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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.\"
Damien Miller20bd4532011-08-06 06:17:30 +100036.\" $OpenBSD: sshd.8,v 1.263 2011/08/02 01:22:11 djm Exp $
37.Dd $Mdocdate: August 2 2011 $
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
Damien Miller32aa1441999-10-29 09:15:49 +100047.Op Fl b Ar bits
Darren Tuckere7140f22008-06-10 23:01:51 +100048.Op Fl C Ar connection_spec
Damien Miller0a80ca12010-02-27 07:55:05 +110049.Op Fl c Ar host_certificate_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
53.Op Fl k Ar key_gen_time
Ben Lindstromade03f62001-12-06 18:22:17 +000054.Op Fl o Ar option
Damien Miller32aa1441999-10-29 09:15:49 +100055.Op Fl p Ar port
Damien Miller942da032000-08-18 13:59:06 +100056.Op Fl u Ar len
Damien Millerffadc582003-02-24 11:52:26 +110057.Ek
Damien Miller22c77262000-04-13 12:26:34 +100058.Sh DESCRIPTION
Damien Miller32aa1441999-10-29 09:15:49 +100059.Nm
Damien Miller99cc4a82006-01-31 21:45:53 +110060(OpenSSH Daemon) is the daemon program for
Damien Miller32aa1441999-10-29 09:15:49 +100061.Xr ssh 1 .
Darren Tucker04354b92007-03-21 20:46:54 +110062Together these programs replace
63.Xr rlogin 1
64and
65.Xr rsh 1 ,
66and provide secure encrypted communications between two untrusted hosts
Damien Miller450a7a12000-03-26 13:04:51 +100067over an insecure network.
Damien Miller32aa1441999-10-29 09:15:49 +100068.Pp
69.Nm
Damien Miller99cc4a82006-01-31 21:45:53 +110070listens for connections from clients.
Damien Miller22c77262000-04-13 12:26:34 +100071It is normally started at boot from
Damien Miller32aa1441999-10-29 09:15:49 +100072.Pa /etc/rc .
73It forks a new
Damien Miller450a7a12000-03-26 13:04:51 +100074daemon for each incoming connection.
75The forked daemons handle
Damien Miller32aa1441999-10-29 09:15:49 +100076key exchange, encryption, authentication, command execution,
77and data exchange.
Damien Miller32aa1441999-10-29 09:15:49 +100078.Pp
79.Nm
Darren Tucker1f203942003-10-15 15:50:42 +100080can be configured using command-line options or a configuration file
81(by default
Damien Miller99cc4a82006-01-31 21:45:53 +110082.Xr sshd_config 5 ) ;
83command-line options override values specified in the
Damien Miller32aa1441999-10-29 09:15:49 +100084configuration file.
Damien Miller6162d121999-11-21 13:23:52 +110085.Nm
86rereads its configuration file when it receives a hangup signal,
Ben Lindstrom49a098d2001-03-05 06:55:18 +000087.Dv SIGHUP ,
Damien Miller208f1ed2006-03-15 11:56:03 +110088by executing itself with the name and options it was started with, e.g.\&
Ben Lindstrom49a098d2001-03-05 06:55:18 +000089.Pa /usr/sbin/sshd .
Damien Miller6162d121999-11-21 13:23:52 +110090.Pp
Damien Miller32aa1441999-10-29 09:15:49 +100091The options are as follows:
92.Bl -tag -width Ds
Darren Tucker1f203942003-10-15 15:50:42 +100093.It Fl 4
94Forces
95.Nm
96to use IPv4 addresses only.
97.It Fl 6
98Forces
99.Nm
100to use IPv6 addresses only.
Damien Miller32aa1441999-10-29 09:15:49 +1000101.It Fl b Ar bits
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000102Specifies the number of bits in the ephemeral protocol version 1
Darren Tucker7499b0c2008-07-02 22:35:43 +1000103server key (default 1024).
Darren Tuckere7f3f752008-06-10 23:06:01 +1000104.It Fl C Ar connection_spec
105Specify the connection parameters to use for the
106.Fl T
107extended test mode.
108If provided, any
109.Cm Match
110directives in the configuration file
111that would apply to the specified user, host, and address will be set before
112the configuration is written to standard output.
113The connection parameters are supplied as keyword=value pairs.
114The keywords are
115.Dq user ,
116.Dq host ,
117and
118.Dq addr .
119All are required and may be supplied in any order, either with multiple
120.Fl C
121options or as a comma-separated list.
Damien Miller15f5b562010-03-03 10:25:21 +1100122.It Fl c Ar host_certificate_file
123Specifies a path to a certificate file to identify
124.Nm
125during key exchange.
126The certificate file must match a host key file specified using the
127.Fl h
128option or the
129.Cm HostKey
130configuration directive.
Darren Tucker1f203942003-10-15 15:50:42 +1000131.It Fl D
132When this option is specified,
133.Nm
134will not detach and does not become a daemon.
135This allows easy monitoring of
136.Nm sshd .
Damien Miller32aa1441999-10-29 09:15:49 +1000137.It Fl d
Damien Miller450a7a12000-03-26 13:04:51 +1000138Debug mode.
Damien Miller74d98252010-02-02 17:01:46 +1100139The server sends verbose debug output to standard error,
140and does not put itself in the background.
Damien Miller450a7a12000-03-26 13:04:51 +1000141The server also will not fork and will only process one connection.
142This option is only intended for debugging for the server.
Damien Millerffadc582003-02-24 11:52:26 +1100143Multiple
144.Fl d
145options increase the debugging level.
Damien Miller874d77b2000-10-14 16:23:11 +1100146Maximum is 3.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000147.It Fl e
148When this option is specified,
149.Nm
150will send the output to the standard error instead of the system log.
Darren Tucker04354b92007-03-21 20:46:54 +1100151.It Fl f Ar config_file
Damien Miller450a7a12000-03-26 13:04:51 +1000152Specifies the name of the configuration file.
153The default is
Damien Miller05eda432002-02-10 18:32:28 +1100154.Pa /etc/ssh/sshd_config .
Damien Miller32aa1441999-10-29 09:15:49 +1000155.Nm
156refuses to start if there is no configuration file.
157.It Fl g Ar login_grace_time
158Gives the grace time for clients to authenticate themselves (default
Damien Millerc1348632002-09-05 14:35:14 +1000159120 seconds).
Damien Miller450a7a12000-03-26 13:04:51 +1000160If the client fails to authenticate the user within
161this many seconds, the server disconnects and exits.
162A value of zero indicates no limit.
Damien Miller32aa1441999-10-29 09:15:49 +1000163.It Fl h Ar host_key_file
Damien Miller7fc23732002-01-22 23:19:11 +1100164Specifies a file from which a host key is read.
Damien Miller32aa1441999-10-29 09:15:49 +1000165This option must be given if
166.Nm
167is not run as root (as the normal
Damien Miller7fc23732002-01-22 23:19:11 +1100168host key files are normally not readable by anyone but root).
169The default is
Damien Miller05eda432002-02-10 18:32:28 +1100170.Pa /etc/ssh/ssh_host_key
Damien Miller7fc23732002-01-22 23:19:11 +1100171for protocol version 1, and
Damien Millereb8b60e2010-08-31 22:41:14 +1000172.Pa /etc/ssh/ssh_host_dsa_key ,
173.Pa /etc/ssh/ssh_host_ecdsa_key
Damien Miller7fc23732002-01-22 23:19:11 +1100174and
Damien Millereb8b60e2010-08-31 22:41:14 +1000175.Pa /etc/ssh/ssh_host_rsa_key
Damien Miller7fc23732002-01-22 23:19:11 +1100176for protocol version 2.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000177It is possible to have multiple host key files for
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000178the different protocol versions and host key algorithms.
Damien Miller32aa1441999-10-29 09:15:49 +1000179.It Fl i
180Specifies that
181.Nm
Damien Millerffadc582003-02-24 11:52:26 +1100182is being run from
183.Xr inetd 8 .
Damien Miller32aa1441999-10-29 09:15:49 +1000184.Nm
185is normally not run
186from inetd because it needs to generate the server key before it can
Damien Miller450a7a12000-03-26 13:04:51 +1000187respond to the client, and this may take tens of seconds.
188Clients would have to wait too long if the key was regenerated every time.
Damien Miller208f1ed2006-03-15 11:56:03 +1100189However, with small key sizes (e.g. 512) using
Damien Miller32aa1441999-10-29 09:15:49 +1000190.Nm
191from inetd may
192be feasible.
193.It Fl k Ar key_gen_time
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000194Specifies how often the ephemeral protocol version 1 server key is
195regenerated (default 3600 seconds, or one hour).
Damien Miller450a7a12000-03-26 13:04:51 +1000196The motivation for regenerating the key fairly
Darren Tucker1f203942003-10-15 15:50:42 +1000197often is that the key is not stored anywhere, and after about an hour
Damien Miller32aa1441999-10-29 09:15:49 +1000198it becomes impossible to recover the key for decrypting intercepted
199communications even if the machine is cracked into or physically
Damien Miller450a7a12000-03-26 13:04:51 +1000200seized.
201A value of zero indicates that the key will never be regenerated.
Ben Lindstromade03f62001-12-06 18:22:17 +0000202.It Fl o Ar option
203Can be used to give options in the format used in the configuration file.
204This is useful for specifying options for which there is no separate
205command-line flag.
Darren Tucker1f203942003-10-15 15:50:42 +1000206For full details of the options, and their values, see
207.Xr sshd_config 5 .
Damien Miller32aa1441999-10-29 09:15:49 +1000208.It Fl p Ar port
209Specifies the port on which the server listens for connections
210(default 22).
Damien Miller7d1ded42002-01-22 23:09:41 +1100211Multiple port options are permitted.
Damien Millerd7f308f2005-12-24 14:55:16 +1100212Ports specified in the configuration file with the
213.Cm Port
214option are ignored when a command-line port is specified.
215Ports specified using the
216.Cm ListenAddress
217option override command-line ports.
Damien Miller32aa1441999-10-29 09:15:49 +1000218.It Fl q
Damien Miller450a7a12000-03-26 13:04:51 +1000219Quiet mode.
220Nothing is sent to the system log.
221Normally the beginning,
Damien Miller32aa1441999-10-29 09:15:49 +1000222authentication, and termination of each connection is logged.
Darren Tuckere7140f22008-06-10 23:01:51 +1000223.It Fl T
224Extended test mode.
225Check the validity of the configuration file, output the effective configuration
226to stdout and then exit.
227Optionally,
228.Cm Match
229rules may be applied by specifying the connection parameters using one or more
230.Fl C
231options.
Darren Tuckere7f3f752008-06-10 23:06:01 +1000232.It Fl t
233Test mode.
234Only check the validity of the configuration file and sanity of the keys.
235This is useful for updating
236.Nm
237reliably as configuration options may change.
Damien Miller942da032000-08-18 13:59:06 +1000238.It Fl u Ar len
239This option is used to specify the size of the field
240in the
241.Li utmp
242structure that holds the remote host name.
243If the resolved host name is longer than
244.Ar len ,
245the dotted decimal value will be used instead.
246This allows hosts with very long host names that
247overflow this field to still be uniquely identified.
248Specifying
249.Fl u0
250indicates that only dotted decimal addresses
251should be put into the
252.Pa utmp
253file.
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000254.Fl u0
Damien Millerffadc582003-02-24 11:52:26 +1100255may also be used to prevent
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000256.Nm
257from making DNS requests unless the authentication
258mechanism or configuration requires it.
259Authentication mechanisms that may require DNS include
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000260.Cm RhostsRSAAuthentication ,
Damien Miller2ac05772006-02-01 22:05:42 +1100261.Cm HostbasedAuthentication ,
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000262and using a
263.Cm from="pattern-list"
264option in a key file.
Ben Lindstromea03db92002-03-05 01:38:57 +0000265Configuration options that require DNS include using a
266USER@HOST pattern in
267.Cm AllowUsers
268or
269.Cm DenyUsers .
Damien Miller32aa1441999-10-29 09:15:49 +1000270.El
Damien Miller8bbdf902006-02-01 22:05:25 +1100271.Sh AUTHENTICATION
272The OpenSSH SSH daemon supports SSH protocols 1 and 2.
Darren Tucker7a4a7652009-10-11 21:51:40 +1100273The default is to use protocol 2 only,
Damien Miller8bbdf902006-02-01 22:05:25 +1100274though this can be changed via the
275.Cm Protocol
276option in
277.Xr sshd_config 5 .
Damien Millereb8b60e2010-08-31 22:41:14 +1000278Protocol 2 supports DSA, ECDSA and RSA keys;
Damien Miller8bbdf902006-02-01 22:05:25 +1100279protocol 1 only supports RSA keys.
280For both protocols,
281each host has a host-specific key,
282normally 2048 bits,
283used to identify the host.
Damien Miller99cc4a82006-01-31 21:45:53 +1100284.Pp
Damien Miller8bbdf902006-02-01 22:05:25 +1100285Forward security for protocol 1 is provided through
286an additional server key,
287normally 768 bits,
288generated when the server starts.
Damien Miller99cc4a82006-01-31 21:45:53 +1100289This key is normally regenerated every hour if it has been used, and
290is never stored on disk.
Damien Miller99cc4a82006-01-31 21:45:53 +1100291Whenever a client connects, the daemon responds with its public
292host and server keys.
293The client compares the
294RSA host key against its own database to verify that it has not changed.
295The client then generates a 256-bit random number.
296It encrypts this
297random number using both the host key and the server key, and sends
298the encrypted number to the server.
299Both sides then use this
300random number as a session key which is used to encrypt all further
301communications in the session.
302The rest of the session is encrypted
303using a conventional cipher, currently Blowfish or 3DES, with 3DES
304being used by default.
305The client selects the encryption algorithm
306to use from those offered by the server.
307.Pp
Damien Miller8bbdf902006-02-01 22:05:25 +1100308For protocol 2,
309forward security is provided through a Diffie-Hellman key agreement.
310This key agreement results in a shared session key.
311The rest of the session is encrypted using a symmetric cipher, currently
312128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES.
313The client selects the encryption algorithm
314to use from those offered by the server.
315Additionally, session integrity is provided
316through a cryptographic message authentication code
Damien Miller20bd4532011-08-06 06:17:30 +1000317(hmac-md5, hmac-sha1, umac-64, hmac-ripemd160,
318hmac-sha2-256 or hmac-sha2-512).
Damien Miller8bbdf902006-02-01 22:05:25 +1100319.Pp
320Finally, the server and the client enter an authentication dialog.
Damien Miller99cc4a82006-01-31 21:45:53 +1100321The client tries to authenticate itself using
Damien Miller8bbdf902006-02-01 22:05:25 +1100322host-based authentication,
323public key authentication,
324challenge-response authentication,
325or password authentication.
Damien Miller99cc4a82006-01-31 21:45:53 +1100326.Pp
327Regardless of the authentication type, the account is checked to
328ensure that it is accessible. An account is not accessible if it is
329locked, listed in
330.Cm DenyUsers
331or its group is listed in
332.Cm DenyGroups
333\&. The definition of a locked account is system dependant. Some platforms
334have their own account database (eg AIX) and some modify the passwd field (
335.Ql \&*LK\&*
336on Solaris and UnixWare,
337.Ql \&*
338on HP-UX, containing
339.Ql Nologin
340on Tru64,
341a leading
342.Ql \&*LOCKED\&*
343on FreeBSD and a leading
Darren Tucker1a9176b2007-08-17 09:42:32 +1000344.Ql \&!
345on most Linuxes).
346If there is a requirement to disable password authentication
Damien Miller99cc4a82006-01-31 21:45:53 +1100347for the account while allowing still public-key, then the passwd field
348should be set to something other than these values (eg
349.Ql NP
350or
351.Ql \&*NP\&*
352).
353.Pp
Damien Miller99cc4a82006-01-31 21:45:53 +1100354If the client successfully authenticates itself, a dialog for
355preparing the session is entered.
356At this time the client may request
357things like allocating a pseudo-tty, forwarding X11 connections,
358forwarding TCP connections, or forwarding the authentication agent
359connection over the secure channel.
360.Pp
Damien Millerc47d7e92006-03-15 11:27:20 +1100361After this, the client either requests a shell or execution of a command.
Damien Miller99cc4a82006-01-31 21:45:53 +1100362The sides then enter session mode.
363In this mode, either side may send
364data at any time, and such data is forwarded to/from the shell or
365command on the server side, and the user terminal in the client side.
366.Pp
367When the user program terminates and all forwarded X11 and other
368connections have been closed, the server sends command exit status to
369the client, and both sides exit.
Damien Miller32aa1441999-10-29 09:15:49 +1000370.Sh LOGIN PROCESS
371When a user successfully logs in,
372.Nm
373does the following:
374.Bl -enum -offset indent
375.It
376If the login is on a tty, and no command has been specified,
Damien Miller22c77262000-04-13 12:26:34 +1000377prints last login time and
Damien Miller32aa1441999-10-29 09:15:49 +1000378.Pa /etc/motd
379(unless prevented in the configuration file or by
Damien Miller167ea5d2005-05-26 12:04:02 +1000380.Pa ~/.hushlogin ;
Damien Miller32aa1441999-10-29 09:15:49 +1000381see the
Damien Miller22c77262000-04-13 12:26:34 +1000382.Sx FILES
Damien Miller32aa1441999-10-29 09:15:49 +1000383section).
384.It
385If the login is on a tty, records login time.
386.It
387Checks
388.Pa /etc/nologin ;
389if it exists, prints contents and quits
390(unless root).
391.It
392Changes to run with normal user privileges.
393.It
394Sets up basic environment.
395.It
Darren Tucker1f203942003-10-15 15:50:42 +1000396Reads the file
Damien Miller167ea5d2005-05-26 12:04:02 +1000397.Pa ~/.ssh/environment ,
Darren Tucker1f203942003-10-15 15:50:42 +1000398if it exists, and users are allowed to change their environment.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000399See the
Ben Lindstromdc7adf22002-08-20 18:38:02 +0000400.Cm PermitUserEnvironment
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000401option in
Ben Lindstromdc7adf22002-08-20 18:38:02 +0000402.Xr sshd_config 5 .
Damien Miller32aa1441999-10-29 09:15:49 +1000403.It
404Changes to user's home directory.
405.It
406If
Damien Miller167ea5d2005-05-26 12:04:02 +1000407.Pa ~/.ssh/rc
Damien Miller32aa1441999-10-29 09:15:49 +1000408exists, runs it; else if
Damien Millerafcc2252002-02-10 18:32:55 +1100409.Pa /etc/ssh/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +1000410exists, runs
Damien Miller450a7a12000-03-26 13:04:51 +1000411it; otherwise runs xauth.
412The
Damien Miller32aa1441999-10-29 09:15:49 +1000413.Dq rc
414files are given the X11
415authentication protocol and cookie in standard input.
Damien Millerfd725cf2006-03-15 11:35:54 +1100416See
417.Sx SSHRC ,
418below.
Damien Miller32aa1441999-10-29 09:15:49 +1000419.It
420Runs user's shell or command.
421.El
Damien Millerfd725cf2006-03-15 11:35:54 +1100422.Sh SSHRC
423If the file
424.Pa ~/.ssh/rc
425exists,
426.Xr sh 1
427runs it after reading the
428environment files but before starting the user's shell or command.
429It must not produce any output on stdout; stderr must be used
430instead.
431If X11 forwarding is in use, it will receive the "proto cookie" pair in
432its standard input (and
433.Ev DISPLAY
434in its environment).
435The script must call
436.Xr xauth 1
437because
438.Nm
439will not run xauth automatically to add X11 cookies.
440.Pp
441The primary purpose of this file is to run any initialization routines
442which may be needed before the user's home directory becomes
443accessible; AFS is a particular example of such an environment.
444.Pp
445This file will probably contain some initialization code followed by
446something similar to:
447.Bd -literal -offset 3n
448if read proto cookie && [ -n "$DISPLAY" ]; then
449 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
450 # X11UseLocalhost=yes
451 echo add unix:`echo $DISPLAY |
452 cut -c11-` $proto $cookie
453 else
454 # X11UseLocalhost=no
455 echo add $DISPLAY $proto $cookie
456 fi | xauth -q -
457fi
458.Ed
459.Pp
460If this file does not exist,
461.Pa /etc/ssh/sshrc
462is run, and if that
463does not exist either, xauth is used to add the cookie.
Damien Miller32aa1441999-10-29 09:15:49 +1000464.Sh AUTHORIZED_KEYS FILE FORMAT
Ben Lindstromf96704d2001-06-25 04:17:12 +0000465.Cm AuthorizedKeysFile
Damien Millerb9132fc2011-05-29 21:41:40 +1000466specifies the files containing public keys for
Damien Millerdcfea272006-03-15 11:31:22 +1100467public key authentication;
Damien Millerb9132fc2011-05-29 21:41:40 +1000468if none is specified, the default is
Damien Millerd8478b62011-05-29 21:39:36 +1000469.Pa ~/.ssh/authorized_keys
470and
471.Pa ~/.ssh/authorized_keys2 .
Damien Miller450a7a12000-03-26 13:04:51 +1000472Each line of the file contains one
Damien Miller32aa1441999-10-29 09:15:49 +1000473key (empty lines and lines starting with a
474.Ql #
475are ignored as
Damien Miller450a7a12000-03-26 13:04:51 +1000476comments).
Damien Millerdcfea272006-03-15 11:31:22 +1100477Protocol 1 public keys consist of the following space-separated fields:
478options, bits, exponent, modulus, comment.
479Protocol 2 public key consist of:
480options, keytype, base64-encoded key, comment.
481The options field is optional;
482its presence is determined by whether the line starts
Damien Millerb83df8d2002-09-04 16:24:55 +1000483with a number or not (the options field never starts with a number).
Damien Millerdcfea272006-03-15 11:31:22 +1100484The bits, exponent, modulus, and comment fields give the RSA key for
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000485protocol version 1; the
Damien Miller32aa1441999-10-29 09:15:49 +1000486comment field is not used for anything (but may be convenient for the
487user to identify the key).
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000488For protocol version 2 the keytype is
Damien Millereb8b60e2010-08-31 22:41:14 +1000489.Dq ecdsa-sha2-nistp256 ,
490.Dq ecdsa-sha2-nistp384 ,
491.Dq ecdsa-sha2-nistp521 ,
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000492.Dq ssh-dss
493or
494.Dq ssh-rsa .
Damien Miller32aa1441999-10-29 09:15:49 +1000495.Pp
496Note that lines in this file are usually several hundred bytes long
Darren Tucker22cc7412004-12-06 22:47:41 +1100497(because of the size of the public key encoding) up to a limit of
4988 kilobytes, which permits DSA keys up to 8 kilobits and RSA
499keys up to 16 kilobits.
Damien Miller450a7a12000-03-26 13:04:51 +1000500You don't want to type them in; instead, copy the
Ben Lindstrom18a82ac2001-04-11 15:59:35 +0000501.Pa identity.pub ,
Damien Millerdcfea272006-03-15 11:31:22 +1100502.Pa id_dsa.pub ,
Damien Millereb8b60e2010-08-31 22:41:14 +1000503.Pa id_ecdsa.pub ,
Ben Lindstrom18a82ac2001-04-11 15:59:35 +0000504or the
505.Pa id_rsa.pub
Damien Miller32aa1441999-10-29 09:15:49 +1000506file and edit it.
507.Pp
Ben Lindstrom0d0be022002-04-02 20:39:29 +0000508.Nm
509enforces a minimum RSA key modulus size for protocol 1
510and protocol 2 keys of 768 bits.
511.Pp
Damien Miller942da032000-08-18 13:59:06 +1000512The options (if present) consist of comma-separated option
Damien Miller450a7a12000-03-26 13:04:51 +1000513specifications.
514No spaces are permitted, except within double quotes.
Ben Lindstrom1c0fd092001-09-12 16:36:17 +0000515The following option specifications are supported (note
516that option keywords are case-insensitive):
Damien Miller32aa1441999-10-29 09:15:49 +1000517.Bl -tag -width Ds
Damien Millercd38c9c2010-03-04 21:51:37 +1100518.It Cm cert-authority
Damien Miller0a80ca12010-02-27 07:55:05 +1100519Specifies that the listed key is a certification authority (CA) that is
520trusted to validate signed certificates for user authentication.
521.Pp
522Certificates may encode access restrictions similar to these key options.
523If both certificate restrictions and key options are present, the most
524restrictive union of the two is applied.
Damien Miller32aa1441999-10-29 09:15:49 +1000525.It Cm command="command"
526Specifies that the command is executed whenever this key is used for
Damien Miller450a7a12000-03-26 13:04:51 +1000527authentication.
528The command supplied by the user (if any) is ignored.
Ben Lindstrom23124ea2001-09-14 23:14:25 +0000529The command is run on a pty if the client requests a pty;
Damien Miller450a7a12000-03-26 13:04:51 +1000530otherwise it is run without a tty.
Damien Millerffadc582003-02-24 11:52:26 +1100531If an 8-bit clean channel is required,
Ben Lindstrom594e2032001-09-12 18:35:30 +0000532one must not request a pty or should specify
Damien Miller33804262001-02-04 23:20:18 +1100533.Cm no-pty .
Damien Miller450a7a12000-03-26 13:04:51 +1000534A quote may be included in the command by quoting it with a backslash.
535This option might be useful
Damien Millerb83df8d2002-09-04 16:24:55 +1000536to restrict certain public keys to perform just a specific operation.
Damien Miller450a7a12000-03-26 13:04:51 +1000537An example might be a key that permits remote backups but nothing else.
Damien Miller7c24b812006-01-14 10:09:56 +1100538Note that the client may specify TCP and/or X11
Damien Miller30c3d422000-05-09 11:02:59 +1000539forwarding unless they are explicitly prohibited.
Damien Millere2754432006-07-24 14:06:47 +1000540The command originally supplied by the client is available in the
541.Ev SSH_ORIGINAL_COMMAND
542environment variable.
Ben Lindstrom20daef72001-09-20 00:54:01 +0000543Note that this option applies to shell, command or subsystem execution.
Damien Miller0a80ca12010-02-27 07:55:05 +1100544Also note that this command may be superseded by either a
545.Xr sshd_config 5
546.Cm ForceCommand
547directive or a command embedded in a certificate.
Damien Miller32aa1441999-10-29 09:15:49 +1000548.It Cm environment="NAME=value"
549Specifies that the string is to be added to the environment when
Damien Miller450a7a12000-03-26 13:04:51 +1000550logging in using this key.
551Environment variables set this way
552override other default environment values.
553Multiple options of this type are permitted.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000554Environment processing is disabled by default and is
555controlled via the
556.Cm PermitUserEnvironment
557option.
Ben Lindstrom38b951c2001-12-06 17:47:47 +0000558This option is automatically disabled if
559.Cm UseLogin
560is enabled.
Damien Miller31bdc522006-03-15 11:31:44 +1100561.It Cm from="pattern-list"
Darren Tucker896ad5a2008-06-11 09:34:46 +1000562Specifies that in addition to public key authentication, either the canonical
Darren Tucker11996732008-06-13 04:32:00 +1000563name of the remote host or its IP address must be present in the
Darren Tucker896ad5a2008-06-11 09:34:46 +1000564comma-separated list of patterns.
Damien Millerc7d5b5e2006-03-15 11:55:08 +1100565See
566.Sx PATTERNS
567in
568.Xr ssh_config 5
569for more information on patterns.
Darren Tucker896ad5a2008-06-11 09:34:46 +1000570.Pp
571In addition to the wildcard matching that may be applied to hostnames or
572addresses, a
573.Cm from
Darren Tucker5837b512009-06-21 17:52:27 +1000574stanza may match IP addresses using CIDR address/masklen notation.
Darren Tucker896ad5a2008-06-11 09:34:46 +1000575.Pp
576The purpose of this option is to optionally increase security: public key
577authentication by itself does not trust the network or name servers or
578anything (but the key); however, if somebody somehow steals the key, the key
579permits an intruder to log in from anywhere in the world.
580This additional option makes using a stolen key more difficult (name
581servers and/or routers would have to be compromised in addition to
582just the key).
Damien Miller31bdc522006-03-15 11:31:44 +1100583.It Cm no-agent-forwarding
584Forbids authentication agent forwarding when this key is used for
585authentication.
Damien Miller32aa1441999-10-29 09:15:49 +1000586.It Cm no-port-forwarding
Damien Miller7c24b812006-01-14 10:09:56 +1100587Forbids TCP forwarding when this key is used for authentication.
Damien Miller450a7a12000-03-26 13:04:51 +1000588Any port forward requests by the client will return an error.
Damien Miller208f1ed2006-03-15 11:56:03 +1100589This might be used, e.g. in connection with the
Damien Miller32aa1441999-10-29 09:15:49 +1000590.Cm command
591option.
Damien Miller31bdc522006-03-15 11:31:44 +1100592.It Cm no-pty
593Prevents tty allocation (a request to allocate a pty will fail).
Damien Miller95e80952008-03-27 11:03:05 +1100594.It Cm no-user-rc
Damien Miller13ba9c22008-04-03 20:52:51 +1100595Disables execution of
Damien Miller95e80952008-03-27 11:03:05 +1100596.Pa ~/.ssh/rc .
Damien Miller32aa1441999-10-29 09:15:49 +1000597.It Cm no-X11-forwarding
598Forbids X11 forwarding when this key is used for authentication.
599Any X11 forward requests by the client will return an error.
Damien Millera243fde2001-03-19 23:16:08 +1100600.It Cm permitopen="host:port"
Ben Lindstrom24643222001-06-25 05:08:11 +0000601Limit local
Damien Millera243fde2001-03-19 23:16:08 +1100602.Li ``ssh -L''
Ben Lindstrom4b3564e2001-04-10 02:41:56 +0000603port forwarding such that it may only connect to the specified host and
Ben Lindstromd71ba572001-09-12 18:03:31 +0000604port.
Damien Miller7fa96602010-08-05 13:03:13 +1000605IPv6 addresses can be specified by enclosing the address in square brackets.
Ben Lindstromd71ba572001-09-12 18:03:31 +0000606Multiple
Damien Millera243fde2001-03-19 23:16:08 +1100607.Cm permitopen
Damien Millerfbf486b2003-05-23 18:44:23 +1000608options may be applied separated by commas.
609No pattern matching is performed on the specified hostnames,
610they must be literal domains or addresses.
Damien Miller30da3442010-05-10 11:58:03 +1000611.It Cm principals="principals"
612On a
613.Cm cert-authority
614line, specifies allowed principals for certificate authentication as a
615comma-separated list.
616At least one name from the list must appear in the certificate's
617list of principals for the certificate to be accepted.
618This option is ignored for keys that are not marked as trusted certificate
619signers using the
620.Cm cert-authority
621option.
Damien Millerd27b9472005-12-13 19:29:02 +1100622.It Cm tunnel="n"
623Force a
624.Xr tun 4
625device on the server.
626Without this option, the next available device will be used if
627the client requests a tunnel.
Damien Miller32aa1441999-10-29 09:15:49 +1000628.El
Damien Miller32aa1441999-10-29 09:15:49 +1000629.Pp
Damien Miller7d2ef022006-03-15 11:32:06 +1100630An example authorized_keys file:
Damien Millerc8f61cf2006-03-15 11:33:25 +1100631.Bd -literal -offset 3n
Damien Miller7d2ef022006-03-15 11:32:06 +1100632# Comments allowed at start of line
633ssh-rsa AAAAB3Nza...LiPk== user@example.net
Damien Millerc8f61cf2006-03-15 11:33:25 +1100634from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
635AAAAB2...19Q== john@example.net
636command="dump /home",no-pty,no-port-forwarding ssh-dss
637AAAAC3...51R== example.net
638permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss
639AAAAB5...21S==
640tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
641jane@example.net
Damien Miller7d2ef022006-03-15 11:32:06 +1100642.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000643.Sh SSH_KNOWN_HOSTS FILE FORMAT
Damien Miller22c77262000-04-13 12:26:34 +1000644The
Damien Millerffadc582003-02-24 11:52:26 +1100645.Pa /etc/ssh/ssh_known_hosts
Damien Miller22c77262000-04-13 12:26:34 +1000646and
Damien Miller167ea5d2005-05-26 12:04:02 +1000647.Pa ~/.ssh/known_hosts
Damien Miller450a7a12000-03-26 13:04:51 +1000648files contain host public keys for all known hosts.
649The global file should
650be prepared by the administrator (optional), and the per-user file is
Damien Miller9a7f2012006-03-15 11:32:42 +1100651maintained automatically: whenever the user connects from an unknown host,
Damien Miller450a7a12000-03-26 13:04:51 +1000652its key is added to the per-user file.
Damien Miller32aa1441999-10-29 09:15:49 +1000653.Pp
Damien Millera7dab8b2010-03-05 10:42:05 +1100654Each line in these files contains the following fields: markers (optional),
655hostnames, bits, exponent, modulus, comment.
Damien Miller450a7a12000-03-26 13:04:51 +1000656The fields are separated by spaces.
Damien Miller32aa1441999-10-29 09:15:49 +1000657.Pp
Damien Millera7dab8b2010-03-05 10:42:05 +1100658The marker is optional, but if it is present then it must be one of
659.Dq @cert-authority ,
660to indicate that the line contains a certification authority (CA) key,
661or
662.Dq @revoked ,
663to indicate that the key contained on the line is revoked and must not ever
664be accepted.
665Only one marker should be used on a key line.
666.Pp
Damien Miller31554322003-05-14 13:44:58 +1000667Hostnames is a comma-separated list of patterns
Damien Miller9a7f2012006-03-15 11:32:42 +1100668.Pf ( Ql *
Damien Millerfbf486b2003-05-23 18:44:23 +1000669and
670.Ql \&?
Damien Miller049245d2003-05-14 13:44:42 +1000671act as
Damien Miller32aa1441999-10-29 09:15:49 +1000672wildcards); each pattern in turn is matched against the canonical host
673name (when authenticating a client) or against the user-supplied
Damien Miller450a7a12000-03-26 13:04:51 +1000674name (when authenticating a server).
675A pattern may also be preceded by
Damien Miller049245d2003-05-14 13:44:42 +1000676.Ql \&!
Damien Miller32aa1441999-10-29 09:15:49 +1000677to indicate negation: if the host name matches a negated
678pattern, it is not accepted (by that line) even if it matched another
679pattern on the line.
Darren Tuckerda345532006-07-10 23:04:19 +1000680A hostname or address may optionally be enclosed within
681.Ql \&[
682and
683.Ql \&]
684brackets then followed by
685.Ql \&:
Darren Tucker11318472006-07-12 22:07:59 +1000686and a non-standard port number.
Damien Miller32aa1441999-10-29 09:15:49 +1000687.Pp
Damien Millere1776152005-03-01 21:47:37 +1100688Alternately, hostnames may be stored in a hashed form which hides host names
Damien Miller718fd4b2005-03-02 12:03:23 +1100689and addresses should the file's contents be disclosed.
690Hashed hostnames start with a
691.Ql |
Damien Millere1776152005-03-01 21:47:37 +1100692character.
693Only one hashed hostname may appear on a single line and none of the above
694negation or wildcard operators may be applied.
695.Pp
Damien Millere247cc42000-05-07 12:03:14 +1000696Bits, exponent, and modulus are taken directly from the RSA host key; they
Damien Miller9a7f2012006-03-15 11:32:42 +1100697can be obtained, for example, from
Damien Miller05eda432002-02-10 18:32:28 +1100698.Pa /etc/ssh/ssh_host_key.pub .
Damien Miller32aa1441999-10-29 09:15:49 +1000699The optional comment field continues to the end of the line, and is not used.
700.Pp
701Lines starting with
702.Ql #
703and empty lines are ignored as comments.
704.Pp
705When performing host authentication, authentication is accepted if any
Damien Millera7dab8b2010-03-05 10:42:05 +1100706matching line has the proper key; either one that matches exactly or,
707if the server has presented a certificate for authentication, the key
708of the certification authority that signed the certificate.
709For a key to be trusted as a certification authority, it must use the
710.Dq @cert-authority
711marker described above.
712.Pp
713The known hosts file also provides a facility to mark keys as revoked,
714for example when it is known that the associated private key has been
715stolen.
716Revoked keys are specified by including the
717.Dq @revoked
718marker at the beginning of the key line, and are never accepted for
719authentication or as certification authorities, but instead will
720produce a warning from
721.Xr ssh 1
722when they are encountered.
723.Pp
724It is permissible (but not
Damien Miller32aa1441999-10-29 09:15:49 +1000725recommended) to have several lines or different host keys for the same
Damien Miller450a7a12000-03-26 13:04:51 +1000726names.
727This will inevitably happen when short forms of host names
728from different domains are put in the file.
729It is possible
Damien Miller32aa1441999-10-29 09:15:49 +1000730that the files contain conflicting information; authentication is
731accepted if valid information can be found from either file.
732.Pp
733Note that the lines in these files are typically hundreds of characters
734long, and you definitely don't want to type in the host keys by hand.
Damien Millera7dab8b2010-03-05 10:42:05 +1100735Rather, generate them by a script,
736.Xr ssh-keyscan 1
Damien Miller22c77262000-04-13 12:26:34 +1000737or by taking
Damien Miller05eda432002-02-10 18:32:28 +1100738.Pa /etc/ssh/ssh_host_key.pub
Damien Miller32aa1441999-10-29 09:15:49 +1000739and adding the host names at the front.
Damien Millera7dab8b2010-03-05 10:42:05 +1100740.Xr ssh-keygen 1
Damien Miller98339052010-03-05 21:30:35 +1100741also offers some basic automated editing for
Damien Millera7dab8b2010-03-05 10:42:05 +1100742.Pa ~/.ssh/known_hosts
743including removing hosts matching a host name and converting all host
744names to their hashed representations.
Damien Millercc00f5e2006-03-15 11:33:00 +1100745.Pp
746An example ssh_known_hosts file:
747.Bd -literal -offset 3n
748# Comments allowed at start of line
749closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
750cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
Damien Millere1776152005-03-01 21:47:37 +1100751# A hashed hostname
752|1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
753AAAA1234.....=
Damien Millera7dab8b2010-03-05 10:42:05 +1100754# A revoked key
755@revoked * ssh-rsa AAAAB5W...
756# A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
757@cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
Damien Millere1776152005-03-01 21:47:37 +1100758.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000759.Sh FILES
Damien Millerd8702e82006-03-15 11:33:56 +1100760.Bl -tag -width Ds -compact
Damien Millerafdae612010-08-31 22:31:14 +1000761.It Pa ~/.hushlogin
Damien Miller70a908e2005-03-01 21:17:09 +1100762This file is used to suppress printing the last login time and
763.Pa /etc/motd ,
764if
765.Cm PrintLastLog
766and
767.Cm PrintMotd ,
768respectively,
769are enabled.
770It does not suppress printing of the banner specified by
771.Cm Banner .
Damien Millerd8702e82006-03-15 11:33:56 +1100772.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000773.It Pa ~/.rhosts
Damien Milleradc35b92006-03-15 11:35:27 +1100774This file is used for host-based authentication (see
775.Xr ssh 1
776for more information).
777On some machines this file may need to be
778world-readable if the user's home directory is on an NFS partition,
779because
780.Nm
781reads it as root.
782Additionally, this file must be owned by the user,
783and must not have write permissions for anyone else.
784The recommended
785permission for most machines is read/write for the user, and not
Damien Miller32aa1441999-10-29 09:15:49 +1000786accessible by others.
787.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000788.It Pa ~/.shosts
Damien Milleradc35b92006-03-15 11:35:27 +1100789This file is used in exactly the same way as
790.Pa .rhosts ,
791but allows host-based authentication without permitting login with
792rlogin/rsh.
Damien Miller32aa1441999-10-29 09:15:49 +1000793.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000794.It Pa ~/.ssh/
Damien Miller520e6152008-02-10 22:46:22 +1100795This directory is the default location for all user-specific configuration
796and authentication information.
797There is no general requirement to keep the entire contents of this directory
798secret, but the recommended permissions are read/write/execute for the user,
799and not accessible by others.
800.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000801.It Pa ~/.ssh/authorized_keys
Damien Millereb8b60e2010-08-31 22:41:14 +1000802Lists the public keys (DSA/ECDSA/RSA) that can be used for logging in
803as this user.
Damien Millerd8702e82006-03-15 11:33:56 +1100804The format of this file is described above.
Damien Miller5d43d492006-08-30 11:07:00 +1000805The content of the file is not highly sensitive, but the recommended
Damien Milleradc35b92006-03-15 11:35:27 +1100806permissions are read/write for the user, and not accessible by others.
Damien Miller32aa1441999-10-29 09:15:49 +1000807.Pp
Damien Miller5d43d492006-08-30 11:07:00 +1000808If this file, the
809.Pa ~/.ssh
810directory, or the user's home directory are writable
811by other users, then the file could be modified or replaced by unauthorized
812users.
813In this case,
814.Nm
815will not allow it to be used unless the
816.Cm StrictModes
817option has been set to
818.Dq no .
Damien Miller5d43d492006-08-30 11:07:00 +1000819.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000820.It Pa ~/.ssh/environment
Damien Miller450a7a12000-03-26 13:04:51 +1000821This file is read into the environment at login (if it exists).
822It can only contain empty lines, comment lines (that start with
Damien Miller32aa1441999-10-29 09:15:49 +1000823.Ql # ) ,
Damien Miller450a7a12000-03-26 13:04:51 +1000824and assignment lines of the form name=value.
825The file should be writable
Damien Miller32aa1441999-10-29 09:15:49 +1000826only by the user; it need not be readable by anyone else.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000827Environment processing is disabled by default and is
828controlled via the
829.Cm PermitUserEnvironment
830option.
Damien Millerd8702e82006-03-15 11:33:56 +1100831.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000832.It Pa ~/.ssh/known_hosts
Damien Milleradc35b92006-03-15 11:35:27 +1100833Contains a list of host keys for all hosts the user has logged into
834that are not already in the systemwide list of known host keys.
835The format of this file is described above.
836This file should be writable only by root/the owner and
Damien Millerd8702e82006-03-15 11:33:56 +1100837can, but need not be, world-readable.
838.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000839.It Pa ~/.ssh/rc
Damien Millerfd725cf2006-03-15 11:35:54 +1100840Contains initialization routines to be run before
841the user's home directory becomes accessible.
Damien Miller32aa1441999-10-29 09:15:49 +1000842This file should be writable only by the user, and need not be
843readable by anyone else.
Damien Millerd8702e82006-03-15 11:33:56 +1100844.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000845.It Pa /etc/hosts.allow
846.It Pa /etc/hosts.deny
Damien Millerd8702e82006-03-15 11:33:56 +1100847Access controls that should be enforced by tcp-wrappers are defined here.
848Further details are described in
849.Xr hosts_access 5 .
850.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000851.It Pa /etc/hosts.equiv
Damien Miller445121f2006-03-15 11:36:18 +1100852This file is for host-based authentication (see
853.Xr ssh 1 ) .
854It should only be writable by root.
Damien Millerd8702e82006-03-15 11:33:56 +1100855.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000856.It Pa /etc/moduli
Damien Millerd8702e82006-03-15 11:33:56 +1100857Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
858The file format is described in
859.Xr moduli 5 .
860.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000861.It Pa /etc/motd
Damien Millerd8702e82006-03-15 11:33:56 +1100862See
863.Xr motd 5 .
864.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000865.It Pa /etc/nologin
Damien Millerd8702e82006-03-15 11:33:56 +1100866If this file exists,
867.Nm
868refuses to let anyone except root log in.
869The contents of the file
870are displayed to anyone trying to log in, and non-root connections are
871refused.
872The file should be world-readable.
873.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000874.It Pa /etc/shosts.equiv
Damien Miller445121f2006-03-15 11:36:18 +1100875This file is used in exactly the same way as
876.Pa hosts.equiv ,
877but allows host-based authentication without permitting login with
878rlogin/rsh.
Damien Millerd8702e82006-03-15 11:33:56 +1100879.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000880.It Pa /etc/ssh/ssh_host_key
881.It Pa /etc/ssh/ssh_host_dsa_key
Damien Millereb8b60e2010-08-31 22:41:14 +1000882.It Pa /etc/ssh/ssh_host_ecdsa_key
Damien Millerafdae612010-08-31 22:31:14 +1000883.It Pa /etc/ssh/ssh_host_rsa_key
Damien Millerd8702e82006-03-15 11:33:56 +1100884These three files contain the private parts of the host keys.
885These files should only be owned by root, readable only by root, and not
886accessible to others.
887Note that
888.Nm
Damien Milleredd03752006-03-15 11:36:45 +1100889does not start if these files are group/world-accessible.
Damien Millerd8702e82006-03-15 11:33:56 +1100890.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000891.It Pa /etc/ssh/ssh_host_key.pub
892.It Pa /etc/ssh/ssh_host_dsa_key.pub
Damien Millereb8b60e2010-08-31 22:41:14 +1000893.It Pa /etc/ssh/ssh_host_ecdsa_key.pub
Damien Millerafdae612010-08-31 22:31:14 +1000894.It Pa /etc/ssh/ssh_host_rsa_key.pub
Damien Millerd8702e82006-03-15 11:33:56 +1100895These three files contain the public parts of the host keys.
896These files should be world-readable but writable only by
897root.
898Their contents should match the respective private parts.
899These files are not
900really used for anything; they are provided for the convenience of
901the user so their contents can be copied to known hosts files.
902These files are created using
903.Xr ssh-keygen 1 .
904.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000905.It Pa /etc/ssh/ssh_known_hosts
Darren Tucker04354b92007-03-21 20:46:54 +1100906Systemwide list of known host keys.
907This file should be prepared by the
908system administrator to contain the public host keys of all machines in the
909organization.
910The format of this file is described above.
911This file should be writable only by root/the owner and
912should be world-readable.
913.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000914.It Pa /etc/ssh/sshd_config
Damien Millerd8702e82006-03-15 11:33:56 +1100915Contains configuration data for
916.Nm sshd .
917The file format and configuration options are described in
918.Xr sshd_config 5 .
919.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000920.It Pa /etc/ssh/sshrc
Damien Millerfd725cf2006-03-15 11:35:54 +1100921Similar to
922.Pa ~/.ssh/rc ,
923it can be used to specify
Damien Miller450a7a12000-03-26 13:04:51 +1000924machine-specific login-time initializations globally.
925This file should be writable only by root, and should be world-readable.
Damien Millerd8702e82006-03-15 11:33:56 +1100926.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000927.It Pa /var/empty
Damien Millerd8702e82006-03-15 11:33:56 +1100928.Xr chroot 2
929directory used by
930.Nm
931during privilege separation in the pre-authentication phase.
932The directory should not contain any files and must be owned by root
933and not group or world-writable.
934.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000935.It Pa /var/run/sshd.pid
Damien Millerd8702e82006-03-15 11:33:56 +1100936Contains the process ID of the
937.Nm
938listening for connections (if there are several daemons running
939concurrently for different ports, this contains the process ID of the one
940started last).
941The content of this file is not sensitive; it can be world-readable.
Damien Miller37023962000-07-11 17:31:38 +1000942.El
Damien Miller32aa1441999-10-29 09:15:49 +1000943.Sh SEE ALSO
Damien Miller32aa1441999-10-29 09:15:49 +1000944.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +1100945.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +1000946.Xr ssh 1 ,
947.Xr ssh-add 1 ,
948.Xr ssh-agent 1 ,
949.Xr ssh-keygen 1 ,
Darren Tucker04354b92007-03-21 20:46:54 +1100950.Xr ssh-keyscan 1 ,
Darren Tucker1f203942003-10-15 15:50:42 +1000951.Xr chroot 2 ,
952.Xr hosts_access 5 ,
Ben Lindstromc8e29ce2001-08-06 20:55:28 +0000953.Xr login.conf 5 ,
954.Xr moduli 5 ,
Ben Lindstrom9f049032002-06-21 00:59:05 +0000955.Xr sshd_config 5 ,
Darren Tucker1f203942003-10-15 15:50:42 +1000956.Xr inetd 8 ,
Ben Lindstromd2bf0d62001-06-25 04:10:54 +0000957.Xr sftp-server 8
Damien Millerf1ce5052003-06-11 22:04:39 +1000958.Sh AUTHORS
959OpenSSH is a derivative of the original and free
960ssh 1.2.12 release by Tatu Ylonen.
961Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
962Theo de Raadt and Dug Song
963removed many bugs, re-added newer features and
964created OpenSSH.
965Markus Friedl contributed the support for SSH
966protocol versions 1.5 and 2.0.
967Niels Provos and Markus Friedl contributed support
968for privilege separation.
Damien Millerc47d7e92006-03-15 11:27:20 +1100969.Sh CAVEATS
970System security is not improved unless
971.Nm rshd ,
972.Nm rlogind ,
973and
974.Nm rexecd
975are disabled (thus completely disabling
976.Xr rlogin
977and
978.Xr rsh
979into the machine).