Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1 | .\" -*- nroff -*- |
| 2 | .\" |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
| 5 | .\" All rights reserved |
| 6 | .\" |
Damien Miller | e4340be | 2000-09-16 13:29:08 +1100 | [diff] [blame] | 7 | .\" 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 Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 12 | .\" |
Ben Lindstrom | 92a2e38 | 2001-03-05 06:59:27 +0000 | [diff] [blame] | 13 | .\" 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 Miller | e4340be | 2000-09-16 13:29:08 +1100 | [diff] [blame] | 16 | .\" |
| 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 Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 36 | .\" |
Ben Lindstrom | 778bf55 | 2002-03-05 01:37:12 +0000 | [diff] [blame^] | 37 | .\" $OpenBSD: sshd.8,v 1.169 2002/02/28 20:36:42 stevesk Exp $ |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 38 | .Dd September 25, 1999 |
| 39 | .Dt SSHD 8 |
| 40 | .Os |
| 41 | .Sh NAME |
| 42 | .Nm sshd |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 43 | .Nd OpenSSH SSH daemon |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 44 | .Sh SYNOPSIS |
| 45 | .Nm sshd |
Ben Lindstrom | dfd1850 | 2001-09-20 01:06:08 +0000 | [diff] [blame] | 46 | .Op Fl deiqtD46 |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 47 | .Op Fl b Ar bits |
| 48 | .Op Fl f Ar config_file |
| 49 | .Op Fl g Ar login_grace_time |
| 50 | .Op Fl h Ar host_key_file |
| 51 | .Op Fl k Ar key_gen_time |
Ben Lindstrom | ade03f6 | 2001-12-06 18:22:17 +0000 | [diff] [blame] | 52 | .Op Fl o Ar option |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 53 | .Op Fl p Ar port |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 54 | .Op Fl u Ar len |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 55 | .Sh DESCRIPTION |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 56 | .Nm |
Ben Lindstrom | d58eb5f | 2001-03-07 06:07:22 +0000 | [diff] [blame] | 57 | (SSH Daemon) is the daemon program for |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 58 | .Xr ssh 1 . |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 59 | Together these programs replace rlogin and rsh, and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 60 | provide secure encrypted communications between two untrusted hosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 61 | over an insecure network. |
| 62 | The programs are intended to be as easy to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 63 | install and use as possible. |
| 64 | .Pp |
| 65 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 66 | is the daemon that listens for connections from clients. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 67 | It is normally started at boot from |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 68 | .Pa /etc/rc . |
| 69 | It forks a new |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 70 | daemon for each incoming connection. |
| 71 | The forked daemons handle |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 72 | key exchange, encryption, authentication, command execution, |
| 73 | and data exchange. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 74 | This implementation of |
| 75 | .Nm |
| 76 | supports both SSH protocol version 1 and 2 simultaneously. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 77 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 78 | works as follows. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 79 | .Pp |
| 80 | .Ss SSH protocol version 1 |
| 81 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 82 | Each host has a host-specific RSA key |
| 83 | (normally 1024 bits) used to identify the host. |
| 84 | Additionally, when |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 85 | the daemon starts, it generates a server RSA key (normally 768 bits). |
| 86 | This key is normally regenerated every hour if it has been used, and |
| 87 | is never stored on disk. |
| 88 | .Pp |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 89 | Whenever a client connects the daemon responds with its public |
| 90 | host and server keys. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 91 | The client compares the |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 92 | RSA host key against its own database to verify that it has not changed. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 93 | The client then generates a 256 bit random number. |
| 94 | It encrypts this |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 95 | random number using both the host key and the server key, and sends |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 96 | the encrypted number to the server. |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 97 | Both sides then use this |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 98 | random number as a session key which is used to encrypt all further |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 99 | communications in the session. |
| 100 | The rest of the session is encrypted |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 101 | using a conventional cipher, currently Blowfish or 3DES, with 3DES |
Damien Miller | b38eff8 | 2000-04-01 11:09:21 +1000 | [diff] [blame] | 102 | being used by default. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 103 | The client selects the encryption algorithm |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 104 | to use from those offered by the server. |
| 105 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 106 | Next, the server and the client enter an authentication dialog. |
| 107 | The client tries to authenticate itself using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 108 | .Pa .rhosts |
| 109 | authentication, |
| 110 | .Pa .rhosts |
| 111 | authentication combined with RSA host |
| 112 | authentication, RSA challenge-response authentication, or password |
| 113 | based authentication. |
| 114 | .Pp |
| 115 | Rhosts authentication is normally disabled |
| 116 | because it is fundamentally insecure, but can be enabled in the server |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 117 | configuration file if desired. |
| 118 | System security is not improved unless |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 119 | .Xr rshd 8 , |
| 120 | .Xr rlogind 8 , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 121 | and |
Ben Lindstrom | 044274b | 2001-09-12 16:46:08 +0000 | [diff] [blame] | 122 | .Xr rexecd 8 |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 123 | are disabled (thus completely disabling |
| 124 | .Xr rlogin 1 |
| 125 | and |
| 126 | .Xr rsh 1 |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 127 | into the machine). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 128 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 129 | .Ss SSH protocol version 2 |
| 130 | .Pp |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 131 | Version 2 works similarly: |
Ben Lindstrom | 07d24dc | 2001-08-06 21:18:57 +0000 | [diff] [blame] | 132 | Each host has a host-specific key (RSA or DSA) used to identify the host. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 133 | However, when the daemon starts, it does not generate a server key. |
| 134 | Forward security is provided through a Diffie-Hellman key agreement. |
| 135 | This key agreement results in a shared session key. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 136 | .Pp |
Ben Lindstrom | fd2e05b | 2001-03-05 07:48:45 +0000 | [diff] [blame] | 137 | The rest of the session is encrypted using a symmetric cipher, currently |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 138 | 128 bit AES, Blowfish, 3DES, CAST128, Arcfour, 192 bit AES, or 256 bit AES. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 139 | The client selects the encryption algorithm |
| 140 | to use from those offered by the server. |
| 141 | Additionally, session integrity is provided |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 142 | through a cryptographic message authentication code |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 143 | (hmac-sha1 or hmac-md5). |
| 144 | .Pp |
| 145 | Protocol version 2 provides a public key based |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 146 | user (PubkeyAuthentication) or |
| 147 | client host (HostbasedAuthentication) authentication method, |
| 148 | conventional password authentication and challenge response based methods. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 149 | .Pp |
| 150 | .Ss Command execution and data forwarding |
| 151 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 152 | If the client successfully authenticates itself, a dialog for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 153 | preparing the session is entered. |
| 154 | At this time the client may request |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 155 | things like allocating a pseudo-tty, forwarding X11 connections, |
| 156 | forwarding TCP/IP connections, or forwarding the authentication agent |
| 157 | connection over the secure channel. |
| 158 | .Pp |
| 159 | Finally, the client either requests a shell or execution of a command. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 160 | The sides then enter session mode. |
| 161 | In this mode, either side may send |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 162 | data at any time, and such data is forwarded to/from the shell or |
| 163 | command on the server side, and the user terminal in the client side. |
| 164 | .Pp |
| 165 | When the user program terminates and all forwarded X11 and other |
| 166 | connections have been closed, the server sends command exit status to |
| 167 | the client, and both sides exit. |
| 168 | .Pp |
| 169 | .Nm |
| 170 | can be configured using command-line options or a configuration |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 171 | file. |
| 172 | Command-line options override values specified in the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 173 | configuration file. |
| 174 | .Pp |
Damien Miller | 6162d12 | 1999-11-21 13:23:52 +1100 | [diff] [blame] | 175 | .Nm |
| 176 | rereads its configuration file when it receives a hangup signal, |
Ben Lindstrom | 49a098d | 2001-03-05 06:55:18 +0000 | [diff] [blame] | 177 | .Dv SIGHUP , |
Ben Lindstrom | d2bf0d6 | 2001-06-25 04:10:54 +0000 | [diff] [blame] | 178 | by executing itself with the name it was started as, i.e., |
Ben Lindstrom | 49a098d | 2001-03-05 06:55:18 +0000 | [diff] [blame] | 179 | .Pa /usr/sbin/sshd . |
Damien Miller | 6162d12 | 1999-11-21 13:23:52 +1100 | [diff] [blame] | 180 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 181 | The options are as follows: |
| 182 | .Bl -tag -width Ds |
| 183 | .It Fl b Ar bits |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 184 | Specifies the number of bits in the ephemeral protocol version 1 |
| 185 | server key (default 768). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 186 | .It Fl d |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 187 | Debug mode. |
| 188 | The server sends verbose debug output to the system |
| 189 | log, and does not put itself in the background. |
| 190 | The server also will not fork and will only process one connection. |
| 191 | This option is only intended for debugging for the server. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 192 | Multiple -d options increase the debugging level. |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 193 | Maximum is 3. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 194 | .It Fl e |
| 195 | When this option is specified, |
| 196 | .Nm |
| 197 | will send the output to the standard error instead of the system log. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 198 | .It Fl f Ar configuration_file |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 199 | Specifies the name of the configuration file. |
| 200 | The default is |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 201 | .Pa /etc/ssh/sshd_config . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 202 | .Nm |
| 203 | refuses to start if there is no configuration file. |
| 204 | .It Fl g Ar login_grace_time |
| 205 | Gives the grace time for clients to authenticate themselves (default |
Kevin Steves | 9ce907c | 2001-01-07 11:53:40 +0000 | [diff] [blame] | 206 | 600 seconds). |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 207 | If the client fails to authenticate the user within |
| 208 | this many seconds, the server disconnects and exits. |
| 209 | A value of zero indicates no limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 210 | .It Fl h Ar host_key_file |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 211 | Specifies a file from which a host key is read. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 212 | This option must be given if |
| 213 | .Nm |
| 214 | is not run as root (as the normal |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 215 | host key files are normally not readable by anyone but root). |
| 216 | The default is |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 217 | .Pa /etc/ssh/ssh_host_key |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 218 | for protocol version 1, and |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 219 | .Pa /etc/ssh/ssh_host_rsa_key |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 220 | and |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 221 | .Pa /etc/ssh/ssh_host_dsa_key |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 222 | for protocol version 2. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 223 | It is possible to have multiple host key files for |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 224 | the different protocol versions and host key algorithms. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 225 | .It Fl i |
| 226 | Specifies that |
| 227 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 228 | is being run from inetd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 229 | .Nm |
| 230 | is normally not run |
| 231 | from inetd because it needs to generate the server key before it can |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 232 | respond to the client, and this may take tens of seconds. |
| 233 | Clients would have to wait too long if the key was regenerated every time. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 234 | However, with small key sizes (e.g., 512) using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 235 | .Nm |
| 236 | from inetd may |
| 237 | be feasible. |
| 238 | .It Fl k Ar key_gen_time |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 239 | Specifies how often the ephemeral protocol version 1 server key is |
| 240 | regenerated (default 3600 seconds, or one hour). |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 241 | The motivation for regenerating the key fairly |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 242 | often is that the key is not stored anywhere, and after about an hour, |
| 243 | it becomes impossible to recover the key for decrypting intercepted |
| 244 | communications even if the machine is cracked into or physically |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 245 | seized. |
| 246 | A value of zero indicates that the key will never be regenerated. |
Ben Lindstrom | ade03f6 | 2001-12-06 18:22:17 +0000 | [diff] [blame] | 247 | .It Fl o Ar option |
| 248 | Can be used to give options in the format used in the configuration file. |
| 249 | This is useful for specifying options for which there is no separate |
| 250 | command-line flag. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 251 | .It Fl p Ar port |
| 252 | Specifies the port on which the server listens for connections |
| 253 | (default 22). |
Damien Miller | 7d1ded4 | 2002-01-22 23:09:41 +1100 | [diff] [blame] | 254 | Multiple port options are permitted. |
| 255 | Ports specified in the configuration file are ignored when a |
| 256 | command-line port is specified. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 257 | .It Fl q |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 258 | Quiet mode. |
| 259 | Nothing is sent to the system log. |
| 260 | Normally the beginning, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 261 | authentication, and termination of each connection is logged. |
Ben Lindstrom | 794325a | 2001-08-06 21:09:07 +0000 | [diff] [blame] | 262 | .It Fl t |
| 263 | Test mode. |
| 264 | Only check the validity of the configuration file and sanity of the keys. |
Damien Miller | 9f0f5c6 | 2001-12-21 14:45:46 +1100 | [diff] [blame] | 265 | This is useful for updating |
Ben Lindstrom | 794325a | 2001-08-06 21:09:07 +0000 | [diff] [blame] | 266 | .Nm |
| 267 | reliably as configuration options may change. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 268 | .It Fl u Ar len |
| 269 | This option is used to specify the size of the field |
| 270 | in the |
| 271 | .Li utmp |
| 272 | structure that holds the remote host name. |
| 273 | If the resolved host name is longer than |
| 274 | .Ar len , |
| 275 | the dotted decimal value will be used instead. |
| 276 | This allows hosts with very long host names that |
| 277 | overflow this field to still be uniquely identified. |
| 278 | Specifying |
| 279 | .Fl u0 |
| 280 | indicates that only dotted decimal addresses |
| 281 | should be put into the |
| 282 | .Pa utmp |
| 283 | file. |
Ben Lindstrom | 6f672c0 | 2001-09-12 17:51:55 +0000 | [diff] [blame] | 284 | .Fl u0 |
| 285 | is also be used to prevent |
| 286 | .Nm |
| 287 | from making DNS requests unless the authentication |
| 288 | mechanism or configuration requires it. |
| 289 | Authentication mechanisms that may require DNS include |
| 290 | .Cm RhostsAuthentication , |
| 291 | .Cm RhostsRSAAuthentication , |
| 292 | .Cm HostbasedAuthentication |
| 293 | and using a |
| 294 | .Cm from="pattern-list" |
| 295 | option in a key file. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 296 | .It Fl D |
| 297 | When this option is specified |
| 298 | .Nm |
| 299 | will not detach and does not become a daemon. |
| 300 | This allows easy monitoring of |
| 301 | .Nm sshd . |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 302 | .It Fl 4 |
| 303 | Forces |
| 304 | .Nm |
| 305 | to use IPv4 addresses only. |
| 306 | .It Fl 6 |
| 307 | Forces |
| 308 | .Nm |
| 309 | to use IPv6 addresses only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 310 | .El |
| 311 | .Sh CONFIGURATION FILE |
| 312 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 313 | reads configuration data from |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 314 | .Pa /etc/ssh/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 315 | (or the file specified with |
| 316 | .Fl f |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 317 | on the command line). |
Ben Lindstrom | 1c0fd09 | 2001-09-12 16:36:17 +0000 | [diff] [blame] | 318 | The file contains keyword-argument pairs, one per line. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 319 | Lines starting with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 320 | .Ql # |
| 321 | and empty lines are interpreted as comments. |
| 322 | .Pp |
Ben Lindstrom | 1c0fd09 | 2001-09-12 16:36:17 +0000 | [diff] [blame] | 323 | The possible |
| 324 | keywords and their meanings are as follows (note that |
| 325 | keywords are case-insensitive and arguments are case-sensitive): |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 326 | .Bl -tag -width Ds |
| 327 | .It Cm AFSTokenPassing |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 328 | Specifies whether an AFS token may be forwarded to the server. |
| 329 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 330 | .Dq yes . |
| 331 | .It Cm AllowGroups |
Damien Miller | df64a68 | 2002-01-22 23:33:45 +1100 | [diff] [blame] | 332 | This keyword can be followed by a list of group name patterns, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 333 | by spaces. |
| 334 | If specified, login is allowed only for users whose primary |
Kevin Steves | 7b61cfa | 2001-01-14 19:11:00 +0000 | [diff] [blame] | 335 | group or supplementary group list matches one of the patterns. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 336 | .Ql \&* |
| 337 | and |
| 338 | .Ql ? |
| 339 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 340 | wildcards in the patterns. |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 341 | Only group names are valid; a numerical group ID is not recognized. |
Damien Miller | df64a68 | 2002-01-22 23:33:45 +1100 | [diff] [blame] | 342 | By default, login is allowed for all groups. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 343 | .Pp |
Damien Miller | 50a41ed | 2000-10-16 12:14:42 +1100 | [diff] [blame] | 344 | .It Cm AllowTcpForwarding |
| 345 | Specifies whether TCP forwarding is permitted. |
| 346 | The default is |
| 347 | .Dq yes . |
| 348 | Note that disabling TCP forwarding does not improve security unless |
| 349 | users are also denied shell access, as they can always install their |
| 350 | own forwarders. |
| 351 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 352 | .It Cm AllowUsers |
Damien Miller | df64a68 | 2002-01-22 23:33:45 +1100 | [diff] [blame] | 353 | This keyword can be followed by a list of user name patterns, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 354 | by spaces. |
| 355 | If specified, login is allowed only for users names that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 356 | match one of the patterns. |
| 357 | .Ql \&* |
| 358 | and |
| 359 | .Ql ? |
| 360 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 361 | wildcards in the patterns. |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 362 | Only user names are valid; a numerical user ID is not recognized. |
Damien Miller | df64a68 | 2002-01-22 23:33:45 +1100 | [diff] [blame] | 363 | By default, login is allowed for all users. |
Ben Lindstrom | 6026002 | 2001-07-04 04:56:44 +0000 | [diff] [blame] | 364 | If the pattern takes the form USER@HOST then USER and HOST |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 365 | are separately checked, restricting logins to particular |
Ben Lindstrom | 6026002 | 2001-07-04 04:56:44 +0000 | [diff] [blame] | 366 | users from particular hosts. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 367 | .Pp |
Ben Lindstrom | bfb3a0e | 2001-06-05 20:25:05 +0000 | [diff] [blame] | 368 | .It Cm AuthorizedKeysFile |
Ben Lindstrom | 07d24dc | 2001-08-06 21:18:57 +0000 | [diff] [blame] | 369 | Specifies the file that contains the public keys that can be used |
| 370 | for user authentication. |
Ben Lindstrom | bfb3a0e | 2001-06-05 20:25:05 +0000 | [diff] [blame] | 371 | .Cm AuthorizedKeysFile |
| 372 | may contain tokens of the form %T which are substituted during connection |
Ben Lindstrom | e59433d | 2001-09-12 16:41:37 +0000 | [diff] [blame] | 373 | set-up. The following tokens are defined: %% is replaced by a literal '%', |
Ben Lindstrom | bfb3a0e | 2001-06-05 20:25:05 +0000 | [diff] [blame] | 374 | %h is replaced by the home directory of the user being authenticated and |
| 375 | %u is replaced by the username of that user. |
| 376 | After expansion, |
| 377 | .Cm AuthorizedKeysFile |
Ben Lindstrom | 34a9968 | 2001-06-12 00:23:12 +0000 | [diff] [blame] | 378 | is taken to be an absolute path or one relative to the user's home |
Ben Lindstrom | bfb3a0e | 2001-06-05 20:25:05 +0000 | [diff] [blame] | 379 | directory. |
| 380 | The default is |
Damien Miller | 70972eb | 2002-01-22 23:19:55 +1100 | [diff] [blame] | 381 | .Dq .ssh/authorized_keys . |
Ben Lindstrom | 48bd7c1 | 2001-01-09 00:35:42 +0000 | [diff] [blame] | 382 | .It Cm Banner |
| 383 | In some jurisdictions, sending a warning message before authentication |
| 384 | may be relevant for getting legal protection. |
| 385 | The contents of the specified file are sent to the remote user before |
| 386 | authentication is allowed. |
| 387 | This option is only available for protocol version 2. |
| 388 | .Pp |
Ben Lindstrom | ff8b494 | 2001-03-06 01:00:03 +0000 | [diff] [blame] | 389 | .It Cm ChallengeResponseAuthentication |
Ben Lindstrom | c8e29ce | 2001-08-06 20:55:28 +0000 | [diff] [blame] | 390 | Specifies whether challenge response authentication is allowed. |
| 391 | All authentication styles from |
| 392 | .Xr login.conf 5 |
| 393 | are supported. |
Ben Lindstrom | ff8b494 | 2001-03-06 01:00:03 +0000 | [diff] [blame] | 394 | The default is |
| 395 | .Dq yes . |
Ben Lindstrom | 608d1d1 | 2001-06-05 19:33:22 +0000 | [diff] [blame] | 396 | .It Cm Ciphers |
| 397 | Specifies the ciphers allowed for protocol version 2. |
| 398 | Multiple ciphers must be comma-separated. |
| 399 | The default is |
Damien Miller | 9c3f950 | 2002-01-22 23:33:15 +1100 | [diff] [blame] | 400 | .Pp |
| 401 | .Bd -literal |
| 402 | ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour, |
| 403 | aes192-cbc,aes256-cbc'' |
| 404 | .Ed |
Ben Lindstrom | 5744dc4 | 2001-04-13 23:28:01 +0000 | [diff] [blame] | 405 | .It Cm ClientAliveInterval |
| 406 | Sets a timeout interval in seconds after which if no data has been received |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 407 | from the client, |
Ben Lindstrom | 5744dc4 | 2001-04-13 23:28:01 +0000 | [diff] [blame] | 408 | .Nm |
| 409 | will send a message through the encrypted |
Ben Lindstrom | a8f3972 | 2001-04-16 02:03:49 +0000 | [diff] [blame] | 410 | channel to request a response from the client. |
| 411 | The default |
Ben Lindstrom | 5744dc4 | 2001-04-13 23:28:01 +0000 | [diff] [blame] | 412 | is 0, indicating that these messages will not be sent to the client. |
Ben Lindstrom | a8f3972 | 2001-04-16 02:03:49 +0000 | [diff] [blame] | 413 | This option applies to protocol version 2 only. |
Ben Lindstrom | 5744dc4 | 2001-04-13 23:28:01 +0000 | [diff] [blame] | 414 | .It Cm ClientAliveCountMax |
| 415 | Sets the number of client alive messages (see above) which may be |
| 416 | sent without |
| 417 | .Nm |
| 418 | receiving any messages back from the client. If this threshold is |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 419 | reached while client alive messages are being sent, |
Ben Lindstrom | 5744dc4 | 2001-04-13 23:28:01 +0000 | [diff] [blame] | 420 | .Nm |
| 421 | will disconnect the client, terminating the session. It is important |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 422 | to note that the use of client alive messages is very different from |
Damien Miller | 60d8aaf | 2001-11-12 11:04:05 +1100 | [diff] [blame] | 423 | .Cm KeepAlive |
Ben Lindstrom | a8f3972 | 2001-04-16 02:03:49 +0000 | [diff] [blame] | 424 | (below). The client alive messages are sent through the |
Ben Lindstrom | 5744dc4 | 2001-04-13 23:28:01 +0000 | [diff] [blame] | 425 | encrypted channel and therefore will not be spoofable. The TCP keepalive |
Ben Lindstrom | a8f3972 | 2001-04-16 02:03:49 +0000 | [diff] [blame] | 426 | option enabled by |
Damien Miller | 60d8aaf | 2001-11-12 11:04:05 +1100 | [diff] [blame] | 427 | .Cm KeepAlive |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 428 | is spoofable. The client alive mechanism is valuable when the client or |
| 429 | server depend on knowing when a connection has become inactive. |
Ben Lindstrom | a8f3972 | 2001-04-16 02:03:49 +0000 | [diff] [blame] | 430 | .Pp |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 431 | The default value is 3. If |
Ben Lindstrom | a8f3972 | 2001-04-16 02:03:49 +0000 | [diff] [blame] | 432 | .Cm ClientAliveInterval |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 433 | (above) is set to 15, and |
Ben Lindstrom | 406b4f0 | 2001-09-20 23:09:16 +0000 | [diff] [blame] | 434 | .Cm ClientAliveCountMax |
| 435 | is left at the default, unresponsive ssh clients |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 436 | will be disconnected after approximately 45 seconds. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 437 | .It Cm DenyGroups |
Damien Miller | df64a68 | 2002-01-22 23:33:45 +1100 | [diff] [blame] | 438 | This keyword can be followed by a list of group name patterns, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 439 | by spaces. |
Damien Miller | df64a68 | 2002-01-22 23:33:45 +1100 | [diff] [blame] | 440 | Login is disallowed for users whose primary group or supplementary |
| 441 | group list matches one of the patterns. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 442 | .Ql \&* |
| 443 | and |
| 444 | .Ql ? |
| 445 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 446 | wildcards in the patterns. |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 447 | Only group names are valid; a numerical group ID is not recognized. |
Damien Miller | df64a68 | 2002-01-22 23:33:45 +1100 | [diff] [blame] | 448 | By default, login is allowed for all groups. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 449 | .Pp |
| 450 | .It Cm DenyUsers |
Damien Miller | df64a68 | 2002-01-22 23:33:45 +1100 | [diff] [blame] | 451 | This keyword can be followed by a list of user name patterns, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 452 | by spaces. |
| 453 | Login is disallowed for user names that match one of the patterns. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 454 | .Ql \&* |
| 455 | and |
| 456 | .Ql ? |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 457 | can be used as wildcards in the patterns. |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 458 | Only user names are valid; a numerical user ID is not recognized. |
Damien Miller | df64a68 | 2002-01-22 23:33:45 +1100 | [diff] [blame] | 459 | By default, login is allowed for all users. |
Ben Lindstrom | 778bf55 | 2002-03-05 01:37:12 +0000 | [diff] [blame^] | 460 | If the pattern takes the form USER@HOST then USER and HOST |
| 461 | are separately checked, restricting logins to particular |
| 462 | users from particular hosts. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 463 | .It Cm GatewayPorts |
| 464 | Specifies whether remote hosts are allowed to connect to ports |
| 465 | forwarded for the client. |
Ben Lindstrom | 60d82be | 2001-09-12 17:58:15 +0000 | [diff] [blame] | 466 | By default, |
| 467 | .Nm |
| 468 | binds remote port forwardings to the loopback addresss. This |
| 469 | prevents other remote hosts from connecting to forwarded ports. |
| 470 | .Cm GatewayPorts |
| 471 | can be used to specify that |
| 472 | .Nm |
| 473 | should bind remote port forwardings to the wildcard address, |
| 474 | thus allowing remote hosts to connect to forwarded ports. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 475 | The argument must be |
| 476 | .Dq yes |
| 477 | or |
| 478 | .Dq no . |
| 479 | The default is |
| 480 | .Dq no . |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 481 | .It Cm HostbasedAuthentication |
| 482 | Specifies whether rhosts or /etc/hosts.equiv authentication together |
| 483 | with successful public key client host authentication is allowed |
| 484 | (hostbased authentication). |
| 485 | This option is similar to |
| 486 | .Cm RhostsRSAAuthentication |
| 487 | and applies to protocol version 2 only. |
| 488 | The default is |
| 489 | .Dq no . |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 490 | .It Cm HostKey |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 491 | Specifies a file containing a private host key |
| 492 | used by SSH. |
| 493 | The default is |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 494 | .Pa /etc/ssh/ssh_host_key |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 495 | for protocol version 1, and |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 496 | .Pa /etc/ssh/ssh_host_rsa_key |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 497 | and |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 498 | .Pa /etc/ssh/ssh_host_dsa_key |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 499 | for protocol version 2. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 500 | Note that |
| 501 | .Nm |
Ben Lindstrom | 226cfa0 | 2001-01-22 05:34:40 +0000 | [diff] [blame] | 502 | will refuse to use a file if it is group/world-accessible. |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 503 | It is possible to have multiple host key files. |
| 504 | .Dq rsa1 |
| 505 | keys are used for version 1 and |
| 506 | .Dq dsa |
| 507 | or |
| 508 | .Dq rsa |
| 509 | are used for version 2 of the SSH protocol. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 510 | .It Cm IgnoreRhosts |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 511 | Specifies that |
| 512 | .Pa .rhosts |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 513 | and |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 514 | .Pa .shosts |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 515 | files will not be used in |
| 516 | .Cm RhostsAuthentication , |
| 517 | .Cm RhostsRSAAuthentication |
| 518 | or |
| 519 | .Cm HostbasedAuthentication . |
| 520 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 521 | .Pa /etc/hosts.equiv |
| 522 | and |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 523 | .Pa /etc/shosts.equiv |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 524 | are still used. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 525 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 526 | .Dq yes . |
Damien Miller | 3226509 | 1999-11-12 11:33:04 +1100 | [diff] [blame] | 527 | .It Cm IgnoreUserKnownHosts |
| 528 | Specifies whether |
| 529 | .Nm |
| 530 | should ignore the user's |
| 531 | .Pa $HOME/.ssh/known_hosts |
| 532 | during |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 533 | .Cm RhostsRSAAuthentication |
| 534 | or |
| 535 | .Cm HostbasedAuthentication . |
Damien Miller | 3226509 | 1999-11-12 11:33:04 +1100 | [diff] [blame] | 536 | The default is |
| 537 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 538 | .It Cm KeepAlive |
Damien Miller | 9749c0c | 2002-02-05 12:23:58 +1100 | [diff] [blame] | 539 | Specifies whether the system should send TCP keepalive messages to the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 540 | other side. |
| 541 | If they are sent, death of the connection or crash of one |
| 542 | of the machines will be properly noticed. |
| 543 | However, this means that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 544 | connections will die if the route is down temporarily, and some people |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 545 | find it annoying. |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 546 | On the other hand, if keepalives are not sent, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 547 | sessions may hang indefinitely on the server, leaving |
| 548 | .Dq ghost |
| 549 | users and consuming server resources. |
| 550 | .Pp |
| 551 | The default is |
| 552 | .Dq yes |
| 553 | (to send keepalives), and the server will notice |
Damien Miller | 9749c0c | 2002-02-05 12:23:58 +1100 | [diff] [blame] | 554 | if the network goes down or the client host crashes. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 555 | This avoids infinitely hanging sessions. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 556 | .Pp |
| 557 | To disable keepalives, the value should be set to |
Damien Miller | 9749c0c | 2002-02-05 12:23:58 +1100 | [diff] [blame] | 558 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 559 | .It Cm KerberosAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 560 | Specifies whether Kerberos authentication is allowed. |
| 561 | This can be in the form of a Kerberos ticket, or if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 562 | .Cm PasswordAuthentication |
| 563 | is yes, the password provided by the user will be validated through |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 564 | the Kerberos KDC. |
| 565 | To use this option, the server needs a |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 566 | Kerberos servtab which allows the verification of the KDC's identity. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 567 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 568 | .Dq yes . |
| 569 | .It Cm KerberosOrLocalPasswd |
| 570 | If set then if password authentication through Kerberos fails then |
| 571 | the password will be validated via any additional local mechanism |
| 572 | such as |
Damien Miller | 62cee00 | 2000-09-23 17:15:56 +1100 | [diff] [blame] | 573 | .Pa /etc/passwd . |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 574 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 575 | .Dq yes . |
| 576 | .It Cm KerberosTgtPassing |
| 577 | Specifies whether a Kerberos TGT may be forwarded to the server. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 578 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 579 | .Dq no , |
| 580 | as this only works when the Kerberos KDC is actually an AFS kaserver. |
| 581 | .It Cm KerberosTicketCleanup |
| 582 | Specifies whether to automatically destroy the user's ticket cache |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 583 | file on logout. |
| 584 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 585 | .Dq yes . |
| 586 | .It Cm KeyRegenerationInterval |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 587 | In protocol version 1, the ephemeral server key is automatically regenerated |
| 588 | after this many seconds (if it has been used). |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 589 | The purpose of regeneration is to prevent |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 590 | decrypting captured sessions by later breaking into the machine and |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 591 | stealing the keys. |
| 592 | The key is never stored anywhere. |
| 593 | If the value is 0, the key is never regenerated. |
| 594 | The default is 3600 (seconds). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 595 | .It Cm ListenAddress |
Ben Lindstrom | 49e57a8 | 2001-04-08 18:02:43 +0000 | [diff] [blame] | 596 | Specifies the local addresses |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 597 | .Nm |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 598 | should listen on. |
Ben Lindstrom | 49e57a8 | 2001-04-08 18:02:43 +0000 | [diff] [blame] | 599 | The following forms may be used: |
| 600 | .Pp |
| 601 | .Bl -item -offset indent -compact |
| 602 | .It |
| 603 | .Cm ListenAddress |
Ben Lindstrom | 1a598a4 | 2001-04-10 02:48:50 +0000 | [diff] [blame] | 604 | .Sm off |
| 605 | .Ar host No | Ar IPv4_addr No | Ar IPv6_addr |
| 606 | .Sm on |
Ben Lindstrom | 49e57a8 | 2001-04-08 18:02:43 +0000 | [diff] [blame] | 607 | .It |
| 608 | .Cm ListenAddress |
Ben Lindstrom | 1a598a4 | 2001-04-10 02:48:50 +0000 | [diff] [blame] | 609 | .Sm off |
| 610 | .Ar host No | Ar IPv4_addr No : Ar port |
| 611 | .Sm on |
Ben Lindstrom | 49e57a8 | 2001-04-08 18:02:43 +0000 | [diff] [blame] | 612 | .It |
| 613 | .Cm ListenAddress |
Ben Lindstrom | 1a598a4 | 2001-04-10 02:48:50 +0000 | [diff] [blame] | 614 | .Sm off |
| 615 | .Oo |
| 616 | .Ar host No | Ar IPv6_addr Oc : Ar port |
| 617 | .Sm on |
Ben Lindstrom | 49e57a8 | 2001-04-08 18:02:43 +0000 | [diff] [blame] | 618 | .El |
| 619 | .Pp |
| 620 | If |
Ben Lindstrom | 1a598a4 | 2001-04-10 02:48:50 +0000 | [diff] [blame] | 621 | .Ar port |
Ben Lindstrom | 49e57a8 | 2001-04-08 18:02:43 +0000 | [diff] [blame] | 622 | is not specified, |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 623 | .Nm |
Ben Lindstrom | 49e57a8 | 2001-04-08 18:02:43 +0000 | [diff] [blame] | 624 | will listen on the address and all prior |
| 625 | .Cm Port |
| 626 | options specified. The default is to listen on all local |
| 627 | addresses. Multiple |
| 628 | .Cm ListenAddress |
| 629 | options are permitted. Additionally, any |
| 630 | .Cm Port |
| 631 | options must precede this option for non port qualified addresses. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 632 | .It Cm LoginGraceTime |
| 633 | The server disconnects after this time if the user has not |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 634 | successfully logged in. |
| 635 | If the value is 0, there is no time limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 636 | The default is 600 (seconds). |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 637 | .It Cm LogLevel |
| 638 | Gives the verbosity level that is used when logging messages from |
| 639 | .Nm sshd . |
| 640 | The possible values are: |
Damien Miller | dc9e067 | 2002-01-22 23:17:51 +1100 | [diff] [blame] | 641 | QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3. |
| 642 | The default is INFO. DEBUG and DEBUG1 are equivalent. DEBUG2 |
| 643 | and DEBUG3 each specify higher levels of debugging output. |
| 644 | Logging with a DEBUG level violates the privacy of users |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 645 | and is not recommended. |
Ben Lindstrom | 06b33aa | 2001-02-15 03:01:59 +0000 | [diff] [blame] | 646 | .It Cm MACs |
| 647 | Specifies the available MAC (message authentication code) algorithms. |
| 648 | The MAC algorithm is used in protocol version 2 |
| 649 | for data integrity protection. |
| 650 | Multiple algorithms must be comma-separated. |
| 651 | The default is |
Ben Lindstrom | bd0e2de | 2001-06-05 19:52:52 +0000 | [diff] [blame] | 652 | .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 . |
Damien Miller | 3702396 | 2000-07-11 17:31:38 +1000 | [diff] [blame] | 653 | .It Cm MaxStartups |
| 654 | Specifies the maximum number of concurrent unauthenticated connections to the |
| 655 | .Nm |
| 656 | daemon. |
| 657 | Additional connections will be dropped until authentication succeeds or the |
| 658 | .Cm LoginGraceTime |
| 659 | expires for a connection. |
| 660 | The default is 10. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 661 | .Pp |
| 662 | Alternatively, random early drop can be enabled by specifying |
| 663 | the three colon separated values |
| 664 | .Dq start:rate:full |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 665 | (e.g., "10:30:60"). |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 666 | .Nm |
Ben Lindstrom | a733350 | 2001-01-29 08:44:03 +0000 | [diff] [blame] | 667 | will refuse connection attempts with a probability of |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 668 | .Dq rate/100 |
| 669 | (30%) |
| 670 | if there are currently |
| 671 | .Dq start |
| 672 | (10) |
| 673 | unauthenticated connections. |
Ben Lindstrom | a733350 | 2001-01-29 08:44:03 +0000 | [diff] [blame] | 674 | The probability increases linearly and all connection attempts |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 675 | are refused if the number of unauthenticated connections reaches |
| 676 | .Dq full |
| 677 | (60). |
Damien Miller | f815442 | 2001-04-25 22:44:14 +1000 | [diff] [blame] | 678 | .It Cm PAMAuthenticationViaKbdInt |
| 679 | Specifies whether PAM challenge response authentication is allowed. This |
| 680 | allows the use of most PAM challenge response authentication modules, but |
| 681 | it will allow password authentication regardless of whether |
| 682 | .Cm PasswordAuthentication |
| 683 | is disabled. |
| 684 | The default is |
| 685 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 686 | .It Cm PasswordAuthentication |
| 687 | Specifies whether password authentication is allowed. |
| 688 | The default is |
| 689 | .Dq yes . |
| 690 | .It Cm PermitEmptyPasswords |
| 691 | When password authentication is allowed, it specifies whether the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 692 | server allows login to accounts with empty password strings. |
| 693 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 694 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 695 | .It Cm PermitRootLogin |
Ben Lindstrom | 323c98f | 2001-03-05 07:40:40 +0000 | [diff] [blame] | 696 | Specifies whether root can login using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 697 | .Xr ssh 1 . |
| 698 | The argument must be |
| 699 | .Dq yes , |
Ben Lindstrom | d8a9021 | 2001-02-15 03:08:27 +0000 | [diff] [blame] | 700 | .Dq without-password , |
| 701 | .Dq forced-commands-only |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 702 | or |
| 703 | .Dq no . |
| 704 | The default is |
| 705 | .Dq yes . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 706 | .Pp |
Ben Lindstrom | d8a9021 | 2001-02-15 03:08:27 +0000 | [diff] [blame] | 707 | If this option is set to |
| 708 | .Dq without-password |
| 709 | password authentication is disabled for root. |
| 710 | .Pp |
| 711 | If this option is set to |
| 712 | .Dq forced-commands-only |
| 713 | root login with public key authentication will be allowed, |
| 714 | but only if the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 715 | .Ar command |
Ben Lindstrom | d8a9021 | 2001-02-15 03:08:27 +0000 | [diff] [blame] | 716 | option has been specified |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 717 | (which may be useful for taking remote backups even if root login is |
Ben Lindstrom | d8a9021 | 2001-02-15 03:08:27 +0000 | [diff] [blame] | 718 | normally not allowed). All other authentication methods are disabled |
| 719 | for root. |
Ben Lindstrom | 323c98f | 2001-03-05 07:40:40 +0000 | [diff] [blame] | 720 | .Pp |
| 721 | If this option is set to |
| 722 | .Dq no |
| 723 | root is not allowed to login. |
Damien Miller | 6f83b8e | 2000-05-02 09:23:45 +1000 | [diff] [blame] | 724 | .It Cm PidFile |
| 725 | Specifies the file that contains the process identifier of the |
| 726 | .Nm |
| 727 | daemon. |
| 728 | The default is |
| 729 | .Pa /var/run/sshd.pid . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 730 | .It Cm Port |
| 731 | Specifies the port number that |
| 732 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 733 | listens on. |
| 734 | The default is 22. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 735 | Multiple options of this type are permitted. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 736 | See also |
| 737 | .Cm ListenAddress . |
Ben Lindstrom | 7bfff36 | 2001-03-26 05:45:53 +0000 | [diff] [blame] | 738 | .It Cm PrintLastLog |
| 739 | Specifies whether |
| 740 | .Nm |
| 741 | should print the date and time when the user last logged in. |
| 742 | The default is |
| 743 | .Dq yes . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 744 | .It Cm PrintMotd |
| 745 | Specifies whether |
| 746 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 747 | should print |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 748 | .Pa /etc/motd |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 749 | when a user logs in interactively. |
| 750 | (On some systems it is also printed by the shell, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 751 | .Pa /etc/profile , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 752 | or equivalent.) |
| 753 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 754 | .Dq yes . |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 755 | .It Cm Protocol |
| 756 | Specifies the protocol versions |
| 757 | .Nm |
| 758 | should support. |
| 759 | The possible values are |
| 760 | .Dq 1 |
| 761 | and |
| 762 | .Dq 2 . |
| 763 | Multiple versions must be comma-separated. |
| 764 | The default is |
Ben Lindstrom | bdc2beb | 2001-04-16 02:11:52 +0000 | [diff] [blame] | 765 | .Dq 2,1 . |
Ben Lindstrom | ff8b494 | 2001-03-06 01:00:03 +0000 | [diff] [blame] | 766 | .It Cm PubkeyAuthentication |
| 767 | Specifies whether public key authentication is allowed. |
| 768 | The default is |
| 769 | .Dq yes . |
| 770 | Note that this option applies to protocol version 2 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 771 | .It Cm RhostsAuthentication |
| 772 | Specifies whether authentication using rhosts or /etc/hosts.equiv |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 773 | files is sufficient. |
| 774 | Normally, this method should not be permitted because it is insecure. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 775 | .Cm RhostsRSAAuthentication |
| 776 | should be used |
| 777 | instead, because it performs RSA-based host authentication in addition |
| 778 | to normal rhosts or /etc/hosts.equiv authentication. |
| 779 | The default is |
| 780 | .Dq no . |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 781 | This option applies to protocol version 1 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 782 | .It Cm RhostsRSAAuthentication |
| 783 | Specifies whether rhosts or /etc/hosts.equiv authentication together |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 784 | with successful RSA host authentication is allowed. |
| 785 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 786 | .Dq no . |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 787 | This option applies to protocol version 1 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 788 | .It Cm RSAAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 789 | Specifies whether pure RSA authentication is allowed. |
| 790 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 791 | .Dq yes . |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 792 | This option applies to protocol version 1 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 793 | .It Cm ServerKeyBits |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 794 | Defines the number of bits in the ephemeral protocol version 1 server key. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 795 | The minimum value is 512, and the default is 768. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 796 | .It Cm StrictModes |
| 797 | Specifies whether |
| 798 | .Nm |
| 799 | should check file modes and ownership of the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 800 | user's files and home directory before accepting login. |
| 801 | This is normally desirable because novices sometimes accidentally leave their |
| 802 | directory or files world-writable. |
| 803 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 804 | .Dq yes . |
Damien Miller | f6d9e22 | 2000-06-18 14:50:44 +1000 | [diff] [blame] | 805 | .It Cm Subsystem |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 806 | Configures an external subsystem (e.g., file transfer daemon). |
| 807 | Arguments should be a subsystem name and a command to execute upon subsystem |
| 808 | request. |
Damien Miller | 7b28dc5 | 2000-09-05 13:34:53 +1100 | [diff] [blame] | 809 | The command |
| 810 | .Xr sftp-server 8 |
| 811 | implements the |
| 812 | .Dq sftp |
| 813 | file transfer subsystem. |
Damien Miller | f6d9e22 | 2000-06-18 14:50:44 +1000 | [diff] [blame] | 814 | By default no subsystems are defined. |
| 815 | Note that this option applies to protocol version 2 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 816 | .It Cm SyslogFacility |
| 817 | Gives the facility code that is used when logging messages from |
| 818 | .Nm sshd . |
| 819 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 820 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
| 821 | The default is AUTH. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 822 | .It Cm UseLogin |
| 823 | Specifies whether |
| 824 | .Xr login 1 |
Damien Miller | d3a1857 | 2000-06-07 19:55:44 +1000 | [diff] [blame] | 825 | is used for interactive login sessions. |
Ben Lindstrom | 699776e | 2001-06-21 03:14:49 +0000 | [diff] [blame] | 826 | The default is |
| 827 | .Dq no . |
Damien Miller | d3a1857 | 2000-06-07 19:55:44 +1000 | [diff] [blame] | 828 | Note that |
| 829 | .Xr login 1 |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 830 | is never used for remote command execution. |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 831 | Note also, that if this is enabled, |
| 832 | .Cm X11Forwarding |
Ben Lindstrom | 699776e | 2001-06-21 03:14:49 +0000 | [diff] [blame] | 833 | will be disabled because |
| 834 | .Xr login 1 |
| 835 | does not know how to handle |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 836 | .Xr xauth 1 |
Ben Lindstrom | 699776e | 2001-06-21 03:14:49 +0000 | [diff] [blame] | 837 | cookies. |
Damien Miller | c5d8635 | 2002-02-05 12:13:41 +1100 | [diff] [blame] | 838 | .It Cm VerifyReverseMapping |
| 839 | Specifies whether |
| 840 | .Nm |
| 841 | should try to verify the remote host name and check that |
| 842 | the resolved host name for the remote IP address maps back to the |
| 843 | very same IP address. |
| 844 | The default is |
| 845 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 846 | .It Cm X11DisplayOffset |
| 847 | Specifies the first display number available for |
| 848 | .Nm sshd Ns 's |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 849 | X11 forwarding. |
| 850 | This prevents |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 851 | .Nm |
| 852 | from interfering with real X11 servers. |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 853 | The default is 10. |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 854 | .It Cm X11Forwarding |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 855 | Specifies whether X11 forwarding is permitted. |
| 856 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 857 | .Dq no . |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 858 | Note that disabling X11 forwarding does not improve security in any |
| 859 | way, as users can always install their own forwarders. |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 860 | X11 forwarding is automatically disabled if |
| 861 | .Cm UseLogin |
| 862 | is enabled. |
Damien Miller | 95c249f | 2002-02-05 12:11:34 +1100 | [diff] [blame] | 863 | .It Cm X11UseLocalhost |
| 864 | Specifies whether |
| 865 | .Nm |
| 866 | should bind the X11 forwarding server to the loopback address or to |
| 867 | the wildcard address. By default, |
| 868 | .Nm |
| 869 | binds the forwarding server to the loopback address and sets the |
| 870 | hostname part of the |
| 871 | .Ev DISPLAY |
| 872 | environment variable to |
| 873 | .Dq localhost . |
| 874 | This prevents remote hosts from connecting to the fake display. |
| 875 | However, some older X11 clients may not function with this |
| 876 | configuration. |
| 877 | .Cm X11UseLocalhost |
| 878 | may be set to |
| 879 | .Dq no |
| 880 | to specify that the forwarding server should be bound to the wildcard |
| 881 | address. |
| 882 | The argument must be |
| 883 | .Dq yes |
| 884 | or |
| 885 | .Dq no . |
| 886 | The default is |
| 887 | .Dq yes . |
Damien Miller | d3a1857 | 2000-06-07 19:55:44 +1000 | [diff] [blame] | 888 | .It Cm XAuthLocation |
| 889 | Specifies the location of the |
| 890 | .Xr xauth 1 |
| 891 | program. |
| 892 | The default is |
| 893 | .Pa /usr/X11R6/bin/xauth . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 894 | .El |
Ben Lindstrom | 1bda4c8 | 2001-06-05 19:59:08 +0000 | [diff] [blame] | 895 | .Ss Time Formats |
| 896 | .Pp |
| 897 | .Nm |
| 898 | command-line arguments and configuration file options that specify time |
| 899 | may be expressed using a sequence of the form: |
| 900 | .Sm off |
| 901 | .Ar time Oo Ar qualifier Oc , |
| 902 | .Sm on |
| 903 | where |
| 904 | .Ar time |
| 905 | is a positive integer value and |
| 906 | .Ar qualifier |
| 907 | is one of the following: |
| 908 | .Pp |
| 909 | .Bl -tag -width Ds -compact -offset indent |
| 910 | .It Cm <none> |
| 911 | seconds |
| 912 | .It Cm s | Cm S |
| 913 | seconds |
| 914 | .It Cm m | Cm M |
| 915 | minutes |
| 916 | .It Cm h | Cm H |
| 917 | hours |
| 918 | .It Cm d | Cm D |
| 919 | days |
| 920 | .It Cm w | Cm W |
| 921 | weeks |
| 922 | .El |
| 923 | .Pp |
| 924 | Each member of the sequence is added together to calculate |
| 925 | the total time value. |
| 926 | .Pp |
| 927 | Time format examples: |
| 928 | .Pp |
| 929 | .Bl -tag -width Ds -compact -offset indent |
| 930 | .It 600 |
| 931 | 600 seconds (10 minutes) |
| 932 | .It 10m |
| 933 | 10 minutes |
| 934 | .It 1h30m |
| 935 | 1 hour 30 minutes (90 minutes) |
| 936 | .El |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 937 | .Sh LOGIN PROCESS |
| 938 | When a user successfully logs in, |
| 939 | .Nm |
| 940 | does the following: |
| 941 | .Bl -enum -offset indent |
| 942 | .It |
| 943 | If the login is on a tty, and no command has been specified, |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 944 | prints last login time and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 945 | .Pa /etc/motd |
| 946 | (unless prevented in the configuration file or by |
| 947 | .Pa $HOME/.hushlogin ; |
| 948 | see the |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 949 | .Sx FILES |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 950 | section). |
| 951 | .It |
| 952 | If the login is on a tty, records login time. |
| 953 | .It |
| 954 | Checks |
| 955 | .Pa /etc/nologin ; |
| 956 | if it exists, prints contents and quits |
| 957 | (unless root). |
| 958 | .It |
| 959 | Changes to run with normal user privileges. |
| 960 | .It |
| 961 | Sets up basic environment. |
| 962 | .It |
| 963 | Reads |
| 964 | .Pa $HOME/.ssh/environment |
| 965 | if it exists. |
| 966 | .It |
| 967 | Changes to user's home directory. |
| 968 | .It |
| 969 | If |
| 970 | .Pa $HOME/.ssh/rc |
| 971 | exists, runs it; else if |
Damien Miller | afcc225 | 2002-02-10 18:32:55 +1100 | [diff] [blame] | 972 | .Pa /etc/ssh/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 973 | exists, runs |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 974 | it; otherwise runs xauth. |
| 975 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 976 | .Dq rc |
| 977 | files are given the X11 |
| 978 | authentication protocol and cookie in standard input. |
| 979 | .It |
| 980 | Runs user's shell or command. |
| 981 | .El |
| 982 | .Sh AUTHORIZED_KEYS FILE FORMAT |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 983 | .Pa $HOME/.ssh/authorized_keys |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 984 | is the default file that lists the public keys that are |
| 985 | permitted for RSA authentication in protocol version 1 |
| 986 | and for public key authentication (PubkeyAuthentication) |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 987 | in protocol version 2. |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 988 | .Cm AuthorizedKeysFile |
Ben Lindstrom | bfb3a0e | 2001-06-05 20:25:05 +0000 | [diff] [blame] | 989 | may be used to specify an alternative file. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 990 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 991 | Each line of the file contains one |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 992 | key (empty lines and lines starting with a |
| 993 | .Ql # |
| 994 | are ignored as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 995 | comments). |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 996 | Each RSA public key consists of the following fields, separated by |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 997 | spaces: options, bits, exponent, modulus, comment. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 998 | Each protocol version 2 public key consists of: |
| 999 | options, keytype, base64 encoded key, comment. |
| 1000 | The options fields |
| 1001 | are optional; its presence is determined by whether the line starts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1002 | with a number or not (the option field never starts with a number). |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 1003 | The bits, exponent, modulus and comment fields give the RSA key for |
| 1004 | protocol version 1; the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1005 | comment field is not used for anything (but may be convenient for the |
| 1006 | user to identify the key). |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 1007 | For protocol version 2 the keytype is |
| 1008 | .Dq ssh-dss |
| 1009 | or |
| 1010 | .Dq ssh-rsa . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1011 | .Pp |
| 1012 | Note that lines in this file are usually several hundred bytes long |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1013 | (because of the size of the RSA key modulus). |
| 1014 | You don't want to type them in; instead, copy the |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 1015 | .Pa identity.pub , |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 1016 | .Pa id_dsa.pub |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 1017 | or the |
| 1018 | .Pa id_rsa.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1019 | file and edit it. |
| 1020 | .Pp |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 1021 | The options (if present) consist of comma-separated option |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1022 | specifications. |
| 1023 | No spaces are permitted, except within double quotes. |
Ben Lindstrom | 1c0fd09 | 2001-09-12 16:36:17 +0000 | [diff] [blame] | 1024 | The following option specifications are supported (note |
| 1025 | that option keywords are case-insensitive): |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1026 | .Bl -tag -width Ds |
| 1027 | .It Cm from="pattern-list" |
| 1028 | Specifies that in addition to RSA authentication, the canonical name |
| 1029 | of the remote host must be present in the comma-separated list of |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1030 | patterns |
| 1031 | .Pf ( Ql * |
| 1032 | and |
| 1033 | .Ql ? |
| 1034 | serve as wildcards). |
| 1035 | The list may also contain |
| 1036 | patterns negated by prefixing them with |
| 1037 | .Ql ! ; |
| 1038 | if the canonical host name matches a negated pattern, the key is not accepted. |
| 1039 | The purpose |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1040 | of this option is to optionally increase security: RSA authentication |
| 1041 | by itself does not trust the network or name servers or anything (but |
| 1042 | the key); however, if somebody somehow steals the key, the key |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1043 | permits an intruder to log in from anywhere in the world. |
| 1044 | This additional option makes using a stolen key more difficult (name |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1045 | servers and/or routers would have to be compromised in addition to |
| 1046 | just the key). |
| 1047 | .It Cm command="command" |
| 1048 | Specifies that the command is executed whenever this key is used for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1049 | authentication. |
| 1050 | The command supplied by the user (if any) is ignored. |
Ben Lindstrom | 23124ea | 2001-09-14 23:14:25 +0000 | [diff] [blame] | 1051 | The command is run on a pty if the client requests a pty; |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1052 | otherwise it is run without a tty. |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 1053 | If a 8-bit clean channel is required, |
| 1054 | one must not request a pty or should specify |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 1055 | .Cm no-pty . |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1056 | A quote may be included in the command by quoting it with a backslash. |
| 1057 | This option might be useful |
| 1058 | to restrict certain RSA keys to perform just a specific operation. |
| 1059 | An example might be a key that permits remote backups but nothing else. |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 1060 | Note that the client may specify TCP/IP and/or X11 |
| 1061 | forwarding unless they are explicitly prohibited. |
Ben Lindstrom | 20daef7 | 2001-09-20 00:54:01 +0000 | [diff] [blame] | 1062 | Note that this option applies to shell, command or subsystem execution. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1063 | .It Cm environment="NAME=value" |
| 1064 | Specifies that the string is to be added to the environment when |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1065 | logging in using this key. |
| 1066 | Environment variables set this way |
| 1067 | override other default environment values. |
| 1068 | Multiple options of this type are permitted. |
Ben Lindstrom | 38b951c | 2001-12-06 17:47:47 +0000 | [diff] [blame] | 1069 | This option is automatically disabled if |
| 1070 | .Cm UseLogin |
| 1071 | is enabled. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1072 | .It Cm no-port-forwarding |
| 1073 | Forbids TCP/IP forwarding when this key is used for authentication. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1074 | Any port forward requests by the client will return an error. |
| 1075 | This might be used, e.g., in connection with the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1076 | .Cm command |
| 1077 | option. |
| 1078 | .It Cm no-X11-forwarding |
| 1079 | Forbids X11 forwarding when this key is used for authentication. |
| 1080 | Any X11 forward requests by the client will return an error. |
| 1081 | .It Cm no-agent-forwarding |
| 1082 | Forbids authentication agent forwarding when this key is used for |
| 1083 | authentication. |
| 1084 | .It Cm no-pty |
| 1085 | Prevents tty allocation (a request to allocate a pty will fail). |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 1086 | .It Cm permitopen="host:port" |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 1087 | Limit local |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 1088 | .Li ``ssh -L'' |
Ben Lindstrom | 4b3564e | 2001-04-10 02:41:56 +0000 | [diff] [blame] | 1089 | port forwarding such that it may only connect to the specified host and |
Ben Lindstrom | d71ba57 | 2001-09-12 18:03:31 +0000 | [diff] [blame] | 1090 | port. |
| 1091 | IPv6 addresses can be specified with an alternative syntax: |
| 1092 | .Ar host/port . |
| 1093 | Multiple |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 1094 | .Cm permitopen |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 1095 | options may be applied separated by commas. No pattern matching is |
| 1096 | performed on the specified hostnames, they must be literal domains or |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 1097 | addresses. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1098 | .El |
| 1099 | .Ss Examples |
| 1100 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar |
| 1101 | .Pp |
| 1102 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula |
| 1103 | .Pp |
| 1104 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 1105 | .Pp |
| 1106 | permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33 23.\|.\|.\|2323 |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1107 | .Sh SSH_KNOWN_HOSTS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1108 | The |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 1109 | .Pa /etc/ssh/ssh_known_hosts , |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1110 | and |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 1111 | .Pa $HOME/.ssh/known_hosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1112 | files contain host public keys for all known hosts. |
| 1113 | The global file should |
| 1114 | be prepared by the administrator (optional), and the per-user file is |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 1115 | maintained automatically: whenever the user connects from an unknown host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1116 | its key is added to the per-user file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1117 | .Pp |
| 1118 | Each line in these files contains the following fields: hostnames, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1119 | bits, exponent, modulus, comment. |
| 1120 | The fields are separated by spaces. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1121 | .Pp |
| 1122 | Hostnames is a comma-separated list of patterns ('*' and '?' act as |
| 1123 | wildcards); each pattern in turn is matched against the canonical host |
| 1124 | name (when authenticating a client) or against the user-supplied |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1125 | name (when authenticating a server). |
| 1126 | A pattern may also be preceded by |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1127 | .Ql ! |
| 1128 | to indicate negation: if the host name matches a negated |
| 1129 | pattern, it is not accepted (by that line) even if it matched another |
| 1130 | pattern on the line. |
| 1131 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1132 | Bits, exponent, and modulus are taken directly from the RSA host key; they |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1133 | can be obtained, e.g., from |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 1134 | .Pa /etc/ssh/ssh_host_key.pub . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1135 | The optional comment field continues to the end of the line, and is not used. |
| 1136 | .Pp |
| 1137 | Lines starting with |
| 1138 | .Ql # |
| 1139 | and empty lines are ignored as comments. |
| 1140 | .Pp |
| 1141 | When performing host authentication, authentication is accepted if any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1142 | matching line has the proper key. |
| 1143 | It is thus permissible (but not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1144 | recommended) to have several lines or different host keys for the same |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1145 | names. |
| 1146 | This will inevitably happen when short forms of host names |
| 1147 | from different domains are put in the file. |
| 1148 | It is possible |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1149 | that the files contain conflicting information; authentication is |
| 1150 | accepted if valid information can be found from either file. |
| 1151 | .Pp |
| 1152 | Note that the lines in these files are typically hundreds of characters |
| 1153 | long, and you definitely don't want to type in the host keys by hand. |
| 1154 | Rather, generate them by a script |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1155 | or by taking |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 1156 | .Pa /etc/ssh/ssh_host_key.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1157 | and adding the host names at the front. |
| 1158 | .Ss Examples |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 1159 | .Bd -literal |
| 1160 | closenet,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi |
| 1161 | cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....= |
| 1162 | .Ed |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1163 | .Sh FILES |
| 1164 | .Bl -tag -width Ds |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 1165 | .It Pa /etc/ssh/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1166 | Contains configuration data for |
| 1167 | .Nm sshd . |
| 1168 | This file should be writable by root only, but it is recommended |
| 1169 | (though not necessary) that it be world-readable. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 1170 | .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 1171 | These three files contain the private parts of the host keys. |
Ben Lindstrom | d7f5b51 | 2001-03-05 06:57:23 +0000 | [diff] [blame] | 1172 | These files should only be owned by root, readable only by root, and not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1173 | accessible to others. |
| 1174 | Note that |
| 1175 | .Nm |
| 1176 | does not start if this file is group/world-accessible. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 1177 | .It Pa /etc/ssh/ssh_host_key.pub, /etc/ssh/ssh_host_dsa_key.pub, /etc/ssh/ssh_host_rsa_key.pub |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 1178 | These three files contain the public parts of the host keys. |
Ben Lindstrom | d7f5b51 | 2001-03-05 06:57:23 +0000 | [diff] [blame] | 1179 | These files should be world-readable but writable only by |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1180 | root. |
Ben Lindstrom | d7f5b51 | 2001-03-05 06:57:23 +0000 | [diff] [blame] | 1181 | Their contents should match the respective private parts. |
| 1182 | These files are not |
| 1183 | really used for anything; they are provided for the convenience of |
| 1184 | the user so their contents can be copied to known hosts files. |
| 1185 | These files are created using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1186 | .Xr ssh-keygen 1 . |
Ben Lindstrom | ae1c51c | 2001-06-25 04:14:59 +0000 | [diff] [blame] | 1187 | .It Pa /etc/moduli |
Damien Miller | e39cacc | 2000-11-29 12:18:44 +1100 | [diff] [blame] | 1188 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1189 | .It Pa /var/run/sshd.pid |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1190 | Contains the process ID of the |
| 1191 | .Nm |
| 1192 | listening for connections (if there are several daemons running |
| 1193 | concurrently for different ports, this contains the pid of the one |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1194 | started last). |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 1195 | The content of this file is not sensitive; it can be world-readable. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1196 | .It Pa $HOME/.ssh/authorized_keys |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 1197 | Lists the public keys (RSA or DSA) that can be used to log into the user's account. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1198 | This file must be readable by root (which may on some machines imply |
| 1199 | it being world-readable if the user's home directory resides on an NFS |
| 1200 | volume). |
| 1201 | It is recommended that it not be accessible by others. |
| 1202 | The format of this file is described above. |
| 1203 | Users will place the contents of their |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 1204 | .Pa identity.pub , |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1205 | .Pa id_dsa.pub |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 1206 | and/or |
| 1207 | .Pa id_rsa.pub |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1208 | files into this file, as described in |
| 1209 | .Xr ssh-keygen 1 . |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 1210 | .It Pa "/etc/ssh/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 1211 | These files are consulted when using rhosts with RSA host |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 1212 | authentication or protocol version 2 hostbased authentication |
| 1213 | to check the public key of the host. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1214 | The key must be listed in one of these files to be accepted. |
Damien Miller | 33e511e | 1999-11-11 11:43:13 +1100 | [diff] [blame] | 1215 | The client uses the same files |
Ben Lindstrom | ebd888d | 2001-03-05 05:49:29 +0000 | [diff] [blame] | 1216 | to verify that it is connecting to the correct remote host. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1217 | These files should be writable only by root/the owner. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 1218 | .Pa /etc/ssh/ssh_known_hosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1219 | should be world-readable, and |
| 1220 | .Pa $HOME/.ssh/known_hosts |
| 1221 | can but need not be world-readable. |
| 1222 | .It Pa /etc/nologin |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1223 | If this file exists, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1224 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1225 | refuses to let anyone except root log in. |
| 1226 | The contents of the file |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1227 | are displayed to anyone trying to log in, and non-root connections are |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1228 | refused. |
| 1229 | The file should be world-readable. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1230 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
Ben Lindstrom | 6149a6c | 2001-10-03 17:15:32 +0000 | [diff] [blame] | 1231 | Access controls that should be enforced by tcp-wrappers are defined here. |
| 1232 | Further details are described in |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1233 | .Xr hosts_access 5 . |
| 1234 | .It Pa $HOME/.rhosts |
| 1235 | This file contains host-username pairs, separated by a space, one per |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1236 | line. |
| 1237 | The given user on the corresponding host is permitted to log in |
| 1238 | without password. |
| 1239 | The same file is used by rlogind and rshd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1240 | The file must |
| 1241 | be writable only by the user; it is recommended that it not be |
| 1242 | accessible by others. |
| 1243 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1244 | If is also possible to use netgroups in the file. |
| 1245 | Either host or user |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1246 | name may be of the form +@groupname to specify all hosts or all users |
| 1247 | in the group. |
| 1248 | .It Pa $HOME/.shosts |
| 1249 | For ssh, |
| 1250 | this file is exactly the same as for |
| 1251 | .Pa .rhosts . |
| 1252 | However, this file is |
| 1253 | not used by rlogin and rshd, so using this permits access using SSH only. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 1254 | .It Pa /etc/hosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1255 | This file is used during |
| 1256 | .Pa .rhosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1257 | authentication. |
| 1258 | In the simplest form, this file contains host names, one per line. |
| 1259 | Users on |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1260 | those hosts are permitted to log in without a password, provided they |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1261 | have the same user name on both machines. |
| 1262 | The host name may also be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1263 | followed by a user name; such users are permitted to log in as |
| 1264 | .Em any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1265 | user on this machine (except root). |
| 1266 | Additionally, the syntax |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1267 | .Dq +@group |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1268 | can be used to specify netgroups. |
| 1269 | Negated entries start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1270 | .Ql \&- . |
| 1271 | .Pp |
| 1272 | If the client host/user is successfully matched in this file, login is |
| 1273 | automatically permitted provided the client and server user names are the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1274 | same. |
| 1275 | Additionally, successful RSA host authentication is normally required. |
| 1276 | This file must be writable only by root; it is recommended |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1277 | that it be world-readable. |
| 1278 | .Pp |
| 1279 | .Sy "Warning: It is almost never a good idea to use user names in" |
| 1280 | .Pa hosts.equiv . |
| 1281 | Beware that it really means that the named user(s) can log in as |
| 1282 | .Em anybody , |
| 1283 | which includes bin, daemon, adm, and other accounts that own critical |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1284 | binaries and directories. |
| 1285 | Using a user name practically grants the user root access. |
| 1286 | The only valid use for user names that I can think |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1287 | of is in negative entries. |
| 1288 | .Pp |
| 1289 | Note that this warning also applies to rsh/rlogin. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1290 | .It Pa /etc/shosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1291 | This is processed exactly as |
| 1292 | .Pa /etc/hosts.equiv . |
| 1293 | However, this file may be useful in environments that want to run both |
| 1294 | rsh/rlogin and ssh. |
| 1295 | .It Pa $HOME/.ssh/environment |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1296 | This file is read into the environment at login (if it exists). |
| 1297 | It can only contain empty lines, comment lines (that start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1298 | .Ql # ) , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1299 | and assignment lines of the form name=value. |
| 1300 | The file should be writable |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1301 | only by the user; it need not be readable by anyone else. |
| 1302 | .It Pa $HOME/.ssh/rc |
| 1303 | If this file exists, it is run with /bin/sh after reading the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1304 | environment files but before starting the user's shell or command. |
| 1305 | If X11 spoofing is in use, this will receive the "proto cookie" pair in |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1306 | standard input (and |
| 1307 | .Ev DISPLAY |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1308 | in environment). |
| 1309 | This must call |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1310 | .Xr xauth 1 |
| 1311 | in that case. |
| 1312 | .Pp |
| 1313 | The primary purpose of this file is to run any initialization routines |
| 1314 | which may be needed before the user's home directory becomes |
| 1315 | accessible; AFS is a particular example of such an environment. |
| 1316 | .Pp |
| 1317 | This file will probably contain some initialization code followed by |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 1318 | something similar to: |
| 1319 | .Bd -literal |
| 1320 | if read proto cookie; then |
| 1321 | echo add $DISPLAY $proto $cookie | xauth -q - |
| 1322 | fi |
| 1323 | .Ed |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1324 | .Pp |
| 1325 | If this file does not exist, |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 1326 | .Pa /etc/ssh/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1327 | is run, and if that |
| 1328 | does not exist either, xauth is used to store the cookie. |
| 1329 | .Pp |
| 1330 | This file should be writable only by the user, and need not be |
| 1331 | readable by anyone else. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 1332 | .It Pa /etc/ssh/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1333 | Like |
| 1334 | .Pa $HOME/.ssh/rc . |
| 1335 | This can be used to specify |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1336 | machine-specific login-time initializations globally. |
| 1337 | This file should be writable only by root, and should be world-readable. |
Damien Miller | 3702396 | 2000-07-11 17:31:38 +1000 | [diff] [blame] | 1338 | .El |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 1339 | .Sh AUTHORS |
Ben Lindstrom | 8eec2c8 | 2001-01-29 08:39:16 +0000 | [diff] [blame] | 1340 | OpenSSH is a derivative of the original and free |
| 1341 | ssh 1.2.12 release by Tatu Ylonen. |
| 1342 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, |
| 1343 | Theo de Raadt and Dug Song |
| 1344 | removed many bugs, re-added newer features and |
| 1345 | created OpenSSH. |
| 1346 | Markus Friedl contributed the support for SSH |
| 1347 | protocol versions 1.5 and 2.0. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1348 | .Sh SEE ALSO |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1349 | .Xr scp 1 , |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 1350 | .Xr sftp 1 , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1351 | .Xr ssh 1 , |
| 1352 | .Xr ssh-add 1 , |
| 1353 | .Xr ssh-agent 1 , |
| 1354 | .Xr ssh-keygen 1 , |
Ben Lindstrom | c8e29ce | 2001-08-06 20:55:28 +0000 | [diff] [blame] | 1355 | .Xr login.conf 5 , |
| 1356 | .Xr moduli 5 , |
Ben Lindstrom | d2bf0d6 | 2001-06-25 04:10:54 +0000 | [diff] [blame] | 1357 | .Xr sftp-server 8 |
Ben Lindstrom | 160ec62 | 2001-04-22 17:17:46 +0000 | [diff] [blame] | 1358 | .Rs |
| 1359 | .%A T. Ylonen |
| 1360 | .%A T. Kivinen |
| 1361 | .%A M. Saarinen |
| 1362 | .%A T. Rinne |
| 1363 | .%A S. Lehtinen |
| 1364 | .%T "SSH Protocol Architecture" |
Ben Lindstrom | 020a869 | 2001-08-06 21:38:10 +0000 | [diff] [blame] | 1365 | .%N draft-ietf-secsh-architecture-09.txt |
| 1366 | .%D July 2001 |
Ben Lindstrom | 160ec62 | 2001-04-22 17:17:46 +0000 | [diff] [blame] | 1367 | .%O work in progress material |
| 1368 | .Re |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 1369 | .Rs |
| 1370 | .%A M. Friedl |
| 1371 | .%A N. Provos |
| 1372 | .%A W. A. Simpson |
| 1373 | .%T "Diffie-Hellman Group Exchange for the SSH Transport Layer Protocol" |
Ben Lindstrom | 3c798d4 | 2001-06-25 04:39:22 +0000 | [diff] [blame] | 1374 | .%N draft-ietf-secsh-dh-group-exchange-01.txt |
| 1375 | .%D April 2001 |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 1376 | .%O work in progress material |
| 1377 | .Re |