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 | 323c98f | 2001-03-05 07:40:40 +0000 | [diff] [blame^] | 37 | .\" $OpenBSD: sshd.8,v 1.100 2001/03/04 11:04:41 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 | 53992c7 | 2001-03-05 04:47:55 +0000 | [diff] [blame] | 43 | .Nd OpenSSH secure shell 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 |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 57 | (Secure Shell 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. |
| 137 | The rest of the session is encrypted |
| 138 | using a symmetric cipher, currently |
| 139 | Blowfish, 3DES or CAST128 in CBC mode or Arcfour. |
| 140 | The client selects the encryption algorithm |
| 141 | to use from those offered by the server. |
| 142 | Additionally, session integrity is provided |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 143 | through a cryptographic message authentication code |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 144 | (hmac-sha1 or hmac-md5). |
| 145 | .Pp |
| 146 | Protocol version 2 provides a public key based |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 147 | user authentication method (PubkeyAuthentication) |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 148 | and conventional password authentication. |
| 149 | .Pp |
| 150 | .Ss Command execution and data forwarding |
| 151 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 152 | If the client successfully authenticates itself, a dialog for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 153 | preparing the session is entered. |
| 154 | At this time the client may request |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 155 | things like allocating a pseudo-tty, forwarding X11 connections, |
| 156 | forwarding TCP/IP connections, or forwarding the authentication agent |
| 157 | connection over the secure channel. |
| 158 | .Pp |
| 159 | Finally, the client either requests a shell or execution of a command. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 160 | The sides then enter session mode. |
| 161 | In this mode, either side may send |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 162 | data at any time, and such data is forwarded to/from the shell or |
| 163 | command on the server side, and the user terminal in the client side. |
| 164 | .Pp |
| 165 | When the user program terminates and all forwarded X11 and other |
| 166 | connections have been closed, the server sends command exit status to |
| 167 | the client, and both sides exit. |
| 168 | .Pp |
| 169 | .Nm |
| 170 | can be configured using command-line options or a configuration |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 171 | file. |
| 172 | Command-line options override values specified in the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 173 | configuration file. |
| 174 | .Pp |
Damien Miller | 6162d12 | 1999-11-21 13:23:52 +1100 | [diff] [blame] | 175 | .Nm |
| 176 | rereads its configuration file when it receives a hangup signal, |
Ben Lindstrom | 49a098d | 2001-03-05 06:55:18 +0000 | [diff] [blame] | 177 | .Dv SIGHUP , |
| 178 | by executing itself with the name it was started as, ie. |
| 179 | .Pa /usr/sbin/sshd . |
Damien Miller | 6162d12 | 1999-11-21 13:23:52 +1100 | [diff] [blame] | 180 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 181 | The options are as follows: |
| 182 | .Bl -tag -width Ds |
| 183 | .It Fl b Ar bits |
| 184 | Specifies the number of bits in the server key (default 768). |
| 185 | .Pp |
| 186 | .It Fl d |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 187 | Debug mode. |
| 188 | The server sends verbose debug output to the system |
| 189 | log, and does not put itself in the background. |
| 190 | The server also will not fork and will only process one connection. |
| 191 | This option is only intended for debugging for the server. |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 192 | Multiple -d options increases the debugging level. |
| 193 | Maximum is 3. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 194 | .It Fl f Ar configuration_file |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 195 | Specifies the name of the configuration file. |
| 196 | The default is |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 197 | .Pa /etc/sshd_config . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 198 | .Nm |
| 199 | refuses to start if there is no configuration file. |
| 200 | .It Fl g Ar login_grace_time |
| 201 | Gives the grace time for clients to authenticate themselves (default |
Kevin Steves | 9ce907c | 2001-01-07 11:53:40 +0000 | [diff] [blame] | 202 | 600 seconds). |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 203 | If the client fails to authenticate the user within |
| 204 | this many seconds, the server disconnects and exits. |
| 205 | A value of zero indicates no limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 206 | .It Fl h Ar host_key_file |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 207 | Specifies the file from which the host key is read (default |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 208 | .Pa /etc/ssh_host_key ) . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 209 | This option must be given if |
| 210 | .Nm |
| 211 | is not run as root (as the normal |
| 212 | host file is normally not readable by anyone but root). |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 213 | It is possible to have multiple host key files for |
| 214 | the different protocol versions. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 215 | .It Fl i |
| 216 | Specifies that |
| 217 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 218 | is being run from inetd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 219 | .Nm |
| 220 | is normally not run |
| 221 | 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] | 222 | respond to the client, and this may take tens of seconds. |
| 223 | 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] | 224 | However, with small key sizes (e.g., 512) using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 225 | .Nm |
| 226 | from inetd may |
| 227 | be feasible. |
| 228 | .It Fl k Ar key_gen_time |
| 229 | Specifies how often the server key is regenerated (default 3600 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 230 | seconds, or one hour). |
| 231 | The motivation for regenerating the key fairly |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 232 | often is that the key is not stored anywhere, and after about an hour, |
| 233 | it becomes impossible to recover the key for decrypting intercepted |
| 234 | communications even if the machine is cracked into or physically |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 235 | seized. |
| 236 | A value of zero indicates that the key will never be regenerated. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 237 | .It Fl p Ar port |
| 238 | Specifies the port on which the server listens for connections |
| 239 | (default 22). |
| 240 | .It Fl q |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 241 | Quiet mode. |
| 242 | Nothing is sent to the system log. |
| 243 | Normally the beginning, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 244 | authentication, and termination of each connection is logged. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 245 | .It Fl u Ar len |
| 246 | This option is used to specify the size of the field |
| 247 | in the |
| 248 | .Li utmp |
| 249 | structure that holds the remote host name. |
| 250 | If the resolved host name is longer than |
| 251 | .Ar len , |
| 252 | the dotted decimal value will be used instead. |
| 253 | This allows hosts with very long host names that |
| 254 | overflow this field to still be uniquely identified. |
| 255 | Specifying |
| 256 | .Fl u0 |
| 257 | indicates that only dotted decimal addresses |
| 258 | should be put into the |
| 259 | .Pa utmp |
| 260 | file. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 261 | .It Fl D |
| 262 | When this option is specified |
| 263 | .Nm |
| 264 | will not detach and does not become a daemon. |
| 265 | This allows easy monitoring of |
| 266 | .Nm sshd . |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 267 | .It Fl V Ar client_protocol_id |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 268 | SSH-2 compatibility mode. |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 269 | When this option is specified |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 270 | .Nm |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 271 | assumes the client has sent the supplied version string |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 272 | and skips the |
| 273 | Protocol Version Identification Exchange. |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 274 | This option is not intended to be called directly. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 275 | .It Fl 4 |
| 276 | Forces |
| 277 | .Nm |
| 278 | to use IPv4 addresses only. |
| 279 | .It Fl 6 |
| 280 | Forces |
| 281 | .Nm |
| 282 | to use IPv6 addresses only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 283 | .El |
| 284 | .Sh CONFIGURATION FILE |
| 285 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 286 | reads configuration data from |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 287 | .Pa /etc/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 288 | (or the file specified with |
| 289 | .Fl f |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 290 | on the command line). |
| 291 | The file contains keyword-value pairs, one per line. |
| 292 | Lines starting with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 293 | .Ql # |
| 294 | and empty lines are interpreted as comments. |
| 295 | .Pp |
| 296 | The following keywords are possible. |
| 297 | .Bl -tag -width Ds |
| 298 | .It Cm AFSTokenPassing |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 299 | Specifies whether an AFS token may be forwarded to the server. |
| 300 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 301 | .Dq yes . |
| 302 | .It Cm AllowGroups |
Ben Lindstrom | a1ebd89 | 2001-02-10 22:19:23 +0000 | [diff] [blame] | 303 | This keyword can be followed by a list of group names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 304 | by spaces. |
| 305 | If specified, login is allowed only for users whose primary |
Kevin Steves | 7b61cfa | 2001-01-14 19:11:00 +0000 | [diff] [blame] | 306 | group or supplementary group list matches one of the patterns. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 307 | .Ql \&* |
| 308 | and |
| 309 | .Ql ? |
| 310 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 311 | wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 312 | Only group names are valid; a numerical group ID isn't recognized. |
Kevin Steves | 7b61cfa | 2001-01-14 19:11:00 +0000 | [diff] [blame] | 313 | By default login is allowed regardless of the group list. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 314 | .Pp |
Damien Miller | 50a41ed | 2000-10-16 12:14:42 +1100 | [diff] [blame] | 315 | .It Cm AllowTcpForwarding |
| 316 | Specifies whether TCP forwarding is permitted. |
| 317 | The default is |
| 318 | .Dq yes . |
| 319 | Note that disabling TCP forwarding does not improve security unless |
| 320 | users are also denied shell access, as they can always install their |
| 321 | own forwarders. |
| 322 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 323 | .It Cm AllowUsers |
Ben Lindstrom | a1ebd89 | 2001-02-10 22:19:23 +0000 | [diff] [blame] | 324 | This keyword can be followed by a list of user names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 325 | by spaces. |
| 326 | If specified, login is allowed only for users names that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 327 | match one of the patterns. |
| 328 | .Ql \&* |
| 329 | and |
| 330 | .Ql ? |
| 331 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 332 | wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 333 | Only user names are valid; a numerical user ID isn't recognized. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 334 | By default login is allowed regardless of the user name. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 335 | .Pp |
Ben Lindstrom | 48bd7c1 | 2001-01-09 00:35:42 +0000 | [diff] [blame] | 336 | .It Cm Banner |
| 337 | In some jurisdictions, sending a warning message before authentication |
| 338 | may be relevant for getting legal protection. |
| 339 | The contents of the specified file are sent to the remote user before |
| 340 | authentication is allowed. |
| 341 | This option is only available for protocol version 2. |
| 342 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 343 | .It Cm Ciphers |
| 344 | Specifies the ciphers allowed for protocol version 2. |
| 345 | Multiple ciphers must be comma-separated. |
| 346 | The default is |
Ben Lindstrom | d26dcf3 | 2001-01-06 15:18:16 +0000 | [diff] [blame] | 347 | .Dq 3des-cbc,blowfish-cbc,cast128-cbc,arcfour,aes128-cbc . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 348 | .It Cm CheckMail |
| 349 | Specifies whether |
| 350 | .Nm |
| 351 | should check for new mail for interactive logins. |
| 352 | The default is |
| 353 | .Dq no . |
| 354 | .It Cm DenyGroups |
| 355 | This keyword can be followed by a number of group names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 356 | by spaces. |
Kevin Steves | 7b61cfa | 2001-01-14 19:11:00 +0000 | [diff] [blame] | 357 | Users whose primary group or supplementary group list matches |
| 358 | one of the patterns aren't allowed to log in. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 359 | .Ql \&* |
| 360 | and |
| 361 | .Ql ? |
| 362 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 363 | wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 364 | Only group names are valid; a numerical group ID isn't recognized. |
Kevin Steves | 7b61cfa | 2001-01-14 19:11:00 +0000 | [diff] [blame] | 365 | By default login is allowed regardless of the group list. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 366 | .Pp |
| 367 | .It Cm DenyUsers |
| 368 | This keyword can be followed by a number of user names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 369 | by spaces. |
| 370 | Login is disallowed for user names that match one of the patterns. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 371 | .Ql \&* |
| 372 | and |
| 373 | .Ql ? |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 374 | can be used as wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 375 | Only user names are valid; a numerical user ID isn't recognized. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 376 | By default login is allowed regardless of the user name. |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 377 | .It Cm PubkeyAuthentication |
| 378 | Specifies whether public key authentication is allowed. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 379 | The default is |
| 380 | .Dq yes . |
| 381 | Note that this option applies to protocol version 2 only. |
| 382 | .It Cm GatewayPorts |
| 383 | Specifies whether remote hosts are allowed to connect to ports |
| 384 | forwarded for the client. |
| 385 | The argument must be |
| 386 | .Dq yes |
| 387 | or |
| 388 | .Dq no . |
| 389 | The default is |
| 390 | .Dq no . |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 391 | .It Cm HostKey |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 392 | Specifies the file containing the private host keys (default |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 393 | .Pa /etc/ssh_host_key ) |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 394 | used by SSH protocol versions 1 and 2. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 395 | Note that |
| 396 | .Nm |
Ben Lindstrom | 226cfa0 | 2001-01-22 05:34:40 +0000 | [diff] [blame] | 397 | will refuse to use a file if it is group/world-accessible. |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 398 | It is possible to have multiple host key files. |
| 399 | .Dq rsa1 |
| 400 | keys are used for version 1 and |
| 401 | .Dq dsa |
| 402 | or |
| 403 | .Dq rsa |
| 404 | are used for version 2 of the SSH protocol. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 405 | .It Cm IgnoreRhosts |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 406 | Specifies that |
| 407 | .Pa .rhosts |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 408 | and |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 409 | .Pa .shosts |
| 410 | files will not be used in authentication. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 411 | .Pa /etc/hosts.equiv |
| 412 | and |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 413 | .Pa /etc/shosts.equiv |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 414 | are still used. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 415 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 416 | .Dq yes . |
Damien Miller | 3226509 | 1999-11-12 11:33:04 +1100 | [diff] [blame] | 417 | .It Cm IgnoreUserKnownHosts |
| 418 | Specifies whether |
| 419 | .Nm |
| 420 | should ignore the user's |
| 421 | .Pa $HOME/.ssh/known_hosts |
| 422 | during |
| 423 | .Cm RhostsRSAAuthentication . |
| 424 | The default is |
| 425 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 426 | .It Cm KeepAlive |
| 427 | Specifies whether the system should send keepalive messages to the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 428 | other side. |
| 429 | If they are sent, death of the connection or crash of one |
| 430 | of the machines will be properly noticed. |
| 431 | However, this means that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 432 | connections will die if the route is down temporarily, and some people |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 433 | find it annoying. |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 434 | On the other hand, if keepalives are not sent, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 435 | sessions may hang indefinitely on the server, leaving |
| 436 | .Dq ghost |
| 437 | users and consuming server resources. |
| 438 | .Pp |
| 439 | The default is |
| 440 | .Dq yes |
| 441 | (to send keepalives), and the server will notice |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 442 | if the network goes down or the client host reboots. |
| 443 | This avoids infinitely hanging sessions. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 444 | .Pp |
| 445 | To disable keepalives, the value should be set to |
| 446 | .Dq no |
| 447 | in both the server and the client configuration files. |
| 448 | .It Cm KerberosAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 449 | Specifies whether Kerberos authentication is allowed. |
| 450 | This can be in the form of a Kerberos ticket, or if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 451 | .Cm PasswordAuthentication |
| 452 | is yes, the password provided by the user will be validated through |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 453 | the Kerberos KDC. |
| 454 | To use this option, the server needs a |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 455 | Kerberos servtab which allows the verification of the KDC's identity. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 456 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 457 | .Dq yes . |
| 458 | .It Cm KerberosOrLocalPasswd |
| 459 | If set then if password authentication through Kerberos fails then |
| 460 | the password will be validated via any additional local mechanism |
| 461 | such as |
Damien Miller | 62cee00 | 2000-09-23 17:15:56 +1100 | [diff] [blame] | 462 | .Pa /etc/passwd . |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 463 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 464 | .Dq yes . |
| 465 | .It Cm KerberosTgtPassing |
| 466 | Specifies whether a Kerberos TGT may be forwarded to the server. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 467 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 468 | .Dq no , |
| 469 | as this only works when the Kerberos KDC is actually an AFS kaserver. |
| 470 | .It Cm KerberosTicketCleanup |
| 471 | Specifies whether to automatically destroy the user's ticket cache |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 472 | file on logout. |
| 473 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 474 | .Dq yes . |
| 475 | .It Cm KeyRegenerationInterval |
| 476 | The server key is automatically regenerated after this many seconds |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 477 | (if it has been used). |
| 478 | The purpose of regeneration is to prevent |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 479 | decrypting captured sessions by later breaking into the machine and |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 480 | stealing the keys. |
| 481 | The key is never stored anywhere. |
| 482 | If the value is 0, the key is never regenerated. |
| 483 | The default is 3600 (seconds). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 484 | .It Cm ListenAddress |
| 485 | Specifies what local address |
| 486 | .Nm |
| 487 | should listen on. |
| 488 | The default is to listen to all local addresses. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 489 | Multiple options of this type are permitted. |
| 490 | Additionally, the |
| 491 | .Cm Ports |
| 492 | options must precede this option. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 493 | .It Cm LoginGraceTime |
| 494 | The server disconnects after this time if the user has not |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 495 | successfully logged in. |
| 496 | If the value is 0, there is no time limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 497 | The default is 600 (seconds). |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 498 | .It Cm LogLevel |
| 499 | Gives the verbosity level that is used when logging messages from |
| 500 | .Nm sshd . |
| 501 | The possible values are: |
Ben Lindstrom | db65e8f | 2001-01-19 04:26:52 +0000 | [diff] [blame] | 502 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
| 503 | The default is INFO. |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 504 | Logging with level DEBUG violates the privacy of users |
| 505 | and is not recommended. |
Ben Lindstrom | 06b33aa | 2001-02-15 03:01:59 +0000 | [diff] [blame] | 506 | .It Cm MACs |
| 507 | Specifies the available MAC (message authentication code) algorithms. |
| 508 | The MAC algorithm is used in protocol version 2 |
| 509 | for data integrity protection. |
| 510 | Multiple algorithms must be comma-separated. |
| 511 | The default is |
| 512 | .Pp |
| 513 | .Bd -literal |
| 514 | ``hmac-sha1,hmac-md5,hmac-ripemd160,hmac-ripemd160@openssh.com, |
| 515 | hmac-sha1-96,hmac-md5-96'' |
| 516 | .Ed |
Damien Miller | 3702396 | 2000-07-11 17:31:38 +1000 | [diff] [blame] | 517 | .It Cm MaxStartups |
| 518 | Specifies the maximum number of concurrent unauthenticated connections to the |
| 519 | .Nm |
| 520 | daemon. |
| 521 | Additional connections will be dropped until authentication succeeds or the |
| 522 | .Cm LoginGraceTime |
| 523 | expires for a connection. |
| 524 | The default is 10. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 525 | .Pp |
| 526 | Alternatively, random early drop can be enabled by specifying |
| 527 | the three colon separated values |
| 528 | .Dq start:rate:full |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 529 | (e.g., "10:30:60"). |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 530 | .Nm |
Ben Lindstrom | a733350 | 2001-01-29 08:44:03 +0000 | [diff] [blame] | 531 | will refuse connection attempts with a probability of |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 532 | .Dq rate/100 |
| 533 | (30%) |
| 534 | if there are currently |
| 535 | .Dq start |
| 536 | (10) |
| 537 | unauthenticated connections. |
Ben Lindstrom | a733350 | 2001-01-29 08:44:03 +0000 | [diff] [blame] | 538 | The probability increases linearly and all connection attempts |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 539 | are refused if the number of unauthenticated connections reaches |
| 540 | .Dq full |
| 541 | (60). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 542 | .It Cm PasswordAuthentication |
| 543 | Specifies whether password authentication is allowed. |
| 544 | The default is |
| 545 | .Dq yes . |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 546 | Note that this option applies to both protocol versions 1 and 2. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 547 | .It Cm PermitEmptyPasswords |
| 548 | When password authentication is allowed, it specifies whether the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 549 | server allows login to accounts with empty password strings. |
| 550 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 551 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 552 | .It Cm PermitRootLogin |
Ben Lindstrom | 323c98f | 2001-03-05 07:40:40 +0000 | [diff] [blame^] | 553 | Specifies whether root can login using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 554 | .Xr ssh 1 . |
| 555 | The argument must be |
| 556 | .Dq yes , |
Ben Lindstrom | d8a9021 | 2001-02-15 03:08:27 +0000 | [diff] [blame] | 557 | .Dq without-password , |
| 558 | .Dq forced-commands-only |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 559 | or |
| 560 | .Dq no . |
| 561 | The default is |
| 562 | .Dq yes . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 563 | .Pp |
Ben Lindstrom | d8a9021 | 2001-02-15 03:08:27 +0000 | [diff] [blame] | 564 | If this option is set to |
| 565 | .Dq without-password |
| 566 | password authentication is disabled for root. |
| 567 | .Pp |
| 568 | If this option is set to |
| 569 | .Dq forced-commands-only |
| 570 | root login with public key authentication will be allowed, |
| 571 | but only if the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 572 | .Ar command |
Ben Lindstrom | d8a9021 | 2001-02-15 03:08:27 +0000 | [diff] [blame] | 573 | option has been specified |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 574 | (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] | 575 | normally not allowed). All other authentication methods are disabled |
| 576 | for root. |
Ben Lindstrom | 323c98f | 2001-03-05 07:40:40 +0000 | [diff] [blame^] | 577 | .Pp |
| 578 | If this option is set to |
| 579 | .Dq no |
| 580 | root is not allowed to login. |
Damien Miller | 6f83b8e | 2000-05-02 09:23:45 +1000 | [diff] [blame] | 581 | .It Cm PidFile |
| 582 | Specifies the file that contains the process identifier of the |
| 583 | .Nm |
| 584 | daemon. |
| 585 | The default is |
| 586 | .Pa /var/run/sshd.pid . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 587 | .It Cm Port |
| 588 | Specifies the port number that |
| 589 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 590 | listens on. |
| 591 | The default is 22. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 592 | Multiple options of this type are permitted. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 593 | .It Cm PrintMotd |
| 594 | Specifies whether |
| 595 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 596 | should print |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 597 | .Pa /etc/motd |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 598 | when a user logs in interactively. |
| 599 | (On some systems it is also printed by the shell, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 600 | .Pa /etc/profile , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 601 | or equivalent.) |
| 602 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 603 | .Dq yes . |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 604 | .It Cm Protocol |
| 605 | Specifies the protocol versions |
| 606 | .Nm |
| 607 | should support. |
| 608 | The possible values are |
| 609 | .Dq 1 |
| 610 | and |
| 611 | .Dq 2 . |
| 612 | Multiple versions must be comma-separated. |
| 613 | The default is |
| 614 | .Dq 1 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 615 | .It Cm RandomSeed |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 616 | Obsolete. |
| 617 | Random number generation uses other techniques. |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 618 | .It Cm ReverseMappingCheck |
| 619 | Specifies whether |
| 620 | .Nm |
| 621 | should try to verify the remote host name and check that |
| 622 | the resolved host name for the remote IP address maps back to the |
| 623 | very same IP address. |
| 624 | The default is |
| 625 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 626 | .It Cm RhostsAuthentication |
| 627 | Specifies whether authentication using rhosts or /etc/hosts.equiv |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 628 | files is sufficient. |
| 629 | Normally, this method should not be permitted because it is insecure. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 630 | .Cm RhostsRSAAuthentication |
| 631 | should be used |
| 632 | instead, because it performs RSA-based host authentication in addition |
| 633 | to normal rhosts or /etc/hosts.equiv authentication. |
| 634 | The default is |
| 635 | .Dq no . |
| 636 | .It Cm RhostsRSAAuthentication |
| 637 | Specifies whether rhosts or /etc/hosts.equiv authentication together |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 638 | with successful RSA host authentication is allowed. |
| 639 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 640 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 641 | .It Cm RSAAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 642 | Specifies whether pure RSA authentication is allowed. |
| 643 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 644 | .Dq yes . |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 645 | Note that this option applies to protocol version 1 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 646 | .It Cm ServerKeyBits |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 647 | Defines the number of bits in the server key. |
| 648 | The minimum value is 512, and the default is 768. |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 649 | .It Cm ChallengeResponseAuthentication |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 650 | Specifies whether |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 651 | challenge reponse |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 652 | authentication is allowed. |
Damien Miller | 1d66c16 | 2001-03-04 00:16:20 +1100 | [diff] [blame] | 653 | Currently there is support for |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 654 | .Xr skey 1 |
Damien Miller | 1d66c16 | 2001-03-04 00:16:20 +1100 | [diff] [blame] | 655 | and PAM authentication. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 656 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 657 | .Dq yes . |
Damien Miller | 1d66c16 | 2001-03-04 00:16:20 +1100 | [diff] [blame] | 658 | Note that enabling ChallengeResponseAuthentication for PAM bypasses |
| 659 | OpenSSH's password checking code, thus rendering options such as |
| 660 | .Cm PasswordAuthentication |
| 661 | and |
| 662 | .Cm PermitEmptyPasswords |
| 663 | ineffective. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 664 | .It Cm StrictModes |
| 665 | Specifies whether |
| 666 | .Nm |
| 667 | should check file modes and ownership of the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 668 | user's files and home directory before accepting login. |
| 669 | This is normally desirable because novices sometimes accidentally leave their |
| 670 | directory or files world-writable. |
| 671 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 672 | .Dq yes . |
Damien Miller | f6d9e22 | 2000-06-18 14:50:44 +1000 | [diff] [blame] | 673 | .It Cm Subsystem |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 674 | Configures an external subsystem (e.g., file transfer daemon). |
| 675 | Arguments should be a subsystem name and a command to execute upon subsystem |
| 676 | request. |
Damien Miller | 7b28dc5 | 2000-09-05 13:34:53 +1100 | [diff] [blame] | 677 | The command |
| 678 | .Xr sftp-server 8 |
| 679 | implements the |
| 680 | .Dq sftp |
| 681 | file transfer subsystem. |
Damien Miller | f6d9e22 | 2000-06-18 14:50:44 +1000 | [diff] [blame] | 682 | By default no subsystems are defined. |
| 683 | Note that this option applies to protocol version 2 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 684 | .It Cm SyslogFacility |
| 685 | Gives the facility code that is used when logging messages from |
| 686 | .Nm sshd . |
| 687 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 688 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
| 689 | The default is AUTH. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 690 | .It Cm UseLogin |
| 691 | Specifies whether |
| 692 | .Xr login 1 |
Damien Miller | d3a1857 | 2000-06-07 19:55:44 +1000 | [diff] [blame] | 693 | is used for interactive login sessions. |
| 694 | Note that |
| 695 | .Xr login 1 |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 696 | is never used for remote command execution. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 697 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 698 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 699 | .It Cm X11DisplayOffset |
| 700 | Specifies the first display number available for |
| 701 | .Nm sshd Ns 's |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 702 | X11 forwarding. |
| 703 | This prevents |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 704 | .Nm |
| 705 | from interfering with real X11 servers. |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 706 | The default is 10. |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 707 | .It Cm X11Forwarding |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 708 | Specifies whether X11 forwarding is permitted. |
| 709 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 710 | .Dq no . |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 711 | Note that disabling X11 forwarding does not improve security in any |
| 712 | way, as users can always install their own forwarders. |
Damien Miller | d3a1857 | 2000-06-07 19:55:44 +1000 | [diff] [blame] | 713 | .It Cm XAuthLocation |
| 714 | Specifies the location of the |
| 715 | .Xr xauth 1 |
| 716 | program. |
| 717 | The default is |
| 718 | .Pa /usr/X11R6/bin/xauth . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 719 | .El |
| 720 | .Sh LOGIN PROCESS |
| 721 | When a user successfully logs in, |
| 722 | .Nm |
| 723 | does the following: |
| 724 | .Bl -enum -offset indent |
| 725 | .It |
| 726 | 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] | 727 | prints last login time and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 728 | .Pa /etc/motd |
| 729 | (unless prevented in the configuration file or by |
| 730 | .Pa $HOME/.hushlogin ; |
| 731 | see the |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 732 | .Sx FILES |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 733 | section). |
| 734 | .It |
| 735 | If the login is on a tty, records login time. |
| 736 | .It |
| 737 | Checks |
| 738 | .Pa /etc/nologin ; |
| 739 | if it exists, prints contents and quits |
| 740 | (unless root). |
| 741 | .It |
| 742 | Changes to run with normal user privileges. |
| 743 | .It |
| 744 | Sets up basic environment. |
| 745 | .It |
| 746 | Reads |
| 747 | .Pa $HOME/.ssh/environment |
| 748 | if it exists. |
| 749 | .It |
| 750 | Changes to user's home directory. |
| 751 | .It |
| 752 | If |
| 753 | .Pa $HOME/.ssh/rc |
| 754 | exists, runs it; else if |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 755 | .Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 756 | exists, runs |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 757 | it; otherwise runs xauth. |
| 758 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 759 | .Dq rc |
| 760 | files are given the X11 |
| 761 | authentication protocol and cookie in standard input. |
| 762 | .It |
| 763 | Runs user's shell or command. |
| 764 | .El |
| 765 | .Sh AUTHORIZED_KEYS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 766 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 767 | .Pa $HOME/.ssh/authorized_keys |
| 768 | file lists the RSA keys that are |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 769 | permitted for RSA authentication in SSH protocols 1.3 and 1.5 |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 770 | Similarly, the |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 771 | .Pa $HOME/.ssh/authorized_keys2 |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 772 | file lists the DSA and RSA keys that are |
| 773 | permitted for public key authentication (PubkeyAuthentication) |
| 774 | in SSH protocol 2.0. |
| 775 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 776 | Each line of the file contains one |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 777 | key (empty lines and lines starting with a |
| 778 | .Ql # |
| 779 | are ignored as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 780 | comments). |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 781 | Each RSA public key consists of the following fields, separated by |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 782 | spaces: options, bits, exponent, modulus, comment. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 783 | Each protocol version 2 public key consists of: |
| 784 | options, keytype, base64 encoded key, comment. |
| 785 | The options fields |
| 786 | are optional; its presence is determined by whether the line starts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 787 | 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] | 788 | The bits, exponent, modulus and comment fields give the RSA key for |
| 789 | protocol version 1; the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 790 | comment field is not used for anything (but may be convenient for the |
| 791 | user to identify the key). |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 792 | For protocol version 2 the keytype is |
| 793 | .Dq ssh-dss |
| 794 | or |
| 795 | .Dq ssh-rsa . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 796 | .Pp |
| 797 | Note that lines in this file are usually several hundred bytes long |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 798 | (because of the size of the RSA key modulus). |
| 799 | You don't want to type them in; instead, copy the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 800 | .Pa identity.pub |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 801 | or the |
| 802 | .Pa id_dsa.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 803 | file and edit it. |
| 804 | .Pp |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 805 | The options (if present) consist of comma-separated option |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 806 | specifications. |
| 807 | No spaces are permitted, except within double quotes. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 808 | The following option specifications are supported: |
| 809 | .Bl -tag -width Ds |
| 810 | .It Cm from="pattern-list" |
| 811 | Specifies that in addition to RSA authentication, the canonical name |
| 812 | 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] | 813 | patterns |
| 814 | .Pf ( Ql * |
| 815 | and |
| 816 | .Ql ? |
| 817 | serve as wildcards). |
| 818 | The list may also contain |
| 819 | patterns negated by prefixing them with |
| 820 | .Ql ! ; |
| 821 | if the canonical host name matches a negated pattern, the key is not accepted. |
| 822 | The purpose |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 823 | of this option is to optionally increase security: RSA authentication |
| 824 | by itself does not trust the network or name servers or anything (but |
| 825 | the key); however, if somebody somehow steals the key, the key |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 826 | permits an intruder to log in from anywhere in the world. |
| 827 | This additional option makes using a stolen key more difficult (name |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 828 | servers and/or routers would have to be compromised in addition to |
| 829 | just the key). |
| 830 | .It Cm command="command" |
| 831 | Specifies that the command is executed whenever this key is used for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 832 | authentication. |
| 833 | The command supplied by the user (if any) is ignored. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 834 | 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] | 835 | otherwise it is run without a tty. |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 836 | Note that if you want a 8-bit clean channel, |
| 837 | you must not request a pty or should specify |
| 838 | .Cm no-pty . |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 839 | A quote may be included in the command by quoting it with a backslash. |
| 840 | This option might be useful |
| 841 | to restrict certain RSA keys to perform just a specific operation. |
| 842 | 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] | 843 | Note that the client may specify TCP/IP and/or X11 |
| 844 | forwarding unless they are explicitly prohibited. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 845 | .It Cm environment="NAME=value" |
| 846 | Specifies that the string is to be added to the environment when |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 847 | logging in using this key. |
| 848 | Environment variables set this way |
| 849 | override other default environment values. |
| 850 | Multiple options of this type are permitted. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 851 | .It Cm no-port-forwarding |
| 852 | Forbids TCP/IP forwarding when this key is used for authentication. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 853 | Any port forward requests by the client will return an error. |
| 854 | This might be used, e.g., in connection with the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 855 | .Cm command |
| 856 | option. |
| 857 | .It Cm no-X11-forwarding |
| 858 | Forbids X11 forwarding when this key is used for authentication. |
| 859 | Any X11 forward requests by the client will return an error. |
| 860 | .It Cm no-agent-forwarding |
| 861 | Forbids authentication agent forwarding when this key is used for |
| 862 | authentication. |
| 863 | .It Cm no-pty |
| 864 | Prevents tty allocation (a request to allocate a pty will fail). |
| 865 | .El |
| 866 | .Ss Examples |
| 867 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar |
| 868 | .Pp |
| 869 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula |
| 870 | .Pp |
| 871 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi |
| 872 | .Sh SSH_KNOWN_HOSTS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 873 | The |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 874 | .Pa /etc/ssh_known_hosts , |
| 875 | .Pa /etc/ssh_known_hosts2 , |
| 876 | .Pa $HOME/.ssh/known_hosts , |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 877 | and |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 878 | .Pa $HOME/.ssh/known_hosts2 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 879 | files contain host public keys for all known hosts. |
| 880 | The global file should |
| 881 | be prepared by the administrator (optional), and the per-user file is |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 882 | maintained automatically: whenever the user connects from an unknown host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 883 | its key is added to the per-user file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 884 | .Pp |
| 885 | Each line in these files contains the following fields: hostnames, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 886 | bits, exponent, modulus, comment. |
| 887 | The fields are separated by spaces. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 888 | .Pp |
| 889 | Hostnames is a comma-separated list of patterns ('*' and '?' act as |
| 890 | wildcards); each pattern in turn is matched against the canonical host |
| 891 | name (when authenticating a client) or against the user-supplied |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 892 | name (when authenticating a server). |
| 893 | A pattern may also be preceded by |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 894 | .Ql ! |
| 895 | to indicate negation: if the host name matches a negated |
| 896 | pattern, it is not accepted (by that line) even if it matched another |
| 897 | pattern on the line. |
| 898 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 899 | 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] | 900 | can be obtained, e.g., from |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 901 | .Pa /etc/ssh_host_key.pub . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 902 | The optional comment field continues to the end of the line, and is not used. |
| 903 | .Pp |
| 904 | Lines starting with |
| 905 | .Ql # |
| 906 | and empty lines are ignored as comments. |
| 907 | .Pp |
| 908 | When performing host authentication, authentication is accepted if any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 909 | matching line has the proper key. |
| 910 | It is thus permissible (but not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 911 | recommended) to have several lines or different host keys for the same |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 912 | names. |
| 913 | This will inevitably happen when short forms of host names |
| 914 | from different domains are put in the file. |
| 915 | It is possible |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 916 | that the files contain conflicting information; authentication is |
| 917 | accepted if valid information can be found from either file. |
| 918 | .Pp |
| 919 | Note that the lines in these files are typically hundreds of characters |
| 920 | long, and you definitely don't want to type in the host keys by hand. |
| 921 | Rather, generate them by a script |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 922 | or by taking |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 923 | .Pa /etc/ssh_host_key.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 924 | and adding the host names at the front. |
| 925 | .Ss Examples |
| 926 | closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi |
| 927 | .Sh FILES |
| 928 | .Bl -tag -width Ds |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 929 | .It Pa /etc/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 930 | Contains configuration data for |
| 931 | .Nm sshd . |
| 932 | This file should be writable by root only, but it is recommended |
| 933 | (though not necessary) that it be world-readable. |
Ben Lindstrom | d7f5b51 | 2001-03-05 06:57:23 +0000 | [diff] [blame] | 934 | .It Pa /etc/ssh_host_key, /etc/ssh_host_dsa_key, /etc/ssh_host_rsa_key |
| 935 | These three files contain the private parts of the |
| 936 | (SSH1, SSH2 DSA, and SSH2 RSA) host keys. |
| 937 | 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] | 938 | accessible to others. |
| 939 | Note that |
| 940 | .Nm |
| 941 | does not start if this file is group/world-accessible. |
Ben Lindstrom | d7f5b51 | 2001-03-05 06:57:23 +0000 | [diff] [blame] | 942 | .It Pa /etc/ssh_host_key.pub, /etc/ssh_host_dsa_key.pub, /etc/ssh_host_rsa_key.pub |
| 943 | There three files contain the public parts of the |
| 944 | (SSH1, SSH2 DSA, and SSH2 RSA) host keys. |
| 945 | These files should be world-readable but writable only by |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 946 | root. |
Ben Lindstrom | d7f5b51 | 2001-03-05 06:57:23 +0000 | [diff] [blame] | 947 | Their contents should match the respective private parts. |
| 948 | These files are not |
| 949 | really used for anything; they are provided for the convenience of |
| 950 | the user so their contents can be copied to known hosts files. |
| 951 | These files are created using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 952 | .Xr ssh-keygen 1 . |
Damien Miller | e39cacc | 2000-11-29 12:18:44 +1100 | [diff] [blame] | 953 | .It Pa /etc/primes |
| 954 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 955 | .It Pa /var/run/sshd.pid |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 956 | Contains the process ID of the |
| 957 | .Nm |
| 958 | listening for connections (if there are several daemons running |
| 959 | concurrently for different ports, this contains the pid of the one |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 960 | started last). |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 961 | 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] | 962 | .It Pa $HOME/.ssh/authorized_keys |
| 963 | Lists the RSA keys that can be used to log into the user's account. |
| 964 | This file must be readable by root (which may on some machines imply |
| 965 | 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] | 966 | volume). |
| 967 | It is recommended that it not be accessible by others. |
| 968 | The format of this file is described above. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 969 | Users will place the contents of their |
| 970 | .Pa identity.pub |
| 971 | files into this file, as described in |
| 972 | .Xr ssh-keygen 1 . |
| 973 | .It Pa $HOME/.ssh/authorized_keys2 |
| 974 | Lists the DSA keys that can be used to log into the user's account. |
| 975 | This file must be readable by root (which may on some machines imply |
| 976 | it being world-readable if the user's home directory resides on an NFS |
| 977 | volume). |
| 978 | It is recommended that it not be accessible by others. |
| 979 | The format of this file is described above. |
| 980 | Users will place the contents of their |
| 981 | .Pa id_dsa.pub |
| 982 | files into this file, as described in |
| 983 | .Xr ssh-keygen 1 . |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 984 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 985 | These files are consulted when using rhosts with RSA host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 986 | authentication to check the public key of the host. |
| 987 | 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] | 988 | The client uses the same files |
Ben Lindstrom | ebd888d | 2001-03-05 05:49:29 +0000 | [diff] [blame] | 989 | to verify that it is connecting to the correct remote host. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 990 | These files should be writable only by root/the owner. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 991 | .Pa /etc/ssh_known_hosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 992 | should be world-readable, and |
| 993 | .Pa $HOME/.ssh/known_hosts |
| 994 | can but need not be world-readable. |
| 995 | .It Pa /etc/nologin |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 996 | If this file exists, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 997 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 998 | refuses to let anyone except root log in. |
| 999 | The contents of the file |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1000 | 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] | 1001 | refused. |
| 1002 | The file should be world-readable. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1003 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
| 1004 | If compiled with |
| 1005 | .Sy LIBWRAP |
| 1006 | support, tcp-wrappers access controls may be defined here as described in |
| 1007 | .Xr hosts_access 5 . |
| 1008 | .It Pa $HOME/.rhosts |
| 1009 | This file contains host-username pairs, separated by a space, one per |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1010 | line. |
| 1011 | The given user on the corresponding host is permitted to log in |
| 1012 | without password. |
| 1013 | The same file is used by rlogind and rshd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1014 | The file must |
| 1015 | be writable only by the user; it is recommended that it not be |
| 1016 | accessible by others. |
| 1017 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1018 | If is also possible to use netgroups in the file. |
| 1019 | Either host or user |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1020 | name may be of the form +@groupname to specify all hosts or all users |
| 1021 | in the group. |
| 1022 | .It Pa $HOME/.shosts |
| 1023 | For ssh, |
| 1024 | this file is exactly the same as for |
| 1025 | .Pa .rhosts . |
| 1026 | However, this file is |
| 1027 | 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] | 1028 | .It Pa /etc/hosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1029 | This file is used during |
| 1030 | .Pa .rhosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1031 | authentication. |
| 1032 | In the simplest form, this file contains host names, one per line. |
| 1033 | Users on |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1034 | those hosts are permitted to log in without a password, provided they |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1035 | have the same user name on both machines. |
| 1036 | The host name may also be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1037 | followed by a user name; such users are permitted to log in as |
| 1038 | .Em any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1039 | user on this machine (except root). |
| 1040 | Additionally, the syntax |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1041 | .Dq +@group |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1042 | can be used to specify netgroups. |
| 1043 | Negated entries start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1044 | .Ql \&- . |
| 1045 | .Pp |
| 1046 | If the client host/user is successfully matched in this file, login is |
| 1047 | automatically permitted provided the client and server user names are the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1048 | same. |
| 1049 | Additionally, successful RSA host authentication is normally required. |
| 1050 | This file must be writable only by root; it is recommended |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1051 | that it be world-readable. |
| 1052 | .Pp |
| 1053 | .Sy "Warning: It is almost never a good idea to use user names in" |
| 1054 | .Pa hosts.equiv . |
| 1055 | Beware that it really means that the named user(s) can log in as |
| 1056 | .Em anybody , |
| 1057 | which includes bin, daemon, adm, and other accounts that own critical |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1058 | binaries and directories. |
| 1059 | Using a user name practically grants the user root access. |
| 1060 | The only valid use for user names that I can think |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1061 | of is in negative entries. |
| 1062 | .Pp |
| 1063 | Note that this warning also applies to rsh/rlogin. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1064 | .It Pa /etc/shosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1065 | This is processed exactly as |
| 1066 | .Pa /etc/hosts.equiv . |
| 1067 | However, this file may be useful in environments that want to run both |
| 1068 | rsh/rlogin and ssh. |
| 1069 | .It Pa $HOME/.ssh/environment |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1070 | This file is read into the environment at login (if it exists). |
| 1071 | It can only contain empty lines, comment lines (that start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1072 | .Ql # ) , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1073 | and assignment lines of the form name=value. |
| 1074 | The file should be writable |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1075 | only by the user; it need not be readable by anyone else. |
| 1076 | .It Pa $HOME/.ssh/rc |
| 1077 | 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] | 1078 | environment files but before starting the user's shell or command. |
| 1079 | 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] | 1080 | standard input (and |
| 1081 | .Ev DISPLAY |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1082 | in environment). |
| 1083 | This must call |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1084 | .Xr xauth 1 |
| 1085 | in that case. |
| 1086 | .Pp |
| 1087 | The primary purpose of this file is to run any initialization routines |
| 1088 | which may be needed before the user's home directory becomes |
| 1089 | accessible; AFS is a particular example of such an environment. |
| 1090 | .Pp |
| 1091 | This file will probably contain some initialization code followed by |
| 1092 | something similar to: "if read proto cookie; then echo add $DISPLAY |
| 1093 | $proto $cookie | xauth -q -; fi". |
| 1094 | .Pp |
| 1095 | If this file does not exist, |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1096 | .Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1097 | is run, and if that |
| 1098 | does not exist either, xauth is used to store the cookie. |
| 1099 | .Pp |
| 1100 | This file should be writable only by the user, and need not be |
| 1101 | readable by anyone else. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1102 | .It Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1103 | Like |
| 1104 | .Pa $HOME/.ssh/rc . |
| 1105 | This can be used to specify |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1106 | machine-specific login-time initializations globally. |
| 1107 | 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] | 1108 | .El |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 1109 | .Sh AUTHORS |
Ben Lindstrom | 8eec2c8 | 2001-01-29 08:39:16 +0000 | [diff] [blame] | 1110 | OpenSSH is a derivative of the original and free |
| 1111 | ssh 1.2.12 release by Tatu Ylonen. |
| 1112 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, |
| 1113 | Theo de Raadt and Dug Song |
| 1114 | removed many bugs, re-added newer features and |
| 1115 | created OpenSSH. |
| 1116 | Markus Friedl contributed the support for SSH |
| 1117 | protocol versions 1.5 and 2.0. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1118 | .Sh SEE ALSO |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1119 | .Xr scp 1 , |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 1120 | .Xr sftp 1 , |
Damien Miller | 7b28dc5 | 2000-09-05 13:34:53 +1100 | [diff] [blame] | 1121 | .Xr sftp-server 8 , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1122 | .Xr ssh 1 , |
| 1123 | .Xr ssh-add 1 , |
| 1124 | .Xr ssh-agent 1 , |
| 1125 | .Xr ssh-keygen 1 , |
Damien Miller | b38eff8 | 2000-04-01 11:09:21 +1000 | [diff] [blame] | 1126 | .Xr rlogin 1 , |
| 1127 | .Xr rsh 1 |