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Damien Miller32aa1441999-10-29 09:15:49 +10001.\" -*- nroff -*-
2.\"
Damien Miller32aa1441999-10-29 09:15:49 +10003.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
Damien Miller32aa1441999-10-29 09:15:49 +10004.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5.\" All rights reserved
6.\"
Damien Millere4340be2000-09-16 13:29:08 +11007.\" As far as I am concerned, the code I have written for this software
8.\" can be used freely for any purpose. Any derived versions of this
9.\" software must be clearly marked as such, and if the derived work is
10.\" incompatible with the protocol description in the RFC file, it must be
11.\" called by a name other than "ssh" or "Secure Shell".
Damien Miller32aa1441999-10-29 09:15:49 +100012.\"
Ben Lindstrom92a2e382001-03-05 06:59:27 +000013.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
14.\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
15.\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
Damien Millere4340be2000-09-16 13:29:08 +110016.\"
17.\" Redistribution and use in source and binary forms, with or without
18.\" modification, are permitted provided that the following conditions
19.\" are met:
20.\" 1. Redistributions of source code must retain the above copyright
21.\" notice, this list of conditions and the following disclaimer.
22.\" 2. Redistributions in binary form must reproduce the above copyright
23.\" notice, this list of conditions and the following disclaimer in the
24.\" documentation and/or other materials provided with the distribution.
25.\"
26.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
27.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
28.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
29.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
30.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
31.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Damien Miller32aa1441999-10-29 09:15:49 +100036.\"
Damien Millereb8b60e2010-08-31 22:41:14 +100037.\" $OpenBSD: sshd.8,v 1.259 2010/08/31 11:54:45 djm Exp $
38.Dd $Mdocdate: August 31 2010 $
Damien Miller32aa1441999-10-29 09:15:49 +100039.Dt SSHD 8
40.Os
41.Sh NAME
42.Nm sshd
Ben Lindstromc65e6a02001-04-23 13:02:16 +000043.Nd OpenSSH SSH daemon
Damien Miller32aa1441999-10-29 09:15:49 +100044.Sh SYNOPSIS
45.Nm sshd
Damien Millerffadc582003-02-24 11:52:26 +110046.Bk -words
Darren Tuckere7f3f752008-06-10 23:06:01 +100047.Op Fl 46DdeiqTt
Damien Miller32aa1441999-10-29 09:15:49 +100048.Op Fl b Ar bits
Darren Tuckere7140f22008-06-10 23:01:51 +100049.Op Fl C Ar connection_spec
Damien Miller0a80ca12010-02-27 07:55:05 +110050.Op Fl c Ar host_certificate_file
Damien Miller32aa1441999-10-29 09:15:49 +100051.Op Fl f Ar config_file
52.Op Fl g Ar login_grace_time
53.Op Fl h Ar host_key_file
54.Op Fl k Ar key_gen_time
Ben Lindstromade03f62001-12-06 18:22:17 +000055.Op Fl o Ar option
Damien Miller32aa1441999-10-29 09:15:49 +100056.Op Fl p Ar port
Damien Miller942da032000-08-18 13:59:06 +100057.Op Fl u Ar len
Damien Millerffadc582003-02-24 11:52:26 +110058.Ek
Damien Miller22c77262000-04-13 12:26:34 +100059.Sh DESCRIPTION
Damien Miller32aa1441999-10-29 09:15:49 +100060.Nm
Damien Miller99cc4a82006-01-31 21:45:53 +110061(OpenSSH Daemon) is the daemon program for
Damien Miller32aa1441999-10-29 09:15:49 +100062.Xr ssh 1 .
Darren Tucker04354b92007-03-21 20:46:54 +110063Together these programs replace
64.Xr rlogin 1
65and
66.Xr rsh 1 ,
67and provide secure encrypted communications between two untrusted hosts
Damien Miller450a7a12000-03-26 13:04:51 +100068over an insecure network.
Damien Miller32aa1441999-10-29 09:15:49 +100069.Pp
70.Nm
Damien Miller99cc4a82006-01-31 21:45:53 +110071listens for connections from clients.
Damien Miller22c77262000-04-13 12:26:34 +100072It is normally started at boot from
Damien Miller32aa1441999-10-29 09:15:49 +100073.Pa /etc/rc .
74It forks a new
Damien Miller450a7a12000-03-26 13:04:51 +100075daemon for each incoming connection.
76The forked daemons handle
Damien Miller32aa1441999-10-29 09:15:49 +100077key exchange, encryption, authentication, command execution,
78and data exchange.
Damien Miller32aa1441999-10-29 09:15:49 +100079.Pp
80.Nm
Darren Tucker1f203942003-10-15 15:50:42 +100081can be configured using command-line options or a configuration file
82(by default
Damien Miller99cc4a82006-01-31 21:45:53 +110083.Xr sshd_config 5 ) ;
84command-line options override values specified in the
Damien Miller32aa1441999-10-29 09:15:49 +100085configuration file.
Damien Miller6162d121999-11-21 13:23:52 +110086.Nm
87rereads its configuration file when it receives a hangup signal,
Ben Lindstrom49a098d2001-03-05 06:55:18 +000088.Dv SIGHUP ,
Damien Miller208f1ed2006-03-15 11:56:03 +110089by executing itself with the name and options it was started with, e.g.\&
Ben Lindstrom49a098d2001-03-05 06:55:18 +000090.Pa /usr/sbin/sshd .
Damien Miller6162d121999-11-21 13:23:52 +110091.Pp
Damien Miller32aa1441999-10-29 09:15:49 +100092The options are as follows:
93.Bl -tag -width Ds
Darren Tucker1f203942003-10-15 15:50:42 +100094.It Fl 4
95Forces
96.Nm
97to use IPv4 addresses only.
98.It Fl 6
99Forces
100.Nm
101to use IPv6 addresses only.
Damien Miller32aa1441999-10-29 09:15:49 +1000102.It Fl b Ar bits
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000103Specifies the number of bits in the ephemeral protocol version 1
Darren Tucker7499b0c2008-07-02 22:35:43 +1000104server key (default 1024).
Darren Tuckere7f3f752008-06-10 23:06:01 +1000105.It Fl C Ar connection_spec
106Specify the connection parameters to use for the
107.Fl T
108extended test mode.
109If provided, any
110.Cm Match
111directives in the configuration file
112that would apply to the specified user, host, and address will be set before
113the configuration is written to standard output.
114The connection parameters are supplied as keyword=value pairs.
115The keywords are
116.Dq user ,
117.Dq host ,
118and
119.Dq addr .
120All are required and may be supplied in any order, either with multiple
121.Fl C
122options or as a comma-separated list.
Damien Miller15f5b562010-03-03 10:25:21 +1100123.It Fl c Ar host_certificate_file
124Specifies a path to a certificate file to identify
125.Nm
126during key exchange.
127The certificate file must match a host key file specified using the
128.Fl h
129option or the
130.Cm HostKey
131configuration directive.
Darren Tucker1f203942003-10-15 15:50:42 +1000132.It Fl D
133When this option is specified,
134.Nm
135will not detach and does not become a daemon.
136This allows easy monitoring of
137.Nm sshd .
Damien Miller32aa1441999-10-29 09:15:49 +1000138.It Fl d
Damien Miller450a7a12000-03-26 13:04:51 +1000139Debug mode.
Damien Miller74d98252010-02-02 17:01:46 +1100140The server sends verbose debug output to standard error,
141and does not put itself in the background.
Damien Miller450a7a12000-03-26 13:04:51 +1000142The server also will not fork and will only process one connection.
143This option is only intended for debugging for the server.
Damien Millerffadc582003-02-24 11:52:26 +1100144Multiple
145.Fl d
146options increase the debugging level.
Damien Miller874d77b2000-10-14 16:23:11 +1100147Maximum is 3.
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000148.It Fl e
149When this option is specified,
150.Nm
151will send the output to the standard error instead of the system log.
Darren Tucker04354b92007-03-21 20:46:54 +1100152.It Fl f Ar config_file
Damien Miller450a7a12000-03-26 13:04:51 +1000153Specifies the name of the configuration file.
154The default is
Damien Miller05eda432002-02-10 18:32:28 +1100155.Pa /etc/ssh/sshd_config .
Damien Miller32aa1441999-10-29 09:15:49 +1000156.Nm
157refuses to start if there is no configuration file.
158.It Fl g Ar login_grace_time
159Gives the grace time for clients to authenticate themselves (default
Damien Millerc1348632002-09-05 14:35:14 +1000160120 seconds).
Damien Miller450a7a12000-03-26 13:04:51 +1000161If the client fails to authenticate the user within
162this many seconds, the server disconnects and exits.
163A value of zero indicates no limit.
Damien Miller32aa1441999-10-29 09:15:49 +1000164.It Fl h Ar host_key_file
Damien Miller7fc23732002-01-22 23:19:11 +1100165Specifies a file from which a host key is read.
Damien Miller32aa1441999-10-29 09:15:49 +1000166This option must be given if
167.Nm
168is not run as root (as the normal
Damien Miller7fc23732002-01-22 23:19:11 +1100169host key files are normally not readable by anyone but root).
170The default is
Damien Miller05eda432002-02-10 18:32:28 +1100171.Pa /etc/ssh/ssh_host_key
Damien Miller7fc23732002-01-22 23:19:11 +1100172for protocol version 1, and
Damien Millereb8b60e2010-08-31 22:41:14 +1000173.Pa /etc/ssh/ssh_host_dsa_key ,
174.Pa /etc/ssh/ssh_host_ecdsa_key
Damien Miller7fc23732002-01-22 23:19:11 +1100175and
Damien Millereb8b60e2010-08-31 22:41:14 +1000176.Pa /etc/ssh/ssh_host_rsa_key
Damien Miller7fc23732002-01-22 23:19:11 +1100177for protocol version 2.
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000178It is possible to have multiple host key files for
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000179the different protocol versions and host key algorithms.
Damien Miller32aa1441999-10-29 09:15:49 +1000180.It Fl i
181Specifies that
182.Nm
Damien Millerffadc582003-02-24 11:52:26 +1100183is being run from
184.Xr inetd 8 .
Damien Miller32aa1441999-10-29 09:15:49 +1000185.Nm
186is normally not run
187from inetd because it needs to generate the server key before it can
Damien Miller450a7a12000-03-26 13:04:51 +1000188respond to the client, and this may take tens of seconds.
189Clients would have to wait too long if the key was regenerated every time.
Damien Miller208f1ed2006-03-15 11:56:03 +1100190However, with small key sizes (e.g. 512) using
Damien Miller32aa1441999-10-29 09:15:49 +1000191.Nm
192from inetd may
193be feasible.
194.It Fl k Ar key_gen_time
Ben Lindstromc65e6a02001-04-23 13:02:16 +0000195Specifies how often the ephemeral protocol version 1 server key is
196regenerated (default 3600 seconds, or one hour).
Damien Miller450a7a12000-03-26 13:04:51 +1000197The motivation for regenerating the key fairly
Darren Tucker1f203942003-10-15 15:50:42 +1000198often is that the key is not stored anywhere, and after about an hour
Damien Miller32aa1441999-10-29 09:15:49 +1000199it becomes impossible to recover the key for decrypting intercepted
200communications even if the machine is cracked into or physically
Damien Miller450a7a12000-03-26 13:04:51 +1000201seized.
202A value of zero indicates that the key will never be regenerated.
Ben Lindstromade03f62001-12-06 18:22:17 +0000203.It Fl o Ar option
204Can be used to give options in the format used in the configuration file.
205This is useful for specifying options for which there is no separate
206command-line flag.
Darren Tucker1f203942003-10-15 15:50:42 +1000207For full details of the options, and their values, see
208.Xr sshd_config 5 .
Damien Miller32aa1441999-10-29 09:15:49 +1000209.It Fl p Ar port
210Specifies the port on which the server listens for connections
211(default 22).
Damien Miller7d1ded42002-01-22 23:09:41 +1100212Multiple port options are permitted.
Damien Millerd7f308f2005-12-24 14:55:16 +1100213Ports specified in the configuration file with the
214.Cm Port
215option are ignored when a command-line port is specified.
216Ports specified using the
217.Cm ListenAddress
218option override command-line ports.
Damien Miller32aa1441999-10-29 09:15:49 +1000219.It Fl q
Damien Miller450a7a12000-03-26 13:04:51 +1000220Quiet mode.
221Nothing is sent to the system log.
222Normally the beginning,
Damien Miller32aa1441999-10-29 09:15:49 +1000223authentication, and termination of each connection is logged.
Darren Tuckere7140f22008-06-10 23:01:51 +1000224.It Fl T
225Extended test mode.
226Check the validity of the configuration file, output the effective configuration
227to stdout and then exit.
228Optionally,
229.Cm Match
230rules may be applied by specifying the connection parameters using one or more
231.Fl C
232options.
Darren Tuckere7f3f752008-06-10 23:06:01 +1000233.It Fl t
234Test mode.
235Only check the validity of the configuration file and sanity of the keys.
236This is useful for updating
237.Nm
238reliably as configuration options may change.
Damien Miller942da032000-08-18 13:59:06 +1000239.It Fl u Ar len
240This option is used to specify the size of the field
241in the
242.Li utmp
243structure that holds the remote host name.
244If the resolved host name is longer than
245.Ar len ,
246the dotted decimal value will be used instead.
247This allows hosts with very long host names that
248overflow this field to still be uniquely identified.
249Specifying
250.Fl u0
251indicates that only dotted decimal addresses
252should be put into the
253.Pa utmp
254file.
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000255.Fl u0
Damien Millerffadc582003-02-24 11:52:26 +1100256may also be used to prevent
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000257.Nm
258from making DNS requests unless the authentication
259mechanism or configuration requires it.
260Authentication mechanisms that may require DNS include
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000261.Cm RhostsRSAAuthentication ,
Damien Miller2ac05772006-02-01 22:05:42 +1100262.Cm HostbasedAuthentication ,
Ben Lindstrom6f672c02001-09-12 17:51:55 +0000263and using a
264.Cm from="pattern-list"
265option in a key file.
Ben Lindstromea03db92002-03-05 01:38:57 +0000266Configuration options that require DNS include using a
267USER@HOST pattern in
268.Cm AllowUsers
269or
270.Cm DenyUsers .
Damien Miller32aa1441999-10-29 09:15:49 +1000271.El
Damien Miller8bbdf902006-02-01 22:05:25 +1100272.Sh AUTHENTICATION
273The OpenSSH SSH daemon supports SSH protocols 1 and 2.
Darren Tucker7a4a7652009-10-11 21:51:40 +1100274The default is to use protocol 2 only,
Damien Miller8bbdf902006-02-01 22:05:25 +1100275though this can be changed via the
276.Cm Protocol
277option in
278.Xr sshd_config 5 .
Damien Millereb8b60e2010-08-31 22:41:14 +1000279Protocol 2 supports DSA, ECDSA and RSA keys;
Damien Miller8bbdf902006-02-01 22:05:25 +1100280protocol 1 only supports RSA keys.
281For both protocols,
282each host has a host-specific key,
283normally 2048 bits,
284used to identify the host.
Damien Miller99cc4a82006-01-31 21:45:53 +1100285.Pp
Damien Miller8bbdf902006-02-01 22:05:25 +1100286Forward security for protocol 1 is provided through
287an additional server key,
288normally 768 bits,
289generated when the server starts.
Damien Miller99cc4a82006-01-31 21:45:53 +1100290This key is normally regenerated every hour if it has been used, and
291is never stored on disk.
Damien Miller99cc4a82006-01-31 21:45:53 +1100292Whenever a client connects, the daemon responds with its public
293host and server keys.
294The client compares the
295RSA host key against its own database to verify that it has not changed.
296The client then generates a 256-bit random number.
297It encrypts this
298random number using both the host key and the server key, and sends
299the encrypted number to the server.
300Both sides then use this
301random number as a session key which is used to encrypt all further
302communications in the session.
303The rest of the session is encrypted
304using a conventional cipher, currently Blowfish or 3DES, with 3DES
305being used by default.
306The client selects the encryption algorithm
307to use from those offered by the server.
308.Pp
Damien Miller8bbdf902006-02-01 22:05:25 +1100309For protocol 2,
310forward security is provided through a Diffie-Hellman key agreement.
311This key agreement results in a shared session key.
312The rest of the session is encrypted using a symmetric cipher, currently
313128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES.
314The client selects the encryption algorithm
315to use from those offered by the server.
316Additionally, session integrity is provided
317through a cryptographic message authentication code
Damien Millere45796f2007-06-11 14:01:42 +1000318(hmac-md5, hmac-sha1, umac-64 or hmac-ripemd160).
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 Millerdcfea272006-03-15 11:31:22 +1100466specifies the file containing public keys for
467public key authentication;
468if none is specified, the default is
469.Pa ~/.ssh/authorized_keys .
Damien Miller450a7a12000-03-26 13:04:51 +1000470Each line of the file contains one
Damien Miller32aa1441999-10-29 09:15:49 +1000471key (empty lines and lines starting with a
472.Ql #
473are ignored as
Damien Miller450a7a12000-03-26 13:04:51 +1000474comments).
Damien Millerdcfea272006-03-15 11:31:22 +1100475Protocol 1 public keys consist of the following space-separated fields:
476options, bits, exponent, modulus, comment.
477Protocol 2 public key consist of:
478options, keytype, base64-encoded key, comment.
479The options field is optional;
480its presence is determined by whether the line starts
Damien Millerb83df8d2002-09-04 16:24:55 +1000481with a number or not (the options field never starts with a number).
Damien Millerdcfea272006-03-15 11:31:22 +1100482The bits, exponent, modulus, and comment fields give the RSA key for
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000483protocol version 1; the
Damien Miller32aa1441999-10-29 09:15:49 +1000484comment field is not used for anything (but may be convenient for the
485user to identify the key).
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000486For protocol version 2 the keytype is
Damien Millereb8b60e2010-08-31 22:41:14 +1000487.Dq ecdsa-sha2-nistp256 ,
488.Dq ecdsa-sha2-nistp384 ,
489.Dq ecdsa-sha2-nistp521 ,
Ben Lindstrom4dccfa52000-12-28 16:40:05 +0000490.Dq ssh-dss
491or
492.Dq ssh-rsa .
Damien Miller32aa1441999-10-29 09:15:49 +1000493.Pp
494Note that lines in this file are usually several hundred bytes long
Darren Tucker22cc7412004-12-06 22:47:41 +1100495(because of the size of the public key encoding) up to a limit of
4968 kilobytes, which permits DSA keys up to 8 kilobits and RSA
497keys up to 16 kilobits.
Damien Miller450a7a12000-03-26 13:04:51 +1000498You don't want to type them in; instead, copy the
Ben Lindstrom18a82ac2001-04-11 15:59:35 +0000499.Pa identity.pub ,
Damien Millerdcfea272006-03-15 11:31:22 +1100500.Pa id_dsa.pub ,
Damien Millereb8b60e2010-08-31 22:41:14 +1000501.Pa id_ecdsa.pub ,
Ben Lindstrom18a82ac2001-04-11 15:59:35 +0000502or the
503.Pa id_rsa.pub
Damien Miller32aa1441999-10-29 09:15:49 +1000504file and edit it.
505.Pp
Ben Lindstrom0d0be022002-04-02 20:39:29 +0000506.Nm
507enforces a minimum RSA key modulus size for protocol 1
508and protocol 2 keys of 768 bits.
509.Pp
Damien Miller942da032000-08-18 13:59:06 +1000510The options (if present) consist of comma-separated option
Damien Miller450a7a12000-03-26 13:04:51 +1000511specifications.
512No spaces are permitted, except within double quotes.
Ben Lindstrom1c0fd092001-09-12 16:36:17 +0000513The following option specifications are supported (note
514that option keywords are case-insensitive):
Damien Miller32aa1441999-10-29 09:15:49 +1000515.Bl -tag -width Ds
Damien Millercd38c9c2010-03-04 21:51:37 +1100516.It Cm cert-authority
Damien Miller0a80ca12010-02-27 07:55:05 +1100517Specifies that the listed key is a certification authority (CA) that is
518trusted to validate signed certificates for user authentication.
519.Pp
520Certificates may encode access restrictions similar to these key options.
521If both certificate restrictions and key options are present, the most
522restrictive union of the two is applied.
Damien Miller32aa1441999-10-29 09:15:49 +1000523.It Cm command="command"
524Specifies that the command is executed whenever this key is used for
Damien Miller450a7a12000-03-26 13:04:51 +1000525authentication.
526The command supplied by the user (if any) is ignored.
Ben Lindstrom23124ea2001-09-14 23:14:25 +0000527The command is run on a pty if the client requests a pty;
Damien Miller450a7a12000-03-26 13:04:51 +1000528otherwise it is run without a tty.
Damien Millerffadc582003-02-24 11:52:26 +1100529If an 8-bit clean channel is required,
Ben Lindstrom594e2032001-09-12 18:35:30 +0000530one must not request a pty or should specify
Damien Miller33804262001-02-04 23:20:18 +1100531.Cm no-pty .
Damien Miller450a7a12000-03-26 13:04:51 +1000532A quote may be included in the command by quoting it with a backslash.
533This option might be useful
Damien Millerb83df8d2002-09-04 16:24:55 +1000534to restrict certain public keys to perform just a specific operation.
Damien Miller450a7a12000-03-26 13:04:51 +1000535An example might be a key that permits remote backups but nothing else.
Damien Miller7c24b812006-01-14 10:09:56 +1100536Note that the client may specify TCP and/or X11
Damien Miller30c3d422000-05-09 11:02:59 +1000537forwarding unless they are explicitly prohibited.
Damien Millere2754432006-07-24 14:06:47 +1000538The command originally supplied by the client is available in the
539.Ev SSH_ORIGINAL_COMMAND
540environment variable.
Ben Lindstrom20daef72001-09-20 00:54:01 +0000541Note that this option applies to shell, command or subsystem execution.
Damien Miller0a80ca12010-02-27 07:55:05 +1100542Also note that this command may be superseded by either a
543.Xr sshd_config 5
544.Cm ForceCommand
545directive or a command embedded in a certificate.
Damien Miller32aa1441999-10-29 09:15:49 +1000546.It Cm environment="NAME=value"
547Specifies that the string is to be added to the environment when
Damien Miller450a7a12000-03-26 13:04:51 +1000548logging in using this key.
549Environment variables set this way
550override other default environment values.
551Multiple options of this type are permitted.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000552Environment processing is disabled by default and is
553controlled via the
554.Cm PermitUserEnvironment
555option.
Ben Lindstrom38b951c2001-12-06 17:47:47 +0000556This option is automatically disabled if
557.Cm UseLogin
558is enabled.
Damien Miller31bdc522006-03-15 11:31:44 +1100559.It Cm from="pattern-list"
Darren Tucker896ad5a2008-06-11 09:34:46 +1000560Specifies that in addition to public key authentication, either the canonical
Darren Tucker11996732008-06-13 04:32:00 +1000561name of the remote host or its IP address must be present in the
Darren Tucker896ad5a2008-06-11 09:34:46 +1000562comma-separated list of patterns.
Damien Millerc7d5b5e2006-03-15 11:55:08 +1100563See
564.Sx PATTERNS
565in
566.Xr ssh_config 5
567for more information on patterns.
Darren Tucker896ad5a2008-06-11 09:34:46 +1000568.Pp
569In addition to the wildcard matching that may be applied to hostnames or
570addresses, a
571.Cm from
Darren Tucker5837b512009-06-21 17:52:27 +1000572stanza may match IP addresses using CIDR address/masklen notation.
Darren Tucker896ad5a2008-06-11 09:34:46 +1000573.Pp
574The purpose of this option is to optionally increase security: public key
575authentication by itself does not trust the network or name servers or
576anything (but the key); however, if somebody somehow steals the key, the key
577permits an intruder to log in from anywhere in the world.
578This additional option makes using a stolen key more difficult (name
579servers and/or routers would have to be compromised in addition to
580just the key).
Damien Miller31bdc522006-03-15 11:31:44 +1100581.It Cm no-agent-forwarding
582Forbids authentication agent forwarding when this key is used for
583authentication.
Damien Miller32aa1441999-10-29 09:15:49 +1000584.It Cm no-port-forwarding
Damien Miller7c24b812006-01-14 10:09:56 +1100585Forbids TCP forwarding when this key is used for authentication.
Damien Miller450a7a12000-03-26 13:04:51 +1000586Any port forward requests by the client will return an error.
Damien Miller208f1ed2006-03-15 11:56:03 +1100587This might be used, e.g. in connection with the
Damien Miller32aa1441999-10-29 09:15:49 +1000588.Cm command
589option.
Damien Miller31bdc522006-03-15 11:31:44 +1100590.It Cm no-pty
591Prevents tty allocation (a request to allocate a pty will fail).
Damien Miller95e80952008-03-27 11:03:05 +1100592.It Cm no-user-rc
Damien Miller13ba9c22008-04-03 20:52:51 +1100593Disables execution of
Damien Miller95e80952008-03-27 11:03:05 +1100594.Pa ~/.ssh/rc .
Damien Miller32aa1441999-10-29 09:15:49 +1000595.It Cm no-X11-forwarding
596Forbids X11 forwarding when this key is used for authentication.
597Any X11 forward requests by the client will return an error.
Damien Millera243fde2001-03-19 23:16:08 +1100598.It Cm permitopen="host:port"
Ben Lindstrom24643222001-06-25 05:08:11 +0000599Limit local
Damien Millera243fde2001-03-19 23:16:08 +1100600.Li ``ssh -L''
Ben Lindstrom4b3564e2001-04-10 02:41:56 +0000601port forwarding such that it may only connect to the specified host and
Ben Lindstromd71ba572001-09-12 18:03:31 +0000602port.
Damien Miller7fa96602010-08-05 13:03:13 +1000603IPv6 addresses can be specified by enclosing the address in square brackets.
Ben Lindstromd71ba572001-09-12 18:03:31 +0000604Multiple
Damien Millera243fde2001-03-19 23:16:08 +1100605.Cm permitopen
Damien Millerfbf486b2003-05-23 18:44:23 +1000606options may be applied separated by commas.
607No pattern matching is performed on the specified hostnames,
608they must be literal domains or addresses.
Damien Miller30da3442010-05-10 11:58:03 +1000609.It Cm principals="principals"
610On a
611.Cm cert-authority
612line, specifies allowed principals for certificate authentication as a
613comma-separated list.
614At least one name from the list must appear in the certificate's
615list of principals for the certificate to be accepted.
616This option is ignored for keys that are not marked as trusted certificate
617signers using the
618.Cm cert-authority
619option.
Damien Millerd27b9472005-12-13 19:29:02 +1100620.It Cm tunnel="n"
621Force a
622.Xr tun 4
623device on the server.
624Without this option, the next available device will be used if
625the client requests a tunnel.
Damien Miller32aa1441999-10-29 09:15:49 +1000626.El
Damien Miller32aa1441999-10-29 09:15:49 +1000627.Pp
Damien Miller7d2ef022006-03-15 11:32:06 +1100628An example authorized_keys file:
Damien Millerc8f61cf2006-03-15 11:33:25 +1100629.Bd -literal -offset 3n
Damien Miller7d2ef022006-03-15 11:32:06 +1100630# Comments allowed at start of line
631ssh-rsa AAAAB3Nza...LiPk== user@example.net
Damien Millerc8f61cf2006-03-15 11:33:25 +1100632from="*.sales.example.net,!pc.sales.example.net" ssh-rsa
633AAAAB2...19Q== john@example.net
634command="dump /home",no-pty,no-port-forwarding ssh-dss
635AAAAC3...51R== example.net
636permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss
637AAAAB5...21S==
638tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...==
639jane@example.net
Damien Miller7d2ef022006-03-15 11:32:06 +1100640.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000641.Sh SSH_KNOWN_HOSTS FILE FORMAT
Damien Miller22c77262000-04-13 12:26:34 +1000642The
Damien Millerffadc582003-02-24 11:52:26 +1100643.Pa /etc/ssh/ssh_known_hosts
Damien Miller22c77262000-04-13 12:26:34 +1000644and
Damien Miller167ea5d2005-05-26 12:04:02 +1000645.Pa ~/.ssh/known_hosts
Damien Miller450a7a12000-03-26 13:04:51 +1000646files contain host public keys for all known hosts.
647The global file should
648be prepared by the administrator (optional), and the per-user file is
Damien Miller9a7f2012006-03-15 11:32:42 +1100649maintained automatically: whenever the user connects from an unknown host,
Damien Miller450a7a12000-03-26 13:04:51 +1000650its key is added to the per-user file.
Damien Miller32aa1441999-10-29 09:15:49 +1000651.Pp
Damien Millera7dab8b2010-03-05 10:42:05 +1100652Each line in these files contains the following fields: markers (optional),
653hostnames, bits, exponent, modulus, comment.
Damien Miller450a7a12000-03-26 13:04:51 +1000654The fields are separated by spaces.
Damien Miller32aa1441999-10-29 09:15:49 +1000655.Pp
Damien Millera7dab8b2010-03-05 10:42:05 +1100656The marker is optional, but if it is present then it must be one of
657.Dq @cert-authority ,
658to indicate that the line contains a certification authority (CA) key,
659or
660.Dq @revoked ,
661to indicate that the key contained on the line is revoked and must not ever
662be accepted.
663Only one marker should be used on a key line.
664.Pp
Damien Miller31554322003-05-14 13:44:58 +1000665Hostnames is a comma-separated list of patterns
Damien Miller9a7f2012006-03-15 11:32:42 +1100666.Pf ( Ql *
Damien Millerfbf486b2003-05-23 18:44:23 +1000667and
668.Ql \&?
Damien Miller049245d2003-05-14 13:44:42 +1000669act as
Damien Miller32aa1441999-10-29 09:15:49 +1000670wildcards); each pattern in turn is matched against the canonical host
671name (when authenticating a client) or against the user-supplied
Damien Miller450a7a12000-03-26 13:04:51 +1000672name (when authenticating a server).
673A pattern may also be preceded by
Damien Miller049245d2003-05-14 13:44:42 +1000674.Ql \&!
Damien Miller32aa1441999-10-29 09:15:49 +1000675to indicate negation: if the host name matches a negated
676pattern, it is not accepted (by that line) even if it matched another
677pattern on the line.
Darren Tuckerda345532006-07-10 23:04:19 +1000678A hostname or address may optionally be enclosed within
679.Ql \&[
680and
681.Ql \&]
682brackets then followed by
683.Ql \&:
Darren Tucker11318472006-07-12 22:07:59 +1000684and a non-standard port number.
Damien Miller32aa1441999-10-29 09:15:49 +1000685.Pp
Damien Millere1776152005-03-01 21:47:37 +1100686Alternately, hostnames may be stored in a hashed form which hides host names
Damien Miller718fd4b2005-03-02 12:03:23 +1100687and addresses should the file's contents be disclosed.
688Hashed hostnames start with a
689.Ql |
Damien Millere1776152005-03-01 21:47:37 +1100690character.
691Only one hashed hostname may appear on a single line and none of the above
692negation or wildcard operators may be applied.
693.Pp
Damien Millere247cc42000-05-07 12:03:14 +1000694Bits, exponent, and modulus are taken directly from the RSA host key; they
Damien Miller9a7f2012006-03-15 11:32:42 +1100695can be obtained, for example, from
Damien Miller05eda432002-02-10 18:32:28 +1100696.Pa /etc/ssh/ssh_host_key.pub .
Damien Miller32aa1441999-10-29 09:15:49 +1000697The optional comment field continues to the end of the line, and is not used.
698.Pp
699Lines starting with
700.Ql #
701and empty lines are ignored as comments.
702.Pp
703When performing host authentication, authentication is accepted if any
Damien Millera7dab8b2010-03-05 10:42:05 +1100704matching line has the proper key; either one that matches exactly or,
705if the server has presented a certificate for authentication, the key
706of the certification authority that signed the certificate.
707For a key to be trusted as a certification authority, it must use the
708.Dq @cert-authority
709marker described above.
710.Pp
711The known hosts file also provides a facility to mark keys as revoked,
712for example when it is known that the associated private key has been
713stolen.
714Revoked keys are specified by including the
715.Dq @revoked
716marker at the beginning of the key line, and are never accepted for
717authentication or as certification authorities, but instead will
718produce a warning from
719.Xr ssh 1
720when they are encountered.
721.Pp
722It is permissible (but not
Damien Miller32aa1441999-10-29 09:15:49 +1000723recommended) to have several lines or different host keys for the same
Damien Miller450a7a12000-03-26 13:04:51 +1000724names.
725This will inevitably happen when short forms of host names
726from different domains are put in the file.
727It is possible
Damien Miller32aa1441999-10-29 09:15:49 +1000728that the files contain conflicting information; authentication is
729accepted if valid information can be found from either file.
730.Pp
731Note that the lines in these files are typically hundreds of characters
732long, and you definitely don't want to type in the host keys by hand.
Damien Millera7dab8b2010-03-05 10:42:05 +1100733Rather, generate them by a script,
734.Xr ssh-keyscan 1
Damien Miller22c77262000-04-13 12:26:34 +1000735or by taking
Damien Miller05eda432002-02-10 18:32:28 +1100736.Pa /etc/ssh/ssh_host_key.pub
Damien Miller32aa1441999-10-29 09:15:49 +1000737and adding the host names at the front.
Damien Millera7dab8b2010-03-05 10:42:05 +1100738.Xr ssh-keygen 1
Damien Miller98339052010-03-05 21:30:35 +1100739also offers some basic automated editing for
Damien Millera7dab8b2010-03-05 10:42:05 +1100740.Pa ~/.ssh/known_hosts
741including removing hosts matching a host name and converting all host
742names to their hashed representations.
Damien Millercc00f5e2006-03-15 11:33:00 +1100743.Pp
744An example ssh_known_hosts file:
745.Bd -literal -offset 3n
746# Comments allowed at start of line
747closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net
748cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
Damien Millere1776152005-03-01 21:47:37 +1100749# A hashed hostname
750|1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
751AAAA1234.....=
Damien Millera7dab8b2010-03-05 10:42:05 +1100752# A revoked key
753@revoked * ssh-rsa AAAAB5W...
754# A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
755@cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
Damien Millere1776152005-03-01 21:47:37 +1100756.Ed
Damien Miller32aa1441999-10-29 09:15:49 +1000757.Sh FILES
Damien Millerd8702e82006-03-15 11:33:56 +1100758.Bl -tag -width Ds -compact
Damien Millerafdae612010-08-31 22:31:14 +1000759.It Pa ~/.hushlogin
Damien Miller70a908e2005-03-01 21:17:09 +1100760This file is used to suppress printing the last login time and
761.Pa /etc/motd ,
762if
763.Cm PrintLastLog
764and
765.Cm PrintMotd ,
766respectively,
767are enabled.
768It does not suppress printing of the banner specified by
769.Cm Banner .
Damien Millerd8702e82006-03-15 11:33:56 +1100770.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000771.It Pa ~/.rhosts
Damien Milleradc35b92006-03-15 11:35:27 +1100772This file is used for host-based authentication (see
773.Xr ssh 1
774for more information).
775On some machines this file may need to be
776world-readable if the user's home directory is on an NFS partition,
777because
778.Nm
779reads it as root.
780Additionally, this file must be owned by the user,
781and must not have write permissions for anyone else.
782The recommended
783permission for most machines is read/write for the user, and not
Damien Miller32aa1441999-10-29 09:15:49 +1000784accessible by others.
785.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000786.It Pa ~/.shosts
Damien Milleradc35b92006-03-15 11:35:27 +1100787This file is used in exactly the same way as
788.Pa .rhosts ,
789but allows host-based authentication without permitting login with
790rlogin/rsh.
Damien Miller32aa1441999-10-29 09:15:49 +1000791.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000792.It Pa ~/.ssh/
Damien Miller520e6152008-02-10 22:46:22 +1100793This directory is the default location for all user-specific configuration
794and authentication information.
795There is no general requirement to keep the entire contents of this directory
796secret, but the recommended permissions are read/write/execute for the user,
797and not accessible by others.
798.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000799.It Pa ~/.ssh/authorized_keys
Damien Millereb8b60e2010-08-31 22:41:14 +1000800Lists the public keys (DSA/ECDSA/RSA) that can be used for logging in
801as this user.
Damien Millerd8702e82006-03-15 11:33:56 +1100802The format of this file is described above.
Damien Miller5d43d492006-08-30 11:07:00 +1000803The content of the file is not highly sensitive, but the recommended
Damien Milleradc35b92006-03-15 11:35:27 +1100804permissions are read/write for the user, and not accessible by others.
Damien Miller32aa1441999-10-29 09:15:49 +1000805.Pp
Damien Miller5d43d492006-08-30 11:07:00 +1000806If this file, the
807.Pa ~/.ssh
808directory, or the user's home directory are writable
809by other users, then the file could be modified or replaced by unauthorized
810users.
811In this case,
812.Nm
813will not allow it to be used unless the
814.Cm StrictModes
815option has been set to
816.Dq no .
Damien Miller5d43d492006-08-30 11:07:00 +1000817.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000818.It Pa ~/.ssh/environment
Damien Miller450a7a12000-03-26 13:04:51 +1000819This file is read into the environment at login (if it exists).
820It can only contain empty lines, comment lines (that start with
Damien Miller32aa1441999-10-29 09:15:49 +1000821.Ql # ) ,
Damien Miller450a7a12000-03-26 13:04:51 +1000822and assignment lines of the form name=value.
823The file should be writable
Damien Miller32aa1441999-10-29 09:15:49 +1000824only by the user; it need not be readable by anyone else.
Ben Lindstrombd9bf382002-08-20 18:54:20 +0000825Environment processing is disabled by default and is
826controlled via the
827.Cm PermitUserEnvironment
828option.
Damien Millerd8702e82006-03-15 11:33:56 +1100829.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000830.It Pa ~/.ssh/known_hosts
Damien Milleradc35b92006-03-15 11:35:27 +1100831Contains a list of host keys for all hosts the user has logged into
832that are not already in the systemwide list of known host keys.
833The format of this file is described above.
834This file should be writable only by root/the owner and
Damien Millerd8702e82006-03-15 11:33:56 +1100835can, but need not be, world-readable.
836.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000837.It Pa ~/.ssh/rc
Damien Millerfd725cf2006-03-15 11:35:54 +1100838Contains initialization routines to be run before
839the user's home directory becomes accessible.
Damien Miller32aa1441999-10-29 09:15:49 +1000840This file should be writable only by the user, and need not be
841readable by anyone else.
Damien Millerd8702e82006-03-15 11:33:56 +1100842.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000843.It Pa /etc/hosts.allow
844.It Pa /etc/hosts.deny
Damien Millerd8702e82006-03-15 11:33:56 +1100845Access controls that should be enforced by tcp-wrappers are defined here.
846Further details are described in
847.Xr hosts_access 5 .
848.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000849.It Pa /etc/hosts.equiv
Damien Miller445121f2006-03-15 11:36:18 +1100850This file is for host-based authentication (see
851.Xr ssh 1 ) .
852It should only be writable by root.
Damien Millerd8702e82006-03-15 11:33:56 +1100853.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000854.It Pa /etc/moduli
Damien Millerd8702e82006-03-15 11:33:56 +1100855Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange".
856The file format is described in
857.Xr moduli 5 .
858.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000859.It Pa /etc/motd
Damien Millerd8702e82006-03-15 11:33:56 +1100860See
861.Xr motd 5 .
862.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000863.It Pa /etc/nologin
Damien Millerd8702e82006-03-15 11:33:56 +1100864If this file exists,
865.Nm
866refuses to let anyone except root log in.
867The contents of the file
868are displayed to anyone trying to log in, and non-root connections are
869refused.
870The file should be world-readable.
871.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000872.It Pa /etc/shosts.equiv
Damien Miller445121f2006-03-15 11:36:18 +1100873This file is used in exactly the same way as
874.Pa hosts.equiv ,
875but allows host-based authentication without permitting login with
876rlogin/rsh.
Damien Millerd8702e82006-03-15 11:33:56 +1100877.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000878.It Pa /etc/ssh/ssh_host_key
879.It Pa /etc/ssh/ssh_host_dsa_key
Damien Millereb8b60e2010-08-31 22:41:14 +1000880.It Pa /etc/ssh/ssh_host_ecdsa_key
Damien Millerafdae612010-08-31 22:31:14 +1000881.It Pa /etc/ssh/ssh_host_rsa_key
Damien Millerd8702e82006-03-15 11:33:56 +1100882These three files contain the private parts of the host keys.
883These files should only be owned by root, readable only by root, and not
884accessible to others.
885Note that
886.Nm
Damien Milleredd03752006-03-15 11:36:45 +1100887does not start if these files are group/world-accessible.
Damien Millerd8702e82006-03-15 11:33:56 +1100888.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000889.It Pa /etc/ssh/ssh_host_key.pub
890.It Pa /etc/ssh/ssh_host_dsa_key.pub
Damien Millereb8b60e2010-08-31 22:41:14 +1000891.It Pa /etc/ssh/ssh_host_ecdsa_key.pub
Damien Millerafdae612010-08-31 22:31:14 +1000892.It Pa /etc/ssh/ssh_host_rsa_key.pub
Damien Millerd8702e82006-03-15 11:33:56 +1100893These three files contain the public parts of the host keys.
894These files should be world-readable but writable only by
895root.
896Their contents should match the respective private parts.
897These files are not
898really used for anything; they are provided for the convenience of
899the user so their contents can be copied to known hosts files.
900These files are created using
901.Xr ssh-keygen 1 .
902.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000903.It Pa /etc/ssh/ssh_known_hosts
Darren Tucker04354b92007-03-21 20:46:54 +1100904Systemwide list of known host keys.
905This file should be prepared by the
906system administrator to contain the public host keys of all machines in the
907organization.
908The format of this file is described above.
909This file should be writable only by root/the owner and
910should be world-readable.
911.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000912.It Pa /etc/ssh/sshd_config
Damien Millerd8702e82006-03-15 11:33:56 +1100913Contains configuration data for
914.Nm sshd .
915The file format and configuration options are described in
916.Xr sshd_config 5 .
917.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000918.It Pa /etc/ssh/sshrc
Damien Millerfd725cf2006-03-15 11:35:54 +1100919Similar to
920.Pa ~/.ssh/rc ,
921it can be used to specify
Damien Miller450a7a12000-03-26 13:04:51 +1000922machine-specific login-time initializations globally.
923This file should be writable only by root, and should be world-readable.
Damien Millerd8702e82006-03-15 11:33:56 +1100924.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000925.It Pa /var/empty
Damien Millerd8702e82006-03-15 11:33:56 +1100926.Xr chroot 2
927directory used by
928.Nm
929during privilege separation in the pre-authentication phase.
930The directory should not contain any files and must be owned by root
931and not group or world-writable.
932.Pp
Damien Millerafdae612010-08-31 22:31:14 +1000933.It Pa /var/run/sshd.pid
Damien Millerd8702e82006-03-15 11:33:56 +1100934Contains the process ID of the
935.Nm
936listening for connections (if there are several daemons running
937concurrently for different ports, this contains the process ID of the one
938started last).
939The content of this file is not sensitive; it can be world-readable.
Damien Miller37023962000-07-11 17:31:38 +1000940.El
Damien Miller32aa1441999-10-29 09:15:49 +1000941.Sh SEE ALSO
Damien Miller32aa1441999-10-29 09:15:49 +1000942.Xr scp 1 ,
Damien Miller33804262001-02-04 23:20:18 +1100943.Xr sftp 1 ,
Damien Miller32aa1441999-10-29 09:15:49 +1000944.Xr ssh 1 ,
945.Xr ssh-add 1 ,
946.Xr ssh-agent 1 ,
947.Xr ssh-keygen 1 ,
Darren Tucker04354b92007-03-21 20:46:54 +1100948.Xr ssh-keyscan 1 ,
Darren Tucker1f203942003-10-15 15:50:42 +1000949.Xr chroot 2 ,
950.Xr hosts_access 5 ,
Ben Lindstromc8e29ce2001-08-06 20:55:28 +0000951.Xr login.conf 5 ,
952.Xr moduli 5 ,
Ben Lindstrom9f049032002-06-21 00:59:05 +0000953.Xr sshd_config 5 ,
Darren Tucker1f203942003-10-15 15:50:42 +1000954.Xr inetd 8 ,
Ben Lindstromd2bf0d62001-06-25 04:10:54 +0000955.Xr sftp-server 8
Damien Millerf1ce5052003-06-11 22:04:39 +1000956.Sh AUTHORS
957OpenSSH is a derivative of the original and free
958ssh 1.2.12 release by Tatu Ylonen.
959Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
960Theo de Raadt and Dug Song
961removed many bugs, re-added newer features and
962created OpenSSH.
963Markus Friedl contributed the support for SSH
964protocol versions 1.5 and 2.0.
965Niels Provos and Markus Friedl contributed support
966for privilege separation.
Damien Millerc47d7e92006-03-15 11:27:20 +1100967.Sh CAVEATS
968System security is not improved unless
969.Nm rshd ,
970.Nm rlogind ,
971and
972.Nm rexecd
973are disabled (thus completely disabling
974.Xr rlogin
975and
976.Xr rsh
977into the machine).