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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.orgfd6dcef2016-11-30 02:57:40 +000036.\" $OpenBSD: sshd.8,v 1.287 2016/11/30 02:57:40 djm Exp $
37.Dd $Mdocdate: November 30 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.
djm@openbsd.orgfd6dcef2016-11-30 02:57:40 +0000484.Pp
Damien Miller450a7a12000-03-26 13:04:51 +1000485This option might be useful
Damien Millerb83df8d2002-09-04 16:24:55 +1000486to restrict certain public keys to perform just a specific operation.
Damien Miller450a7a12000-03-26 13:04:51 +1000487An example might be a key that permits remote backups but nothing else.
Damien Miller7c24b812006-01-14 10:09:56 +1100488Note that the client may specify TCP and/or X11
djm@openbsd.orgfd6dcef2016-11-30 02:57:40 +0000489forwarding unless they are explicitly prohibited, e.g. using the
490.Cm restrict
491key option.
492.Pp
Damien Millere2754432006-07-24 14:06:47 +1000493The command originally supplied by the client is available in the
494.Ev SSH_ORIGINAL_COMMAND
495environment variable.
Ben Lindstrom20daef72001-09-20 00:54:01 +0000496Note that this option applies to shell, command or subsystem execution.
djm@openbsd.orgfd6dcef2016-11-30 02:57:40 +0000497Also note that this command may be superseded by a
Damien Miller0a80ca12010-02-27 07:55:05 +1100498.Xr sshd_config 5
499.Cm ForceCommand
djm@openbsd.orgfd6dcef2016-11-30 02:57:40 +0000500directive.
501.Pp
502If a command is specified and a forced-command is embedded in a certificate
503used for authentication, then the certificate will be accepted only if the
504two commands are identical.
Damien Miller32aa1441999-10-29 09:15:49 +1000505.It Cm environment="NAME=value"
506Specifies that the string is to be added to the environment when
Damien Miller450a7a12000-03-26 13:04:51 +1000507logging in using this key.
508Environment variables set this way
509override other default environment values.
510Multiple options of this type are permitted.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000511Environment processing is disabled by default and is
512controlled via the
513.Cm PermitUserEnvironment
514option.
Damien Miller31bdc522006-03-15 11:31:44 +1100515.It Cm from="pattern-list"
Darren Tucker896ad5a2008-06-11 09:34:46 +1000516Specifies that in addition to public key authentication, either the canonical
Darren Tucker11996732008-06-13 04:32:00 +1000517name of the remote host or its IP address must be present in the
Darren Tucker896ad5a2008-06-11 09:34:46 +1000518comma-separated list of patterns.
Damien Millerfecfd112013-07-18 16:11:50 +1000519See PATTERNS in
Damien Millerc7d5b5e2006-03-15 11:55:08 +1100520.Xr ssh_config 5
521for more information on patterns.
Darren Tucker896ad5a2008-06-11 09:34:46 +1000522.Pp
523In addition to the wildcard matching that may be applied to hostnames or
524addresses, a
525.Cm from
Darren Tucker5837b512009-06-21 17:52:27 +1000526stanza may match IP addresses using CIDR address/masklen notation.
Darren Tucker896ad5a2008-06-11 09:34:46 +1000527.Pp
528The purpose of this option is to optionally increase security: public key
529authentication by itself does not trust the network or name servers or
530anything (but the key); however, if somebody somehow steals the key, the key
531permits an intruder to log in from anywhere in the world.
532This additional option makes using a stolen key more difficult (name
533servers and/or routers would have to be compromised in addition to
534just the key).
Damien Miller31bdc522006-03-15 11:31:44 +1100535.It Cm no-agent-forwarding
536Forbids authentication agent forwarding when this key is used for
537authentication.
Damien Miller32aa1441999-10-29 09:15:49 +1000538.It Cm no-port-forwarding
Damien Miller7c24b812006-01-14 10:09:56 +1100539Forbids TCP forwarding when this key is used for authentication.
Damien Miller450a7a12000-03-26 13:04:51 +1000540Any port forward requests by the client will return an error.
Damien Miller208f1ed2006-03-15 11:56:03 +1100541This might be used, e.g. in connection with the
Damien Miller32aa1441999-10-29 09:15:49 +1000542.Cm command
543option.
Damien Miller31bdc522006-03-15 11:31:44 +1100544.It Cm no-pty
545Prevents tty allocation (a request to allocate a pty will fail).
Damien Miller95e80952008-03-27 11:03:05 +1100546.It Cm no-user-rc
Damien Miller13ba9c22008-04-03 20:52:51 +1100547Disables execution of
Damien Miller95e80952008-03-27 11:03:05 +1100548.Pa ~/.ssh/rc .
Damien Miller32aa1441999-10-29 09:15:49 +1000549.It Cm no-X11-forwarding
550Forbids X11 forwarding when this key is used for authentication.
551Any X11 forward requests by the client will return an error.
Damien Millera243fde2001-03-19 23:16:08 +1100552.It Cm permitopen="host:port"
bentley@openbsd.orgda8af832014-11-15 14:41:03 +0000553Limit local port forwarding with
554.Xr ssh 1
555.Fl L
556such that it may only connect to the specified host and port.
Damien Miller7fa96602010-08-05 13:03:13 +1000557IPv6 addresses can be specified by enclosing the address in square brackets.
Ben Lindstromd71ba572001-09-12 18:03:31 +0000558Multiple
Damien Millera243fde2001-03-19 23:16:08 +1100559.Cm permitopen
Damien Millerfbf486b2003-05-23 18:44:23 +1000560options may be applied separated by commas.
561No pattern matching is performed on the specified hostnames,
562they must be literal domains or addresses.
Darren Tucker1338b9e2011-10-02 18:57:35 +1100563A port specification of
564.Cm *
565matches any port.
djm@openbsd.org383f10f2015-11-16 00:30:02 +0000566.It Cm port-forwarding
567Enable port forwarding previously disabled by the
568.Cm restrict
Damien Miller30da3442010-05-10 11:58:03 +1000569.It Cm principals="principals"
570On a
571.Cm cert-authority
572line, specifies allowed principals for certificate authentication as a
573comma-separated list.
574At least one name from the list must appear in the certificate's
575list of principals for the certificate to be accepted.
576This option is ignored for keys that are not marked as trusted certificate
577signers using the
578.Cm cert-authority
579option.
djm@openbsd.org383f10f2015-11-16 00:30:02 +0000580.It Cm pty
581Permits tty allocation previously disabled by the
582.Cm restrict
583option.
584.It Cm restrict
585Enable all restrictions, i.e. disable port, agent and X11 forwarding,
586as well as disabling PTY allocation
587and execution of
588.Pa ~/.ssh/rc .
589If any future restriction capabilities are added to authorized_keys files
590they will be included in this set.
Damien Millerd27b9472005-12-13 19:29:02 +1100591.It Cm tunnel="n"
592Force a
593.Xr tun 4
594device on the server.
595Without this option, the next available device will be used if
596the client requests a tunnel.
djm@openbsd.org383f10f2015-11-16 00:30:02 +0000597.It Cm user-rc
598Enables execution of
599.Pa ~/.ssh/rc
600previously disabled by the
601.Cm restrict
602option.
603.It Cm X11-forwarding
604Permits X11 forwarding previously disabled by the
605.Cm restrict
606option.
Damien Miller32aa1441999-10-29 09:15:49 +1000607.El
Damien Miller32aa1441999-10-29 09:15:49 +1000608.Pp
Damien Miller7d2ef022006-03-15 11:32:06 +1100609An example authorized_keys file:
Damien Millerc8f61cf2006-03-15 11:33:25 +1100610.Bd -literal -offset 3n
Damien Miller7d2ef022006-03-15 11:32:06 +1100611# Comments allowed at start of line
612ssh-rsa AAAAB3Nza...LiPk== user@example.net
Damien Millerc8f61cf2006-03-15 11:33:25 +1100613from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
614AAAAB2...19Q== john@example.net
615command="dump /home",no-pty,no-port-forwarding ssh-dss
616AAAAC3...51R== example.net
617permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss
618AAAAB5...21S==
619tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
620jane@example.net
djm@openbsd.org383f10f2015-11-16 00:30:02 +0000621restrict,command="uptime" ssh-rsa AAAA1C8...32Tv==
622user@example.net
623restrict,pty,command="nethack" ssh-rsa AAAA1f8...IrrC5==
624user@example.net
Damien Miller7d2ef022006-03-15 11:32:06 +1100625.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000626.Sh SSH_KNOWN_HOSTS FILE FORMAT
Damien Miller22c77262000-04-13 12:26:34 +1000627The
Damien Millerffadc582003-02-24 11:52:26 +1100628.Pa /etc/ssh/ssh_known_hosts
Damien Miller22c77262000-04-13 12:26:34 +1000629and
Damien Miller167ea5d2005-05-26 12:04:02 +1000630.Pa ~/.ssh/known_hosts
Damien Miller450a7a12000-03-26 13:04:51 +1000631files contain host public keys for all known hosts.
632The global file should
633be prepared by the administrator (optional), and the per-user file is
Damien Miller9a7f2012006-03-15 11:32:42 +1100634maintained automatically: whenever the user connects from an unknown host,
Damien Miller450a7a12000-03-26 13:04:51 +1000635its key is added to the per-user file.
Damien Miller32aa1441999-10-29 09:15:49 +1000636.Pp
Damien Millera7dab8b2010-03-05 10:42:05 +1100637Each line in these files contains the following fields: markers (optional),
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000638hostnames, keytype, base64-encoded key, comment.
Damien Miller450a7a12000-03-26 13:04:51 +1000639The fields are separated by spaces.
Damien Miller32aa1441999-10-29 09:15:49 +1000640.Pp
Damien Millera7dab8b2010-03-05 10:42:05 +1100641The marker is optional, but if it is present then it must be one of
642.Dq @cert-authority ,
643to indicate that the line contains a certification authority (CA) key,
644or
645.Dq @revoked ,
646to indicate that the key contained on the line is revoked and must not ever
647be accepted.
648Only one marker should be used on a key line.
649.Pp
Damien Miller31554322003-05-14 13:44:58 +1000650Hostnames is a comma-separated list of patterns
Damien Miller9a7f2012006-03-15 11:32:42 +1100651.Pf ( Ql *
Damien Millerfbf486b2003-05-23 18:44:23 +1000652and
653.Ql \&?
Damien Miller049245d2003-05-14 13:44:42 +1000654act as
Damien Miller32aa1441999-10-29 09:15:49 +1000655wildcards); each pattern in turn is matched against the canonical host
656name (when authenticating a client) or against the user-supplied
Damien Miller450a7a12000-03-26 13:04:51 +1000657name (when authenticating a server).
658A pattern may also be preceded by
Damien Miller049245d2003-05-14 13:44:42 +1000659.Ql \&!
Damien Miller32aa1441999-10-29 09:15:49 +1000660to indicate negation: if the host name matches a negated
661pattern, it is not accepted (by that line) even if it matched another
662pattern on the line.
Darren Tuckerda345532006-07-10 23:04:19 +1000663A hostname or address may optionally be enclosed within
664.Ql \&[
665and
666.Ql \&]
667brackets then followed by
668.Ql \&:
Darren Tucker11318472006-07-12 22:07:59 +1000669and a non-standard port number.
Damien Miller32aa1441999-10-29 09:15:49 +1000670.Pp
Damien Millere1776152005-03-01 21:47:37 +1100671Alternately, hostnames may be stored in a hashed form which hides host names
Damien Miller718fd4b2005-03-02 12:03:23 +1100672and addresses should the file's contents be disclosed.
673Hashed hostnames start with a
674.Ql |
Damien Millere1776152005-03-01 21:47:37 +1100675character.
676Only one hashed hostname may appear on a single line and none of the above
677negation or wildcard operators may be applied.
678.Pp
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000679The keytype and base64-encoded key are taken directly from the host key; they
Damien Miller9a7f2012006-03-15 11:32:42 +1100680can be obtained, for example, from
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000681.Pa /etc/ssh/ssh_host_rsa_key.pub .
Damien Miller32aa1441999-10-29 09:15:49 +1000682The optional comment field continues to the end of the line, and is not used.
683.Pp
684Lines starting with
685.Ql #
686and empty lines are ignored as comments.
687.Pp
688When performing host authentication, authentication is accepted if any
Damien Millera7dab8b2010-03-05 10:42:05 +1100689matching line has the proper key; either one that matches exactly or,
690if the server has presented a certificate for authentication, the key
691of the certification authority that signed the certificate.
692For a key to be trusted as a certification authority, it must use the
693.Dq @cert-authority
694marker described above.
695.Pp
696The known hosts file also provides a facility to mark keys as revoked,
697for example when it is known that the associated private key has been
698stolen.
699Revoked keys are specified by including the
700.Dq @revoked
701marker at the beginning of the key line, and are never accepted for
702authentication or as certification authorities, but instead will
703produce a warning from
704.Xr ssh 1
705when they are encountered.
706.Pp
707It is permissible (but not
Damien Miller32aa1441999-10-29 09:15:49 +1000708recommended) to have several lines or different host keys for the same
Damien Miller450a7a12000-03-26 13:04:51 +1000709names.
710This will inevitably happen when short forms of host names
711from different domains are put in the file.
712It is possible
Damien Miller32aa1441999-10-29 09:15:49 +1000713that the files contain conflicting information; authentication is
714accepted if valid information can be found from either file.
715.Pp
716Note that the lines in these files are typically hundreds of characters
717long, and you definitely don't want to type in the host keys by hand.
Damien Millera7dab8b2010-03-05 10:42:05 +1100718Rather, generate them by a script,
719.Xr ssh-keyscan 1
naddy@openbsd.orgffe65492016-08-15 12:32:04 +0000720or by taking, for example,
721.Pa /etc/ssh/ssh_host_rsa_key.pub
Damien Miller32aa1441999-10-29 09:15:49 +1000722and adding the host names at the front.
Damien Millera7dab8b2010-03-05 10:42:05 +1100723.Xr ssh-keygen 1
Damien Miller98339052010-03-05 21:30:35 +1100724also offers some basic automated editing for
Damien Millera7dab8b2010-03-05 10:42:05 +1100725.Pa ~/.ssh/known_hosts
726including removing hosts matching a host name and converting all host
727names to their hashed representations.
Damien Millercc00f5e2006-03-15 11:33:00 +1100728.Pp
729An example ssh_known_hosts file:
730.Bd -literal -offset 3n
731# Comments allowed at start of line
732closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
733cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
Damien Millere1776152005-03-01 21:47:37 +1100734# A hashed hostname
735|1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
736AAAA1234.....=
Damien Millera7dab8b2010-03-05 10:42:05 +1100737# A revoked key
738@revoked * ssh-rsa AAAAB5W...
739# A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
740@cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
Damien Millere1776152005-03-01 21:47:37 +1100741.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000742.Sh FILES
Damien Millerd8702e82006-03-15 11:33:56 +1100743.Bl -tag -width Ds -compact
Damien Millerafdae612010-08-31 22:31:14 +1000744.It Pa ~/.hushlogin
Damien Miller70a908e2005-03-01 21:17:09 +1100745This file is used to suppress printing the last login time and
746.Pa /etc/motd ,
747if
748.Cm PrintLastLog
749and
750.Cm PrintMotd ,
751respectively,
752are enabled.
753It does not suppress printing of the banner specified by
754.Cm Banner .
Damien Millerd8702e82006-03-15 11:33:56 +1100755.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000756.It Pa ~/.rhosts
Damien Milleradc35b92006-03-15 11:35:27 +1100757This file is used for host-based authentication (see
758.Xr ssh 1
759for more information).
760On some machines this file may need to be
761world-readable if the user's home directory is on an NFS partition,
762because
763.Nm
764reads it as root.
765Additionally, this file must be owned by the user,
766and must not have write permissions for anyone else.
767The recommended
768permission for most machines is read/write for the user, and not
Damien Miller32aa1441999-10-29 09:15:49 +1000769accessible by others.
770.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000771.It Pa ~/.shosts
Damien Milleradc35b92006-03-15 11:35:27 +1100772This file is used in exactly the same way as
773.Pa .rhosts ,
774but allows host-based authentication without permitting login with
775rlogin/rsh.
Damien Miller32aa1441999-10-29 09:15:49 +1000776.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000777.It Pa ~/.ssh/
Damien Miller520e6152008-02-10 22:46:22 +1100778This directory is the default location for all user-specific configuration
779and authentication information.
780There is no general requirement to keep the entire contents of this directory
781secret, but the recommended permissions are read/write/execute for the user,
782and not accessible by others.
783.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000784.It Pa ~/.ssh/authorized_keys
sobrado@openbsd.orgf70b22b2014-08-30 15:33:50 +0000785Lists the public keys (DSA, ECDSA, Ed25519, RSA)
Damien Miller8ba0ead2013-12-18 17:46:27 +1100786that can be used for logging in as this user.
Damien Millerd8702e82006-03-15 11:33:56 +1100787The format of this file is described above.
Damien Miller5d43d492006-08-30 11:07:00 +1000788The content of the file is not highly sensitive, but the recommended
Damien Milleradc35b92006-03-15 11:35:27 +1100789permissions are read/write for the user, and not accessible by others.
Damien Miller32aa1441999-10-29 09:15:49 +1000790.Pp
Damien Miller5d43d492006-08-30 11:07:00 +1000791If this file, the
792.Pa ~/.ssh
793directory, or the user's home directory are writable
794by other users, then the file could be modified or replaced by unauthorized
795users.
796In this case,
797.Nm
798will not allow it to be used unless the
799.Cm StrictModes
800option has been set to
801.Dq no .
Damien Miller5d43d492006-08-30 11:07:00 +1000802.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000803.It Pa ~/.ssh/environment
Damien Miller450a7a12000-03-26 13:04:51 +1000804This file is read into the environment at login (if it exists).
805It can only contain empty lines, comment lines (that start with
Damien Miller32aa1441999-10-29 09:15:49 +1000806.Ql # ) ,
Damien Miller450a7a12000-03-26 13:04:51 +1000807and assignment lines of the form name=value.
808The file should be writable
Damien Miller32aa1441999-10-29 09:15:49 +1000809only by the user; it need not be readable by anyone else.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000810Environment processing is disabled by default and is
811controlled via the
812.Cm PermitUserEnvironment
813option.
Damien Millerd8702e82006-03-15 11:33:56 +1100814.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000815.It Pa ~/.ssh/known_hosts
Damien Milleradc35b92006-03-15 11:35:27 +1100816Contains a list of host keys for all hosts the user has logged into
817that are not already in the systemwide list of known host keys.
818The format of this file is described above.
819This file should be writable only by root/the owner and
Damien Millerd8702e82006-03-15 11:33:56 +1100820can, but need not be, world-readable.
821.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000822.It Pa ~/.ssh/rc
Damien Millerfd725cf2006-03-15 11:35:54 +1100823Contains initialization routines to be run before
824the user's home directory becomes accessible.
Damien Miller32aa1441999-10-29 09:15:49 +1000825This file should be writable only by the user, and need not be
826readable by anyone else.
Damien Millerd8702e82006-03-15 11:33:56 +1100827.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000828.It Pa /etc/hosts.equiv
Damien Miller445121f2006-03-15 11:36:18 +1100829This file is for host-based authentication (see
830.Xr ssh 1 ) .
831It should only be writable by root.
Damien Millerd8702e82006-03-15 11:33:56 +1100832.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000833.It Pa /etc/moduli
djm@openbsd.orgdeae7d52016-02-05 03:07:06 +0000834Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange"
835key exchange method.
Damien Millerd8702e82006-03-15 11:33:56 +1100836The file format is described in
837.Xr moduli 5 .
djm@openbsd.orgdeae7d52016-02-05 03:07:06 +0000838If no usable groups are found in this file then fixed internal groups will
839be used.
Damien Millerd8702e82006-03-15 11:33:56 +1100840.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000841.It Pa /etc/motd
Damien Millerd8702e82006-03-15 11:33:56 +1100842See
843.Xr motd 5 .
844.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000845.It Pa /etc/nologin
Damien Millerd8702e82006-03-15 11:33:56 +1100846If this file exists,
847.Nm
848refuses to let anyone except root log in.
849The contents of the file
850are displayed to anyone trying to log in, and non-root connections are
851refused.
852The file should be world-readable.
853.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000854.It Pa /etc/shosts.equiv
Damien Miller445121f2006-03-15 11:36:18 +1100855This file is used in exactly the same way as
856.Pa hosts.equiv ,
857but allows host-based authentication without permitting login with
858rlogin/rsh.
Damien Millerd8702e82006-03-15 11:33:56 +1100859.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000860.It Pa /etc/ssh/ssh_host_dsa_key
Damien Millereb8b60e2010-08-31 22:41:14 +1000861.It Pa /etc/ssh/ssh_host_ecdsa_key
Damien Miller8ba0ead2013-12-18 17:46:27 +1100862.It Pa /etc/ssh/ssh_host_ed25519_key
Damien Millerafdae612010-08-31 22:31:14 +1000863.It Pa /etc/ssh/ssh_host_rsa_key
Damien Millerb9902cf2012-06-20 21:52:58 +1000864These files contain the private parts of the host keys.
Damien Millerd8702e82006-03-15 11:33:56 +1100865These files should only be owned by root, readable only by root, and not
866accessible to others.
867Note that
868.Nm
Damien Milleredd03752006-03-15 11:36:45 +1100869does not start if these files are group/world-accessible.
Damien Millerd8702e82006-03-15 11:33:56 +1100870.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000871.It Pa /etc/ssh/ssh_host_dsa_key.pub
Damien Millereb8b60e2010-08-31 22:41:14 +1000872.It Pa /etc/ssh/ssh_host_ecdsa_key.pub
Damien Miller8ba0ead2013-12-18 17:46:27 +1100873.It Pa /etc/ssh/ssh_host_ed25519_key.pub
Damien Millerafdae612010-08-31 22:31:14 +1000874.It Pa /etc/ssh/ssh_host_rsa_key.pub
Damien Millerb9902cf2012-06-20 21:52:58 +1000875These files contain the public parts of the host keys.
Damien Millerd8702e82006-03-15 11:33:56 +1100876These files should be world-readable but writable only by
877root.
878Their contents should match the respective private parts.
879These files are not
880really used for anything; they are provided for the convenience of
881the user so their contents can be copied to known hosts files.
882These files are created using
883.Xr ssh-keygen 1 .
884.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000885.It Pa /etc/ssh/ssh_known_hosts
Darren Tucker04354b92007-03-21 20:46:54 +1100886Systemwide list of known host keys.
887This file should be prepared by the
888system administrator to contain the public host keys of all machines in the
889organization.
890The format of this file is described above.
891This file should be writable only by root/the owner and
892should be world-readable.
893.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000894.It Pa /etc/ssh/sshd_config
Damien Millerd8702e82006-03-15 11:33:56 +1100895Contains configuration data for
896.Nm sshd .
897The file format and configuration options are described in
898.Xr sshd_config 5 .
899.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000900.It Pa /etc/ssh/sshrc
Damien Millerfd725cf2006-03-15 11:35:54 +1100901Similar to
902.Pa ~/.ssh/rc ,
903it can be used to specify
Damien Miller450a7a12000-03-26 13:04:51 +1000904machine-specific login-time initializations globally.
905This file should be writable only by root, and should be world-readable.
Damien Millerd8702e82006-03-15 11:33:56 +1100906.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000907.It Pa /var/empty
Damien Millerd8702e82006-03-15 11:33:56 +1100908.Xr chroot 2
909directory used by
910.Nm
911during privilege separation in the pre-authentication phase.
912The directory should not contain any files and must be owned by root
913and not group or world-writable.
914.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000915.It Pa /var/run/sshd.pid
Damien Millerd8702e82006-03-15 11:33:56 +1100916Contains the process ID of the
917.Nm
918listening for connections (if there are several daemons running
919concurrently for different ports, this contains the process ID of the one
920started last).
921The content of this file is not sensitive; it can be world-readable.
Damien Miller37023962000-07-11 17:31:38 +1000922.El
Damien Miller32aa1441999-10-29 09:15:49 +1000923.Sh SEE ALSO
Damien Miller32aa1441999-10-29 09:15:49 +1000924.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +1100925.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +1000926.Xr ssh 1 ,
927.Xr ssh-add 1 ,
928.Xr ssh-agent 1 ,
929.Xr ssh-keygen 1 ,
Darren Tucker04354b92007-03-21 20:46:54 +1100930.Xr ssh-keyscan 1 ,
Darren Tucker1f203942003-10-15 15:50:42 +1000931.Xr chroot 2 ,
Ben Lindstromc8e29ce2001-08-06 20:55:28 +0000932.Xr login.conf 5 ,
933.Xr moduli 5 ,
Ben Lindstrom9f049032002-06-21 00:59:05 +0000934.Xr sshd_config 5 ,
Darren Tucker1f203942003-10-15 15:50:42 +1000935.Xr inetd 8 ,
Ben Lindstromd2bf0d62001-06-25 04:10:54 +0000936.Xr sftp-server 8
Damien Millerf1ce5052003-06-11 22:04:39 +1000937.Sh AUTHORS
938OpenSSH is a derivative of the original and free
939ssh 1.2.12 release by Tatu Ylonen.
940Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
941Theo de Raadt and Dug Song
942removed many bugs, re-added newer features and
943created OpenSSH.
944Markus Friedl contributed the support for SSH
945protocol versions 1.5 and 2.0.
946Niels Provos and Markus Friedl contributed support
947for privilege separation.