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 | .\" |
Damien Miller | bc1936a | 2006-03-15 11:35:05 +1100 | [diff] [blame^] | 37 | .\" $OpenBSD: sshd.8,v 1.224 2006/02/15 16:55:33 jmc 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 |
Damien Miller | ffadc58 | 2003-02-24 11:52:26 +1100 | [diff] [blame] | 46 | .Bk -words |
Darren Tucker | 1f20394 | 2003-10-15 15:50:42 +1000 | [diff] [blame] | 47 | .Op Fl 46Ddeiqt |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 48 | .Op Fl b Ar bits |
| 49 | .Op Fl f Ar config_file |
| 50 | .Op Fl g Ar login_grace_time |
| 51 | .Op Fl h Ar host_key_file |
| 52 | .Op Fl k Ar key_gen_time |
Ben Lindstrom | ade03f6 | 2001-12-06 18:22:17 +0000 | [diff] [blame] | 53 | .Op Fl o Ar option |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 54 | .Op Fl p Ar port |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 55 | .Op Fl u Ar len |
Damien Miller | ffadc58 | 2003-02-24 11:52:26 +1100 | [diff] [blame] | 56 | .Ek |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 57 | .Sh DESCRIPTION |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 58 | .Nm |
Damien Miller | 99cc4a8 | 2006-01-31 21:45:53 +1100 | [diff] [blame] | 59 | (OpenSSH Daemon) is the daemon program for |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 60 | .Xr ssh 1 . |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 61 | Together these programs replace rlogin and rsh, and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 62 | provide secure encrypted communications between two untrusted hosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 63 | over an insecure network. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 64 | .Pp |
| 65 | .Nm |
Damien Miller | 99cc4a8 | 2006-01-31 21:45:53 +1100 | [diff] [blame] | 66 | 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 | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 74 | .Pp |
| 75 | .Nm |
Darren Tucker | 1f20394 | 2003-10-15 15:50:42 +1000 | [diff] [blame] | 76 | can be configured using command-line options or a configuration file |
| 77 | (by default |
Damien Miller | 99cc4a8 | 2006-01-31 21:45:53 +1100 | [diff] [blame] | 78 | .Xr sshd_config 5 ) ; |
| 79 | command-line options override values specified in the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 80 | configuration file. |
Damien Miller | 6162d12 | 1999-11-21 13:23:52 +1100 | [diff] [blame] | 81 | .Nm |
| 82 | rereads its configuration file when it receives a hangup signal, |
Ben Lindstrom | 49a098d | 2001-03-05 06:55:18 +0000 | [diff] [blame] | 83 | .Dv SIGHUP , |
Darren Tucker | 097e1e9 | 2004-05-02 22:15:08 +1000 | [diff] [blame] | 84 | by executing itself with the name and options it was started with, e.g., |
Ben Lindstrom | 49a098d | 2001-03-05 06:55:18 +0000 | [diff] [blame] | 85 | .Pa /usr/sbin/sshd . |
Damien Miller | 6162d12 | 1999-11-21 13:23:52 +1100 | [diff] [blame] | 86 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 87 | The options are as follows: |
| 88 | .Bl -tag -width Ds |
Darren Tucker | 1f20394 | 2003-10-15 15:50:42 +1000 | [diff] [blame] | 89 | .It Fl 4 |
| 90 | Forces |
| 91 | .Nm |
| 92 | to use IPv4 addresses only. |
| 93 | .It Fl 6 |
| 94 | Forces |
| 95 | .Nm |
| 96 | to use IPv6 addresses only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 97 | .It Fl b Ar bits |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 98 | Specifies the number of bits in the ephemeral protocol version 1 |
| 99 | server key (default 768). |
Darren Tucker | 1f20394 | 2003-10-15 15:50:42 +1000 | [diff] [blame] | 100 | .It Fl D |
| 101 | When this option is specified, |
| 102 | .Nm |
| 103 | will not detach and does not become a daemon. |
| 104 | This allows easy monitoring of |
| 105 | .Nm sshd . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 106 | .It Fl d |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 107 | Debug mode. |
| 108 | The server sends verbose debug output to the system |
| 109 | log, and does not put itself in the background. |
| 110 | The server also will not fork and will only process one connection. |
| 111 | This option is only intended for debugging for the server. |
Damien Miller | ffadc58 | 2003-02-24 11:52:26 +1100 | [diff] [blame] | 112 | Multiple |
| 113 | .Fl d |
| 114 | options increase the debugging level. |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 115 | Maximum is 3. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 116 | .It Fl e |
| 117 | When this option is specified, |
| 118 | .Nm |
| 119 | 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] | 120 | .It Fl f Ar configuration_file |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 121 | Specifies the name of the configuration file. |
| 122 | The default is |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 123 | .Pa /etc/ssh/sshd_config . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 124 | .Nm |
| 125 | refuses to start if there is no configuration file. |
| 126 | .It Fl g Ar login_grace_time |
| 127 | Gives the grace time for clients to authenticate themselves (default |
Damien Miller | c134863 | 2002-09-05 14:35:14 +1000 | [diff] [blame] | 128 | 120 seconds). |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 129 | If the client fails to authenticate the user within |
| 130 | this many seconds, the server disconnects and exits. |
| 131 | A value of zero indicates no limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 132 | .It Fl h Ar host_key_file |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 133 | Specifies a file from which a host key is read. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 134 | This option must be given if |
| 135 | .Nm |
| 136 | is not run as root (as the normal |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 137 | host key files are normally not readable by anyone but root). |
| 138 | The default is |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 139 | .Pa /etc/ssh/ssh_host_key |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 140 | for protocol version 1, and |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 141 | .Pa /etc/ssh/ssh_host_rsa_key |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 142 | and |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 143 | .Pa /etc/ssh/ssh_host_dsa_key |
Damien Miller | 7fc2373 | 2002-01-22 23:19:11 +1100 | [diff] [blame] | 144 | for protocol version 2. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 145 | It is possible to have multiple host key files for |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 146 | the different protocol versions and host key algorithms. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 147 | .It Fl i |
| 148 | Specifies that |
| 149 | .Nm |
Damien Miller | ffadc58 | 2003-02-24 11:52:26 +1100 | [diff] [blame] | 150 | is being run from |
| 151 | .Xr inetd 8 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 152 | .Nm |
| 153 | is normally not run |
| 154 | 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] | 155 | respond to the client, and this may take tens of seconds. |
| 156 | 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] | 157 | However, with small key sizes (e.g., 512) using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 158 | .Nm |
| 159 | from inetd may |
| 160 | be feasible. |
| 161 | .It Fl k Ar key_gen_time |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 162 | Specifies how often the ephemeral protocol version 1 server key is |
| 163 | regenerated (default 3600 seconds, or one hour). |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 164 | The motivation for regenerating the key fairly |
Darren Tucker | 1f20394 | 2003-10-15 15:50:42 +1000 | [diff] [blame] | 165 | often is that the key is not stored anywhere, and after about an hour |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 166 | it becomes impossible to recover the key for decrypting intercepted |
| 167 | communications even if the machine is cracked into or physically |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 168 | seized. |
| 169 | A value of zero indicates that the key will never be regenerated. |
Ben Lindstrom | ade03f6 | 2001-12-06 18:22:17 +0000 | [diff] [blame] | 170 | .It Fl o Ar option |
| 171 | Can be used to give options in the format used in the configuration file. |
| 172 | This is useful for specifying options for which there is no separate |
| 173 | command-line flag. |
Darren Tucker | 1f20394 | 2003-10-15 15:50:42 +1000 | [diff] [blame] | 174 | For full details of the options, and their values, see |
| 175 | .Xr sshd_config 5 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 176 | .It Fl p Ar port |
| 177 | Specifies the port on which the server listens for connections |
| 178 | (default 22). |
Damien Miller | 7d1ded4 | 2002-01-22 23:09:41 +1100 | [diff] [blame] | 179 | Multiple port options are permitted. |
Damien Miller | d7f308f | 2005-12-24 14:55:16 +1100 | [diff] [blame] | 180 | Ports specified in the configuration file with the |
| 181 | .Cm Port |
| 182 | option are ignored when a command-line port is specified. |
| 183 | Ports specified using the |
| 184 | .Cm ListenAddress |
| 185 | option override command-line ports. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 186 | .It Fl q |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 187 | Quiet mode. |
| 188 | Nothing is sent to the system log. |
| 189 | Normally the beginning, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 190 | authentication, and termination of each connection is logged. |
Ben Lindstrom | 794325a | 2001-08-06 21:09:07 +0000 | [diff] [blame] | 191 | .It Fl t |
| 192 | Test mode. |
| 193 | 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] | 194 | This is useful for updating |
Ben Lindstrom | 794325a | 2001-08-06 21:09:07 +0000 | [diff] [blame] | 195 | .Nm |
| 196 | reliably as configuration options may change. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 197 | .It Fl u Ar len |
| 198 | This option is used to specify the size of the field |
| 199 | in the |
| 200 | .Li utmp |
| 201 | structure that holds the remote host name. |
| 202 | If the resolved host name is longer than |
| 203 | .Ar len , |
| 204 | the dotted decimal value will be used instead. |
| 205 | This allows hosts with very long host names that |
| 206 | overflow this field to still be uniquely identified. |
| 207 | Specifying |
| 208 | .Fl u0 |
| 209 | indicates that only dotted decimal addresses |
| 210 | should be put into the |
| 211 | .Pa utmp |
| 212 | file. |
Ben Lindstrom | 6f672c0 | 2001-09-12 17:51:55 +0000 | [diff] [blame] | 213 | .Fl u0 |
Damien Miller | ffadc58 | 2003-02-24 11:52:26 +1100 | [diff] [blame] | 214 | may also be used to prevent |
Ben Lindstrom | 6f672c0 | 2001-09-12 17:51:55 +0000 | [diff] [blame] | 215 | .Nm |
| 216 | from making DNS requests unless the authentication |
| 217 | mechanism or configuration requires it. |
| 218 | Authentication mechanisms that may require DNS include |
Ben Lindstrom | 6f672c0 | 2001-09-12 17:51:55 +0000 | [diff] [blame] | 219 | .Cm RhostsRSAAuthentication , |
Damien Miller | 2ac0577 | 2006-02-01 22:05:42 +1100 | [diff] [blame] | 220 | .Cm HostbasedAuthentication , |
Ben Lindstrom | 6f672c0 | 2001-09-12 17:51:55 +0000 | [diff] [blame] | 221 | and using a |
| 222 | .Cm from="pattern-list" |
| 223 | option in a key file. |
Ben Lindstrom | ea03db9 | 2002-03-05 01:38:57 +0000 | [diff] [blame] | 224 | Configuration options that require DNS include using a |
| 225 | USER@HOST pattern in |
| 226 | .Cm AllowUsers |
| 227 | or |
| 228 | .Cm DenyUsers . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 229 | .El |
Damien Miller | 8bbdf90 | 2006-02-01 22:05:25 +1100 | [diff] [blame] | 230 | .Sh AUTHENTICATION |
| 231 | The OpenSSH SSH daemon supports SSH protocols 1 and 2. |
| 232 | Both protocols are supported by default, |
| 233 | though this can be changed via the |
| 234 | .Cm Protocol |
| 235 | option in |
| 236 | .Xr sshd_config 5 . |
| 237 | Protocol 2 supports both RSA and DSA keys; |
| 238 | protocol 1 only supports RSA keys. |
| 239 | For both protocols, |
| 240 | each host has a host-specific key, |
| 241 | normally 2048 bits, |
| 242 | used to identify the host. |
Damien Miller | 99cc4a8 | 2006-01-31 21:45:53 +1100 | [diff] [blame] | 243 | .Pp |
Damien Miller | 8bbdf90 | 2006-02-01 22:05:25 +1100 | [diff] [blame] | 244 | Forward security for protocol 1 is provided through |
| 245 | an additional server key, |
| 246 | normally 768 bits, |
| 247 | generated when the server starts. |
Damien Miller | 99cc4a8 | 2006-01-31 21:45:53 +1100 | [diff] [blame] | 248 | This key is normally regenerated every hour if it has been used, and |
| 249 | is never stored on disk. |
Damien Miller | 99cc4a8 | 2006-01-31 21:45:53 +1100 | [diff] [blame] | 250 | Whenever a client connects, the daemon responds with its public |
| 251 | host and server keys. |
| 252 | The client compares the |
| 253 | RSA host key against its own database to verify that it has not changed. |
| 254 | The client then generates a 256-bit random number. |
| 255 | It encrypts this |
| 256 | random number using both the host key and the server key, and sends |
| 257 | the encrypted number to the server. |
| 258 | Both sides then use this |
| 259 | random number as a session key which is used to encrypt all further |
| 260 | communications in the session. |
| 261 | The rest of the session is encrypted |
| 262 | using a conventional cipher, currently Blowfish or 3DES, with 3DES |
| 263 | being used by default. |
| 264 | The client selects the encryption algorithm |
| 265 | to use from those offered by the server. |
| 266 | .Pp |
Damien Miller | 8bbdf90 | 2006-02-01 22:05:25 +1100 | [diff] [blame] | 267 | For protocol 2, |
| 268 | forward security is provided through a Diffie-Hellman key agreement. |
| 269 | This key agreement results in a shared session key. |
| 270 | The rest of the session is encrypted using a symmetric cipher, currently |
| 271 | 128-bit AES, Blowfish, 3DES, CAST128, Arcfour, 192-bit AES, or 256-bit AES. |
| 272 | The client selects the encryption algorithm |
| 273 | to use from those offered by the server. |
| 274 | Additionally, session integrity is provided |
| 275 | through a cryptographic message authentication code |
| 276 | (hmac-sha1 or hmac-md5). |
| 277 | .Pp |
| 278 | Finally, the server and the client enter an authentication dialog. |
Damien Miller | 99cc4a8 | 2006-01-31 21:45:53 +1100 | [diff] [blame] | 279 | The client tries to authenticate itself using |
Damien Miller | 8bbdf90 | 2006-02-01 22:05:25 +1100 | [diff] [blame] | 280 | host-based authentication, |
| 281 | public key authentication, |
| 282 | challenge-response authentication, |
| 283 | or password authentication. |
Damien Miller | 99cc4a8 | 2006-01-31 21:45:53 +1100 | [diff] [blame] | 284 | .Pp |
| 285 | Regardless of the authentication type, the account is checked to |
| 286 | ensure that it is accessible. An account is not accessible if it is |
| 287 | locked, listed in |
| 288 | .Cm DenyUsers |
| 289 | or its group is listed in |
| 290 | .Cm DenyGroups |
| 291 | \&. The definition of a locked account is system dependant. Some platforms |
| 292 | have their own account database (eg AIX) and some modify the passwd field ( |
| 293 | .Ql \&*LK\&* |
| 294 | on Solaris and UnixWare, |
| 295 | .Ql \&* |
| 296 | on HP-UX, containing |
| 297 | .Ql Nologin |
| 298 | on Tru64, |
| 299 | a leading |
| 300 | .Ql \&*LOCKED\&* |
| 301 | on FreeBSD and a leading |
| 302 | .Ql \&!! |
| 303 | on Linux). If there is a requirement to disable password authentication |
| 304 | for the account while allowing still public-key, then the passwd field |
| 305 | should be set to something other than these values (eg |
| 306 | .Ql NP |
| 307 | or |
| 308 | .Ql \&*NP\&* |
| 309 | ). |
| 310 | .Pp |
Damien Miller | 99cc4a8 | 2006-01-31 21:45:53 +1100 | [diff] [blame] | 311 | If the client successfully authenticates itself, a dialog for |
| 312 | preparing the session is entered. |
| 313 | At this time the client may request |
| 314 | things like allocating a pseudo-tty, forwarding X11 connections, |
| 315 | forwarding TCP connections, or forwarding the authentication agent |
| 316 | connection over the secure channel. |
| 317 | .Pp |
Damien Miller | c47d7e9 | 2006-03-15 11:27:20 +1100 | [diff] [blame] | 318 | After this, the client either requests a shell or execution of a command. |
Damien Miller | 99cc4a8 | 2006-01-31 21:45:53 +1100 | [diff] [blame] | 319 | The sides then enter session mode. |
| 320 | In this mode, either side may send |
| 321 | data at any time, and such data is forwarded to/from the shell or |
| 322 | command on the server side, and the user terminal in the client side. |
| 323 | .Pp |
| 324 | When the user program terminates and all forwarded X11 and other |
| 325 | connections have been closed, the server sends command exit status to |
| 326 | the client, and both sides exit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 327 | .Sh LOGIN PROCESS |
| 328 | When a user successfully logs in, |
| 329 | .Nm |
| 330 | does the following: |
| 331 | .Bl -enum -offset indent |
| 332 | .It |
| 333 | 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] | 334 | prints last login time and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 335 | .Pa /etc/motd |
| 336 | (unless prevented in the configuration file or by |
Damien Miller | 167ea5d | 2005-05-26 12:04:02 +1000 | [diff] [blame] | 337 | .Pa ~/.hushlogin ; |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 338 | see the |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 339 | .Sx FILES |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 340 | section). |
| 341 | .It |
| 342 | If the login is on a tty, records login time. |
| 343 | .It |
| 344 | Checks |
| 345 | .Pa /etc/nologin ; |
| 346 | if it exists, prints contents and quits |
| 347 | (unless root). |
| 348 | .It |
| 349 | Changes to run with normal user privileges. |
| 350 | .It |
| 351 | Sets up basic environment. |
| 352 | .It |
Darren Tucker | 1f20394 | 2003-10-15 15:50:42 +1000 | [diff] [blame] | 353 | Reads the file |
Damien Miller | 167ea5d | 2005-05-26 12:04:02 +1000 | [diff] [blame] | 354 | .Pa ~/.ssh/environment , |
Darren Tucker | 1f20394 | 2003-10-15 15:50:42 +1000 | [diff] [blame] | 355 | if it exists, and users are allowed to change their environment. |
Ben Lindstrom | bd9bf38 | 2002-08-20 18:54:20 +0000 | [diff] [blame] | 356 | See the |
Ben Lindstrom | dc7adf2 | 2002-08-20 18:38:02 +0000 | [diff] [blame] | 357 | .Cm PermitUserEnvironment |
Ben Lindstrom | bd9bf38 | 2002-08-20 18:54:20 +0000 | [diff] [blame] | 358 | option in |
Ben Lindstrom | dc7adf2 | 2002-08-20 18:38:02 +0000 | [diff] [blame] | 359 | .Xr sshd_config 5 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 360 | .It |
| 361 | Changes to user's home directory. |
| 362 | .It |
| 363 | If |
Damien Miller | 167ea5d | 2005-05-26 12:04:02 +1000 | [diff] [blame] | 364 | .Pa ~/.ssh/rc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 365 | exists, runs it; else if |
Damien Miller | afcc225 | 2002-02-10 18:32:55 +1100 | [diff] [blame] | 366 | .Pa /etc/ssh/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 367 | exists, runs |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 368 | it; otherwise runs xauth. |
| 369 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 370 | .Dq rc |
| 371 | files are given the X11 |
| 372 | authentication protocol and cookie in standard input. |
| 373 | .It |
| 374 | Runs user's shell or command. |
| 375 | .El |
| 376 | .Sh AUTHORIZED_KEYS FILE FORMAT |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 377 | .Cm AuthorizedKeysFile |
Damien Miller | dcfea27 | 2006-03-15 11:31:22 +1100 | [diff] [blame] | 378 | specifies the file containing public keys for |
| 379 | public key authentication; |
| 380 | if none is specified, the default is |
| 381 | .Pa ~/.ssh/authorized_keys . |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 382 | Each line of the file contains one |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 383 | key (empty lines and lines starting with a |
| 384 | .Ql # |
| 385 | are ignored as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 386 | comments). |
Damien Miller | dcfea27 | 2006-03-15 11:31:22 +1100 | [diff] [blame] | 387 | Protocol 1 public keys consist of the following space-separated fields: |
| 388 | options, bits, exponent, modulus, comment. |
| 389 | Protocol 2 public key consist of: |
| 390 | options, keytype, base64-encoded key, comment. |
| 391 | The options field is optional; |
| 392 | its presence is determined by whether the line starts |
Damien Miller | b83df8d | 2002-09-04 16:24:55 +1000 | [diff] [blame] | 393 | with a number or not (the options field never starts with a number). |
Damien Miller | dcfea27 | 2006-03-15 11:31:22 +1100 | [diff] [blame] | 394 | The bits, exponent, modulus, and comment fields give the RSA key for |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 395 | protocol version 1; the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 396 | comment field is not used for anything (but may be convenient for the |
| 397 | user to identify the key). |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 398 | For protocol version 2 the keytype is |
| 399 | .Dq ssh-dss |
| 400 | or |
| 401 | .Dq ssh-rsa . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 402 | .Pp |
| 403 | Note that lines in this file are usually several hundred bytes long |
Darren Tucker | 22cc741 | 2004-12-06 22:47:41 +1100 | [diff] [blame] | 404 | (because of the size of the public key encoding) up to a limit of |
| 405 | 8 kilobytes, which permits DSA keys up to 8 kilobits and RSA |
| 406 | keys up to 16 kilobits. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 407 | You don't want to type them in; instead, copy the |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 408 | .Pa identity.pub , |
Damien Miller | dcfea27 | 2006-03-15 11:31:22 +1100 | [diff] [blame] | 409 | .Pa id_dsa.pub , |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 410 | or the |
| 411 | .Pa id_rsa.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 412 | file and edit it. |
| 413 | .Pp |
Ben Lindstrom | 0d0be02 | 2002-04-02 20:39:29 +0000 | [diff] [blame] | 414 | .Nm |
| 415 | enforces a minimum RSA key modulus size for protocol 1 |
| 416 | and protocol 2 keys of 768 bits. |
| 417 | .Pp |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 418 | The options (if present) consist of comma-separated option |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 419 | specifications. |
| 420 | No spaces are permitted, except within double quotes. |
Ben Lindstrom | 1c0fd09 | 2001-09-12 16:36:17 +0000 | [diff] [blame] | 421 | The following option specifications are supported (note |
| 422 | that option keywords are case-insensitive): |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 423 | .Bl -tag -width Ds |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 424 | .It Cm command="command" |
| 425 | Specifies that the command is executed whenever this key is used for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 426 | authentication. |
| 427 | The command supplied by the user (if any) is ignored. |
Ben Lindstrom | 23124ea | 2001-09-14 23:14:25 +0000 | [diff] [blame] | 428 | 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] | 429 | otherwise it is run without a tty. |
Damien Miller | ffadc58 | 2003-02-24 11:52:26 +1100 | [diff] [blame] | 430 | If an 8-bit clean channel is required, |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 431 | one must not request a pty or should specify |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 432 | .Cm no-pty . |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 433 | A quote may be included in the command by quoting it with a backslash. |
| 434 | This option might be useful |
Damien Miller | b83df8d | 2002-09-04 16:24:55 +1000 | [diff] [blame] | 435 | to restrict certain public keys to perform just a specific operation. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 436 | An example might be a key that permits remote backups but nothing else. |
Damien Miller | 7c24b81 | 2006-01-14 10:09:56 +1100 | [diff] [blame] | 437 | Note that the client may specify TCP and/or X11 |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 438 | forwarding unless they are explicitly prohibited. |
Ben Lindstrom | 20daef7 | 2001-09-20 00:54:01 +0000 | [diff] [blame] | 439 | Note that this option applies to shell, command or subsystem execution. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 440 | .It Cm environment="NAME=value" |
| 441 | Specifies that the string is to be added to the environment when |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 442 | logging in using this key. |
| 443 | Environment variables set this way |
| 444 | override other default environment values. |
| 445 | Multiple options of this type are permitted. |
Ben Lindstrom | bd9bf38 | 2002-08-20 18:54:20 +0000 | [diff] [blame] | 446 | Environment processing is disabled by default and is |
| 447 | controlled via the |
| 448 | .Cm PermitUserEnvironment |
| 449 | option. |
Ben Lindstrom | 38b951c | 2001-12-06 17:47:47 +0000 | [diff] [blame] | 450 | This option is automatically disabled if |
| 451 | .Cm UseLogin |
| 452 | is enabled. |
Damien Miller | 31bdc52 | 2006-03-15 11:31:44 +1100 | [diff] [blame] | 453 | .It Cm from="pattern-list" |
| 454 | Specifies that in addition to public key authentication, the canonical name |
| 455 | of the remote host must be present in the comma-separated list of |
| 456 | patterns |
Damien Miller | c8f61cf | 2006-03-15 11:33:25 +1100 | [diff] [blame] | 457 | .Pf ( Ql * |
Damien Miller | 31bdc52 | 2006-03-15 11:31:44 +1100 | [diff] [blame] | 458 | and |
| 459 | .Ql \&? |
| 460 | serve as wildcards). |
| 461 | The list may also contain |
| 462 | patterns negated by prefixing them with |
| 463 | .Ql \&! ; |
| 464 | if the canonical host name matches a negated pattern, the key is not accepted. |
| 465 | The purpose |
| 466 | of this option is to optionally increase security: public key authentication |
| 467 | by itself does not trust the network or name servers or anything (but |
| 468 | the key); however, if somebody somehow steals the key, the key |
| 469 | permits an intruder to log in from anywhere in the world. |
| 470 | This additional option makes using a stolen key more difficult (name |
| 471 | servers and/or routers would have to be compromised in addition to |
| 472 | just the key). |
| 473 | .It Cm no-agent-forwarding |
| 474 | Forbids authentication agent forwarding when this key is used for |
| 475 | authentication. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 476 | .It Cm no-port-forwarding |
Damien Miller | 7c24b81 | 2006-01-14 10:09:56 +1100 | [diff] [blame] | 477 | Forbids TCP forwarding when this key is used for authentication. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 478 | Any port forward requests by the client will return an error. |
| 479 | This might be used, e.g., in connection with the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 480 | .Cm command |
| 481 | option. |
Damien Miller | 31bdc52 | 2006-03-15 11:31:44 +1100 | [diff] [blame] | 482 | .It Cm no-pty |
| 483 | Prevents tty allocation (a request to allocate a pty will fail). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 484 | .It Cm no-X11-forwarding |
| 485 | Forbids X11 forwarding when this key is used for authentication. |
| 486 | Any X11 forward requests by the client will return an error. |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 487 | .It Cm permitopen="host:port" |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 488 | Limit local |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 489 | .Li ``ssh -L'' |
Ben Lindstrom | 4b3564e | 2001-04-10 02:41:56 +0000 | [diff] [blame] | 490 | 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] | 491 | port. |
| 492 | IPv6 addresses can be specified with an alternative syntax: |
Darren Tucker | 1f20394 | 2003-10-15 15:50:42 +1000 | [diff] [blame] | 493 | .Ar host Ns / Ns Ar port . |
Ben Lindstrom | d71ba57 | 2001-09-12 18:03:31 +0000 | [diff] [blame] | 494 | Multiple |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 495 | .Cm permitopen |
Damien Miller | fbf486b | 2003-05-23 18:44:23 +1000 | [diff] [blame] | 496 | options may be applied separated by commas. |
| 497 | No pattern matching is performed on the specified hostnames, |
| 498 | they must be literal domains or addresses. |
Damien Miller | d27b947 | 2005-12-13 19:29:02 +1100 | [diff] [blame] | 499 | .It Cm tunnel="n" |
| 500 | Force a |
| 501 | .Xr tun 4 |
| 502 | device on the server. |
| 503 | Without this option, the next available device will be used if |
| 504 | the client requests a tunnel. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 505 | .El |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 506 | .Pp |
Damien Miller | 7d2ef02 | 2006-03-15 11:32:06 +1100 | [diff] [blame] | 507 | An example authorized_keys file: |
Damien Miller | c8f61cf | 2006-03-15 11:33:25 +1100 | [diff] [blame] | 508 | .Bd -literal -offset 3n |
Damien Miller | 7d2ef02 | 2006-03-15 11:32:06 +1100 | [diff] [blame] | 509 | # Comments allowed at start of line |
| 510 | ssh-rsa AAAAB3Nza...LiPk== user@example.net |
Damien Miller | c8f61cf | 2006-03-15 11:33:25 +1100 | [diff] [blame] | 511 | from="*.sales.example.net,!pc.sales.example.net" ssh-rsa |
| 512 | AAAAB2...19Q== john@example.net |
| 513 | command="dump /home",no-pty,no-port-forwarding ssh-dss |
| 514 | AAAAC3...51R== example.net |
| 515 | permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-dss |
| 516 | AAAAB5...21S== |
| 517 | tunnel="0",command="sh /etc/netstart tun0" ssh-rsa AAAA...== |
| 518 | jane@example.net |
Damien Miller | 7d2ef02 | 2006-03-15 11:32:06 +1100 | [diff] [blame] | 519 | .Ed |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 520 | .Sh SSH_KNOWN_HOSTS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 521 | The |
Damien Miller | ffadc58 | 2003-02-24 11:52:26 +1100 | [diff] [blame] | 522 | .Pa /etc/ssh/ssh_known_hosts |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 523 | and |
Damien Miller | 167ea5d | 2005-05-26 12:04:02 +1000 | [diff] [blame] | 524 | .Pa ~/.ssh/known_hosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 525 | files contain host public keys for all known hosts. |
| 526 | The global file should |
| 527 | be prepared by the administrator (optional), and the per-user file is |
Damien Miller | 9a7f201 | 2006-03-15 11:32:42 +1100 | [diff] [blame] | 528 | maintained automatically: whenever the user connects from an unknown host, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 529 | its key is added to the per-user file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 530 | .Pp |
| 531 | Each line in these files contains the following fields: hostnames, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 532 | bits, exponent, modulus, comment. |
| 533 | The fields are separated by spaces. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 534 | .Pp |
Damien Miller | 3155432 | 2003-05-14 13:44:58 +1000 | [diff] [blame] | 535 | Hostnames is a comma-separated list of patterns |
Damien Miller | 9a7f201 | 2006-03-15 11:32:42 +1100 | [diff] [blame] | 536 | .Pf ( Ql * |
Damien Miller | fbf486b | 2003-05-23 18:44:23 +1000 | [diff] [blame] | 537 | and |
| 538 | .Ql \&? |
Damien Miller | 049245d | 2003-05-14 13:44:42 +1000 | [diff] [blame] | 539 | act as |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 540 | wildcards); each pattern in turn is matched against the canonical host |
| 541 | name (when authenticating a client) or against the user-supplied |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 542 | name (when authenticating a server). |
| 543 | A pattern may also be preceded by |
Damien Miller | 049245d | 2003-05-14 13:44:42 +1000 | [diff] [blame] | 544 | .Ql \&! |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 545 | to indicate negation: if the host name matches a negated |
| 546 | pattern, it is not accepted (by that line) even if it matched another |
| 547 | pattern on the line. |
| 548 | .Pp |
Damien Miller | e177615 | 2005-03-01 21:47:37 +1100 | [diff] [blame] | 549 | Alternately, hostnames may be stored in a hashed form which hides host names |
Damien Miller | 718fd4b | 2005-03-02 12:03:23 +1100 | [diff] [blame] | 550 | and addresses should the file's contents be disclosed. |
| 551 | Hashed hostnames start with a |
| 552 | .Ql | |
Damien Miller | e177615 | 2005-03-01 21:47:37 +1100 | [diff] [blame] | 553 | character. |
| 554 | Only one hashed hostname may appear on a single line and none of the above |
| 555 | negation or wildcard operators may be applied. |
| 556 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 557 | Bits, exponent, and modulus are taken directly from the RSA host key; they |
Damien Miller | 9a7f201 | 2006-03-15 11:32:42 +1100 | [diff] [blame] | 558 | can be obtained, for example, from |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 559 | .Pa /etc/ssh/ssh_host_key.pub . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 560 | The optional comment field continues to the end of the line, and is not used. |
| 561 | .Pp |
| 562 | Lines starting with |
| 563 | .Ql # |
| 564 | and empty lines are ignored as comments. |
| 565 | .Pp |
| 566 | When performing host authentication, authentication is accepted if any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 567 | matching line has the proper key. |
| 568 | It is thus permissible (but not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 569 | recommended) to have several lines or different host keys for the same |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 570 | names. |
| 571 | This will inevitably happen when short forms of host names |
| 572 | from different domains are put in the file. |
| 573 | It is possible |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 574 | that the files contain conflicting information; authentication is |
| 575 | accepted if valid information can be found from either file. |
| 576 | .Pp |
| 577 | Note that the lines in these files are typically hundreds of characters |
| 578 | long, and you definitely don't want to type in the host keys by hand. |
| 579 | Rather, generate them by a script |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 580 | or by taking |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 581 | .Pa /etc/ssh/ssh_host_key.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 582 | and adding the host names at the front. |
Damien Miller | cc00f5e | 2006-03-15 11:33:00 +1100 | [diff] [blame] | 583 | .Pp |
| 584 | An example ssh_known_hosts file: |
| 585 | .Bd -literal -offset 3n |
| 586 | # Comments allowed at start of line |
| 587 | closenet,...,192.0.2.53 1024 37 159...93 closenet.example.net |
| 588 | cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....= |
Damien Miller | e177615 | 2005-03-01 21:47:37 +1100 | [diff] [blame] | 589 | # A hashed hostname |
| 590 | |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa |
| 591 | AAAA1234.....= |
| 592 | .Ed |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 593 | .Sh FILES |
Damien Miller | d8702e8 | 2006-03-15 11:33:56 +1100 | [diff] [blame] | 594 | .Bl -tag -width Ds -compact |
| 595 | .It ~/.hushlogin |
Damien Miller | 70a908e | 2005-03-01 21:17:09 +1100 | [diff] [blame] | 596 | This file is used to suppress printing the last login time and |
| 597 | .Pa /etc/motd , |
| 598 | if |
| 599 | .Cm PrintLastLog |
| 600 | and |
| 601 | .Cm PrintMotd , |
| 602 | respectively, |
| 603 | are enabled. |
| 604 | It does not suppress printing of the banner specified by |
| 605 | .Cm Banner . |
Damien Miller | d8702e8 | 2006-03-15 11:33:56 +1100 | [diff] [blame] | 606 | .Pp |
| 607 | .It ~/.rhosts |
Darren Tucker | db69390 | 2004-08-29 16:37:24 +1000 | [diff] [blame] | 608 | This file is used during |
| 609 | .Cm RhostsRSAAuthentication |
| 610 | and |
| 611 | .Cm HostbasedAuthentication |
| 612 | and contains host-username pairs, separated by a space, one per |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 613 | line. |
| 614 | The given user on the corresponding host is permitted to log in |
Damien Miller | ffadc58 | 2003-02-24 11:52:26 +1100 | [diff] [blame] | 615 | without a password. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 616 | The same file is used by rlogind and rshd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 617 | The file must |
| 618 | be writable only by the user; it is recommended that it not be |
| 619 | accessible by others. |
| 620 | .Pp |
Darren Tucker | 1f20394 | 2003-10-15 15:50:42 +1000 | [diff] [blame] | 621 | It is also possible to use netgroups in the file. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 622 | Either host or user |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 623 | name may be of the form +@groupname to specify all hosts or all users |
| 624 | in the group. |
Damien Miller | d8702e8 | 2006-03-15 11:33:56 +1100 | [diff] [blame] | 625 | .Pp |
| 626 | .It ~/.shosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 627 | For ssh, |
| 628 | this file is exactly the same as for |
| 629 | .Pa .rhosts . |
| 630 | However, this file is |
| 631 | not used by rlogin and rshd, so using this permits access using SSH only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 632 | .Pp |
Damien Miller | d8702e8 | 2006-03-15 11:33:56 +1100 | [diff] [blame] | 633 | .It ~/.ssh/authorized_keys |
| 634 | Lists the public keys (RSA or DSA) that can be used to log into the user's account. |
| 635 | This file must be readable by root (which may on some machines imply |
| 636 | it being world-readable if the user's home directory resides on an NFS |
| 637 | volume). |
| 638 | It is recommended that it not be accessible by others. |
| 639 | The format of this file is described above. |
| 640 | Users will place the contents of their |
| 641 | .Pa identity.pub , |
| 642 | .Pa id_dsa.pub |
| 643 | and/or |
| 644 | .Pa id_rsa.pub |
| 645 | files into this file, as described in |
| 646 | .Xr ssh-keygen 1 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 647 | .Pp |
Damien Miller | d8702e8 | 2006-03-15 11:33:56 +1100 | [diff] [blame] | 648 | .It ~/.ssh/environment |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 649 | This file is read into the environment at login (if it exists). |
| 650 | It can only contain empty lines, comment lines (that start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 651 | .Ql # ) , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 652 | and assignment lines of the form name=value. |
| 653 | The file should be writable |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 654 | only by the user; it need not be readable by anyone else. |
Ben Lindstrom | bd9bf38 | 2002-08-20 18:54:20 +0000 | [diff] [blame] | 655 | Environment processing is disabled by default and is |
| 656 | controlled via the |
| 657 | .Cm PermitUserEnvironment |
| 658 | option. |
Damien Miller | d8702e8 | 2006-03-15 11:33:56 +1100 | [diff] [blame] | 659 | .Pp |
| 660 | .It ~/.ssh/known_hosts |
| 661 | .It /etc/ssh/ssh_known_hosts |
| 662 | These files are consulted when using rhosts with RSA host |
| 663 | authentication or protocol version 2 hostbased authentication |
| 664 | to check the public key of the host. |
| 665 | The key must be listed in one of these files to be accepted. |
| 666 | The client uses the same files |
| 667 | to verify that it is connecting to the correct remote host. |
| 668 | These files should be writable only by root/the owner. |
| 669 | .Pa /etc/ssh/ssh_known_hosts |
| 670 | should be world-readable, and |
| 671 | .Pa ~/.ssh/known_hosts |
| 672 | can, but need not be, world-readable. |
| 673 | .Pp |
| 674 | .It ~/.ssh/rc |
Damien Miller | ffadc58 | 2003-02-24 11:52:26 +1100 | [diff] [blame] | 675 | If this file exists, it is run with |
| 676 | .Pa /bin/sh |
| 677 | after reading the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 678 | environment files but before starting the user's shell or command. |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 679 | It must not produce any output on stdout; stderr must be used |
| 680 | instead. |
| 681 | If X11 forwarding is in use, it will receive the "proto cookie" pair in |
| 682 | its standard input (and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 683 | .Ev DISPLAY |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 684 | in its environment). |
| 685 | The script must call |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 686 | .Xr xauth 1 |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 687 | because |
| 688 | .Nm |
| 689 | will not run xauth automatically to add X11 cookies. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 690 | .Pp |
| 691 | The primary purpose of this file is to run any initialization routines |
| 692 | which may be needed before the user's home directory becomes |
| 693 | accessible; AFS is a particular example of such an environment. |
| 694 | .Pp |
| 695 | This file will probably contain some initialization code followed by |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 696 | something similar to: |
| 697 | .Bd -literal |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 698 | if read proto cookie && [ -n "$DISPLAY" ]; then |
| 699 | if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]; then |
| 700 | # X11UseLocalhost=yes |
Damien Miller | dcbb6c2 | 2002-09-25 12:20:52 +1000 | [diff] [blame] | 701 | echo add unix:`echo $DISPLAY | |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 702 | cut -c11-` $proto $cookie |
| 703 | else |
| 704 | # X11UseLocalhost=no |
Damien Miller | dcbb6c2 | 2002-09-25 12:20:52 +1000 | [diff] [blame] | 705 | echo add $DISPLAY $proto $cookie |
| 706 | fi | xauth -q - |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 707 | fi |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 708 | .Ed |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 709 | .Pp |
| 710 | If this file does not exist, |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 711 | .Pa /etc/ssh/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 712 | is run, and if that |
Ben Lindstrom | a11e270 | 2002-04-05 22:18:48 +0000 | [diff] [blame] | 713 | does not exist either, xauth is used to add the cookie. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 714 | .Pp |
| 715 | This file should be writable only by the user, and need not be |
| 716 | readable by anyone else. |
Damien Miller | d8702e8 | 2006-03-15 11:33:56 +1100 | [diff] [blame] | 717 | .Pp |
| 718 | .It /etc/hosts.allow |
| 719 | .It /etc/hosts.deny |
| 720 | Access controls that should be enforced by tcp-wrappers are defined here. |
| 721 | Further details are described in |
| 722 | .Xr hosts_access 5 . |
| 723 | .Pp |
| 724 | .It /etc/hosts.equiv |
| 725 | This file is used during |
| 726 | .Cm RhostsRSAAuthentication |
| 727 | and |
| 728 | .Cm HostbasedAuthentication |
| 729 | authentication. |
| 730 | In the simplest form, this file contains host names, one per line. |
| 731 | Users on |
| 732 | those hosts are permitted to log in without a password, provided they |
| 733 | have the same user name on both machines. |
| 734 | The host name may also be |
| 735 | followed by a user name; such users are permitted to log in as |
| 736 | .Em any |
| 737 | user on this machine (except root). |
| 738 | Additionally, the syntax |
| 739 | .Dq +@group |
| 740 | can be used to specify netgroups. |
| 741 | Negated entries start with |
| 742 | .Ql \&- . |
| 743 | .Pp |
| 744 | If the client host/user is successfully matched in this file, login is |
| 745 | automatically permitted provided the client and server user names are the |
| 746 | same. |
| 747 | Additionally, successful client host key authentication is required. |
| 748 | This file must be writable only by root; it is recommended |
| 749 | that it be world-readable. |
| 750 | .Pp |
| 751 | .Sy "Warning: It is almost never a good idea to use user names in" |
| 752 | .Pa hosts.equiv . |
| 753 | Beware that it really means that the named user(s) can log in as |
| 754 | .Em anybody , |
| 755 | which includes bin, daemon, adm, and other accounts that own critical |
| 756 | binaries and directories. |
| 757 | Using a user name practically grants the user root access. |
| 758 | The only valid use for user names that I can think |
| 759 | of is in negative entries. |
| 760 | .Pp |
| 761 | Note that this warning also applies to rsh/rlogin. |
| 762 | .Pp |
| 763 | .It /etc/moduli |
| 764 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". |
| 765 | The file format is described in |
| 766 | .Xr moduli 5 . |
| 767 | .Pp |
| 768 | .It /etc/motd |
| 769 | See |
| 770 | .Xr motd 5 . |
| 771 | .Pp |
| 772 | .It /etc/nologin |
| 773 | If this file exists, |
| 774 | .Nm |
| 775 | refuses to let anyone except root log in. |
| 776 | The contents of the file |
| 777 | are displayed to anyone trying to log in, and non-root connections are |
| 778 | refused. |
| 779 | The file should be world-readable. |
| 780 | .Pp |
| 781 | .It /etc/shosts.equiv |
| 782 | This is processed exactly as |
| 783 | .Pa /etc/hosts.equiv . |
| 784 | However, this file may be useful in environments that want to run both |
| 785 | rsh/rlogin and ssh. |
| 786 | .Pp |
| 787 | .It /etc/ssh/ssh_host_key |
| 788 | .It /etc/ssh/ssh_host_dsa_key |
| 789 | .It /etc/ssh/ssh_host_rsa_key |
| 790 | These three files contain the private parts of the host keys. |
| 791 | These files should only be owned by root, readable only by root, and not |
| 792 | accessible to others. |
| 793 | Note that |
| 794 | .Nm |
| 795 | does not start if this file is group/world-accessible. |
| 796 | .Pp |
| 797 | .It /etc/ssh/ssh_host_key.pub |
| 798 | .It /etc/ssh/ssh_host_dsa_key.pub |
| 799 | .It /etc/ssh/ssh_host_rsa_key.pub |
| 800 | These three files contain the public parts of the host keys. |
| 801 | These files should be world-readable but writable only by |
| 802 | root. |
| 803 | Their contents should match the respective private parts. |
| 804 | These files are not |
| 805 | really used for anything; they are provided for the convenience of |
| 806 | the user so their contents can be copied to known hosts files. |
| 807 | These files are created using |
| 808 | .Xr ssh-keygen 1 . |
| 809 | .Pp |
| 810 | .It /etc/ssh/sshd_config |
| 811 | Contains configuration data for |
| 812 | .Nm sshd . |
| 813 | The file format and configuration options are described in |
| 814 | .Xr sshd_config 5 . |
| 815 | .Pp |
| 816 | .It /etc/ssh/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 817 | Like |
Damien Miller | 167ea5d | 2005-05-26 12:04:02 +1000 | [diff] [blame] | 818 | .Pa ~/.ssh/rc . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 819 | This can be used to specify |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 820 | machine-specific login-time initializations globally. |
| 821 | This file should be writable only by root, and should be world-readable. |
Damien Miller | d8702e8 | 2006-03-15 11:33:56 +1100 | [diff] [blame] | 822 | .Pp |
| 823 | .It /var/empty |
| 824 | .Xr chroot 2 |
| 825 | directory used by |
| 826 | .Nm |
| 827 | during privilege separation in the pre-authentication phase. |
| 828 | The directory should not contain any files and must be owned by root |
| 829 | and not group or world-writable. |
| 830 | .Pp |
| 831 | .It /var/run/sshd.pid |
| 832 | Contains the process ID of the |
| 833 | .Nm |
| 834 | listening for connections (if there are several daemons running |
| 835 | concurrently for different ports, this contains the process ID of the one |
| 836 | started last). |
| 837 | The content of this file is not sensitive; it can be world-readable. |
Damien Miller | 3702396 | 2000-07-11 17:31:38 +1000 | [diff] [blame] | 838 | .El |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 839 | .Sh SEE ALSO |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 840 | .Xr scp 1 , |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 841 | .Xr sftp 1 , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 842 | .Xr ssh 1 , |
| 843 | .Xr ssh-add 1 , |
| 844 | .Xr ssh-agent 1 , |
| 845 | .Xr ssh-keygen 1 , |
Darren Tucker | 1f20394 | 2003-10-15 15:50:42 +1000 | [diff] [blame] | 846 | .Xr chroot 2 , |
| 847 | .Xr hosts_access 5 , |
Ben Lindstrom | c8e29ce | 2001-08-06 20:55:28 +0000 | [diff] [blame] | 848 | .Xr login.conf 5 , |
| 849 | .Xr moduli 5 , |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 850 | .Xr sshd_config 5 , |
Darren Tucker | 1f20394 | 2003-10-15 15:50:42 +1000 | [diff] [blame] | 851 | .Xr inetd 8 , |
Ben Lindstrom | d2bf0d6 | 2001-06-25 04:10:54 +0000 | [diff] [blame] | 852 | .Xr sftp-server 8 |
Damien Miller | f1ce505 | 2003-06-11 22:04:39 +1000 | [diff] [blame] | 853 | .Sh AUTHORS |
| 854 | OpenSSH is a derivative of the original and free |
| 855 | ssh 1.2.12 release by Tatu Ylonen. |
| 856 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, |
| 857 | Theo de Raadt and Dug Song |
| 858 | removed many bugs, re-added newer features and |
| 859 | created OpenSSH. |
| 860 | Markus Friedl contributed the support for SSH |
| 861 | protocol versions 1.5 and 2.0. |
| 862 | Niels Provos and Markus Friedl contributed support |
| 863 | for privilege separation. |
Damien Miller | c47d7e9 | 2006-03-15 11:27:20 +1100 | [diff] [blame] | 864 | .Sh CAVEATS |
| 865 | System security is not improved unless |
| 866 | .Nm rshd , |
| 867 | .Nm rlogind , |
| 868 | and |
| 869 | .Nm rexecd |
| 870 | are disabled (thus completely disabling |
| 871 | .Xr rlogin |
| 872 | and |
| 873 | .Xr rsh |
| 874 | into the machine). |