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Damien Miller32aa1441999-10-29 09:15:49 +10001.\" -*- nroff -*-
2.\"
Damien Miller32aa1441999-10-29 09:15:49 +10003.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
Damien Miller32aa1441999-10-29 09:15:49 +10004.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5.\" All rights reserved
6.\"
Damien Millere4340be2000-09-16 13:29:08 +11007.\" As far as I am concerned, the code I have written for this software
8.\" can be used freely for any purpose. Any derived versions of this
9.\" software must be clearly marked as such, and if the derived work is
10.\" incompatible with the protocol description in the RFC file, it must be
11.\" called by a name other than "ssh" or "Secure Shell".
Damien Miller32aa1441999-10-29 09:15:49 +100012.\"
Ben Lindstrom92a2e382001-03-05 06:59:27 +000013.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
14.\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
15.\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
Damien Millere4340be2000-09-16 13:29:08 +110016.\"
17.\" Redistribution and use in source and binary forms, with or without
18.\" modification, are permitted provided that the following conditions
19.\" are met:
20.\" 1. Redistributions of source code must retain the above copyright
21.\" notice, this list of conditions and the following disclaimer.
22.\" 2. Redistributions in binary form must reproduce the above copyright
23.\" notice, this list of conditions and the following disclaimer in the
24.\" documentation and/or other materials provided with the distribution.
25.\"
26.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
27.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
28.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
29.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
30.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
31.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Damien Miller32aa1441999-10-29 09:15:49 +100036.\"
Ben Lindstromf1813842002-03-27 17:18:31 +000037.\" $OpenBSD: ssh.1,v 1.150 2002/03/26 11:34:49 markus Exp $
Damien Miller32aa1441999-10-29 09:15:49 +100038.Dd September 25, 1999
39.Dt SSH 1
40.Os
41.Sh NAME
42.Nm ssh
Ben Lindstromd58eb5f2001-03-07 06:07:22 +000043.Nd OpenSSH SSH client (remote login program)
Damien Miller32aa1441999-10-29 09:15:49 +100044.Sh SYNOPSIS
45.Nm ssh
46.Op Fl l Ar login_name
Ben Lindstroma10aed82001-09-12 16:43:26 +000047.Ar hostname | user@hostname
Damien Miller32aa1441999-10-29 09:15:49 +100048.Op Ar command
49.Pp
50.Nm ssh
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +000051.Op Fl afgknqstvxACNPTX1246
Ben Lindstrome0f88042001-04-30 13:06:24 +000052.Op Fl b Ar bind_address
Damien Miller30c3d422000-05-09 11:02:59 +100053.Op Fl c Ar cipher_spec
Damien Miller32aa1441999-10-29 09:15:49 +100054.Op Fl e Ar escape_char
55.Op Fl i Ar identity_file
56.Op Fl l Ar login_name
Ben Lindstrom06b33aa2001-02-15 03:01:59 +000057.Op Fl m Ar mac_spec
Damien Miller32aa1441999-10-29 09:15:49 +100058.Op Fl o Ar option
59.Op Fl p Ar port
Ben Lindstrom14f31ab2001-09-12 17:48:04 +000060.Op Fl F Ar configfile
Damien Miller32aa1441999-10-29 09:15:49 +100061.Oo Fl L Xo
62.Sm off
Damien Miller32aa1441999-10-29 09:15:49 +100063.Ar port :
Damien Miller396691a2000-01-20 22:44:08 +110064.Ar host :
Damien Miller32aa1441999-10-29 09:15:49 +100065.Ar hostport
66.Sm on
67.Xc
68.Oc
69.Oo Fl R Xo
70.Sm off
Damien Miller32aa1441999-10-29 09:15:49 +100071.Ar port :
Damien Miller396691a2000-01-20 22:44:08 +110072.Ar host :
Damien Miller32aa1441999-10-29 09:15:49 +100073.Ar hostport
74.Sm on
75.Xc
76.Oc
Ben Lindstrom6e69d532001-09-12 17:59:59 +000077.Op Fl D Ar port
Ben Lindstroma10aed82001-09-12 16:43:26 +000078.Ar hostname | user@hostname
Damien Miller32aa1441999-10-29 09:15:49 +100079.Op Ar command
Damien Miller22c77262000-04-13 12:26:34 +100080.Sh DESCRIPTION
Damien Miller32aa1441999-10-29 09:15:49 +100081.Nm
Ben Lindstromd58eb5f2001-03-07 06:07:22 +000082(SSH client) is a program for logging into a remote machine and for
Damien Miller7684ee12000-03-17 23:40:15 +110083executing commands on a remote machine.
84It is intended to replace
Damien Miller32aa1441999-10-29 09:15:49 +100085rlogin and rsh, and provide secure encrypted communications between
Damien Miller7684ee12000-03-17 23:40:15 +110086two untrusted hosts over an insecure network.
87X11 connections and
Damien Miller32aa1441999-10-29 09:15:49 +100088arbitrary TCP/IP ports can also be forwarded over the secure channel.
89.Pp
90.Nm
Damien Miller22c77262000-04-13 12:26:34 +100091connects and logs into the specified
Damien Miller32aa1441999-10-29 09:15:49 +100092.Ar hostname .
93The user must prove
Damien Millere247cc42000-05-07 12:03:14 +100094his/her identity to the remote machine using one of several methods
95depending on the protocol version used:
96.Pp
97.Ss SSH protocol version 1
Damien Miller32aa1441999-10-29 09:15:49 +100098.Pp
99First, if the machine the user logs in from is listed in
100.Pa /etc/hosts.equiv
101or
Damien Miller886c63a2000-01-20 23:13:36 +1100102.Pa /etc/shosts.equiv
Damien Miller32aa1441999-10-29 09:15:49 +1000103on the remote machine, and the user names are
104the same on both sides, the user is immediately permitted to log in.
Damien Miller22c77262000-04-13 12:26:34 +1000105Second, if
Damien Miller32aa1441999-10-29 09:15:49 +1000106.Pa \&.rhosts
107or
108.Pa \&.shosts
109exists in the user's home directory on the
110remote machine and contains a line containing the name of the client
111machine and the name of the user on that machine, the user is
Damien Miller7684ee12000-03-17 23:40:15 +1100112permitted to log in.
113This form of authentication alone is normally not
Damien Miller32aa1441999-10-29 09:15:49 +1000114allowed by the server because it is not secure.
115.Pp
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000116The second authentication method is the
Damien Miller32aa1441999-10-29 09:15:49 +1000117.Pa rhosts
118or
119.Pa hosts.equiv
Damien Miller7684ee12000-03-17 23:40:15 +1100120method combined with RSA-based host authentication.
121It means that if the login would be permitted by
Damien Millere247cc42000-05-07 12:03:14 +1000122.Pa $HOME/.rhosts ,
123.Pa $HOME/.shosts ,
Damien Miller32aa1441999-10-29 09:15:49 +1000124.Pa /etc/hosts.equiv ,
125or
Damien Miller886c63a2000-01-20 23:13:36 +1100126.Pa /etc/shosts.equiv ,
Damien Miller32aa1441999-10-29 09:15:49 +1000127and if additionally the server can verify the client's
Damien Miller22c77262000-04-13 12:26:34 +1000128host key (see
Damien Miller05eda432002-02-10 18:32:28 +1100129.Pa /etc/ssh/ssh_known_hosts
Damien Miller33e511e1999-11-11 11:43:13 +1100130and
131.Pa $HOME/.ssh/known_hosts
Damien Miller32aa1441999-10-29 09:15:49 +1000132in the
133.Sx FILES
Damien Miller7684ee12000-03-17 23:40:15 +1100134section), only then login is permitted.
135This authentication method closes security holes due to IP
136spoofing, DNS spoofing and routing spoofing.
137[Note to the administrator:
Damien Miller32aa1441999-10-29 09:15:49 +1000138.Pa /etc/hosts.equiv ,
Damien Millere247cc42000-05-07 12:03:14 +1000139.Pa $HOME/.rhosts ,
Damien Miller32aa1441999-10-29 09:15:49 +1000140and the rlogin/rsh protocol in general, are inherently insecure and should be
141disabled if security is desired.]
142.Pp
Damien Miller22c77262000-04-13 12:26:34 +1000143As a third authentication method,
Damien Miller32aa1441999-10-29 09:15:49 +1000144.Nm
145supports RSA based authentication.
146The scheme is based on public-key cryptography: there are cryptosystems
147where encryption and decryption are done using separate keys, and it
148is not possible to derive the decryption key from the encryption key.
Damien Miller7684ee12000-03-17 23:40:15 +1100149RSA is one such system.
Damien Miller22c77262000-04-13 12:26:34 +1000150The idea is that each user creates a public/private
Damien Miller7684ee12000-03-17 23:40:15 +1100151key pair for authentication purposes.
152The server knows the public key, and only the user knows the private key.
Damien Miller22c77262000-04-13 12:26:34 +1000153The file
Damien Miller32aa1441999-10-29 09:15:49 +1000154.Pa $HOME/.ssh/authorized_keys
155lists the public keys that are permitted for logging
Damien Miller7684ee12000-03-17 23:40:15 +1100156in.
157When the user logs in, the
Damien Miller32aa1441999-10-29 09:15:49 +1000158.Nm
159program tells the server which key pair it would like to use for
Damien Miller7684ee12000-03-17 23:40:15 +1100160authentication.
161The server checks if this key is permitted, and if
Damien Miller32aa1441999-10-29 09:15:49 +1000162so, sends the user (actually the
163.Nm
164program running on behalf of the user) a challenge, a random number,
Damien Miller7684ee12000-03-17 23:40:15 +1100165encrypted by the user's public key.
166The challenge can only be
167decrypted using the proper private key.
168The user's client then decrypts the
Damien Miller32aa1441999-10-29 09:15:49 +1000169challenge using the private key, proving that he/she knows the private
170key but without disclosing it to the server.
171.Pp
172.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100173implements the RSA authentication protocol automatically.
174The user creates his/her RSA key pair by running
Damien Miller32aa1441999-10-29 09:15:49 +1000175.Xr ssh-keygen 1 .
Damien Miller22c77262000-04-13 12:26:34 +1000176This stores the private key in
Damien Millere247cc42000-05-07 12:03:14 +1000177.Pa $HOME/.ssh/identity
Damien Miller32aa1441999-10-29 09:15:49 +1000178and the public key in
Damien Millere247cc42000-05-07 12:03:14 +1000179.Pa $HOME/.ssh/identity.pub
Damien Miller7684ee12000-03-17 23:40:15 +1100180in the user's home directory.
181The user should then copy the
Damien Miller32aa1441999-10-29 09:15:49 +1000182.Pa identity.pub
Damien Miller22c77262000-04-13 12:26:34 +1000183to
Damien Millere247cc42000-05-07 12:03:14 +1000184.Pa $HOME/.ssh/authorized_keys
Damien Miller22c77262000-04-13 12:26:34 +1000185in his/her home directory on the remote machine (the
Damien Miller32aa1441999-10-29 09:15:49 +1000186.Pa authorized_keys
Damien Miller22c77262000-04-13 12:26:34 +1000187file corresponds to the conventional
Damien Millere247cc42000-05-07 12:03:14 +1000188.Pa $HOME/.rhosts
Damien Miller32aa1441999-10-29 09:15:49 +1000189file, and has one key
Damien Miller7684ee12000-03-17 23:40:15 +1100190per line, though the lines can be very long).
191After this, the user can log in without giving the password.
192RSA authentication is much
Damien Miller32aa1441999-10-29 09:15:49 +1000193more secure than rhosts authentication.
194.Pp
195The most convenient way to use RSA authentication may be with an
Damien Miller7684ee12000-03-17 23:40:15 +1100196authentication agent.
197See
Damien Miller32aa1441999-10-29 09:15:49 +1000198.Xr ssh-agent 1
199for more information.
200.Pp
Damien Miller22c77262000-04-13 12:26:34 +1000201If other authentication methods fail,
Damien Miller32aa1441999-10-29 09:15:49 +1000202.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100203prompts the user for a password.
204The password is sent to the remote
Damien Miller32aa1441999-10-29 09:15:49 +1000205host for checking; however, since all communications are encrypted,
206the password cannot be seen by someone listening on the network.
207.Pp
Damien Millere247cc42000-05-07 12:03:14 +1000208.Ss SSH protocol version 2
209.Pp
Damien Miller07a2d422002-02-05 12:16:15 +1100210When a user connects using protocol version 2
211similar authentication methods are available.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000212Using the default values for
213.Cm PreferredAuthentications ,
Ben Lindstroma9086a12001-08-06 20:58:51 +0000214the client will try to authenticate first using the hostbased method;
215if this method fails public key authentication is attempted,
216and finally if this method fails keyboard-interactive and
217password authentication are tried.
Damien Millere247cc42000-05-07 12:03:14 +1000218.Pp
219The public key method is similar to RSA authentication described
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000220in the previous section and allows the RSA or DSA algorithm to be used:
Ben Lindstrom18a82ac2001-04-11 15:59:35 +0000221The client uses his private key,
Damien Millere247cc42000-05-07 12:03:14 +1000222.Pa $HOME/.ssh/id_dsa
Ben Lindstrom18a82ac2001-04-11 15:59:35 +0000223or
224.Pa $HOME/.ssh/id_rsa ,
Damien Millere247cc42000-05-07 12:03:14 +1000225to sign the session identifier and sends the result to the server.
226The server checks whether the matching public key is listed in
Ben Lindstromf96704d2001-06-25 04:17:12 +0000227.Pa $HOME/.ssh/authorized_keys
Damien Millere247cc42000-05-07 12:03:14 +1000228and grants access if both the key is found and the signature is correct.
229The session identifier is derived from a shared Diffie-Hellman value
230and is only known to the client and the server.
231.Pp
232If public key authentication fails or is not available a password
233can be sent encrypted to the remote host for proving the user's identity.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000234.Pp
235Additionally,
236.Nm
237supports hostbased or challenge response authentication.
Damien Millere247cc42000-05-07 12:03:14 +1000238.Pp
239Protocol 2 provides additional mechanisms for confidentiality
Damien Miller30c3d422000-05-09 11:02:59 +1000240(the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour)
Ben Lindstromec26fb12001-03-06 01:05:23 +0000241and integrity (hmac-md5, hmac-sha1).
Damien Millere247cc42000-05-07 12:03:14 +1000242Note that protocol 1 lacks a strong mechanism for ensuring the
243integrity of the connection.
244.Pp
245.Ss Login session and remote execution
246.Pp
Damien Miller32aa1441999-10-29 09:15:49 +1000247When the user's identity has been accepted by the server, the server
248either executes the given command, or logs into the machine and gives
Damien Miller7684ee12000-03-17 23:40:15 +1100249the user a normal shell on the remote machine.
250All communication with
Damien Miller32aa1441999-10-29 09:15:49 +1000251the remote command or shell will be automatically encrypted.
252.Pp
253If a pseudo-terminal has been allocated (normal login session), the
Ben Lindstrom9ffdcb52001-04-20 12:50:51 +0000254user may use the escape characters noted below.
Damien Miller32aa1441999-10-29 09:15:49 +1000255.Pp
256If no pseudo tty has been allocated, the
257session is transparent and can be used to reliably transfer binary
Damien Miller7684ee12000-03-17 23:40:15 +1100258data.
259On most systems, setting the escape character to
Damien Miller32aa1441999-10-29 09:15:49 +1000260.Dq none
261will also make the session transparent even if a tty is used.
262.Pp
Ben Lindstroma6885612000-12-09 03:45:32 +0000263The session terminates when the command or shell on the remote
Ben Lindstromebd888d2001-03-05 05:49:29 +0000264machine exits and all X11 and TCP/IP connections have been closed.
Damien Miller32aa1441999-10-29 09:15:49 +1000265The exit status of the remote program is returned as the exit status
266of
267.Nm ssh .
268.Pp
Ben Lindstrom9ffdcb52001-04-20 12:50:51 +0000269.Ss Escape Characters
270.Pp
271When a pseudo terminal has been requested, ssh supports a number of functions
Ben Lindstrom24643222001-06-25 05:08:11 +0000272through the use of an escape character.
Ben Lindstrom9ffdcb52001-04-20 12:50:51 +0000273.Pp
274A single tilde character can be sent as
275.Ic ~~
Ben Lindstrom66007692001-07-22 20:41:59 +0000276or by following the tilde by a character other than those described below.
Ben Lindstrom9ffdcb52001-04-20 12:50:51 +0000277The escape character must always follow a newline to be interpreted as
278special.
279The escape character can be changed in configuration files using the
280.Cm EscapeChar
Ben Lindstrom24643222001-06-25 05:08:11 +0000281configuration directive or on the command line by the
Ben Lindstrom9ffdcb52001-04-20 12:50:51 +0000282.Fl e
283option.
284.Pp
285The supported escapes (assuming the default
286.Ql ~ )
287are:
288.Bl -tag -width Ds
289.It Cm ~.
290Disconnect
291.It Cm ~^Z
292Background ssh
293.It Cm ~#
294List forwarded connections
295.It Cm ~&
296Background ssh at logout when waiting for forwarded connection / X11 sessions
Damien Miller1f8dddc2001-11-12 11:02:25 +1100297to terminate
Ben Lindstrom9ffdcb52001-04-20 12:50:51 +0000298.It Cm ~?
299Display a list of escape characters
Ben Lindstrom5589f4b2002-03-22 03:24:32 +0000300.It Cm ~C
301Open command line (only useful for adding port forwardings using the
302.Fl L
303and
304.Fl R
305options)
Ben Lindstrom9ffdcb52001-04-20 12:50:51 +0000306.It Cm ~R
Ben Lindstromf8d24572001-04-22 17:11:56 +0000307Request rekeying of the connection (only useful for SSH protocol version 2
308and if the peer supports it)
Ben Lindstrom9ffdcb52001-04-20 12:50:51 +0000309.El
310.Pp
Damien Millere247cc42000-05-07 12:03:14 +1000311.Ss X11 and TCP forwarding
312.Pp
Ben Lindstrom71215072001-05-17 03:16:18 +0000313If the
314.Cm ForwardX11
315variable is set to
316.Dq yes
317(or, see the description of the
318.Fl X
319and
320.Fl x
321options described later)
322and the user is using X11 (the
Damien Miller32aa1441999-10-29 09:15:49 +1000323.Ev DISPLAY
324environment variable is set), the connection to the X11 display is
325automatically forwarded to the remote side in such a way that any X11
326programs started from the shell (or command) will go through the
327encrypted channel, and the connection to the real X server will be made
Damien Miller7684ee12000-03-17 23:40:15 +1100328from the local machine.
329The user should not manually set
Damien Miller32aa1441999-10-29 09:15:49 +1000330.Ev DISPLAY .
331Forwarding of X11 connections can be
332configured on the command line or in configuration files.
333.Pp
334The
Damien Miller22c77262000-04-13 12:26:34 +1000335.Ev DISPLAY
Damien Miller32aa1441999-10-29 09:15:49 +1000336value set by
337.Nm
338will point to the server machine, but with a display number greater
Damien Miller7684ee12000-03-17 23:40:15 +1100339than zero.
340This is normal, and happens because
Damien Miller32aa1441999-10-29 09:15:49 +1000341.Nm
342creates a
343.Dq proxy
344X server on the server machine for forwarding the
345connections over the encrypted channel.
346.Pp
347.Nm
348will also automatically set up Xauthority data on the server machine.
349For this purpose, it will generate a random authorization cookie,
350store it in Xauthority on the server, and verify that any forwarded
351connections carry this cookie and replace it by the real cookie when
Damien Miller7684ee12000-03-17 23:40:15 +1100352the connection is opened.
353The real authentication cookie is never
Damien Miller32aa1441999-10-29 09:15:49 +1000354sent to the server machine (and no cookies are sent in the plain).
355.Pp
356If the user is using an authentication agent, the connection to the agent
357is automatically forwarded to the remote side unless disabled on
Ben Lindstrom979c9812001-07-22 20:45:39 +0000358the command line or in a configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000359.Pp
360Forwarding of arbitrary TCP/IP connections over the secure channel can
Ben Lindstrom979c9812001-07-22 20:45:39 +0000361be specified either on the command line or in a configuration file.
Damien Miller7684ee12000-03-17 23:40:15 +1100362One possible application of TCP/IP forwarding is a secure connection to an
Ben Lindstromebd888d2001-03-05 05:49:29 +0000363electronic purse; another is going through firewalls.
Damien Miller32aa1441999-10-29 09:15:49 +1000364.Pp
Damien Millere247cc42000-05-07 12:03:14 +1000365.Ss Server authentication
366.Pp
Damien Miller32aa1441999-10-29 09:15:49 +1000367.Nm
Damien Millere247cc42000-05-07 12:03:14 +1000368automatically maintains and checks a database containing
Damien Miller7684ee12000-03-17 23:40:15 +1100369identifications for all hosts it has ever been used with.
Ben Lindstromd6481ea2001-06-25 04:37:41 +0000370Host keys are stored in
Damien Millere247cc42000-05-07 12:03:14 +1000371.Pa $HOME/.ssh/known_hosts
Damien Miller7684ee12000-03-17 23:40:15 +1100372in the user's home directory.
Ben Lindstromd6481ea2001-06-25 04:37:41 +0000373Additionally, the file
Damien Miller05eda432002-02-10 18:32:28 +1100374.Pa /etc/ssh/ssh_known_hosts
Ben Lindstromd6481ea2001-06-25 04:37:41 +0000375is automatically checked for known hosts.
Damien Miller7684ee12000-03-17 23:40:15 +1100376Any new hosts are automatically added to the user's file.
377If a host's identification
Damien Miller32aa1441999-10-29 09:15:49 +1000378ever changes,
379.Nm
380warns about this and disables password authentication to prevent a
Damien Miller7684ee12000-03-17 23:40:15 +1100381trojan horse from getting the user's password.
382Another purpose of
Damien Miller32aa1441999-10-29 09:15:49 +1000383this mechanism is to prevent man-in-the-middle attacks which could
Damien Miller7684ee12000-03-17 23:40:15 +1100384otherwise be used to circumvent the encryption.
385The
Damien Miller32aa1441999-10-29 09:15:49 +1000386.Cm StrictHostKeyChecking
387option (see below) can be used to prevent logins to machines whose
388host key is not known or has changed.
Damien Miller0bc1bd82000-11-13 22:57:25 +1100389.Pp
390The options are as follows:
Damien Miller32aa1441999-10-29 09:15:49 +1000391.Bl -tag -width Ds
392.It Fl a
Damien Miller450a7a12000-03-26 13:04:51 +1000393Disables forwarding of the authentication agent connection.
Damien Millerb1715dc2000-05-30 13:44:51 +1000394.It Fl A
395Enables forwarding of the authentication agent connection.
396This can also be specified on a per-host basis in a configuration file.
Ben Lindstrome0f88042001-04-30 13:06:24 +0000397.It Fl b Ar bind_address
398Specify the interface to transmit from on machines with multiple
399interfaces or aliased addresses.
Ben Lindstromffa1dd62001-09-12 16:52:28 +0000400.It Fl c Ar blowfish|3des|des
Damien Miller22c77262000-04-13 12:26:34 +1000401Selects the cipher to use for encrypting the session.
Damien Miller32aa1441999-10-29 09:15:49 +1000402.Ar 3des
Damien Miller7684ee12000-03-17 23:40:15 +1100403is used by default.
Damien Miller22c77262000-04-13 12:26:34 +1000404It is believed to be secure.
Damien Miller32aa1441999-10-29 09:15:49 +1000405.Ar 3des
406(triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
Damien Miller32aa1441999-10-29 09:15:49 +1000407.Ar blowfish
408is a fast block cipher, it appears very secure and is much faster than
Damien Miller7684ee12000-03-17 23:40:15 +1100409.Ar 3des .
Ben Lindstromffa1dd62001-09-12 16:52:28 +0000410.Ar des
411is only supported in the
412.Nm
413client for interoperability with legacy protocol 1 implementations
414that do not support the
415.Ar 3des
416cipher. Its use is strongly discouraged due to cryptographic
417weaknesses.
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000418.It Fl c Ar cipher_spec
Damien Miller30c3d422000-05-09 11:02:59 +1000419Additionally, for protocol version 2 a comma-separated list of ciphers can
Damien Miller874d77b2000-10-14 16:23:11 +1100420be specified in order of preference.
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000421See
422.Cm Ciphers
423for more information.
Damien Miller32aa1441999-10-29 09:15:49 +1000424.It Fl e Ar ch|^ch|none
425Sets the escape character for sessions with a pty (default:
426.Ql ~ ) .
Damien Miller7684ee12000-03-17 23:40:15 +1100427The escape character is only recognized at the beginning of a line.
428The escape character followed by a dot
Damien Miller32aa1441999-10-29 09:15:49 +1000429.Pq Ql \&.
430closes the connection, followed
431by control-Z suspends the connection, and followed by itself sends the
Damien Miller7684ee12000-03-17 23:40:15 +1100432escape character once.
433Setting the character to
Damien Miller32aa1441999-10-29 09:15:49 +1000434.Dq none
435disables any escapes and makes the session fully transparent.
436.It Fl f
437Requests
438.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100439to go to background just before command execution.
440This is useful if
Damien Miller32aa1441999-10-29 09:15:49 +1000441.Nm
442is going to ask for passwords or passphrases, but the user
Damien Miller7684ee12000-03-17 23:40:15 +1100443wants it in the background.
Damien Miller22c77262000-04-13 12:26:34 +1000444This implies
Damien Miller32aa1441999-10-29 09:15:49 +1000445.Fl n .
446The recommended way to start X11 programs at a remote site is with
447something like
448.Ic ssh -f host xterm .
Damien Miller396691a2000-01-20 22:44:08 +1100449.It Fl g
450Allows remote hosts to connect to local forwarded ports.
Damien Miller32aa1441999-10-29 09:15:49 +1000451.It Fl i Ar identity_file
Damien Millerfae23862002-01-22 23:32:26 +1100452Selects a file from which the identity (private key) for
Damien Miller0bc1bd82000-11-13 22:57:25 +1100453RSA or DSA authentication is read.
Damien Millerfae23862002-01-22 23:32:26 +1100454The default is
Damien Millere247cc42000-05-07 12:03:14 +1000455.Pa $HOME/.ssh/identity
Damien Millerfae23862002-01-22 23:32:26 +1100456for protocol version 1, and
457.Pa $HOME/.ssh/id_rsa
458and
459.Pa $HOME/.ssh/id_dsa
460for protocol version 2.
Damien Miller7684ee12000-03-17 23:40:15 +1100461Identity files may also be specified on
462a per-host basis in the configuration file.
463It is possible to have multiple
Damien Miller32aa1441999-10-29 09:15:49 +1000464.Fl i
465options (and multiple identities specified in
466configuration files).
Ben Lindstromae996bf2001-08-06 21:27:53 +0000467.It Fl I Ar smartcard_device
468Specifies which smartcard device to use. The argument is
469the device
470.Nm
471should use to communicate with a smartcard used for storing the user's
472private RSA key.
Damien Miller32aa1441999-10-29 09:15:49 +1000473.It Fl k
Damien Miller450a7a12000-03-26 13:04:51 +1000474Disables forwarding of Kerberos tickets and AFS tokens.
475This may also be specified on a per-host basis in the configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000476.It Fl l Ar login_name
Damien Miller7684ee12000-03-17 23:40:15 +1100477Specifies the user to log in as on the remote machine.
478This also may be specified on a per-host basis in the configuration file.
Ben Lindstrom06b33aa2001-02-15 03:01:59 +0000479.It Fl m Ar mac_spec
480Additionally, for protocol version 2 a comma-separated list of MAC
481(message authentication code) algorithms can
482be specified in order of preference.
483See the
484.Cm MACs
485keyword for more information.
Damien Miller32aa1441999-10-29 09:15:49 +1000486.It Fl n
487Redirects stdin from
488.Pa /dev/null
489(actually, prevents reading from stdin).
490This must be used when
491.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100492is run in the background.
493A common trick is to use this to run X11 programs on a remote machine.
494For example,
Damien Miller32aa1441999-10-29 09:15:49 +1000495.Ic ssh -n shadows.cs.hut.fi emacs &
496will start an emacs on shadows.cs.hut.fi, and the X11
497connection will be automatically forwarded over an encrypted channel.
498The
499.Nm
500program will be put in the background.
501(This does not work if
502.Nm
503needs to ask for a password or passphrase; see also the
504.Fl f
505option.)
Damien Millerdcb6ecd2000-05-17 22:34:22 +1000506.It Fl N
507Do not execute a remote command.
Ben Lindstrom594e2032001-09-12 18:35:30 +0000508This is useful for just forwarding ports
Damien Millerdcb6ecd2000-05-17 22:34:22 +1000509(protocol version 2 only).
Damien Miller32aa1441999-10-29 09:15:49 +1000510.It Fl o Ar option
Ben Lindstrom14c62eb2001-08-15 23:25:46 +0000511Can be used to give options in the format used in the configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000512This is useful for specifying options for which there is no separate
Damien Miller7684ee12000-03-17 23:40:15 +1100513command-line flag.
Damien Miller32aa1441999-10-29 09:15:49 +1000514.It Fl p Ar port
Damien Miller7684ee12000-03-17 23:40:15 +1100515Port to connect to on the remote host.
516This can be specified on a
Damien Miller32aa1441999-10-29 09:15:49 +1000517per-host basis in the configuration file.
518.It Fl P
519Use a non-privileged port for outgoing connections.
Ben Lindstrom594e2032001-09-12 18:35:30 +0000520This can be used if a firewall does
Damien Miller32aa1441999-10-29 09:15:49 +1000521not permit connections from privileged ports.
Damien Millera34a28b1999-12-14 10:47:15 +1100522Note that this option turns off
Damien Miller32aa1441999-10-29 09:15:49 +1000523.Cm RhostsAuthentication
524and
Kevin Stevesfcec7f82000-12-15 19:55:48 +0000525.Cm RhostsRSAAuthentication
526for older servers.
Damien Miller32aa1441999-10-29 09:15:49 +1000527.It Fl q
Damien Miller7684ee12000-03-17 23:40:15 +1100528Quiet mode.
529Causes all warning and diagnostic messages to be suppressed.
Damien Miller832562e2001-01-30 09:30:01 +1100530.It Fl s
Ben Lindstrom24643222001-06-25 05:08:11 +0000531May be used to request invocation of a subsystem on the remote system. Subsystems are a feature of the SSH2 protocol which facilitate the use
532of SSH as a secure transport for other applications (eg. sftp). The
Damien Miller832562e2001-01-30 09:30:01 +1100533subsystem is specified as the remote command.
Damien Miller32aa1441999-10-29 09:15:49 +1000534.It Fl t
Damien Miller7684ee12000-03-17 23:40:15 +1100535Force pseudo-tty allocation.
Damien Miller450a7a12000-03-26 13:04:51 +1000536This can be used to execute arbitrary
Damien Miller7684ee12000-03-17 23:40:15 +1100537screen-based programs on a remote machine, which can be very useful,
538e.g., when implementing menu services.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000539Multiple
540.Fl t
541options force tty allocation, even if
542.Nm
543has no local tty.
Damien Millerdcb6ecd2000-05-17 22:34:22 +1000544.It Fl T
Ben Lindstromc72745a2000-12-02 19:03:54 +0000545Disable pseudo-tty allocation.
Damien Miller32aa1441999-10-29 09:15:49 +1000546.It Fl v
Damien Miller7684ee12000-03-17 23:40:15 +1100547Verbose mode.
548Causes
Damien Miller32aa1441999-10-29 09:15:49 +1000549.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100550to print debugging messages about its progress.
551This is helpful in
Damien Miller32aa1441999-10-29 09:15:49 +1000552debugging connection, authentication, and configuration problems.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000553Multiple
554.Fl v
555options increases the verbosity.
Damien Miller874d77b2000-10-14 16:23:11 +1100556Maximum is 3.
Damien Miller32aa1441999-10-29 09:15:49 +1000557.It Fl x
Damien Miller7684ee12000-03-17 23:40:15 +1100558Disables X11 forwarding.
Damien Miller32aa1441999-10-29 09:15:49 +1000559.It Fl X
560Enables X11 forwarding.
Damien Millerb1715dc2000-05-30 13:44:51 +1000561This can also be specified on a per-host basis in a configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000562.It Fl C
563Requests compression of all data (including stdin, stdout, stderr, and
Damien Miller7684ee12000-03-17 23:40:15 +1100564data for forwarded X11 and TCP/IP connections).
565The compression algorithm is the same used by
Damien Miller396691a2000-01-20 22:44:08 +1100566.Xr gzip 1 ,
567and the
Damien Miller32aa1441999-10-29 09:15:49 +1000568.Dq level
569can be controlled by the
570.Cm CompressionLevel
Damien Miller7684ee12000-03-17 23:40:15 +1100571option (see below).
572Compression is desirable on modem lines and other
Damien Miller32aa1441999-10-29 09:15:49 +1000573slow connections, but will only slow down things on fast networks.
574The default value can be set on a host-by-host basis in the
575configuration files; see the
Ben Lindstrome2b9b062001-08-06 20:50:55 +0000576.Cm Compression
Damien Miller32aa1441999-10-29 09:15:49 +1000577option below.
Ben Lindstrom14f31ab2001-09-12 17:48:04 +0000578.It Fl F Ar configfile
579Specifies an alternative per-user configuration file.
580If a configuration file is given on the command line,
581the system-wide configuration file
Damien Miller05eda432002-02-10 18:32:28 +1100582.Pq Pa /etc/ssh/ssh_config
Ben Lindstrom14f31ab2001-09-12 17:48:04 +0000583will be ignored.
584The default for the per-user configuration file is
585.Pa $HOME/.ssh/config .
Damien Miller32aa1441999-10-29 09:15:49 +1000586.It Fl L Ar port:host:hostport
587Specifies that the given port on the local (client) host is to be
Damien Miller7684ee12000-03-17 23:40:15 +1100588forwarded to the given host and port on the remote side.
589This works by allocating a socket to listen to
Damien Miller32aa1441999-10-29 09:15:49 +1000590.Ar port
591on the local side, and whenever a connection is made to this port, the
592connection is forwarded over the secure channel, and a connection is
593made to
Damien Miller34132e52000-01-14 15:45:46 +1100594.Ar host
595port
596.Ar hostport
Damien Miller7684ee12000-03-17 23:40:15 +1100597from the remote machine.
598Port forwardings can also be specified in the configuration file.
599Only root can forward privileged ports.
Damien Miller34132e52000-01-14 15:45:46 +1100600IPv6 addresses can be specified with an alternative syntax:
601.Ar port/host/hostport
Damien Miller32aa1441999-10-29 09:15:49 +1000602.It Fl R Ar port:host:hostport
603Specifies that the given port on the remote (server) host is to be
Damien Miller7684ee12000-03-17 23:40:15 +1100604forwarded to the given host and port on the local side.
605This works by allocating a socket to listen to
Damien Miller32aa1441999-10-29 09:15:49 +1000606.Ar port
607on the remote side, and whenever a connection is made to this port, the
608connection is forwarded over the secure channel, and a connection is
609made to
Damien Miller34132e52000-01-14 15:45:46 +1100610.Ar host
611port
612.Ar hostport
Damien Miller7684ee12000-03-17 23:40:15 +1100613from the local machine.
614Port forwardings can also be specified in the configuration file.
615Privileged ports can be forwarded only when
Damien Miller32aa1441999-10-29 09:15:49 +1000616logging in as root on the remote machine.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000617IPv6 addresses can be specified with an alternative syntax:
618.Ar port/host/hostport
Ben Lindstrom19ceb172001-09-12 17:54:24 +0000619.It Fl D Ar port
620Specifies a local
621.Dq dynamic
622application-level port forwarding.
623This works by allocating a socket to listen to
624.Ar port
625on the local side, and whenever a connection is made to this port, the
626connection is forwarded over the secure channel, and the application
627protocol is then used to determine where to connect to from the
628remote machine. Currently the SOCKS4 protocol is supported, and
629.Nm
630will act as a SOCKS4 server.
631Only root can forward privileged ports.
632Dynamic port forwardings can also be specified in the configuration file.
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000633.It Fl 1
634Forces
635.Nm
636to try protocol version 1 only.
Damien Miller4af51302000-04-16 11:18:38 +1000637.It Fl 2
638Forces
639.Nm
Damien Millere247cc42000-05-07 12:03:14 +1000640to try protocol version 2 only.
Damien Miller34132e52000-01-14 15:45:46 +1100641.It Fl 4
642Forces
643.Nm
644to use IPv4 addresses only.
645.It Fl 6
646Forces
647.Nm
648to use IPv6 addresses only.
Damien Miller32aa1441999-10-29 09:15:49 +1000649.El
650.Sh CONFIGURATION FILES
651.Nm
Ben Lindstrom14c62eb2001-08-15 23:25:46 +0000652obtains configuration data from the following sources in
653the following order:
Damien Miller32aa1441999-10-29 09:15:49 +1000654command line options, user's configuration file
655.Pq Pa $HOME/.ssh/config ,
656and system-wide configuration file
Damien Miller05eda432002-02-10 18:32:28 +1100657.Pq Pa /etc/ssh/ssh_config .
Damien Miller32aa1441999-10-29 09:15:49 +1000658For each parameter, the first obtained value
Damien Miller7684ee12000-03-17 23:40:15 +1100659will be used.
660The configuration files contain sections bracketed by
661.Dq Host
662specifications, and that section is only applied for hosts that
663match one of the patterns given in the specification.
664The matched host name is the one given on the command line.
Damien Miller32aa1441999-10-29 09:15:49 +1000665.Pp
666Since the first obtained value for each parameter is used, more
667host-specific declarations should be given near the beginning of the
668file, and general defaults at the end.
669.Pp
670The configuration file has the following format:
671.Pp
672Empty lines and lines starting with
673.Ql #
674are comments.
675.Pp
676Otherwise a line is of the format
677.Dq keyword arguments .
Ben Lindstrom14c62eb2001-08-15 23:25:46 +0000678Configuration options may be separated by whitespace or
679optional whitespace and exactly one
680.Ql = ;
681the latter format is useful to avoid the need to quote whitespace
682when specifying configuration options using the
683.Nm ssh ,
684.Nm scp
685and
686.Nm sftp
687.Fl o
688option.
689.Pp
Damien Miller32aa1441999-10-29 09:15:49 +1000690The possible
Ben Lindstrom1c0fd092001-09-12 16:36:17 +0000691keywords and their meanings are as follows (note that
692keywords are case-insensitive and arguments are case-sensitive):
Damien Miller32aa1441999-10-29 09:15:49 +1000693.Bl -tag -width Ds
694.It Cm Host
695Restricts the following declarations (up to the next
696.Cm Host
697keyword) to be only for those hosts that match one of the patterns
698given after the keyword.
699.Ql \&*
700and
701.Ql ?
702can be used as wildcards in the
Damien Miller7684ee12000-03-17 23:40:15 +1100703patterns.
704A single
Damien Miller32aa1441999-10-29 09:15:49 +1000705.Ql \&*
706as a pattern can be used to provide global
Damien Miller7684ee12000-03-17 23:40:15 +1100707defaults for all hosts.
708The host is the
Damien Miller32aa1441999-10-29 09:15:49 +1000709.Ar hostname
710argument given on the command line (i.e., the name is not converted to
711a canonicalized host name before matching).
712.It Cm AFSTokenPassing
Damien Miller450a7a12000-03-26 13:04:51 +1000713Specifies whether to pass AFS tokens to remote host.
714The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +1000715.Dq yes
716or
717.Dq no .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000718This option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000719.It Cm BatchMode
720If set to
721.Dq yes ,
Damien Miller7684ee12000-03-17 23:40:15 +1100722passphrase/password querying will be disabled.
Ben Lindstrom594e2032001-09-12 18:35:30 +0000723This option is useful in scripts and other batch jobs where no user
724is present to supply the password.
Damien Miller7684ee12000-03-17 23:40:15 +1100725The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000726.Dq yes
727or
728.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000729The default is
730.Dq no .
Ben Lindstrome0f88042001-04-30 13:06:24 +0000731.It Cm BindAddress
732Specify the interface to transmit from on machines with multiple
733interfaces or aliased addresses.
734Note that this option does not work if
735.Cm UsePrivilegedPort
736is set to
737.Dq yes .
Damien Miller396691a2000-01-20 22:44:08 +1100738.It Cm CheckHostIP
739If this flag is set to
740.Dq yes ,
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000741ssh will additionally check the host IP address in the
Damien Miller396691a2000-01-20 22:44:08 +1100742.Pa known_hosts
Damien Miller450a7a12000-03-26 13:04:51 +1000743file.
744This allows ssh to detect if a host key changed due to DNS spoofing.
Damien Miller396691a2000-01-20 22:44:08 +1100745If the option is set to
746.Dq no ,
747the check will not be executed.
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000748The default is
749.Dq yes .
Damien Miller32aa1441999-10-29 09:15:49 +1000750.It Cm Cipher
Damien Miller50a41ed2000-10-16 12:14:42 +1100751Specifies the cipher to use for encrypting the session
Damien Miller69b69aa2000-10-28 14:19:58 +1100752in protocol version 1.
Damien Miller7684ee12000-03-17 23:40:15 +1100753Currently,
Ben Lindstromffa1dd62001-09-12 16:52:28 +0000754.Dq blowfish ,
755.Dq 3des ,
Damien Miller32aa1441999-10-29 09:15:49 +1000756and
Ben Lindstromffa1dd62001-09-12 16:52:28 +0000757.Dq des
Damien Miller7684ee12000-03-17 23:40:15 +1100758are supported.
Ben Lindstromffa1dd62001-09-12 16:52:28 +0000759.Ar des
760is only supported in the
761.Nm
762client for interoperability with legacy protocol 1 implementations
763that do not support the
764.Ar 3des
765cipher. Its use is strongly discouraged due to cryptographic
766weaknesses.
Damien Miller7684ee12000-03-17 23:40:15 +1100767The default is
Damien Miller32aa1441999-10-29 09:15:49 +1000768.Dq 3des .
Damien Miller22c77262000-04-13 12:26:34 +1000769.It Cm Ciphers
770Specifies the ciphers allowed for protocol version 2
771in order of preference.
772Multiple ciphers must be comma-separated.
773The default is
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000774.Pp
775.Bd -literal
Ben Lindstromec26fb12001-03-06 01:05:23 +0000776 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000777 aes192-cbc,aes256-cbc''
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000778.Ed
Ben Lindstrom2b7a0e92001-09-20 00:57:55 +0000779.It Cm ClearAllForwardings
780Specifies that all local, remote and dynamic port forwardings
781specified in the configuration files or on the command line be
782cleared. This option is primarily useful when used from the
783.Nm
784command line to clear port forwardings set in
785configuration files, and is automatically set by
786.Xr scp 1
787and
788.Xr sftp 1 .
789The argument must be
790.Dq yes
791or
792.Dq no .
793The default is
794.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000795.It Cm Compression
Damien Miller7684ee12000-03-17 23:40:15 +1100796Specifies whether to use compression.
797The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000798.Dq yes
799or
800.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000801The default is
802.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000803.It Cm CompressionLevel
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000804Specifies the compression level to use if compression is enabled.
Damien Miller7684ee12000-03-17 23:40:15 +1100805The argument must be an integer from 1 (fast) to 9 (slow, best).
806The default level is 6, which is good for most applications.
807The meaning of the values is the same as in
Damien Miller396691a2000-01-20 22:44:08 +1100808.Xr gzip 1 .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000809Note that this option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000810.It Cm ConnectionAttempts
811Specifies the number of tries (one per second) to make before falling
Damien Miller7684ee12000-03-17 23:40:15 +1100812back to rsh or exiting.
813The argument must be an integer.
814This may be useful in scripts if the connection sometimes fails.
Ben Lindstromf9cedb92001-08-06 21:07:11 +0000815The default is 1.
Ben Lindstrom19ceb172001-09-12 17:54:24 +0000816.It Cm DynamicForward
817Specifies that a TCP/IP port on the local machine be forwarded
818over the secure channel, and the application
819protocol is then used to determine where to connect to from the
820remote machine. The argument must be a port number.
821Currently the SOCKS4 protocol is supported, and
822.Nm
823will act as a SOCKS4 server.
824Multiple forwardings may be specified, and
825additional forwardings can be given on the command line. Only
826the superuser can forward privileged ports.
Damien Miller32aa1441999-10-29 09:15:49 +1000827.It Cm EscapeChar
828Sets the escape character (default:
829.Ql ~ ) .
830The escape character can also
Damien Miller7684ee12000-03-17 23:40:15 +1100831be set on the command line.
832The argument should be a single character,
Damien Miller32aa1441999-10-29 09:15:49 +1000833.Ql ^
834followed by a letter, or
835.Dq none
836to disable the escape
837character entirely (making the connection transparent for binary
838data).
Damien Miller22c77262000-04-13 12:26:34 +1000839.It Cm FallBackToRsh
Damien Miller32aa1441999-10-29 09:15:49 +1000840Specifies that if connecting via
841.Nm
842fails due to a connection refused error (there is no
843.Xr sshd 8
Damien Miller22c77262000-04-13 12:26:34 +1000844listening on the remote host),
Damien Miller32aa1441999-10-29 09:15:49 +1000845.Xr rsh 1
846should automatically be used instead (after a suitable warning about
Damien Miller7684ee12000-03-17 23:40:15 +1100847the session being unencrypted).
848The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000849.Dq yes
850or
851.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000852The default is
853.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000854.It Cm ForwardAgent
855Specifies whether the connection to the authentication agent (if any)
Damien Miller7684ee12000-03-17 23:40:15 +1100856will be forwarded to the remote machine.
857The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000858.Dq yes
859or
860.Dq no .
Damien Millerb1715dc2000-05-30 13:44:51 +1000861The default is
862.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000863.It Cm ForwardX11
864Specifies whether X11 connections will be automatically redirected
Damien Miller22c77262000-04-13 12:26:34 +1000865over the secure channel and
Damien Miller32aa1441999-10-29 09:15:49 +1000866.Ev DISPLAY
Damien Miller7684ee12000-03-17 23:40:15 +1100867set.
Damien Miller22c77262000-04-13 12:26:34 +1000868The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000869.Dq yes
870or
871.Dq no .
Damien Miller98c7ad62000-03-09 21:27:49 +1100872The default is
873.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000874.It Cm GatewayPorts
875Specifies whether remote hosts are allowed to connect to local
876forwarded ports.
Ben Lindstrom60d82be2001-09-12 17:58:15 +0000877By default,
878.Nm
879binds local port forwardings to the loopback addresss. This
880prevents other remote hosts from connecting to forwarded ports.
881.Cm GatewayPorts
882can be used to specify that
883.Nm
884should bind local port forwardings to the wildcard address,
885thus allowing remote hosts to connect to forwarded ports.
Damien Miller32aa1441999-10-29 09:15:49 +1000886The argument must be
887.Dq yes
888or
889.Dq no .
890The default is
891.Dq no .
892.It Cm GlobalKnownHostsFile
Ben Lindstromd6481ea2001-06-25 04:37:41 +0000893Specifies a file to use for the global
Ben Lindstrom1e621742001-03-06 01:10:53 +0000894host key database instead of
Damien Miller05eda432002-02-10 18:32:28 +1100895.Pa /etc/ssh/ssh_known_hosts .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000896.It Cm HostbasedAuthentication
897Specifies whether to try rhosts based authentication with public key
898authentication.
899The argument must be
900.Dq yes
901or
902.Dq no .
903The default is
Ben Lindstrom1bfe2912001-06-05 19:37:25 +0000904.Dq no .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000905This option applies to protocol version 2 only and
906is similar to
907.Cm RhostsRSAAuthentication .
Ben Lindstrom982dbbc2001-04-17 18:11:36 +0000908.It Cm HostKeyAlgorithms
Ben Lindstromf0609f82001-05-04 22:38:43 +0000909Specifies the protocol version 2 host key algorithms
Ben Lindstrom982dbbc2001-04-17 18:11:36 +0000910that the client wants to use in order of preference.
911The default for this option is:
Damien Miller70972eb2002-01-22 23:19:55 +1100912.Dq ssh-rsa,ssh-dss .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000913.It Cm HostKeyAlias
914Specifies an alias that should be used instead of the
915real host name when looking up or saving the host key
916in the host key database files.
917This option is useful for tunneling ssh connections
Ben Lindstrom594e2032001-09-12 18:35:30 +0000918or for multiple servers running on a single host.
Damien Miller32aa1441999-10-29 09:15:49 +1000919.It Cm HostName
Damien Miller7684ee12000-03-17 23:40:15 +1100920Specifies the real host name to log into.
921This can be used to specify nicknames or abbreviations for hosts.
922Default is the name given on the command line.
923Numeric IP addresses are also permitted (both on the command line and in
Damien Miller32aa1441999-10-29 09:15:49 +1000924.Cm HostName
925specifications).
926.It Cm IdentityFile
Damien Millerfae23862002-01-22 23:32:26 +1100927Specifies a file from which the user's RSA or DSA authentication identity
928is read. The default is
Damien Millere247cc42000-05-07 12:03:14 +1000929.Pa $HOME/.ssh/identity
Damien Millerfae23862002-01-22 23:32:26 +1100930for protocol version 1, and
931.Pa $HOME/.ssh/id_rsa
932and
933.Pa $HOME/.ssh/id_dsa
934for protocol version 2.
Damien Miller32aa1441999-10-29 09:15:49 +1000935Additionally, any identities represented by the authentication agent
Damien Miller7684ee12000-03-17 23:40:15 +1100936will be used for authentication.
937The file name may use the tilde
938syntax to refer to a user's home directory.
939It is possible to have
Damien Miller32aa1441999-10-29 09:15:49 +1000940multiple identity files specified in configuration files; all these
941identities will be tried in sequence.
942.It Cm KeepAlive
Damien Miller9749c0c2002-02-05 12:23:58 +1100943Specifies whether the system should send TCP keepalive messages to the
Damien Miller7684ee12000-03-17 23:40:15 +1100944other side.
945If they are sent, death of the connection or crash of one
946of the machines will be properly noticed.
947However, this means that
Damien Miller32aa1441999-10-29 09:15:49 +1000948connections will die if the route is down temporarily, and some people
Damien Miller450a7a12000-03-26 13:04:51 +1000949find it annoying.
Damien Miller32aa1441999-10-29 09:15:49 +1000950.Pp
951The default is
952.Dq yes
953(to send keepalives), and the client will notice
Damien Miller7684ee12000-03-17 23:40:15 +1100954if the network goes down or the remote host dies.
955This is important in scripts, and many users want it too.
Damien Miller32aa1441999-10-29 09:15:49 +1000956.Pp
957To disable keepalives, the value should be set to
Damien Miller9749c0c2002-02-05 12:23:58 +1100958.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000959.It Cm KerberosAuthentication
Damien Miller450a7a12000-03-26 13:04:51 +1000960Specifies whether Kerberos authentication will be used.
961The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +1000962.Dq yes
963or
964.Dq no .
965.It Cm KerberosTgtPassing
Damien Miller450a7a12000-03-26 13:04:51 +1000966Specifies whether a Kerberos TGT will be forwarded to the server.
967This will only work if the Kerberos server is actually an AFS kaserver.
968The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +1000969.Dq yes
970or
971.Dq no .
972.It Cm LocalForward
973Specifies that a TCP/IP port on the local machine be forwarded over
Ben Lindstrom62c25a42001-09-12 18:01:59 +0000974the secure channel to the specified host and port from the remote machine.
Damien Miller7684ee12000-03-17 23:40:15 +1100975The first argument must be a port number, and the second must be
Ben Lindstrom62c25a42001-09-12 18:01:59 +0000976.Ar host:port .
977IPv6 addresses can be specified with an alternative syntax:
978.Ar host/port .
Damien Miller7684ee12000-03-17 23:40:15 +1100979Multiple forwardings may be specified, and additional
980forwardings can be given on the command line.
981Only the superuser can forward privileged ports.
Damien Miller5ce662a1999-11-11 17:57:39 +1100982.It Cm LogLevel
983Gives the verbosity level that is used when logging messages from
984.Nm ssh .
985The possible values are:
Damien Millerdc9e0672002-01-22 23:17:51 +1100986QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
987The default is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2
988and DEBUG3 each specify higher levels of verbose output.
Ben Lindstrom06b33aa2001-02-15 03:01:59 +0000989.It Cm MACs
Ben Lindstrom24643222001-06-25 05:08:11 +0000990Specifies the MAC (message authentication code) algorithms
Ben Lindstrom06b33aa2001-02-15 03:01:59 +0000991in order of preference.
992The MAC algorithm is used in protocol version 2
993for data integrity protection.
994Multiple algorithms must be comma-separated.
995The default is
Ben Lindstrombd0e2de2001-06-05 19:52:52 +0000996.Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
Ben Lindstrom3cecc9a2001-10-03 17:39:38 +0000997.It Cm NoHostAuthenticationForLocalhost
998This option can be used if the home directory is shared across machines.
999In this case localhost will refer to a different machine on each of
1000the machines and the user will get many warnings about changed host keys.
1001However, this option disables host authentication for localhost.
1002The argument to this keyword must be
1003.Dq yes
1004or
1005.Dq no .
1006The default is to check the host key for localhost.
Damien Miller32aa1441999-10-29 09:15:49 +10001007.It Cm NumberOfPasswordPrompts
Damien Miller450a7a12000-03-26 13:04:51 +10001008Specifies the number of password prompts before giving up.
1009The argument to this keyword must be an integer.
1010Default is 3.
Damien Miller396691a2000-01-20 22:44:08 +11001011.It Cm PasswordAuthentication
Damien Miller7684ee12000-03-17 23:40:15 +11001012Specifies whether to use password authentication.
1013The argument to this keyword must be
Damien Miller396691a2000-01-20 22:44:08 +11001014.Dq yes
1015or
1016.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +00001017The default is
1018.Dq yes .
Damien Miller32aa1441999-10-29 09:15:49 +10001019.It Cm Port
Damien Miller7684ee12000-03-17 23:40:15 +11001020Specifies the port number to connect on the remote host.
1021Default is 22.
Damien Miller1e42f302001-03-19 23:59:11 +11001022.It Cm PreferredAuthentications
Ben Lindstrom24643222001-06-25 05:08:11 +00001023Specifies the order in which the client should try protocol 2
1024authentication methods. This allows a client to prefer one method (e.g.
Damien Miller1e42f302001-03-19 23:59:11 +11001025.Cm keyboard-interactive )
1026over another method (e.g.
1027.Cm password )
1028The default for this option is:
Damien Miller70972eb2002-01-22 23:19:55 +11001029.Dq hostbased,publickey,keyboard-interactive,password .
Damien Miller22c77262000-04-13 12:26:34 +10001030.It Cm Protocol
1031Specifies the protocol versions
1032.Nm
1033should support in order of preference.
1034The possible values are
1035.Dq 1
1036and
1037.Dq 2 .
1038Multiple versions must be comma-separated.
1039The default is
Ben Lindstromf3272352001-04-05 23:29:59 +00001040.Dq 2,1 .
Damien Millere247cc42000-05-07 12:03:14 +10001041This means that
1042.Nm
Ben Lindstromf3272352001-04-05 23:29:59 +00001043tries version 2 and falls back to version 1
1044if version 2 is not available.
Damien Miller32aa1441999-10-29 09:15:49 +10001045.It Cm ProxyCommand
Damien Miller7684ee12000-03-17 23:40:15 +11001046Specifies the command to use to connect to the server.
1047The command
1048string extends to the end of the line, and is executed with
1049.Pa /bin/sh .
1050In the command string,
1051.Ql %h
1052will be substituted by the host name to
1053connect and
1054.Ql %p
1055by the port.
1056The command can be basically anything,
1057and should read from its standard input and write to its standard output.
1058It should eventually connect an
Damien Miller32aa1441999-10-29 09:15:49 +10001059.Xr sshd 8
1060server running on some machine, or execute
1061.Ic sshd -i
Damien Miller7684ee12000-03-17 23:40:15 +11001062somewhere.
1063Host key management will be done using the
Damien Miller32aa1441999-10-29 09:15:49 +10001064HostName of the host being connected (defaulting to the name typed by
1065the user).
Damien Milleraae6c611999-12-06 11:47:28 +11001066Note that
1067.Cm CheckHostIP
1068is not available for connects with a proxy command.
Damien Miller32aa1441999-10-29 09:15:49 +10001069.Pp
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001070.It Cm PubkeyAuthentication
1071Specifies whether to try public key authentication.
1072The argument to this keyword must be
1073.Dq yes
1074or
1075.Dq no .
1076The default is
1077.Dq yes .
1078This option applies to protocol version 2 only.
Damien Miller32aa1441999-10-29 09:15:49 +10001079.It Cm RemoteForward
1080Specifies that a TCP/IP port on the remote machine be forwarded over
Ben Lindstrom62c25a42001-09-12 18:01:59 +00001081the secure channel to the specified host and port from the local machine.
Damien Miller7684ee12000-03-17 23:40:15 +11001082The first argument must be a port number, and the second must be
Ben Lindstrom62c25a42001-09-12 18:01:59 +00001083.Ar host:port .
1084IPv6 addresses can be specified with an alternative syntax:
1085.Ar host/port .
Damien Miller7684ee12000-03-17 23:40:15 +11001086Multiple forwardings may be specified, and additional
1087forwardings can be given on the command line.
1088Only the superuser can forward privileged ports.
Damien Miller32aa1441999-10-29 09:15:49 +10001089.It Cm RhostsAuthentication
Damien Miller7684ee12000-03-17 23:40:15 +11001090Specifies whether to try rhosts based authentication.
1091Note that this
Damien Miller32aa1441999-10-29 09:15:49 +10001092declaration only affects the client side and has no effect whatsoever
Damien Miller7684ee12000-03-17 23:40:15 +11001093on security.
1094Disabling rhosts authentication may reduce
Damien Miller32aa1441999-10-29 09:15:49 +10001095authentication time on slow connections when rhosts authentication is
Damien Miller7684ee12000-03-17 23:40:15 +11001096not used.
1097Most servers do not permit RhostsAuthentication because it
Ben Lindstrom24643222001-06-25 05:08:11 +00001098is not secure (see
Ben Lindstromd2bf0d62001-06-25 04:10:54 +00001099.Cm RhostsRSAAuthentication ) .
Damien Miller7684ee12000-03-17 23:40:15 +11001100The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +10001101.Dq yes
1102or
1103.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +00001104The default is
1105.Dq yes .
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001106This option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +10001107.It Cm RhostsRSAAuthentication
1108Specifies whether to try rhosts based authentication with RSA host
Damien Miller7684ee12000-03-17 23:40:15 +11001109authentication.
Damien Miller7684ee12000-03-17 23:40:15 +11001110The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +10001111.Dq yes
1112or
1113.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +00001114The default is
1115.Dq yes .
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001116This option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +10001117.It Cm RSAAuthentication
Damien Miller7684ee12000-03-17 23:40:15 +11001118Specifies whether to try RSA authentication.
1119The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +10001120.Dq yes
1121or
1122.Dq no .
1123RSA authentication will only be
1124attempted if the identity file exists, or an authentication agent is
1125running.
Ben Lindstrom89b0bd62001-03-29 00:27:11 +00001126The default is
1127.Dq yes .
Damien Millere247cc42000-05-07 12:03:14 +10001128Note that this option applies to protocol version 1 only.
Damien Miller33804262001-02-04 23:20:18 +11001129.It Cm ChallengeResponseAuthentication
1130Specifies whether to use challenge response authentication.
Damien Miller7684ee12000-03-17 23:40:15 +11001131The argument to this keyword must be
Damien Miller95def091999-11-25 00:26:21 +11001132.Dq yes
1133or
1134.Dq no .
1135The default is
Ben Lindstrom0076d752001-08-06 20:53:26 +00001136.Dq yes .
Ben Lindstromae996bf2001-08-06 21:27:53 +00001137.It Cm SmartcardDevice
1138Specifies which smartcard device to use. The argument to this keyword is
1139the device
1140.Nm
1141should use to communicate with a smartcard used for storing the user's
1142private RSA key. By default, no device is specified and smartcard support
1143is not activated.
Damien Miller32aa1441999-10-29 09:15:49 +10001144.It Cm StrictHostKeyChecking
1145If this flag is set to
Damien Miller22c77262000-04-13 12:26:34 +10001146.Dq yes ,
Damien Miller32aa1441999-10-29 09:15:49 +10001147.Nm
Ben Lindstromeb930d42001-01-29 08:37:08 +00001148will never automatically add host keys to the
Damien Miller32aa1441999-10-29 09:15:49 +10001149.Pa $HOME/.ssh/known_hosts
Ben Lindstromd6481ea2001-06-25 04:37:41 +00001150file, and refuses to connect to hosts whose host key has changed.
Ben Lindstrom594e2032001-09-12 18:35:30 +00001151This provides maximum protection against trojan horse attacks,
1152however, can be annoying when the
Damien Miller05eda432002-02-10 18:32:28 +11001153.Pa /etc/ssh/ssh_known_hosts
Ben Lindstrom594e2032001-09-12 18:35:30 +00001154file is poorly maintained, or connections to new hosts are
1155frequently made.
Ben Lindstromeb930d42001-01-29 08:37:08 +00001156This option forces the user to manually
1157add all new hosts.
1158If this flag is set to
1159.Dq no ,
1160.Nm
1161will automatically add new host keys to the
1162user known hosts files.
1163If this flag is set to
1164.Dq ask ,
1165new host keys
1166will be added to the user known host files only after the user
1167has confirmed that is what they really want to do, and
1168.Nm
1169will refuse to connect to hosts whose host key has changed.
Damien Miller7684ee12000-03-17 23:40:15 +11001170The host keys of
Ben Lindstromeb930d42001-01-29 08:37:08 +00001171known hosts will be verified automatically in all cases.
Damien Miller7684ee12000-03-17 23:40:15 +11001172The argument must be
Ben Lindstromeb930d42001-01-29 08:37:08 +00001173.Dq yes ,
1174.Dq no
Damien Miller32aa1441999-10-29 09:15:49 +10001175or
Ben Lindstromeb930d42001-01-29 08:37:08 +00001176.Dq ask .
1177The default is
1178.Dq ask .
Damien Miller32aa1441999-10-29 09:15:49 +10001179.It Cm UsePrivilegedPort
1180Specifies whether to use a privileged port for outgoing connections.
1181The argument must be
1182.Dq yes
1183or
1184.Dq no .
1185The default is
Ben Lindstromcebc8582001-03-08 03:39:10 +00001186.Dq no .
Ben Lindstrom594e2032001-09-12 18:35:30 +00001187Note that this option must be set to
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001188.Dq yes
Ben Lindstrom594e2032001-09-12 18:35:30 +00001189if
Damien Miller32aa1441999-10-29 09:15:49 +10001190.Cm RhostsAuthentication
1191and
Kevin Stevesfcec7f82000-12-15 19:55:48 +00001192.Cm RhostsRSAAuthentication
Ben Lindstrom594e2032001-09-12 18:35:30 +00001193authentications are needed with older servers.
Damien Miller396691a2000-01-20 22:44:08 +11001194.It Cm User
Damien Miller7684ee12000-03-17 23:40:15 +11001195Specifies the user to log in as.
Ben Lindstrom594e2032001-09-12 18:35:30 +00001196This can be useful when a different user name is used on different machines.
Damien Miller7684ee12000-03-17 23:40:15 +11001197This saves the trouble of
Damien Miller396691a2000-01-20 22:44:08 +11001198having to remember to give the user name on the command line.
1199.It Cm UserKnownHostsFile
Ben Lindstromd6481ea2001-06-25 04:37:41 +00001200Specifies a file to use for the user
Ben Lindstrom1e621742001-03-06 01:10:53 +00001201host key database instead of
Damien Miller396691a2000-01-20 22:44:08 +11001202.Pa $HOME/.ssh/known_hosts .
Damien Miller32aa1441999-10-29 09:15:49 +10001203.It Cm UseRsh
Damien Miller7684ee12000-03-17 23:40:15 +11001204Specifies that rlogin/rsh should be used for this host.
1205It is possible that the host does not at all support the
Damien Miller32aa1441999-10-29 09:15:49 +10001206.Nm
Damien Miller7684ee12000-03-17 23:40:15 +11001207protocol.
1208This causes
Damien Miller32aa1441999-10-29 09:15:49 +10001209.Nm
Damien Miller7684ee12000-03-17 23:40:15 +11001210to immediately execute
Damien Miller32aa1441999-10-29 09:15:49 +10001211.Xr rsh 1 .
1212All other options (except
1213.Cm HostName )
Damien Miller7684ee12000-03-17 23:40:15 +11001214are ignored if this has been specified.
1215The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +10001216.Dq yes
1217or
1218.Dq no .
Damien Millerd3a18572000-06-07 19:55:44 +10001219.It Cm XAuthLocation
1220Specifies the location of the
1221.Xr xauth 1
1222program.
1223The default is
1224.Pa /usr/X11R6/bin/xauth .
Damien Miller7b28dc52000-09-05 13:34:53 +11001225.El
Damien Miller32aa1441999-10-29 09:15:49 +10001226.Sh ENVIRONMENT
1227.Nm
1228will normally set the following environment variables:
1229.Bl -tag -width Ds
1230.It Ev DISPLAY
1231The
1232.Ev DISPLAY
Damien Miller7684ee12000-03-17 23:40:15 +11001233variable indicates the location of the X11 server.
Damien Miller22c77262000-04-13 12:26:34 +10001234It is automatically set by
Damien Miller32aa1441999-10-29 09:15:49 +10001235.Nm
1236to point to a value of the form
1237.Dq hostname:n
1238where hostname indicates
Damien Miller7684ee12000-03-17 23:40:15 +11001239the host where the shell runs, and n is an integer >= 1.
1240.Nm
1241uses this special value to forward X11 connections over the secure
1242channel.
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001243The user should normally not set
1244.Ev DISPLAY
1245explicitly, as that
Damien Miller32aa1441999-10-29 09:15:49 +10001246will render the X11 connection insecure (and will require the user to
1247manually copy any required authorization cookies).
1248.It Ev HOME
1249Set to the path of the user's home directory.
1250.It Ev LOGNAME
1251Synonym for
1252.Ev USER ;
1253set for compatibility with systems that use this variable.
1254.It Ev MAIL
Ben Lindstrome59433d2001-09-12 16:41:37 +00001255Set to the path of the user's mailbox.
Damien Miller7684ee12000-03-17 23:40:15 +11001256.It Ev PATH
Damien Miller32aa1441999-10-29 09:15:49 +10001257Set to the default
1258.Ev PATH ,
1259as specified when compiling
1260.Nm ssh .
Ben Lindstrom5bf5d672001-07-04 04:31:38 +00001261.It Ev SSH_ASKPASS
1262If
1263.Nm
1264needs a passphrase, it will read the passphrase from the current
1265terminal if it was run from a terminal.
1266If
1267.Nm
1268does not have a terminal associated with it but
1269.Ev DISPLAY
1270and
1271.Ev SSH_ASKPASS
1272are set, it will execute the program specified by
1273.Ev SSH_ASKPASS
1274and open an X11 window to read the passphrase.
1275This is particularly useful when calling
1276.Nm
1277from a
1278.Pa .Xsession
1279or related script.
1280(Note that on some machines it
1281may be necessary to redirect the input from
1282.Pa /dev/null
1283to make this work.)
Damien Miller32aa1441999-10-29 09:15:49 +10001284.It Ev SSH_AUTH_SOCK
Ben Lindstrome59433d2001-09-12 16:41:37 +00001285Identifies the path of a unix-domain socket used to communicate with the
Damien Miller32aa1441999-10-29 09:15:49 +10001286agent.
1287.It Ev SSH_CLIENT
Damien Miller7684ee12000-03-17 23:40:15 +11001288Identifies the client end of the connection.
1289The variable contains
Damien Miller32aa1441999-10-29 09:15:49 +10001290three space-separated values: client ip-address, client port number,
1291and server port number.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001292.It Ev SSH_ORIGINAL_COMMAND
1293The variable contains the original command line if a forced command
1294is executed.
1295It can be used to extract the original arguments.
Damien Miller32aa1441999-10-29 09:15:49 +10001296.It Ev SSH_TTY
1297This is set to the name of the tty (path to the device) associated
Damien Miller7684ee12000-03-17 23:40:15 +11001298with the current shell or command.
1299If the current session has no tty,
Damien Miller32aa1441999-10-29 09:15:49 +10001300this variable is not set.
1301.It Ev TZ
1302The timezone variable is set to indicate the present timezone if it
Damien Miller942da032000-08-18 13:59:06 +10001303was set when the daemon was started (i.e., the daemon passes the value
Damien Miller32aa1441999-10-29 09:15:49 +10001304on to new connections).
1305.It Ev USER
1306Set to the name of the user logging in.
1307.El
1308.Pp
Damien Miller22c77262000-04-13 12:26:34 +10001309Additionally,
Damien Miller32aa1441999-10-29 09:15:49 +10001310.Nm
Damien Miller22c77262000-04-13 12:26:34 +10001311reads
1312.Pa $HOME/.ssh/environment ,
Damien Miller32aa1441999-10-29 09:15:49 +10001313and adds lines of the format
1314.Dq VARNAME=value
1315to the environment.
1316.Sh FILES
Damien Miller98c7ad62000-03-09 21:27:49 +11001317.Bl -tag -width Ds
Ben Lindstromd6481ea2001-06-25 04:37:41 +00001318.It Pa $HOME/.ssh/known_hosts
Ben Lindstrome59433d2001-09-12 16:41:37 +00001319Records host keys for all hosts the user has logged into that are not
Damien Miller32aa1441999-10-29 09:15:49 +10001320in
Damien Miller05eda432002-02-10 18:32:28 +11001321.Pa /etc/ssh/ssh_known_hosts .
Damien Miller32aa1441999-10-29 09:15:49 +10001322See
1323.Xr sshd 8 .
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001324.It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
1325Contains the authentication identity of the user.
1326They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
Damien Millere247cc42000-05-07 12:03:14 +10001327These files
1328contain sensitive data and should be readable by the user but not
Damien Miller32aa1441999-10-29 09:15:49 +10001329accessible by others (read/write/execute).
1330Note that
1331.Nm
Damien Millere247cc42000-05-07 12:03:14 +10001332ignores a private key file if it is accessible by others.
Damien Miller32aa1441999-10-29 09:15:49 +10001333It is possible to specify a passphrase when
1334generating the key; the passphrase will be used to encrypt the
1335sensitive part of this file using 3DES.
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001336.It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub
Damien Miller32aa1441999-10-29 09:15:49 +10001337Contains the public key for authentication (public part of the
Damien Miller7684ee12000-03-17 23:40:15 +11001338identity file in human-readable form).
Damien Millere247cc42000-05-07 12:03:14 +10001339The contents of the
1340.Pa $HOME/.ssh/identity.pub
1341file should be added to
Damien Miller32aa1441999-10-29 09:15:49 +10001342.Pa $HOME/.ssh/authorized_keys
1343on all machines
Ben Lindstrom594e2032001-09-12 18:35:30 +00001344where the user wishes to log in using protocol version 1 RSA authentication.
Damien Millere247cc42000-05-07 12:03:14 +10001345The contents of the
1346.Pa $HOME/.ssh/id_dsa.pub
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001347and
1348.Pa $HOME/.ssh/id_rsa.pub
Damien Millere247cc42000-05-07 12:03:14 +10001349file should be added to
Ben Lindstromf96704d2001-06-25 04:17:12 +00001350.Pa $HOME/.ssh/authorized_keys
Damien Millere247cc42000-05-07 12:03:14 +10001351on all machines
Ben Lindstrom594e2032001-09-12 18:35:30 +00001352where the user wishes to log in using protocol version 2 DSA/RSA authentication.
Damien Millere247cc42000-05-07 12:03:14 +10001353These files are not
Damien Miller7684ee12000-03-17 23:40:15 +11001354sensitive and can (but need not) be readable by anyone.
Damien Millere247cc42000-05-07 12:03:14 +10001355These files are
Kevin Steves3c034ae2001-02-05 13:47:11 +00001356never used automatically and are not necessary; they are only provided for
Damien Miller32aa1441999-10-29 09:15:49 +10001357the convenience of the user.
1358.It Pa $HOME/.ssh/config
Damien Miller7684ee12000-03-17 23:40:15 +11001359This is the per-user configuration file.
1360The format of this file is described above.
1361This file is used by the
Damien Miller32aa1441999-10-29 09:15:49 +10001362.Nm
Damien Miller7684ee12000-03-17 23:40:15 +11001363client.
1364This file does not usually contain any sensitive information,
Damien Miller32aa1441999-10-29 09:15:49 +10001365but the recommended permissions are read/write for the user, and not
1366accessible by others.
1367.It Pa $HOME/.ssh/authorized_keys
Ben Lindstromf96704d2001-06-25 04:17:12 +00001368Lists the public keys (RSA/DSA) that can be used for logging in as this user.
Damien Miller7684ee12000-03-17 23:40:15 +11001369The format of this file is described in the
Damien Miller32aa1441999-10-29 09:15:49 +10001370.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001371manual page.
Ben Lindstromd6481ea2001-06-25 04:37:41 +00001372In the simplest form the format is the same as the .pub
1373identity files.
Damien Millere247cc42000-05-07 12:03:14 +10001374This file is not highly sensitive, but the recommended
1375permissions are read/write for the user, and not accessible by others.
Damien Miller05eda432002-02-10 18:32:28 +11001376.It Pa /etc/ssh/ssh_known_hosts
Damien Miller7684ee12000-03-17 23:40:15 +11001377Systemwide list of known host keys.
Ben Lindstromd6481ea2001-06-25 04:37:41 +00001378This file should be prepared by the
Damien Miller32aa1441999-10-29 09:15:49 +10001379system administrator to contain the public host keys of all machines in the
Damien Miller7684ee12000-03-17 23:40:15 +11001380organization.
1381This file should be world-readable.
1382This file contains
Damien Miller32aa1441999-10-29 09:15:49 +10001383public keys, one per line, in the following format (fields separated
Ben Lindstromd6481ea2001-06-25 04:37:41 +00001384by spaces): system name, public key and optional comment field.
Damien Miller7684ee12000-03-17 23:40:15 +11001385When different names are used
Damien Miller32aa1441999-10-29 09:15:49 +10001386for the same machine, all such names should be listed, separated by
Damien Miller7684ee12000-03-17 23:40:15 +11001387commas.
1388The format is described on the
Damien Miller32aa1441999-10-29 09:15:49 +10001389.Xr sshd 8
1390manual page.
1391.Pp
1392The canonical system name (as returned by name servers) is used by
1393.Xr sshd 8
1394to verify the client host when logging in; other names are needed because
1395.Nm
1396does not convert the user-supplied name to a canonical name before
1397checking the key, because someone with access to the name servers
1398would then be able to fool host authentication.
Damien Miller05eda432002-02-10 18:32:28 +11001399.It Pa /etc/ssh/ssh_config
Damien Miller7684ee12000-03-17 23:40:15 +11001400Systemwide configuration file.
1401This file provides defaults for those
Damien Miller32aa1441999-10-29 09:15:49 +10001402values that are not specified in the user's configuration file, and
Damien Miller7684ee12000-03-17 23:40:15 +11001403for those users who do not have a configuration file.
1404This file must be world-readable.
Damien Miller05eda432002-02-10 18:32:28 +11001405.It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key
Damien Miller705499b2001-11-12 11:05:38 +11001406These three files contain the private parts of the host keys
1407and are used for
1408.Cm RhostsRSAAuthentication
1409and
1410.Cm HostbasedAuthentication .
1411Since they are readable only by root
1412.Nm
1413must be setuid root if these authentication methods are desired.
Damien Miller32aa1441999-10-29 09:15:49 +10001414.It Pa $HOME/.rhosts
1415This file is used in
1416.Pa \&.rhosts
1417authentication to list the
Damien Miller7684ee12000-03-17 23:40:15 +11001418host/user pairs that are permitted to log in.
1419(Note that this file is
Damien Miller32aa1441999-10-29 09:15:49 +10001420also used by rlogin and rsh, which makes using this file insecure.)
1421Each line of the file contains a host name (in the canonical form
1422returned by name servers), and then a user name on that host,
Damien Miller7684ee12000-03-17 23:40:15 +11001423separated by a space.
Ben Lindstromebd888d2001-03-05 05:49:29 +00001424On some machines this file may need to be
Damien Miller32aa1441999-10-29 09:15:49 +10001425world-readable if the user's home directory is on a NFS partition,
1426because
1427.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001428reads it as root.
1429Additionally, this file must be owned by the user,
1430and must not have write permissions for anyone else.
1431The recommended
Damien Miller32aa1441999-10-29 09:15:49 +10001432permission for most machines is read/write for the user, and not
1433accessible by others.
1434.Pp
1435Note that by default
1436.Xr sshd 8
1437will be installed so that it requires successful RSA host
Damien Miller7684ee12000-03-17 23:40:15 +11001438authentication before permitting \s+2.\s0rhosts authentication.
Ben Lindstrom594e2032001-09-12 18:35:30 +00001439If the server machine does not have the client's host key in
Damien Miller05eda432002-02-10 18:32:28 +11001440.Pa /etc/ssh/ssh_known_hosts ,
Ben Lindstrom594e2032001-09-12 18:35:30 +00001441it can be stored in
Damien Miller32aa1441999-10-29 09:15:49 +10001442.Pa $HOME/.ssh/known_hosts .
1443The easiest way to do this is to
1444connect back to the client from the server machine using ssh; this
Damien Millere247cc42000-05-07 12:03:14 +10001445will automatically add the host key to
Damien Miller32aa1441999-10-29 09:15:49 +10001446.Pa $HOME/.ssh/known_hosts .
1447.It Pa $HOME/.shosts
1448This file is used exactly the same way as
1449.Pa \&.rhosts .
1450The purpose for
1451having this file is to be able to use rhosts authentication with
1452.Nm
1453without permitting login with
1454.Xr rlogin 1
1455or
1456.Xr rsh 1 .
1457.It Pa /etc/hosts.equiv
1458This file is used during
Damien Miller7684ee12000-03-17 23:40:15 +11001459.Pa \&.rhosts authentication.
1460It contains
Damien Miller32aa1441999-10-29 09:15:49 +10001461canonical hosts names, one per line (the full format is described on
1462the
1463.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001464manual page).
1465If the client host is found in this file, login is
Damien Miller32aa1441999-10-29 09:15:49 +10001466automatically permitted provided client and server user names are the
Damien Miller7684ee12000-03-17 23:40:15 +11001467same.
1468Additionally, successful RSA host authentication is normally
1469required.
1470This file should only be writable by root.
Damien Miller886c63a2000-01-20 23:13:36 +11001471.It Pa /etc/shosts.equiv
Damien Miller22c77262000-04-13 12:26:34 +10001472This file is processed exactly as
Damien Miller32aa1441999-10-29 09:15:49 +10001473.Pa /etc/hosts.equiv .
1474This file may be useful to permit logins using
1475.Nm
1476but not using rsh/rlogin.
Damien Miller05eda432002-02-10 18:32:28 +11001477.It Pa /etc/ssh/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +10001478Commands in this file are executed by
1479.Nm
1480when the user logs in just before the user's shell (or command) is started.
1481See the
1482.Xr sshd 8
1483manual page for more information.
1484.It Pa $HOME/.ssh/rc
1485Commands in this file are executed by
1486.Nm
1487when the user logs in just before the user's shell (or command) is
1488started.
Damien Miller22c77262000-04-13 12:26:34 +10001489See the
Damien Miller32aa1441999-10-29 09:15:49 +10001490.Xr sshd 8
1491manual page for more information.
Damien Miller4f0fa561999-12-26 14:24:41 +11001492.It Pa $HOME/.ssh/environment
1493Contains additional definitions for environment variables, see section
1494.Sx ENVIRONMENT
1495above.
Damien Miller7b28dc52000-09-05 13:34:53 +11001496.El
Damien Miller07a2d422002-02-05 12:16:15 +11001497.Sh DIAGNOSTICS
1498.Nm
1499exits with the exit status of the remote command or with 255
1500if an error occurred.
Damien Miller0bc1bd82000-11-13 22:57:25 +11001501.Sh AUTHORS
Ben Lindstrom035782e2001-01-29 08:34:16 +00001502OpenSSH is a derivative of the original and free
1503ssh 1.2.12 release by Tatu Ylonen.
1504Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1505Theo de Raadt and Dug Song
1506removed many bugs, re-added newer features and
1507created OpenSSH.
1508Markus Friedl contributed the support for SSH
1509protocol versions 1.5 and 2.0.
Damien Miller32aa1441999-10-29 09:15:49 +10001510.Sh SEE ALSO
1511.Xr rlogin 1 ,
1512.Xr rsh 1 ,
1513.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +11001514.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +10001515.Xr ssh-add 1 ,
1516.Xr ssh-agent 1 ,
1517.Xr ssh-keygen 1 ,
1518.Xr telnet 1 ,
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +00001519.Xr sshd 8
Ben Lindstrom160ec622001-04-22 17:17:46 +00001520.Rs
1521.%A T. Ylonen
1522.%A T. Kivinen
1523.%A M. Saarinen
1524.%A T. Rinne
1525.%A S. Lehtinen
1526.%T "SSH Protocol Architecture"
Ben Lindstromf1813842002-03-27 17:18:31 +00001527.%N draft-ietf-secsh-architecture-12.txt
1528.%D January 2002
Ben Lindstrom160ec622001-04-22 17:17:46 +00001529.%O work in progress material
1530.Re