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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 Lindstromf0609f82001-05-04 22:38:43 +000037.\" $OpenBSD: ssh.1,v 1.109 2001/05/04 14:21:55 stevesk 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
Damien Miller32aa1441999-10-29 09:15:49 +1000307If the user is using X11 (the
308.Ev DISPLAY
309environment variable is set), the connection to the X11 display is
310automatically forwarded to the remote side in such a way that any X11
311programs started from the shell (or command) will go through the
312encrypted channel, and the connection to the real X server will be made
Damien Miller7684ee12000-03-17 23:40:15 +1100313from the local machine.
314The user should not manually set
Damien Miller32aa1441999-10-29 09:15:49 +1000315.Ev DISPLAY .
316Forwarding of X11 connections can be
317configured on the command line or in configuration files.
318.Pp
319The
Damien Miller22c77262000-04-13 12:26:34 +1000320.Ev DISPLAY
Damien Miller32aa1441999-10-29 09:15:49 +1000321value set by
322.Nm
323will point to the server machine, but with a display number greater
Damien Miller7684ee12000-03-17 23:40:15 +1100324than zero.
325This is normal, and happens because
Damien Miller32aa1441999-10-29 09:15:49 +1000326.Nm
327creates a
328.Dq proxy
329X server on the server machine for forwarding the
330connections over the encrypted channel.
331.Pp
332.Nm
333will also automatically set up Xauthority data on the server machine.
334For this purpose, it will generate a random authorization cookie,
335store it in Xauthority on the server, and verify that any forwarded
336connections carry this cookie and replace it by the real cookie when
Damien Miller7684ee12000-03-17 23:40:15 +1100337the connection is opened.
338The real authentication cookie is never
Damien Miller32aa1441999-10-29 09:15:49 +1000339sent to the server machine (and no cookies are sent in the plain).
340.Pp
341If the user is using an authentication agent, the connection to the agent
342is automatically forwarded to the remote side unless disabled on
343command line or in a configuration file.
344.Pp
345Forwarding of arbitrary TCP/IP connections over the secure channel can
Damien Miller7684ee12000-03-17 23:40:15 +1100346be specified either on command line or in a configuration file.
347One possible application of TCP/IP forwarding is a secure connection to an
Ben Lindstromebd888d2001-03-05 05:49:29 +0000348electronic purse; another is going through firewalls.
Damien Miller32aa1441999-10-29 09:15:49 +1000349.Pp
Damien Millere247cc42000-05-07 12:03:14 +1000350.Ss Server authentication
351.Pp
Damien Miller32aa1441999-10-29 09:15:49 +1000352.Nm
Damien Millere247cc42000-05-07 12:03:14 +1000353automatically maintains and checks a database containing
Damien Miller7684ee12000-03-17 23:40:15 +1100354identifications for all hosts it has ever been used with.
Damien Millere247cc42000-05-07 12:03:14 +1000355RSA host keys are stored in
356.Pa $HOME/.ssh/known_hosts
357and
Damien Miller0bc1bd82000-11-13 22:57:25 +1100358host keys used in the protocol version 2 are stored in
Damien Millere247cc42000-05-07 12:03:14 +1000359.Pa $HOME/.ssh/known_hosts2
Damien Miller7684ee12000-03-17 23:40:15 +1100360in the user's home directory.
Damien Millere247cc42000-05-07 12:03:14 +1000361Additionally, the files
Damien Miller886c63a2000-01-20 23:13:36 +1100362.Pa /etc/ssh_known_hosts
Damien Millere247cc42000-05-07 12:03:14 +1000363and
364.Pa /etc/ssh_known_hosts2
365are automatically checked for known hosts.
Damien Miller7684ee12000-03-17 23:40:15 +1100366Any new hosts are automatically added to the user's file.
367If a host's identification
Damien Miller32aa1441999-10-29 09:15:49 +1000368ever changes,
369.Nm
370warns about this and disables password authentication to prevent a
Damien Miller7684ee12000-03-17 23:40:15 +1100371trojan horse from getting the user's password.
372Another purpose of
Damien Miller32aa1441999-10-29 09:15:49 +1000373this mechanism is to prevent man-in-the-middle attacks which could
Damien Miller7684ee12000-03-17 23:40:15 +1100374otherwise be used to circumvent the encryption.
375The
Damien Miller32aa1441999-10-29 09:15:49 +1000376.Cm StrictHostKeyChecking
377option (see below) can be used to prevent logins to machines whose
378host key is not known or has changed.
Damien Miller0bc1bd82000-11-13 22:57:25 +1100379.Pp
380The options are as follows:
Damien Miller32aa1441999-10-29 09:15:49 +1000381.Bl -tag -width Ds
382.It Fl a
Damien Miller450a7a12000-03-26 13:04:51 +1000383Disables forwarding of the authentication agent connection.
Damien Millerb1715dc2000-05-30 13:44:51 +1000384.It Fl A
385Enables forwarding of the authentication agent connection.
386This can also be specified on a per-host basis in a configuration file.
Ben Lindstrome0f88042001-04-30 13:06:24 +0000387.It Fl b Ar bind_address
388Specify the interface to transmit from on machines with multiple
389interfaces or aliased addresses.
Damien Miller32aa1441999-10-29 09:15:49 +1000390.It Fl c Ar blowfish|3des
Damien Miller22c77262000-04-13 12:26:34 +1000391Selects the cipher to use for encrypting the session.
Damien Miller32aa1441999-10-29 09:15:49 +1000392.Ar 3des
Damien Miller7684ee12000-03-17 23:40:15 +1100393is used by default.
Damien Miller22c77262000-04-13 12:26:34 +1000394It is believed to be secure.
Damien Miller32aa1441999-10-29 09:15:49 +1000395.Ar 3des
396(triple-des) is an encrypt-decrypt-encrypt triple with three different keys.
397It is presumably more secure than the
398.Ar des
Damien Miller69b69aa2000-10-28 14:19:58 +1100399cipher which is no longer fully supported in
Damien Miller30c3d422000-05-09 11:02:59 +1000400.Nm ssh .
Damien Miller32aa1441999-10-29 09:15:49 +1000401.Ar blowfish
402is a fast block cipher, it appears very secure and is much faster than
Damien Miller7684ee12000-03-17 23:40:15 +1100403.Ar 3des .
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000404.It Fl c Ar cipher_spec
Damien Miller30c3d422000-05-09 11:02:59 +1000405Additionally, for protocol version 2 a comma-separated list of ciphers can
Damien Miller874d77b2000-10-14 16:23:11 +1100406be specified in order of preference.
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000407See
408.Cm Ciphers
409for more information.
Damien Miller32aa1441999-10-29 09:15:49 +1000410.It Fl e Ar ch|^ch|none
411Sets the escape character for sessions with a pty (default:
412.Ql ~ ) .
Damien Miller7684ee12000-03-17 23:40:15 +1100413The escape character is only recognized at the beginning of a line.
414The escape character followed by a dot
Damien Miller32aa1441999-10-29 09:15:49 +1000415.Pq Ql \&.
416closes the connection, followed
417by control-Z suspends the connection, and followed by itself sends the
Damien Miller7684ee12000-03-17 23:40:15 +1100418escape character once.
419Setting the character to
Damien Miller32aa1441999-10-29 09:15:49 +1000420.Dq none
421disables any escapes and makes the session fully transparent.
422.It Fl f
423Requests
424.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100425to go to background just before command execution.
426This is useful if
Damien Miller32aa1441999-10-29 09:15:49 +1000427.Nm
428is going to ask for passwords or passphrases, but the user
Damien Miller7684ee12000-03-17 23:40:15 +1100429wants it in the background.
Damien Miller22c77262000-04-13 12:26:34 +1000430This implies
Damien Miller32aa1441999-10-29 09:15:49 +1000431.Fl n .
432The recommended way to start X11 programs at a remote site is with
433something like
434.Ic ssh -f host xterm .
Damien Miller396691a2000-01-20 22:44:08 +1100435.It Fl g
436Allows remote hosts to connect to local forwarded ports.
Damien Miller32aa1441999-10-29 09:15:49 +1000437.It Fl i Ar identity_file
Damien Miller22c77262000-04-13 12:26:34 +1000438Selects the file from which the identity (private key) for
Damien Miller0bc1bd82000-11-13 22:57:25 +1100439RSA or DSA authentication is read.
Damien Miller22c77262000-04-13 12:26:34 +1000440Default is
Damien Millere247cc42000-05-07 12:03:14 +1000441.Pa $HOME/.ssh/identity
Damien Miller7684ee12000-03-17 23:40:15 +1100442in the user's home directory.
443Identity files may also be specified on
444a per-host basis in the configuration file.
445It is possible to have multiple
Damien Miller32aa1441999-10-29 09:15:49 +1000446.Fl i
447options (and multiple identities specified in
448configuration files).
Damien Miller32aa1441999-10-29 09:15:49 +1000449.It Fl k
Damien Miller450a7a12000-03-26 13:04:51 +1000450Disables forwarding of Kerberos tickets and AFS tokens.
451This may also be specified on a per-host basis in the configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000452.It Fl l Ar login_name
Damien Miller7684ee12000-03-17 23:40:15 +1100453Specifies the user to log in as on the remote machine.
454This also may be specified on a per-host basis in the configuration file.
Ben Lindstrom06b33aa2001-02-15 03:01:59 +0000455.It Fl m Ar mac_spec
456Additionally, for protocol version 2 a comma-separated list of MAC
457(message authentication code) algorithms can
458be specified in order of preference.
459See the
460.Cm MACs
461keyword for more information.
Damien Miller32aa1441999-10-29 09:15:49 +1000462.It Fl n
463Redirects stdin from
464.Pa /dev/null
465(actually, prevents reading from stdin).
466This must be used when
467.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100468is run in the background.
469A common trick is to use this to run X11 programs on a remote machine.
470For example,
Damien Miller32aa1441999-10-29 09:15:49 +1000471.Ic ssh -n shadows.cs.hut.fi emacs &
472will start an emacs on shadows.cs.hut.fi, and the X11
473connection will be automatically forwarded over an encrypted channel.
474The
475.Nm
476program will be put in the background.
477(This does not work if
478.Nm
479needs to ask for a password or passphrase; see also the
480.Fl f
481option.)
Damien Millerdcb6ecd2000-05-17 22:34:22 +1000482.It Fl N
483Do not execute a remote command.
Ben Lindstromc72745a2000-12-02 19:03:54 +0000484This is useful if you just want to forward ports
Damien Millerdcb6ecd2000-05-17 22:34:22 +1000485(protocol version 2 only).
Damien Miller32aa1441999-10-29 09:15:49 +1000486.It Fl o Ar option
487Can be used to give options in the format used in the config file.
488This is useful for specifying options for which there is no separate
Damien Miller7684ee12000-03-17 23:40:15 +1100489command-line flag.
490The option has the same format as a line in the configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000491.It Fl p Ar port
Damien Miller7684ee12000-03-17 23:40:15 +1100492Port to connect to on the remote host.
493This can be specified on a
Damien Miller32aa1441999-10-29 09:15:49 +1000494per-host basis in the configuration file.
495.It Fl P
496Use a non-privileged port for outgoing connections.
497This can be used if your firewall does
498not permit connections from privileged ports.
Damien Millera34a28b1999-12-14 10:47:15 +1100499Note that this option turns off
Damien Miller32aa1441999-10-29 09:15:49 +1000500.Cm RhostsAuthentication
501and
Kevin Stevesfcec7f82000-12-15 19:55:48 +0000502.Cm RhostsRSAAuthentication
503for older servers.
Damien Miller32aa1441999-10-29 09:15:49 +1000504.It Fl q
Damien Miller7684ee12000-03-17 23:40:15 +1100505Quiet mode.
506Causes all warning and diagnostic messages to be suppressed.
507Only fatal errors are displayed.
Damien Miller832562e2001-01-30 09:30:01 +1100508.It Fl s
509May 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 +0000510of SSH as a secure transport for other applications (eg. sftp). The
Damien Miller832562e2001-01-30 09:30:01 +1100511subsystem is specified as the remote command.
Damien Miller32aa1441999-10-29 09:15:49 +1000512.It Fl t
Damien Miller7684ee12000-03-17 23:40:15 +1100513Force pseudo-tty allocation.
Damien Miller450a7a12000-03-26 13:04:51 +1000514This can be used to execute arbitrary
Damien Miller7684ee12000-03-17 23:40:15 +1100515screen-based programs on a remote machine, which can be very useful,
516e.g., when implementing menu services.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000517Multiple
518.Fl t
519options force tty allocation, even if
520.Nm
521has no local tty.
Damien Millerdcb6ecd2000-05-17 22:34:22 +1000522.It Fl T
Ben Lindstromc72745a2000-12-02 19:03:54 +0000523Disable pseudo-tty allocation.
Damien Miller32aa1441999-10-29 09:15:49 +1000524.It Fl v
Damien Miller7684ee12000-03-17 23:40:15 +1100525Verbose mode.
526Causes
Damien Miller32aa1441999-10-29 09:15:49 +1000527.Nm
Damien Miller7684ee12000-03-17 23:40:15 +1100528to print debugging messages about its progress.
529This is helpful in
Damien Miller32aa1441999-10-29 09:15:49 +1000530debugging connection, authentication, and configuration problems.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000531Multiple
532.Fl v
533options increases the verbosity.
Damien Miller874d77b2000-10-14 16:23:11 +1100534Maximum is 3.
Damien Miller32aa1441999-10-29 09:15:49 +1000535.It Fl x
Damien Miller7684ee12000-03-17 23:40:15 +1100536Disables X11 forwarding.
Damien Miller32aa1441999-10-29 09:15:49 +1000537.It Fl X
538Enables X11 forwarding.
Damien Millerb1715dc2000-05-30 13:44:51 +1000539This can also be specified on a per-host basis in a configuration file.
Damien Miller32aa1441999-10-29 09:15:49 +1000540.It Fl C
541Requests compression of all data (including stdin, stdout, stderr, and
Damien Miller7684ee12000-03-17 23:40:15 +1100542data for forwarded X11 and TCP/IP connections).
543The compression algorithm is the same used by
Damien Miller396691a2000-01-20 22:44:08 +1100544.Xr gzip 1 ,
545and the
Damien Miller32aa1441999-10-29 09:15:49 +1000546.Dq level
547can be controlled by the
548.Cm CompressionLevel
Damien Miller7684ee12000-03-17 23:40:15 +1100549option (see below).
550Compression is desirable on modem lines and other
Damien Miller32aa1441999-10-29 09:15:49 +1000551slow connections, but will only slow down things on fast networks.
552The default value can be set on a host-by-host basis in the
553configuration files; see the
554.Cm Compress
555option below.
556.It Fl L Ar port:host:hostport
557Specifies that the given port on the local (client) host is to be
Damien Miller7684ee12000-03-17 23:40:15 +1100558forwarded to the given host and port on the remote side.
559This works by allocating a socket to listen to
Damien Miller32aa1441999-10-29 09:15:49 +1000560.Ar port
561on the local side, and whenever a connection is made to this port, the
562connection is forwarded over the secure channel, and a connection is
563made to
Damien Miller34132e52000-01-14 15:45:46 +1100564.Ar host
565port
566.Ar hostport
Damien Miller7684ee12000-03-17 23:40:15 +1100567from the remote machine.
568Port forwardings can also be specified in the configuration file.
569Only root can forward privileged ports.
Damien Miller34132e52000-01-14 15:45:46 +1100570IPv6 addresses can be specified with an alternative syntax:
571.Ar port/host/hostport
Damien Miller32aa1441999-10-29 09:15:49 +1000572.It Fl R Ar port:host:hostport
573Specifies that the given port on the remote (server) host is to be
Damien Miller7684ee12000-03-17 23:40:15 +1100574forwarded to the given host and port on the local side.
575This works by allocating a socket to listen to
Damien Miller32aa1441999-10-29 09:15:49 +1000576.Ar port
577on the remote side, and whenever a connection is made to this port, the
578connection is forwarded over the secure channel, and a connection is
579made to
Damien Miller34132e52000-01-14 15:45:46 +1100580.Ar host
581port
582.Ar hostport
Damien Miller7684ee12000-03-17 23:40:15 +1100583from the local machine.
584Port forwardings can also be specified in the configuration file.
585Privileged ports can be forwarded only when
Damien Miller32aa1441999-10-29 09:15:49 +1000586logging in as root on the remote machine.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000587IPv6 addresses can be specified with an alternative syntax:
588.Ar port/host/hostport
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000589.It Fl 1
590Forces
591.Nm
592to try protocol version 1 only.
Damien Miller4af51302000-04-16 11:18:38 +1000593.It Fl 2
594Forces
595.Nm
Damien Millere247cc42000-05-07 12:03:14 +1000596to try protocol version 2 only.
Damien Miller34132e52000-01-14 15:45:46 +1100597.It Fl 4
598Forces
599.Nm
600to use IPv4 addresses only.
601.It Fl 6
602Forces
603.Nm
604to use IPv6 addresses only.
Damien Miller32aa1441999-10-29 09:15:49 +1000605.El
606.Sh CONFIGURATION FILES
607.Nm
608obtains configuration data from the following sources (in this order):
609command line options, user's configuration file
610.Pq Pa $HOME/.ssh/config ,
611and system-wide configuration file
Damien Miller886c63a2000-01-20 23:13:36 +1100612.Pq Pa /etc/ssh_config .
Damien Miller32aa1441999-10-29 09:15:49 +1000613For each parameter, the first obtained value
Damien Miller7684ee12000-03-17 23:40:15 +1100614will be used.
615The configuration files contain sections bracketed by
616.Dq Host
617specifications, and that section is only applied for hosts that
618match one of the patterns given in the specification.
619The matched host name is the one given on the command line.
Damien Miller32aa1441999-10-29 09:15:49 +1000620.Pp
621Since the first obtained value for each parameter is used, more
622host-specific declarations should be given near the beginning of the
623file, and general defaults at the end.
624.Pp
625The configuration file has the following format:
626.Pp
627Empty lines and lines starting with
628.Ql #
629are comments.
630.Pp
631Otherwise a line is of the format
632.Dq keyword arguments .
633The possible
634keywords and their meanings are as follows (note that the
635configuration files are case-sensitive):
636.Bl -tag -width Ds
637.It Cm Host
638Restricts the following declarations (up to the next
639.Cm Host
640keyword) to be only for those hosts that match one of the patterns
641given after the keyword.
642.Ql \&*
643and
644.Ql ?
645can be used as wildcards in the
Damien Miller7684ee12000-03-17 23:40:15 +1100646patterns.
647A single
Damien Miller32aa1441999-10-29 09:15:49 +1000648.Ql \&*
649as a pattern can be used to provide global
Damien Miller7684ee12000-03-17 23:40:15 +1100650defaults for all hosts.
651The host is the
Damien Miller32aa1441999-10-29 09:15:49 +1000652.Ar hostname
653argument given on the command line (i.e., the name is not converted to
654a canonicalized host name before matching).
655.It Cm AFSTokenPassing
Damien Miller450a7a12000-03-26 13:04:51 +1000656Specifies whether to pass AFS tokens to remote host.
657The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +1000658.Dq yes
659or
660.Dq no .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000661This option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000662.It Cm BatchMode
663If set to
664.Dq yes ,
Damien Miller7684ee12000-03-17 23:40:15 +1100665passphrase/password querying will be disabled.
666This option is useful in scripts and other batch jobs where you have no
667user to supply the password.
668The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000669.Dq yes
670or
671.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000672The default is
673.Dq no .
Ben Lindstrome0f88042001-04-30 13:06:24 +0000674.It Cm BindAddress
675Specify the interface to transmit from on machines with multiple
676interfaces or aliased addresses.
677Note that this option does not work if
678.Cm UsePrivilegedPort
679is set to
680.Dq yes .
Damien Miller396691a2000-01-20 22:44:08 +1100681.It Cm CheckHostIP
682If this flag is set to
683.Dq yes ,
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000684ssh will additionally check the host IP address in the
Damien Miller396691a2000-01-20 22:44:08 +1100685.Pa known_hosts
Damien Miller450a7a12000-03-26 13:04:51 +1000686file.
687This allows ssh to detect if a host key changed due to DNS spoofing.
Damien Miller396691a2000-01-20 22:44:08 +1100688If the option is set to
689.Dq no ,
690the check will not be executed.
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000691The default is
692.Dq yes .
Damien Miller32aa1441999-10-29 09:15:49 +1000693.It Cm Cipher
Damien Miller50a41ed2000-10-16 12:14:42 +1100694Specifies the cipher to use for encrypting the session
Damien Miller69b69aa2000-10-28 14:19:58 +1100695in protocol version 1.
Damien Miller7684ee12000-03-17 23:40:15 +1100696Currently,
Damien Miller69b69aa2000-10-28 14:19:58 +1100697.Dq blowfish
Damien Miller32aa1441999-10-29 09:15:49 +1000698and
699.Dq 3des
Damien Miller7684ee12000-03-17 23:40:15 +1100700are supported.
701The default is
Damien Miller32aa1441999-10-29 09:15:49 +1000702.Dq 3des .
Damien Miller22c77262000-04-13 12:26:34 +1000703.It Cm Ciphers
704Specifies the ciphers allowed for protocol version 2
705in order of preference.
706Multiple ciphers must be comma-separated.
707The default is
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000708.Pp
709.Bd -literal
Ben Lindstromec26fb12001-03-06 01:05:23 +0000710 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000711 aes192-cbc,aes256-cbc''
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +0000712.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000713.It Cm Compression
Damien Miller7684ee12000-03-17 23:40:15 +1100714Specifies whether to use compression.
715The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000716.Dq yes
717or
718.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000719The default is
720.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000721.It Cm CompressionLevel
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000722Specifies the compression level to use if compression is enabled.
Damien Miller7684ee12000-03-17 23:40:15 +1100723The argument must be an integer from 1 (fast) to 9 (slow, best).
724The default level is 6, which is good for most applications.
725The meaning of the values is the same as in
Damien Miller396691a2000-01-20 22:44:08 +1100726.Xr gzip 1 .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000727Note that this option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000728.It Cm ConnectionAttempts
729Specifies the number of tries (one per second) to make before falling
Damien Miller7684ee12000-03-17 23:40:15 +1100730back to rsh or exiting.
731The argument must be an integer.
732This may be useful in scripts if the connection sometimes fails.
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000733The default is 4.
Damien Miller32aa1441999-10-29 09:15:49 +1000734.It Cm EscapeChar
735Sets the escape character (default:
736.Ql ~ ) .
737The escape character can also
Damien Miller7684ee12000-03-17 23:40:15 +1100738be set on the command line.
739The argument should be a single character,
Damien Miller32aa1441999-10-29 09:15:49 +1000740.Ql ^
741followed by a letter, or
742.Dq none
743to disable the escape
744character entirely (making the connection transparent for binary
745data).
Damien Miller22c77262000-04-13 12:26:34 +1000746.It Cm FallBackToRsh
Damien Miller32aa1441999-10-29 09:15:49 +1000747Specifies that if connecting via
748.Nm
749fails due to a connection refused error (there is no
750.Xr sshd 8
Damien Miller22c77262000-04-13 12:26:34 +1000751listening on the remote host),
Damien Miller32aa1441999-10-29 09:15:49 +1000752.Xr rsh 1
753should automatically be used instead (after a suitable warning about
Damien Miller7684ee12000-03-17 23:40:15 +1100754the session being unencrypted).
755The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000756.Dq yes
757or
758.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000759The default is
760.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000761.It Cm ForwardAgent
762Specifies whether the connection to the authentication agent (if any)
Damien Miller7684ee12000-03-17 23:40:15 +1100763will be forwarded to the remote machine.
764The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000765.Dq yes
766or
767.Dq no .
Damien Millerb1715dc2000-05-30 13:44:51 +1000768The default is
769.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000770.It Cm ForwardX11
771Specifies whether X11 connections will be automatically redirected
Damien Miller22c77262000-04-13 12:26:34 +1000772over the secure channel and
Damien Miller32aa1441999-10-29 09:15:49 +1000773.Ev DISPLAY
Damien Miller7684ee12000-03-17 23:40:15 +1100774set.
Damien Miller22c77262000-04-13 12:26:34 +1000775The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000776.Dq yes
777or
778.Dq no .
Damien Miller98c7ad62000-03-09 21:27:49 +1100779The default is
780.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000781.It Cm GatewayPorts
782Specifies whether remote hosts are allowed to connect to local
783forwarded ports.
784The argument must be
785.Dq yes
786or
787.Dq no .
788The default is
789.Dq no .
790.It Cm GlobalKnownHostsFile
Ben Lindstrom1e621742001-03-06 01:10:53 +0000791Specifies a file to use for the protocol version 1 global
792host key database instead of
Damien Miller886c63a2000-01-20 23:13:36 +1100793.Pa /etc/ssh_known_hosts .
Ben Lindstrom1e621742001-03-06 01:10:53 +0000794.It Cm GlobalKnownHostsFile2
795Specifies a file to use for the protocol version 2 global
796host key database instead of
797.Pa /etc/ssh_known_hosts2 .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000798.It Cm HostbasedAuthentication
799Specifies whether to try rhosts based authentication with public key
800authentication.
801The argument must be
802.Dq yes
803or
804.Dq no .
805The default is
806.Dq yes .
807This option applies to protocol version 2 only and
808is similar to
809.Cm RhostsRSAAuthentication .
Ben Lindstrom982dbbc2001-04-17 18:11:36 +0000810.It Cm HostKeyAlgorithms
Ben Lindstromf0609f82001-05-04 22:38:43 +0000811Specifies the protocol version 2 host key algorithms
Ben Lindstrom982dbbc2001-04-17 18:11:36 +0000812that the client wants to use in order of preference.
813The default for this option is:
814.Dq ssh-rsa,ssh-dss
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000815.It Cm HostKeyAlias
816Specifies an alias that should be used instead of the
817real host name when looking up or saving the host key
818in the host key database files.
819This option is useful for tunneling ssh connections
820or if you have multiple servers running on a single host.
Damien Miller32aa1441999-10-29 09:15:49 +1000821.It Cm HostName
Damien Miller7684ee12000-03-17 23:40:15 +1100822Specifies the real host name to log into.
823This can be used to specify nicknames or abbreviations for hosts.
824Default is the name given on the command line.
825Numeric IP addresses are also permitted (both on the command line and in
Damien Miller32aa1441999-10-29 09:15:49 +1000826.Cm HostName
827specifications).
828.It Cm IdentityFile
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000829Specifies the file from which the user's RSA or DSA authentication identity
Damien Miller32aa1441999-10-29 09:15:49 +1000830is read (default
Damien Millere247cc42000-05-07 12:03:14 +1000831.Pa $HOME/.ssh/identity
Damien Miller32aa1441999-10-29 09:15:49 +1000832in the user's home directory).
833Additionally, any identities represented by the authentication agent
Damien Miller7684ee12000-03-17 23:40:15 +1100834will be used for authentication.
835The file name may use the tilde
836syntax to refer to a user's home directory.
837It is possible to have
Damien Miller32aa1441999-10-29 09:15:49 +1000838multiple identity files specified in configuration files; all these
839identities will be tried in sequence.
840.It Cm KeepAlive
841Specifies whether the system should send keepalive messages to the
Damien Miller7684ee12000-03-17 23:40:15 +1100842other side.
843If they are sent, death of the connection or crash of one
844of the machines will be properly noticed.
845However, this means that
Damien Miller32aa1441999-10-29 09:15:49 +1000846connections will die if the route is down temporarily, and some people
Damien Miller450a7a12000-03-26 13:04:51 +1000847find it annoying.
Damien Miller32aa1441999-10-29 09:15:49 +1000848.Pp
849The default is
850.Dq yes
851(to send keepalives), and the client will notice
Damien Miller7684ee12000-03-17 23:40:15 +1100852if the network goes down or the remote host dies.
853This is important in scripts, and many users want it too.
Damien Miller32aa1441999-10-29 09:15:49 +1000854.Pp
855To disable keepalives, the value should be set to
856.Dq no
857in both the server and the client configuration files.
858.It Cm KerberosAuthentication
Damien Miller450a7a12000-03-26 13:04:51 +1000859Specifies whether Kerberos authentication will be used.
860The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +1000861.Dq yes
862or
863.Dq no .
864.It Cm KerberosTgtPassing
Damien Miller450a7a12000-03-26 13:04:51 +1000865Specifies whether a Kerberos TGT will be forwarded to the server.
866This will only work if the Kerberos server is actually an AFS kaserver.
867The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +1000868.Dq yes
869or
870.Dq no .
871.It Cm LocalForward
872Specifies that a TCP/IP port on the local machine be forwarded over
Damien Miller7684ee12000-03-17 23:40:15 +1100873the secure channel to given host:port from the remote machine.
874The first argument must be a port number, and the second must be
875host:port.
876Multiple forwardings may be specified, and additional
877forwardings can be given on the command line.
878Only the superuser can forward privileged ports.
Damien Miller5ce662a1999-11-11 17:57:39 +1100879.It Cm LogLevel
880Gives the verbosity level that is used when logging messages from
881.Nm ssh .
882The possible values are:
Ben Lindstromdb65e8f2001-01-19 04:26:52 +0000883QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG.
884The default is INFO.
Ben Lindstrom06b33aa2001-02-15 03:01:59 +0000885.It Cm MACs
886Specifies the MAC (message authentication code) algorithms
887in order of preference.
888The MAC algorithm is used in protocol version 2
889for data integrity protection.
890Multiple algorithms must be comma-separated.
891The default is
892.Pp
893.Bd -literal
Ben Lindstromec26fb12001-03-06 01:05:23 +0000894 ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,
Ben Lindstrom06b33aa2001-02-15 03:01:59 +0000895 hmac-sha1-96,hmac-md5-96''
896.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000897.It Cm NumberOfPasswordPrompts
Damien Miller450a7a12000-03-26 13:04:51 +1000898Specifies the number of password prompts before giving up.
899The argument to this keyword must be an integer.
900Default is 3.
Damien Miller396691a2000-01-20 22:44:08 +1100901.It Cm PasswordAuthentication
Damien Miller7684ee12000-03-17 23:40:15 +1100902Specifies whether to use password authentication.
903The argument to this keyword must be
Damien Miller396691a2000-01-20 22:44:08 +1100904.Dq yes
905or
906.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000907The default is
908.Dq yes .
Damien Miller32aa1441999-10-29 09:15:49 +1000909.It Cm Port
Damien Miller7684ee12000-03-17 23:40:15 +1100910Specifies the port number to connect on the remote host.
911Default is 22.
Damien Miller1e42f302001-03-19 23:59:11 +1100912.It Cm PreferredAuthentications
913Specifies the order in which the client should try protocol 2
914authentication methods. This allows a client to prefer one method (e.g.
915.Cm keyboard-interactive )
916over another method (e.g.
917.Cm password )
918The default for this option is:
919.Dq publickey, password, keyboard-interactive
Damien Miller22c77262000-04-13 12:26:34 +1000920.It Cm Protocol
921Specifies the protocol versions
922.Nm
923should support in order of preference.
924The possible values are
925.Dq 1
926and
927.Dq 2 .
928Multiple versions must be comma-separated.
929The default is
Ben Lindstromf3272352001-04-05 23:29:59 +0000930.Dq 2,1 .
Damien Millere247cc42000-05-07 12:03:14 +1000931This means that
932.Nm
Ben Lindstromf3272352001-04-05 23:29:59 +0000933tries version 2 and falls back to version 1
934if version 2 is not available.
Damien Miller32aa1441999-10-29 09:15:49 +1000935.It Cm ProxyCommand
Damien Miller7684ee12000-03-17 23:40:15 +1100936Specifies the command to use to connect to the server.
937The command
938string extends to the end of the line, and is executed with
939.Pa /bin/sh .
940In the command string,
941.Ql %h
942will be substituted by the host name to
943connect and
944.Ql %p
945by the port.
946The command can be basically anything,
947and should read from its standard input and write to its standard output.
948It should eventually connect an
Damien Miller32aa1441999-10-29 09:15:49 +1000949.Xr sshd 8
950server running on some machine, or execute
951.Ic sshd -i
Damien Miller7684ee12000-03-17 23:40:15 +1100952somewhere.
953Host key management will be done using the
Damien Miller32aa1441999-10-29 09:15:49 +1000954HostName of the host being connected (defaulting to the name typed by
955the user).
Damien Milleraae6c611999-12-06 11:47:28 +1100956Note that
957.Cm CheckHostIP
958is not available for connects with a proxy command.
Damien Miller32aa1441999-10-29 09:15:49 +1000959.Pp
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000960.It Cm PubkeyAuthentication
961Specifies whether to try public key authentication.
962The argument to this keyword must be
963.Dq yes
964or
965.Dq no .
966The default is
967.Dq yes .
968This option applies to protocol version 2 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000969.It Cm RemoteForward
970Specifies that a TCP/IP port on the remote machine be forwarded over
Damien Miller7684ee12000-03-17 23:40:15 +1100971the secure channel to given host:port from the local machine.
972The first argument must be a port number, and the second must be
973host:port.
974Multiple forwardings may be specified, and additional
975forwardings can be given on the command line.
976Only the superuser can forward privileged ports.
Damien Miller32aa1441999-10-29 09:15:49 +1000977.It Cm RhostsAuthentication
Damien Miller7684ee12000-03-17 23:40:15 +1100978Specifies whether to try rhosts based authentication.
979Note that this
Damien Miller32aa1441999-10-29 09:15:49 +1000980declaration only affects the client side and has no effect whatsoever
Damien Miller7684ee12000-03-17 23:40:15 +1100981on security.
982Disabling rhosts authentication may reduce
Damien Miller32aa1441999-10-29 09:15:49 +1000983authentication time on slow connections when rhosts authentication is
Damien Miller7684ee12000-03-17 23:40:15 +1100984not used.
985Most servers do not permit RhostsAuthentication because it
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000986is not secure (see
987.Cm RhostsRSAAuthentication ).
Damien Miller7684ee12000-03-17 23:40:15 +1100988The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +1000989.Dq yes
990or
991.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +0000992The default is
993.Dq yes .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000994This option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000995.It Cm RhostsRSAAuthentication
996Specifies whether to try rhosts based authentication with RSA host
Damien Miller7684ee12000-03-17 23:40:15 +1100997authentication.
Damien Miller7684ee12000-03-17 23:40:15 +1100998The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +1000999.Dq yes
1000or
1001.Dq no .
Ben Lindstrom89b0bd62001-03-29 00:27:11 +00001002The default is
1003.Dq yes .
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001004This option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +10001005.It Cm RSAAuthentication
Damien Miller7684ee12000-03-17 23:40:15 +11001006Specifies whether to try RSA authentication.
1007The argument to this keyword must be
Damien Miller32aa1441999-10-29 09:15:49 +10001008.Dq yes
1009or
1010.Dq no .
1011RSA authentication will only be
1012attempted if the identity file exists, or an authentication agent is
1013running.
Ben Lindstrom89b0bd62001-03-29 00:27:11 +00001014The default is
1015.Dq yes .
Damien Millere247cc42000-05-07 12:03:14 +10001016Note that this option applies to protocol version 1 only.
Damien Miller33804262001-02-04 23:20:18 +11001017.It Cm ChallengeResponseAuthentication
1018Specifies whether to use challenge response authentication.
1019Currently there is only support for
Damien Miller95def091999-11-25 00:26:21 +11001020.Xr skey 1
Damien Miller7684ee12000-03-17 23:40:15 +11001021authentication.
1022The argument to this keyword must be
Damien Miller95def091999-11-25 00:26:21 +11001023.Dq yes
1024or
1025.Dq no .
1026The default is
1027.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +10001028.It Cm StrictHostKeyChecking
1029If this flag is set to
Damien Miller22c77262000-04-13 12:26:34 +10001030.Dq yes ,
Damien Miller32aa1441999-10-29 09:15:49 +10001031.Nm
Ben Lindstromeb930d42001-01-29 08:37:08 +00001032will never automatically add host keys to the
Damien Miller32aa1441999-10-29 09:15:49 +10001033.Pa $HOME/.ssh/known_hosts
Damien Millere247cc42000-05-07 12:03:14 +10001034and
1035.Pa $HOME/.ssh/known_hosts2
Ben Lindstromeb930d42001-01-29 08:37:08 +00001036files, and refuses to connect to hosts whose host key has changed.
Damien Miller7684ee12000-03-17 23:40:15 +11001037This provides maximum protection against trojan horse attacks.
1038However, it can be somewhat annoying if you don't have good
Damien Miller886c63a2000-01-20 23:13:36 +11001039.Pa /etc/ssh_known_hosts
Damien Millere247cc42000-05-07 12:03:14 +10001040and
1041.Pa /etc/ssh_known_hosts2
Damien Miller32aa1441999-10-29 09:15:49 +10001042files installed and frequently
Ben Lindstromeb930d42001-01-29 08:37:08 +00001043connect to new hosts.
1044This option forces the user to manually
1045add all new hosts.
1046If this flag is set to
1047.Dq no ,
1048.Nm
1049will automatically add new host keys to the
1050user known hosts files.
1051If this flag is set to
1052.Dq ask ,
1053new host keys
1054will be added to the user known host files only after the user
1055has confirmed that is what they really want to do, and
1056.Nm
1057will refuse to connect to hosts whose host key has changed.
Damien Miller7684ee12000-03-17 23:40:15 +11001058The host keys of
Ben Lindstromeb930d42001-01-29 08:37:08 +00001059known hosts will be verified automatically in all cases.
Damien Miller7684ee12000-03-17 23:40:15 +11001060The argument must be
Ben Lindstromeb930d42001-01-29 08:37:08 +00001061.Dq yes ,
1062.Dq no
Damien Miller32aa1441999-10-29 09:15:49 +10001063or
Ben Lindstromeb930d42001-01-29 08:37:08 +00001064.Dq ask .
1065The default is
1066.Dq ask .
Damien Miller32aa1441999-10-29 09:15:49 +10001067.It Cm UsePrivilegedPort
1068Specifies whether to use a privileged port for outgoing connections.
1069The argument must be
1070.Dq yes
1071or
1072.Dq no .
1073The default is
Ben Lindstromcebc8582001-03-08 03:39:10 +00001074.Dq no .
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001075Note that you need to set this option to
1076.Dq yes
1077if you want to use
Damien Miller32aa1441999-10-29 09:15:49 +10001078.Cm RhostsAuthentication
1079and
Kevin Stevesfcec7f82000-12-15 19:55:48 +00001080.Cm RhostsRSAAuthentication
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001081with older servers.
Damien Miller396691a2000-01-20 22:44:08 +11001082.It Cm User
Damien Miller7684ee12000-03-17 23:40:15 +11001083Specifies the user to log in as.
1084This can be useful if you have a different user name on different machines.
1085This saves the trouble of
Damien Miller396691a2000-01-20 22:44:08 +11001086having to remember to give the user name on the command line.
1087.It Cm UserKnownHostsFile
Ben Lindstrom1e621742001-03-06 01:10:53 +00001088Specifies a file to use for the protocol version 1 user
1089host key database instead of
Damien Miller396691a2000-01-20 22:44:08 +11001090.Pa $HOME/.ssh/known_hosts .
Ben Lindstrom1e621742001-03-06 01:10:53 +00001091.It Cm UserKnownHostsFile2
1092Specifies a file to use for the protocol version 2 user
1093host key database instead of
1094.Pa $HOME/.ssh/known_hosts2 .
Damien Miller32aa1441999-10-29 09:15:49 +10001095.It Cm UseRsh
Damien Miller7684ee12000-03-17 23:40:15 +11001096Specifies that rlogin/rsh should be used for this host.
1097It is possible that the host does not at all support the
Damien Miller32aa1441999-10-29 09:15:49 +10001098.Nm
Damien Miller7684ee12000-03-17 23:40:15 +11001099protocol.
1100This causes
Damien Miller32aa1441999-10-29 09:15:49 +10001101.Nm
Damien Miller7684ee12000-03-17 23:40:15 +11001102to immediately execute
Damien Miller32aa1441999-10-29 09:15:49 +10001103.Xr rsh 1 .
1104All other options (except
1105.Cm HostName )
Damien Miller7684ee12000-03-17 23:40:15 +11001106are ignored if this has been specified.
1107The argument must be
Damien Miller32aa1441999-10-29 09:15:49 +10001108.Dq yes
1109or
1110.Dq no .
Damien Millerd3a18572000-06-07 19:55:44 +10001111.It Cm XAuthLocation
1112Specifies the location of the
1113.Xr xauth 1
1114program.
1115The default is
1116.Pa /usr/X11R6/bin/xauth .
Damien Miller7b28dc52000-09-05 13:34:53 +11001117.El
Damien Miller32aa1441999-10-29 09:15:49 +10001118.Sh ENVIRONMENT
1119.Nm
1120will normally set the following environment variables:
1121.Bl -tag -width Ds
1122.It Ev DISPLAY
1123The
1124.Ev DISPLAY
Damien Miller7684ee12000-03-17 23:40:15 +11001125variable indicates the location of the X11 server.
Damien Miller22c77262000-04-13 12:26:34 +10001126It is automatically set by
Damien Miller32aa1441999-10-29 09:15:49 +10001127.Nm
1128to point to a value of the form
1129.Dq hostname:n
1130where hostname indicates
Damien Miller7684ee12000-03-17 23:40:15 +11001131the host where the shell runs, and n is an integer >= 1.
1132.Nm
1133uses this special value to forward X11 connections over the secure
1134channel.
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001135The user should normally not set
1136.Ev DISPLAY
1137explicitly, as that
Damien Miller32aa1441999-10-29 09:15:49 +10001138will render the X11 connection insecure (and will require the user to
1139manually copy any required authorization cookies).
1140.It Ev HOME
1141Set to the path of the user's home directory.
1142.It Ev LOGNAME
1143Synonym for
1144.Ev USER ;
1145set for compatibility with systems that use this variable.
1146.It Ev MAIL
1147Set to point the user's mailbox.
Damien Miller7684ee12000-03-17 23:40:15 +11001148.It Ev PATH
Damien Miller32aa1441999-10-29 09:15:49 +10001149Set to the default
1150.Ev PATH ,
1151as specified when compiling
1152.Nm ssh .
1153.It Ev SSH_AUTH_SOCK
1154indicates the path of a unix-domain socket used to communicate with the
1155agent.
1156.It Ev SSH_CLIENT
Damien Miller7684ee12000-03-17 23:40:15 +11001157Identifies the client end of the connection.
1158The variable contains
Damien Miller32aa1441999-10-29 09:15:49 +10001159three space-separated values: client ip-address, client port number,
1160and server port number.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001161.It Ev SSH_ORIGINAL_COMMAND
1162The variable contains the original command line if a forced command
1163is executed.
1164It can be used to extract the original arguments.
Damien Miller32aa1441999-10-29 09:15:49 +10001165.It Ev SSH_TTY
1166This is set to the name of the tty (path to the device) associated
Damien Miller7684ee12000-03-17 23:40:15 +11001167with the current shell or command.
1168If the current session has no tty,
Damien Miller32aa1441999-10-29 09:15:49 +10001169this variable is not set.
1170.It Ev TZ
1171The timezone variable is set to indicate the present timezone if it
Damien Miller942da032000-08-18 13:59:06 +10001172was set when the daemon was started (i.e., the daemon passes the value
Damien Miller32aa1441999-10-29 09:15:49 +10001173on to new connections).
1174.It Ev USER
1175Set to the name of the user logging in.
1176.El
1177.Pp
Damien Miller22c77262000-04-13 12:26:34 +10001178Additionally,
Damien Miller32aa1441999-10-29 09:15:49 +10001179.Nm
Damien Miller22c77262000-04-13 12:26:34 +10001180reads
1181.Pa $HOME/.ssh/environment ,
Damien Miller32aa1441999-10-29 09:15:49 +10001182and adds lines of the format
1183.Dq VARNAME=value
1184to the environment.
1185.Sh FILES
Damien Miller98c7ad62000-03-09 21:27:49 +11001186.Bl -tag -width Ds
Ben Lindstrom1e621742001-03-06 01:10:53 +00001187.It Pa $HOME/.ssh/known_hosts, $HOME/.ssh/known_hosts2
Damien Miller32aa1441999-10-29 09:15:49 +10001188Records host keys for all hosts the user has logged into (that are not
1189in
Ben Lindstrom1e621742001-03-06 01:10:53 +00001190.Pa /etc/ssh_known_hosts
1191for protocol version 1 or
1192.Pa /etc/ssh_known_hosts2
1193for protocol version 2).
Damien Miller32aa1441999-10-29 09:15:49 +10001194See
1195.Xr sshd 8 .
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001196.It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa
1197Contains the authentication identity of the user.
1198They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively.
Damien Millere247cc42000-05-07 12:03:14 +10001199These files
1200contain sensitive data and should be readable by the user but not
Damien Miller32aa1441999-10-29 09:15:49 +10001201accessible by others (read/write/execute).
1202Note that
1203.Nm
Damien Millere247cc42000-05-07 12:03:14 +10001204ignores a private key file if it is accessible by others.
Damien Miller32aa1441999-10-29 09:15:49 +10001205It is possible to specify a passphrase when
1206generating the key; the passphrase will be used to encrypt the
1207sensitive part of this file using 3DES.
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001208.It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub
Damien Miller32aa1441999-10-29 09:15:49 +10001209Contains the public key for authentication (public part of the
Damien Miller7684ee12000-03-17 23:40:15 +11001210identity file in human-readable form).
Damien Millere247cc42000-05-07 12:03:14 +10001211The contents of the
1212.Pa $HOME/.ssh/identity.pub
1213file should be added to
Damien Miller32aa1441999-10-29 09:15:49 +10001214.Pa $HOME/.ssh/authorized_keys
1215on all machines
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001216where you wish to log in using protocol version 1 RSA authentication.
Damien Millere247cc42000-05-07 12:03:14 +10001217The contents of the
1218.Pa $HOME/.ssh/id_dsa.pub
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001219and
1220.Pa $HOME/.ssh/id_rsa.pub
Damien Millere247cc42000-05-07 12:03:14 +10001221file should be added to
1222.Pa $HOME/.ssh/authorized_keys2
1223on all machines
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001224where you wish to log in using protocol version 2 DSA/RSA authentication.
Damien Millere247cc42000-05-07 12:03:14 +10001225These files are not
Damien Miller7684ee12000-03-17 23:40:15 +11001226sensitive and can (but need not) be readable by anyone.
Damien Millere247cc42000-05-07 12:03:14 +10001227These files are
Kevin Steves3c034ae2001-02-05 13:47:11 +00001228never used automatically and are not necessary; they are only provided for
Damien Miller32aa1441999-10-29 09:15:49 +10001229the convenience of the user.
1230.It Pa $HOME/.ssh/config
Damien Miller7684ee12000-03-17 23:40:15 +11001231This is the per-user configuration file.
1232The format of this file is described above.
1233This file is used by the
Damien Miller32aa1441999-10-29 09:15:49 +10001234.Nm
Damien Miller7684ee12000-03-17 23:40:15 +11001235client.
1236This file does not usually contain any sensitive information,
Damien Miller32aa1441999-10-29 09:15:49 +10001237but the recommended permissions are read/write for the user, and not
1238accessible by others.
1239.It Pa $HOME/.ssh/authorized_keys
Damien Miller7684ee12000-03-17 23:40:15 +11001240Lists the RSA keys that can be used for logging in as this user.
1241The format of this file is described in the
Damien Miller32aa1441999-10-29 09:15:49 +10001242.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001243manual page.
1244In the simplest form the format is the same as the .pub
Damien Miller32aa1441999-10-29 09:15:49 +10001245identity files (that is, each line contains the number of bits in
1246modulus, public exponent, modulus, and comment fields, separated by
Damien Miller7684ee12000-03-17 23:40:15 +11001247spaces).
1248This file is not highly sensitive, but the recommended
Damien Miller32aa1441999-10-29 09:15:49 +10001249permissions are read/write for the user, and not accessible by others.
Damien Millere247cc42000-05-07 12:03:14 +10001250.It Pa $HOME/.ssh/authorized_keys2
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001251Lists the public keys (RSA/DSA) that can be used for logging in as this user.
Damien Millere247cc42000-05-07 12:03:14 +10001252This file is not highly sensitive, but the recommended
1253permissions are read/write for the user, and not accessible by others.
1254.It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2
Damien Miller7684ee12000-03-17 23:40:15 +11001255Systemwide list of known host keys.
Damien Millere247cc42000-05-07 12:03:14 +10001256.Pa /etc/ssh_known_hosts
1257contains RSA and
1258.Pa /etc/ssh_known_hosts2
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001259contains RSA or DSA keys for protocol version 2.
Damien Millere247cc42000-05-07 12:03:14 +10001260These files should be prepared by the
Damien Miller32aa1441999-10-29 09:15:49 +10001261system administrator to contain the public host keys of all machines in the
Damien Miller7684ee12000-03-17 23:40:15 +11001262organization.
1263This file should be world-readable.
1264This file contains
Damien Miller32aa1441999-10-29 09:15:49 +10001265public keys, one per line, in the following format (fields separated
1266by spaces): system name, number of bits in modulus, public exponent,
Damien Miller7684ee12000-03-17 23:40:15 +11001267modulus, and optional comment field.
1268When different names are used
Damien Miller32aa1441999-10-29 09:15:49 +10001269for the same machine, all such names should be listed, separated by
Damien Miller7684ee12000-03-17 23:40:15 +11001270commas.
1271The format is described on the
Damien Miller32aa1441999-10-29 09:15:49 +10001272.Xr sshd 8
1273manual page.
1274.Pp
1275The canonical system name (as returned by name servers) is used by
1276.Xr sshd 8
1277to verify the client host when logging in; other names are needed because
1278.Nm
1279does not convert the user-supplied name to a canonical name before
1280checking the key, because someone with access to the name servers
1281would then be able to fool host authentication.
Damien Miller886c63a2000-01-20 23:13:36 +11001282.It Pa /etc/ssh_config
Damien Miller7684ee12000-03-17 23:40:15 +11001283Systemwide configuration file.
1284This file provides defaults for those
Damien Miller32aa1441999-10-29 09:15:49 +10001285values that are not specified in the user's configuration file, and
Damien Miller7684ee12000-03-17 23:40:15 +11001286for those users who do not have a configuration file.
1287This file must be world-readable.
Damien Miller32aa1441999-10-29 09:15:49 +10001288.It Pa $HOME/.rhosts
1289This file is used in
1290.Pa \&.rhosts
1291authentication to list the
Damien Miller7684ee12000-03-17 23:40:15 +11001292host/user pairs that are permitted to log in.
1293(Note that this file is
Damien Miller32aa1441999-10-29 09:15:49 +10001294also used by rlogin and rsh, which makes using this file insecure.)
1295Each line of the file contains a host name (in the canonical form
1296returned by name servers), and then a user name on that host,
Damien Miller7684ee12000-03-17 23:40:15 +11001297separated by a space.
Ben Lindstromebd888d2001-03-05 05:49:29 +00001298On some machines this file may need to be
Damien Miller32aa1441999-10-29 09:15:49 +10001299world-readable if the user's home directory is on a NFS partition,
1300because
1301.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001302reads it as root.
1303Additionally, this file must be owned by the user,
1304and must not have write permissions for anyone else.
1305The recommended
Damien Miller32aa1441999-10-29 09:15:49 +10001306permission for most machines is read/write for the user, and not
1307accessible by others.
1308.Pp
1309Note that by default
1310.Xr sshd 8
1311will be installed so that it requires successful RSA host
Damien Miller7684ee12000-03-17 23:40:15 +11001312authentication before permitting \s+2.\s0rhosts authentication.
1313If your server machine does not have the client's host key in
Damien Miller886c63a2000-01-20 23:13:36 +11001314.Pa /etc/ssh_known_hosts ,
Damien Miller32aa1441999-10-29 09:15:49 +10001315you can store it in
1316.Pa $HOME/.ssh/known_hosts .
1317The easiest way to do this is to
1318connect back to the client from the server machine using ssh; this
Damien Millere247cc42000-05-07 12:03:14 +10001319will automatically add the host key to
Damien Miller32aa1441999-10-29 09:15:49 +10001320.Pa $HOME/.ssh/known_hosts .
1321.It Pa $HOME/.shosts
1322This file is used exactly the same way as
1323.Pa \&.rhosts .
1324The purpose for
1325having this file is to be able to use rhosts authentication with
1326.Nm
1327without permitting login with
1328.Xr rlogin 1
1329or
1330.Xr rsh 1 .
1331.It Pa /etc/hosts.equiv
1332This file is used during
Damien Miller7684ee12000-03-17 23:40:15 +11001333.Pa \&.rhosts authentication.
1334It contains
Damien Miller32aa1441999-10-29 09:15:49 +10001335canonical hosts names, one per line (the full format is described on
1336the
1337.Xr sshd 8
Damien Miller7684ee12000-03-17 23:40:15 +11001338manual page).
1339If the client host is found in this file, login is
Damien Miller32aa1441999-10-29 09:15:49 +10001340automatically permitted provided client and server user names are the
Damien Miller7684ee12000-03-17 23:40:15 +11001341same.
1342Additionally, successful RSA host authentication is normally
1343required.
1344This file should only be writable by root.
Damien Miller886c63a2000-01-20 23:13:36 +11001345.It Pa /etc/shosts.equiv
Damien Miller22c77262000-04-13 12:26:34 +10001346This file is processed exactly as
Damien Miller32aa1441999-10-29 09:15:49 +10001347.Pa /etc/hosts.equiv .
1348This file may be useful to permit logins using
1349.Nm
1350but not using rsh/rlogin.
Damien Miller886c63a2000-01-20 23:13:36 +11001351.It Pa /etc/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +10001352Commands in this file are executed by
1353.Nm
1354when the user logs in just before the user's shell (or command) is started.
1355See the
1356.Xr sshd 8
1357manual page for more information.
1358.It Pa $HOME/.ssh/rc
1359Commands in this file are executed by
1360.Nm
1361when the user logs in just before the user's shell (or command) is
1362started.
Damien Miller22c77262000-04-13 12:26:34 +10001363See the
Damien Miller32aa1441999-10-29 09:15:49 +10001364.Xr sshd 8
1365manual page for more information.
Damien Miller4f0fa561999-12-26 14:24:41 +11001366.It Pa $HOME/.ssh/environment
1367Contains additional definitions for environment variables, see section
1368.Sx ENVIRONMENT
1369above.
Damien Miller7b28dc52000-09-05 13:34:53 +11001370.El
Damien Miller0bc1bd82000-11-13 22:57:25 +11001371.Sh AUTHORS
Ben Lindstrom035782e2001-01-29 08:34:16 +00001372OpenSSH is a derivative of the original and free
1373ssh 1.2.12 release by Tatu Ylonen.
1374Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1375Theo de Raadt and Dug Song
1376removed many bugs, re-added newer features and
1377created OpenSSH.
1378Markus Friedl contributed the support for SSH
1379protocol versions 1.5 and 2.0.
Damien Miller32aa1441999-10-29 09:15:49 +10001380.Sh SEE ALSO
1381.Xr rlogin 1 ,
1382.Xr rsh 1 ,
1383.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +11001384.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +10001385.Xr ssh-add 1 ,
1386.Xr ssh-agent 1 ,
1387.Xr ssh-keygen 1 ,
1388.Xr telnet 1 ,
Ben Lindstrom5ab6ae12001-02-10 22:08:03 +00001389.Xr sshd 8
Ben Lindstrom160ec622001-04-22 17:17:46 +00001390.Rs
1391.%A T. Ylonen
1392.%A T. Kivinen
1393.%A M. Saarinen
1394.%A T. Rinne
1395.%A S. Lehtinen
1396.%T "SSH Protocol Architecture"
1397.%N draft-ietf-secsh-architecture-07.txt
1398.%D January 2001
1399.%O work in progress material
1400.Re