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 | 7bfff36 | 2001-03-26 05:45:53 +0000 | [diff] [blame^] | 37 | .\" $OpenBSD: sshd.8,v 1.108 2001/03/25 13:16:11 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 | d58eb5f | 2001-03-07 06:07:22 +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 | c12a6b7 | 2001-01-29 08:41:05 +0000 | [diff] [blame] | 46 | .Op Fl diqD46 |
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 |
| 52 | .Op Fl p Ar port |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 53 | .Op Fl u Ar len |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 54 | .Op Fl V Ar client_protocol_id |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 55 | .Sh DESCRIPTION |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 56 | .Nm |
Ben Lindstrom | d58eb5f | 2001-03-07 06:07:22 +0000 | [diff] [blame] | 57 | (SSH Daemon) is the daemon program for |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 58 | .Xr ssh 1 . |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 59 | Together these programs replace rlogin and rsh, and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 60 | provide secure encrypted communications between two untrusted hosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 61 | over an insecure network. |
| 62 | The programs are intended to be as easy to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 63 | install and use as possible. |
| 64 | .Pp |
| 65 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 66 | is the daemon that listens for connections from clients. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 67 | It is normally started at boot from |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 68 | .Pa /etc/rc . |
| 69 | It forks a new |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 70 | daemon for each incoming connection. |
| 71 | The forked daemons handle |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 72 | key exchange, encryption, authentication, command execution, |
| 73 | and data exchange. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 74 | This implementation of |
| 75 | .Nm |
| 76 | supports both SSH protocol version 1 and 2 simultaneously. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 77 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 78 | works as follows. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 79 | .Pp |
| 80 | .Ss SSH protocol version 1 |
| 81 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 82 | Each host has a host-specific RSA key |
| 83 | (normally 1024 bits) used to identify the host. |
| 84 | Additionally, when |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 85 | the daemon starts, it generates a server RSA key (normally 768 bits). |
| 86 | This key is normally regenerated every hour if it has been used, and |
| 87 | is never stored on disk. |
| 88 | .Pp |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 89 | Whenever a client connects the daemon responds with its public |
| 90 | host and server keys. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 91 | The client compares the |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 92 | RSA host key against its own database to verify that it has not changed. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 93 | The client then generates a 256 bit random number. |
| 94 | It encrypts this |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 95 | random number using both the host key and the server key, and sends |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 96 | the encrypted number to the server. |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 97 | Both sides then use this |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 98 | random number as a session key which is used to encrypt all further |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 99 | communications in the session. |
| 100 | The rest of the session is encrypted |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 101 | using a conventional cipher, currently Blowfish or 3DES, with 3DES |
Damien Miller | b38eff8 | 2000-04-01 11:09:21 +1000 | [diff] [blame] | 102 | being used by default. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 103 | The client selects the encryption algorithm |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 104 | to use from those offered by the server. |
| 105 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 106 | Next, the server and the client enter an authentication dialog. |
| 107 | The client tries to authenticate itself using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 108 | .Pa .rhosts |
| 109 | authentication, |
| 110 | .Pa .rhosts |
| 111 | authentication combined with RSA host |
| 112 | authentication, RSA challenge-response authentication, or password |
| 113 | based authentication. |
| 114 | .Pp |
| 115 | Rhosts authentication is normally disabled |
| 116 | because it is fundamentally insecure, but can be enabled in the server |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 117 | configuration file if desired. |
| 118 | System security is not improved unless |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 119 | .Xr rshd 8 , |
| 120 | .Xr rlogind 8 , |
| 121 | .Xr rexecd 8 , |
| 122 | and |
| 123 | .Xr rexd 8 |
| 124 | are disabled (thus completely disabling |
| 125 | .Xr rlogin 1 |
| 126 | and |
| 127 | .Xr rsh 1 |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 128 | into the machine). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 129 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 130 | .Ss SSH protocol version 2 |
| 131 | .Pp |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 132 | Version 2 works similarly: |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 133 | Each host has a host-specific DSA key used to identify the host. |
| 134 | However, when the daemon starts, it does not generate a server key. |
| 135 | Forward security is provided through a Diffie-Hellman key agreement. |
| 136 | This key agreement results in a shared session key. |
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 |
| 138 | Blowfish, 3DES, CAST128, Arcfour, 128 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 |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 146 | user authentication method (PubkeyAuthentication) |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 147 | and conventional password authentication. |
| 148 | .Pp |
| 149 | .Ss Command execution and data forwarding |
| 150 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 151 | If the client successfully authenticates itself, a dialog for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 152 | preparing the session is entered. |
| 153 | At this time the client may request |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 154 | things like allocating a pseudo-tty, forwarding X11 connections, |
| 155 | forwarding TCP/IP connections, or forwarding the authentication agent |
| 156 | connection over the secure channel. |
| 157 | .Pp |
| 158 | Finally, the client either requests a shell or execution of a command. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 159 | The sides then enter session mode. |
| 160 | In this mode, either side may send |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 161 | data at any time, and such data is forwarded to/from the shell or |
| 162 | command on the server side, and the user terminal in the client side. |
| 163 | .Pp |
| 164 | When the user program terminates and all forwarded X11 and other |
| 165 | connections have been closed, the server sends command exit status to |
| 166 | the client, and both sides exit. |
| 167 | .Pp |
| 168 | .Nm |
| 169 | can be configured using command-line options or a configuration |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 170 | file. |
| 171 | Command-line options override values specified in the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 172 | configuration file. |
| 173 | .Pp |
Damien Miller | 6162d12 | 1999-11-21 13:23:52 +1100 | [diff] [blame] | 174 | .Nm |
| 175 | rereads its configuration file when it receives a hangup signal, |
Ben Lindstrom | 49a098d | 2001-03-05 06:55:18 +0000 | [diff] [blame] | 176 | .Dv SIGHUP , |
| 177 | by executing itself with the name it was started as, ie. |
| 178 | .Pa /usr/sbin/sshd . |
Damien Miller | 6162d12 | 1999-11-21 13:23:52 +1100 | [diff] [blame] | 179 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 180 | The options are as follows: |
| 181 | .Bl -tag -width Ds |
| 182 | .It Fl b Ar bits |
| 183 | Specifies the number of bits in the server key (default 768). |
| 184 | .Pp |
| 185 | .It Fl d |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 186 | Debug mode. |
| 187 | The server sends verbose debug output to the system |
| 188 | log, and does not put itself in the background. |
| 189 | The server also will not fork and will only process one connection. |
| 190 | This option is only intended for debugging for the server. |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 191 | Multiple -d options increases the debugging level. |
| 192 | Maximum is 3. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 193 | .It Fl f Ar configuration_file |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 194 | Specifies the name of the configuration file. |
| 195 | The default is |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 196 | .Pa /etc/sshd_config . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 197 | .Nm |
| 198 | refuses to start if there is no configuration file. |
| 199 | .It Fl g Ar login_grace_time |
| 200 | Gives the grace time for clients to authenticate themselves (default |
Kevin Steves | 9ce907c | 2001-01-07 11:53:40 +0000 | [diff] [blame] | 201 | 600 seconds). |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 202 | If the client fails to authenticate the user within |
| 203 | this many seconds, the server disconnects and exits. |
| 204 | A value of zero indicates no limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 205 | .It Fl h Ar host_key_file |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 206 | Specifies the file from which the host key is read (default |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 207 | .Pa /etc/ssh_host_key ) . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 208 | This option must be given if |
| 209 | .Nm |
| 210 | is not run as root (as the normal |
| 211 | host file is normally not readable by anyone but root). |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 212 | It is possible to have multiple host key files for |
| 213 | the different protocol versions. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 214 | .It Fl i |
| 215 | Specifies that |
| 216 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 217 | is being run from inetd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 218 | .Nm |
| 219 | is normally not run |
| 220 | 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] | 221 | respond to the client, and this may take tens of seconds. |
| 222 | 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] | 223 | However, with small key sizes (e.g., 512) using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 224 | .Nm |
| 225 | from inetd may |
| 226 | be feasible. |
| 227 | .It Fl k Ar key_gen_time |
| 228 | Specifies how often the server key is regenerated (default 3600 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 229 | seconds, or one hour). |
| 230 | The motivation for regenerating the key fairly |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 231 | often is that the key is not stored anywhere, and after about an hour, |
| 232 | it becomes impossible to recover the key for decrypting intercepted |
| 233 | communications even if the machine is cracked into or physically |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 234 | seized. |
| 235 | A value of zero indicates that the key will never be regenerated. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 236 | .It Fl p Ar port |
| 237 | Specifies the port on which the server listens for connections |
| 238 | (default 22). |
| 239 | .It Fl q |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 240 | Quiet mode. |
| 241 | Nothing is sent to the system log. |
| 242 | Normally the beginning, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 243 | authentication, and termination of each connection is logged. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 244 | .It Fl u Ar len |
| 245 | This option is used to specify the size of the field |
| 246 | in the |
| 247 | .Li utmp |
| 248 | structure that holds the remote host name. |
| 249 | If the resolved host name is longer than |
| 250 | .Ar len , |
| 251 | the dotted decimal value will be used instead. |
| 252 | This allows hosts with very long host names that |
| 253 | overflow this field to still be uniquely identified. |
| 254 | Specifying |
| 255 | .Fl u0 |
| 256 | indicates that only dotted decimal addresses |
| 257 | should be put into the |
| 258 | .Pa utmp |
| 259 | file. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 260 | .It Fl D |
| 261 | When this option is specified |
| 262 | .Nm |
| 263 | will not detach and does not become a daemon. |
| 264 | This allows easy monitoring of |
| 265 | .Nm sshd . |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 266 | .It Fl V Ar client_protocol_id |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 267 | SSH-2 compatibility mode. |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 268 | When this option is specified |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 269 | .Nm |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 270 | assumes the client has sent the supplied version string |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 271 | and skips the |
| 272 | Protocol Version Identification Exchange. |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 273 | This option is not intended to be called directly. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 274 | .It Fl 4 |
| 275 | Forces |
| 276 | .Nm |
| 277 | to use IPv4 addresses only. |
| 278 | .It Fl 6 |
| 279 | Forces |
| 280 | .Nm |
| 281 | to use IPv6 addresses only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 282 | .El |
| 283 | .Sh CONFIGURATION FILE |
| 284 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 285 | reads configuration data from |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 286 | .Pa /etc/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 287 | (or the file specified with |
| 288 | .Fl f |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 289 | on the command line). |
| 290 | The file contains keyword-value pairs, one per line. |
| 291 | Lines starting with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 292 | .Ql # |
| 293 | and empty lines are interpreted as comments. |
| 294 | .Pp |
| 295 | The following keywords are possible. |
| 296 | .Bl -tag -width Ds |
| 297 | .It Cm AFSTokenPassing |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 298 | Specifies whether an AFS token may be forwarded to the server. |
| 299 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 300 | .Dq yes . |
| 301 | .It Cm AllowGroups |
Ben Lindstrom | a1ebd89 | 2001-02-10 22:19:23 +0000 | [diff] [blame] | 302 | This keyword can be followed by a list of group names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 303 | by spaces. |
| 304 | If specified, login is allowed only for users whose primary |
Kevin Steves | 7b61cfa | 2001-01-14 19:11:00 +0000 | [diff] [blame] | 305 | group or supplementary group list matches one of the patterns. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 306 | .Ql \&* |
| 307 | and |
| 308 | .Ql ? |
| 309 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 310 | wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 311 | Only group names are valid; a numerical group ID isn't recognized. |
Kevin Steves | 7b61cfa | 2001-01-14 19:11:00 +0000 | [diff] [blame] | 312 | By default login is allowed regardless of the group list. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 313 | .Pp |
Damien Miller | 50a41ed | 2000-10-16 12:14:42 +1100 | [diff] [blame] | 314 | .It Cm AllowTcpForwarding |
| 315 | Specifies whether TCP forwarding is permitted. |
| 316 | The default is |
| 317 | .Dq yes . |
| 318 | Note that disabling TCP forwarding does not improve security unless |
| 319 | users are also denied shell access, as they can always install their |
| 320 | own forwarders. |
| 321 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 322 | .It Cm AllowUsers |
Ben Lindstrom | a1ebd89 | 2001-02-10 22:19:23 +0000 | [diff] [blame] | 323 | This keyword can be followed by a list of user names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 324 | by spaces. |
| 325 | If specified, login is allowed only for users names that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 326 | match one of the patterns. |
| 327 | .Ql \&* |
| 328 | and |
| 329 | .Ql ? |
| 330 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 331 | wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 332 | Only user names are valid; a numerical user ID isn't recognized. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 333 | By default login is allowed regardless of the user name. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 334 | .Pp |
Ben Lindstrom | 48bd7c1 | 2001-01-09 00:35:42 +0000 | [diff] [blame] | 335 | .It Cm Banner |
| 336 | In some jurisdictions, sending a warning message before authentication |
| 337 | may be relevant for getting legal protection. |
| 338 | The contents of the specified file are sent to the remote user before |
| 339 | authentication is allowed. |
| 340 | This option is only available for protocol version 2. |
| 341 | .Pp |
Ben Lindstrom | ff8b494 | 2001-03-06 01:00:03 +0000 | [diff] [blame] | 342 | .It Cm ChallengeResponseAuthentication |
| 343 | Specifies whether |
| 344 | challenge response |
| 345 | authentication is allowed. |
| 346 | Currently there is only support for |
| 347 | .Xr skey 1 |
| 348 | authentication. |
| 349 | The default is |
| 350 | .Dq yes . |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 351 | .It Cm Ciphers |
| 352 | Specifies the ciphers allowed for protocol version 2. |
| 353 | Multiple ciphers must be comma-separated. |
| 354 | The default is |
Ben Lindstrom | c78a187 | 2001-03-06 01:06:58 +0000 | [diff] [blame] | 355 | .Dq aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 356 | .It Cm CheckMail |
| 357 | Specifies whether |
| 358 | .Nm |
| 359 | should check for new mail for interactive logins. |
| 360 | The default is |
| 361 | .Dq no . |
| 362 | .It Cm DenyGroups |
| 363 | This keyword can be followed by a number of group names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 364 | by spaces. |
Kevin Steves | 7b61cfa | 2001-01-14 19:11:00 +0000 | [diff] [blame] | 365 | Users whose primary group or supplementary group list matches |
| 366 | one of the patterns aren't allowed to log in. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 367 | .Ql \&* |
| 368 | and |
| 369 | .Ql ? |
| 370 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 371 | wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 372 | Only group names are valid; a numerical group ID isn't recognized. |
Kevin Steves | 7b61cfa | 2001-01-14 19:11:00 +0000 | [diff] [blame] | 373 | By default login is allowed regardless of the group list. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 374 | .Pp |
| 375 | .It Cm DenyUsers |
| 376 | This keyword can be followed by a number of user names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 377 | by spaces. |
| 378 | Login is disallowed for user names that match one of the patterns. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 379 | .Ql \&* |
| 380 | and |
| 381 | .Ql ? |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 382 | can be used as wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 383 | Only user names are valid; a numerical user ID isn't recognized. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 384 | By default login is allowed regardless of the user name. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 385 | .It Cm GatewayPorts |
| 386 | Specifies whether remote hosts are allowed to connect to ports |
| 387 | forwarded for the client. |
| 388 | The argument must be |
| 389 | .Dq yes |
| 390 | or |
| 391 | .Dq no . |
| 392 | The default is |
| 393 | .Dq no . |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 394 | .It Cm HostKey |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 395 | Specifies the file containing the private host keys (default |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 396 | .Pa /etc/ssh_host_key ) |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 397 | used by SSH protocol versions 1 and 2. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 398 | Note that |
| 399 | .Nm |
Ben Lindstrom | 226cfa0 | 2001-01-22 05:34:40 +0000 | [diff] [blame] | 400 | will refuse to use a file if it is group/world-accessible. |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 401 | It is possible to have multiple host key files. |
| 402 | .Dq rsa1 |
| 403 | keys are used for version 1 and |
| 404 | .Dq dsa |
| 405 | or |
| 406 | .Dq rsa |
| 407 | are used for version 2 of the SSH protocol. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 408 | .It Cm IgnoreRhosts |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 409 | Specifies that |
| 410 | .Pa .rhosts |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 411 | and |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 412 | .Pa .shosts |
| 413 | files will not be used in authentication. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 414 | .Pa /etc/hosts.equiv |
| 415 | and |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 416 | .Pa /etc/shosts.equiv |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 417 | are still used. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 418 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 419 | .Dq yes . |
Damien Miller | 3226509 | 1999-11-12 11:33:04 +1100 | [diff] [blame] | 420 | .It Cm IgnoreUserKnownHosts |
| 421 | Specifies whether |
| 422 | .Nm |
| 423 | should ignore the user's |
| 424 | .Pa $HOME/.ssh/known_hosts |
| 425 | during |
| 426 | .Cm RhostsRSAAuthentication . |
| 427 | The default is |
| 428 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 429 | .It Cm KeepAlive |
| 430 | Specifies whether the system should send keepalive messages to the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 431 | other side. |
| 432 | If they are sent, death of the connection or crash of one |
| 433 | of the machines will be properly noticed. |
| 434 | However, this means that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 435 | connections will die if the route is down temporarily, and some people |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 436 | find it annoying. |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 437 | On the other hand, if keepalives are not sent, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 438 | sessions may hang indefinitely on the server, leaving |
| 439 | .Dq ghost |
| 440 | users and consuming server resources. |
| 441 | .Pp |
| 442 | The default is |
| 443 | .Dq yes |
| 444 | (to send keepalives), and the server will notice |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 445 | if the network goes down or the client host reboots. |
| 446 | This avoids infinitely hanging sessions. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 447 | .Pp |
| 448 | To disable keepalives, the value should be set to |
| 449 | .Dq no |
| 450 | in both the server and the client configuration files. |
| 451 | .It Cm KerberosAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 452 | Specifies whether Kerberos authentication is allowed. |
| 453 | This can be in the form of a Kerberos ticket, or if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 454 | .Cm PasswordAuthentication |
| 455 | is yes, the password provided by the user will be validated through |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 456 | the Kerberos KDC. |
| 457 | To use this option, the server needs a |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 458 | Kerberos servtab which allows the verification of the KDC's identity. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 459 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 460 | .Dq yes . |
| 461 | .It Cm KerberosOrLocalPasswd |
| 462 | If set then if password authentication through Kerberos fails then |
| 463 | the password will be validated via any additional local mechanism |
| 464 | such as |
Damien Miller | 62cee00 | 2000-09-23 17:15:56 +1100 | [diff] [blame] | 465 | .Pa /etc/passwd . |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 466 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 467 | .Dq yes . |
| 468 | .It Cm KerberosTgtPassing |
| 469 | Specifies whether a Kerberos TGT may be forwarded to the server. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 470 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 471 | .Dq no , |
| 472 | as this only works when the Kerberos KDC is actually an AFS kaserver. |
| 473 | .It Cm KerberosTicketCleanup |
| 474 | Specifies whether to automatically destroy the user's ticket cache |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 475 | file on logout. |
| 476 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 477 | .Dq yes . |
| 478 | .It Cm KeyRegenerationInterval |
| 479 | The server key is automatically regenerated after this many seconds |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 480 | (if it has been used). |
| 481 | The purpose of regeneration is to prevent |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 482 | decrypting captured sessions by later breaking into the machine and |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 483 | stealing the keys. |
| 484 | The key is never stored anywhere. |
| 485 | If the value is 0, the key is never regenerated. |
| 486 | The default is 3600 (seconds). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 487 | .It Cm ListenAddress |
| 488 | Specifies what local address |
| 489 | .Nm |
| 490 | should listen on. |
| 491 | The default is to listen to all local addresses. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 492 | Multiple options of this type are permitted. |
| 493 | Additionally, the |
| 494 | .Cm Ports |
| 495 | options must precede this option. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 496 | .It Cm LoginGraceTime |
| 497 | The server disconnects after this time if the user has not |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 498 | successfully logged in. |
| 499 | If the value is 0, there is no time limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 500 | The default is 600 (seconds). |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 501 | .It Cm LogLevel |
| 502 | Gives the verbosity level that is used when logging messages from |
| 503 | .Nm sshd . |
| 504 | The possible values are: |
Ben Lindstrom | db65e8f | 2001-01-19 04:26:52 +0000 | [diff] [blame] | 505 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
| 506 | The default is INFO. |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 507 | Logging with level DEBUG violates the privacy of users |
| 508 | and is not recommended. |
Ben Lindstrom | 06b33aa | 2001-02-15 03:01:59 +0000 | [diff] [blame] | 509 | .It Cm MACs |
| 510 | Specifies the available MAC (message authentication code) algorithms. |
| 511 | The MAC algorithm is used in protocol version 2 |
| 512 | for data integrity protection. |
| 513 | Multiple algorithms must be comma-separated. |
| 514 | The default is |
| 515 | .Pp |
| 516 | .Bd -literal |
Ben Lindstrom | c78a187 | 2001-03-06 01:06:58 +0000 | [diff] [blame] | 517 | ``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com, |
Ben Lindstrom | 06b33aa | 2001-02-15 03:01:59 +0000 | [diff] [blame] | 518 | hmac-sha1-96,hmac-md5-96'' |
| 519 | .Ed |
Damien Miller | 3702396 | 2000-07-11 17:31:38 +1000 | [diff] [blame] | 520 | .It Cm MaxStartups |
| 521 | Specifies the maximum number of concurrent unauthenticated connections to the |
| 522 | .Nm |
| 523 | daemon. |
| 524 | Additional connections will be dropped until authentication succeeds or the |
| 525 | .Cm LoginGraceTime |
| 526 | expires for a connection. |
| 527 | The default is 10. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 528 | .Pp |
| 529 | Alternatively, random early drop can be enabled by specifying |
| 530 | the three colon separated values |
| 531 | .Dq start:rate:full |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 532 | (e.g., "10:30:60"). |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 533 | .Nm |
Ben Lindstrom | a733350 | 2001-01-29 08:44:03 +0000 | [diff] [blame] | 534 | will refuse connection attempts with a probability of |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 535 | .Dq rate/100 |
| 536 | (30%) |
| 537 | if there are currently |
| 538 | .Dq start |
| 539 | (10) |
| 540 | unauthenticated connections. |
Ben Lindstrom | a733350 | 2001-01-29 08:44:03 +0000 | [diff] [blame] | 541 | The probability increases linearly and all connection attempts |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 542 | are refused if the number of unauthenticated connections reaches |
| 543 | .Dq full |
| 544 | (60). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 545 | .It Cm PasswordAuthentication |
| 546 | Specifies whether password authentication is allowed. |
| 547 | The default is |
| 548 | .Dq yes . |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 549 | Note that this option applies to both protocol versions 1 and 2. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 550 | .It Cm PermitEmptyPasswords |
| 551 | When password authentication is allowed, it specifies whether the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 552 | server allows login to accounts with empty password strings. |
| 553 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 554 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 555 | .It Cm PermitRootLogin |
Ben Lindstrom | 323c98f | 2001-03-05 07:40:40 +0000 | [diff] [blame] | 556 | Specifies whether root can login using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 557 | .Xr ssh 1 . |
| 558 | The argument must be |
| 559 | .Dq yes , |
Ben Lindstrom | d8a9021 | 2001-02-15 03:08:27 +0000 | [diff] [blame] | 560 | .Dq without-password , |
| 561 | .Dq forced-commands-only |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 562 | or |
| 563 | .Dq no . |
| 564 | The default is |
| 565 | .Dq yes . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 566 | .Pp |
Ben Lindstrom | d8a9021 | 2001-02-15 03:08:27 +0000 | [diff] [blame] | 567 | If this option is set to |
| 568 | .Dq without-password |
| 569 | password authentication is disabled for root. |
| 570 | .Pp |
| 571 | If this option is set to |
| 572 | .Dq forced-commands-only |
| 573 | root login with public key authentication will be allowed, |
| 574 | but only if the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 575 | .Ar command |
Ben Lindstrom | d8a9021 | 2001-02-15 03:08:27 +0000 | [diff] [blame] | 576 | option has been specified |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 577 | (which may be useful for taking remote backups even if root login is |
Ben Lindstrom | d8a9021 | 2001-02-15 03:08:27 +0000 | [diff] [blame] | 578 | normally not allowed). All other authentication methods are disabled |
| 579 | for root. |
Ben Lindstrom | 323c98f | 2001-03-05 07:40:40 +0000 | [diff] [blame] | 580 | .Pp |
| 581 | If this option is set to |
| 582 | .Dq no |
| 583 | root is not allowed to login. |
Damien Miller | 6f83b8e | 2000-05-02 09:23:45 +1000 | [diff] [blame] | 584 | .It Cm PidFile |
| 585 | Specifies the file that contains the process identifier of the |
| 586 | .Nm |
| 587 | daemon. |
| 588 | The default is |
| 589 | .Pa /var/run/sshd.pid . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 590 | .It Cm Port |
| 591 | Specifies the port number that |
| 592 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 593 | listens on. |
| 594 | The default is 22. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 595 | Multiple options of this type are permitted. |
Ben Lindstrom | 7bfff36 | 2001-03-26 05:45:53 +0000 | [diff] [blame^] | 596 | .It Cm PrintLastLog |
| 597 | Specifies whether |
| 598 | .Nm |
| 599 | should print the date and time when the user last logged in. |
| 600 | The default is |
| 601 | .Dq yes . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 602 | .It Cm PrintMotd |
| 603 | Specifies whether |
| 604 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 605 | should print |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 606 | .Pa /etc/motd |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 607 | when a user logs in interactively. |
| 608 | (On some systems it is also printed by the shell, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 609 | .Pa /etc/profile , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 610 | or equivalent.) |
| 611 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 612 | .Dq yes . |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 613 | .It Cm Protocol |
| 614 | Specifies the protocol versions |
| 615 | .Nm |
| 616 | should support. |
| 617 | The possible values are |
| 618 | .Dq 1 |
| 619 | and |
| 620 | .Dq 2 . |
| 621 | Multiple versions must be comma-separated. |
| 622 | The default is |
| 623 | .Dq 1 . |
Ben Lindstrom | ff8b494 | 2001-03-06 01:00:03 +0000 | [diff] [blame] | 624 | .It Cm PubkeyAuthentication |
| 625 | Specifies whether public key authentication is allowed. |
| 626 | The default is |
| 627 | .Dq yes . |
| 628 | Note that this option applies to protocol version 2 only. |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 629 | .It Cm ReverseMappingCheck |
| 630 | Specifies whether |
| 631 | .Nm |
| 632 | should try to verify the remote host name and check that |
| 633 | the resolved host name for the remote IP address maps back to the |
| 634 | very same IP address. |
| 635 | The default is |
| 636 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 637 | .It Cm RhostsAuthentication |
| 638 | Specifies whether authentication using rhosts or /etc/hosts.equiv |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 639 | files is sufficient. |
| 640 | Normally, this method should not be permitted because it is insecure. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 641 | .Cm RhostsRSAAuthentication |
| 642 | should be used |
| 643 | instead, because it performs RSA-based host authentication in addition |
| 644 | to normal rhosts or /etc/hosts.equiv authentication. |
| 645 | The default is |
| 646 | .Dq no . |
| 647 | .It Cm RhostsRSAAuthentication |
| 648 | Specifies whether rhosts or /etc/hosts.equiv authentication together |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 649 | with successful RSA host authentication is allowed. |
| 650 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 651 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 652 | .It Cm RSAAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 653 | Specifies whether pure RSA authentication is allowed. |
| 654 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 655 | .Dq yes . |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 656 | Note that this option applies to protocol version 1 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 657 | .It Cm ServerKeyBits |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 658 | Defines the number of bits in the server key. |
| 659 | The minimum value is 512, and the default is 768. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 660 | .It Cm StrictModes |
| 661 | Specifies whether |
| 662 | .Nm |
| 663 | should check file modes and ownership of the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 664 | user's files and home directory before accepting login. |
| 665 | This is normally desirable because novices sometimes accidentally leave their |
| 666 | directory or files world-writable. |
| 667 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 668 | .Dq yes . |
Damien Miller | f6d9e22 | 2000-06-18 14:50:44 +1000 | [diff] [blame] | 669 | .It Cm Subsystem |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 670 | Configures an external subsystem (e.g., file transfer daemon). |
| 671 | Arguments should be a subsystem name and a command to execute upon subsystem |
| 672 | request. |
Damien Miller | 7b28dc5 | 2000-09-05 13:34:53 +1100 | [diff] [blame] | 673 | The command |
| 674 | .Xr sftp-server 8 |
| 675 | implements the |
| 676 | .Dq sftp |
| 677 | file transfer subsystem. |
Damien Miller | f6d9e22 | 2000-06-18 14:50:44 +1000 | [diff] [blame] | 678 | By default no subsystems are defined. |
| 679 | Note that this option applies to protocol version 2 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 680 | .It Cm SyslogFacility |
| 681 | Gives the facility code that is used when logging messages from |
| 682 | .Nm sshd . |
| 683 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 684 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
| 685 | The default is AUTH. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 686 | .It Cm UseLogin |
| 687 | Specifies whether |
| 688 | .Xr login 1 |
Damien Miller | d3a1857 | 2000-06-07 19:55:44 +1000 | [diff] [blame] | 689 | is used for interactive login sessions. |
| 690 | Note that |
| 691 | .Xr login 1 |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 692 | is never used for remote command execution. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 693 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 694 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 695 | .It Cm X11DisplayOffset |
| 696 | Specifies the first display number available for |
| 697 | .Nm sshd Ns 's |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 698 | X11 forwarding. |
| 699 | This prevents |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 700 | .Nm |
| 701 | from interfering with real X11 servers. |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 702 | The default is 10. |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 703 | .It Cm X11Forwarding |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 704 | Specifies whether X11 forwarding is permitted. |
| 705 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 706 | .Dq no . |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 707 | Note that disabling X11 forwarding does not improve security in any |
| 708 | way, as users can always install their own forwarders. |
Damien Miller | d3a1857 | 2000-06-07 19:55:44 +1000 | [diff] [blame] | 709 | .It Cm XAuthLocation |
| 710 | Specifies the location of the |
| 711 | .Xr xauth 1 |
| 712 | program. |
| 713 | The default is |
| 714 | .Pa /usr/X11R6/bin/xauth . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 715 | .El |
| 716 | .Sh LOGIN PROCESS |
| 717 | When a user successfully logs in, |
| 718 | .Nm |
| 719 | does the following: |
| 720 | .Bl -enum -offset indent |
| 721 | .It |
| 722 | 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] | 723 | prints last login time and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 724 | .Pa /etc/motd |
| 725 | (unless prevented in the configuration file or by |
| 726 | .Pa $HOME/.hushlogin ; |
| 727 | see the |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 728 | .Sx FILES |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 729 | section). |
| 730 | .It |
| 731 | If the login is on a tty, records login time. |
| 732 | .It |
| 733 | Checks |
| 734 | .Pa /etc/nologin ; |
| 735 | if it exists, prints contents and quits |
| 736 | (unless root). |
| 737 | .It |
| 738 | Changes to run with normal user privileges. |
| 739 | .It |
| 740 | Sets up basic environment. |
| 741 | .It |
| 742 | Reads |
| 743 | .Pa $HOME/.ssh/environment |
| 744 | if it exists. |
| 745 | .It |
| 746 | Changes to user's home directory. |
| 747 | .It |
| 748 | If |
| 749 | .Pa $HOME/.ssh/rc |
| 750 | exists, runs it; else if |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 751 | .Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 752 | exists, runs |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 753 | it; otherwise runs xauth. |
| 754 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 755 | .Dq rc |
| 756 | files are given the X11 |
| 757 | authentication protocol and cookie in standard input. |
| 758 | .It |
| 759 | Runs user's shell or command. |
| 760 | .El |
| 761 | .Sh AUTHORIZED_KEYS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 762 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 763 | .Pa $HOME/.ssh/authorized_keys |
| 764 | file lists the RSA keys that are |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 765 | permitted for RSA authentication in SSH protocols 1.3 and 1.5 |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 766 | Similarly, the |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 767 | .Pa $HOME/.ssh/authorized_keys2 |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 768 | file lists the DSA and RSA keys that are |
| 769 | permitted for public key authentication (PubkeyAuthentication) |
| 770 | in SSH protocol 2.0. |
| 771 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 772 | Each line of the file contains one |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 773 | key (empty lines and lines starting with a |
| 774 | .Ql # |
| 775 | are ignored as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 776 | comments). |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 777 | Each RSA public key consists of the following fields, separated by |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 778 | spaces: options, bits, exponent, modulus, comment. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 779 | Each protocol version 2 public key consists of: |
| 780 | options, keytype, base64 encoded key, comment. |
| 781 | The options fields |
| 782 | are optional; its presence is determined by whether the line starts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 783 | 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] | 784 | The bits, exponent, modulus and comment fields give the RSA key for |
| 785 | protocol version 1; the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 786 | comment field is not used for anything (but may be convenient for the |
| 787 | user to identify the key). |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 788 | For protocol version 2 the keytype is |
| 789 | .Dq ssh-dss |
| 790 | or |
| 791 | .Dq ssh-rsa . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 792 | .Pp |
| 793 | Note that lines in this file are usually several hundred bytes long |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 794 | (because of the size of the RSA key modulus). |
| 795 | You don't want to type them in; instead, copy the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 796 | .Pa identity.pub |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 797 | or the |
| 798 | .Pa id_dsa.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 799 | file and edit it. |
| 800 | .Pp |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 801 | The options (if present) consist of comma-separated option |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 802 | specifications. |
| 803 | No spaces are permitted, except within double quotes. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 804 | The following option specifications are supported: |
| 805 | .Bl -tag -width Ds |
| 806 | .It Cm from="pattern-list" |
| 807 | Specifies that in addition to RSA authentication, the canonical name |
| 808 | 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] | 809 | patterns |
| 810 | .Pf ( Ql * |
| 811 | and |
| 812 | .Ql ? |
| 813 | serve as wildcards). |
| 814 | The list may also contain |
| 815 | patterns negated by prefixing them with |
| 816 | .Ql ! ; |
| 817 | if the canonical host name matches a negated pattern, the key is not accepted. |
| 818 | The purpose |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 819 | of this option is to optionally increase security: RSA authentication |
| 820 | by itself does not trust the network or name servers or anything (but |
| 821 | the key); however, if somebody somehow steals the key, the key |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 822 | permits an intruder to log in from anywhere in the world. |
| 823 | This additional option makes using a stolen key more difficult (name |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 824 | servers and/or routers would have to be compromised in addition to |
| 825 | just the key). |
| 826 | .It Cm command="command" |
| 827 | Specifies that the command is executed whenever this key is used for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 828 | authentication. |
| 829 | The command supplied by the user (if any) is ignored. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 830 | The command is run on a pty if the connection requests a pty; |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 831 | otherwise it is run without a tty. |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 832 | Note that if you want a 8-bit clean channel, |
| 833 | you must not request a pty or should specify |
| 834 | .Cm no-pty . |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 835 | A quote may be included in the command by quoting it with a backslash. |
| 836 | This option might be useful |
| 837 | to restrict certain RSA keys to perform just a specific operation. |
| 838 | 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] | 839 | Note that the client may specify TCP/IP and/or X11 |
| 840 | forwarding unless they are explicitly prohibited. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 841 | .It Cm environment="NAME=value" |
| 842 | Specifies that the string is to be added to the environment when |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 843 | logging in using this key. |
| 844 | Environment variables set this way |
| 845 | override other default environment values. |
| 846 | Multiple options of this type are permitted. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 847 | .It Cm no-port-forwarding |
| 848 | Forbids TCP/IP forwarding when this key is used for authentication. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 849 | Any port forward requests by the client will return an error. |
| 850 | This might be used, e.g., in connection with the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 851 | .Cm command |
| 852 | option. |
| 853 | .It Cm no-X11-forwarding |
| 854 | Forbids X11 forwarding when this key is used for authentication. |
| 855 | Any X11 forward requests by the client will return an error. |
| 856 | .It Cm no-agent-forwarding |
| 857 | Forbids authentication agent forwarding when this key is used for |
| 858 | authentication. |
| 859 | .It Cm no-pty |
| 860 | Prevents tty allocation (a request to allocate a pty will fail). |
Damien Miller | a243fde | 2001-03-19 23:16:08 +1100 | [diff] [blame] | 861 | .It Cm permitopen="host:port" |
| 862 | Limit local |
| 863 | .Li ``ssh -L'' |
| 864 | port-forwading such that it may only connect to the specified host and |
| 865 | port. Multiple |
| 866 | .Cm permitopen |
| 867 | options may be applied seperated by commas. No pattern matching is |
| 868 | performed on the specified hostnames, they must be literal domains or |
| 869 | addresses. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 870 | .El |
| 871 | .Ss Examples |
| 872 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar |
| 873 | .Pp |
| 874 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula |
| 875 | .Pp |
| 876 | 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] | 877 | .Pp |
| 878 | 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] | 879 | .Sh SSH_KNOWN_HOSTS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 880 | The |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 881 | .Pa /etc/ssh_known_hosts , |
| 882 | .Pa /etc/ssh_known_hosts2 , |
| 883 | .Pa $HOME/.ssh/known_hosts , |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 884 | and |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 885 | .Pa $HOME/.ssh/known_hosts2 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 886 | files contain host public keys for all known hosts. |
| 887 | The global file should |
| 888 | be prepared by the administrator (optional), and the per-user file is |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 889 | maintained automatically: whenever the user connects from an unknown host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 890 | its key is added to the per-user file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 891 | .Pp |
| 892 | Each line in these files contains the following fields: hostnames, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 893 | bits, exponent, modulus, comment. |
| 894 | The fields are separated by spaces. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 895 | .Pp |
| 896 | Hostnames is a comma-separated list of patterns ('*' and '?' act as |
| 897 | wildcards); each pattern in turn is matched against the canonical host |
| 898 | name (when authenticating a client) or against the user-supplied |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 899 | name (when authenticating a server). |
| 900 | A pattern may also be preceded by |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 901 | .Ql ! |
| 902 | to indicate negation: if the host name matches a negated |
| 903 | pattern, it is not accepted (by that line) even if it matched another |
| 904 | pattern on the line. |
| 905 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 906 | 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] | 907 | can be obtained, e.g., from |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 908 | .Pa /etc/ssh_host_key.pub . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 909 | The optional comment field continues to the end of the line, and is not used. |
| 910 | .Pp |
| 911 | Lines starting with |
| 912 | .Ql # |
| 913 | and empty lines are ignored as comments. |
| 914 | .Pp |
| 915 | When performing host authentication, authentication is accepted if any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 916 | matching line has the proper key. |
| 917 | It is thus permissible (but not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 918 | recommended) to have several lines or different host keys for the same |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 919 | names. |
| 920 | This will inevitably happen when short forms of host names |
| 921 | from different domains are put in the file. |
| 922 | It is possible |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 923 | that the files contain conflicting information; authentication is |
| 924 | accepted if valid information can be found from either file. |
| 925 | .Pp |
| 926 | Note that the lines in these files are typically hundreds of characters |
| 927 | long, and you definitely don't want to type in the host keys by hand. |
| 928 | Rather, generate them by a script |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 929 | or by taking |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 930 | .Pa /etc/ssh_host_key.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 931 | and adding the host names at the front. |
| 932 | .Ss Examples |
| 933 | closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi |
| 934 | .Sh FILES |
| 935 | .Bl -tag -width Ds |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 936 | .It Pa /etc/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 937 | Contains configuration data for |
| 938 | .Nm sshd . |
| 939 | This file should be writable by root only, but it is recommended |
| 940 | (though not necessary) that it be world-readable. |
Ben Lindstrom | d7f5b51 | 2001-03-05 06:57:23 +0000 | [diff] [blame] | 941 | .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key |
| 942 | These three files contain the private parts of the |
| 943 | (SSH1, SSH2 DSA, and SSH2 RSA) host keys. |
| 944 | 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] | 945 | accessible to others. |
| 946 | Note that |
| 947 | .Nm |
| 948 | does not start if this file is group/world-accessible. |
Ben Lindstrom | d7f5b51 | 2001-03-05 06:57:23 +0000 | [diff] [blame] | 949 | .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub |
| 950 | There three files contain the public parts of the |
| 951 | (SSH1, SSH2 DSA, and SSH2 RSA) host keys. |
| 952 | These files should be world-readable but writable only by |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 953 | root. |
Ben Lindstrom | d7f5b51 | 2001-03-05 06:57:23 +0000 | [diff] [blame] | 954 | Their contents should match the respective private parts. |
| 955 | These files are not |
| 956 | really used for anything; they are provided for the convenience of |
| 957 | the user so their contents can be copied to known hosts files. |
| 958 | These files are created using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 959 | .Xr ssh-keygen 1 . |
Damien Miller | e39cacc | 2000-11-29 12:18:44 +1100 | [diff] [blame] | 960 | .It Pa /etc/primes |
| 961 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 962 | .It Pa /var/run/sshd.pid |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 963 | Contains the process ID of the |
| 964 | .Nm |
| 965 | listening for connections (if there are several daemons running |
| 966 | concurrently for different ports, this contains the pid of the one |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 967 | started last). |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 968 | 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] | 969 | .It Pa $HOME/.ssh/authorized_keys |
| 970 | Lists the RSA keys that can be used to log into the user's account. |
| 971 | This file must be readable by root (which may on some machines imply |
| 972 | it being world-readable if the user's home directory resides on an NFS |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 973 | volume). |
| 974 | It is recommended that it not be accessible by others. |
| 975 | The format of this file is described above. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 976 | Users will place the contents of their |
| 977 | .Pa identity.pub |
| 978 | files into this file, as described in |
| 979 | .Xr ssh-keygen 1 . |
| 980 | .It Pa $HOME/.ssh/authorized_keys2 |
| 981 | Lists the DSA keys that can be used to log into the user's account. |
| 982 | This file must be readable by root (which may on some machines imply |
| 983 | it being world-readable if the user's home directory resides on an NFS |
| 984 | volume). |
| 985 | It is recommended that it not be accessible by others. |
| 986 | The format of this file is described above. |
| 987 | Users will place the contents of their |
| 988 | .Pa id_dsa.pub |
| 989 | files into this file, as described in |
| 990 | .Xr ssh-keygen 1 . |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 991 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 992 | These files are consulted when using rhosts with RSA host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 993 | authentication to check the public key of the host. |
| 994 | 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] | 995 | The client uses the same files |
Ben Lindstrom | ebd888d | 2001-03-05 05:49:29 +0000 | [diff] [blame] | 996 | to verify that it is connecting to the correct remote host. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 997 | These files should be writable only by root/the owner. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 998 | .Pa /etc/ssh_known_hosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 999 | should be world-readable, and |
| 1000 | .Pa $HOME/.ssh/known_hosts |
| 1001 | can but need not be world-readable. |
| 1002 | .It Pa /etc/nologin |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1003 | If this file exists, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1004 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1005 | refuses to let anyone except root log in. |
| 1006 | The contents of the file |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1007 | 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] | 1008 | refused. |
| 1009 | The file should be world-readable. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1010 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
| 1011 | If compiled with |
| 1012 | .Sy LIBWRAP |
| 1013 | support, tcp-wrappers access controls may be defined here as described in |
| 1014 | .Xr hosts_access 5 . |
| 1015 | .It Pa $HOME/.rhosts |
| 1016 | This file contains host-username pairs, separated by a space, one per |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1017 | line. |
| 1018 | The given user on the corresponding host is permitted to log in |
| 1019 | without password. |
| 1020 | The same file is used by rlogind and rshd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1021 | The file must |
| 1022 | be writable only by the user; it is recommended that it not be |
| 1023 | accessible by others. |
| 1024 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1025 | If is also possible to use netgroups in the file. |
| 1026 | Either host or user |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1027 | name may be of the form +@groupname to specify all hosts or all users |
| 1028 | in the group. |
| 1029 | .It Pa $HOME/.shosts |
| 1030 | For ssh, |
| 1031 | this file is exactly the same as for |
| 1032 | .Pa .rhosts . |
| 1033 | However, this file is |
| 1034 | 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] | 1035 | .It Pa /etc/hosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1036 | This file is used during |
| 1037 | .Pa .rhosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1038 | authentication. |
| 1039 | In the simplest form, this file contains host names, one per line. |
| 1040 | Users on |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1041 | those hosts are permitted to log in without a password, provided they |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1042 | have the same user name on both machines. |
| 1043 | The host name may also be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1044 | followed by a user name; such users are permitted to log in as |
| 1045 | .Em any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1046 | user on this machine (except root). |
| 1047 | Additionally, the syntax |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1048 | .Dq +@group |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1049 | can be used to specify netgroups. |
| 1050 | Negated entries start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1051 | .Ql \&- . |
| 1052 | .Pp |
| 1053 | If the client host/user is successfully matched in this file, login is |
| 1054 | automatically permitted provided the client and server user names are the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1055 | same. |
| 1056 | Additionally, successful RSA host authentication is normally required. |
| 1057 | This file must be writable only by root; it is recommended |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1058 | that it be world-readable. |
| 1059 | .Pp |
| 1060 | .Sy "Warning: It is almost never a good idea to use user names in" |
| 1061 | .Pa hosts.equiv . |
| 1062 | Beware that it really means that the named user(s) can log in as |
| 1063 | .Em anybody , |
| 1064 | which includes bin, daemon, adm, and other accounts that own critical |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1065 | binaries and directories. |
| 1066 | Using a user name practically grants the user root access. |
| 1067 | The only valid use for user names that I can think |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1068 | of is in negative entries. |
| 1069 | .Pp |
| 1070 | Note that this warning also applies to rsh/rlogin. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1071 | .It Pa /etc/shosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1072 | This is processed exactly as |
| 1073 | .Pa /etc/hosts.equiv . |
| 1074 | However, this file may be useful in environments that want to run both |
| 1075 | rsh/rlogin and ssh. |
| 1076 | .It Pa $HOME/.ssh/environment |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1077 | This file is read into the environment at login (if it exists). |
| 1078 | It can only contain empty lines, comment lines (that start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1079 | .Ql # ) , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1080 | and assignment lines of the form name=value. |
| 1081 | The file should be writable |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1082 | only by the user; it need not be readable by anyone else. |
| 1083 | .It Pa $HOME/.ssh/rc |
| 1084 | 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] | 1085 | environment files but before starting the user's shell or command. |
| 1086 | If X11 spoofing is in use, this will receive the "proto cookie" pair in |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1087 | standard input (and |
| 1088 | .Ev DISPLAY |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1089 | in environment). |
| 1090 | This must call |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1091 | .Xr xauth 1 |
| 1092 | in that case. |
| 1093 | .Pp |
| 1094 | The primary purpose of this file is to run any initialization routines |
| 1095 | which may be needed before the user's home directory becomes |
| 1096 | accessible; AFS is a particular example of such an environment. |
| 1097 | .Pp |
| 1098 | This file will probably contain some initialization code followed by |
| 1099 | something similar to: "if read proto cookie; then echo add $DISPLAY |
| 1100 | $proto $cookie | xauth -q -; fi". |
| 1101 | .Pp |
| 1102 | If this file does not exist, |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1103 | .Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1104 | is run, and if that |
| 1105 | does not exist either, xauth is used to store the cookie. |
| 1106 | .Pp |
| 1107 | This file should be writable only by the user, and need not be |
| 1108 | readable by anyone else. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1109 | .It Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1110 | Like |
| 1111 | .Pa $HOME/.ssh/rc . |
| 1112 | This can be used to specify |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1113 | machine-specific login-time initializations globally. |
| 1114 | 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] | 1115 | .El |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 1116 | .Sh AUTHORS |
Ben Lindstrom | 8eec2c8 | 2001-01-29 08:39:16 +0000 | [diff] [blame] | 1117 | OpenSSH is a derivative of the original and free |
| 1118 | ssh 1.2.12 release by Tatu Ylonen. |
| 1119 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, |
| 1120 | Theo de Raadt and Dug Song |
| 1121 | removed many bugs, re-added newer features and |
| 1122 | created OpenSSH. |
| 1123 | Markus Friedl contributed the support for SSH |
| 1124 | protocol versions 1.5 and 2.0. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1125 | .Sh SEE ALSO |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1126 | .Xr scp 1 , |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 1127 | .Xr sftp 1 , |
Damien Miller | 7b28dc5 | 2000-09-05 13:34:53 +1100 | [diff] [blame] | 1128 | .Xr sftp-server 8 , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1129 | .Xr ssh 1 , |
| 1130 | .Xr ssh-add 1 , |
| 1131 | .Xr ssh-agent 1 , |
| 1132 | .Xr ssh-keygen 1 , |
Damien Miller | b38eff8 | 2000-04-01 11:09:21 +1000 | [diff] [blame] | 1133 | .Xr rlogin 1 , |
| 1134 | .Xr rsh 1 |