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Damien Miller32aa1441999-10-29 09:15:49 +10001.\"
Damien Miller32aa1441999-10-29 09:15:49 +10002.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
Damien Miller32aa1441999-10-29 09:15:49 +10003.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4.\" All rights reserved
5.\"
Damien Millere4340be2000-09-16 13:29:08 +11006.\" As far as I am concerned, the code I have written for this software
7.\" can be used freely for any purpose. Any derived versions of this
8.\" software must be clearly marked as such, and if the derived work is
9.\" incompatible with the protocol description in the RFC file, it must be
10.\" called by a name other than "ssh" or "Secure Shell".
Damien Miller32aa1441999-10-29 09:15:49 +100011.\"
Ben Lindstrom92a2e382001-03-05 06:59:27 +000012.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13.\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14.\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
Damien Millere4340be2000-09-16 13:29:08 +110015.\"
16.\" Redistribution and use in source and binary forms, with or without
17.\" modification, are permitted provided that the following conditions
18.\" are met:
19.\" 1. Redistributions of source code must retain the above copyright
20.\" notice, this list of conditions and the following disclaimer.
21.\" 2. Redistributions in binary form must reproduce the above copyright
22.\" notice, this list of conditions and the following disclaimer in the
23.\" documentation and/or other materials provided with the distribution.
24.\"
25.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
31.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
32.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
34.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Damien Miller32aa1441999-10-29 09:15:49 +100035.\"
djm@openbsd.org83b58182016-08-19 03:18:06 +000036.\" $OpenBSD: sshd.8,v 1.286 2016/08/19 03:18:06 djm Exp $
37.Dd $Mdocdate: August 19 2016 $
Damien Miller32aa1441999-10-29 09:15:49 +100038.Dt SSHD 8
39.Os
40.Sh NAME
41.Nm sshd
Ben Lindstromc65e6a02001-04-23 13:02:16 +000042.Nd OpenSSH SSH daemon
Damien Miller32aa1441999-10-29 09:15:49 +100043.Sh SYNOPSIS
44.Nm sshd
Damien Millerffadc582003-02-24 11:52:26 +110045.Bk -words
Darren Tuckere7f3f752008-06-10 23:06:01 +100046.Op Fl 46DdeiqTt
Darren Tuckere7140f22008-06-10 23:01:51 +100047.Op Fl C Ar connection_spec
Damien Miller0a80ca12010-02-27 07:55:05 +110048.Op Fl c Ar host_certificate_file
Damien Miller03d4d7e2013-04-23 15:21:06 +100049.Op Fl E Ar log_file
Damien Miller32aa1441999-10-29 09:15:49 +100050.Op Fl f Ar config_file
51.Op Fl g Ar login_grace_time
52.Op Fl h Ar host_key_file
Ben Lindstromade03f62001-12-06 18:22:17 +000053.Op Fl o Ar option
Damien Miller32aa1441999-10-29 09:15:49 +100054.Op Fl p Ar port
Damien Miller942da032000-08-18 13:59:06 +100055.Op Fl u Ar len
Damien Millerffadc582003-02-24 11:52:26 +110056.Ek
Damien Miller22c77262000-04-13 12:26:34 +100057.Sh DESCRIPTION
Damien Miller32aa1441999-10-29 09:15:49 +100058.Nm
Damien Miller99cc4a82006-01-31 21:45:53 +110059(OpenSSH Daemon) is the daemon program for
Damien Miller32aa1441999-10-29 09:15:49 +100060.Xr ssh 1 .
Damien Miller69cb24b2014-04-20 13:29:06 +100061Together these programs replace rlogin and rsh,
Darren Tucker04354b92007-03-21 20:46:54 +110062and provide secure encrypted communications between two untrusted hosts
Damien Miller450a7a12000-03-26 13:04:51 +100063over an insecure network.
Damien Miller32aa1441999-10-29 09:15:49 +100064.Pp
65.Nm
Damien Miller99cc4a82006-01-31 21:45:53 +110066listens 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 Miller32aa1441999-10-29 09:15:49 +100074.Pp
75.Nm
Darren Tucker1f203942003-10-15 15:50:42 +100076can be configured using command-line options or a configuration file
77(by default
Damien Miller99cc4a82006-01-31 21:45:53 +110078.Xr sshd_config 5 ) ;
79command-line options override values specified in the
Damien Miller32aa1441999-10-29 09:15:49 +100080configuration file.
Damien Miller6162d121999-11-21 13:23:52 +110081.Nm
82rereads its configuration file when it receives a hangup signal,
Ben Lindstrom49a098d2001-03-05 06:55:18 +000083.Dv SIGHUP ,
Damien Miller208f1ed2006-03-15 11:56:03 +110084by executing itself with the name and options it was started with, e.g.\&
Ben Lindstrom49a098d2001-03-05 06:55:18 +000085.Pa /usr/sbin/sshd .
Damien Miller6162d121999-11-21 13:23:52 +110086.Pp
Damien Miller32aa1441999-10-29 09:15:49 +100087The options are as follows:
88.Bl -tag -width Ds
Darren Tucker1f203942003-10-15 15:50:42 +100089.It Fl 4
90Forces
91.Nm
92to use IPv4 addresses only.
93.It Fl 6
94Forces
95.Nm
96to use IPv6 addresses only.
Darren Tuckere7f3f752008-06-10 23:06:01 +100097.It Fl C Ar connection_spec
98Specify the connection parameters to use for the
99.Fl T
100extended test mode.
101If provided, any
102.Cm Match
103directives in the configuration file
104that would apply to the specified user, host, and address will be set before
105the configuration is written to standard output.
106The connection parameters are supplied as keyword=value pairs.
107The keywords are
108.Dq user ,
109.Dq host ,
Darren Tuckerfbcf8272012-05-19 19:37:01 +1000110.Dq laddr ,
111.Dq lport ,
Darren Tuckere7f3f752008-06-10 23:06:01 +1000112and
113.Dq addr .
114All are required and may be supplied in any order, either with multiple
115.Fl C
116options or as a comma-separated list.
Damien Miller15f5b562010-03-03 10:25:21 +1100117.It Fl c Ar host_certificate_file
118Specifies a path to a certificate file to identify
119.Nm
120during key exchange.
121The certificate file must match a host key file specified using the
122.Fl h
123option or the
124.Cm HostKey
125configuration directive.
Darren Tucker1f203942003-10-15 15:50:42 +1000126.It Fl D
127When this option is specified,
128.Nm
129will not detach and does not become a daemon.
130This allows easy monitoring of
131.Nm sshd .
Damien Miller32aa1441999-10-29 09:15:49 +1000132.It Fl d
Damien Miller450a7a12000-03-26 13:04:51 +1000133Debug mode.
Damien Miller74d98252010-02-02 17:01:46 +1100134The server sends verbose debug output to standard error,
135and does not put itself in the background.
Damien Miller450a7a12000-03-26 13:04:51 +1000136The server also will not fork and will only process one connection.
137This option is only intended for debugging for the server.
Damien Millerffadc582003-02-24 11:52:26 +1100138Multiple
139.Fl d
140options increase the debugging level.
Damien Miller874d77b2000-10-14 16:23:11 +1100141Maximum is 3.
Damien Miller03d4d7e2013-04-23 15:21:06 +1000142.It Fl E Ar log_file
143Append debug logs to
144.Ar log_file
145instead of the system log.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000146.It Fl e
Damien Miller69010322013-04-23 15:21:24 +1000147Write debug logs to standard error instead of the system log.
Darren Tucker04354b92007-03-21 20:46:54 +1100148.It Fl f Ar config_file
Damien Miller450a7a12000-03-26 13:04:51 +1000149Specifies the name of the configuration file.
150The default is
Damien Miller05eda432002-02-10 18:32:28 +1100151.Pa /etc/ssh/sshd_config .
Damien Miller32aa1441999-10-29 09:15:49 +1000152.Nm
153refuses to start if there is no configuration file.
154.It Fl g Ar login_grace_time
155Gives the grace time for clients to authenticate themselves (default
Damien Millerc1348632002-09-05 14:35:14 +1000156120 seconds).
Damien Miller450a7a12000-03-26 13:04:51 +1000157If the client fails to authenticate the user within
158this many seconds, the server disconnects and exits.
159A value of zero indicates no limit.
Damien Miller32aa1441999-10-29 09:15:49 +1000160.It Fl h Ar host_key_file
Damien Miller7fc23732002-01-22 23:19:11 +1100161Specifies a file from which a host key is read.
Damien Miller32aa1441999-10-29 09:15:49 +1000162This option must be given if
163.Nm
164is not run as root (as the normal
Damien Miller7fc23732002-01-22 23:19:11 +1100165host key files are normally not readable by anyone but root).
166The default is
Damien Millereb8b60e2010-08-31 22:41:14 +1000167.Pa /etc/ssh/ssh_host_dsa_key ,
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000168.Pa /etc/ssh/ssh_host_ecdsa_key ,
Damien Miller8ba0ead2013-12-18 17:46:27 +1100169.Pa /etc/ssh/ssh_host_ed25519_key
Damien Miller7fc23732002-01-22 23:19:11 +1100170and
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000171.Pa /etc/ssh/ssh_host_rsa_key .
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000172It is possible to have multiple host key files for
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000173the different host key algorithms.
Damien Miller32aa1441999-10-29 09:15:49 +1000174.It Fl i
175Specifies that
176.Nm
Damien Millerffadc582003-02-24 11:52:26 +1100177is being run from
178.Xr inetd 8 .
Ben Lindstromade03f62001-12-06 18:22:17 +0000179.It Fl o Ar option
180Can be used to give options in the format used in the configuration file.
181This is useful for specifying options for which there is no separate
182command-line flag.
Darren Tucker1f203942003-10-15 15:50:42 +1000183For full details of the options, and their values, see
184.Xr sshd_config 5 .
Damien Miller32aa1441999-10-29 09:15:49 +1000185.It Fl p Ar port
186Specifies the port on which the server listens for connections
187(default 22).
Damien Miller7d1ded42002-01-22 23:09:41 +1100188Multiple port options are permitted.
Damien Millerd7f308f2005-12-24 14:55:16 +1100189Ports specified in the configuration file with the
190.Cm Port
191option are ignored when a command-line port is specified.
192Ports specified using the
193.Cm ListenAddress
194option override command-line ports.
Damien Miller32aa1441999-10-29 09:15:49 +1000195.It Fl q
Damien Miller450a7a12000-03-26 13:04:51 +1000196Quiet mode.
197Nothing is sent to the system log.
198Normally the beginning,
Damien Miller32aa1441999-10-29 09:15:49 +1000199authentication, and termination of each connection is logged.
Darren Tuckere7140f22008-06-10 23:01:51 +1000200.It Fl T
201Extended test mode.
202Check the validity of the configuration file, output the effective configuration
203to stdout and then exit.
204Optionally,
205.Cm Match
206rules may be applied by specifying the connection parameters using one or more
207.Fl C
208options.
Darren Tuckere7f3f752008-06-10 23:06:01 +1000209.It Fl t
210Test mode.
211Only check the validity of the configuration file and sanity of the keys.
212This is useful for updating
213.Nm
214reliably as configuration options may change.
Damien Miller942da032000-08-18 13:59:06 +1000215.It Fl u Ar len
216This option is used to specify the size of the field
217in the
218.Li utmp
219structure that holds the remote host name.
220If the resolved host name is longer than
221.Ar len ,
222the dotted decimal value will be used instead.
223This allows hosts with very long host names that
224overflow this field to still be uniquely identified.
225Specifying
226.Fl u0
227indicates that only dotted decimal addresses
228should be put into the
229.Pa utmp
230file.
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000231.Fl u0
Damien Millerffadc582003-02-24 11:52:26 +1100232may also be used to prevent
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000233.Nm
234from making DNS requests unless the authentication
235mechanism or configuration requires it.
236Authentication mechanisms that may require DNS include
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000237.Cm HostbasedAuthentication
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000238and using a
239.Cm from="pattern-list"
240option in a key file.
Ben Lindstromea03db92002-03-05 01:38:57 +0000241Configuration options that require DNS include using a
242USER@HOST pattern in
243.Cm AllowUsers
244or
245.Cm DenyUsers .
Damien Miller32aa1441999-10-29 09:15:49 +1000246.El
Damien Miller8bbdf902006-02-01 22:05:25 +1100247.Sh AUTHENTICATION
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000248The OpenSSH SSH daemon supports SSH protocol 2 only.
jmc@openbsd.orga685ae82016-02-17 07:38:19 +0000249Each host has a host-specific key,
250used to identify the host.
Damien Miller99cc4a82006-01-31 21:45:53 +1100251Whenever a client connects, the daemon responds with its public
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000252host key.
Damien Miller99cc4a82006-01-31 21:45:53 +1100253The client compares the
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000254host key against its own database to verify that it has not changed.
255Forward security is provided through a Diffie-Hellman key agreement.
Damien Miller8bbdf902006-02-01 22:05:25 +1100256This key agreement results in a shared session key.
257The rest of the session is encrypted using a symmetric cipher, currently
258128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES.
259The client selects the encryption algorithm
260to use from those offered by the server.
261Additionally, session integrity is provided
262through a cryptographic message authentication code
Darren Tucker427e4092012-10-05 11:02:39 +1000263(hmac-md5, hmac-sha1, umac-64, umac-128, hmac-ripemd160,
Damien Miller20bd4532011-08-06 06:17:30 +1000264hmac-sha2-256 or hmac-sha2-512).
Damien Miller8bbdf902006-02-01 22:05:25 +1100265.Pp
266Finally, the server and the client enter an authentication dialog.
Damien Miller99cc4a82006-01-31 21:45:53 +1100267The client tries to authenticate itself using
Damien Miller8bbdf902006-02-01 22:05:25 +1100268host-based authentication,
269public key authentication,
270challenge-response authentication,
271or password authentication.
Damien Miller99cc4a82006-01-31 21:45:53 +1100272.Pp
273Regardless of the authentication type, the account is checked to
274ensure that it is accessible. An account is not accessible if it is
275locked, listed in
276.Cm DenyUsers
277or its group is listed in
278.Cm DenyGroups
279\&. The definition of a locked account is system dependant. Some platforms
280have their own account database (eg AIX) and some modify the passwd field (
281.Ql \&*LK\&*
282on Solaris and UnixWare,
283.Ql \&*
284on HP-UX, containing
285.Ql Nologin
286on Tru64,
287a leading
288.Ql \&*LOCKED\&*
289on FreeBSD and a leading
Darren Tucker1a9176b2007-08-17 09:42:32 +1000290.Ql \&!
291on most Linuxes).
292If there is a requirement to disable password authentication
Damien Miller99cc4a82006-01-31 21:45:53 +1100293for the account while allowing still public-key, then the passwd field
294should be set to something other than these values (eg
295.Ql NP
296or
297.Ql \&*NP\&*
298).
299.Pp
Damien Miller99cc4a82006-01-31 21:45:53 +1100300If the client successfully authenticates itself, a dialog for
301preparing the session is entered.
302At this time the client may request
303things like allocating a pseudo-tty, forwarding X11 connections,
304forwarding TCP connections, or forwarding the authentication agent
305connection over the secure channel.
306.Pp
Damien Millerc47d7e92006-03-15 11:27:20 +1100307After this, the client either requests a shell or execution of a command.
Damien Miller99cc4a82006-01-31 21:45:53 +1100308The sides then enter session mode.
309In this mode, either side may send
310data at any time, and such data is forwarded to/from the shell or
311command on the server side, and the user terminal in the client side.
312.Pp
313When the user program terminates and all forwarded X11 and other
314connections have been closed, the server sends command exit status to
315the client, and both sides exit.
Damien Miller32aa1441999-10-29 09:15:49 +1000316.Sh LOGIN PROCESS
317When a user successfully logs in,
318.Nm
319does the following:
320.Bl -enum -offset indent
321.It
322If the login is on a tty, and no command has been specified,
Damien Miller22c77262000-04-13 12:26:34 +1000323prints last login time and
Damien Miller32aa1441999-10-29 09:15:49 +1000324.Pa /etc/motd
325(unless prevented in the configuration file or by
Damien Miller167ea5d2005-05-26 12:04:02 +1000326.Pa ~/.hushlogin ;
Damien Miller32aa1441999-10-29 09:15:49 +1000327see the
Damien Miller22c77262000-04-13 12:26:34 +1000328.Sx FILES
Damien Miller32aa1441999-10-29 09:15:49 +1000329section).
330.It
331If the login is on a tty, records login time.
332.It
333Checks
334.Pa /etc/nologin ;
335if it exists, prints contents and quits
336(unless root).
337.It
338Changes to run with normal user privileges.
339.It
340Sets up basic environment.
341.It
Darren Tucker1f203942003-10-15 15:50:42 +1000342Reads the file
Damien Miller167ea5d2005-05-26 12:04:02 +1000343.Pa ~/.ssh/environment ,
Darren Tucker1f203942003-10-15 15:50:42 +1000344if it exists, and users are allowed to change their environment.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000345See the
Ben Lindstromdc7adf22002-08-20 18:38:02 +0000346.Cm PermitUserEnvironment
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000347option in
Ben Lindstromdc7adf22002-08-20 18:38:02 +0000348.Xr sshd_config 5 .
Damien Miller32aa1441999-10-29 09:15:49 +1000349.It
350Changes to user's home directory.
351.It
352If
Damien Miller167ea5d2005-05-26 12:04:02 +1000353.Pa ~/.ssh/rc
Damien Miller72e6b5c2014-07-04 09:00:04 +1000354exists and the
355.Xr sshd_config 5
356.Cm PermitUserRC
357option is set, runs it; else if
Damien Millerafcc2252002-02-10 18:32:55 +1100358.Pa /etc/ssh/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +1000359exists, runs
Damien Miller450a7a12000-03-26 13:04:51 +1000360it; otherwise runs xauth.
361The
Damien Miller32aa1441999-10-29 09:15:49 +1000362.Dq rc
363files are given the X11
364authentication protocol and cookie in standard input.
Damien Millerfd725cf2006-03-15 11:35:54 +1100365See
366.Sx SSHRC ,
367below.
Damien Miller32aa1441999-10-29 09:15:49 +1000368.It
369Runs user's shell or command.
djm@openbsd.org8d4d1bf2015-05-01 07:11:47 +0000370All commands are run under the user's login shell as specified in the
371system password database.
Damien Miller32aa1441999-10-29 09:15:49 +1000372.El
Damien Millerfd725cf2006-03-15 11:35:54 +1100373.Sh SSHRC
374If the file
375.Pa ~/.ssh/rc
376exists,
377.Xr sh 1
378runs it after reading the
379environment files but before starting the user's shell or command.
380It must not produce any output on stdout; stderr must be used
381instead.
382If X11 forwarding is in use, it will receive the "proto cookie" pair in
383its standard input (and
384.Ev DISPLAY
385in its environment).
386The script must call
387.Xr xauth 1
388because
389.Nm
390will not run xauth automatically to add X11 cookies.
391.Pp
392The primary purpose of this file is to run any initialization routines
393which may be needed before the user's home directory becomes
394accessible; AFS is a particular example of such an environment.
395.Pp
396This file will probably contain some initialization code followed by
397something similar to:
398.Bd -literal -offset 3n
399if read proto cookie && [ -n "$DISPLAY" ]; then
400 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
401 # X11UseLocalhost=yes
402 echo add unix:`echo $DISPLAY |
403 cut -c11-` $proto $cookie
404 else
405 # X11UseLocalhost=no
406 echo add $DISPLAY $proto $cookie
407 fi | xauth -q -
408fi
409.Ed
410.Pp
411If this file does not exist,
412.Pa /etc/ssh/sshrc
413is run, and if that
414does not exist either, xauth is used to add the cookie.
Damien Miller32aa1441999-10-29 09:15:49 +1000415.Sh AUTHORIZED_KEYS FILE FORMAT
Ben Lindstromf96704d2001-06-25 04:17:12 +0000416.Cm AuthorizedKeysFile
Damien Millerb9132fc2011-05-29 21:41:40 +1000417specifies the files containing public keys for
Damien Millerdcfea272006-03-15 11:31:22 +1100418public key authentication;
djm@openbsd.org2bca8a42015-09-11 03:13:36 +0000419if this option is not specified, the default is
Damien Millerd8478b62011-05-29 21:39:36 +1000420.Pa ~/.ssh/authorized_keys
421and
422.Pa ~/.ssh/authorized_keys2 .
Damien Miller450a7a12000-03-26 13:04:51 +1000423Each line of the file contains one
Damien Miller32aa1441999-10-29 09:15:49 +1000424key (empty lines and lines starting with a
425.Ql #
426are ignored as
Damien Miller450a7a12000-03-26 13:04:51 +1000427comments).
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000428Public keys consist of the following space-separated fields:
Damien Millerdcfea272006-03-15 11:31:22 +1100429options, keytype, base64-encoded key, comment.
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000430The options field is optional.
431The keytype is
Damien Millereb8b60e2010-08-31 22:41:14 +1000432.Dq ecdsa-sha2-nistp256 ,
433.Dq ecdsa-sha2-nistp384 ,
434.Dq ecdsa-sha2-nistp521 ,
Damien Millera7827c12013-12-07 11:24:30 +1100435.Dq ssh-ed25519 ,
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000436.Dq ssh-dss
437or
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000438.Dq ssh-rsa ;
439the comment field is not used for anything (but may be convenient for the
440user to identify the key).
Damien Miller32aa1441999-10-29 09:15:49 +1000441.Pp
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000442Note that lines in this file can be several hundred bytes long
Darren Tucker22cc7412004-12-06 22:47:41 +1100443(because of the size of the public key encoding) up to a limit of
4448 kilobytes, which permits DSA keys up to 8 kilobits and RSA
445keys up to 16 kilobits.
Damien Miller450a7a12000-03-26 13:04:51 +1000446You don't want to type them in; instead, copy the
Damien Millerdcfea272006-03-15 11:31:22 +1100447.Pa id_dsa.pub ,
Damien Millereb8b60e2010-08-31 22:41:14 +1000448.Pa id_ecdsa.pub ,
Damien Miller8ba0ead2013-12-18 17:46:27 +1100449.Pa id_ed25519.pub ,
Ben Lindstrom18a82ac2001-04-11 15:59:35 +0000450or the
451.Pa id_rsa.pub
Damien Miller32aa1441999-10-29 09:15:49 +1000452file and edit it.
453.Pp
Ben Lindstrom0d0be022002-04-02 20:39:29 +0000454.Nm
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000455enforces a minimum RSA key modulus size of 768 bits.
Ben Lindstrom0d0be022002-04-02 20:39:29 +0000456.Pp
Damien Miller942da032000-08-18 13:59:06 +1000457The options (if present) consist of comma-separated option
Damien Miller450a7a12000-03-26 13:04:51 +1000458specifications.
459No spaces are permitted, except within double quotes.
Ben Lindstrom1c0fd092001-09-12 16:36:17 +0000460The following option specifications are supported (note
461that option keywords are case-insensitive):
Damien Miller32aa1441999-10-29 09:15:49 +1000462.Bl -tag -width Ds
djm@openbsd.org383f10f2015-11-16 00:30:02 +0000463.It Cm agent-forwarding
464Enable authentication agent forwarding previously disabled by the
465.Cm restrict
466option.
Damien Millercd38c9c2010-03-04 21:51:37 +1100467.It Cm cert-authority
Damien Miller0a80ca12010-02-27 07:55:05 +1100468Specifies that the listed key is a certification authority (CA) that is
469trusted to validate signed certificates for user authentication.
470.Pp
471Certificates may encode access restrictions similar to these key options.
472If both certificate restrictions and key options are present, the most
473restrictive union of the two is applied.
Damien Miller32aa1441999-10-29 09:15:49 +1000474.It Cm command="command"
475Specifies that the command is executed whenever this key is used for
Damien Miller450a7a12000-03-26 13:04:51 +1000476authentication.
477The command supplied by the user (if any) is ignored.
Ben Lindstrom23124ea2001-09-14 23:14:25 +0000478The command is run on a pty if the client requests a pty;
Damien Miller450a7a12000-03-26 13:04:51 +1000479otherwise it is run without a tty.
Damien Millerffadc582003-02-24 11:52:26 +1100480If an 8-bit clean channel is required,
Ben Lindstrom594e2032001-09-12 18:35:30 +0000481one must not request a pty or should specify
Damien Miller33804262001-02-04 23:20:18 +1100482.Cm no-pty .
Damien Miller450a7a12000-03-26 13:04:51 +1000483A quote may be included in the command by quoting it with a backslash.
484This option might be useful
Damien Millerb83df8d2002-09-04 16:24:55 +1000485to restrict certain public keys to perform just a specific operation.
Damien Miller450a7a12000-03-26 13:04:51 +1000486An example might be a key that permits remote backups but nothing else.
Damien Miller7c24b812006-01-14 10:09:56 +1100487Note that the client may specify TCP and/or X11
Damien Miller30c3d422000-05-09 11:02:59 +1000488forwarding unless they are explicitly prohibited.
Damien Millere2754432006-07-24 14:06:47 +1000489The command originally supplied by the client is available in the
490.Ev SSH_ORIGINAL_COMMAND
491environment variable.
Ben Lindstrom20daef72001-09-20 00:54:01 +0000492Note that this option applies to shell, command or subsystem execution.
Damien Miller0a80ca12010-02-27 07:55:05 +1100493Also note that this command may be superseded by either a
494.Xr sshd_config 5
495.Cm ForceCommand
496directive or a command embedded in a certificate.
Damien Miller32aa1441999-10-29 09:15:49 +1000497.It Cm environment="NAME=value"
498Specifies that the string is to be added to the environment when
Damien Miller450a7a12000-03-26 13:04:51 +1000499logging in using this key.
500Environment variables set this way
501override other default environment values.
502Multiple options of this type are permitted.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000503Environment processing is disabled by default and is
504controlled via the
505.Cm PermitUserEnvironment
506option.
Damien Miller31bdc522006-03-15 11:31:44 +1100507.It Cm from="pattern-list"
Darren Tucker896ad5a2008-06-11 09:34:46 +1000508Specifies that in addition to public key authentication, either the canonical
Darren Tucker11996732008-06-13 04:32:00 +1000509name of the remote host or its IP address must be present in the
Darren Tucker896ad5a2008-06-11 09:34:46 +1000510comma-separated list of patterns.
Damien Millerfecfd112013-07-18 16:11:50 +1000511See PATTERNS in
Damien Millerc7d5b5e2006-03-15 11:55:08 +1100512.Xr ssh_config 5
513for more information on patterns.
Darren Tucker896ad5a2008-06-11 09:34:46 +1000514.Pp
515In addition to the wildcard matching that may be applied to hostnames or
516addresses, a
517.Cm from
Darren Tucker5837b512009-06-21 17:52:27 +1000518stanza may match IP addresses using CIDR address/masklen notation.
Darren Tucker896ad5a2008-06-11 09:34:46 +1000519.Pp
520The purpose of this option is to optionally increase security: public key
521authentication by itself does not trust the network or name servers or
522anything (but the key); however, if somebody somehow steals the key, the key
523permits an intruder to log in from anywhere in the world.
524This additional option makes using a stolen key more difficult (name
525servers and/or routers would have to be compromised in addition to
526just the key).
Damien Miller31bdc522006-03-15 11:31:44 +1100527.It Cm no-agent-forwarding
528Forbids authentication agent forwarding when this key is used for
529authentication.
Damien Miller32aa1441999-10-29 09:15:49 +1000530.It Cm no-port-forwarding
Damien Miller7c24b812006-01-14 10:09:56 +1100531Forbids TCP forwarding when this key is used for authentication.
Damien Miller450a7a12000-03-26 13:04:51 +1000532Any port forward requests by the client will return an error.
Damien Miller208f1ed2006-03-15 11:56:03 +1100533This might be used, e.g. in connection with the
Damien Miller32aa1441999-10-29 09:15:49 +1000534.Cm command
535option.
Damien Miller31bdc522006-03-15 11:31:44 +1100536.It Cm no-pty
537Prevents tty allocation (a request to allocate a pty will fail).
Damien Miller95e80952008-03-27 11:03:05 +1100538.It Cm no-user-rc
Damien Miller13ba9c22008-04-03 20:52:51 +1100539Disables execution of
Damien Miller95e80952008-03-27 11:03:05 +1100540.Pa ~/.ssh/rc .
Damien Miller32aa1441999-10-29 09:15:49 +1000541.It Cm no-X11-forwarding
542Forbids X11 forwarding when this key is used for authentication.
543Any X11 forward requests by the client will return an error.
Damien Millera243fde2001-03-19 23:16:08 +1100544.It Cm permitopen="host:port"
bentley@openbsd.orgda8af832014-11-15 14:41:03 +0000545Limit local port forwarding with
546.Xr ssh 1
547.Fl L
548such that it may only connect to the specified host and port.
Damien Miller7fa96602010-08-05 13:03:13 +1000549IPv6 addresses can be specified by enclosing the address in square brackets.
Ben Lindstromd71ba572001-09-12 18:03:31 +0000550Multiple
Damien Millera243fde2001-03-19 23:16:08 +1100551.Cm permitopen
Damien Millerfbf486b2003-05-23 18:44:23 +1000552options may be applied separated by commas.
553No pattern matching is performed on the specified hostnames,
554they must be literal domains or addresses.
Darren Tucker1338b9e2011-10-02 18:57:35 +1100555A port specification of
556.Cm *
557matches any port.
djm@openbsd.org383f10f2015-11-16 00:30:02 +0000558.It Cm port-forwarding
559Enable port forwarding previously disabled by the
560.Cm restrict
Damien Miller30da3442010-05-10 11:58:03 +1000561.It Cm principals="principals"
562On a
563.Cm cert-authority
564line, specifies allowed principals for certificate authentication as a
565comma-separated list.
566At least one name from the list must appear in the certificate's
567list of principals for the certificate to be accepted.
568This option is ignored for keys that are not marked as trusted certificate
569signers using the
570.Cm cert-authority
571option.
djm@openbsd.org383f10f2015-11-16 00:30:02 +0000572.It Cm pty
573Permits tty allocation previously disabled by the
574.Cm restrict
575option.
576.It Cm restrict
577Enable all restrictions, i.e. disable port, agent and X11 forwarding,
578as well as disabling PTY allocation
579and execution of
580.Pa ~/.ssh/rc .
581If any future restriction capabilities are added to authorized_keys files
582they will be included in this set.
Damien Millerd27b9472005-12-13 19:29:02 +1100583.It Cm tunnel="n"
584Force a
585.Xr tun 4
586device on the server.
587Without this option, the next available device will be used if
588the client requests a tunnel.
djm@openbsd.org383f10f2015-11-16 00:30:02 +0000589.It Cm user-rc
590Enables execution of
591.Pa ~/.ssh/rc
592previously disabled by the
593.Cm restrict
594option.
595.It Cm X11-forwarding
596Permits X11 forwarding previously disabled by the
597.Cm restrict
598option.
Damien Miller32aa1441999-10-29 09:15:49 +1000599.El
Damien Miller32aa1441999-10-29 09:15:49 +1000600.Pp
Damien Miller7d2ef022006-03-15 11:32:06 +1100601An example authorized_keys file:
Damien Millerc8f61cf2006-03-15 11:33:25 +1100602.Bd -literal -offset 3n
Damien Miller7d2ef022006-03-15 11:32:06 +1100603# Comments allowed at start of line
604ssh-rsa AAAAB3Nza...LiPk== user@example.net
Damien Millerc8f61cf2006-03-15 11:33:25 +1100605from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
606AAAAB2...19Q== john@example.net
607command="dump /home",no-pty,no-port-forwarding ssh-dss
608AAAAC3...51R== example.net
609permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss
610AAAAB5...21S==
611tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
612jane@example.net
djm@openbsd.org383f10f2015-11-16 00:30:02 +0000613restrict,command="uptime" ssh-rsa AAAA1C8...32Tv==
614user@example.net
615restrict,pty,command="nethack" ssh-rsa AAAA1f8...IrrC5==
616user@example.net
Damien Miller7d2ef022006-03-15 11:32:06 +1100617.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000618.Sh SSH_KNOWN_HOSTS FILE FORMAT
Damien Miller22c77262000-04-13 12:26:34 +1000619The
Damien Millerffadc582003-02-24 11:52:26 +1100620.Pa /etc/ssh/ssh_known_hosts
Damien Miller22c77262000-04-13 12:26:34 +1000621and
Damien Miller167ea5d2005-05-26 12:04:02 +1000622.Pa ~/.ssh/known_hosts
Damien Miller450a7a12000-03-26 13:04:51 +1000623files contain host public keys for all known hosts.
624The global file should
625be prepared by the administrator (optional), and the per-user file is
Damien Miller9a7f2012006-03-15 11:32:42 +1100626maintained automatically: whenever the user connects from an unknown host,
Damien Miller450a7a12000-03-26 13:04:51 +1000627its key is added to the per-user file.
Damien Miller32aa1441999-10-29 09:15:49 +1000628.Pp
Damien Millera7dab8b2010-03-05 10:42:05 +1100629Each line in these files contains the following fields: markers (optional),
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000630hostnames, keytype, base64-encoded key, comment.
Damien Miller450a7a12000-03-26 13:04:51 +1000631The fields are separated by spaces.
Damien Miller32aa1441999-10-29 09:15:49 +1000632.Pp
Damien Millera7dab8b2010-03-05 10:42:05 +1100633The marker is optional, but if it is present then it must be one of
634.Dq @cert-authority ,
635to indicate that the line contains a certification authority (CA) key,
636or
637.Dq @revoked ,
638to indicate that the key contained on the line is revoked and must not ever
639be accepted.
640Only one marker should be used on a key line.
641.Pp
Damien Miller31554322003-05-14 13:44:58 +1000642Hostnames is a comma-separated list of patterns
Damien Miller9a7f2012006-03-15 11:32:42 +1100643.Pf ( Ql *
Damien Millerfbf486b2003-05-23 18:44:23 +1000644and
645.Ql \&?
Damien Miller049245d2003-05-14 13:44:42 +1000646act as
Damien Miller32aa1441999-10-29 09:15:49 +1000647wildcards); each pattern in turn is matched against the canonical host
648name (when authenticating a client) or against the user-supplied
Damien Miller450a7a12000-03-26 13:04:51 +1000649name (when authenticating a server).
650A pattern may also be preceded by
Damien Miller049245d2003-05-14 13:44:42 +1000651.Ql \&!
Damien Miller32aa1441999-10-29 09:15:49 +1000652to indicate negation: if the host name matches a negated
653pattern, it is not accepted (by that line) even if it matched another
654pattern on the line.
Darren Tuckerda345532006-07-10 23:04:19 +1000655A hostname or address may optionally be enclosed within
656.Ql \&[
657and
658.Ql \&]
659brackets then followed by
660.Ql \&:
Darren Tucker11318472006-07-12 22:07:59 +1000661and a non-standard port number.
Damien Miller32aa1441999-10-29 09:15:49 +1000662.Pp
Damien Millere1776152005-03-01 21:47:37 +1100663Alternately, hostnames may be stored in a hashed form which hides host names
Damien Miller718fd4b2005-03-02 12:03:23 +1100664and addresses should the file's contents be disclosed.
665Hashed hostnames start with a
666.Ql |
Damien Millere1776152005-03-01 21:47:37 +1100667character.
668Only one hashed hostname may appear on a single line and none of the above
669negation or wildcard operators may be applied.
670.Pp
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000671The keytype and base64-encoded key are taken directly from the host key; they
Damien Miller9a7f2012006-03-15 11:32:42 +1100672can be obtained, for example, from
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000673.Pa /etc/ssh/ssh_host_rsa_key.pub .
Damien Miller32aa1441999-10-29 09:15:49 +1000674The optional comment field continues to the end of the line, and is not used.
675.Pp
676Lines starting with
677.Ql #
678and empty lines are ignored as comments.
679.Pp
680When performing host authentication, authentication is accepted if any
Damien Millera7dab8b2010-03-05 10:42:05 +1100681matching line has the proper key; either one that matches exactly or,
682if the server has presented a certificate for authentication, the key
683of the certification authority that signed the certificate.
684For a key to be trusted as a certification authority, it must use the
685.Dq @cert-authority
686marker described above.
687.Pp
688The known hosts file also provides a facility to mark keys as revoked,
689for example when it is known that the associated private key has been
690stolen.
691Revoked keys are specified by including the
692.Dq @revoked
693marker at the beginning of the key line, and are never accepted for
694authentication or as certification authorities, but instead will
695produce a warning from
696.Xr ssh 1
697when they are encountered.
698.Pp
699It is permissible (but not
Damien Miller32aa1441999-10-29 09:15:49 +1000700recommended) to have several lines or different host keys for the same
Damien Miller450a7a12000-03-26 13:04:51 +1000701names.
702This will inevitably happen when short forms of host names
703from different domains are put in the file.
704It is possible
Damien Miller32aa1441999-10-29 09:15:49 +1000705that the files contain conflicting information; authentication is
706accepted if valid information can be found from either file.
707.Pp
708Note that the lines in these files are typically hundreds of characters
709long, and you definitely don't want to type in the host keys by hand.
Damien Millera7dab8b2010-03-05 10:42:05 +1100710Rather, generate them by a script,
711.Xr ssh-keyscan 1
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000712or by taking, for example,
713.Pa /etc/ssh/ssh_host_rsa_key.pub
Damien Miller32aa1441999-10-29 09:15:49 +1000714and adding the host names at the front.
Damien Millera7dab8b2010-03-05 10:42:05 +1100715.Xr ssh-keygen 1
Damien Miller98339052010-03-05 21:30:35 +1100716also offers some basic automated editing for
Damien Millera7dab8b2010-03-05 10:42:05 +1100717.Pa ~/.ssh/known_hosts
718including removing hosts matching a host name and converting all host
719names to their hashed representations.
Damien Millercc00f5e2006-03-15 11:33:00 +1100720.Pp
721An example ssh_known_hosts file:
722.Bd -literal -offset 3n
723# Comments allowed at start of line
724closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
725cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
Damien Millere1776152005-03-01 21:47:37 +1100726# A hashed hostname
727|1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
728AAAA1234.....=
Damien Millera7dab8b2010-03-05 10:42:05 +1100729# A revoked key
730@revoked * ssh-rsa AAAAB5W...
731# A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
732@cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
Damien Millere1776152005-03-01 21:47:37 +1100733.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000734.Sh FILES
Damien Millerd8702e82006-03-15 11:33:56 +1100735.Bl -tag -width Ds -compact
Damien Millerafdae612010-08-31 22:31:14 +1000736.It Pa ~/.hushlogin
Damien Miller70a908e2005-03-01 21:17:09 +1100737This file is used to suppress printing the last login time and
738.Pa /etc/motd ,
739if
740.Cm PrintLastLog
741and
742.Cm PrintMotd ,
743respectively,
744are enabled.
745It does not suppress printing of the banner specified by
746.Cm Banner .
Damien Millerd8702e82006-03-15 11:33:56 +1100747.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000748.It Pa ~/.rhosts
Damien Milleradc35b92006-03-15 11:35:27 +1100749This file is used for host-based authentication (see
750.Xr ssh 1
751for more information).
752On some machines this file may need to be
753world-readable if the user's home directory is on an NFS partition,
754because
755.Nm
756reads it as root.
757Additionally, this file must be owned by the user,
758and must not have write permissions for anyone else.
759The recommended
760permission for most machines is read/write for the user, and not
Damien Miller32aa1441999-10-29 09:15:49 +1000761accessible by others.
762.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000763.It Pa ~/.shosts
Damien Milleradc35b92006-03-15 11:35:27 +1100764This file is used in exactly the same way as
765.Pa .rhosts ,
766but allows host-based authentication without permitting login with
767rlogin/rsh.
Damien Miller32aa1441999-10-29 09:15:49 +1000768.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000769.It Pa ~/.ssh/
Damien Miller520e6152008-02-10 22:46:22 +1100770This directory is the default location for all user-specific configuration
771and authentication information.
772There is no general requirement to keep the entire contents of this directory
773secret, but the recommended permissions are read/write/execute for the user,
774and not accessible by others.
775.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000776.It Pa ~/.ssh/authorized_keys
sobrado@openbsd.orgf70b22b2014-08-30 15:33:50 +0000777Lists the public keys (DSA, ECDSA, Ed25519, RSA)
Damien Miller8ba0ead2013-12-18 17:46:27 +1100778that can be used for logging in as this user.
Damien Millerd8702e82006-03-15 11:33:56 +1100779The format of this file is described above.
Damien Miller5d43d492006-08-30 11:07:00 +1000780The content of the file is not highly sensitive, but the recommended
Damien Milleradc35b92006-03-15 11:35:27 +1100781permissions are read/write for the user, and not accessible by others.
Damien Miller32aa1441999-10-29 09:15:49 +1000782.Pp
Damien Miller5d43d492006-08-30 11:07:00 +1000783If this file, the
784.Pa ~/.ssh
785directory, or the user's home directory are writable
786by other users, then the file could be modified or replaced by unauthorized
787users.
788In this case,
789.Nm
790will not allow it to be used unless the
791.Cm StrictModes
792option has been set to
793.Dq no .
Damien Miller5d43d492006-08-30 11:07:00 +1000794.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000795.It Pa ~/.ssh/environment
Damien Miller450a7a12000-03-26 13:04:51 +1000796This file is read into the environment at login (if it exists).
797It can only contain empty lines, comment lines (that start with
Damien Miller32aa1441999-10-29 09:15:49 +1000798.Ql # ) ,
Damien Miller450a7a12000-03-26 13:04:51 +1000799and assignment lines of the form name=value.
800The file should be writable
Damien Miller32aa1441999-10-29 09:15:49 +1000801only by the user; it need not be readable by anyone else.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000802Environment processing is disabled by default and is
803controlled via the
804.Cm PermitUserEnvironment
805option.
Damien Millerd8702e82006-03-15 11:33:56 +1100806.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000807.It Pa ~/.ssh/known_hosts
Damien Milleradc35b92006-03-15 11:35:27 +1100808Contains a list of host keys for all hosts the user has logged into
809that are not already in the systemwide list of known host keys.
810The format of this file is described above.
811This file should be writable only by root/the owner and
Damien Millerd8702e82006-03-15 11:33:56 +1100812can, but need not be, world-readable.
813.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000814.It Pa ~/.ssh/rc
Damien Millerfd725cf2006-03-15 11:35:54 +1100815Contains initialization routines to be run before
816the user's home directory becomes accessible.
Damien Miller32aa1441999-10-29 09:15:49 +1000817This file should be writable only by the user, and need not be
818readable by anyone else.
Damien Millerd8702e82006-03-15 11:33:56 +1100819.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000820.It Pa /etc/hosts.equiv
Damien Miller445121f2006-03-15 11:36:18 +1100821This file is for host-based authentication (see
822.Xr ssh 1 ) .
823It should only be writable by root.
Damien Millerd8702e82006-03-15 11:33:56 +1100824.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000825.It Pa /etc/moduli
djm@openbsd.orgdeae7d52016-02-05 03:07:06 +0000826Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange"
827key exchange method.
Damien Millerd8702e82006-03-15 11:33:56 +1100828The file format is described in
829.Xr moduli 5 .
djm@openbsd.orgdeae7d52016-02-05 03:07:06 +0000830If no usable groups are found in this file then fixed internal groups will
831be used.
Damien Millerd8702e82006-03-15 11:33:56 +1100832.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000833.It Pa /etc/motd
Damien Millerd8702e82006-03-15 11:33:56 +1100834See
835.Xr motd 5 .
836.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000837.It Pa /etc/nologin
Damien Millerd8702e82006-03-15 11:33:56 +1100838If this file exists,
839.Nm
840refuses to let anyone except root log in.
841The contents of the file
842are displayed to anyone trying to log in, and non-root connections are
843refused.
844The file should be world-readable.
845.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000846.It Pa /etc/shosts.equiv
Damien Miller445121f2006-03-15 11:36:18 +1100847This file is used in exactly the same way as
848.Pa hosts.equiv ,
849but allows host-based authentication without permitting login with
850rlogin/rsh.
Damien Millerd8702e82006-03-15 11:33:56 +1100851.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000852.It Pa /etc/ssh/ssh_host_dsa_key
Damien Millereb8b60e2010-08-31 22:41:14 +1000853.It Pa /etc/ssh/ssh_host_ecdsa_key
Damien Miller8ba0ead2013-12-18 17:46:27 +1100854.It Pa /etc/ssh/ssh_host_ed25519_key
Damien Millerafdae612010-08-31 22:31:14 +1000855.It Pa /etc/ssh/ssh_host_rsa_key
Damien Millerb9902cf2012-06-20 21:52:58 +1000856These files contain the private parts of the host keys.
Damien Millerd8702e82006-03-15 11:33:56 +1100857These files should only be owned by root, readable only by root, and not
858accessible to others.
859Note that
860.Nm
Damien Milleredd03752006-03-15 11:36:45 +1100861does not start if these files are group/world-accessible.
Damien Millerd8702e82006-03-15 11:33:56 +1100862.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000863.It Pa /etc/ssh/ssh_host_dsa_key.pub
Damien Millereb8b60e2010-08-31 22:41:14 +1000864.It Pa /etc/ssh/ssh_host_ecdsa_key.pub
Damien Miller8ba0ead2013-12-18 17:46:27 +1100865.It Pa /etc/ssh/ssh_host_ed25519_key.pub
Damien Millerafdae612010-08-31 22:31:14 +1000866.It Pa /etc/ssh/ssh_host_rsa_key.pub
Damien Millerb9902cf2012-06-20 21:52:58 +1000867These files contain the public parts of the host keys.
Damien Millerd8702e82006-03-15 11:33:56 +1100868These files should be world-readable but writable only by
869root.
870Their contents should match the respective private parts.
871These files are not
872really used for anything; they are provided for the convenience of
873the user so their contents can be copied to known hosts files.
874These files are created using
875.Xr ssh-keygen 1 .
876.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000877.It Pa /etc/ssh/ssh_known_hosts
Darren Tucker04354b92007-03-21 20:46:54 +1100878Systemwide list of known host keys.
879This file should be prepared by the
880system administrator to contain the public host keys of all machines in the
881organization.
882The format of this file is described above.
883This file should be writable only by root/the owner and
884should be world-readable.
885.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000886.It Pa /etc/ssh/sshd_config
Damien Millerd8702e82006-03-15 11:33:56 +1100887Contains configuration data for
888.Nm sshd .
889The file format and configuration options are described in
890.Xr sshd_config 5 .
891.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000892.It Pa /etc/ssh/sshrc
Damien Millerfd725cf2006-03-15 11:35:54 +1100893Similar to
894.Pa ~/.ssh/rc ,
895it can be used to specify
Damien Miller450a7a12000-03-26 13:04:51 +1000896machine-specific login-time initializations globally.
897This file should be writable only by root, and should be world-readable.
Damien Millerd8702e82006-03-15 11:33:56 +1100898.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000899.It Pa /var/empty
Damien Millerd8702e82006-03-15 11:33:56 +1100900.Xr chroot 2
901directory used by
902.Nm
903during privilege separation in the pre-authentication phase.
904The directory should not contain any files and must be owned by root
905and not group or world-writable.
906.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000907.It Pa /var/run/sshd.pid
Damien Millerd8702e82006-03-15 11:33:56 +1100908Contains the process ID of the
909.Nm
910listening for connections (if there are several daemons running
911concurrently for different ports, this contains the process ID of the one
912started last).
913The content of this file is not sensitive; it can be world-readable.
Damien Miller37023962000-07-11 17:31:38 +1000914.El
Damien Miller32aa1441999-10-29 09:15:49 +1000915.Sh SEE ALSO
Damien Miller32aa1441999-10-29 09:15:49 +1000916.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +1100917.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +1000918.Xr ssh 1 ,
919.Xr ssh-add 1 ,
920.Xr ssh-agent 1 ,
921.Xr ssh-keygen 1 ,
Darren Tucker04354b92007-03-21 20:46:54 +1100922.Xr ssh-keyscan 1 ,
Darren Tucker1f203942003-10-15 15:50:42 +1000923.Xr chroot 2 ,
Ben Lindstromc8e29ce2001-08-06 20:55:28 +0000924.Xr login.conf 5 ,
925.Xr moduli 5 ,
Ben Lindstrom9f049032002-06-21 00:59:05 +0000926.Xr sshd_config 5 ,
Darren Tucker1f203942003-10-15 15:50:42 +1000927.Xr inetd 8 ,
Ben Lindstromd2bf0d62001-06-25 04:10:54 +0000928.Xr sftp-server 8
Damien Millerf1ce5052003-06-11 22:04:39 +1000929.Sh AUTHORS
930OpenSSH is a derivative of the original and free
931ssh 1.2.12 release by Tatu Ylonen.
932Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
933Theo de Raadt and Dug Song
934removed many bugs, re-added newer features and
935created OpenSSH.
936Markus Friedl contributed the support for SSH
937protocol versions 1.5 and 2.0.
938Niels Provos and Markus Friedl contributed support
939for privilege separation.