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 | .\" |
Damien Miller | e4340be | 2000-09-16 13:29:08 +1100 | [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. |
| 16 | .\" |
| 17 | .\" Redistribution and use in source and binary forms, with or without |
| 18 | .\" modification, are permitted provided that the following conditions |
| 19 | .\" are met: |
| 20 | .\" 1. Redistributions of source code must retain the above copyright |
| 21 | .\" notice, this list of conditions and the following disclaimer. |
| 22 | .\" 2. Redistributions in binary form must reproduce the above copyright |
| 23 | .\" notice, this list of conditions and the following disclaimer in the |
| 24 | .\" documentation and/or other materials provided with the distribution. |
| 25 | .\" |
| 26 | .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
| 27 | .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
| 28 | .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
| 29 | .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
| 30 | .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
| 31 | .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| 32 | .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| 33 | .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| 34 | .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
| 35 | .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 36 | .\" |
Damien Miller | e39cacc | 2000-11-29 12:18:44 +1100 | [diff] [blame] | 37 | .\" $OpenBSD: sshd.8,v 1.73 2000/11/22 15:38:30 provos 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 |
| 43 | .Nd secure shell daemon |
| 44 | .Sh SYNOPSIS |
| 45 | .Nm sshd |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 46 | .Op Fl diqQ46 |
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, |
| 177 | .Dv SIGHUP . |
| 178 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 179 | The options are as follows: |
| 180 | .Bl -tag -width Ds |
| 181 | .It Fl b Ar bits |
| 182 | Specifies the number of bits in the server key (default 768). |
| 183 | .Pp |
| 184 | .It Fl d |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 185 | Debug mode. |
| 186 | The server sends verbose debug output to the system |
| 187 | log, and does not put itself in the background. |
| 188 | The server also will not fork and will only process one connection. |
| 189 | This option is only intended for debugging for the server. |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 190 | Multiple -d options increases the debugging level. |
| 191 | Maximum is 3. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 192 | .It Fl f Ar configuration_file |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 193 | Specifies the name of the configuration file. |
| 194 | The default is |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 195 | .Pa /etc/sshd_config . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 196 | .Nm |
| 197 | refuses to start if there is no configuration file. |
| 198 | .It Fl g Ar login_grace_time |
| 199 | Gives the grace time for clients to authenticate themselves (default |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 200 | 300 seconds). |
| 201 | If the client fails to authenticate the user within |
| 202 | this many seconds, the server disconnects and exits. |
| 203 | A value of zero indicates no limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 204 | .It Fl h Ar host_key_file |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 205 | Specifies the file from which the RSA host key is read (default |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 206 | .Pa /etc/ssh_host_key ) . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 207 | This option must be given if |
| 208 | .Nm |
| 209 | is not run as root (as the normal |
| 210 | host file is normally not readable by anyone but root). |
| 211 | .It Fl i |
| 212 | Specifies that |
| 213 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 214 | is being run from inetd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 215 | .Nm |
| 216 | is normally not run |
| 217 | 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] | 218 | respond to the client, and this may take tens of seconds. |
| 219 | 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] | 220 | However, with small key sizes (e.g., 512) using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 221 | .Nm |
| 222 | from inetd may |
| 223 | be feasible. |
| 224 | .It Fl k Ar key_gen_time |
| 225 | Specifies how often the server key is regenerated (default 3600 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 226 | seconds, or one hour). |
| 227 | The motivation for regenerating the key fairly |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 228 | often is that the key is not stored anywhere, and after about an hour, |
| 229 | it becomes impossible to recover the key for decrypting intercepted |
| 230 | communications even if the machine is cracked into or physically |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 231 | seized. |
| 232 | A value of zero indicates that the key will never be regenerated. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 233 | .It Fl p Ar port |
| 234 | Specifies the port on which the server listens for connections |
| 235 | (default 22). |
| 236 | .It Fl q |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 237 | Quiet mode. |
| 238 | Nothing is sent to the system log. |
| 239 | Normally the beginning, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 240 | authentication, and termination of each connection is logged. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 241 | .It Fl u Ar len |
| 242 | This option is used to specify the size of the field |
| 243 | in the |
| 244 | .Li utmp |
| 245 | structure that holds the remote host name. |
| 246 | If the resolved host name is longer than |
| 247 | .Ar len , |
| 248 | the dotted decimal value will be used instead. |
| 249 | This allows hosts with very long host names that |
| 250 | overflow this field to still be uniquely identified. |
| 251 | Specifying |
| 252 | .Fl u0 |
| 253 | indicates that only dotted decimal addresses |
| 254 | should be put into the |
| 255 | .Pa utmp |
| 256 | file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 257 | .It Fl Q |
| 258 | Do not print an error message if RSA support is missing. |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 259 | .It Fl V Ar client_protocol_id |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 260 | SSH-2 compatibility mode. |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 261 | When this option is specified |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 262 | .Nm |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 263 | assumes the client has sent the supplied version string |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 264 | and skips the |
| 265 | Protocol Version Identification Exchange. |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 266 | This option is not intended to be called directly. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 267 | .It Fl 4 |
| 268 | Forces |
| 269 | .Nm |
| 270 | to use IPv4 addresses only. |
| 271 | .It Fl 6 |
| 272 | Forces |
| 273 | .Nm |
| 274 | to use IPv6 addresses only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 275 | .El |
| 276 | .Sh CONFIGURATION FILE |
| 277 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 278 | reads configuration data from |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 279 | .Pa /etc/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 280 | (or the file specified with |
| 281 | .Fl f |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 282 | on the command line). |
| 283 | The file contains keyword-value pairs, one per line. |
| 284 | Lines starting with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 285 | .Ql # |
| 286 | and empty lines are interpreted as comments. |
| 287 | .Pp |
| 288 | The following keywords are possible. |
| 289 | .Bl -tag -width Ds |
| 290 | .It Cm AFSTokenPassing |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 291 | Specifies whether an AFS token may be forwarded to the server. |
| 292 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 293 | .Dq yes . |
| 294 | .It Cm AllowGroups |
| 295 | This keyword can be followed by a number of group names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 296 | by spaces. |
| 297 | If specified, login is allowed only for users whose primary |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 298 | group matches one of the patterns. |
| 299 | .Ql \&* |
| 300 | and |
| 301 | .Ql ? |
| 302 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 303 | wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 304 | Only group names are valid; a numerical group ID isn't recognized. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 305 | By default login is allowed regardless of the primary group. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 306 | .Pp |
Damien Miller | 50a41ed | 2000-10-16 12:14:42 +1100 | [diff] [blame] | 307 | .It Cm AllowTcpForwarding |
| 308 | Specifies whether TCP forwarding is permitted. |
| 309 | The default is |
| 310 | .Dq yes . |
| 311 | Note that disabling TCP forwarding does not improve security unless |
| 312 | users are also denied shell access, as they can always install their |
| 313 | own forwarders. |
| 314 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 315 | .It Cm AllowUsers |
| 316 | This keyword can be followed by a number of user names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 317 | by spaces. |
| 318 | If specified, login is allowed only for users names that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 319 | match one of the patterns. |
| 320 | .Ql \&* |
| 321 | and |
| 322 | .Ql ? |
| 323 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 324 | wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 325 | Only user names are valid; a numerical user ID isn't recognized. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 326 | By default login is allowed regardless of the user name. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 327 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 328 | .It Cm Ciphers |
| 329 | Specifies the ciphers allowed for protocol version 2. |
| 330 | Multiple ciphers must be comma-separated. |
| 331 | The default is |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 332 | .Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 333 | .It Cm CheckMail |
| 334 | Specifies whether |
| 335 | .Nm |
| 336 | should check for new mail for interactive logins. |
| 337 | The default is |
| 338 | .Dq no . |
| 339 | .It Cm DenyGroups |
| 340 | This keyword can be followed by a number of group names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 341 | by spaces. |
| 342 | Users whose primary group matches one of the patterns |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 343 | aren't allowed to log in. |
| 344 | .Ql \&* |
| 345 | and |
| 346 | .Ql ? |
| 347 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 348 | wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 349 | Only group names are valid; a numerical group ID isn't recognized. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 350 | By default login is allowed regardless of the primary group. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 351 | .Pp |
| 352 | .It Cm DenyUsers |
| 353 | This keyword can be followed by a number of user names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 354 | by spaces. |
| 355 | Login is disallowed for user names that match one of the patterns. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 356 | .Ql \&* |
| 357 | and |
| 358 | .Ql ? |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 359 | can be used as wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 360 | Only user names are valid; a numerical user ID isn't recognized. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 361 | By default login is allowed regardless of the user name. |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 362 | .It Cm PubkeyAuthentication |
| 363 | Specifies whether public key authentication is allowed. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 364 | The default is |
| 365 | .Dq yes . |
| 366 | Note that this option applies to protocol version 2 only. |
| 367 | .It Cm GatewayPorts |
| 368 | Specifies whether remote hosts are allowed to connect to ports |
| 369 | forwarded for the client. |
| 370 | The argument must be |
| 371 | .Dq yes |
| 372 | or |
| 373 | .Dq no . |
| 374 | The default is |
| 375 | .Dq no . |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 376 | .It Cm HostKey |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 377 | Specifies the file containing the private host keys (default |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 378 | .Pa /etc/ssh_host_key ) |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 379 | used by SSH protocol versions 1 and 2. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 380 | Note that |
| 381 | .Nm |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 382 | if this file is group/world-accessible. |
| 383 | It is possible to have multiple host key files. |
| 384 | .Dq rsa1 |
| 385 | keys are used for version 1 and |
| 386 | .Dq dsa |
| 387 | or |
| 388 | .Dq rsa |
| 389 | are used for version 2 of the SSH protocol. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 390 | .It Cm IgnoreRhosts |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 391 | Specifies that |
| 392 | .Pa .rhosts |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 393 | and |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 394 | .Pa .shosts |
| 395 | files will not be used in authentication. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 396 | .Pa /etc/hosts.equiv |
| 397 | and |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 398 | .Pa /etc/shosts.equiv |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 399 | are still used. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 400 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 401 | .Dq yes . |
Damien Miller | 3226509 | 1999-11-12 11:33:04 +1100 | [diff] [blame] | 402 | .It Cm IgnoreUserKnownHosts |
| 403 | Specifies whether |
| 404 | .Nm |
| 405 | should ignore the user's |
| 406 | .Pa $HOME/.ssh/known_hosts |
| 407 | during |
| 408 | .Cm RhostsRSAAuthentication . |
| 409 | The default is |
| 410 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 411 | .It Cm KeepAlive |
| 412 | Specifies whether the system should send keepalive messages to the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 413 | other side. |
| 414 | If they are sent, death of the connection or crash of one |
| 415 | of the machines will be properly noticed. |
| 416 | However, this means that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 417 | connections will die if the route is down temporarily, and some people |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 418 | find it annoying. |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 419 | On the other hand, if keepalives are not sent, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 420 | sessions may hang indefinitely on the server, leaving |
| 421 | .Dq ghost |
| 422 | users and consuming server resources. |
| 423 | .Pp |
| 424 | The default is |
| 425 | .Dq yes |
| 426 | (to send keepalives), and the server will notice |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 427 | if the network goes down or the client host reboots. |
| 428 | This avoids infinitely hanging sessions. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 429 | .Pp |
| 430 | To disable keepalives, the value should be set to |
| 431 | .Dq no |
| 432 | in both the server and the client configuration files. |
| 433 | .It Cm KerberosAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 434 | Specifies whether Kerberos authentication is allowed. |
| 435 | This can be in the form of a Kerberos ticket, or if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 436 | .Cm PasswordAuthentication |
| 437 | is yes, the password provided by the user will be validated through |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 438 | the Kerberos KDC. |
| 439 | To use this option, the server needs a |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 440 | Kerberos servtab which allows the verification of the KDC's identity. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 441 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 442 | .Dq yes . |
| 443 | .It Cm KerberosOrLocalPasswd |
| 444 | If set then if password authentication through Kerberos fails then |
| 445 | the password will be validated via any additional local mechanism |
| 446 | such as |
Damien Miller | 62cee00 | 2000-09-23 17:15:56 +1100 | [diff] [blame] | 447 | .Pa /etc/passwd . |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 448 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 449 | .Dq yes . |
| 450 | .It Cm KerberosTgtPassing |
| 451 | Specifies whether a Kerberos TGT may be forwarded to the server. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 452 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 453 | .Dq no , |
| 454 | as this only works when the Kerberos KDC is actually an AFS kaserver. |
| 455 | .It Cm KerberosTicketCleanup |
| 456 | Specifies whether to automatically destroy the user's ticket cache |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 457 | file on logout. |
| 458 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 459 | .Dq yes . |
| 460 | .It Cm KeyRegenerationInterval |
| 461 | The server key is automatically regenerated after this many seconds |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 462 | (if it has been used). |
| 463 | The purpose of regeneration is to prevent |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 464 | decrypting captured sessions by later breaking into the machine and |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 465 | stealing the keys. |
| 466 | The key is never stored anywhere. |
| 467 | If the value is 0, the key is never regenerated. |
| 468 | The default is 3600 (seconds). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 469 | .It Cm ListenAddress |
| 470 | Specifies what local address |
| 471 | .Nm |
| 472 | should listen on. |
| 473 | The default is to listen to all local addresses. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 474 | Multiple options of this type are permitted. |
| 475 | Additionally, the |
| 476 | .Cm Ports |
| 477 | options must precede this option. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 478 | .It Cm LoginGraceTime |
| 479 | The server disconnects after this time if the user has not |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 480 | successfully logged in. |
| 481 | If the value is 0, there is no time limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 482 | The default is 600 (seconds). |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 483 | .It Cm LogLevel |
| 484 | Gives the verbosity level that is used when logging messages from |
| 485 | .Nm sshd . |
| 486 | The possible values are: |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 487 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 488 | The default is INFO. |
| 489 | Logging with level DEBUG violates the privacy of users |
| 490 | and is not recommended. |
Damien Miller | 3702396 | 2000-07-11 17:31:38 +1000 | [diff] [blame] | 491 | .It Cm MaxStartups |
| 492 | Specifies the maximum number of concurrent unauthenticated connections to the |
| 493 | .Nm |
| 494 | daemon. |
| 495 | Additional connections will be dropped until authentication succeeds or the |
| 496 | .Cm LoginGraceTime |
| 497 | expires for a connection. |
| 498 | The default is 10. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 499 | .Pp |
| 500 | Alternatively, random early drop can be enabled by specifying |
| 501 | the three colon separated values |
| 502 | .Dq start:rate:full |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 503 | (e.g., "10:30:60"). |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 504 | .Nm |
| 505 | will refuse connection attempts with a probabillity of |
| 506 | .Dq rate/100 |
| 507 | (30%) |
| 508 | if there are currently |
| 509 | .Dq start |
| 510 | (10) |
| 511 | unauthenticated connections. |
| 512 | The probabillity increases linearly and all connection attempts |
| 513 | are refused if the number of unauthenticated connections reaches |
| 514 | .Dq full |
| 515 | (60). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 516 | .It Cm PasswordAuthentication |
| 517 | Specifies whether password authentication is allowed. |
| 518 | The default is |
| 519 | .Dq yes . |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 520 | Note that this option applies to both protocol versions 1 and 2. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 521 | .It Cm PermitEmptyPasswords |
| 522 | When password authentication is allowed, it specifies whether the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 523 | server allows login to accounts with empty password strings. |
| 524 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 525 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 526 | .It Cm PermitRootLogin |
| 527 | Specifies whether the root can log in using |
| 528 | .Xr ssh 1 . |
| 529 | The argument must be |
| 530 | .Dq yes , |
| 531 | .Dq without-password |
| 532 | or |
| 533 | .Dq no . |
| 534 | The default is |
| 535 | .Dq yes . |
| 536 | If this options is set to |
| 537 | .Dq without-password |
| 538 | only password authentication is disabled for root. |
| 539 | .Pp |
| 540 | Root login with RSA authentication when the |
| 541 | .Ar command |
| 542 | option has been |
| 543 | specified will be allowed regardless of the value of this setting |
| 544 | (which may be useful for taking remote backups even if root login is |
| 545 | normally not allowed). |
Damien Miller | 6f83b8e | 2000-05-02 09:23:45 +1000 | [diff] [blame] | 546 | .It Cm PidFile |
| 547 | Specifies the file that contains the process identifier of the |
| 548 | .Nm |
| 549 | daemon. |
| 550 | The default is |
| 551 | .Pa /var/run/sshd.pid . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 552 | .It Cm Port |
| 553 | Specifies the port number that |
| 554 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 555 | listens on. |
| 556 | The default is 22. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 557 | Multiple options of this type are permitted. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 558 | .It Cm PrintMotd |
| 559 | Specifies whether |
| 560 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 561 | should print |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 562 | .Pa /etc/motd |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 563 | when a user logs in interactively. |
| 564 | (On some systems it is also printed by the shell, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 565 | .Pa /etc/profile , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 566 | or equivalent.) |
| 567 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 568 | .Dq yes . |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 569 | .It Cm Protocol |
| 570 | Specifies the protocol versions |
| 571 | .Nm |
| 572 | should support. |
| 573 | The possible values are |
| 574 | .Dq 1 |
| 575 | and |
| 576 | .Dq 2 . |
| 577 | Multiple versions must be comma-separated. |
| 578 | The default is |
| 579 | .Dq 1 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 580 | .It Cm RandomSeed |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 581 | Obsolete. |
| 582 | Random number generation uses other techniques. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 583 | .It Cm RhostsAuthentication |
| 584 | Specifies whether authentication using rhosts or /etc/hosts.equiv |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 585 | files is sufficient. |
| 586 | Normally, this method should not be permitted because it is insecure. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 587 | .Cm RhostsRSAAuthentication |
| 588 | should be used |
| 589 | instead, because it performs RSA-based host authentication in addition |
| 590 | to normal rhosts or /etc/hosts.equiv authentication. |
| 591 | The default is |
| 592 | .Dq no . |
| 593 | .It Cm RhostsRSAAuthentication |
| 594 | Specifies whether rhosts or /etc/hosts.equiv authentication together |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 595 | with successful RSA host authentication is allowed. |
| 596 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 597 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 598 | .It Cm RSAAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 599 | Specifies whether pure RSA authentication is allowed. |
| 600 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 601 | .Dq yes . |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 602 | Note that this option applies to protocol version 1 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 603 | .It Cm ServerKeyBits |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 604 | Defines the number of bits in the server key. |
| 605 | The minimum value is 512, and the default is 768. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 606 | .It Cm SkeyAuthentication |
| 607 | Specifies whether |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 608 | .Xr skey 1 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 609 | authentication is allowed. |
| 610 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 611 | .Dq yes . |
| 612 | Note that s/key authentication is enabled only if |
| 613 | .Cm PasswordAuthentication |
| 614 | is allowed, too. |
| 615 | .It Cm StrictModes |
| 616 | Specifies whether |
| 617 | .Nm |
| 618 | should check file modes and ownership of the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 619 | user's files and home directory before accepting login. |
| 620 | This is normally desirable because novices sometimes accidentally leave their |
| 621 | directory or files world-writable. |
| 622 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 623 | .Dq yes . |
Damien Miller | f6d9e22 | 2000-06-18 14:50:44 +1000 | [diff] [blame] | 624 | .It Cm Subsystem |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 625 | Configures an external subsystem (e.g., file transfer daemon). |
| 626 | Arguments should be a subsystem name and a command to execute upon subsystem |
| 627 | request. |
Damien Miller | 7b28dc5 | 2000-09-05 13:34:53 +1100 | [diff] [blame] | 628 | The command |
| 629 | .Xr sftp-server 8 |
| 630 | implements the |
| 631 | .Dq sftp |
| 632 | file transfer subsystem. |
Damien Miller | f6d9e22 | 2000-06-18 14:50:44 +1000 | [diff] [blame] | 633 | By default no subsystems are defined. |
| 634 | Note that this option applies to protocol version 2 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 635 | .It Cm SyslogFacility |
| 636 | Gives the facility code that is used when logging messages from |
| 637 | .Nm sshd . |
| 638 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 639 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
| 640 | The default is AUTH. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 641 | .It Cm UseLogin |
| 642 | Specifies whether |
| 643 | .Xr login 1 |
Damien Miller | d3a1857 | 2000-06-07 19:55:44 +1000 | [diff] [blame] | 644 | is used for interactive login sessions. |
| 645 | Note that |
| 646 | .Xr login 1 |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 647 | is never used for remote command execution. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 648 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 649 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 650 | .It Cm X11DisplayOffset |
| 651 | Specifies the first display number available for |
| 652 | .Nm sshd Ns 's |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 653 | X11 forwarding. |
| 654 | This prevents |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 655 | .Nm |
| 656 | from interfering with real X11 servers. |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 657 | The default is 10. |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 658 | .It Cm X11Forwarding |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 659 | Specifies whether X11 forwarding is permitted. |
| 660 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 661 | .Dq no . |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 662 | Note that disabling X11 forwarding does not improve security in any |
| 663 | way, as users can always install their own forwarders. |
Damien Miller | d3a1857 | 2000-06-07 19:55:44 +1000 | [diff] [blame] | 664 | .It Cm XAuthLocation |
| 665 | Specifies the location of the |
| 666 | .Xr xauth 1 |
| 667 | program. |
| 668 | The default is |
| 669 | .Pa /usr/X11R6/bin/xauth . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 670 | .El |
| 671 | .Sh LOGIN PROCESS |
| 672 | When a user successfully logs in, |
| 673 | .Nm |
| 674 | does the following: |
| 675 | .Bl -enum -offset indent |
| 676 | .It |
| 677 | 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] | 678 | prints last login time and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 679 | .Pa /etc/motd |
| 680 | (unless prevented in the configuration file or by |
| 681 | .Pa $HOME/.hushlogin ; |
| 682 | see the |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 683 | .Sx FILES |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 684 | section). |
| 685 | .It |
| 686 | If the login is on a tty, records login time. |
| 687 | .It |
| 688 | Checks |
| 689 | .Pa /etc/nologin ; |
| 690 | if it exists, prints contents and quits |
| 691 | (unless root). |
| 692 | .It |
| 693 | Changes to run with normal user privileges. |
| 694 | .It |
| 695 | Sets up basic environment. |
| 696 | .It |
| 697 | Reads |
| 698 | .Pa $HOME/.ssh/environment |
| 699 | if it exists. |
| 700 | .It |
| 701 | Changes to user's home directory. |
| 702 | .It |
| 703 | If |
| 704 | .Pa $HOME/.ssh/rc |
| 705 | exists, runs it; else if |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 706 | .Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 707 | exists, runs |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 708 | it; otherwise runs xauth. |
| 709 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 710 | .Dq rc |
| 711 | files are given the X11 |
| 712 | authentication protocol and cookie in standard input. |
| 713 | .It |
| 714 | Runs user's shell or command. |
| 715 | .El |
| 716 | .Sh AUTHORIZED_KEYS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 717 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 718 | .Pa $HOME/.ssh/authorized_keys |
| 719 | file lists the RSA keys that are |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 720 | permitted for RSA authentication in SSH protocols 1.3 and 1.5 |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 721 | Similarly, the |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 722 | .Pa $HOME/.ssh/authorized_keys2 |
| 723 | file lists the DSA keys that are |
| 724 | permitted for DSA authentication in SSH protocol 2.0. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 725 | Each line of the file contains one |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 726 | key (empty lines and lines starting with a |
| 727 | .Ql # |
| 728 | are ignored as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 729 | comments). |
| 730 | Each line consists of the following fields, separated by |
| 731 | spaces: options, bits, exponent, modulus, comment. |
| 732 | The options field |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 733 | is optional; its presence is determined by whether the line starts |
| 734 | with a number or not (the option field never starts with a number). |
| 735 | The bits, exponent, modulus and comment fields give the RSA key; the |
| 736 | comment field is not used for anything (but may be convenient for the |
| 737 | user to identify the key). |
| 738 | .Pp |
| 739 | Note that lines in this file are usually several hundred bytes long |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 740 | (because of the size of the RSA key modulus). |
| 741 | You don't want to type them in; instead, copy the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 742 | .Pa identity.pub |
| 743 | file and edit it. |
| 744 | .Pp |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 745 | The options (if present) consist of comma-separated option |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 746 | specifications. |
| 747 | No spaces are permitted, except within double quotes. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 748 | The following option specifications are supported: |
| 749 | .Bl -tag -width Ds |
| 750 | .It Cm from="pattern-list" |
| 751 | Specifies that in addition to RSA authentication, the canonical name |
| 752 | 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] | 753 | patterns |
| 754 | .Pf ( Ql * |
| 755 | and |
| 756 | .Ql ? |
| 757 | serve as wildcards). |
| 758 | The list may also contain |
| 759 | patterns negated by prefixing them with |
| 760 | .Ql ! ; |
| 761 | if the canonical host name matches a negated pattern, the key is not accepted. |
| 762 | The purpose |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 763 | of this option is to optionally increase security: RSA authentication |
| 764 | by itself does not trust the network or name servers or anything (but |
| 765 | the key); however, if somebody somehow steals the key, the key |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 766 | permits an intruder to log in from anywhere in the world. |
| 767 | This additional option makes using a stolen key more difficult (name |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 768 | servers and/or routers would have to be compromised in addition to |
| 769 | just the key). |
| 770 | .It Cm command="command" |
| 771 | Specifies that the command is executed whenever this key is used for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 772 | authentication. |
| 773 | The command supplied by the user (if any) is ignored. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 774 | 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] | 775 | otherwise it is run without a tty. |
| 776 | A quote may be included in the command by quoting it with a backslash. |
| 777 | This option might be useful |
| 778 | to restrict certain RSA keys to perform just a specific operation. |
| 779 | 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] | 780 | Note that the client may specify TCP/IP and/or X11 |
| 781 | forwarding unless they are explicitly prohibited. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 782 | .It Cm environment="NAME=value" |
| 783 | Specifies that the string is to be added to the environment when |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 784 | logging in using this key. |
| 785 | Environment variables set this way |
| 786 | override other default environment values. |
| 787 | Multiple options of this type are permitted. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 788 | .It Cm no-port-forwarding |
| 789 | Forbids TCP/IP forwarding when this key is used for authentication. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 790 | Any port forward requests by the client will return an error. |
| 791 | This might be used, e.g., in connection with the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 792 | .Cm command |
| 793 | option. |
| 794 | .It Cm no-X11-forwarding |
| 795 | Forbids X11 forwarding when this key is used for authentication. |
| 796 | Any X11 forward requests by the client will return an error. |
| 797 | .It Cm no-agent-forwarding |
| 798 | Forbids authentication agent forwarding when this key is used for |
| 799 | authentication. |
| 800 | .It Cm no-pty |
| 801 | Prevents tty allocation (a request to allocate a pty will fail). |
| 802 | .El |
| 803 | .Ss Examples |
| 804 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar |
| 805 | .Pp |
| 806 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula |
| 807 | .Pp |
| 808 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi |
| 809 | .Sh SSH_KNOWN_HOSTS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 810 | The |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 811 | .Pa /etc/ssh_known_hosts , |
| 812 | .Pa /etc/ssh_known_hosts2 , |
| 813 | .Pa $HOME/.ssh/known_hosts , |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 814 | and |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 815 | .Pa $HOME/.ssh/known_hosts2 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 816 | files contain host public keys for all known hosts. |
| 817 | The global file should |
| 818 | be prepared by the administrator (optional), and the per-user file is |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 819 | maintained automatically: whenever the user connects from an unknown host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 820 | its key is added to the per-user file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 821 | .Pp |
| 822 | Each line in these files contains the following fields: hostnames, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 823 | bits, exponent, modulus, comment. |
| 824 | The fields are separated by spaces. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 825 | .Pp |
| 826 | Hostnames is a comma-separated list of patterns ('*' and '?' act as |
| 827 | wildcards); each pattern in turn is matched against the canonical host |
| 828 | name (when authenticating a client) or against the user-supplied |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 829 | name (when authenticating a server). |
| 830 | A pattern may also be preceded by |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 831 | .Ql ! |
| 832 | to indicate negation: if the host name matches a negated |
| 833 | pattern, it is not accepted (by that line) even if it matched another |
| 834 | pattern on the line. |
| 835 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 836 | 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] | 837 | can be obtained, e.g., from |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 838 | .Pa /etc/ssh_host_key.pub . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 839 | The optional comment field continues to the end of the line, and is not used. |
| 840 | .Pp |
| 841 | Lines starting with |
| 842 | .Ql # |
| 843 | and empty lines are ignored as comments. |
| 844 | .Pp |
| 845 | When performing host authentication, authentication is accepted if any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 846 | matching line has the proper key. |
| 847 | It is thus permissible (but not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 848 | recommended) to have several lines or different host keys for the same |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 849 | names. |
| 850 | This will inevitably happen when short forms of host names |
| 851 | from different domains are put in the file. |
| 852 | It is possible |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 853 | that the files contain conflicting information; authentication is |
| 854 | accepted if valid information can be found from either file. |
| 855 | .Pp |
| 856 | Note that the lines in these files are typically hundreds of characters |
| 857 | long, and you definitely don't want to type in the host keys by hand. |
| 858 | Rather, generate them by a script |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 859 | or by taking |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 860 | .Pa /etc/ssh_host_key.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 861 | and adding the host names at the front. |
| 862 | .Ss Examples |
| 863 | closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi |
| 864 | .Sh FILES |
| 865 | .Bl -tag -width Ds |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 866 | .It Pa /etc/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 867 | Contains configuration data for |
| 868 | .Nm sshd . |
| 869 | This file should be writable by root only, but it is recommended |
| 870 | (though not necessary) that it be world-readable. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 871 | .It Pa /etc/ssh_host_key |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 872 | Contains the private part of the host key. |
| 873 | This file should only be owned by root, readable only by root, and not |
| 874 | accessible to others. |
| 875 | Note that |
| 876 | .Nm |
| 877 | does not start if this file is group/world-accessible. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 878 | .It Pa /etc/ssh_host_key.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 879 | Contains the public part of the host key. |
| 880 | This file should be world-readable but writable only by |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 881 | root. |
| 882 | Its contents should match the private part. |
| 883 | This file is not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 884 | really used for anything; it is only provided for the convenience of |
| 885 | the user so its contents can be copied to known hosts files. |
| 886 | These two files are created using |
| 887 | .Xr ssh-keygen 1 . |
Damien Miller | e39cacc | 2000-11-29 12:18:44 +1100 | [diff] [blame] | 888 | .It Pa /etc/primes |
| 889 | Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange". |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 890 | .It Pa /var/run/sshd.pid |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 891 | Contains the process ID of the |
| 892 | .Nm |
| 893 | listening for connections (if there are several daemons running |
| 894 | concurrently for different ports, this contains the pid of the one |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 895 | started last). |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 896 | 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] | 897 | .It Pa $HOME/.ssh/authorized_keys |
| 898 | Lists the RSA keys that can be used to log into the user's account. |
| 899 | This file must be readable by root (which may on some machines imply |
| 900 | 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] | 901 | volume). |
| 902 | It is recommended that it not be accessible by others. |
| 903 | The format of this file is described above. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 904 | Users will place the contents of their |
| 905 | .Pa identity.pub |
| 906 | files into this file, as described in |
| 907 | .Xr ssh-keygen 1 . |
| 908 | .It Pa $HOME/.ssh/authorized_keys2 |
| 909 | Lists the DSA keys that can be used to log into the user's account. |
| 910 | This file must be readable by root (which may on some machines imply |
| 911 | it being world-readable if the user's home directory resides on an NFS |
| 912 | volume). |
| 913 | It is recommended that it not be accessible by others. |
| 914 | The format of this file is described above. |
| 915 | Users will place the contents of their |
| 916 | .Pa id_dsa.pub |
| 917 | files into this file, as described in |
| 918 | .Xr ssh-keygen 1 . |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 919 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 920 | These files are consulted when using rhosts with RSA host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 921 | authentication to check the public key of the host. |
| 922 | 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] | 923 | The client uses the same files |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 924 | to verify that the remote host is the one it intended to connect. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 925 | These files should be writable only by root/the owner. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 926 | .Pa /etc/ssh_known_hosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 927 | should be world-readable, and |
| 928 | .Pa $HOME/.ssh/known_hosts |
| 929 | can but need not be world-readable. |
| 930 | .It Pa /etc/nologin |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 931 | If this file exists, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 932 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 933 | refuses to let anyone except root log in. |
| 934 | The contents of the file |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 935 | 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] | 936 | refused. |
| 937 | The file should be world-readable. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 938 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
| 939 | If compiled with |
| 940 | .Sy LIBWRAP |
| 941 | support, tcp-wrappers access controls may be defined here as described in |
| 942 | .Xr hosts_access 5 . |
| 943 | .It Pa $HOME/.rhosts |
| 944 | This file contains host-username pairs, separated by a space, one per |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 945 | line. |
| 946 | The given user on the corresponding host is permitted to log in |
| 947 | without password. |
| 948 | The same file is used by rlogind and rshd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 949 | The file must |
| 950 | be writable only by the user; it is recommended that it not be |
| 951 | accessible by others. |
| 952 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 953 | If is also possible to use netgroups in the file. |
| 954 | Either host or user |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 955 | name may be of the form +@groupname to specify all hosts or all users |
| 956 | in the group. |
| 957 | .It Pa $HOME/.shosts |
| 958 | For ssh, |
| 959 | this file is exactly the same as for |
| 960 | .Pa .rhosts . |
| 961 | However, this file is |
| 962 | 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] | 963 | .It Pa /etc/hosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 964 | This file is used during |
| 965 | .Pa .rhosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 966 | authentication. |
| 967 | In the simplest form, this file contains host names, one per line. |
| 968 | Users on |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 969 | those hosts are permitted to log in without a password, provided they |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 970 | have the same user name on both machines. |
| 971 | The host name may also be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 972 | followed by a user name; such users are permitted to log in as |
| 973 | .Em any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 974 | user on this machine (except root). |
| 975 | Additionally, the syntax |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 976 | .Dq +@group |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 977 | can be used to specify netgroups. |
| 978 | Negated entries start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 979 | .Ql \&- . |
| 980 | .Pp |
| 981 | If the client host/user is successfully matched in this file, login is |
| 982 | automatically permitted provided the client and server user names are the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 983 | same. |
| 984 | Additionally, successful RSA host authentication is normally required. |
| 985 | This file must be writable only by root; it is recommended |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 986 | that it be world-readable. |
| 987 | .Pp |
| 988 | .Sy "Warning: It is almost never a good idea to use user names in" |
| 989 | .Pa hosts.equiv . |
| 990 | Beware that it really means that the named user(s) can log in as |
| 991 | .Em anybody , |
| 992 | which includes bin, daemon, adm, and other accounts that own critical |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 993 | binaries and directories. |
| 994 | Using a user name practically grants the user root access. |
| 995 | The only valid use for user names that I can think |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 996 | of is in negative entries. |
| 997 | .Pp |
| 998 | Note that this warning also applies to rsh/rlogin. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 999 | .It Pa /etc/shosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1000 | This is processed exactly as |
| 1001 | .Pa /etc/hosts.equiv . |
| 1002 | However, this file may be useful in environments that want to run both |
| 1003 | rsh/rlogin and ssh. |
| 1004 | .It Pa $HOME/.ssh/environment |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1005 | This file is read into the environment at login (if it exists). |
| 1006 | It can only contain empty lines, comment lines (that start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1007 | .Ql # ) , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1008 | and assignment lines of the form name=value. |
| 1009 | The file should be writable |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1010 | only by the user; it need not be readable by anyone else. |
| 1011 | .It Pa $HOME/.ssh/rc |
| 1012 | 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] | 1013 | environment files but before starting the user's shell or command. |
| 1014 | 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] | 1015 | standard input (and |
| 1016 | .Ev DISPLAY |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1017 | in environment). |
| 1018 | This must call |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1019 | .Xr xauth 1 |
| 1020 | in that case. |
| 1021 | .Pp |
| 1022 | The primary purpose of this file is to run any initialization routines |
| 1023 | which may be needed before the user's home directory becomes |
| 1024 | accessible; AFS is a particular example of such an environment. |
| 1025 | .Pp |
| 1026 | This file will probably contain some initialization code followed by |
| 1027 | something similar to: "if read proto cookie; then echo add $DISPLAY |
| 1028 | $proto $cookie | xauth -q -; fi". |
| 1029 | .Pp |
| 1030 | If this file does not exist, |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1031 | .Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1032 | is run, and if that |
| 1033 | does not exist either, xauth is used to store the cookie. |
| 1034 | .Pp |
| 1035 | This file should be writable only by the user, and need not be |
| 1036 | readable by anyone else. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1037 | .It Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1038 | Like |
| 1039 | .Pa $HOME/.ssh/rc . |
| 1040 | This can be used to specify |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1041 | machine-specific login-time initializations globally. |
| 1042 | 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] | 1043 | .El |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 1044 | .Sh AUTHORS |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1045 | OpenSSH |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 1046 | is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1047 | but with bugs removed and newer features re-added. |
| 1048 | Rapidly after the |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 1049 | 1.2.12 release, newer versions of the original ssh bore successively |
| 1050 | more restrictive licenses, and thus demand for a free version was born. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1051 | .Pp |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 1052 | This version of OpenSSH |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1053 | .Bl -bullet |
| 1054 | .It |
Damien Miller | e4340be | 2000-09-16 13:29:08 +1100 | [diff] [blame] | 1055 | has all components of a restrictive nature (i.e., patents, see |
| 1056 | .Xr crypto 3 ) |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1057 | directly removed from the source code; any licensed or patented components |
| 1058 | are chosen from |
| 1059 | external libraries. |
| 1060 | .It |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1061 | has been updated to support SSH protocol 1.5 and 2, making it compatible with |
| 1062 | all other SSH clients and servers. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1063 | .It |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1064 | contains added support for |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1065 | .Xr kerberos 8 |
| 1066 | authentication and ticket passing. |
| 1067 | .It |
| 1068 | supports one-time password authentication with |
| 1069 | .Xr skey 1 . |
| 1070 | .El |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1071 | .Pp |
| 1072 | OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl, |
| 1073 | Niels Provos, Theo de Raadt, and Dug Song. |
| 1074 | .Pp |
| 1075 | The support for SSH protocol 2 was written by Markus Friedl. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1076 | .Sh SEE ALSO |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1077 | .Xr scp 1 , |
Damien Miller | 7b28dc5 | 2000-09-05 13:34:53 +1100 | [diff] [blame] | 1078 | .Xr sftp-server 8 , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1079 | .Xr ssh 1 , |
| 1080 | .Xr ssh-add 1 , |
| 1081 | .Xr ssh-agent 1 , |
| 1082 | .Xr ssh-keygen 1 , |
Damien Miller | e4340be | 2000-09-16 13:29:08 +1100 | [diff] [blame] | 1083 | .Xr crypto 3 , |
Damien Miller | b38eff8 | 2000-04-01 11:09:21 +1000 | [diff] [blame] | 1084 | .Xr rlogin 1 , |
| 1085 | .Xr rsh 1 |