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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.\"
Damien Miller9749c0c2002-02-05 12:23:58 +110037.\" $OpenBSD: sshd.8,v 1.166 2002/02/03 22:35:57 stevesk Exp $
Damien Miller32aa1441999-10-29 09:15:49 +100038.Dd September 25, 1999
39.Dt SSHD 8
40.Os
41.Sh NAME
42.Nm sshd
Ben Lindstromc65e6a02001-04-23 13:02:16 +000043.Nd OpenSSH SSH daemon
Damien Miller32aa1441999-10-29 09:15:49 +100044.Sh SYNOPSIS
45.Nm sshd
Ben Lindstromdfd18502001-09-20 01:06:08 +000046.Op Fl deiqtD46
Damien Miller32aa1441999-10-29 09:15:49 +100047.Op Fl b Ar bits
48.Op Fl f Ar config_file
49.Op Fl g Ar login_grace_time
50.Op Fl h Ar host_key_file
51.Op Fl k Ar key_gen_time
Ben Lindstromade03f62001-12-06 18:22:17 +000052.Op Fl o Ar option
Damien Miller32aa1441999-10-29 09:15:49 +100053.Op Fl p Ar port
Damien Miller942da032000-08-18 13:59:06 +100054.Op Fl u Ar len
Damien Miller22c77262000-04-13 12:26:34 +100055.Sh DESCRIPTION
Damien Miller32aa1441999-10-29 09:15:49 +100056.Nm
Ben Lindstromd58eb5f2001-03-07 06:07:22 +000057(SSH Daemon) is the daemon program for
Damien Miller32aa1441999-10-29 09:15:49 +100058.Xr ssh 1 .
Damien Miller35dabd02000-05-01 21:10:33 +100059Together these programs replace rlogin and rsh, and
Damien Miller32aa1441999-10-29 09:15:49 +100060provide secure encrypted communications between two untrusted hosts
Damien Miller450a7a12000-03-26 13:04:51 +100061over an insecure network.
62The programs are intended to be as easy to
Damien Miller32aa1441999-10-29 09:15:49 +100063install and use as possible.
64.Pp
65.Nm
Damien Miller450a7a12000-03-26 13:04:51 +100066is the daemon that listens for connections from clients.
Damien Miller22c77262000-04-13 12:26:34 +100067It is normally started at boot from
Damien Miller32aa1441999-10-29 09:15:49 +100068.Pa /etc/rc .
69It forks a new
Damien Miller450a7a12000-03-26 13:04:51 +100070daemon for each incoming connection.
71The forked daemons handle
Damien Miller32aa1441999-10-29 09:15:49 +100072key exchange, encryption, authentication, command execution,
73and data exchange.
Damien Millere247cc42000-05-07 12:03:14 +100074This implementation of
75.Nm
76supports both SSH protocol version 1 and 2 simultaneously.
Damien Miller32aa1441999-10-29 09:15:49 +100077.Nm
Damien Miller450a7a12000-03-26 13:04:51 +100078works as follows.
Damien Millere247cc42000-05-07 12:03:14 +100079.Pp
80.Ss SSH protocol version 1
81.Pp
Damien Miller450a7a12000-03-26 13:04:51 +100082Each host has a host-specific RSA key
83(normally 1024 bits) used to identify the host.
84Additionally, when
Damien Miller32aa1441999-10-29 09:15:49 +100085the daemon starts, it generates a server RSA key (normally 768 bits).
86This key is normally regenerated every hour if it has been used, and
87is never stored on disk.
88.Pp
Damien Miller35dabd02000-05-01 21:10:33 +100089Whenever a client connects the daemon responds with its public
90host and server keys.
Damien Miller450a7a12000-03-26 13:04:51 +100091The client compares the
Damien Millere247cc42000-05-07 12:03:14 +100092RSA host key against its own database to verify that it has not changed.
Damien Miller450a7a12000-03-26 13:04:51 +100093The client then generates a 256 bit random number.
94It encrypts this
Damien Miller32aa1441999-10-29 09:15:49 +100095random number using both the host key and the server key, and sends
Damien Miller450a7a12000-03-26 13:04:51 +100096the encrypted number to the server.
Damien Miller35dabd02000-05-01 21:10:33 +100097Both sides then use this
Damien Miller32aa1441999-10-29 09:15:49 +100098random number as a session key which is used to encrypt all further
Damien Miller450a7a12000-03-26 13:04:51 +100099communications in the session.
100The rest of the session is encrypted
Damien Miller35dabd02000-05-01 21:10:33 +1000101using a conventional cipher, currently Blowfish or 3DES, with 3DES
Damien Millerb38eff82000-04-01 11:09:21 +1000102being used by default.
Damien Miller450a7a12000-03-26 13:04:51 +1000103The client selects the encryption algorithm
Damien Miller32aa1441999-10-29 09:15:49 +1000104to use from those offered by the server.
105.Pp
Damien Miller450a7a12000-03-26 13:04:51 +1000106Next, the server and the client enter an authentication dialog.
107The client tries to authenticate itself using
Damien Miller32aa1441999-10-29 09:15:49 +1000108.Pa .rhosts
109authentication,
110.Pa .rhosts
111authentication combined with RSA host
112authentication, RSA challenge-response authentication, or password
113based authentication.
114.Pp
115Rhosts authentication is normally disabled
116because it is fundamentally insecure, but can be enabled in the server
Damien Miller450a7a12000-03-26 13:04:51 +1000117configuration file if desired.
118System security is not improved unless
Damien Miller32aa1441999-10-29 09:15:49 +1000119.Xr rshd 8 ,
120.Xr rlogind 8 ,
Damien Miller32aa1441999-10-29 09:15:49 +1000121and
Ben Lindstrom044274b2001-09-12 16:46:08 +0000122.Xr rexecd 8
Damien Miller32aa1441999-10-29 09:15:49 +1000123are disabled (thus completely disabling
124.Xr rlogin 1
125and
126.Xr rsh 1
Damien Miller35dabd02000-05-01 21:10:33 +1000127into the machine).
Damien Miller32aa1441999-10-29 09:15:49 +1000128.Pp
Damien Millere247cc42000-05-07 12:03:14 +1000129.Ss SSH protocol version 2
130.Pp
Damien Miller942da032000-08-18 13:59:06 +1000131Version 2 works similarly:
Ben Lindstrom07d24dc2001-08-06 21:18:57 +0000132Each host has a host-specific key (RSA or DSA) used to identify the host.
Damien Millere247cc42000-05-07 12:03:14 +1000133However, when the daemon starts, it does not generate a server key.
134Forward security is provided through a Diffie-Hellman key agreement.
135This key agreement results in a shared session key.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000136.Pp
Ben Lindstromfd2e05b2001-03-05 07:48:45 +0000137The rest of the session is encrypted using a symmetric cipher, currently
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000138128 bit AES, Blowfish, 3DES, CAST128, Arcfour, 192 bit AES, or 256 bit AES.
Damien Millere247cc42000-05-07 12:03:14 +1000139The client selects the encryption algorithm
140to use from those offered by the server.
141Additionally, session integrity is provided
Damien Miller30c3d422000-05-09 11:02:59 +1000142through a cryptographic message authentication code
Damien Millere247cc42000-05-07 12:03:14 +1000143(hmac-sha1 or hmac-md5).
144.Pp
145Protocol version 2 provides a public key based
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000146user (PubkeyAuthentication) or
147client host (HostbasedAuthentication) authentication method,
148conventional password authentication and challenge response based methods.
Damien Millere247cc42000-05-07 12:03:14 +1000149.Pp
150.Ss Command execution and data forwarding
151.Pp
Damien Miller32aa1441999-10-29 09:15:49 +1000152If the client successfully authenticates itself, a dialog for
Damien Miller450a7a12000-03-26 13:04:51 +1000153preparing the session is entered.
154At this time the client may request
Damien Miller32aa1441999-10-29 09:15:49 +1000155things like allocating a pseudo-tty, forwarding X11 connections,
156forwarding TCP/IP connections, or forwarding the authentication agent
157connection over the secure channel.
158.Pp
159Finally, the client either requests a shell or execution of a command.
Damien Miller450a7a12000-03-26 13:04:51 +1000160The sides then enter session mode.
161In this mode, either side may send
Damien Miller32aa1441999-10-29 09:15:49 +1000162data at any time, and such data is forwarded to/from the shell or
163command on the server side, and the user terminal in the client side.
164.Pp
165When the user program terminates and all forwarded X11 and other
166connections have been closed, the server sends command exit status to
167the client, and both sides exit.
168.Pp
169.Nm
170can be configured using command-line options or a configuration
Damien Miller450a7a12000-03-26 13:04:51 +1000171file.
172Command-line options override values specified in the
Damien Miller32aa1441999-10-29 09:15:49 +1000173configuration file.
174.Pp
Damien Miller6162d121999-11-21 13:23:52 +1100175.Nm
176rereads its configuration file when it receives a hangup signal,
Ben Lindstrom49a098d2001-03-05 06:55:18 +0000177.Dv SIGHUP ,
Ben Lindstromd2bf0d62001-06-25 04:10:54 +0000178by executing itself with the name it was started as, i.e.,
Ben Lindstrom49a098d2001-03-05 06:55:18 +0000179.Pa /usr/sbin/sshd .
Damien Miller6162d121999-11-21 13:23:52 +1100180.Pp
Damien Miller32aa1441999-10-29 09:15:49 +1000181The options are as follows:
182.Bl -tag -width Ds
183.It Fl b Ar bits
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000184Specifies the number of bits in the ephemeral protocol version 1
185server key (default 768).
Damien Miller32aa1441999-10-29 09:15:49 +1000186.It Fl d
Damien Miller450a7a12000-03-26 13:04:51 +1000187Debug mode.
188The server sends verbose debug output to the system
189log, and does not put itself in the background.
190The server also will not fork and will only process one connection.
191This option is only intended for debugging for the server.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000192Multiple -d options increase the debugging level.
Damien Miller874d77b2000-10-14 16:23:11 +1100193Maximum is 3.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000194.It Fl e
195When this option is specified,
196.Nm
197will send the output to the standard error instead of the system log.
Damien Miller32aa1441999-10-29 09:15:49 +1000198.It Fl f Ar configuration_file
Damien Miller450a7a12000-03-26 13:04:51 +1000199Specifies the name of the configuration file.
200The default is
Damien Miller886c63a2000-01-20 23:13:36 +1100201.Pa /etc/sshd_config .
Damien Miller32aa1441999-10-29 09:15:49 +1000202.Nm
203refuses to start if there is no configuration file.
204.It Fl g Ar login_grace_time
205Gives the grace time for clients to authenticate themselves (default
Kevin Steves9ce907c2001-01-07 11:53:40 +0000206600 seconds).
Damien Miller450a7a12000-03-26 13:04:51 +1000207If the client fails to authenticate the user within
208this many seconds, the server disconnects and exits.
209A value of zero indicates no limit.
Damien Miller32aa1441999-10-29 09:15:49 +1000210.It Fl h Ar host_key_file
Damien Miller7fc23732002-01-22 23:19:11 +1100211Specifies a file from which a host key is read.
Damien Miller32aa1441999-10-29 09:15:49 +1000212This option must be given if
213.Nm
214is not run as root (as the normal
Damien Miller7fc23732002-01-22 23:19:11 +1100215host key files are normally not readable by anyone but root).
216The default is
217.Pa /etc/ssh_host_key
218for protocol version 1, and
219.Pa /etc/ssh_host_rsa_key
220and
221.Pa /etc/ssh_host_dsa_key
222for protocol version 2.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000223It is possible to have multiple host key files for
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000224the different protocol versions and host key algorithms.
Damien Miller32aa1441999-10-29 09:15:49 +1000225.It Fl i
226Specifies that
227.Nm
Damien Miller22c77262000-04-13 12:26:34 +1000228is being run from inetd.
Damien Miller32aa1441999-10-29 09:15:49 +1000229.Nm
230is normally not run
231from inetd because it needs to generate the server key before it can
Damien Miller450a7a12000-03-26 13:04:51 +1000232respond to the client, and this may take tens of seconds.
233Clients would have to wait too long if the key was regenerated every time.
Damien Miller7684ee12000-03-17 23:40:15 +1100234However, with small key sizes (e.g., 512) using
Damien Miller32aa1441999-10-29 09:15:49 +1000235.Nm
236from inetd may
237be feasible.
238.It Fl k Ar key_gen_time
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000239Specifies how often the ephemeral protocol version 1 server key is
240regenerated (default 3600 seconds, or one hour).
Damien Miller450a7a12000-03-26 13:04:51 +1000241The motivation for regenerating the key fairly
Damien Miller32aa1441999-10-29 09:15:49 +1000242often is that the key is not stored anywhere, and after about an hour,
243it becomes impossible to recover the key for decrypting intercepted
244communications even if the machine is cracked into or physically
Damien Miller450a7a12000-03-26 13:04:51 +1000245seized.
246A value of zero indicates that the key will never be regenerated.
Ben Lindstromade03f62001-12-06 18:22:17 +0000247.It Fl o Ar option
248Can be used to give options in the format used in the configuration file.
249This is useful for specifying options for which there is no separate
250command-line flag.
Damien Miller32aa1441999-10-29 09:15:49 +1000251.It Fl p Ar port
252Specifies the port on which the server listens for connections
253(default 22).
Damien Miller7d1ded42002-01-22 23:09:41 +1100254Multiple port options are permitted.
255Ports specified in the configuration file are ignored when a
256command-line port is specified.
Damien Miller32aa1441999-10-29 09:15:49 +1000257.It Fl q
Damien Miller450a7a12000-03-26 13:04:51 +1000258Quiet mode.
259Nothing is sent to the system log.
260Normally the beginning,
Damien Miller32aa1441999-10-29 09:15:49 +1000261authentication, and termination of each connection is logged.
Ben Lindstrom794325a2001-08-06 21:09:07 +0000262.It Fl t
263Test mode.
264Only check the validity of the configuration file and sanity of the keys.
Damien Miller9f0f5c62001-12-21 14:45:46 +1100265This is useful for updating
Ben Lindstrom794325a2001-08-06 21:09:07 +0000266.Nm
267reliably as configuration options may change.
Damien Miller942da032000-08-18 13:59:06 +1000268.It Fl u Ar len
269This option is used to specify the size of the field
270in the
271.Li utmp
272structure that holds the remote host name.
273If the resolved host name is longer than
274.Ar len ,
275the dotted decimal value will be used instead.
276This allows hosts with very long host names that
277overflow this field to still be uniquely identified.
278Specifying
279.Fl u0
280indicates that only dotted decimal addresses
281should be put into the
282.Pa utmp
283file.
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000284.Fl u0
285is also be used to prevent
286.Nm
287from making DNS requests unless the authentication
288mechanism or configuration requires it.
289Authentication mechanisms that may require DNS include
290.Cm RhostsAuthentication ,
291.Cm RhostsRSAAuthentication ,
292.Cm HostbasedAuthentication
293and using a
294.Cm from="pattern-list"
295option in a key file.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000296.It Fl D
297When this option is specified
298.Nm
299will not detach and does not become a daemon.
300This allows easy monitoring of
301.Nm sshd .
Damien Miller34132e52000-01-14 15:45:46 +1100302.It Fl 4
303Forces
304.Nm
305to use IPv4 addresses only.
306.It Fl 6
307Forces
308.Nm
309to use IPv6 addresses only.
Damien Miller32aa1441999-10-29 09:15:49 +1000310.El
311.Sh CONFIGURATION FILE
312.Nm
Damien Miller22c77262000-04-13 12:26:34 +1000313reads configuration data from
Damien Miller886c63a2000-01-20 23:13:36 +1100314.Pa /etc/sshd_config
Damien Miller32aa1441999-10-29 09:15:49 +1000315(or the file specified with
316.Fl f
Damien Miller450a7a12000-03-26 13:04:51 +1000317on the command line).
Ben Lindstrom1c0fd092001-09-12 16:36:17 +0000318The file contains keyword-argument pairs, one per line.
Damien Miller450a7a12000-03-26 13:04:51 +1000319Lines starting with
Damien Miller32aa1441999-10-29 09:15:49 +1000320.Ql #
321and empty lines are interpreted as comments.
322.Pp
Ben Lindstrom1c0fd092001-09-12 16:36:17 +0000323The possible
324keywords and their meanings are as follows (note that
325keywords are case-insensitive and arguments are case-sensitive):
Damien Miller32aa1441999-10-29 09:15:49 +1000326.Bl -tag -width Ds
327.It Cm AFSTokenPassing
Damien Miller450a7a12000-03-26 13:04:51 +1000328Specifies whether an AFS token may be forwarded to the server.
329Default is
Damien Miller32aa1441999-10-29 09:15:49 +1000330.Dq yes .
331.It Cm AllowGroups
Damien Millerdf64a682002-01-22 23:33:45 +1100332This keyword can be followed by a list of group name patterns, separated
Damien Miller450a7a12000-03-26 13:04:51 +1000333by spaces.
334If specified, login is allowed only for users whose primary
Kevin Steves7b61cfa2001-01-14 19:11:00 +0000335group or supplementary group list matches one of the patterns.
Damien Miller32aa1441999-10-29 09:15:49 +1000336.Ql \&*
337and
338.Ql ?
339can be used as
Damien Miller450a7a12000-03-26 13:04:51 +1000340wildcards in the patterns.
Ben Lindstrom594e2032001-09-12 18:35:30 +0000341Only group names are valid; a numerical group ID is not recognized.
Damien Millerdf64a682002-01-22 23:33:45 +1100342By default, login is allowed for all groups.
Damien Miller32aa1441999-10-29 09:15:49 +1000343.Pp
Damien Miller50a41ed2000-10-16 12:14:42 +1100344.It Cm AllowTcpForwarding
345Specifies whether TCP forwarding is permitted.
346The default is
347.Dq yes .
348Note that disabling TCP forwarding does not improve security unless
349users are also denied shell access, as they can always install their
350own forwarders.
351.Pp
Damien Miller32aa1441999-10-29 09:15:49 +1000352.It Cm AllowUsers
Damien Millerdf64a682002-01-22 23:33:45 +1100353This keyword can be followed by a list of user name patterns, separated
Damien Miller450a7a12000-03-26 13:04:51 +1000354by spaces.
355If specified, login is allowed only for users names that
Damien Miller32aa1441999-10-29 09:15:49 +1000356match one of the patterns.
357.Ql \&*
358and
359.Ql ?
360can be used as
Damien Miller450a7a12000-03-26 13:04:51 +1000361wildcards in the patterns.
Ben Lindstrom594e2032001-09-12 18:35:30 +0000362Only user names are valid; a numerical user ID is not recognized.
Damien Millerdf64a682002-01-22 23:33:45 +1100363By default, login is allowed for all users.
Ben Lindstrom60260022001-07-04 04:56:44 +0000364If the pattern takes the form USER@HOST then USER and HOST
Ben Lindstrom594e2032001-09-12 18:35:30 +0000365are separately checked, restricting logins to particular
Ben Lindstrom60260022001-07-04 04:56:44 +0000366users from particular hosts.
Damien Miller32aa1441999-10-29 09:15:49 +1000367.Pp
Ben Lindstrombfb3a0e2001-06-05 20:25:05 +0000368.It Cm AuthorizedKeysFile
Ben Lindstrom07d24dc2001-08-06 21:18:57 +0000369Specifies the file that contains the public keys that can be used
370for user authentication.
Ben Lindstrombfb3a0e2001-06-05 20:25:05 +0000371.Cm AuthorizedKeysFile
372may contain tokens of the form %T which are substituted during connection
Ben Lindstrome59433d2001-09-12 16:41:37 +0000373set-up. The following tokens are defined: %% is replaced by a literal '%',
Ben Lindstrombfb3a0e2001-06-05 20:25:05 +0000374%h is replaced by the home directory of the user being authenticated and
375%u is replaced by the username of that user.
376After expansion,
377.Cm AuthorizedKeysFile
Ben Lindstrom34a99682001-06-12 00:23:12 +0000378is taken to be an absolute path or one relative to the user's home
Ben Lindstrombfb3a0e2001-06-05 20:25:05 +0000379directory.
380The default is
Damien Miller70972eb2002-01-22 23:19:55 +1100381.Dq .ssh/authorized_keys .
Ben Lindstrom48bd7c12001-01-09 00:35:42 +0000382.It Cm Banner
383In some jurisdictions, sending a warning message before authentication
384may be relevant for getting legal protection.
385The contents of the specified file are sent to the remote user before
386authentication is allowed.
387This option is only available for protocol version 2.
388.Pp
Ben Lindstromff8b4942001-03-06 01:00:03 +0000389.It Cm ChallengeResponseAuthentication
Ben Lindstromc8e29ce2001-08-06 20:55:28 +0000390Specifies whether challenge response authentication is allowed.
391All authentication styles from
392.Xr login.conf 5
393are supported.
Ben Lindstromff8b4942001-03-06 01:00:03 +0000394The default is
395.Dq yes .
Ben Lindstrom608d1d12001-06-05 19:33:22 +0000396.It Cm Ciphers
397Specifies the ciphers allowed for protocol version 2.
398Multiple ciphers must be comma-separated.
399The default is
Damien Miller9c3f9502002-01-22 23:33:15 +1100400.Pp
401.Bd -literal
402 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
403 aes192-cbc,aes256-cbc''
404.Ed
Ben Lindstrom5744dc42001-04-13 23:28:01 +0000405.It Cm ClientAliveInterval
406Sets a timeout interval in seconds after which if no data has been received
Ben Lindstrom24643222001-06-25 05:08:11 +0000407from the client,
Ben Lindstrom5744dc42001-04-13 23:28:01 +0000408.Nm
409will send a message through the encrypted
Ben Lindstroma8f39722001-04-16 02:03:49 +0000410channel to request a response from the client.
411The default
Ben Lindstrom5744dc42001-04-13 23:28:01 +0000412is 0, indicating that these messages will not be sent to the client.
Ben Lindstroma8f39722001-04-16 02:03:49 +0000413This option applies to protocol version 2 only.
Ben Lindstrom5744dc42001-04-13 23:28:01 +0000414.It Cm ClientAliveCountMax
415Sets the number of client alive messages (see above) which may be
416sent without
417.Nm
418receiving any messages back from the client. If this threshold is
Ben Lindstrom24643222001-06-25 05:08:11 +0000419reached while client alive messages are being sent,
Ben Lindstrom5744dc42001-04-13 23:28:01 +0000420.Nm
421will disconnect the client, terminating the session. It is important
Ben Lindstrom24643222001-06-25 05:08:11 +0000422to note that the use of client alive messages is very different from
Damien Miller60d8aaf2001-11-12 11:04:05 +1100423.Cm KeepAlive
Ben Lindstroma8f39722001-04-16 02:03:49 +0000424(below). The client alive messages are sent through the
Ben Lindstrom5744dc42001-04-13 23:28:01 +0000425encrypted channel and therefore will not be spoofable. The TCP keepalive
Ben Lindstroma8f39722001-04-16 02:03:49 +0000426option enabled by
Damien Miller60d8aaf2001-11-12 11:04:05 +1100427.Cm KeepAlive
Ben Lindstrom594e2032001-09-12 18:35:30 +0000428is spoofable. The client alive mechanism is valuable when the client or
429server depend on knowing when a connection has become inactive.
Ben Lindstroma8f39722001-04-16 02:03:49 +0000430.Pp
Ben Lindstrom594e2032001-09-12 18:35:30 +0000431The default value is 3. If
Ben Lindstroma8f39722001-04-16 02:03:49 +0000432.Cm ClientAliveInterval
Ben Lindstrom594e2032001-09-12 18:35:30 +0000433(above) is set to 15, and
Ben Lindstrom406b4f02001-09-20 23:09:16 +0000434.Cm ClientAliveCountMax
435is left at the default, unresponsive ssh clients
Ben Lindstrom24643222001-06-25 05:08:11 +0000436will be disconnected after approximately 45 seconds.
Damien Miller32aa1441999-10-29 09:15:49 +1000437.It Cm DenyGroups
Damien Millerdf64a682002-01-22 23:33:45 +1100438This keyword can be followed by a list of group name patterns, separated
Damien Miller450a7a12000-03-26 13:04:51 +1000439by spaces.
Damien Millerdf64a682002-01-22 23:33:45 +1100440Login is disallowed for users whose primary group or supplementary
441group list matches one of the patterns.
Damien Miller32aa1441999-10-29 09:15:49 +1000442.Ql \&*
443and
444.Ql ?
445can be used as
Damien Miller450a7a12000-03-26 13:04:51 +1000446wildcards in the patterns.
Ben Lindstrom594e2032001-09-12 18:35:30 +0000447Only group names are valid; a numerical group ID is not recognized.
Damien Millerdf64a682002-01-22 23:33:45 +1100448By default, login is allowed for all groups.
Damien Miller32aa1441999-10-29 09:15:49 +1000449.Pp
450.It Cm DenyUsers
Damien Millerdf64a682002-01-22 23:33:45 +1100451This keyword can be followed by a list of user name patterns, separated
Damien Miller450a7a12000-03-26 13:04:51 +1000452by spaces.
453Login is disallowed for user names that match one of the patterns.
Damien Miller32aa1441999-10-29 09:15:49 +1000454.Ql \&*
455and
456.Ql ?
Damien Miller450a7a12000-03-26 13:04:51 +1000457can be used as wildcards in the patterns.
Ben Lindstrom594e2032001-09-12 18:35:30 +0000458Only user names are valid; a numerical user ID is not recognized.
Damien Millerdf64a682002-01-22 23:33:45 +1100459By default, login is allowed for all users.
Damien Millere247cc42000-05-07 12:03:14 +1000460.It Cm GatewayPorts
461Specifies whether remote hosts are allowed to connect to ports
462forwarded for the client.
Ben Lindstrom60d82be2001-09-12 17:58:15 +0000463By default,
464.Nm
465binds remote port forwardings to the loopback addresss. This
466prevents other remote hosts from connecting to forwarded ports.
467.Cm GatewayPorts
468can be used to specify that
469.Nm
470should bind remote port forwardings to the wildcard address,
471thus allowing remote hosts to connect to forwarded ports.
Damien Millere247cc42000-05-07 12:03:14 +1000472The argument must be
473.Dq yes
474or
475.Dq no .
476The default is
477.Dq no .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000478.It Cm HostbasedAuthentication
479Specifies whether rhosts or /etc/hosts.equiv authentication together
480with successful public key client host authentication is allowed
481(hostbased authentication).
482This option is similar to
483.Cm RhostsRSAAuthentication
484and applies to protocol version 2 only.
485The default is
486.Dq no .
Damien Millere247cc42000-05-07 12:03:14 +1000487.It Cm HostKey
Damien Miller7fc23732002-01-22 23:19:11 +1100488Specifies a file containing a private host key
489used by SSH.
490The default is
491.Pa /etc/ssh_host_key
492for protocol version 1, and
493.Pa /etc/ssh_host_rsa_key
494and
495.Pa /etc/ssh_host_dsa_key
496for protocol version 2.
Damien Millere247cc42000-05-07 12:03:14 +1000497Note that
498.Nm
Ben Lindstrom226cfa02001-01-22 05:34:40 +0000499will refuse to use a file if it is group/world-accessible.
Damien Miller0bc1bd82000-11-13 22:57:25 +1100500It is possible to have multiple host key files.
501.Dq rsa1
502keys are used for version 1 and
503.Dq dsa
504or
505.Dq rsa
506are used for version 2 of the SSH protocol.
Damien Miller32aa1441999-10-29 09:15:49 +1000507.It Cm IgnoreRhosts
Damien Miller98c7ad62000-03-09 21:27:49 +1100508Specifies that
509.Pa .rhosts
Damien Miller22c77262000-04-13 12:26:34 +1000510and
Damien Miller98c7ad62000-03-09 21:27:49 +1100511.Pa .shosts
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000512files will not be used in
513.Cm RhostsAuthentication ,
514.Cm RhostsRSAAuthentication
515or
516.Cm HostbasedAuthentication .
517.Pp
Damien Miller32aa1441999-10-29 09:15:49 +1000518.Pa /etc/hosts.equiv
519and
Damien Miller22c77262000-04-13 12:26:34 +1000520.Pa /etc/shosts.equiv
Damien Miller450a7a12000-03-26 13:04:51 +1000521are still used.
Damien Miller22c77262000-04-13 12:26:34 +1000522The default is
Damien Miller98c7ad62000-03-09 21:27:49 +1100523.Dq yes .
Damien Miller32265091999-11-12 11:33:04 +1100524.It Cm IgnoreUserKnownHosts
525Specifies whether
526.Nm
527should ignore the user's
528.Pa $HOME/.ssh/known_hosts
529during
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000530.Cm RhostsRSAAuthentication
531or
532.Cm HostbasedAuthentication .
Damien Miller32265091999-11-12 11:33:04 +1100533The default is
534.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000535.It Cm KeepAlive
Damien Miller9749c0c2002-02-05 12:23:58 +1100536Specifies whether the system should send TCP keepalive messages to the
Damien Miller450a7a12000-03-26 13:04:51 +1000537other side.
538If they are sent, death of the connection or crash of one
539of the machines will be properly noticed.
540However, this means that
Damien Miller32aa1441999-10-29 09:15:49 +1000541connections will die if the route is down temporarily, and some people
Damien Miller450a7a12000-03-26 13:04:51 +1000542find it annoying.
Damien Miller30c3d422000-05-09 11:02:59 +1000543On the other hand, if keepalives are not sent,
Damien Miller32aa1441999-10-29 09:15:49 +1000544sessions may hang indefinitely on the server, leaving
545.Dq ghost
546users and consuming server resources.
547.Pp
548The default is
549.Dq yes
550(to send keepalives), and the server will notice
Damien Miller9749c0c2002-02-05 12:23:58 +1100551if the network goes down or the client host crashes.
Damien Miller450a7a12000-03-26 13:04:51 +1000552This avoids infinitely hanging sessions.
Damien Miller32aa1441999-10-29 09:15:49 +1000553.Pp
554To disable keepalives, the value should be set to
Damien Miller9749c0c2002-02-05 12:23:58 +1100555.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000556.It Cm KerberosAuthentication
Damien Miller450a7a12000-03-26 13:04:51 +1000557Specifies whether Kerberos authentication is allowed.
558This can be in the form of a Kerberos ticket, or if
Damien Miller32aa1441999-10-29 09:15:49 +1000559.Cm PasswordAuthentication
560is yes, the password provided by the user will be validated through
Damien Miller874d77b2000-10-14 16:23:11 +1100561the Kerberos KDC.
562To use this option, the server needs a
Damien Miller942da032000-08-18 13:59:06 +1000563Kerberos servtab which allows the verification of the KDC's identity.
Damien Miller450a7a12000-03-26 13:04:51 +1000564Default is
Damien Miller32aa1441999-10-29 09:15:49 +1000565.Dq yes .
566.It Cm KerberosOrLocalPasswd
567If set then if password authentication through Kerberos fails then
568the password will be validated via any additional local mechanism
569such as
Damien Miller62cee002000-09-23 17:15:56 +1100570.Pa /etc/passwd .
Damien Miller450a7a12000-03-26 13:04:51 +1000571Default is
Damien Miller32aa1441999-10-29 09:15:49 +1000572.Dq yes .
573.It Cm KerberosTgtPassing
574Specifies whether a Kerberos TGT may be forwarded to the server.
Damien Miller22c77262000-04-13 12:26:34 +1000575Default is
Damien Miller32aa1441999-10-29 09:15:49 +1000576.Dq no ,
577as this only works when the Kerberos KDC is actually an AFS kaserver.
578.It Cm KerberosTicketCleanup
579Specifies whether to automatically destroy the user's ticket cache
Damien Miller450a7a12000-03-26 13:04:51 +1000580file on logout.
581Default is
Damien Miller32aa1441999-10-29 09:15:49 +1000582.Dq yes .
583.It Cm KeyRegenerationInterval
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000584In protocol version 1, the ephemeral server key is automatically regenerated
585after this many seconds (if it has been used).
Damien Miller450a7a12000-03-26 13:04:51 +1000586The purpose of regeneration is to prevent
Damien Miller32aa1441999-10-29 09:15:49 +1000587decrypting captured sessions by later breaking into the machine and
Damien Miller450a7a12000-03-26 13:04:51 +1000588stealing the keys.
589The key is never stored anywhere.
590If the value is 0, the key is never regenerated.
591The default is 3600 (seconds).
Damien Miller32aa1441999-10-29 09:15:49 +1000592.It Cm ListenAddress
Ben Lindstrom49e57a82001-04-08 18:02:43 +0000593Specifies the local addresses
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000594.Nm
Damien Miller32aa1441999-10-29 09:15:49 +1000595should listen on.
Ben Lindstrom49e57a82001-04-08 18:02:43 +0000596The following forms may be used:
597.Pp
598.Bl -item -offset indent -compact
599.It
600.Cm ListenAddress
Ben Lindstrom1a598a42001-04-10 02:48:50 +0000601.Sm off
602.Ar host No | Ar IPv4_addr No | Ar IPv6_addr
603.Sm on
Ben Lindstrom49e57a82001-04-08 18:02:43 +0000604.It
605.Cm ListenAddress
Ben Lindstrom1a598a42001-04-10 02:48:50 +0000606.Sm off
607.Ar host No | Ar IPv4_addr No : Ar port
608.Sm on
Ben Lindstrom49e57a82001-04-08 18:02:43 +0000609.It
610.Cm ListenAddress
Ben Lindstrom1a598a42001-04-10 02:48:50 +0000611.Sm off
612.Oo
613.Ar host No | Ar IPv6_addr Oc : Ar port
614.Sm on
Ben Lindstrom49e57a82001-04-08 18:02:43 +0000615.El
616.Pp
617If
Ben Lindstrom1a598a42001-04-10 02:48:50 +0000618.Ar port
Ben Lindstrom49e57a82001-04-08 18:02:43 +0000619is not specified,
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000620.Nm
Ben Lindstrom49e57a82001-04-08 18:02:43 +0000621will listen on the address and all prior
622.Cm Port
623options specified. The default is to listen on all local
624addresses. Multiple
625.Cm ListenAddress
626options are permitted. Additionally, any
627.Cm Port
628options must precede this option for non port qualified addresses.
Damien Miller32aa1441999-10-29 09:15:49 +1000629.It Cm LoginGraceTime
630The server disconnects after this time if the user has not
Damien Miller450a7a12000-03-26 13:04:51 +1000631successfully logged in.
632If the value is 0, there is no time limit.
Damien Miller32aa1441999-10-29 09:15:49 +1000633The default is 600 (seconds).
Damien Miller5ce662a1999-11-11 17:57:39 +1100634.It Cm LogLevel
635Gives the verbosity level that is used when logging messages from
636.Nm sshd .
637The possible values are:
Damien Millerdc9e0672002-01-22 23:17:51 +1100638QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
639The default is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2
640and DEBUG3 each specify higher levels of debugging output.
641Logging with a DEBUG level violates the privacy of users
Damien Miller5ce662a1999-11-11 17:57:39 +1100642and is not recommended.
Ben Lindstrom06b33aa2001-02-15 03:01:59 +0000643.It Cm MACs
644Specifies the available MAC (message authentication code) algorithms.
645The MAC algorithm is used in protocol version 2
646for data integrity protection.
647Multiple algorithms must be comma-separated.
648The default is
Ben Lindstrombd0e2de2001-06-05 19:52:52 +0000649.Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
Damien Miller37023962000-07-11 17:31:38 +1000650.It Cm MaxStartups
651Specifies the maximum number of concurrent unauthenticated connections to the
652.Nm
653daemon.
654Additional connections will be dropped until authentication succeeds or the
655.Cm LoginGraceTime
656expires for a connection.
657The default is 10.
Damien Miller942da032000-08-18 13:59:06 +1000658.Pp
659Alternatively, random early drop can be enabled by specifying
660the three colon separated values
661.Dq start:rate:full
Damien Miller874d77b2000-10-14 16:23:11 +1100662(e.g., "10:30:60").
Damien Miller942da032000-08-18 13:59:06 +1000663.Nm
Ben Lindstroma7333502001-01-29 08:44:03 +0000664will refuse connection attempts with a probability of
Damien Miller942da032000-08-18 13:59:06 +1000665.Dq rate/100
666(30%)
667if there are currently
668.Dq start
669(10)
670unauthenticated connections.
Ben Lindstroma7333502001-01-29 08:44:03 +0000671The probability increases linearly and all connection attempts
Damien Miller942da032000-08-18 13:59:06 +1000672are refused if the number of unauthenticated connections reaches
673.Dq full
674(60).
Damien Millerf8154422001-04-25 22:44:14 +1000675.It Cm PAMAuthenticationViaKbdInt
676Specifies whether PAM challenge response authentication is allowed. This
677allows the use of most PAM challenge response authentication modules, but
678it will allow password authentication regardless of whether
679.Cm PasswordAuthentication
680is disabled.
681The default is
682.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000683.It Cm PasswordAuthentication
684Specifies whether password authentication is allowed.
685The default is
686.Dq yes .
687.It Cm PermitEmptyPasswords
688When password authentication is allowed, it specifies whether the
Damien Miller450a7a12000-03-26 13:04:51 +1000689server allows login to accounts with empty password strings.
690The default is
Damien Miller98c7ad62000-03-09 21:27:49 +1100691.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000692.It Cm PermitRootLogin
Ben Lindstrom323c98f2001-03-05 07:40:40 +0000693Specifies whether root can login using
Damien Miller32aa1441999-10-29 09:15:49 +1000694.Xr ssh 1 .
695The argument must be
696.Dq yes ,
Ben Lindstromd8a90212001-02-15 03:08:27 +0000697.Dq without-password ,
698.Dq forced-commands-only
Damien Miller32aa1441999-10-29 09:15:49 +1000699or
700.Dq no .
701The default is
702.Dq yes .
Damien Miller32aa1441999-10-29 09:15:49 +1000703.Pp
Ben Lindstromd8a90212001-02-15 03:08:27 +0000704If this option is set to
705.Dq without-password
706password authentication is disabled for root.
707.Pp
708If this option is set to
709.Dq forced-commands-only
710root login with public key authentication will be allowed,
711but only if the
Damien Miller32aa1441999-10-29 09:15:49 +1000712.Ar command
Ben Lindstromd8a90212001-02-15 03:08:27 +0000713option has been specified
Damien Miller32aa1441999-10-29 09:15:49 +1000714(which may be useful for taking remote backups even if root login is
Ben Lindstromd8a90212001-02-15 03:08:27 +0000715normally not allowed). All other authentication methods are disabled
716for root.
Ben Lindstrom323c98f2001-03-05 07:40:40 +0000717.Pp
718If this option is set to
719.Dq no
720root is not allowed to login.
Damien Miller6f83b8e2000-05-02 09:23:45 +1000721.It Cm PidFile
722Specifies the file that contains the process identifier of the
723.Nm
724daemon.
725The default is
726.Pa /var/run/sshd.pid .
Damien Miller32aa1441999-10-29 09:15:49 +1000727.It Cm Port
728Specifies the port number that
729.Nm
Damien Miller450a7a12000-03-26 13:04:51 +1000730listens on.
731The default is 22.
Damien Miller34132e52000-01-14 15:45:46 +1100732Multiple options of this type are permitted.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000733See also
734.Cm ListenAddress .
Ben Lindstrom7bfff362001-03-26 05:45:53 +0000735.It Cm PrintLastLog
736Specifies whether
737.Nm
738should print the date and time when the user last logged in.
739The default is
740.Dq yes .
Damien Miller32aa1441999-10-29 09:15:49 +1000741.It Cm PrintMotd
742Specifies whether
743.Nm
Damien Miller22c77262000-04-13 12:26:34 +1000744should print
Damien Miller32aa1441999-10-29 09:15:49 +1000745.Pa /etc/motd
Damien Miller450a7a12000-03-26 13:04:51 +1000746when a user logs in interactively.
747(On some systems it is also printed by the shell,
Damien Miller32aa1441999-10-29 09:15:49 +1000748.Pa /etc/profile ,
Damien Miller450a7a12000-03-26 13:04:51 +1000749or equivalent.)
750The default is
Damien Miller32aa1441999-10-29 09:15:49 +1000751.Dq yes .
Damien Miller22c77262000-04-13 12:26:34 +1000752.It Cm Protocol
753Specifies the protocol versions
754.Nm
755should support.
756The possible values are
757.Dq 1
758and
759.Dq 2 .
760Multiple versions must be comma-separated.
761The default is
Ben Lindstrombdc2beb2001-04-16 02:11:52 +0000762.Dq 2,1 .
Ben Lindstromff8b4942001-03-06 01:00:03 +0000763.It Cm PubkeyAuthentication
764Specifies whether public key authentication is allowed.
765The default is
766.Dq yes .
767Note that this option applies to protocol version 2 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000768.It Cm RhostsAuthentication
769Specifies whether authentication using rhosts or /etc/hosts.equiv
Damien Miller450a7a12000-03-26 13:04:51 +1000770files is sufficient.
771Normally, this method should not be permitted because it is insecure.
Damien Miller32aa1441999-10-29 09:15:49 +1000772.Cm RhostsRSAAuthentication
773should be used
774instead, because it performs RSA-based host authentication in addition
775to normal rhosts or /etc/hosts.equiv authentication.
776The default is
777.Dq no .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000778This option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000779.It Cm RhostsRSAAuthentication
780Specifies whether rhosts or /etc/hosts.equiv authentication together
Damien Miller450a7a12000-03-26 13:04:51 +1000781with successful RSA host authentication is allowed.
782The default is
Damien Miller98c7ad62000-03-09 21:27:49 +1100783.Dq no .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000784This option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000785.It Cm RSAAuthentication
Damien Miller450a7a12000-03-26 13:04:51 +1000786Specifies whether pure RSA authentication is allowed.
787The default is
Damien Miller32aa1441999-10-29 09:15:49 +1000788.Dq yes .
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000789This option applies to protocol version 1 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000790.It Cm ServerKeyBits
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000791Defines the number of bits in the ephemeral protocol version 1 server key.
Damien Miller450a7a12000-03-26 13:04:51 +1000792The minimum value is 512, and the default is 768.
Damien Miller32aa1441999-10-29 09:15:49 +1000793.It Cm StrictModes
794Specifies whether
795.Nm
796should check file modes and ownership of the
Damien Miller450a7a12000-03-26 13:04:51 +1000797user's files and home directory before accepting login.
798This is normally desirable because novices sometimes accidentally leave their
799directory or files world-writable.
800The default is
Damien Miller32aa1441999-10-29 09:15:49 +1000801.Dq yes .
Damien Millerf6d9e222000-06-18 14:50:44 +1000802.It Cm Subsystem
Damien Miller874d77b2000-10-14 16:23:11 +1100803Configures an external subsystem (e.g., file transfer daemon).
804Arguments should be a subsystem name and a command to execute upon subsystem
805request.
Damien Miller7b28dc52000-09-05 13:34:53 +1100806The command
807.Xr sftp-server 8
808implements the
809.Dq sftp
810file transfer subsystem.
Damien Millerf6d9e222000-06-18 14:50:44 +1000811By default no subsystems are defined.
812Note that this option applies to protocol version 2 only.
Damien Miller32aa1441999-10-29 09:15:49 +1000813.It Cm SyslogFacility
814Gives the facility code that is used when logging messages from
815.Nm sshd .
816The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
Damien Miller450a7a12000-03-26 13:04:51 +1000817LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
818The default is AUTH.
Damien Miller32aa1441999-10-29 09:15:49 +1000819.It Cm UseLogin
820Specifies whether
821.Xr login 1
Damien Millerd3a18572000-06-07 19:55:44 +1000822is used for interactive login sessions.
Ben Lindstrom699776e2001-06-21 03:14:49 +0000823The default is
824.Dq no .
Damien Millerd3a18572000-06-07 19:55:44 +1000825Note that
826.Xr login 1
Damien Miller942da032000-08-18 13:59:06 +1000827is never used for remote command execution.
Ben Lindstrom24643222001-06-25 05:08:11 +0000828Note also, that if this is enabled,
829.Cm X11Forwarding
Ben Lindstrom699776e2001-06-21 03:14:49 +0000830will be disabled because
831.Xr login 1
832does not know how to handle
Ben Lindstrom24643222001-06-25 05:08:11 +0000833.Xr xauth 1
Ben Lindstrom699776e2001-06-21 03:14:49 +0000834cookies.
Damien Millerc5d86352002-02-05 12:13:41 +1100835.It Cm VerifyReverseMapping
836Specifies whether
837.Nm
838should try to verify the remote host name and check that
839the resolved host name for the remote IP address maps back to the
840very same IP address.
841The default is
842.Dq no .
Damien Miller32aa1441999-10-29 09:15:49 +1000843.It Cm X11DisplayOffset
844Specifies the first display number available for
845.Nm sshd Ns 's
Damien Miller450a7a12000-03-26 13:04:51 +1000846X11 forwarding.
847This prevents
Damien Miller32aa1441999-10-29 09:15:49 +1000848.Nm
849from interfering with real X11 servers.
Damien Miller98c7ad62000-03-09 21:27:49 +1100850The default is 10.
Damien Miller396691a2000-01-20 22:44:08 +1100851.It Cm X11Forwarding
Damien Miller450a7a12000-03-26 13:04:51 +1000852Specifies whether X11 forwarding is permitted.
853The default is
Damien Miller98c7ad62000-03-09 21:27:49 +1100854.Dq no .
Damien Miller396691a2000-01-20 22:44:08 +1100855Note that disabling X11 forwarding does not improve security in any
856way, as users can always install their own forwarders.
Ben Lindstrom24643222001-06-25 05:08:11 +0000857X11 forwarding is automatically disabled if
858.Cm UseLogin
859is enabled.
Damien Miller95c249f2002-02-05 12:11:34 +1100860.It Cm X11UseLocalhost
861Specifies whether
862.Nm
863should bind the X11 forwarding server to the loopback address or to
864the wildcard address. By default,
865.Nm
866binds the forwarding server to the loopback address and sets the
867hostname part of the
868.Ev DISPLAY
869environment variable to
870.Dq localhost .
871This prevents remote hosts from connecting to the fake display.
872However, some older X11 clients may not function with this
873configuration.
874.Cm X11UseLocalhost
875may be set to
876.Dq no
877to specify that the forwarding server should be bound to the wildcard
878address.
879The argument must be
880.Dq yes
881or
882.Dq no .
883The default is
884.Dq yes .
Damien Millerd3a18572000-06-07 19:55:44 +1000885.It Cm XAuthLocation
886Specifies the location of the
887.Xr xauth 1
888program.
889The default is
890.Pa /usr/X11R6/bin/xauth .
Damien Miller32aa1441999-10-29 09:15:49 +1000891.El
Ben Lindstrom1bda4c82001-06-05 19:59:08 +0000892.Ss Time Formats
893.Pp
894.Nm
895command-line arguments and configuration file options that specify time
896may be expressed using a sequence of the form:
897.Sm off
898.Ar time Oo Ar qualifier Oc ,
899.Sm on
900where
901.Ar time
902is a positive integer value and
903.Ar qualifier
904is one of the following:
905.Pp
906.Bl -tag -width Ds -compact -offset indent
907.It Cm <none>
908seconds
909.It Cm s | Cm S
910seconds
911.It Cm m | Cm M
912minutes
913.It Cm h | Cm H
914hours
915.It Cm d | Cm D
916days
917.It Cm w | Cm W
918weeks
919.El
920.Pp
921Each member of the sequence is added together to calculate
922the total time value.
923.Pp
924Time format examples:
925.Pp
926.Bl -tag -width Ds -compact -offset indent
927.It 600
928600 seconds (10 minutes)
929.It 10m
93010 minutes
931.It 1h30m
9321 hour 30 minutes (90 minutes)
933.El
Damien Miller32aa1441999-10-29 09:15:49 +1000934.Sh LOGIN PROCESS
935When a user successfully logs in,
936.Nm
937does the following:
938.Bl -enum -offset indent
939.It
940If the login is on a tty, and no command has been specified,
Damien Miller22c77262000-04-13 12:26:34 +1000941prints last login time and
Damien Miller32aa1441999-10-29 09:15:49 +1000942.Pa /etc/motd
943(unless prevented in the configuration file or by
944.Pa $HOME/.hushlogin ;
945see the
Damien Miller22c77262000-04-13 12:26:34 +1000946.Sx FILES
Damien Miller32aa1441999-10-29 09:15:49 +1000947section).
948.It
949If the login is on a tty, records login time.
950.It
951Checks
952.Pa /etc/nologin ;
953if it exists, prints contents and quits
954(unless root).
955.It
956Changes to run with normal user privileges.
957.It
958Sets up basic environment.
959.It
960Reads
961.Pa $HOME/.ssh/environment
962if it exists.
963.It
964Changes to user's home directory.
965.It
966If
967.Pa $HOME/.ssh/rc
968exists, runs it; else if
Damien Miller886c63a2000-01-20 23:13:36 +1100969.Pa /etc/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +1000970exists, runs
Damien Miller450a7a12000-03-26 13:04:51 +1000971it; otherwise runs xauth.
972The
Damien Miller32aa1441999-10-29 09:15:49 +1000973.Dq rc
974files are given the X11
975authentication protocol and cookie in standard input.
976.It
977Runs user's shell or command.
978.El
979.Sh AUTHORIZED_KEYS FILE FORMAT
Damien Miller32aa1441999-10-29 09:15:49 +1000980.Pa $HOME/.ssh/authorized_keys
Ben Lindstromf96704d2001-06-25 04:17:12 +0000981is the default file that lists the public keys that are
982permitted for RSA authentication in protocol version 1
983and for public key authentication (PubkeyAuthentication)
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000984in protocol version 2.
Ben Lindstromf96704d2001-06-25 04:17:12 +0000985.Cm AuthorizedKeysFile
Ben Lindstrombfb3a0e2001-06-05 20:25:05 +0000986may be used to specify an alternative file.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000987.Pp
Damien Miller450a7a12000-03-26 13:04:51 +1000988Each line of the file contains one
Damien Miller32aa1441999-10-29 09:15:49 +1000989key (empty lines and lines starting with a
990.Ql #
991are ignored as
Damien Miller450a7a12000-03-26 13:04:51 +1000992comments).
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000993Each RSA public key consists of the following fields, separated by
Damien Miller450a7a12000-03-26 13:04:51 +1000994spaces: options, bits, exponent, modulus, comment.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000995Each protocol version 2 public key consists of:
996options, keytype, base64 encoded key, comment.
997The options fields
998are optional; its presence is determined by whether the line starts
Damien Miller32aa1441999-10-29 09:15:49 +1000999with a number or not (the option field never starts with a number).
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001000The bits, exponent, modulus and comment fields give the RSA key for
1001protocol version 1; the
Damien Miller32aa1441999-10-29 09:15:49 +10001002comment field is not used for anything (but may be convenient for the
1003user to identify the key).
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001004For protocol version 2 the keytype is
1005.Dq ssh-dss
1006or
1007.Dq ssh-rsa .
Damien Miller32aa1441999-10-29 09:15:49 +10001008.Pp
1009Note that lines in this file are usually several hundred bytes long
Damien Miller450a7a12000-03-26 13:04:51 +10001010(because of the size of the RSA key modulus).
1011You don't want to type them in; instead, copy the
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001012.Pa identity.pub ,
Ben Lindstrom4dccfa52000-12-28 16:40:05 +00001013.Pa id_dsa.pub
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001014or the
1015.Pa id_rsa.pub
Damien Miller32aa1441999-10-29 09:15:49 +10001016file and edit it.
1017.Pp
Damien Miller942da032000-08-18 13:59:06 +10001018The options (if present) consist of comma-separated option
Damien Miller450a7a12000-03-26 13:04:51 +10001019specifications.
1020No spaces are permitted, except within double quotes.
Ben Lindstrom1c0fd092001-09-12 16:36:17 +00001021The following option specifications are supported (note
1022that option keywords are case-insensitive):
Damien Miller32aa1441999-10-29 09:15:49 +10001023.Bl -tag -width Ds
1024.It Cm from="pattern-list"
1025Specifies that in addition to RSA authentication, the canonical name
1026of the remote host must be present in the comma-separated list of
Damien Miller450a7a12000-03-26 13:04:51 +10001027patterns
1028.Pf ( Ql *
1029and
1030.Ql ?
1031serve as wildcards).
1032The list may also contain
1033patterns negated by prefixing them with
1034.Ql ! ;
1035if the canonical host name matches a negated pattern, the key is not accepted.
1036The purpose
Damien Miller32aa1441999-10-29 09:15:49 +10001037of this option is to optionally increase security: RSA authentication
1038by itself does not trust the network or name servers or anything (but
1039the key); however, if somebody somehow steals the key, the key
Damien Miller450a7a12000-03-26 13:04:51 +10001040permits an intruder to log in from anywhere in the world.
1041This additional option makes using a stolen key more difficult (name
Damien Miller32aa1441999-10-29 09:15:49 +10001042servers and/or routers would have to be compromised in addition to
1043just the key).
1044.It Cm command="command"
1045Specifies that the command is executed whenever this key is used for
Damien Miller450a7a12000-03-26 13:04:51 +10001046authentication.
1047The command supplied by the user (if any) is ignored.
Ben Lindstrom23124ea2001-09-14 23:14:25 +00001048The command is run on a pty if the client requests a pty;
Damien Miller450a7a12000-03-26 13:04:51 +10001049otherwise it is run without a tty.
Ben Lindstrom594e2032001-09-12 18:35:30 +00001050If a 8-bit clean channel is required,
1051one must not request a pty or should specify
Damien Miller33804262001-02-04 23:20:18 +11001052.Cm no-pty .
Damien Miller450a7a12000-03-26 13:04:51 +10001053A quote may be included in the command by quoting it with a backslash.
1054This option might be useful
1055to restrict certain RSA keys to perform just a specific operation.
1056An example might be a key that permits remote backups but nothing else.
Damien Miller30c3d422000-05-09 11:02:59 +10001057Note that the client may specify TCP/IP and/or X11
1058forwarding unless they are explicitly prohibited.
Ben Lindstrom20daef72001-09-20 00:54:01 +00001059Note that this option applies to shell, command or subsystem execution.
Damien Miller32aa1441999-10-29 09:15:49 +10001060.It Cm environment="NAME=value"
1061Specifies that the string is to be added to the environment when
Damien Miller450a7a12000-03-26 13:04:51 +10001062logging in using this key.
1063Environment variables set this way
1064override other default environment values.
1065Multiple options of this type are permitted.
Ben Lindstrom38b951c2001-12-06 17:47:47 +00001066This option is automatically disabled if
1067.Cm UseLogin
1068is enabled.
Damien Miller32aa1441999-10-29 09:15:49 +10001069.It Cm no-port-forwarding
1070Forbids TCP/IP forwarding when this key is used for authentication.
Damien Miller450a7a12000-03-26 13:04:51 +10001071Any port forward requests by the client will return an error.
1072This might be used, e.g., in connection with the
Damien Miller32aa1441999-10-29 09:15:49 +10001073.Cm command
1074option.
1075.It Cm no-X11-forwarding
1076Forbids X11 forwarding when this key is used for authentication.
1077Any X11 forward requests by the client will return an error.
1078.It Cm no-agent-forwarding
1079Forbids authentication agent forwarding when this key is used for
1080authentication.
1081.It Cm no-pty
1082Prevents tty allocation (a request to allocate a pty will fail).
Damien Millera243fde2001-03-19 23:16:08 +11001083.It Cm permitopen="host:port"
Ben Lindstrom24643222001-06-25 05:08:11 +00001084Limit local
Damien Millera243fde2001-03-19 23:16:08 +11001085.Li ``ssh -L''
Ben Lindstrom4b3564e2001-04-10 02:41:56 +00001086port forwarding such that it may only connect to the specified host and
Ben Lindstromd71ba572001-09-12 18:03:31 +00001087port.
1088IPv6 addresses can be specified with an alternative syntax:
1089.Ar host/port .
1090Multiple
Damien Millera243fde2001-03-19 23:16:08 +11001091.Cm permitopen
Ben Lindstrom24643222001-06-25 05:08:11 +00001092options may be applied separated by commas. No pattern matching is
1093performed on the specified hostnames, they must be literal domains or
Damien Millera243fde2001-03-19 23:16:08 +11001094addresses.
Damien Miller32aa1441999-10-29 09:15:49 +10001095.El
1096.Ss Examples
10971024 33 12121.\|.\|.\|312314325 ylo@foo.bar
1098.Pp
1099from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula
1100.Pp
1101command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi
Damien Millera243fde2001-03-19 23:16:08 +11001102.Pp
1103permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323
Damien Miller32aa1441999-10-29 09:15:49 +10001104.Sh SSH_KNOWN_HOSTS FILE FORMAT
Damien Miller22c77262000-04-13 12:26:34 +10001105The
Damien Millere247cc42000-05-07 12:03:14 +10001106.Pa /etc/ssh_known_hosts ,
Damien Miller22c77262000-04-13 12:26:34 +10001107and
Ben Lindstromd6481ea2001-06-25 04:37:41 +00001108.Pa $HOME/.ssh/known_hosts
Damien Miller450a7a12000-03-26 13:04:51 +10001109files contain host public keys for all known hosts.
1110The global file should
1111be prepared by the administrator (optional), and the per-user file is
Damien Miller942da032000-08-18 13:59:06 +10001112maintained automatically: whenever the user connects from an unknown host
Damien Miller450a7a12000-03-26 13:04:51 +10001113its key is added to the per-user file.
Damien Miller32aa1441999-10-29 09:15:49 +10001114.Pp
1115Each line in these files contains the following fields: hostnames,
Damien Miller450a7a12000-03-26 13:04:51 +10001116bits, exponent, modulus, comment.
1117The fields are separated by spaces.
Damien Miller32aa1441999-10-29 09:15:49 +10001118.Pp
1119Hostnames is a comma-separated list of patterns ('*' and '?' act as
1120wildcards); each pattern in turn is matched against the canonical host
1121name (when authenticating a client) or against the user-supplied
Damien Miller450a7a12000-03-26 13:04:51 +10001122name (when authenticating a server).
1123A pattern may also be preceded by
Damien Miller32aa1441999-10-29 09:15:49 +10001124.Ql !
1125to indicate negation: if the host name matches a negated
1126pattern, it is not accepted (by that line) even if it matched another
1127pattern on the line.
1128.Pp
Damien Millere247cc42000-05-07 12:03:14 +10001129Bits, exponent, and modulus are taken directly from the RSA host key; they
Damien Miller32aa1441999-10-29 09:15:49 +10001130can be obtained, e.g., from
Damien Miller886c63a2000-01-20 23:13:36 +11001131.Pa /etc/ssh_host_key.pub .
Damien Miller32aa1441999-10-29 09:15:49 +10001132The optional comment field continues to the end of the line, and is not used.
1133.Pp
1134Lines starting with
1135.Ql #
1136and empty lines are ignored as comments.
1137.Pp
1138When performing host authentication, authentication is accepted if any
Damien Miller450a7a12000-03-26 13:04:51 +10001139matching line has the proper key.
1140It is thus permissible (but not
Damien Miller32aa1441999-10-29 09:15:49 +10001141recommended) to have several lines or different host keys for the same
Damien Miller450a7a12000-03-26 13:04:51 +10001142names.
1143This will inevitably happen when short forms of host names
1144from different domains are put in the file.
1145It is possible
Damien Miller32aa1441999-10-29 09:15:49 +10001146that the files contain conflicting information; authentication is
1147accepted if valid information can be found from either file.
1148.Pp
1149Note that the lines in these files are typically hundreds of characters
1150long, and you definitely don't want to type in the host keys by hand.
1151Rather, generate them by a script
Damien Miller22c77262000-04-13 12:26:34 +10001152or by taking
Damien Miller886c63a2000-01-20 23:13:36 +11001153.Pa /etc/ssh_host_key.pub
Damien Miller32aa1441999-10-29 09:15:49 +10001154and adding the host names at the front.
1155.Ss Examples
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001156.Bd -literal
1157closenet,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi
1158cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....=
1159.Ed
Damien Miller32aa1441999-10-29 09:15:49 +10001160.Sh FILES
1161.Bl -tag -width Ds
Damien Miller886c63a2000-01-20 23:13:36 +11001162.It Pa /etc/sshd_config
Damien Miller32aa1441999-10-29 09:15:49 +10001163Contains configuration data for
1164.Nm sshd .
1165This file should be writable by root only, but it is recommended
1166(though not necessary) that it be world-readable.
Ben Lindstromd7f5b512001-03-05 06:57:23 +00001167.It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001168These three files contain the private parts of the host keys.
Ben Lindstromd7f5b512001-03-05 06:57:23 +00001169These files should only be owned by root, readable only by root, and not
Damien Miller32aa1441999-10-29 09:15:49 +10001170accessible to others.
1171Note that
1172.Nm
1173does not start if this file is group/world-accessible.
Ben Lindstromd7f5b512001-03-05 06:57:23 +00001174.It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001175These three files contain the public parts of the host keys.
Ben Lindstromd7f5b512001-03-05 06:57:23 +00001176These files should be world-readable but writable only by
Damien Miller450a7a12000-03-26 13:04:51 +10001177root.
Ben Lindstromd7f5b512001-03-05 06:57:23 +00001178Their contents should match the respective private parts.
1179These files are not
1180really used for anything; they are provided for the convenience of
1181the user so their contents can be copied to known hosts files.
1182These files are created using
Damien Miller32aa1441999-10-29 09:15:49 +10001183.Xr ssh-keygen 1 .
Ben Lindstromae1c51c2001-06-25 04:14:59 +00001184.It Pa /etc/moduli
Damien Millere39cacc2000-11-29 12:18:44 +11001185Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
Damien Miller886c63a2000-01-20 23:13:36 +11001186.It Pa /var/run/sshd.pid
Damien Miller32aa1441999-10-29 09:15:49 +10001187Contains the process ID of the
1188.Nm
1189listening for connections (if there are several daemons running
1190concurrently for different ports, this contains the pid of the one
Damien Miller450a7a12000-03-26 13:04:51 +10001191started last).
Damien Miller942da032000-08-18 13:59:06 +10001192The content of this file is not sensitive; it can be world-readable.
Damien Miller32aa1441999-10-29 09:15:49 +10001193.It Pa $HOME/.ssh/authorized_keys
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001194Lists the public keys (RSA or DSA) that can be used to log into the user's account.
Damien Millere247cc42000-05-07 12:03:14 +10001195This file must be readable by root (which may on some machines imply
1196it being world-readable if the user's home directory resides on an NFS
1197volume).
1198It is recommended that it not be accessible by others.
1199The format of this file is described above.
1200Users will place the contents of their
Ben Lindstromf96704d2001-06-25 04:17:12 +00001201.Pa identity.pub ,
Damien Millere247cc42000-05-07 12:03:14 +10001202.Pa id_dsa.pub
Ben Lindstrom18a82ac2001-04-11 15:59:35 +00001203and/or
1204.Pa id_rsa.pub
Damien Millere247cc42000-05-07 12:03:14 +10001205files into this file, as described in
1206.Xr ssh-keygen 1 .
Damien Miller886c63a2000-01-20 23:13:36 +11001207.It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts"
Damien Miller5ce662a1999-11-11 17:57:39 +11001208These files are consulted when using rhosts with RSA host
Ben Lindstromd6481ea2001-06-25 04:37:41 +00001209authentication or protocol version 2 hostbased authentication
1210to check the public key of the host.
Damien Miller450a7a12000-03-26 13:04:51 +10001211The key must be listed in one of these files to be accepted.
Damien Miller33e511e1999-11-11 11:43:13 +11001212The client uses the same files
Ben Lindstromebd888d2001-03-05 05:49:29 +00001213to verify that it is connecting to the correct remote host.
Damien Miller450a7a12000-03-26 13:04:51 +10001214These files should be writable only by root/the owner.
Damien Miller886c63a2000-01-20 23:13:36 +11001215.Pa /etc/ssh_known_hosts
Damien Miller32aa1441999-10-29 09:15:49 +10001216should be world-readable, and
1217.Pa $HOME/.ssh/known_hosts
1218can but need not be world-readable.
1219.It Pa /etc/nologin
Damien Miller22c77262000-04-13 12:26:34 +10001220If this file exists,
Damien Miller32aa1441999-10-29 09:15:49 +10001221.Nm
Damien Miller450a7a12000-03-26 13:04:51 +10001222refuses to let anyone except root log in.
1223The contents of the file
Damien Miller32aa1441999-10-29 09:15:49 +10001224are displayed to anyone trying to log in, and non-root connections are
Damien Miller450a7a12000-03-26 13:04:51 +10001225refused.
1226The file should be world-readable.
Damien Miller32aa1441999-10-29 09:15:49 +10001227.It Pa /etc/hosts.allow, /etc/hosts.deny
Ben Lindstrom6149a6c2001-10-03 17:15:32 +00001228Access controls that should be enforced by tcp-wrappers are defined here.
1229Further details are described in
Damien Miller32aa1441999-10-29 09:15:49 +10001230.Xr hosts_access 5 .
1231.It Pa $HOME/.rhosts
1232This file contains host-username pairs, separated by a space, one per
Damien Miller450a7a12000-03-26 13:04:51 +10001233line.
1234The given user on the corresponding host is permitted to log in
1235without password.
1236The same file is used by rlogind and rshd.
Damien Miller32aa1441999-10-29 09:15:49 +10001237The file must
1238be writable only by the user; it is recommended that it not be
1239accessible by others.
1240.Pp
Damien Miller450a7a12000-03-26 13:04:51 +10001241If is also possible to use netgroups in the file.
1242Either host or user
Damien Miller32aa1441999-10-29 09:15:49 +10001243name may be of the form +@groupname to specify all hosts or all users
1244in the group.
1245.It Pa $HOME/.shosts
1246For ssh,
1247this file is exactly the same as for
1248.Pa .rhosts .
1249However, this file is
1250not used by rlogin and rshd, so using this permits access using SSH only.
Damien Miller942da032000-08-18 13:59:06 +10001251.It Pa /etc/hosts.equiv
Damien Miller32aa1441999-10-29 09:15:49 +10001252This file is used during
1253.Pa .rhosts
Damien Miller450a7a12000-03-26 13:04:51 +10001254authentication.
1255In the simplest form, this file contains host names, one per line.
1256Users on
Damien Miller32aa1441999-10-29 09:15:49 +10001257those hosts are permitted to log in without a password, provided they
Damien Miller450a7a12000-03-26 13:04:51 +10001258have the same user name on both machines.
1259The host name may also be
Damien Miller32aa1441999-10-29 09:15:49 +10001260followed by a user name; such users are permitted to log in as
1261.Em any
Damien Miller450a7a12000-03-26 13:04:51 +10001262user on this machine (except root).
1263Additionally, the syntax
Damien Miller32aa1441999-10-29 09:15:49 +10001264.Dq +@group
Damien Miller450a7a12000-03-26 13:04:51 +10001265can be used to specify netgroups.
1266Negated entries start with
Damien Miller32aa1441999-10-29 09:15:49 +10001267.Ql \&- .
1268.Pp
1269If the client host/user is successfully matched in this file, login is
1270automatically permitted provided the client and server user names are the
Damien Miller450a7a12000-03-26 13:04:51 +10001271same.
1272Additionally, successful RSA host authentication is normally required.
1273This file must be writable only by root; it is recommended
Damien Miller32aa1441999-10-29 09:15:49 +10001274that it be world-readable.
1275.Pp
1276.Sy "Warning: It is almost never a good idea to use user names in"
1277.Pa hosts.equiv .
1278Beware that it really means that the named user(s) can log in as
1279.Em anybody ,
1280which includes bin, daemon, adm, and other accounts that own critical
Damien Miller450a7a12000-03-26 13:04:51 +10001281binaries and directories.
1282Using a user name practically grants the user root access.
1283The only valid use for user names that I can think
Damien Miller32aa1441999-10-29 09:15:49 +10001284of is in negative entries.
1285.Pp
1286Note that this warning also applies to rsh/rlogin.
Damien Miller886c63a2000-01-20 23:13:36 +11001287.It Pa /etc/shosts.equiv
Damien Miller32aa1441999-10-29 09:15:49 +10001288This is processed exactly as
1289.Pa /etc/hosts.equiv .
1290However, this file may be useful in environments that want to run both
1291rsh/rlogin and ssh.
1292.It Pa $HOME/.ssh/environment
Damien Miller450a7a12000-03-26 13:04:51 +10001293This file is read into the environment at login (if it exists).
1294It can only contain empty lines, comment lines (that start with
Damien Miller32aa1441999-10-29 09:15:49 +10001295.Ql # ) ,
Damien Miller450a7a12000-03-26 13:04:51 +10001296and assignment lines of the form name=value.
1297The file should be writable
Damien Miller32aa1441999-10-29 09:15:49 +10001298only by the user; it need not be readable by anyone else.
1299.It Pa $HOME/.ssh/rc
1300If this file exists, it is run with /bin/sh after reading the
Damien Miller450a7a12000-03-26 13:04:51 +10001301environment files but before starting the user's shell or command.
1302If X11 spoofing is in use, this will receive the "proto cookie" pair in
Damien Miller32aa1441999-10-29 09:15:49 +10001303standard input (and
1304.Ev DISPLAY
Damien Miller450a7a12000-03-26 13:04:51 +10001305in environment).
1306This must call
Damien Miller32aa1441999-10-29 09:15:49 +10001307.Xr xauth 1
1308in that case.
1309.Pp
1310The primary purpose of this file is to run any initialization routines
1311which may be needed before the user's home directory becomes
1312accessible; AFS is a particular example of such an environment.
1313.Pp
1314This file will probably contain some initialization code followed by
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001315something similar to:
1316.Bd -literal
1317 if read proto cookie; then
1318 echo add $DISPLAY $proto $cookie | xauth -q -
1319 fi
1320.Ed
Damien Miller32aa1441999-10-29 09:15:49 +10001321.Pp
1322If this file does not exist,
Damien Miller886c63a2000-01-20 23:13:36 +11001323.Pa /etc/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +10001324is run, and if that
1325does not exist either, xauth is used to store the cookie.
1326.Pp
1327This file should be writable only by the user, and need not be
1328readable by anyone else.
Damien Miller886c63a2000-01-20 23:13:36 +11001329.It Pa /etc/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +10001330Like
1331.Pa $HOME/.ssh/rc .
1332This can be used to specify
Damien Miller450a7a12000-03-26 13:04:51 +10001333machine-specific login-time initializations globally.
1334This file should be writable only by root, and should be world-readable.
Damien Miller37023962000-07-11 17:31:38 +10001335.El
Damien Miller0bc1bd82000-11-13 22:57:25 +11001336.Sh AUTHORS
Ben Lindstrom8eec2c82001-01-29 08:39:16 +00001337OpenSSH is a derivative of the original and free
1338ssh 1.2.12 release by Tatu Ylonen.
1339Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1340Theo de Raadt and Dug Song
1341removed many bugs, re-added newer features and
1342created OpenSSH.
1343Markus Friedl contributed the support for SSH
1344protocol versions 1.5 and 2.0.
Damien Miller32aa1441999-10-29 09:15:49 +10001345.Sh SEE ALSO
Damien Miller32aa1441999-10-29 09:15:49 +10001346.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +11001347.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +10001348.Xr ssh 1 ,
1349.Xr ssh-add 1 ,
1350.Xr ssh-agent 1 ,
1351.Xr ssh-keygen 1 ,
Ben Lindstromc8e29ce2001-08-06 20:55:28 +00001352.Xr login.conf 5 ,
1353.Xr moduli 5 ,
Ben Lindstromd2bf0d62001-06-25 04:10:54 +00001354.Xr sftp-server 8
Ben Lindstrom160ec622001-04-22 17:17:46 +00001355.Rs
1356.%A T. Ylonen
1357.%A T. Kivinen
1358.%A M. Saarinen
1359.%A T. Rinne
1360.%A S. Lehtinen
1361.%T "SSH Protocol Architecture"
Ben Lindstrom020a8692001-08-06 21:38:10 +00001362.%N draft-ietf-secsh-architecture-09.txt
1363.%D July 2001
Ben Lindstrom160ec622001-04-22 17:17:46 +00001364.%O work in progress material
1365.Re
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001366.Rs
1367.%A M. Friedl
1368.%A N. Provos
1369.%A W. A. Simpson
1370.%T "Diffie-Hellman Group Exchange for the SSH Transport Layer Protocol"
Ben Lindstrom3c798d42001-06-25 04:39:22 +00001371.%N draft-ietf-secsh-dh-group-exchange-01.txt
1372.%D April 2001
Ben Lindstromc65e6a02001-04-23 13:02:16 +00001373.%O work in progress material
1374.Re