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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.\"
Darren Tucker427e4092012-10-05 11:02:39 +100036.\" $OpenBSD: sshd.8,v 1.267 2012/10/04 13:21:50 markus Exp $
37.Dd $Mdocdate: October 4 2012 $
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 ,
Darren Tuckerfbcf8272012-05-19 19:37:01 +1000117.Dq laddr ,
118.Dq lport ,
Darren Tuckere7f3f752008-06-10 23:06:01 +1000119and
120.Dq addr .
121All are required and may be supplied in any order, either with multiple
122.Fl C
123options or as a comma-separated list.
Damien Miller15f5b562010-03-03 10:25:21 +1100124.It Fl c Ar host_certificate_file
125Specifies a path to a certificate file to identify
126.Nm
127during key exchange.
128The certificate file must match a host key file specified using the
129.Fl h
130option or the
131.Cm HostKey
132configuration directive.
Darren Tucker1f203942003-10-15 15:50:42 +1000133.It Fl D
134When this option is specified,
135.Nm
136will not detach and does not become a daemon.
137This allows easy monitoring of
138.Nm sshd .
Damien Miller32aa1441999-10-29 09:15:49 +1000139.It Fl d
Damien Miller450a7a12000-03-26 13:04:51 +1000140Debug mode.
Damien Miller74d98252010-02-02 17:01:46 +1100141The server sends verbose debug output to standard error,
142and does not put itself in the background.
Damien Miller450a7a12000-03-26 13:04:51 +1000143The server also will not fork and will only process one connection.
144This option is only intended for debugging for the server.
Damien Millerffadc582003-02-24 11:52:26 +1100145Multiple
146.Fl d
147options increase the debugging level.
Damien Miller874d77b2000-10-14 16:23:11 +1100148Maximum is 3.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000149.It Fl e
150When this option is specified,
151.Nm
152will send the output to the standard error instead of the system log.
Darren Tucker04354b92007-03-21 20:46:54 +1100153.It Fl f Ar config_file
Damien Miller450a7a12000-03-26 13:04:51 +1000154Specifies the name of the configuration file.
155The default is
Damien Miller05eda432002-02-10 18:32:28 +1100156.Pa /etc/ssh/sshd_config .
Damien Miller32aa1441999-10-29 09:15:49 +1000157.Nm
158refuses to start if there is no configuration file.
159.It Fl g Ar login_grace_time
160Gives the grace time for clients to authenticate themselves (default
Damien Millerc1348632002-09-05 14:35:14 +1000161120 seconds).
Damien Miller450a7a12000-03-26 13:04:51 +1000162If the client fails to authenticate the user within
163this many seconds, the server disconnects and exits.
164A value of zero indicates no limit.
Damien Miller32aa1441999-10-29 09:15:49 +1000165.It Fl h Ar host_key_file
Damien Miller7fc23732002-01-22 23:19:11 +1100166Specifies a file from which a host key is read.
Damien Miller32aa1441999-10-29 09:15:49 +1000167This option must be given if
168.Nm
169is not run as root (as the normal
Damien Miller7fc23732002-01-22 23:19:11 +1100170host key files are normally not readable by anyone but root).
171The default is
Damien Miller05eda432002-02-10 18:32:28 +1100172.Pa /etc/ssh/ssh_host_key
Damien Miller7fc23732002-01-22 23:19:11 +1100173for protocol version 1, and
Damien Millereb8b60e2010-08-31 22:41:14 +1000174.Pa /etc/ssh/ssh_host_dsa_key ,
175.Pa /etc/ssh/ssh_host_ecdsa_key
Damien Miller7fc23732002-01-22 23:19:11 +1100176and
Damien Millereb8b60e2010-08-31 22:41:14 +1000177.Pa /etc/ssh/ssh_host_rsa_key
Damien Miller7fc23732002-01-22 23:19:11 +1100178for protocol version 2.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000179It is possible to have multiple host key files for
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000180the different protocol versions and host key algorithms.
Damien Miller32aa1441999-10-29 09:15:49 +1000181.It Fl i
182Specifies that
183.Nm
Damien Millerffadc582003-02-24 11:52:26 +1100184is being run from
185.Xr inetd 8 .
Damien Miller32aa1441999-10-29 09:15:49 +1000186.Nm
187is normally not run
188from inetd because it needs to generate the server key before it can
Damien Miller450a7a12000-03-26 13:04:51 +1000189respond to the client, and this may take tens of seconds.
190Clients would have to wait too long if the key was regenerated every time.
Damien Miller208f1ed2006-03-15 11:56:03 +1100191However, with small key sizes (e.g. 512) using
Damien Miller32aa1441999-10-29 09:15:49 +1000192.Nm
193from inetd may
194be feasible.
195.It Fl k Ar key_gen_time
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000196Specifies how often the ephemeral protocol version 1 server key is
197regenerated (default 3600 seconds, or one hour).
Damien Miller450a7a12000-03-26 13:04:51 +1000198The motivation for regenerating the key fairly
Darren Tucker1f203942003-10-15 15:50:42 +1000199often is that the key is not stored anywhere, and after about an hour
Damien Miller32aa1441999-10-29 09:15:49 +1000200it becomes impossible to recover the key for decrypting intercepted
201communications even if the machine is cracked into or physically
Damien Miller450a7a12000-03-26 13:04:51 +1000202seized.
203A value of zero indicates that the key will never be regenerated.
Ben Lindstromade03f62001-12-06 18:22:17 +0000204.It Fl o Ar option
205Can be used to give options in the format used in the configuration file.
206This is useful for specifying options for which there is no separate
207command-line flag.
Darren Tucker1f203942003-10-15 15:50:42 +1000208For full details of the options, and their values, see
209.Xr sshd_config 5 .
Damien Miller32aa1441999-10-29 09:15:49 +1000210.It Fl p Ar port
211Specifies the port on which the server listens for connections
212(default 22).
Damien Miller7d1ded42002-01-22 23:09:41 +1100213Multiple port options are permitted.
Damien Millerd7f308f2005-12-24 14:55:16 +1100214Ports specified in the configuration file with the
215.Cm Port
216option are ignored when a command-line port is specified.
217Ports specified using the
218.Cm ListenAddress
219option override command-line ports.
Damien Miller32aa1441999-10-29 09:15:49 +1000220.It Fl q
Damien Miller450a7a12000-03-26 13:04:51 +1000221Quiet mode.
222Nothing is sent to the system log.
223Normally the beginning,
Damien Miller32aa1441999-10-29 09:15:49 +1000224authentication, and termination of each connection is logged.
Darren Tuckere7140f22008-06-10 23:01:51 +1000225.It Fl T
226Extended test mode.
227Check the validity of the configuration file, output the effective configuration
228to stdout and then exit.
229Optionally,
230.Cm Match
231rules may be applied by specifying the connection parameters using one or more
232.Fl C
233options.
Darren Tuckere7f3f752008-06-10 23:06:01 +1000234.It Fl t
235Test mode.
236Only check the validity of the configuration file and sanity of the keys.
237This is useful for updating
238.Nm
239reliably as configuration options may change.
Damien Miller942da032000-08-18 13:59:06 +1000240.It Fl u Ar len
241This option is used to specify the size of the field
242in the
243.Li utmp
244structure that holds the remote host name.
245If the resolved host name is longer than
246.Ar len ,
247the dotted decimal value will be used instead.
248This allows hosts with very long host names that
249overflow this field to still be uniquely identified.
250Specifying
251.Fl u0
252indicates that only dotted decimal addresses
253should be put into the
254.Pa utmp
255file.
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000256.Fl u0
Damien Millerffadc582003-02-24 11:52:26 +1100257may also be used to prevent
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000258.Nm
259from making DNS requests unless the authentication
260mechanism or configuration requires it.
261Authentication mechanisms that may require DNS include
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000262.Cm RhostsRSAAuthentication ,
Damien Miller2ac05772006-02-01 22:05:42 +1100263.Cm HostbasedAuthentication ,
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000264and using a
265.Cm from="pattern-list"
266option in a key file.
Ben Lindstromea03db92002-03-05 01:38:57 +0000267Configuration options that require DNS include using a
268USER@HOST pattern in
269.Cm AllowUsers
270or
271.Cm DenyUsers .
Damien Miller32aa1441999-10-29 09:15:49 +1000272.El
Damien Miller8bbdf902006-02-01 22:05:25 +1100273.Sh AUTHENTICATION
274The OpenSSH SSH daemon supports SSH protocols 1 and 2.
Darren Tucker7a4a7652009-10-11 21:51:40 +1100275The default is to use protocol 2 only,
Damien Miller8bbdf902006-02-01 22:05:25 +1100276though this can be changed via the
277.Cm Protocol
278option in
279.Xr sshd_config 5 .
Damien Millereb8b60e2010-08-31 22:41:14 +1000280Protocol 2 supports DSA, ECDSA and RSA keys;
Damien Miller8bbdf902006-02-01 22:05:25 +1100281protocol 1 only supports RSA keys.
282For both protocols,
283each host has a host-specific key,
284normally 2048 bits,
285used to identify the host.
Damien Miller99cc4a82006-01-31 21:45:53 +1100286.Pp
Damien Miller8bbdf902006-02-01 22:05:25 +1100287Forward security for protocol 1 is provided through
288an additional server key,
289normally 768 bits,
290generated when the server starts.
Damien Miller99cc4a82006-01-31 21:45:53 +1100291This key is normally regenerated every hour if it has been used, and
292is never stored on disk.
Damien Miller99cc4a82006-01-31 21:45:53 +1100293Whenever a client connects, the daemon responds with its public
294host and server keys.
295The client compares the
296RSA host key against its own database to verify that it has not changed.
297The client then generates a 256-bit random number.
298It encrypts this
299random number using both the host key and the server key, and sends
300the encrypted number to the server.
301Both sides then use this
302random number as a session key which is used to encrypt all further
303communications in the session.
304The rest of the session is encrypted
305using a conventional cipher, currently Blowfish or 3DES, with 3DES
306being used by default.
307The client selects the encryption algorithm
308to use from those offered by the server.
309.Pp
Damien Miller8bbdf902006-02-01 22:05:25 +1100310For protocol 2,
311forward security is provided through a Diffie-Hellman key agreement.
312This key agreement results in a shared session key.
313The rest of the session is encrypted using a symmetric cipher, currently
314128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES.
315The client selects the encryption algorithm
316to use from those offered by the server.
317Additionally, session integrity is provided
318through a cryptographic message authentication code
Darren Tucker427e4092012-10-05 11:02:39 +1000319(hmac-md5, hmac-sha1, umac-64, umac-128, hmac-ripemd160,
Damien Miller20bd4532011-08-06 06:17:30 +1000320hmac-sha2-256 or hmac-sha2-512).
Damien Miller8bbdf902006-02-01 22:05:25 +1100321.Pp
322Finally, the server and the client enter an authentication dialog.
Damien Miller99cc4a82006-01-31 21:45:53 +1100323The client tries to authenticate itself using
Damien Miller8bbdf902006-02-01 22:05:25 +1100324host-based authentication,
325public key authentication,
326challenge-response authentication,
327or password authentication.
Damien Miller99cc4a82006-01-31 21:45:53 +1100328.Pp
329Regardless of the authentication type, the account is checked to
330ensure that it is accessible. An account is not accessible if it is
331locked, listed in
332.Cm DenyUsers
333or its group is listed in
334.Cm DenyGroups
335\&. The definition of a locked account is system dependant. Some platforms
336have their own account database (eg AIX) and some modify the passwd field (
337.Ql \&*LK\&*
338on Solaris and UnixWare,
339.Ql \&*
340on HP-UX, containing
341.Ql Nologin
342on Tru64,
343a leading
344.Ql \&*LOCKED\&*
345on FreeBSD and a leading
Darren Tucker1a9176b2007-08-17 09:42:32 +1000346.Ql \&!
347on most Linuxes).
348If there is a requirement to disable password authentication
Damien Miller99cc4a82006-01-31 21:45:53 +1100349for the account while allowing still public-key, then the passwd field
350should be set to something other than these values (eg
351.Ql NP
352or
353.Ql \&*NP\&*
354).
355.Pp
Damien Miller99cc4a82006-01-31 21:45:53 +1100356If the client successfully authenticates itself, a dialog for
357preparing the session is entered.
358At this time the client may request
359things like allocating a pseudo-tty, forwarding X11 connections,
360forwarding TCP connections, or forwarding the authentication agent
361connection over the secure channel.
362.Pp
Damien Millerc47d7e92006-03-15 11:27:20 +1100363After this, the client either requests a shell or execution of a command.
Damien Miller99cc4a82006-01-31 21:45:53 +1100364The sides then enter session mode.
365In this mode, either side may send
366data at any time, and such data is forwarded to/from the shell or
367command on the server side, and the user terminal in the client side.
368.Pp
369When the user program terminates and all forwarded X11 and other
370connections have been closed, the server sends command exit status to
371the client, and both sides exit.
Damien Miller32aa1441999-10-29 09:15:49 +1000372.Sh LOGIN PROCESS
373When a user successfully logs in,
374.Nm
375does the following:
376.Bl -enum -offset indent
377.It
378If the login is on a tty, and no command has been specified,
Damien Miller22c77262000-04-13 12:26:34 +1000379prints last login time and
Damien Miller32aa1441999-10-29 09:15:49 +1000380.Pa /etc/motd
381(unless prevented in the configuration file or by
Damien Miller167ea5d2005-05-26 12:04:02 +1000382.Pa ~/.hushlogin ;
Damien Miller32aa1441999-10-29 09:15:49 +1000383see the
Damien Miller22c77262000-04-13 12:26:34 +1000384.Sx FILES
Damien Miller32aa1441999-10-29 09:15:49 +1000385section).
386.It
387If the login is on a tty, records login time.
388.It
389Checks
390.Pa /etc/nologin ;
391if it exists, prints contents and quits
392(unless root).
393.It
394Changes to run with normal user privileges.
395.It
396Sets up basic environment.
397.It
Darren Tucker1f203942003-10-15 15:50:42 +1000398Reads the file
Damien Miller167ea5d2005-05-26 12:04:02 +1000399.Pa ~/.ssh/environment ,
Darren Tucker1f203942003-10-15 15:50:42 +1000400if it exists, and users are allowed to change their environment.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000401See the
Ben Lindstromdc7adf22002-08-20 18:38:02 +0000402.Cm PermitUserEnvironment
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000403option in
Ben Lindstromdc7adf22002-08-20 18:38:02 +0000404.Xr sshd_config 5 .
Damien Miller32aa1441999-10-29 09:15:49 +1000405.It
406Changes to user's home directory.
407.It
408If
Damien Miller167ea5d2005-05-26 12:04:02 +1000409.Pa ~/.ssh/rc
Damien Miller32aa1441999-10-29 09:15:49 +1000410exists, runs it; else if
Damien Millerafcc2252002-02-10 18:32:55 +1100411.Pa /etc/ssh/sshrc
Damien Miller32aa1441999-10-29 09:15:49 +1000412exists, runs
Damien Miller450a7a12000-03-26 13:04:51 +1000413it; otherwise runs xauth.
414The
Damien Miller32aa1441999-10-29 09:15:49 +1000415.Dq rc
416files are given the X11
417authentication protocol and cookie in standard input.
Damien Millerfd725cf2006-03-15 11:35:54 +1100418See
419.Sx SSHRC ,
420below.
Damien Miller32aa1441999-10-29 09:15:49 +1000421.It
422Runs user's shell or command.
423.El
Damien Millerfd725cf2006-03-15 11:35:54 +1100424.Sh SSHRC
425If the file
426.Pa ~/.ssh/rc
427exists,
428.Xr sh 1
429runs it after reading the
430environment files but before starting the user's shell or command.
431It must not produce any output on stdout; stderr must be used
432instead.
433If X11 forwarding is in use, it will receive the "proto cookie" pair in
434its standard input (and
435.Ev DISPLAY
436in its environment).
437The script must call
438.Xr xauth 1
439because
440.Nm
441will not run xauth automatically to add X11 cookies.
442.Pp
443The primary purpose of this file is to run any initialization routines
444which may be needed before the user's home directory becomes
445accessible; AFS is a particular example of such an environment.
446.Pp
447This file will probably contain some initialization code followed by
448something similar to:
449.Bd -literal -offset 3n
450if read proto cookie && [ -n "$DISPLAY" ]; then
451 if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then
452 # X11UseLocalhost=yes
453 echo add unix:`echo $DISPLAY |
454 cut -c11-` $proto $cookie
455 else
456 # X11UseLocalhost=no
457 echo add $DISPLAY $proto $cookie
458 fi | xauth -q -
459fi
460.Ed
461.Pp
462If this file does not exist,
463.Pa /etc/ssh/sshrc
464is run, and if that
465does not exist either, xauth is used to add the cookie.
Damien Miller32aa1441999-10-29 09:15:49 +1000466.Sh AUTHORIZED_KEYS FILE FORMAT
Ben Lindstromf96704d2001-06-25 04:17:12 +0000467.Cm AuthorizedKeysFile
Damien Millerb9132fc2011-05-29 21:41:40 +1000468specifies the files containing public keys for
Damien Millerdcfea272006-03-15 11:31:22 +1100469public key authentication;
Damien Millerb9132fc2011-05-29 21:41:40 +1000470if none is specified, the default is
Damien Millerd8478b62011-05-29 21:39:36 +1000471.Pa ~/.ssh/authorized_keys
472and
473.Pa ~/.ssh/authorized_keys2 .
Damien Miller450a7a12000-03-26 13:04:51 +1000474Each line of the file contains one
Damien Miller32aa1441999-10-29 09:15:49 +1000475key (empty lines and lines starting with a
476.Ql #
477are ignored as
Damien Miller450a7a12000-03-26 13:04:51 +1000478comments).
Damien Millerdcfea272006-03-15 11:31:22 +1100479Protocol 1 public keys consist of the following space-separated fields:
480options, bits, exponent, modulus, comment.
481Protocol 2 public key consist of:
482options, keytype, base64-encoded key, comment.
483The options field is optional;
484its presence is determined by whether the line starts
Damien Millerb83df8d2002-09-04 16:24:55 +1000485with a number or not (the options field never starts with a number).
Damien Millerdcfea272006-03-15 11:31:22 +1100486The bits, exponent, modulus, and comment fields give the RSA key for
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000487protocol version 1; the
Damien Miller32aa1441999-10-29 09:15:49 +1000488comment field is not used for anything (but may be convenient for the
489user to identify the key).
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000490For protocol version 2 the keytype is
Damien Millereb8b60e2010-08-31 22:41:14 +1000491.Dq ecdsa-sha2-nistp256 ,
492.Dq ecdsa-sha2-nistp384 ,
493.Dq ecdsa-sha2-nistp521 ,
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000494.Dq ssh-dss
495or
496.Dq ssh-rsa .
Damien Miller32aa1441999-10-29 09:15:49 +1000497.Pp
498Note that lines in this file are usually several hundred bytes long
Darren Tucker22cc7412004-12-06 22:47:41 +1100499(because of the size of the public key encoding) up to a limit of
5008 kilobytes, which permits DSA keys up to 8 kilobits and RSA
501keys up to 16 kilobits.
Damien Miller450a7a12000-03-26 13:04:51 +1000502You don't want to type them in; instead, copy the
Ben Lindstrom18a82ac2001-04-11 15:59:35 +0000503.Pa identity.pub ,
Damien Millerdcfea272006-03-15 11:31:22 +1100504.Pa id_dsa.pub ,
Damien Millereb8b60e2010-08-31 22:41:14 +1000505.Pa id_ecdsa.pub ,
Ben Lindstrom18a82ac2001-04-11 15:59:35 +0000506or the
507.Pa id_rsa.pub
Damien Miller32aa1441999-10-29 09:15:49 +1000508file and edit it.
509.Pp
Ben Lindstrom0d0be022002-04-02 20:39:29 +0000510.Nm
511enforces a minimum RSA key modulus size for protocol 1
512and protocol 2 keys of 768 bits.
513.Pp
Damien Miller942da032000-08-18 13:59:06 +1000514The options (if present) consist of comma-separated option
Damien Miller450a7a12000-03-26 13:04:51 +1000515specifications.
516No spaces are permitted, except within double quotes.
Ben Lindstrom1c0fd092001-09-12 16:36:17 +0000517The following option specifications are supported (note
518that option keywords are case-insensitive):
Damien Miller32aa1441999-10-29 09:15:49 +1000519.Bl -tag -width Ds
Damien Millercd38c9c2010-03-04 21:51:37 +1100520.It Cm cert-authority
Damien Miller0a80ca12010-02-27 07:55:05 +1100521Specifies that the listed key is a certification authority (CA) that is
522trusted to validate signed certificates for user authentication.
523.Pp
524Certificates may encode access restrictions similar to these key options.
525If both certificate restrictions and key options are present, the most
526restrictive union of the two is applied.
Damien Miller32aa1441999-10-29 09:15:49 +1000527.It Cm command="command"
528Specifies that the command is executed whenever this key is used for
Damien Miller450a7a12000-03-26 13:04:51 +1000529authentication.
530The command supplied by the user (if any) is ignored.
Ben Lindstrom23124ea2001-09-14 23:14:25 +0000531The command is run on a pty if the client requests a pty;
Damien Miller450a7a12000-03-26 13:04:51 +1000532otherwise it is run without a tty.
Damien Millerffadc582003-02-24 11:52:26 +1100533If an 8-bit clean channel is required,
Ben Lindstrom594e2032001-09-12 18:35:30 +0000534one must not request a pty or should specify
Damien Miller33804262001-02-04 23:20:18 +1100535.Cm no-pty .
Damien Miller450a7a12000-03-26 13:04:51 +1000536A quote may be included in the command by quoting it with a backslash.
537This option might be useful
Damien Millerb83df8d2002-09-04 16:24:55 +1000538to restrict certain public keys to perform just a specific operation.
Damien Miller450a7a12000-03-26 13:04:51 +1000539An example might be a key that permits remote backups but nothing else.
Damien Miller7c24b812006-01-14 10:09:56 +1100540Note that the client may specify TCP and/or X11
Damien Miller30c3d422000-05-09 11:02:59 +1000541forwarding unless they are explicitly prohibited.
Damien Millere2754432006-07-24 14:06:47 +1000542The command originally supplied by the client is available in the
543.Ev SSH_ORIGINAL_COMMAND
544environment variable.
Ben Lindstrom20daef72001-09-20 00:54:01 +0000545Note that this option applies to shell, command or subsystem execution.
Damien Miller0a80ca12010-02-27 07:55:05 +1100546Also note that this command may be superseded by either a
547.Xr sshd_config 5
548.Cm ForceCommand
549directive or a command embedded in a certificate.
Damien Miller32aa1441999-10-29 09:15:49 +1000550.It Cm environment="NAME=value"
551Specifies that the string is to be added to the environment when
Damien Miller450a7a12000-03-26 13:04:51 +1000552logging in using this key.
553Environment variables set this way
554override other default environment values.
555Multiple options of this type are permitted.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000556Environment processing is disabled by default and is
557controlled via the
558.Cm PermitUserEnvironment
559option.
Ben Lindstrom38b951c2001-12-06 17:47:47 +0000560This option is automatically disabled if
561.Cm UseLogin
562is enabled.
Damien Miller31bdc522006-03-15 11:31:44 +1100563.It Cm from="pattern-list"
Darren Tucker896ad5a2008-06-11 09:34:46 +1000564Specifies that in addition to public key authentication, either the canonical
Darren Tucker11996732008-06-13 04:32:00 +1000565name of the remote host or its IP address must be present in the
Darren Tucker896ad5a2008-06-11 09:34:46 +1000566comma-separated list of patterns.
Damien Millerc7d5b5e2006-03-15 11:55:08 +1100567See
568.Sx PATTERNS
569in
570.Xr ssh_config 5
571for more information on patterns.
Darren Tucker896ad5a2008-06-11 09:34:46 +1000572.Pp
573In addition to the wildcard matching that may be applied to hostnames or
574addresses, a
575.Cm from
Darren Tucker5837b512009-06-21 17:52:27 +1000576stanza may match IP addresses using CIDR address/masklen notation.
Darren Tucker896ad5a2008-06-11 09:34:46 +1000577.Pp
578The purpose of this option is to optionally increase security: public key
579authentication by itself does not trust the network or name servers or
580anything (but the key); however, if somebody somehow steals the key, the key
581permits an intruder to log in from anywhere in the world.
582This additional option makes using a stolen key more difficult (name
583servers and/or routers would have to be compromised in addition to
584just the key).
Damien Miller31bdc522006-03-15 11:31:44 +1100585.It Cm no-agent-forwarding
586Forbids authentication agent forwarding when this key is used for
587authentication.
Damien Miller32aa1441999-10-29 09:15:49 +1000588.It Cm no-port-forwarding
Damien Miller7c24b812006-01-14 10:09:56 +1100589Forbids TCP forwarding when this key is used for authentication.
Damien Miller450a7a12000-03-26 13:04:51 +1000590Any port forward requests by the client will return an error.
Damien Miller208f1ed2006-03-15 11:56:03 +1100591This might be used, e.g. in connection with the
Damien Miller32aa1441999-10-29 09:15:49 +1000592.Cm command
593option.
Damien Miller31bdc522006-03-15 11:31:44 +1100594.It Cm no-pty
595Prevents tty allocation (a request to allocate a pty will fail).
Damien Miller95e80952008-03-27 11:03:05 +1100596.It Cm no-user-rc
Damien Miller13ba9c22008-04-03 20:52:51 +1100597Disables execution of
Damien Miller95e80952008-03-27 11:03:05 +1100598.Pa ~/.ssh/rc .
Damien Miller32aa1441999-10-29 09:15:49 +1000599.It Cm no-X11-forwarding
600Forbids X11 forwarding when this key is used for authentication.
601Any X11 forward requests by the client will return an error.
Damien Millera243fde2001-03-19 23:16:08 +1100602.It Cm permitopen="host:port"
Ben Lindstrom24643222001-06-25 05:08:11 +0000603Limit local
Damien Millera243fde2001-03-19 23:16:08 +1100604.Li ``ssh -L''
Ben Lindstrom4b3564e2001-04-10 02:41:56 +0000605port forwarding such that it may only connect to the specified host and
Ben Lindstromd71ba572001-09-12 18:03:31 +0000606port.
Damien Miller7fa96602010-08-05 13:03:13 +1000607IPv6 addresses can be specified by enclosing the address in square brackets.
Ben Lindstromd71ba572001-09-12 18:03:31 +0000608Multiple
Damien Millera243fde2001-03-19 23:16:08 +1100609.Cm permitopen
Damien Millerfbf486b2003-05-23 18:44:23 +1000610options may be applied separated by commas.
611No pattern matching is performed on the specified hostnames,
612they must be literal domains or addresses.
Darren Tucker1338b9e2011-10-02 18:57:35 +1100613A port specification of
614.Cm *
615matches any port.
Damien Miller30da3442010-05-10 11:58:03 +1000616.It Cm principals="principals"
617On a
618.Cm cert-authority
619line, specifies allowed principals for certificate authentication as a
620comma-separated list.
621At least one name from the list must appear in the certificate's
622list of principals for the certificate to be accepted.
623This option is ignored for keys that are not marked as trusted certificate
624signers using the
625.Cm cert-authority
626option.
Damien Millerd27b9472005-12-13 19:29:02 +1100627.It Cm tunnel="n"
628Force a
629.Xr tun 4
630device on the server.
631Without this option, the next available device will be used if
632the client requests a tunnel.
Damien Miller32aa1441999-10-29 09:15:49 +1000633.El
Damien Miller32aa1441999-10-29 09:15:49 +1000634.Pp
Damien Miller7d2ef022006-03-15 11:32:06 +1100635An example authorized_keys file:
Damien Millerc8f61cf2006-03-15 11:33:25 +1100636.Bd -literal -offset 3n
Damien Miller7d2ef022006-03-15 11:32:06 +1100637# Comments allowed at start of line
638ssh-rsa AAAAB3Nza...LiPk== user@example.net
Damien Millerc8f61cf2006-03-15 11:33:25 +1100639from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
640AAAAB2...19Q== john@example.net
641command="dump /home",no-pty,no-port-forwarding ssh-dss
642AAAAC3...51R== example.net
643permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss
644AAAAB5...21S==
645tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
646jane@example.net
Damien Miller7d2ef022006-03-15 11:32:06 +1100647.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000648.Sh SSH_KNOWN_HOSTS FILE FORMAT
Damien Miller22c77262000-04-13 12:26:34 +1000649The
Damien Millerffadc582003-02-24 11:52:26 +1100650.Pa /etc/ssh/ssh_known_hosts
Damien Miller22c77262000-04-13 12:26:34 +1000651and
Damien Miller167ea5d2005-05-26 12:04:02 +1000652.Pa ~/.ssh/known_hosts
Damien Miller450a7a12000-03-26 13:04:51 +1000653files contain host public keys for all known hosts.
654The global file should
655be prepared by the administrator (optional), and the per-user file is
Damien Miller9a7f2012006-03-15 11:32:42 +1100656maintained automatically: whenever the user connects from an unknown host,
Damien Miller450a7a12000-03-26 13:04:51 +1000657its key is added to the per-user file.
Damien Miller32aa1441999-10-29 09:15:49 +1000658.Pp
Damien Millera7dab8b2010-03-05 10:42:05 +1100659Each line in these files contains the following fields: markers (optional),
660hostnames, bits, exponent, modulus, comment.
Damien Miller450a7a12000-03-26 13:04:51 +1000661The fields are separated by spaces.
Damien Miller32aa1441999-10-29 09:15:49 +1000662.Pp
Damien Millera7dab8b2010-03-05 10:42:05 +1100663The marker is optional, but if it is present then it must be one of
664.Dq @cert-authority ,
665to indicate that the line contains a certification authority (CA) key,
666or
667.Dq @revoked ,
668to indicate that the key contained on the line is revoked and must not ever
669be accepted.
670Only one marker should be used on a key line.
671.Pp
Damien Miller31554322003-05-14 13:44:58 +1000672Hostnames is a comma-separated list of patterns
Damien Miller9a7f2012006-03-15 11:32:42 +1100673.Pf ( Ql *
Damien Millerfbf486b2003-05-23 18:44:23 +1000674and
675.Ql \&?
Damien Miller049245d2003-05-14 13:44:42 +1000676act as
Damien Miller32aa1441999-10-29 09:15:49 +1000677wildcards); each pattern in turn is matched against the canonical host
678name (when authenticating a client) or against the user-supplied
Damien Miller450a7a12000-03-26 13:04:51 +1000679name (when authenticating a server).
680A pattern may also be preceded by
Damien Miller049245d2003-05-14 13:44:42 +1000681.Ql \&!
Damien Miller32aa1441999-10-29 09:15:49 +1000682to indicate negation: if the host name matches a negated
683pattern, it is not accepted (by that line) even if it matched another
684pattern on the line.
Darren Tuckerda345532006-07-10 23:04:19 +1000685A hostname or address may optionally be enclosed within
686.Ql \&[
687and
688.Ql \&]
689brackets then followed by
690.Ql \&:
Darren Tucker11318472006-07-12 22:07:59 +1000691and a non-standard port number.
Damien Miller32aa1441999-10-29 09:15:49 +1000692.Pp
Damien Millere1776152005-03-01 21:47:37 +1100693Alternately, hostnames may be stored in a hashed form which hides host names
Damien Miller718fd4b2005-03-02 12:03:23 +1100694and addresses should the file's contents be disclosed.
695Hashed hostnames start with a
696.Ql |
Damien Millere1776152005-03-01 21:47:37 +1100697character.
698Only one hashed hostname may appear on a single line and none of the above
699negation or wildcard operators may be applied.
700.Pp
Damien Millere247cc42000-05-07 12:03:14 +1000701Bits, exponent, and modulus are taken directly from the RSA host key; they
Damien Miller9a7f2012006-03-15 11:32:42 +1100702can be obtained, for example, from
Damien Miller05eda432002-02-10 18:32:28 +1100703.Pa /etc/ssh/ssh_host_key.pub .
Damien Miller32aa1441999-10-29 09:15:49 +1000704The optional comment field continues to the end of the line, and is not used.
705.Pp
706Lines starting with
707.Ql #
708and empty lines are ignored as comments.
709.Pp
710When performing host authentication, authentication is accepted if any
Damien Millera7dab8b2010-03-05 10:42:05 +1100711matching line has the proper key; either one that matches exactly or,
712if the server has presented a certificate for authentication, the key
713of the certification authority that signed the certificate.
714For a key to be trusted as a certification authority, it must use the
715.Dq @cert-authority
716marker described above.
717.Pp
718The known hosts file also provides a facility to mark keys as revoked,
719for example when it is known that the associated private key has been
720stolen.
721Revoked keys are specified by including the
722.Dq @revoked
723marker at the beginning of the key line, and are never accepted for
724authentication or as certification authorities, but instead will
725produce a warning from
726.Xr ssh 1
727when they are encountered.
728.Pp
729It is permissible (but not
Damien Miller32aa1441999-10-29 09:15:49 +1000730recommended) to have several lines or different host keys for the same
Damien Miller450a7a12000-03-26 13:04:51 +1000731names.
732This will inevitably happen when short forms of host names
733from different domains are put in the file.
734It is possible
Damien Miller32aa1441999-10-29 09:15:49 +1000735that the files contain conflicting information; authentication is
736accepted if valid information can be found from either file.
737.Pp
738Note that the lines in these files are typically hundreds of characters
739long, and you definitely don't want to type in the host keys by hand.
Damien Millera7dab8b2010-03-05 10:42:05 +1100740Rather, generate them by a script,
741.Xr ssh-keyscan 1
Damien Miller22c77262000-04-13 12:26:34 +1000742or by taking
Damien Miller05eda432002-02-10 18:32:28 +1100743.Pa /etc/ssh/ssh_host_key.pub
Damien Miller32aa1441999-10-29 09:15:49 +1000744and adding the host names at the front.
Damien Millera7dab8b2010-03-05 10:42:05 +1100745.Xr ssh-keygen 1
Damien Miller98339052010-03-05 21:30:35 +1100746also offers some basic automated editing for
Damien Millera7dab8b2010-03-05 10:42:05 +1100747.Pa ~/.ssh/known_hosts
748including removing hosts matching a host name and converting all host
749names to their hashed representations.
Damien Millercc00f5e2006-03-15 11:33:00 +1100750.Pp
751An example ssh_known_hosts file:
752.Bd -literal -offset 3n
753# Comments allowed at start of line
754closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
755cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
Damien Millere1776152005-03-01 21:47:37 +1100756# A hashed hostname
757|1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
758AAAA1234.....=
Damien Millera7dab8b2010-03-05 10:42:05 +1100759# A revoked key
760@revoked * ssh-rsa AAAAB5W...
761# A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
762@cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
Damien Millere1776152005-03-01 21:47:37 +1100763.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000764.Sh FILES
Damien Millerd8702e82006-03-15 11:33:56 +1100765.Bl -tag -width Ds -compact
Damien Millerafdae612010-08-31 22:31:14 +1000766.It Pa ~/.hushlogin
Damien Miller70a908e2005-03-01 21:17:09 +1100767This file is used to suppress printing the last login time and
768.Pa /etc/motd ,
769if
770.Cm PrintLastLog
771and
772.Cm PrintMotd ,
773respectively,
774are enabled.
775It does not suppress printing of the banner specified by
776.Cm Banner .
Damien Millerd8702e82006-03-15 11:33:56 +1100777.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000778.It Pa ~/.rhosts
Damien Milleradc35b92006-03-15 11:35:27 +1100779This file is used for host-based authentication (see
780.Xr ssh 1
781for more information).
782On some machines this file may need to be
783world-readable if the user's home directory is on an NFS partition,
784because
785.Nm
786reads it as root.
787Additionally, this file must be owned by the user,
788and must not have write permissions for anyone else.
789The recommended
790permission for most machines is read/write for the user, and not
Damien Miller32aa1441999-10-29 09:15:49 +1000791accessible by others.
792.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000793.It Pa ~/.shosts
Damien Milleradc35b92006-03-15 11:35:27 +1100794This file is used in exactly the same way as
795.Pa .rhosts ,
796but allows host-based authentication without permitting login with
797rlogin/rsh.
Damien Miller32aa1441999-10-29 09:15:49 +1000798.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000799.It Pa ~/.ssh/
Damien Miller520e6152008-02-10 22:46:22 +1100800This directory is the default location for all user-specific configuration
801and authentication information.
802There is no general requirement to keep the entire contents of this directory
803secret, but the recommended permissions are read/write/execute for the user,
804and not accessible by others.
805.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000806.It Pa ~/.ssh/authorized_keys
Damien Millereb8b60e2010-08-31 22:41:14 +1000807Lists the public keys (DSA/ECDSA/RSA) that can be used for logging in
808as this user.
Damien Millerd8702e82006-03-15 11:33:56 +1100809The format of this file is described above.
Damien Miller5d43d492006-08-30 11:07:00 +1000810The content of the file is not highly sensitive, but the recommended
Damien Milleradc35b92006-03-15 11:35:27 +1100811permissions are read/write for the user, and not accessible by others.
Damien Miller32aa1441999-10-29 09:15:49 +1000812.Pp
Damien Miller5d43d492006-08-30 11:07:00 +1000813If this file, the
814.Pa ~/.ssh
815directory, or the user's home directory are writable
816by other users, then the file could be modified or replaced by unauthorized
817users.
818In this case,
819.Nm
820will not allow it to be used unless the
821.Cm StrictModes
822option has been set to
823.Dq no .
Damien Miller5d43d492006-08-30 11:07:00 +1000824.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000825.It Pa ~/.ssh/environment
Damien Miller450a7a12000-03-26 13:04:51 +1000826This file is read into the environment at login (if it exists).
827It can only contain empty lines, comment lines (that start with
Damien Miller32aa1441999-10-29 09:15:49 +1000828.Ql # ) ,
Damien Miller450a7a12000-03-26 13:04:51 +1000829and assignment lines of the form name=value.
830The file should be writable
Damien Miller32aa1441999-10-29 09:15:49 +1000831only by the user; it need not be readable by anyone else.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000832Environment processing is disabled by default and is
833controlled via the
834.Cm PermitUserEnvironment
835option.
Damien Millerd8702e82006-03-15 11:33:56 +1100836.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000837.It Pa ~/.ssh/known_hosts
Damien Milleradc35b92006-03-15 11:35:27 +1100838Contains a list of host keys for all hosts the user has logged into
839that are not already in the systemwide list of known host keys.
840The format of this file is described above.
841This file should be writable only by root/the owner and
Damien Millerd8702e82006-03-15 11:33:56 +1100842can, but need not be, world-readable.
843.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000844.It Pa ~/.ssh/rc
Damien Millerfd725cf2006-03-15 11:35:54 +1100845Contains initialization routines to be run before
846the user's home directory becomes accessible.
Damien Miller32aa1441999-10-29 09:15:49 +1000847This file should be writable only by the user, and need not be
848readable by anyone else.
Damien Millerd8702e82006-03-15 11:33:56 +1100849.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000850.It Pa /etc/hosts.allow
851.It Pa /etc/hosts.deny
Damien Millerd8702e82006-03-15 11:33:56 +1100852Access controls that should be enforced by tcp-wrappers are defined here.
853Further details are described in
854.Xr hosts_access 5 .
855.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000856.It Pa /etc/hosts.equiv
Damien Miller445121f2006-03-15 11:36:18 +1100857This file is for host-based authentication (see
858.Xr ssh 1 ) .
859It should only be writable by root.
Damien Millerd8702e82006-03-15 11:33:56 +1100860.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000861.It Pa /etc/moduli
Damien Millerd8702e82006-03-15 11:33:56 +1100862Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
863The file format is described in
864.Xr moduli 5 .
865.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000866.It Pa /etc/motd
Damien Millerd8702e82006-03-15 11:33:56 +1100867See
868.Xr motd 5 .
869.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000870.It Pa /etc/nologin
Damien Millerd8702e82006-03-15 11:33:56 +1100871If this file exists,
872.Nm
873refuses to let anyone except root log in.
874The contents of the file
875are displayed to anyone trying to log in, and non-root connections are
876refused.
877The file should be world-readable.
878.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000879.It Pa /etc/shosts.equiv
Damien Miller445121f2006-03-15 11:36:18 +1100880This file is used in exactly the same way as
881.Pa hosts.equiv ,
882but allows host-based authentication without permitting login with
883rlogin/rsh.
Damien Millerd8702e82006-03-15 11:33:56 +1100884.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000885.It Pa /etc/ssh/ssh_host_key
886.It Pa /etc/ssh/ssh_host_dsa_key
Damien Millereb8b60e2010-08-31 22:41:14 +1000887.It Pa /etc/ssh/ssh_host_ecdsa_key
Damien Millerafdae612010-08-31 22:31:14 +1000888.It Pa /etc/ssh/ssh_host_rsa_key
Damien Millerb9902cf2012-06-20 21:52:58 +1000889These files contain the private parts of the host keys.
Damien Millerd8702e82006-03-15 11:33:56 +1100890These files should only be owned by root, readable only by root, and not
891accessible to others.
892Note that
893.Nm
Damien Milleredd03752006-03-15 11:36:45 +1100894does not start if these files are group/world-accessible.
Damien Millerd8702e82006-03-15 11:33:56 +1100895.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000896.It Pa /etc/ssh/ssh_host_key.pub
897.It Pa /etc/ssh/ssh_host_dsa_key.pub
Damien Millereb8b60e2010-08-31 22:41:14 +1000898.It Pa /etc/ssh/ssh_host_ecdsa_key.pub
Damien Millerafdae612010-08-31 22:31:14 +1000899.It Pa /etc/ssh/ssh_host_rsa_key.pub
Damien Millerb9902cf2012-06-20 21:52:58 +1000900These files contain the public parts of the host keys.
Damien Millerd8702e82006-03-15 11:33:56 +1100901These files should be world-readable but writable only by
902root.
903Their contents should match the respective private parts.
904These files are not
905really used for anything; they are provided for the convenience of
906the user so their contents can be copied to known hosts files.
907These files are created using
908.Xr ssh-keygen 1 .
909.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000910.It Pa /etc/ssh/ssh_known_hosts
Darren Tucker04354b92007-03-21 20:46:54 +1100911Systemwide list of known host keys.
912This file should be prepared by the
913system administrator to contain the public host keys of all machines in the
914organization.
915The format of this file is described above.
916This file should be writable only by root/the owner and
917should be world-readable.
918.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000919.It Pa /etc/ssh/sshd_config
Damien Millerd8702e82006-03-15 11:33:56 +1100920Contains configuration data for
921.Nm sshd .
922The file format and configuration options are described in
923.Xr sshd_config 5 .
924.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000925.It Pa /etc/ssh/sshrc
Damien Millerfd725cf2006-03-15 11:35:54 +1100926Similar to
927.Pa ~/.ssh/rc ,
928it can be used to specify
Damien Miller450a7a12000-03-26 13:04:51 +1000929machine-specific login-time initializations globally.
930This file should be writable only by root, and should be world-readable.
Damien Millerd8702e82006-03-15 11:33:56 +1100931.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000932.It Pa /var/empty
Damien Millerd8702e82006-03-15 11:33:56 +1100933.Xr chroot 2
934directory used by
935.Nm
936during privilege separation in the pre-authentication phase.
937The directory should not contain any files and must be owned by root
938and not group or world-writable.
939.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000940.It Pa /var/run/sshd.pid
Damien Millerd8702e82006-03-15 11:33:56 +1100941Contains the process ID of the
942.Nm
943listening for connections (if there are several daemons running
944concurrently for different ports, this contains the process ID of the one
945started last).
946The content of this file is not sensitive; it can be world-readable.
Damien Miller37023962000-07-11 17:31:38 +1000947.El
Damien Miller32aa1441999-10-29 09:15:49 +1000948.Sh SEE ALSO
Damien Miller32aa1441999-10-29 09:15:49 +1000949.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +1100950.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +1000951.Xr ssh 1 ,
952.Xr ssh-add 1 ,
953.Xr ssh-agent 1 ,
954.Xr ssh-keygen 1 ,
Darren Tucker04354b92007-03-21 20:46:54 +1100955.Xr ssh-keyscan 1 ,
Darren Tucker1f203942003-10-15 15:50:42 +1000956.Xr chroot 2 ,
957.Xr hosts_access 5 ,
Ben Lindstromc8e29ce2001-08-06 20:55:28 +0000958.Xr login.conf 5 ,
959.Xr moduli 5 ,
Ben Lindstrom9f049032002-06-21 00:59:05 +0000960.Xr sshd_config 5 ,
Darren Tucker1f203942003-10-15 15:50:42 +1000961.Xr inetd 8 ,
Ben Lindstromd2bf0d62001-06-25 04:10:54 +0000962.Xr sftp-server 8
Damien Millerf1ce5052003-06-11 22:04:39 +1000963.Sh AUTHORS
964OpenSSH is a derivative of the original and free
965ssh 1.2.12 release by Tatu Ylonen.
966Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
967Theo de Raadt and Dug Song
968removed many bugs, re-added newer features and
969created OpenSSH.
970Markus Friedl contributed the support for SSH
971protocol versions 1.5 and 2.0.
972Niels Provos and Markus Friedl contributed support
973for privilege separation.
Damien Millerc47d7e92006-03-15 11:27:20 +1100974.Sh CAVEATS
975System security is not improved unless
976.Nm rshd ,
977.Nm rlogind ,
978and
979.Nm rexecd
980are disabled (thus completely disabling
981.Xr rlogin
982and
983.Xr rsh
984into the machine).