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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 Lindstrombd0e2de2001-06-05 19:52:52 +000037.\" $OpenBSD: ssh.1,v 1.113 2001/05/19 16:46:19 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
47.Op Ar hostname | user@hostname
48.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
60.Oo Fl L Xo
61.Sm off
Damien Miller32aa1441999-10-29 09:15:49 +100062.Ar port :
Damien Miller396691a2000-01-20 22:44:08 +110063.Ar host :
Damien Miller32aa1441999-10-29 09:15:49 +100064.Ar hostport
65.Sm on
66.Xc
67.Oc
68.Oo Fl R Xo
69.Sm off
Damien Miller32aa1441999-10-29 09:15:49 +100070.Ar port :
Damien Miller396691a2000-01-20 22:44:08 +110071.Ar host :
Damien Miller32aa1441999-10-29 09:15:49 +100072.Ar hostport
73.Sm on
74.Xc
75.Oc
76.Op Ar hostname | user@hostname
77.Op Ar command
Damien Miller22c77262000-04-13 12:26:34 +100078.Sh DESCRIPTION
Damien Miller32aa1441999-10-29 09:15:49 +100079.Nm
Ben Lindstromd58eb5f2001-03-07 06:07:22 +000080(SSH client) is a program for logging into a remote machine and for
Damien Miller7684ee12000-03-17 23:40:15 +110081executing commands on a remote machine.
82It is intended to replace
Damien Miller32aa1441999-10-29 09:15:49 +100083rlogin and rsh, and provide secure encrypted communications between
Damien Miller7684ee12000-03-17 23:40:15 +110084two untrusted hosts over an insecure network.
85X11 connections and
Damien Miller32aa1441999-10-29 09:15:49 +100086arbitrary TCP/IP ports can also be forwarded over the secure channel.
87.Pp
88.Nm
Damien Miller22c77262000-04-13 12:26:34 +100089connects and logs into the specified
Damien Miller32aa1441999-10-29 09:15:49 +100090.Ar hostname .
91The user must prove
Damien Millere247cc42000-05-07 12:03:14 +100092his/her identity to the remote machine using one of several methods
93depending on the protocol version used:
94.Pp
95.Ss SSH protocol version 1
Damien Miller32aa1441999-10-29 09:15:49 +100096.Pp
97First, if the machine the user logs in from is listed in
98.Pa /etc/hosts.equiv
99or
Damien Miller886c63a2000-01-20 23:13:36 +1100100.Pa /etc/shosts.equiv
Damien Miller32aa1441999-10-29 09:15:49 +1000101on the remote machine, and the user names are
102the same on both sides, the user is immediately permitted to log in.
Damien Miller22c77262000-04-13 12:26:34 +1000103Second, if
Damien Miller32aa1441999-10-29 09:15:49 +1000104.Pa \&.rhosts
105or
106.Pa \&.shosts
107exists in the user's home directory on the
108remote machine and contains a line containing the name of the client
109machine and the name of the user on that machine, the user is
Damien Miller7684ee12000-03-17 23:40:15 +1100110permitted to log in.
111This form of authentication alone is normally not
Damien Miller32aa1441999-10-29 09:15:49 +1000112allowed by the server because it is not secure.
113.Pp
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000114The second authentication method is the
Damien Miller32aa1441999-10-29 09:15:49 +1000115.Pa rhosts
116or
117.Pa hosts.equiv
Damien Miller7684ee12000-03-17 23:40:15 +1100118method combined with RSA-based host authentication.
119It means that if the login would be permitted by
Damien Millere247cc42000-05-07 12:03:14 +1000120.Pa $HOME/.rhosts ,
121.Pa $HOME/.shosts ,
Damien Miller32aa1441999-10-29 09:15:49 +1000122.Pa /etc/hosts.equiv ,
123or
Damien Miller886c63a2000-01-20 23:13:36 +1100124.Pa /etc/shosts.equiv ,
Damien Miller32aa1441999-10-29 09:15:49 +1000125and if additionally the server can verify the client's
Damien Miller22c77262000-04-13 12:26:34 +1000126host key (see
Damien Miller886c63a2000-01-20 23:13:36 +1100127.Pa /etc/ssh_known_hosts
Damien Miller33e511e1999-11-11 11:43:13 +1100128and
129.Pa $HOME/.ssh/known_hosts
Damien Miller32aa1441999-10-29 09:15:49 +1000130in the
131.Sx FILES
Damien Miller7684ee12000-03-17 23:40:15 +1100132section), only then login is permitted.
133This authentication method closes security holes due to IP
134spoofing, DNS spoofing and routing spoofing.
135[Note to the administrator:
Damien Miller32aa1441999-10-29 09:15:49 +1000136.Pa /etc/hosts.equiv ,
Damien Millere247cc42000-05-07 12:03:14 +1000137.Pa $HOME/.rhosts ,
Damien Miller32aa1441999-10-29 09:15:49 +1000138and the rlogin/rsh protocol in general, are inherently insecure and should be
139disabled if security is desired.]
140.Pp
Damien Miller22c77262000-04-13 12:26:34 +1000141As a third authentication method,
Damien Miller32aa1441999-10-29 09:15:49 +1000142.Nm
143supports RSA based authentication.
144The scheme is based on public-key cryptography: there are cryptosystems
145where encryption and decryption are done using separate keys, and it
146is not possible to derive the decryption key from the encryption key.
Damien Miller7684ee12000-03-17 23:40:15 +1100147RSA is one such system.
Damien Miller22c77262000-04-13 12:26:34 +1000148The idea is that each user creates a public/private
Damien Miller7684ee12000-03-17 23:40:15 +1100149key pair for authentication purposes.
150The server knows the public key, and only the user knows the private key.
Damien Miller22c77262000-04-13 12:26:34 +1000151The file
Damien Miller32aa1441999-10-29 09:15:49 +1000152.Pa $HOME/.ssh/authorized_keys
153lists the public keys that are permitted for logging
Damien Miller7684ee12000-03-17 23:40:15 +1100154in.
155When the user logs in, the
Damien Miller32aa1441999-10-29 09:15:49 +1000156.Nm
157program tells the server which key pair it would like to use for
Damien Miller7684ee12000-03-17 23:40:15 +1100158authentication.
159The server checks if this key is permitted, and if
Damien Miller32aa1441999-10-29 09:15:49 +1000160so, sends the user (actually the
161.Nm
162program running on behalf of the user) a challenge, a random number,
Damien Miller7684ee12000-03-17 23:40:15 +1100163encrypted by the user's public key.
164The challenge can only be
165decrypted using the proper private key.
166The user's client then decrypts the
Damien Miller32aa1441999-10-29 09:15:49 +1000167challenge using the private key, proving that he/she knows the private
168key but without disclosing it to the server.
169.Pp
170.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100171implements the RSA authentication protocol automatically.
172The user creates his/her RSA key pair by running
Damien Miller32aa1441999-10-29 09:15:49 +1000173.Xr ssh-keygen 1 .
Damien Miller22c77262000-04-13 12:26:34 +1000174This stores the private key in
Damien Millere247cc42000-05-07 12:03:14 +1000175.Pa $HOME/.ssh/identity
Damien Miller32aa1441999-10-29 09:15:49 +1000176and the public key in
Damien Millere247cc42000-05-07 12:03:14 +1000177.Pa $HOME/.ssh/identity.pub
Damien Miller7684ee12000-03-17 23:40:15 +1100178in the user's home directory.
179The user should then copy the
Damien Miller32aa1441999-10-29 09:15:49 +1000180.Pa identity.pub
Damien Miller22c77262000-04-13 12:26:34 +1000181to
Damien Millere247cc42000-05-07 12:03:14 +1000182.Pa $HOME/.ssh/authorized_keys
Damien Miller22c77262000-04-13 12:26:34 +1000183in his/her home directory on the remote machine (the
Damien Miller32aa1441999-10-29 09:15:49 +1000184.Pa authorized_keys
Damien Miller22c77262000-04-13 12:26:34 +1000185file corresponds to the conventional
Damien Millere247cc42000-05-07 12:03:14 +1000186.Pa $HOME/.rhosts
Damien Miller32aa1441999-10-29 09:15:49 +1000187file, and has one key
Damien Miller7684ee12000-03-17 23:40:15 +1100188per line, though the lines can be very long).
189After this, the user can log in without giving the password.
190RSA authentication is much
Damien Miller32aa1441999-10-29 09:15:49 +1000191more secure than rhosts authentication.
192.Pp
193The most convenient way to use RSA authentication may be with an
Damien Miller7684ee12000-03-17 23:40:15 +1100194authentication agent.
195See
Damien Miller32aa1441999-10-29 09:15:49 +1000196.Xr ssh-agent 1
197for more information.
198.Pp
Damien Miller22c77262000-04-13 12:26:34 +1000199If other authentication methods fail,
Damien Miller32aa1441999-10-29 09:15:49 +1000200.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100201prompts the user for a password.
202The password is sent to the remote
Damien Miller32aa1441999-10-29 09:15:49 +1000203host for checking; however, since all communications are encrypted,
204the password cannot be seen by someone listening on the network.
205.Pp
Damien Millere247cc42000-05-07 12:03:14 +1000206.Ss SSH protocol version 2
207.Pp
208When a user connects using the protocol version 2
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000209different authentication methods are available.
210Using the default values for
211.Cm PreferredAuthentications ,
212the client will try to authenticate first using the public key method;
213if this method fails password authentication is attempted,
214and finally if this method fails keyboard-interactive authentication
215is attempted.
216If this method fails password authentication is
217tried.
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
227.Pa $HOME/.ssh/authorized_keys2
228and 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 Lindstromf8d24572001-04-22 17:11:56 +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 ~~
276(or by following the tilde by a character other than those described above).
277The 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
281configuration directive or on the command line by the
282.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
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000297to terminate (protocol version 1 only)
Ben Lindstrom9ffdcb52001-04-20 12:50:51 +0000298.It Cm ~?
299Display a list of escape characters
300.It Cm ~R
Ben Lindstromf8d24572001-04-22 17:11:56 +0000301Request rekeying of the connection (only useful for SSH protocol version 2
302and if the peer supports it)
Ben Lindstrom9ffdcb52001-04-20 12:50:51 +0000303.El
304.Pp
Damien Millere247cc42000-05-07 12:03:14 +1000305.Ss X11 and TCP forwarding
306.Pp
Ben Lindstrom71215072001-05-17 03:16:18 +0000307If the
308.Cm ForwardX11
309variable is set to
310.Dq yes
311(or, see the description of the
312.Fl X
313and
314.Fl x
315options described later)
316and the user is using X11 (the
Damien Miller32aa1441999-10-29 09:15:49 +1000317.Ev DISPLAY
318environment variable is set), the connection to the X11 display is
319automatically forwarded to the remote side in such a way that any X11
320programs started from the shell (or command) will go through the
321encrypted channel, and the connection to the real X server will be made
Damien Miller7684ee12000-03-17 23:40:15 +1100322from the local machine.
323The user should not manually set
Damien Miller32aa1441999-10-29 09:15:49 +1000324.Ev DISPLAY .
325Forwarding of X11 connections can be
326configured on the command line or in configuration files.
327.Pp
328The
Damien Miller22c77262000-04-13 12:26:34 +1000329.Ev DISPLAY
Damien Miller32aa1441999-10-29 09:15:49 +1000330value set by
331.Nm
332will point to the server machine, but with a display number greater
Damien Miller7684ee12000-03-17 23:40:15 +1100333than zero.
334This is normal, and happens because
Damien Miller32aa1441999-10-29 09:15:49 +1000335.Nm
336creates a
337.Dq proxy
338X server on the server machine for forwarding the
339connections over the encrypted channel.
340.Pp
341.Nm
342will also automatically set up Xauthority data on the server machine.
343For this purpose, it will generate a random authorization cookie,
344store it in Xauthority on the server, and verify that any forwarded
345connections carry this cookie and replace it by the real cookie when
Damien Miller7684ee12000-03-17 23:40:15 +1100346the connection is opened.
347The real authentication cookie is never
Damien Miller32aa1441999-10-29 09:15:49 +1000348sent to the server machine (and no cookies are sent in the plain).
349.Pp
350If the user is using an authentication agent, the connection to the agent
351is automatically forwarded to the remote side unless disabled on
352command line or in a configuration file.
353.Pp
354Forwarding of arbitrary TCP/IP connections over the secure channel can
Damien Miller7684ee12000-03-17 23:40:15 +1100355be specified either on command line or in a configuration file.
356One possible application of TCP/IP forwarding is a secure connection to an
Ben Lindstromebd888d2001-03-05 05:49:29 +0000357electronic purse; another is going through firewalls.
Damien Miller32aa1441999-10-29 09:15:49 +1000358.Pp
Damien Millere247cc42000-05-07 12:03:14 +1000359.Ss Server authentication
360.Pp
Damien Miller32aa1441999-10-29 09:15:49 +1000361.Nm
Damien Millere247cc42000-05-07 12:03:14 +1000362automatically maintains and checks a database containing
Damien Miller7684ee12000-03-17 23:40:15 +1100363identifications for all hosts it has ever been used with.
Damien Millere247cc42000-05-07 12:03:14 +1000364RSA host keys are stored in
365.Pa $HOME/.ssh/known_hosts
366and
Damien Miller0bc1bd82000-11-13 22:57:25 +1100367host keys used in the protocol version 2 are stored in
Damien Millere247cc42000-05-07 12:03:14 +1000368.Pa $HOME/.ssh/known_hosts2
Damien Miller7684ee12000-03-17 23:40:15 +1100369in the user's home directory.
Damien Millere247cc42000-05-07 12:03:14 +1000370Additionally, the files
Damien Miller886c63a2000-01-20 23:13:36 +1100371.Pa /etc/ssh_known_hosts
Damien Millere247cc42000-05-07 12:03:14 +1000372and
373.Pa /etc/ssh_known_hosts2
374are automatically checked for known hosts.
Damien Miller7684ee12000-03-17 23:40:15 +1100375Any new hosts are automatically added to the user's file.
376If a host's identification
Damien Miller32aa1441999-10-29 09:15:49 +1000377ever changes,
378.Nm
379warns about this and disables password authentication to prevent a
Damien Miller7684ee12000-03-17 23:40:15 +1100380trojan horse from getting the user's password.
381Another purpose of
Damien Miller32aa1441999-10-29 09:15:49 +1000382this mechanism is to prevent man-in-the-middle attacks which could
Damien Miller7684ee12000-03-17 23:40:15 +1100383otherwise be used to circumvent the encryption.
384The
Damien Miller32aa1441999-10-29 09:15:49 +1000385.Cm StrictHostKeyChecking
386option (see below) can be used to prevent logins to machines whose
387host key is not known or has changed.
Damien Miller0bc1bd82000-11-13 22:57:25 +1100388.Pp
389The options are as follows:
Damien Miller32aa1441999-10-29 09:15:49 +1000390.Bl -tag -width Ds
391.It Fl a
Damien Miller450a7a12000-03-26 13:04:51 +1000392Disables forwarding of the authentication agent connection.
Damien Millerb1715dc2000-05-30 13:44:51 +1000393.It Fl A
394Enables forwarding of the authentication agent connection.
395This can also be specified on a per-host basis in a configuration file.
Ben Lindstrome0f88042001-04-30 13:06:24 +0000396.It Fl b Ar bind_address
397Specify the interface to transmit from on machines with multiple
398interfaces or aliased addresses.
Damien Miller32aa1441999-10-29 09:15:49 +1000399.It Fl c Ar blowfish|3des
Damien Miller22c77262000-04-13 12:26:34 +1000400Selects the cipher to use for encrypting the session.
Damien Miller32aa1441999-10-29 09:15:49 +1000401.Ar 3des
Damien Miller7684ee12000-03-17 23:40:15 +1100402is used by default.
Damien Miller22c77262000-04-13 12:26:34 +1000403It is believed to be secure.
Damien Miller32aa1441999-10-29 09:15:49 +1000404.Ar 3des
405(triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
406It is presumably more secure than the
407.Ar des
Damien Miller69b69aa2000-10-28 14:19:58 +1100408cipher which is no longer fully supported in
Damien Miller30c3d422000-05-09 11:02:59 +1000409.Nm ssh .
Damien Miller32aa1441999-10-29 09:15:49 +1000410.Ar blowfish
411is a fast block cipher, it appears very secure and is much faster than
Damien Miller7684ee12000-03-17 23:40:15 +1100412.Ar 3des .
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000413.It Fl c Ar cipher_spec
Damien Miller30c3d422000-05-09 11:02:59 +1000414Additionally, for protocol version 2 a comma-separated list of ciphers can
Damien Miller874d77b2000-10-14 16:23:11 +1100415be specified in order of preference.
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000416See
417.Cm Ciphers
418for more information.
Damien Miller32aa1441999-10-29 09:15:49 +1000419.It Fl e Ar ch|^ch|none
420Sets the escape character for sessions with a pty (default:
421.Ql ~ ) .
Damien Miller7684ee12000-03-17 23:40:15 +1100422The escape character is only recognized at the beginning of a line.
423The escape character followed by a dot
Damien Miller32aa1441999-10-29 09:15:49 +1000424.Pq Ql \&.
425closes the connection, followed
426by control-Z suspends the connection, and followed by itself sends the
Damien Miller7684ee12000-03-17 23:40:15 +1100427escape character once.
428Setting the character to
Damien Miller32aa1441999-10-29 09:15:49 +1000429.Dq none
430disables any escapes and makes the session fully transparent.
431.It Fl f
432Requests
433.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100434to go to background just before command execution.
435This is useful if
Damien Miller32aa1441999-10-29 09:15:49 +1000436.Nm
437is going to ask for passwords or passphrases, but the user
Damien Miller7684ee12000-03-17 23:40:15 +1100438wants it in the background.
Damien Miller22c77262000-04-13 12:26:34 +1000439This implies
Damien Miller32aa1441999-10-29 09:15:49 +1000440.Fl n .
441The recommended way to start X11 programs at a remote site is with
442something like
443.Ic ssh -f host xterm .
Damien Miller396691a2000-01-20 22:44:08 +1100444.It Fl g
445Allows remote hosts to connect to local forwarded ports.
Damien Miller32aa1441999-10-29 09:15:49 +1000446.It Fl i Ar identity_file
Damien Miller22c77262000-04-13 12:26:34 +1000447Selects the file from which the identity (private key) for
Damien Miller0bc1bd82000-11-13 22:57:25 +1100448RSA or DSA authentication is read.
Damien Miller22c77262000-04-13 12:26:34 +1000449Default is
Damien Millere247cc42000-05-07 12:03:14 +1000450.Pa $HOME/.ssh/identity
Damien Miller7684ee12000-03-17 23:40:15 +1100451in the user's home directory.
452Identity files may also be specified on
453a per-host basis in the configuration file.
454It is possible to have multiple
Damien Miller32aa1441999-10-29 09:15:49 +1000455.Fl i
456options (and multiple identities specified in
457configuration files).
Damien Miller32aa1441999-10-29 09:15:49 +1000458.It Fl k
Damien Miller450a7a12000-03-26 13:04:51 +1000459Disables forwarding of Kerberos tickets and AFS tokens.
460This may also be specified on a per-host basis in the configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000461.It Fl l Ar login_name
Damien Miller7684ee12000-03-17 23:40:15 +1100462Specifies the user to log in as on the remote machine.
463This also may be specified on a per-host basis in the configuration file.
Ben Lindstrom06b33aa2001-02-15 03:01:59 +0000464.It Fl m Ar mac_spec
465Additionally, for protocol version 2 a comma-separated list of MAC
466(message authentication code) algorithms can
467be specified in order of preference.
468See the
469.Cm MACs
470keyword for more information.
Damien Miller32aa1441999-10-29 09:15:49 +1000471.It Fl n
472Redirects stdin from
473.Pa /dev/null
474(actually, prevents reading from stdin).
475This must be used when
476.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100477is run in the background.
478A common trick is to use this to run X11 programs on a remote machine.
479For example,
Damien Miller32aa1441999-10-29 09:15:49 +1000480.Ic ssh -n shadows.cs.hut.fi emacs &
481will start an emacs on shadows.cs.hut.fi, and the X11
482connection will be automatically forwarded over an encrypted channel.
483The
484.Nm
485program will be put in the background.
486(This does not work if
487.Nm
488needs to ask for a password or passphrase; see also the
489.Fl f
490option.)
Damien Millerdcb6ecd2000-05-17 22:34:22 +1000491.It Fl N
492Do not execute a remote command.
Ben Lindstromc72745a2000-12-02 19:03:54 +0000493This is useful if you just want to forward ports
Damien Millerdcb6ecd2000-05-17 22:34:22 +1000494(protocol version 2 only).
Damien Miller32aa1441999-10-29 09:15:49 +1000495.It Fl o Ar option
496Can be used to give options in the format used in the config file.
497This is useful for specifying options for which there is no separate
Damien Miller7684ee12000-03-17 23:40:15 +1100498command-line flag.
499The option has the same format as a line in the configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000500.It Fl p Ar port
Damien Miller7684ee12000-03-17 23:40:15 +1100501Port to connect to on the remote host.
502This can be specified on a
Damien Miller32aa1441999-10-29 09:15:49 +1000503per-host basis in the configuration file.
504.It Fl P
505Use a non-privileged port for outgoing connections.
506This can be used if your firewall does
507not permit connections from privileged ports.
Damien Millera34a28b1999-12-14 10:47:15 +1100508Note that this option turns off
Damien Miller32aa1441999-10-29 09:15:49 +1000509.Cm RhostsAuthentication
510and
Kevin Stevesfcec7f82000-12-15 19:55:48 +0000511.Cm RhostsRSAAuthentication
512for older servers.
Damien Miller32aa1441999-10-29 09:15:49 +1000513.It Fl q
Damien Miller7684ee12000-03-17 23:40:15 +1100514Quiet mode.
515Causes all warning and diagnostic messages to be suppressed.
516Only fatal errors are displayed.
Damien Miller832562e2001-01-30 09:30:01 +1100517.It Fl s
518May be used to request invocation of a subsystem on the remote system. Subsystems are a feature of the SSH2 protocol which facilitate the use
Ben Lindstromf0609f82001-05-04 22:38:43 +0000519of SSH as a secure transport for other applications (eg. sftp). The
Damien Miller832562e2001-01-30 09:30:01 +1100520subsystem is specified as the remote command.
Damien Miller32aa1441999-10-29 09:15:49 +1000521.It Fl t
Damien Miller7684ee12000-03-17 23:40:15 +1100522Force pseudo-tty allocation.
Damien Miller450a7a12000-03-26 13:04:51 +1000523This can be used to execute arbitrary
Damien Miller7684ee12000-03-17 23:40:15 +1100524screen-based programs on a remote machine, which can be very useful,
525e.g., when implementing menu services.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000526Multiple
527.Fl t
528options force tty allocation, even if
529.Nm
530has no local tty.
Damien Millerdcb6ecd2000-05-17 22:34:22 +1000531.It Fl T
Ben Lindstromc72745a2000-12-02 19:03:54 +0000532Disable pseudo-tty allocation.
Damien Miller32aa1441999-10-29 09:15:49 +1000533.It Fl v
Damien Miller7684ee12000-03-17 23:40:15 +1100534Verbose mode.
535Causes
Damien Miller32aa1441999-10-29 09:15:49 +1000536.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100537to print debugging messages about its progress.
538This is helpful in
Damien Miller32aa1441999-10-29 09:15:49 +1000539debugging connection, authentication, and configuration problems.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000540Multiple
541.Fl v
542options increases the verbosity.
Damien Miller874d77b2000-10-14 16:23:11 +1100543Maximum is 3.
Damien Miller32aa1441999-10-29 09:15:49 +1000544.It Fl x
Damien Miller7684ee12000-03-17 23:40:15 +1100545Disables X11 forwarding.
Damien Miller32aa1441999-10-29 09:15:49 +1000546.It Fl X
547Enables X11 forwarding.
Damien Millerb1715dc2000-05-30 13:44:51 +1000548This can also be specified on a per-host basis in a configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000549.It Fl C
550Requests compression of all data (including stdin, stdout, stderr, and
Damien Miller7684ee12000-03-17 23:40:15 +1100551data for forwarded X11 and TCP/IP connections).
552The compression algorithm is the same used by
Damien Miller396691a2000-01-20 22:44:08 +1100553.Xr gzip 1 ,
554and the
Damien Miller32aa1441999-10-29 09:15:49 +1000555.Dq level
556can be controlled by the
557.Cm CompressionLevel
Damien Miller7684ee12000-03-17 23:40:15 +1100558option (see below).
559Compression is desirable on modem lines and other
Damien Miller32aa1441999-10-29 09:15:49 +1000560slow connections, but will only slow down things on fast networks.
561The default value can be set on a host-by-host basis in the
562configuration files; see the
563.Cm Compress
564option below.
565.It Fl L Ar port:host:hostport
566Specifies that the given port on the local (client) host is to be
Damien Miller7684ee12000-03-17 23:40:15 +1100567forwarded to the given host and port on the remote side.
568This works by allocating a socket to listen to
Damien Miller32aa1441999-10-29 09:15:49 +1000569.Ar port
570on the local side, and whenever a connection is made to this port, the
571connection is forwarded over the secure channel, and a connection is
572made to
Damien Miller34132e52000-01-14 15:45:46 +1100573.Ar host
574port
575.Ar hostport
Damien Miller7684ee12000-03-17 23:40:15 +1100576from the remote machine.
577Port forwardings can also be specified in the configuration file.
578Only root can forward privileged ports.
Damien Miller34132e52000-01-14 15:45:46 +1100579IPv6 addresses can be specified with an alternative syntax:
580.Ar port/host/hostport
Damien Miller32aa1441999-10-29 09:15:49 +1000581.It Fl R Ar port:host:hostport
582Specifies that the given port on the remote (server) host is to be
Damien Miller7684ee12000-03-17 23:40:15 +1100583forwarded to the given host and port on the local side.
584This works by allocating a socket to listen to
Damien Miller32aa1441999-10-29 09:15:49 +1000585.Ar port
586on the remote side, and whenever a connection is made to this port, the
587connection is forwarded over the secure channel, and a connection is
588made to
Damien Miller34132e52000-01-14 15:45:46 +1100589.Ar host
590port
591.Ar hostport
Damien Miller7684ee12000-03-17 23:40:15 +1100592from the local machine.
593Port forwardings can also be specified in the configuration file.
594Privileged ports can be forwarded only when
Damien Miller32aa1441999-10-29 09:15:49 +1000595logging in as root on the remote machine.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000596IPv6 addresses can be specified with an alternative syntax:
597.Ar port/host/hostport
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000598.It Fl 1
599Forces
600.Nm
601to try protocol version 1 only.
Damien Miller4af51302000-04-16 11:18:38 +1000602.It Fl 2
603Forces
604.Nm
Damien Millere247cc42000-05-07 12:03:14 +1000605to try protocol version 2 only.
Damien Miller34132e52000-01-14 15:45:46 +1100606.It Fl 4
607Forces
608.Nm
609to use IPv4 addresses only.
610.It Fl 6
611Forces
612.Nm
613to use IPv6 addresses only.
Damien Miller32aa1441999-10-29 09:15:49 +1000614.El
615.Sh CONFIGURATION FILES
616.Nm
617obtains configuration data from the following sources (in this order):
618command line options, user's configuration file
619.Pq Pa $HOME/.ssh/config ,
620and system-wide configuration file
Damien Miller886c63a2000-01-20 23:13:36 +1100621.Pq Pa /etc/ssh_config .
Damien Miller32aa1441999-10-29 09:15:49 +1000622For each parameter, the first obtained value
Damien Miller7684ee12000-03-17 23:40:15 +1100623will be used.
624The configuration files contain sections bracketed by
625.Dq Host
626specifications, and that section is only applied for hosts that
627match one of the patterns given in the specification.
628The matched host name is the one given on the command line.
Damien Miller32aa1441999-10-29 09:15:49 +1000629.Pp
630Since the first obtained value for each parameter is used, more
631host-specific declarations should be given near the beginning of the
632file, and general defaults at the end.
633.Pp
634The configuration file has the following format:
635.Pp
636Empty lines and lines starting with
637.Ql #
638are comments.
639.Pp
640Otherwise a line is of the format
641.Dq keyword arguments .
642The possible
643keywords and their meanings are as follows (note that the
644configuration files are case-sensitive):
645.Bl -tag -width Ds
646.It Cm Host
647Restricts the following declarations (up to the next
648.Cm Host
649keyword) to be only for those hosts that match one of the patterns
650given after the keyword.
651.Ql \&*
652and
653.Ql ?
654can be used as wildcards in the
Damien Miller7684ee12000-03-17 23:40:15 +1100655patterns.
656A single
Damien Miller32aa1441999-10-29 09:15:49 +1000657.Ql \&*
658as a pattern can be used to provide global
Damien Miller7684ee12000-03-17 23:40:15 +1100659defaults for all hosts.
660The host is the
Damien Miller32aa1441999-10-29 09:15:49 +1000661.Ar hostname
662argument given on the command line (i.e., the name is not converted to
663a canonicalized host name before matching).
664.It Cm AFSTokenPassing
Damien Miller450a7a12000-03-26 13:04:51 +1000665Specifies whether to pass AFS tokens to remote host.
666The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +1000667.Dq yes
668or
669.Dq no .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000670This option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000671.It Cm BatchMode
672If set to
673.Dq yes ,
Damien Miller7684ee12000-03-17 23:40:15 +1100674passphrase/password querying will be disabled.
675This option is useful in scripts and other batch jobs where you have no
676user to supply the password.
677The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000678.Dq yes
679or
680.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000681The default is
682.Dq no .
Ben Lindstrome0f88042001-04-30 13:06:24 +0000683.It Cm BindAddress
684Specify the interface to transmit from on machines with multiple
685interfaces or aliased addresses.
686Note that this option does not work if
687.Cm UsePrivilegedPort
688is set to
689.Dq yes .
Damien Miller396691a2000-01-20 22:44:08 +1100690.It Cm CheckHostIP
691If this flag is set to
692.Dq yes ,
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000693ssh will additionally check the host IP address in the
Damien Miller396691a2000-01-20 22:44:08 +1100694.Pa known_hosts
Damien Miller450a7a12000-03-26 13:04:51 +1000695file.
696This allows ssh to detect if a host key changed due to DNS spoofing.
Damien Miller396691a2000-01-20 22:44:08 +1100697If the option is set to
698.Dq no ,
699the check will not be executed.
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000700The default is
701.Dq yes .
Damien Miller32aa1441999-10-29 09:15:49 +1000702.It Cm Cipher
Damien Miller50a41ed2000-10-16 12:14:42 +1100703Specifies the cipher to use for encrypting the session
Damien Miller69b69aa2000-10-28 14:19:58 +1100704in protocol version 1.
Damien Miller7684ee12000-03-17 23:40:15 +1100705Currently,
Damien Miller69b69aa2000-10-28 14:19:58 +1100706.Dq blowfish
Damien Miller32aa1441999-10-29 09:15:49 +1000707and
708.Dq 3des
Damien Miller7684ee12000-03-17 23:40:15 +1100709are supported.
710The default is
Damien Miller32aa1441999-10-29 09:15:49 +1000711.Dq 3des .
Damien Miller22c77262000-04-13 12:26:34 +1000712.It Cm Ciphers
713Specifies the ciphers allowed for protocol version 2
714in order of preference.
715Multiple ciphers must be comma-separated.
716The default is
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000717.Pp
718.Bd -literal
Ben Lindstromec26fb12001-03-06 01:05:23 +0000719 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000720 aes192-cbc,aes256-cbc''
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000721.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000722.It Cm Compression
Damien Miller7684ee12000-03-17 23:40:15 +1100723Specifies whether to use compression.
724The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000725.Dq yes
726or
727.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000728The default is
729.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000730.It Cm CompressionLevel
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000731Specifies the compression level to use if compression is enabled.
Damien Miller7684ee12000-03-17 23:40:15 +1100732The argument must be an integer from 1 (fast) to 9 (slow, best).
733The default level is 6, which is good for most applications.
734The meaning of the values is the same as in
Damien Miller396691a2000-01-20 22:44:08 +1100735.Xr gzip 1 .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000736Note that this option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000737.It Cm ConnectionAttempts
738Specifies the number of tries (one per second) to make before falling
Damien Miller7684ee12000-03-17 23:40:15 +1100739back to rsh or exiting.
740The argument must be an integer.
741This may be useful in scripts if the connection sometimes fails.
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000742The default is 4.
Damien Miller32aa1441999-10-29 09:15:49 +1000743.It Cm EscapeChar
744Sets the escape character (default:
745.Ql ~ ) .
746The escape character can also
Damien Miller7684ee12000-03-17 23:40:15 +1100747be set on the command line.
748The argument should be a single character,
Damien Miller32aa1441999-10-29 09:15:49 +1000749.Ql ^
750followed by a letter, or
751.Dq none
752to disable the escape
753character entirely (making the connection transparent for binary
754data).
Damien Miller22c77262000-04-13 12:26:34 +1000755.It Cm FallBackToRsh
Damien Miller32aa1441999-10-29 09:15:49 +1000756Specifies that if connecting via
757.Nm
758fails due to a connection refused error (there is no
759.Xr sshd 8
Damien Miller22c77262000-04-13 12:26:34 +1000760listening on the remote host),
Damien Miller32aa1441999-10-29 09:15:49 +1000761.Xr rsh 1
762should automatically be used instead (after a suitable warning about
Damien Miller7684ee12000-03-17 23:40:15 +1100763the session being unencrypted).
764The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000765.Dq yes
766or
767.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000768The default is
769.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000770.It Cm ForwardAgent
771Specifies whether the connection to the authentication agent (if any)
Damien Miller7684ee12000-03-17 23:40:15 +1100772will be forwarded to the remote machine.
773The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000774.Dq yes
775or
776.Dq no .
Damien Millerb1715dc2000-05-30 13:44:51 +1000777The default is
778.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000779.It Cm ForwardX11
780Specifies whether X11 connections will be automatically redirected
Damien Miller22c77262000-04-13 12:26:34 +1000781over the secure channel and
Damien Miller32aa1441999-10-29 09:15:49 +1000782.Ev DISPLAY
Damien Miller7684ee12000-03-17 23:40:15 +1100783set.
Damien Miller22c77262000-04-13 12:26:34 +1000784The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000785.Dq yes
786or
787.Dq no .
Damien Miller98c7ad62000-03-09 21:27:49 +1100788The default is
789.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000790.It Cm GatewayPorts
791Specifies whether remote hosts are allowed to connect to local
792forwarded ports.
793The argument must be
794.Dq yes
795or
796.Dq no .
797The default is
798.Dq no .
799.It Cm GlobalKnownHostsFile
Ben Lindstrom1e621742001-03-06 01:10:53 +0000800Specifies a file to use for the protocol version 1 global
801host key database instead of
Damien Miller886c63a2000-01-20 23:13:36 +1100802.Pa /etc/ssh_known_hosts .
Ben Lindstrom1e621742001-03-06 01:10:53 +0000803.It Cm GlobalKnownHostsFile2
804Specifies a file to use for the protocol version 2 global
805host key database instead of
806.Pa /etc/ssh_known_hosts2 .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000807.It Cm HostbasedAuthentication
808Specifies whether to try rhosts based authentication with public key
809authentication.
810The argument must be
811.Dq yes
812or
813.Dq no .
814The default is
Ben Lindstrom1bfe2912001-06-05 19:37:25 +0000815.Dq no .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000816This option applies to protocol version 2 only and
817is similar to
818.Cm RhostsRSAAuthentication .
Ben Lindstrom982dbbc2001-04-17 18:11:36 +0000819.It Cm HostKeyAlgorithms
Ben Lindstromf0609f82001-05-04 22:38:43 +0000820Specifies the protocol version 2 host key algorithms
Ben Lindstrom982dbbc2001-04-17 18:11:36 +0000821that the client wants to use in order of preference.
822The default for this option is:
823.Dq ssh-rsa,ssh-dss
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000824.It Cm HostKeyAlias
825Specifies an alias that should be used instead of the
826real host name when looking up or saving the host key
827in the host key database files.
828This option is useful for tunneling ssh connections
829or if you have multiple servers running on a single host.
Damien Miller32aa1441999-10-29 09:15:49 +1000830.It Cm HostName
Damien Miller7684ee12000-03-17 23:40:15 +1100831Specifies the real host name to log into.
832This can be used to specify nicknames or abbreviations for hosts.
833Default is the name given on the command line.
834Numeric IP addresses are also permitted (both on the command line and in
Damien Miller32aa1441999-10-29 09:15:49 +1000835.Cm HostName
836specifications).
837.It Cm IdentityFile
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000838Specifies the file from which the user's RSA or DSA authentication identity
Damien Miller32aa1441999-10-29 09:15:49 +1000839is read (default
Damien Millere247cc42000-05-07 12:03:14 +1000840.Pa $HOME/.ssh/identity
Damien Miller32aa1441999-10-29 09:15:49 +1000841in the user's home directory).
842Additionally, any identities represented by the authentication agent
Damien Miller7684ee12000-03-17 23:40:15 +1100843will be used for authentication.
844The file name may use the tilde
845syntax to refer to a user's home directory.
846It is possible to have
Damien Miller32aa1441999-10-29 09:15:49 +1000847multiple identity files specified in configuration files; all these
848identities will be tried in sequence.
849.It Cm KeepAlive
850Specifies whether the system should send keepalive messages to the
Damien Miller7684ee12000-03-17 23:40:15 +1100851other side.
852If they are sent, death of the connection or crash of one
853of the machines will be properly noticed.
854However, this means that
Damien Miller32aa1441999-10-29 09:15:49 +1000855connections will die if the route is down temporarily, and some people
Damien Miller450a7a12000-03-26 13:04:51 +1000856find it annoying.
Damien Miller32aa1441999-10-29 09:15:49 +1000857.Pp
858The default is
859.Dq yes
860(to send keepalives), and the client will notice
Damien Miller7684ee12000-03-17 23:40:15 +1100861if the network goes down or the remote host dies.
862This is important in scripts, and many users want it too.
Damien Miller32aa1441999-10-29 09:15:49 +1000863.Pp
864To disable keepalives, the value should be set to
865.Dq no
866in both the server and the client configuration files.
867.It Cm KerberosAuthentication
Damien Miller450a7a12000-03-26 13:04:51 +1000868Specifies whether Kerberos authentication will be used.
869The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +1000870.Dq yes
871or
872.Dq no .
873.It Cm KerberosTgtPassing
Damien Miller450a7a12000-03-26 13:04:51 +1000874Specifies whether a Kerberos TGT will be forwarded to the server.
875This will only work if the Kerberos server is actually an AFS kaserver.
876The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +1000877.Dq yes
878or
879.Dq no .
880.It Cm LocalForward
881Specifies that a TCP/IP port on the local machine be forwarded over
Damien Miller7684ee12000-03-17 23:40:15 +1100882the secure channel to given host:port from the remote machine.
883The first argument must be a port number, and the second must be
884host:port.
885Multiple forwardings may be specified, and additional
886forwardings can be given on the command line.
887Only the superuser can forward privileged ports.
Damien Miller5ce662a1999-11-11 17:57:39 +1100888.It Cm LogLevel
889Gives the verbosity level that is used when logging messages from
890.Nm ssh .
891The possible values are:
Ben Lindstromdb65e8f2001-01-19 04:26:52 +0000892QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
893The default is INFO.
Ben Lindstrom06b33aa2001-02-15 03:01:59 +0000894.It Cm MACs
895Specifies the MAC (message authentication code) algorithms
896in order of preference.
897The MAC algorithm is used in protocol version 2
898for data integrity protection.
899Multiple algorithms must be comma-separated.
900The default is
Ben Lindstrombd0e2de2001-06-05 19:52:52 +0000901.Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
Damien Miller32aa1441999-10-29 09:15:49 +1000902.It Cm NumberOfPasswordPrompts
Damien Miller450a7a12000-03-26 13:04:51 +1000903Specifies the number of password prompts before giving up.
904The argument to this keyword must be an integer.
905Default is 3.
Damien Miller396691a2000-01-20 22:44:08 +1100906.It Cm PasswordAuthentication
Damien Miller7684ee12000-03-17 23:40:15 +1100907Specifies whether to use password authentication.
908The argument to this keyword must be
Damien Miller396691a2000-01-20 22:44:08 +1100909.Dq yes
910or
911.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000912The default is
913.Dq yes .
Damien Miller32aa1441999-10-29 09:15:49 +1000914.It Cm Port
Damien Miller7684ee12000-03-17 23:40:15 +1100915Specifies the port number to connect on the remote host.
916Default is 22.
Damien Miller1e42f302001-03-19 23:59:11 +1100917.It Cm PreferredAuthentications
918Specifies the order in which the client should try protocol 2
919authentication methods. This allows a client to prefer one method (e.g.
920.Cm keyboard-interactive )
921over another method (e.g.
922.Cm password )
923The default for this option is:
Ben Lindstrom1bfe2912001-06-05 19:37:25 +0000924.Dq publickey,hostbased,password,keyboard-interactive
Damien Miller22c77262000-04-13 12:26:34 +1000925.It Cm Protocol
926Specifies the protocol versions
927.Nm
928should support in order of preference.
929The possible values are
930.Dq 1
931and
932.Dq 2 .
933Multiple versions must be comma-separated.
934The default is
Ben Lindstromf3272352001-04-05 23:29:59 +0000935.Dq 2,1 .
Damien Millere247cc42000-05-07 12:03:14 +1000936This means that
937.Nm
Ben Lindstromf3272352001-04-05 23:29:59 +0000938tries version 2 and falls back to version 1
939if version 2 is not available.
Damien Miller32aa1441999-10-29 09:15:49 +1000940.It Cm ProxyCommand
Damien Miller7684ee12000-03-17 23:40:15 +1100941Specifies the command to use to connect to the server.
942The command
943string extends to the end of the line, and is executed with
944.Pa /bin/sh .
945In the command string,
946.Ql %h
947will be substituted by the host name to
948connect and
949.Ql %p
950by the port.
951The command can be basically anything,
952and should read from its standard input and write to its standard output.
953It should eventually connect an
Damien Miller32aa1441999-10-29 09:15:49 +1000954.Xr sshd 8
955server running on some machine, or execute
956.Ic sshd -i
Damien Miller7684ee12000-03-17 23:40:15 +1100957somewhere.
958Host key management will be done using the
Damien Miller32aa1441999-10-29 09:15:49 +1000959HostName of the host being connected (defaulting to the name typed by
960the user).
Damien Milleraae6c611999-12-06 11:47:28 +1100961Note that
962.Cm CheckHostIP
963is not available for connects with a proxy command.
Damien Miller32aa1441999-10-29 09:15:49 +1000964.Pp
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000965.It Cm PubkeyAuthentication
966Specifies whether to try public key authentication.
967The argument to this keyword must be
968.Dq yes
969or
970.Dq no .
971The default is
972.Dq yes .
973This option applies to protocol version 2 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000974.It Cm RemoteForward
975Specifies that a TCP/IP port on the remote machine be forwarded over
Damien Miller7684ee12000-03-17 23:40:15 +1100976the secure channel to given host:port from the local machine.
977The first argument must be a port number, and the second must be
978host:port.
979Multiple forwardings may be specified, and additional
980forwardings can be given on the command line.
981Only the superuser can forward privileged ports.
Damien Miller32aa1441999-10-29 09:15:49 +1000982.It Cm RhostsAuthentication
Damien Miller7684ee12000-03-17 23:40:15 +1100983Specifies whether to try rhosts based authentication.
984Note that this
Damien Miller32aa1441999-10-29 09:15:49 +1000985declaration only affects the client side and has no effect whatsoever
Damien Miller7684ee12000-03-17 23:40:15 +1100986on security.
987Disabling rhosts authentication may reduce
Damien Miller32aa1441999-10-29 09:15:49 +1000988authentication time on slow connections when rhosts authentication is
Damien Miller7684ee12000-03-17 23:40:15 +1100989not used.
990Most servers do not permit RhostsAuthentication because it
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000991is not secure (see
992.Cm RhostsRSAAuthentication ).
Damien Miller7684ee12000-03-17 23:40:15 +1100993The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +1000994.Dq yes
995or
996.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000997The default is
998.Dq yes .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000999This option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +10001000.It Cm RhostsRSAAuthentication
1001Specifies whether to try rhosts based authentication with RSA host
Damien Miller7684ee12000-03-17 23:40:15 +11001002authentication.
Damien Miller7684ee12000-03-17 23:40:15 +11001003The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +10001004.Dq yes
1005or
1006.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +00001007The default is
1008.Dq yes .
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001009This option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +10001010.It Cm RSAAuthentication
Damien Miller7684ee12000-03-17 23:40:15 +11001011Specifies whether to try RSA authentication.
1012The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +10001013.Dq yes
1014or
1015.Dq no .
1016RSA authentication will only be
1017attempted if the identity file exists, or an authentication agent is
1018running.
Ben Lindstrom89b0bd62001-03-29 00:27:11 +00001019The default is
1020.Dq yes .
Damien Millere247cc42000-05-07 12:03:14 +10001021Note that this option applies to protocol version 1 only.
Damien Miller33804262001-02-04 23:20:18 +11001022.It Cm ChallengeResponseAuthentication
1023Specifies whether to use challenge response authentication.
1024Currently there is only support for
Damien Miller95def091999-11-25 00:26:21 +11001025.Xr skey 1
Damien Miller7684ee12000-03-17 23:40:15 +11001026authentication.
1027The argument to this keyword must be
Damien Miller95def091999-11-25 00:26:21 +11001028.Dq yes
1029or
1030.Dq no .
1031The default is
1032.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +10001033.It Cm StrictHostKeyChecking
1034If this flag is set to
Damien Miller22c77262000-04-13 12:26:34 +10001035.Dq yes ,
Damien Miller32aa1441999-10-29 09:15:49 +10001036.Nm
Ben Lindstromeb930d42001-01-29 08:37:08 +00001037will never automatically add host keys to the
Damien Miller32aa1441999-10-29 09:15:49 +10001038.Pa $HOME/.ssh/known_hosts
Damien Millere247cc42000-05-07 12:03:14 +10001039and
1040.Pa $HOME/.ssh/known_hosts2
Ben Lindstromeb930d42001-01-29 08:37:08 +00001041files, and refuses to connect to hosts whose host key has changed.
Damien Miller7684ee12000-03-17 23:40:15 +11001042This provides maximum protection against trojan horse attacks.
1043However, it can be somewhat annoying if you don't have good
Damien Miller886c63a2000-01-20 23:13:36 +11001044.Pa /etc/ssh_known_hosts
Damien Millere247cc42000-05-07 12:03:14 +10001045and
1046.Pa /etc/ssh_known_hosts2
Damien Miller32aa1441999-10-29 09:15:49 +10001047files installed and frequently
Ben Lindstromeb930d42001-01-29 08:37:08 +00001048connect to new hosts.
1049This option forces the user to manually
1050add all new hosts.
1051If this flag is set to
1052.Dq no ,
1053.Nm
1054will automatically add new host keys to the
1055user known hosts files.
1056If this flag is set to
1057.Dq ask ,
1058new host keys
1059will be added to the user known host files only after the user
1060has confirmed that is what they really want to do, and
1061.Nm
1062will refuse to connect to hosts whose host key has changed.
Damien Miller7684ee12000-03-17 23:40:15 +11001063The host keys of
Ben Lindstromeb930d42001-01-29 08:37:08 +00001064known hosts will be verified automatically in all cases.
Damien Miller7684ee12000-03-17 23:40:15 +11001065The argument must be
Ben Lindstromeb930d42001-01-29 08:37:08 +00001066.Dq yes ,
1067.Dq no
Damien Miller32aa1441999-10-29 09:15:49 +10001068or
Ben Lindstromeb930d42001-01-29 08:37:08 +00001069.Dq ask .
1070The default is
1071.Dq ask .
Damien Miller32aa1441999-10-29 09:15:49 +10001072.It Cm UsePrivilegedPort
1073Specifies whether to use a privileged port for outgoing connections.
1074The argument must be
1075.Dq yes
1076or
1077.Dq no .
1078The default is
Ben Lindstromcebc8582001-03-08 03:39:10 +00001079.Dq no .
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001080Note that you need to set this option to
1081.Dq yes
1082if you want to use
Damien Miller32aa1441999-10-29 09:15:49 +10001083.Cm RhostsAuthentication
1084and
Kevin Stevesfcec7f82000-12-15 19:55:48 +00001085.Cm RhostsRSAAuthentication
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001086with older servers.
Damien Miller396691a2000-01-20 22:44:08 +11001087.It Cm User
Damien Miller7684ee12000-03-17 23:40:15 +11001088Specifies the user to log in as.
1089This can be useful if you have a different user name on different machines.
1090This saves the trouble of
Damien Miller396691a2000-01-20 22:44:08 +11001091having to remember to give the user name on the command line.
1092.It Cm UserKnownHostsFile
Ben Lindstrom1e621742001-03-06 01:10:53 +00001093Specifies a file to use for the protocol version 1 user
1094host key database instead of
Damien Miller396691a2000-01-20 22:44:08 +11001095.Pa $HOME/.ssh/known_hosts .
Ben Lindstrom1e621742001-03-06 01:10:53 +00001096.It Cm UserKnownHostsFile2
1097Specifies a file to use for the protocol version 2 user
1098host key database instead of
1099.Pa $HOME/.ssh/known_hosts2 .
Damien Miller32aa1441999-10-29 09:15:49 +10001100.It Cm UseRsh
Damien Miller7684ee12000-03-17 23:40:15 +11001101Specifies that rlogin/rsh should be used for this host.
1102It is possible that the host does not at all support the
Damien Miller32aa1441999-10-29 09:15:49 +10001103.Nm
Damien Miller7684ee12000-03-17 23:40:15 +11001104protocol.
1105This causes
Damien Miller32aa1441999-10-29 09:15:49 +10001106.Nm
Damien Miller7684ee12000-03-17 23:40:15 +11001107to immediately execute
Damien Miller32aa1441999-10-29 09:15:49 +10001108.Xr rsh 1 .
1109All other options (except
1110.Cm HostName )
Damien Miller7684ee12000-03-17 23:40:15 +11001111are ignored if this has been specified.
1112The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +10001113.Dq yes
1114or
1115.Dq no .
Damien Millerd3a18572000-06-07 19:55:44 +10001116.It Cm XAuthLocation
1117Specifies the location of the
1118.Xr xauth 1
1119program.
1120The default is
1121.Pa /usr/X11R6/bin/xauth .
Damien Miller7b28dc52000-09-05 13:34:53 +11001122.El
Damien Miller32aa1441999-10-29 09:15:49 +10001123.Sh ENVIRONMENT
1124.Nm
1125will normally set the following environment variables:
1126.Bl -tag -width Ds
1127.It Ev DISPLAY
1128The
1129.Ev DISPLAY
Damien Miller7684ee12000-03-17 23:40:15 +11001130variable indicates the location of the X11 server.
Damien Miller22c77262000-04-13 12:26:34 +10001131It is automatically set by
Damien Miller32aa1441999-10-29 09:15:49 +10001132.Nm
1133to point to a value of the form
1134.Dq hostname:n
1135where hostname indicates
Damien Miller7684ee12000-03-17 23:40:15 +11001136the host where the shell runs, and n is an integer >= 1.
1137.Nm
1138uses this special value to forward X11 connections over the secure
1139channel.
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001140The user should normally not set
1141.Ev DISPLAY
1142explicitly, as that
Damien Miller32aa1441999-10-29 09:15:49 +10001143will render the X11 connection insecure (and will require the user to
1144manually copy any required authorization cookies).
1145.It Ev HOME
1146Set to the path of the user's home directory.
1147.It Ev LOGNAME
1148Synonym for
1149.Ev USER ;
1150set for compatibility with systems that use this variable.
1151.It Ev MAIL
1152Set to point the user's mailbox.
Damien Miller7684ee12000-03-17 23:40:15 +11001153.It Ev PATH
Damien Miller32aa1441999-10-29 09:15:49 +10001154Set to the default
1155.Ev PATH ,
1156as specified when compiling
1157.Nm ssh .
1158.It Ev SSH_AUTH_SOCK
1159indicates the path of a unix-domain socket used to communicate with the
1160agent.
1161.It Ev SSH_CLIENT
Damien Miller7684ee12000-03-17 23:40:15 +11001162Identifies the client end of the connection.
1163The variable contains
Damien Miller32aa1441999-10-29 09:15:49 +10001164three space-separated values: client ip-address, client port number,
1165and server port number.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001166.It Ev SSH_ORIGINAL_COMMAND
1167The variable contains the original command line if a forced command
1168is executed.
1169It can be used to extract the original arguments.
Damien Miller32aa1441999-10-29 09:15:49 +10001170.It Ev SSH_TTY
1171This is set to the name of the tty (path to the device) associated
Damien Miller7684ee12000-03-17 23:40:15 +11001172with the current shell or command.
1173If the current session has no tty,
Damien Miller32aa1441999-10-29 09:15:49 +10001174this variable is not set.
1175.It Ev TZ
1176The timezone variable is set to indicate the present timezone if it
Damien Miller942da032000-08-18 13:59:06 +10001177was set when the daemon was started (i.e., the daemon passes the value
Damien Miller32aa1441999-10-29 09:15:49 +10001178on to new connections).
1179.It Ev USER
1180Set to the name of the user logging in.
1181.El
1182.Pp
Damien Miller22c77262000-04-13 12:26:34 +10001183Additionally,
Damien Miller32aa1441999-10-29 09:15:49 +10001184.Nm
Damien Miller22c77262000-04-13 12:26:34 +10001185reads
1186.Pa $HOME/.ssh/environment ,
Damien Miller32aa1441999-10-29 09:15:49 +10001187and adds lines of the format
1188.Dq VARNAME=value
1189to the environment.
1190.Sh FILES
Damien Miller98c7ad62000-03-09 21:27:49 +11001191.Bl -tag -width Ds
Ben Lindstrom1e621742001-03-06 01:10:53 +00001192.It Pa $HOME/.ssh/known_hosts, $HOME/.ssh/known_hosts2
Damien Miller32aa1441999-10-29 09:15:49 +10001193Records host keys for all hosts the user has logged into (that are not
1194in
Ben Lindstrom1e621742001-03-06 01:10:53 +00001195.Pa /etc/ssh_known_hosts
1196for protocol version 1 or
1197.Pa /etc/ssh_known_hosts2
1198for protocol version 2).
Damien Miller32aa1441999-10-29 09:15:49 +10001199See
1200.Xr sshd 8 .
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001201.It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
1202Contains the authentication identity of the user.
1203They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
Damien Millere247cc42000-05-07 12:03:14 +10001204These files
1205contain sensitive data and should be readable by the user but not
Damien Miller32aa1441999-10-29 09:15:49 +10001206accessible by others (read/write/execute).
1207Note that
1208.Nm
Damien Millere247cc42000-05-07 12:03:14 +10001209ignores a private key file if it is accessible by others.
Damien Miller32aa1441999-10-29 09:15:49 +10001210It is possible to specify a passphrase when
1211generating the key; the passphrase will be used to encrypt the
1212sensitive part of this file using 3DES.
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001213.It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub
Damien Miller32aa1441999-10-29 09:15:49 +10001214Contains the public key for authentication (public part of the
Damien Miller7684ee12000-03-17 23:40:15 +11001215identity file in human-readable form).
Damien Millere247cc42000-05-07 12:03:14 +10001216The contents of the
1217.Pa $HOME/.ssh/identity.pub
1218file should be added to
Damien Miller32aa1441999-10-29 09:15:49 +10001219.Pa $HOME/.ssh/authorized_keys
1220on all machines
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001221where you wish to log in using protocol version 1 RSA authentication.
Damien Millere247cc42000-05-07 12:03:14 +10001222The contents of the
1223.Pa $HOME/.ssh/id_dsa.pub
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001224and
1225.Pa $HOME/.ssh/id_rsa.pub
Damien Millere247cc42000-05-07 12:03:14 +10001226file should be added to
1227.Pa $HOME/.ssh/authorized_keys2
1228on all machines
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001229where you wish to log in using protocol version 2 DSA/RSA authentication.
Damien Millere247cc42000-05-07 12:03:14 +10001230These files are not
Damien Miller7684ee12000-03-17 23:40:15 +11001231sensitive and can (but need not) be readable by anyone.
Damien Millere247cc42000-05-07 12:03:14 +10001232These files are
Kevin Steves3c034ae2001-02-05 13:47:11 +00001233never used automatically and are not necessary; they are only provided for
Damien Miller32aa1441999-10-29 09:15:49 +10001234the convenience of the user.
1235.It Pa $HOME/.ssh/config
Damien Miller7684ee12000-03-17 23:40:15 +11001236This is the per-user configuration file.
1237The format of this file is described above.
1238This file is used by the
Damien Miller32aa1441999-10-29 09:15:49 +10001239.Nm
Damien Miller7684ee12000-03-17 23:40:15 +11001240client.
1241This file does not usually contain any sensitive information,
Damien Miller32aa1441999-10-29 09:15:49 +10001242but the recommended permissions are read/write for the user, and not
1243accessible by others.
1244.It Pa $HOME/.ssh/authorized_keys
Damien Miller7684ee12000-03-17 23:40:15 +11001245Lists the RSA keys that can be used for logging in as this user.
1246The format of this file is described in the
Damien Miller32aa1441999-10-29 09:15:49 +10001247.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001248manual page.
1249In the simplest form the format is the same as the .pub
Damien Miller32aa1441999-10-29 09:15:49 +10001250identity files (that is, each line contains the number of bits in
1251modulus, public exponent, modulus, and comment fields, separated by
Damien Miller7684ee12000-03-17 23:40:15 +11001252spaces).
1253This file is not highly sensitive, but the recommended
Damien Miller32aa1441999-10-29 09:15:49 +10001254permissions are read/write for the user, and not accessible by others.
Damien Millere247cc42000-05-07 12:03:14 +10001255.It Pa $HOME/.ssh/authorized_keys2
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001256Lists the public keys (RSA/DSA) that can be used for logging in as this user.
Damien Millere247cc42000-05-07 12:03:14 +10001257This file is not highly sensitive, but the recommended
1258permissions are read/write for the user, and not accessible by others.
1259.It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2
Damien Miller7684ee12000-03-17 23:40:15 +11001260Systemwide list of known host keys.
Damien Millere247cc42000-05-07 12:03:14 +10001261.Pa /etc/ssh_known_hosts
1262contains RSA and
1263.Pa /etc/ssh_known_hosts2
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001264contains RSA or DSA keys for protocol version 2.
Damien Millere247cc42000-05-07 12:03:14 +10001265These files should be prepared by the
Damien Miller32aa1441999-10-29 09:15:49 +10001266system administrator to contain the public host keys of all machines in the
Damien Miller7684ee12000-03-17 23:40:15 +11001267organization.
1268This file should be world-readable.
1269This file contains
Damien Miller32aa1441999-10-29 09:15:49 +10001270public keys, one per line, in the following format (fields separated
1271by spaces): system name, number of bits in modulus, public exponent,
Damien Miller7684ee12000-03-17 23:40:15 +11001272modulus, and optional comment field.
1273When different names are used
Damien Miller32aa1441999-10-29 09:15:49 +10001274for the same machine, all such names should be listed, separated by
Damien Miller7684ee12000-03-17 23:40:15 +11001275commas.
1276The format is described on the
Damien Miller32aa1441999-10-29 09:15:49 +10001277.Xr sshd 8
1278manual page.
1279.Pp
1280The canonical system name (as returned by name servers) is used by
1281.Xr sshd 8
1282to verify the client host when logging in; other names are needed because
1283.Nm
1284does not convert the user-supplied name to a canonical name before
1285checking the key, because someone with access to the name servers
1286would then be able to fool host authentication.
Damien Miller886c63a2000-01-20 23:13:36 +11001287.It Pa /etc/ssh_config
Damien Miller7684ee12000-03-17 23:40:15 +11001288Systemwide configuration file.
1289This file provides defaults for those
Damien Miller32aa1441999-10-29 09:15:49 +10001290values that are not specified in the user's configuration file, and
Damien Miller7684ee12000-03-17 23:40:15 +11001291for those users who do not have a configuration file.
1292This file must be world-readable.
Damien Miller32aa1441999-10-29 09:15:49 +10001293.It Pa $HOME/.rhosts
1294This file is used in
1295.Pa \&.rhosts
1296authentication to list the
Damien Miller7684ee12000-03-17 23:40:15 +11001297host/user pairs that are permitted to log in.
1298(Note that this file is
Damien Miller32aa1441999-10-29 09:15:49 +10001299also used by rlogin and rsh, which makes using this file insecure.)
1300Each line of the file contains a host name (in the canonical form
1301returned by name servers), and then a user name on that host,
Damien Miller7684ee12000-03-17 23:40:15 +11001302separated by a space.
Ben Lindstromebd888d2001-03-05 05:49:29 +00001303On some machines this file may need to be
Damien Miller32aa1441999-10-29 09:15:49 +10001304world-readable if the user's home directory is on a NFS partition,
1305because
1306.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001307reads it as root.
1308Additionally, this file must be owned by the user,
1309and must not have write permissions for anyone else.
1310The recommended
Damien Miller32aa1441999-10-29 09:15:49 +10001311permission for most machines is read/write for the user, and not
1312accessible by others.
1313.Pp
1314Note that by default
1315.Xr sshd 8
1316will be installed so that it requires successful RSA host
Damien Miller7684ee12000-03-17 23:40:15 +11001317authentication before permitting \s+2.\s0rhosts authentication.
1318If your server machine does not have the client's host key in
Damien Miller886c63a2000-01-20 23:13:36 +11001319.Pa /etc/ssh_known_hosts ,
Damien Miller32aa1441999-10-29 09:15:49 +10001320you can store it in
1321.Pa $HOME/.ssh/known_hosts .
1322The easiest way to do this is to
1323connect back to the client from the server machine using ssh; this
Damien Millere247cc42000-05-07 12:03:14 +10001324will automatically add the host key to
Damien Miller32aa1441999-10-29 09:15:49 +10001325.Pa $HOME/.ssh/known_hosts .
1326.It Pa $HOME/.shosts
1327This file is used exactly the same way as
1328.Pa \&.rhosts .
1329The purpose for
1330having this file is to be able to use rhosts authentication with
1331.Nm
1332without permitting login with
1333.Xr rlogin 1
1334or
1335.Xr rsh 1 .
1336.It Pa /etc/hosts.equiv
1337This file is used during
Damien Miller7684ee12000-03-17 23:40:15 +11001338.Pa \&.rhosts authentication.
1339It contains
Damien Miller32aa1441999-10-29 09:15:49 +10001340canonical hosts names, one per line (the full format is described on
1341the
1342.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001343manual page).
1344If the client host is found in this file, login is
Damien Miller32aa1441999-10-29 09:15:49 +10001345automatically permitted provided client and server user names are the
Damien Miller7684ee12000-03-17 23:40:15 +11001346same.
1347Additionally, successful RSA host authentication is normally
1348required.
1349This file should only be writable by root.
Damien Miller886c63a2000-01-20 23:13:36 +11001350.It Pa /etc/shosts.equiv
Damien Miller22c77262000-04-13 12:26:34 +10001351This file is processed exactly as
Damien Miller32aa1441999-10-29 09:15:49 +10001352.Pa /etc/hosts.equiv .
1353This file may be useful to permit logins using
1354.Nm
1355but not using rsh/rlogin.
Damien Miller886c63a2000-01-20 23:13:36 +11001356.It Pa /etc/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +10001357Commands in this file are executed by
1358.Nm
1359when the user logs in just before the user's shell (or command) is started.
1360See the
1361.Xr sshd 8
1362manual page for more information.
1363.It Pa $HOME/.ssh/rc
1364Commands in this file are executed by
1365.Nm
1366when the user logs in just before the user's shell (or command) is
1367started.
Damien Miller22c77262000-04-13 12:26:34 +10001368See the
Damien Miller32aa1441999-10-29 09:15:49 +10001369.Xr sshd 8
1370manual page for more information.
Damien Miller4f0fa561999-12-26 14:24:41 +11001371.It Pa $HOME/.ssh/environment
1372Contains additional definitions for environment variables, see section
1373.Sx ENVIRONMENT
1374above.
Damien Miller7b28dc52000-09-05 13:34:53 +11001375.El
Damien Miller0bc1bd82000-11-13 22:57:25 +11001376.Sh AUTHORS
Ben Lindstrom035782e2001-01-29 08:34:16 +00001377OpenSSH is a derivative of the original and free
1378ssh 1.2.12 release by Tatu Ylonen.
1379Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1380Theo de Raadt and Dug Song
1381removed many bugs, re-added newer features and
1382created OpenSSH.
1383Markus Friedl contributed the support for SSH
1384protocol versions 1.5 and 2.0.
Damien Miller32aa1441999-10-29 09:15:49 +10001385.Sh SEE ALSO
1386.Xr rlogin 1 ,
1387.Xr rsh 1 ,
1388.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +11001389.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +10001390.Xr ssh-add 1 ,
1391.Xr ssh-agent 1 ,
1392.Xr ssh-keygen 1 ,
1393.Xr telnet 1 ,
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +00001394.Xr sshd 8
Ben Lindstrom160ec622001-04-22 17:17:46 +00001395.Rs
1396.%A T. Ylonen
1397.%A T. Kivinen
1398.%A M. Saarinen
1399.%A T. Rinne
1400.%A S. Lehtinen
1401.%T "SSH Protocol Architecture"
1402.%N draft-ietf-secsh-architecture-07.txt
1403.%D January 2001
1404.%O work in progress material
1405.Re