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 | 624e3f2 | 2002-06-23 00:32:57 +0000 | [diff] [blame^] | 37 | .\" $OpenBSD: sshd.8,v 1.185 2002/06/22 16:32:54 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 |
Ben Lindstrom | c57bbf1 | 2002-05-15 21:36:45 +0000 | [diff] [blame] | 119 | .Nm rshd , |
| 120 | .Nm rlogind , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 121 | and |
Ben Lindstrom | c57bbf1 | 2002-05-15 21:36:45 +0000 | [diff] [blame] | 122 | .Xr rexecd |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 123 | are disabled (thus completely disabling |
Ben Lindstrom | c57bbf1 | 2002-05-15 21:36:45 +0000 | [diff] [blame] | 124 | .Xr rlogin |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 125 | and |
Ben Lindstrom | c57bbf1 | 2002-05-15 21:36:45 +0000 | [diff] [blame] | 126 | .Xr rsh |
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 | ea03db9 | 2002-03-05 01:38:57 +0000 | [diff] [blame] | 296 | Configuration options that require DNS include using a |
| 297 | USER@HOST pattern in |
| 298 | .Cm AllowUsers |
| 299 | or |
| 300 | .Cm DenyUsers . |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 301 | .It Fl D |
| 302 | When this option is specified |
| 303 | .Nm |
| 304 | will not detach and does not become a daemon. |
| 305 | This allows easy monitoring of |
| 306 | .Nm sshd . |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 307 | .It Fl 4 |
| 308 | Forces |
| 309 | .Nm |
| 310 | to use IPv4 addresses only. |
| 311 | .It Fl 6 |
| 312 | Forces |
| 313 | .Nm |
| 314 | to use IPv6 addresses only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 315 | .El |
| 316 | .Sh CONFIGURATION FILE |
| 317 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 318 | reads configuration data from |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 319 | .Pa /etc/ssh/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 320 | (or the file specified with |
| 321 | .Fl f |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 322 | on the command line). |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 323 | The file format and configuration options are described in |
| 324 | .Xr sshd_config 5 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 325 | .Sh LOGIN PROCESS |
| 326 | When a user successfully logs in, |
| 327 | .Nm |
| 328 | does the following: |
| 329 | .Bl -enum -offset indent |
| 330 | .It |
| 331 | 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] | 332 | prints last login time and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 333 | .Pa /etc/motd |
| 334 | (unless prevented in the configuration file or by |
| 335 | .Pa $HOME/.hushlogin ; |
| 336 | see the |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 337 | .Sx FILES |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 338 | section). |
| 339 | .It |
| 340 | If the login is on a tty, records login time. |
| 341 | .It |
| 342 | Checks |
| 343 | .Pa /etc/nologin ; |
| 344 | if it exists, prints contents and quits |
| 345 | (unless root). |
| 346 | .It |
| 347 | Changes to run with normal user privileges. |
| 348 | .It |
| 349 | Sets up basic environment. |
| 350 | .It |
| 351 | Reads |
| 352 | .Pa $HOME/.ssh/environment |
| 353 | if it exists. |
| 354 | .It |
| 355 | Changes to user's home directory. |
| 356 | .It |
| 357 | If |
| 358 | .Pa $HOME/.ssh/rc |
| 359 | exists, runs it; else if |
Damien Miller | afcc225 | 2002-02-10 18:32:55 +1100 | [diff] [blame] | 360 | .Pa /etc/ssh/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 361 | exists, runs |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 362 | it; otherwise runs xauth. |
| 363 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 364 | .Dq rc |
| 365 | files are given the X11 |
| 366 | authentication protocol and cookie in standard input. |
| 367 | .It |
| 368 | Runs user's shell or command. |
| 369 | .El |
| 370 | .Sh AUTHORIZED_KEYS FILE FORMAT |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 371 | .Pa $HOME/.ssh/authorized_keys |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 372 | is the default file that lists the public keys that are |
| 373 | permitted for RSA authentication in protocol version 1 |
| 374 | and for public key authentication (PubkeyAuthentication) |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 375 | in protocol version 2. |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 376 | .Cm AuthorizedKeysFile |
Ben Lindstrom | bfb3a0e | 2001-06-05 20:25:05 +0000 | [diff] [blame] | 377 | may be used to specify an alternative file. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 378 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 379 | Each line of the file contains one |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 380 | key (empty lines and lines starting with a |
| 381 | .Ql # |
| 382 | are ignored as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 383 | comments). |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 384 | Each RSA public key consists of the following fields, separated by |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 385 | spaces: options, bits, exponent, modulus, comment. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 386 | Each protocol version 2 public key consists of: |
| 387 | options, keytype, base64 encoded key, comment. |
| 388 | The options fields |
| 389 | are optional; its presence is determined by whether the line starts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 390 | 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] | 391 | The bits, exponent, modulus and comment fields give the RSA key for |
| 392 | protocol version 1; the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 393 | comment field is not used for anything (but may be convenient for the |
| 394 | user to identify the key). |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 395 | For protocol version 2 the keytype is |
| 396 | .Dq ssh-dss |
| 397 | or |
| 398 | .Dq ssh-rsa . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 399 | .Pp |
| 400 | Note that lines in this file are usually several hundred bytes long |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 401 | (because of the size of the RSA key modulus). |
| 402 | You don't want to type them in; instead, copy the |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 403 | .Pa identity.pub , |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 404 | .Pa id_dsa.pub |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 405 | or the |
| 406 | .Pa id_rsa.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 407 | file and edit it. |
| 408 | .Pp |
Ben Lindstrom | 0d0be02 | 2002-04-02 20:39:29 +0000 | [diff] [blame] | 409 | .Nm |
| 410 | enforces a minimum RSA key modulus size for protocol 1 |
| 411 | and protocol 2 keys of 768 bits. |
| 412 | .Pp |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 413 | The options (if present) consist of comma-separated option |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 414 | specifications. |
| 415 | No spaces are permitted, except within double quotes. |
Ben Lindstrom | 1c0fd09 | 2001-09-12 16:36:17 +0000 | [diff] [blame] | 416 | The following option specifications are supported (note |
| 417 | that option keywords are case-insensitive): |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 418 | .Bl -tag -width Ds |
| 419 | .It Cm from="pattern-list" |
| 420 | Specifies that in addition to RSA authentication, the canonical name |
| 421 | 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] | 422 | patterns |
| 423 | .Pf ( Ql * |
| 424 | and |
| 425 | .Ql ? |
| 426 | serve as wildcards). |
| 427 | The list may also contain |
| 428 | patterns negated by prefixing them with |
| 429 | .Ql ! ; |
| 430 | if the canonical host name matches a negated pattern, the key is not accepted. |
| 431 | The purpose |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 432 | of this option is to optionally increase security: RSA authentication |
| 433 | by itself does not trust the network or name servers or anything (but |
| 434 | the key); however, if somebody somehow steals the key, the key |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 435 | permits an intruder to log in from anywhere in the world. |
| 436 | This additional option makes using a stolen key more difficult (name |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 437 | servers and/or routers would have to be compromised in addition to |
| 438 | just the key). |
| 439 | .It Cm command="command" |
| 440 | Specifies that the command is executed whenever this key is used for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 441 | authentication. |
| 442 | The command supplied by the user (if any) is ignored. |
Ben Lindstrom | 23124ea | 2001-09-14 23:14:25 +0000 | [diff] [blame] | 443 | 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] | 444 | otherwise it is run without a tty. |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 445 | If a 8-bit clean channel is required, |
| 446 | one must not request a pty or should specify |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 447 | .Cm no-pty . |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 448 | A quote may be included in the command by quoting it with a backslash. |
| 449 | This option might be useful |
| 450 | to restrict certain RSA keys to perform just a specific operation. |
| 451 | 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] | 452 | Note that the client may specify TCP/IP and/or X11 |
| 453 | forwarding unless they are explicitly prohibited. |
Ben Lindstrom | 20daef7 | 2001-09-20 00:54:01 +0000 | [diff] [blame] | 454 | Note that this option applies to shell, command or subsystem execution. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 455 | .It Cm environment="NAME=value" |
| 456 | Specifies that the string is to be added to the environment when |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 457 | logging in using this key. |
| 458 | Environment variables set this way |
| 459 | override other default environment values. |
| 460 | Multiple options of this type are permitted. |
Ben Lindstrom | 38b951c | 2001-12-06 17:47:47 +0000 | [diff] [blame] | 461 | This option is automatically disabled if |
| 462 | .Cm UseLogin |
| 463 | is enabled. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 464 | .It Cm no-port-forwarding |
| 465 | Forbids TCP/IP forwarding when this key is used for authentication. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 466 | Any port forward requests by the client will return an error. |
| 467 | This might be used, e.g., in connection with the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 468 | .Cm command |
| 469 | option. |
| 470 | .It Cm no-X11-forwarding |
| 471 | Forbids X11 forwarding when this key is used for authentication. |
| 472 | Any X11 forward requests by the client will return an error. |
| 473 | .It Cm no-agent-forwarding |
| 474 | Forbids authentication agent forwarding when this key is used for |
| 475 | authentication. |
| 476 | .It Cm no-pty |
| 477 | Prevents tty allocation (a request to allocate a pty will fail). |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 478 | .It Cm permitopen="host:port" |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 479 | Limit local |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 480 | .Li ``ssh -L'' |
Ben Lindstrom | 4b3564e | 2001-04-10 02:41:56 +0000 | [diff] [blame] | 481 | 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] | 482 | port. |
| 483 | IPv6 addresses can be specified with an alternative syntax: |
| 484 | .Ar host/port . |
| 485 | Multiple |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 486 | .Cm permitopen |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 487 | options may be applied separated by commas. No pattern matching is |
| 488 | performed on the specified hostnames, they must be literal domains or |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 489 | addresses. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 490 | .El |
| 491 | .Ss Examples |
| 492 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar |
| 493 | .Pp |
| 494 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula |
| 495 | .Pp |
| 496 | 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] | 497 | .Pp |
| 498 | 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] | 499 | .Sh SSH_KNOWN_HOSTS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 500 | The |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 501 | .Pa /etc/ssh/ssh_known_hosts , |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 502 | and |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 503 | .Pa $HOME/.ssh/known_hosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 504 | files contain host public keys for all known hosts. |
| 505 | The global file should |
| 506 | be prepared by the administrator (optional), and the per-user file is |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 507 | maintained automatically: whenever the user connects from an unknown host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 508 | its key is added to the per-user file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 509 | .Pp |
| 510 | Each line in these files contains the following fields: hostnames, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 511 | bits, exponent, modulus, comment. |
| 512 | The fields are separated by spaces. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 513 | .Pp |
| 514 | Hostnames is a comma-separated list of patterns ('*' and '?' act as |
| 515 | wildcards); each pattern in turn is matched against the canonical host |
| 516 | name (when authenticating a client) or against the user-supplied |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 517 | name (when authenticating a server). |
| 518 | A pattern may also be preceded by |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 519 | .Ql ! |
| 520 | to indicate negation: if the host name matches a negated |
| 521 | pattern, it is not accepted (by that line) even if it matched another |
| 522 | pattern on the line. |
| 523 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 524 | 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] | 525 | can be obtained, e.g., from |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 526 | .Pa /etc/ssh/ssh_host_key.pub . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 527 | The optional comment field continues to the end of the line, and is not used. |
| 528 | .Pp |
| 529 | Lines starting with |
| 530 | .Ql # |
| 531 | and empty lines are ignored as comments. |
| 532 | .Pp |
| 533 | When performing host authentication, authentication is accepted if any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 534 | matching line has the proper key. |
| 535 | It is thus permissible (but not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 536 | recommended) to have several lines or different host keys for the same |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 537 | names. |
| 538 | This will inevitably happen when short forms of host names |
| 539 | from different domains are put in the file. |
| 540 | It is possible |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 541 | that the files contain conflicting information; authentication is |
| 542 | accepted if valid information can be found from either file. |
| 543 | .Pp |
| 544 | Note that the lines in these files are typically hundreds of characters |
| 545 | long, and you definitely don't want to type in the host keys by hand. |
| 546 | Rather, generate them by a script |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 547 | or by taking |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 548 | .Pa /etc/ssh/ssh_host_key.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 549 | and adding the host names at the front. |
| 550 | .Ss Examples |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 551 | .Bd -literal |
| 552 | closenet,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi |
| 553 | cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....= |
| 554 | .Ed |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 555 | .Sh FILES |
| 556 | .Bl -tag -width Ds |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 557 | .It Pa /etc/ssh/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 558 | Contains configuration data for |
| 559 | .Nm sshd . |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 560 | The file format and configuration options are described in |
| 561 | .Xr sshd_config 5 . |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 562 | .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] | 563 | These three files contain the private parts of the host keys. |
Ben Lindstrom | d7f5b51 | 2001-03-05 06:57:23 +0000 | [diff] [blame] | 564 | 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] | 565 | accessible to others. |
| 566 | Note that |
| 567 | .Nm |
| 568 | does not start if this file is group/world-accessible. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 569 | .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] | 570 | These three files contain the public parts of the host keys. |
Ben Lindstrom | d7f5b51 | 2001-03-05 06:57:23 +0000 | [diff] [blame] | 571 | These files should be world-readable but writable only by |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 572 | root. |
Ben Lindstrom | d7f5b51 | 2001-03-05 06:57:23 +0000 | [diff] [blame] | 573 | Their contents should match the respective private parts. |
| 574 | These files are not |
| 575 | really used for anything; they are provided for the convenience of |
| 576 | the user so their contents can be copied to known hosts files. |
| 577 | These files are created using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 578 | .Xr ssh-keygen 1 . |
Ben Lindstrom | ae1c51c | 2001-06-25 04:14:59 +0000 | [diff] [blame] | 579 | .It Pa /etc/moduli |
Damien Miller | e39cacc | 2000-11-29 12:18:44 +1100 | [diff] [blame] | 580 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". |
Ben Lindstrom | 624e3f2 | 2002-06-23 00:32:57 +0000 | [diff] [blame^] | 581 | .It Pa /var/empty |
| 582 | .Xr chroot 2 |
| 583 | directory used by |
| 584 | .Nm |
| 585 | during privilege separation in the pre-authentication phase. |
| 586 | The directory should not contain any files and must be owned by root |
| 587 | and not group or world-writable. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 588 | .It Pa /var/run/sshd.pid |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 589 | Contains the process ID of the |
| 590 | .Nm |
| 591 | listening for connections (if there are several daemons running |
| 592 | concurrently for different ports, this contains the pid of the one |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 593 | started last). |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 594 | 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] | 595 | .It Pa $HOME/.ssh/authorized_keys |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 596 | Lists the public keys (RSA or DSA) that can be used to log into the user's account. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 597 | This file must be readable by root (which may on some machines imply |
| 598 | it being world-readable if the user's home directory resides on an NFS |
| 599 | volume). |
| 600 | It is recommended that it not be accessible by others. |
| 601 | The format of this file is described above. |
| 602 | Users will place the contents of their |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 603 | .Pa identity.pub , |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 604 | .Pa id_dsa.pub |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 605 | and/or |
| 606 | .Pa id_rsa.pub |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 607 | files into this file, as described in |
| 608 | .Xr ssh-keygen 1 . |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 609 | .It Pa "/etc/ssh/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 610 | These files are consulted when using rhosts with RSA host |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 611 | authentication or protocol version 2 hostbased authentication |
| 612 | to check the public key of the host. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 613 | 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] | 614 | The client uses the same files |
Ben Lindstrom | ebd888d | 2001-03-05 05:49:29 +0000 | [diff] [blame] | 615 | to verify that it is connecting to the correct remote host. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 616 | These files should be writable only by root/the owner. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 617 | .Pa /etc/ssh/ssh_known_hosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 618 | should be world-readable, and |
| 619 | .Pa $HOME/.ssh/known_hosts |
| 620 | can but need not be world-readable. |
| 621 | .It Pa /etc/nologin |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 622 | If this file exists, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 623 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 624 | refuses to let anyone except root log in. |
| 625 | The contents of the file |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 626 | 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] | 627 | refused. |
| 628 | The file should be world-readable. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 629 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
Ben Lindstrom | 6149a6c | 2001-10-03 17:15:32 +0000 | [diff] [blame] | 630 | Access controls that should be enforced by tcp-wrappers are defined here. |
| 631 | Further details are described in |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 632 | .Xr hosts_access 5 . |
| 633 | .It Pa $HOME/.rhosts |
| 634 | This file contains host-username pairs, separated by a space, one per |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 635 | line. |
| 636 | The given user on the corresponding host is permitted to log in |
| 637 | without password. |
| 638 | The same file is used by rlogind and rshd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 639 | The file must |
| 640 | be writable only by the user; it is recommended that it not be |
| 641 | accessible by others. |
| 642 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 643 | If is also possible to use netgroups in the file. |
| 644 | Either host or user |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 645 | name may be of the form +@groupname to specify all hosts or all users |
| 646 | in the group. |
| 647 | .It Pa $HOME/.shosts |
| 648 | For ssh, |
| 649 | this file is exactly the same as for |
| 650 | .Pa .rhosts . |
| 651 | However, this file is |
| 652 | 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] | 653 | .It Pa /etc/hosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 654 | This file is used during |
| 655 | .Pa .rhosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 656 | authentication. |
| 657 | In the simplest form, this file contains host names, one per line. |
| 658 | Users on |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 659 | those hosts are permitted to log in without a password, provided they |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 660 | have the same user name on both machines. |
| 661 | The host name may also be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 662 | followed by a user name; such users are permitted to log in as |
| 663 | .Em any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 664 | user on this machine (except root). |
| 665 | Additionally, the syntax |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 666 | .Dq +@group |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 667 | can be used to specify netgroups. |
| 668 | Negated entries start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 669 | .Ql \&- . |
| 670 | .Pp |
| 671 | If the client host/user is successfully matched in this file, login is |
| 672 | automatically permitted provided the client and server user names are the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 673 | same. |
| 674 | Additionally, successful RSA host authentication is normally required. |
| 675 | This file must be writable only by root; it is recommended |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 676 | that it be world-readable. |
| 677 | .Pp |
| 678 | .Sy "Warning: It is almost never a good idea to use user names in" |
| 679 | .Pa hosts.equiv . |
| 680 | Beware that it really means that the named user(s) can log in as |
| 681 | .Em anybody , |
| 682 | which includes bin, daemon, adm, and other accounts that own critical |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 683 | binaries and directories. |
| 684 | Using a user name practically grants the user root access. |
| 685 | The only valid use for user names that I can think |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 686 | of is in negative entries. |
| 687 | .Pp |
| 688 | Note that this warning also applies to rsh/rlogin. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 689 | .It Pa /etc/shosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 690 | This is processed exactly as |
| 691 | .Pa /etc/hosts.equiv . |
| 692 | However, this file may be useful in environments that want to run both |
| 693 | rsh/rlogin and ssh. |
| 694 | .It Pa $HOME/.ssh/environment |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 695 | This file is read into the environment at login (if it exists). |
| 696 | It can only contain empty lines, comment lines (that start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 697 | .Ql # ) , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 698 | and assignment lines of the form name=value. |
| 699 | The file should be writable |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 700 | only by the user; it need not be readable by anyone else. |
| 701 | .It Pa $HOME/.ssh/rc |
| 702 | If this file exists, it is run with /bin/sh after reading the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 703 | environment files but before starting the user's shell or command. |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 704 | It must not produce any output on stdout; stderr must be used |
| 705 | instead. |
| 706 | If X11 forwarding is in use, it will receive the "proto cookie" pair in |
| 707 | its standard input (and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 708 | .Ev DISPLAY |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 709 | in its environment). |
| 710 | The script must call |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 711 | .Xr xauth 1 |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 712 | because |
| 713 | .Nm |
| 714 | will not run xauth automatically to add X11 cookies. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 715 | .Pp |
| 716 | The primary purpose of this file is to run any initialization routines |
| 717 | which may be needed before the user's home directory becomes |
| 718 | accessible; AFS is a particular example of such an environment. |
| 719 | .Pp |
| 720 | This file will probably contain some initialization code followed by |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 721 | something similar to: |
| 722 | .Bd -literal |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 723 | if read proto cookie && [ -n "$DISPLAY" ]; then |
| 724 | if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then |
| 725 | # X11UseLocalhost=yes |
| 726 | xauth add unix:`echo $DISPLAY | |
| 727 | cut -c11-` $proto $cookie |
| 728 | else |
| 729 | # X11UseLocalhost=no |
| 730 | xauth add $DISPLAY $proto $cookie |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 731 | fi |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 732 | fi |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 733 | .Ed |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 734 | .Pp |
| 735 | If this file does not exist, |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 736 | .Pa /etc/ssh/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 737 | is run, and if that |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 738 | does not exist either, xauth is used to add the cookie. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 739 | .Pp |
| 740 | This file should be writable only by the user, and need not be |
| 741 | readable by anyone else. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 742 | .It Pa /etc/ssh/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 743 | Like |
| 744 | .Pa $HOME/.ssh/rc . |
| 745 | This can be used to specify |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 746 | machine-specific login-time initializations globally. |
| 747 | 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] | 748 | .El |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 749 | .Sh AUTHORS |
Ben Lindstrom | 8eec2c8 | 2001-01-29 08:39:16 +0000 | [diff] [blame] | 750 | OpenSSH is a derivative of the original and free |
| 751 | ssh 1.2.12 release by Tatu Ylonen. |
| 752 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, |
| 753 | Theo de Raadt and Dug Song |
| 754 | removed many bugs, re-added newer features and |
| 755 | created OpenSSH. |
| 756 | Markus Friedl contributed the support for SSH |
| 757 | protocol versions 1.5 and 2.0. |
Ben Lindstrom | 000dda5 | 2002-03-22 02:33:12 +0000 | [diff] [blame] | 758 | Niels Provos and Markus Friedl contributed support |
| 759 | for privilege separation. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 760 | .Sh SEE ALSO |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 761 | .Xr scp 1 , |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 762 | .Xr sftp 1 , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 763 | .Xr ssh 1 , |
| 764 | .Xr ssh-add 1 , |
| 765 | .Xr ssh-agent 1 , |
| 766 | .Xr ssh-keygen 1 , |
Ben Lindstrom | c8e29ce | 2001-08-06 20:55:28 +0000 | [diff] [blame] | 767 | .Xr login.conf 5 , |
| 768 | .Xr moduli 5 , |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 769 | .Xr sshd_config 5 , |
Ben Lindstrom | d2bf0d6 | 2001-06-25 04:10:54 +0000 | [diff] [blame] | 770 | .Xr sftp-server 8 |
Ben Lindstrom | 160ec62 | 2001-04-22 17:17:46 +0000 | [diff] [blame] | 771 | .Rs |
| 772 | .%A T. Ylonen |
| 773 | .%A T. Kivinen |
| 774 | .%A M. Saarinen |
| 775 | .%A T. Rinne |
| 776 | .%A S. Lehtinen |
| 777 | .%T "SSH Protocol Architecture" |
Ben Lindstrom | f181384 | 2002-03-27 17:18:31 +0000 | [diff] [blame] | 778 | .%N draft-ietf-secsh-architecture-12.txt |
| 779 | .%D January 2002 |
Ben Lindstrom | 160ec62 | 2001-04-22 17:17:46 +0000 | [diff] [blame] | 780 | .%O work in progress material |
| 781 | .Re |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 782 | .Rs |
| 783 | .%A M. Friedl |
| 784 | .%A N. Provos |
| 785 | .%A W. A. Simpson |
| 786 | .%T "Diffie-Hellman Group Exchange for the SSH Transport Layer Protocol" |
Ben Lindstrom | f181384 | 2002-03-27 17:18:31 +0000 | [diff] [blame] | 787 | .%N draft-ietf-secsh-dh-group-exchange-02.txt |
| 788 | .%D January 2002 |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 789 | .%O work in progress material |
| 790 | .Re |