (SSH) Key Fingerprints
Damien Miller39a93a32006-03-15 11:34:45 +11001519.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001520.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001521.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001522.%A F. Cusack
1523.%A M. Forssen
1524.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001525.%R RFC 4256
Darren Tucker628a3fd2012-10-05 10:50:15 +10001526.%T Generic Message Exchange Authentication for the Secure Shell Protocol (SSH)
Damien Miller39a93a32006-03-15 11:34:45 +11001527.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001528.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001529.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001530.%A J. Galbraith
1531.%A P. Remaker
1532.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001533.%R RFC 4335
Darren Tucker628a3fd2012-10-05 10:50:15 +10001534.%T The Secure Shell (SSH) Session Channel Break Extension
Damien Miller39a93a32006-03-15 11:34:45 +11001535.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001536.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001537.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001538.%A M. Bellare
1539.%A T. Kohno
1540.%A C. Namprempre
1541.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001542.%R RFC 4344
Darren Tucker628a3fd2012-10-05 10:50:15 +10001543.%T The Secure Shell (SSH) Transport Layer Encryption Modes
Damien Miller39a93a32006-03-15 11:34:45 +11001544.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001545.Pp
Damien Miller39a93a32006-03-15 11:34:45 +11001546.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001547.%A B. Harris
1548.%D January 2006
Damien Miller39a93a32006-03-15 11:34:45 +11001549.%R RFC 4345
Darren Tucker628a3fd2012-10-05 10:50:15 +10001550.%T Improved Arcfour Modes for the Secure Shell (SSH) Transport Layer Protocol
Ben Lindstrom160ec622001-04-22 17:17:46 +00001551.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001552.Pp
Damien Miller3e96d742006-03-25 23:39:29 +11001553.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001554.%A M. Friedl
1555.%A N. Provos
1556.%A W. Simpson
1557.%D March 2006
Damien Miller3e96d742006-03-25 23:39:29 +11001558.%R RFC 4419
Darren Tucker628a3fd2012-10-05 10:50:15 +10001559.%T Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer Protocol
Damien Miller3e96d742006-03-25 23:39:29 +11001560.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001561.Pp
Damien Millerc0367fb2007-01-05 16:25:46 +11001562.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001563.%A J. Galbraith
1564.%A R. Thayer
1565.%D November 2006
Damien Millerc0367fb2007-01-05 16:25:46 +11001566.%R RFC 4716
Darren Tucker628a3fd2012-10-05 10:50:15 +10001567.%T The Secure Shell (SSH) Public Key File Format
Damien Millerc0367fb2007-01-05 16:25:46 +11001568.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001569.Pp
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001570.Rs
Darren Tucker628a3fd2012-10-05 10:50:15 +10001571.%A D. Stebila
1572.%A J. Green
1573.%D December 2009
Damien Miller1ca94692010-09-24 22:01:22 +10001574.%R RFC 5656
Darren Tucker628a3fd2012-10-05 10:50:15 +10001575.%T Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer
Damien Miller1ca94692010-09-24 22:01:22 +10001576.Re
Darren Tucker628a3fd2012-10-05 10:50:15 +10001577.Pp
Damien Miller1ca94692010-09-24 22:01:22 +10001578.Rs
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001579.%A A. Perrig
1580.%A D. Song
1581.%D 1999
Darren Tucker628a3fd2012-10-05 10:50:15 +10001582.%O International Workshop on Cryptographic Techniques and E-Commerce (CrypTEC '99)
1583.%T Hash Visualization: a New Technique to improve Real-World Security
Darren Tuckerf6bffb12008-06-14 09:04:26 +10001584.Re
Damien Millerf1ce5052003-06-11 22:04:39 +10001585.Sh AUTHORS
1586OpenSSH is a derivative of the original and free
1587ssh 1.2.12 release by Tatu Ylonen.
1588Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1589Theo de Raadt and Dug Song
1590removed many bugs, re-added newer features and
1591created OpenSSH.
1592Markus Friedl contributed the support for SSH
1593protocol versions 1.5 and 2.0.