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 | .\" |
| 37 | .Dd September 25, 1999 |
| 38 | .Dt SSHD 8 |
| 39 | .Os |
| 40 | .Sh NAME |
| 41 | .Nm sshd |
| 42 | .Nd secure shell daemon |
| 43 | .Sh SYNOPSIS |
| 44 | .Nm sshd |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 45 | .Op Fl diqQ46 |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 46 | .Op Fl b Ar bits |
| 47 | .Op Fl f Ar config_file |
| 48 | .Op Fl g Ar login_grace_time |
| 49 | .Op Fl h Ar host_key_file |
| 50 | .Op Fl k Ar key_gen_time |
| 51 | .Op Fl p Ar port |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 52 | .Op Fl u Ar len |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 53 | .Op Fl V Ar client_protocol_id |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 54 | .Sh DESCRIPTION |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 55 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 56 | (Secure Shell Daemon) is the daemon program for |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 57 | .Xr ssh 1 . |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 58 | Together these programs replace rlogin and rsh, and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 59 | provide secure encrypted communications between two untrusted hosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 60 | over an insecure network. |
| 61 | The programs are intended to be as easy to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 62 | install and use as possible. |
| 63 | .Pp |
| 64 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 65 | is the daemon that listens for connections from clients. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 66 | It is normally started at boot from |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 67 | .Pa /etc/rc . |
| 68 | It forks a new |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 69 | daemon for each incoming connection. |
| 70 | The forked daemons handle |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 71 | key exchange, encryption, authentication, command execution, |
| 72 | and data exchange. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 73 | This implementation of |
| 74 | .Nm |
| 75 | supports both SSH protocol version 1 and 2 simultaneously. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 76 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 77 | works as follows. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 78 | .Pp |
| 79 | .Ss SSH protocol version 1 |
| 80 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 81 | Each host has a host-specific RSA key |
| 82 | (normally 1024 bits) used to identify the host. |
| 83 | Additionally, when |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 84 | the daemon starts, it generates a server RSA key (normally 768 bits). |
| 85 | This key is normally regenerated every hour if it has been used, and |
| 86 | is never stored on disk. |
| 87 | .Pp |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 88 | Whenever a client connects the daemon responds with its public |
| 89 | host and server keys. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 90 | The client compares the |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 91 | 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] | 92 | The client then generates a 256 bit random number. |
| 93 | It encrypts this |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 94 | 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] | 95 | the encrypted number to the server. |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 96 | Both sides then use this |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 97 | 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] | 98 | communications in the session. |
| 99 | The rest of the session is encrypted |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 100 | using a conventional cipher, currently Blowfish or 3DES, with 3DES |
Damien Miller | b38eff8 | 2000-04-01 11:09:21 +1000 | [diff] [blame] | 101 | being used by default. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 102 | The client selects the encryption algorithm |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 103 | to use from those offered by the server. |
| 104 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 105 | Next, the server and the client enter an authentication dialog. |
| 106 | The client tries to authenticate itself using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 107 | .Pa .rhosts |
| 108 | authentication, |
| 109 | .Pa .rhosts |
| 110 | authentication combined with RSA host |
| 111 | authentication, RSA challenge-response authentication, or password |
| 112 | based authentication. |
| 113 | .Pp |
| 114 | Rhosts authentication is normally disabled |
| 115 | because it is fundamentally insecure, but can be enabled in the server |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 116 | configuration file if desired. |
| 117 | System security is not improved unless |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 118 | .Xr rshd 8 , |
| 119 | .Xr rlogind 8 , |
| 120 | .Xr rexecd 8 , |
| 121 | and |
| 122 | .Xr rexd 8 |
| 123 | are disabled (thus completely disabling |
| 124 | .Xr rlogin 1 |
| 125 | and |
| 126 | .Xr rsh 1 |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 127 | into the machine). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 128 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 129 | .Ss SSH protocol version 2 |
| 130 | .Pp |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 131 | Version 2 works similarly: |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 132 | Each host has a host-specific DSA key used to identify the host. |
| 133 | However, when the daemon starts, it does not generate a server key. |
| 134 | Forward security is provided through a Diffie-Hellman key agreement. |
| 135 | This key agreement results in a shared session key. |
| 136 | The rest of the session is encrypted |
| 137 | using a symmetric cipher, currently |
| 138 | Blowfish, 3DES or CAST128 in CBC mode or Arcfour. |
| 139 | The client selects the encryption algorithm |
| 140 | to use from those offered by the server. |
| 141 | Additionally, session integrity is provided |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 142 | through a cryptographic message authentication code |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 143 | (hmac-sha1 or hmac-md5). |
| 144 | .Pp |
| 145 | Protocol version 2 provides a public key based |
| 146 | user authentication method (DSAAuthentication) |
| 147 | and conventional password authentication. |
| 148 | .Pp |
| 149 | .Ss Command execution and data forwarding |
| 150 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 151 | If the client successfully authenticates itself, a dialog for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 152 | preparing the session is entered. |
| 153 | At this time the client may request |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 154 | things like allocating a pseudo-tty, forwarding X11 connections, |
| 155 | forwarding TCP/IP connections, or forwarding the authentication agent |
| 156 | connection over the secure channel. |
| 157 | .Pp |
| 158 | Finally, the client either requests a shell or execution of a command. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 159 | The sides then enter session mode. |
| 160 | In this mode, either side may send |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 161 | data at any time, and such data is forwarded to/from the shell or |
| 162 | command on the server side, and the user terminal in the client side. |
| 163 | .Pp |
| 164 | When the user program terminates and all forwarded X11 and other |
| 165 | connections have been closed, the server sends command exit status to |
| 166 | the client, and both sides exit. |
| 167 | .Pp |
| 168 | .Nm |
| 169 | can be configured using command-line options or a configuration |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 170 | file. |
| 171 | Command-line options override values specified in the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 172 | configuration file. |
| 173 | .Pp |
Damien Miller | 6162d12 | 1999-11-21 13:23:52 +1100 | [diff] [blame] | 174 | .Nm |
| 175 | rereads its configuration file when it receives a hangup signal, |
| 176 | .Dv SIGHUP . |
| 177 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 178 | The options are as follows: |
| 179 | .Bl -tag -width Ds |
| 180 | .It Fl b Ar bits |
| 181 | Specifies the number of bits in the server key (default 768). |
| 182 | .Pp |
| 183 | .It Fl d |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 184 | Debug mode. |
| 185 | The server sends verbose debug output to the system |
| 186 | log, and does not put itself in the background. |
| 187 | The server also will not fork and will only process one connection. |
| 188 | This option is only intended for debugging for the server. |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 189 | Multiple -d options increases the debugging level. |
| 190 | Maximum is 3. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 191 | .It Fl f Ar configuration_file |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 192 | Specifies the name of the configuration file. |
| 193 | The default is |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 194 | .Pa /etc/sshd_config . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 195 | .Nm |
| 196 | refuses to start if there is no configuration file. |
| 197 | .It Fl g Ar login_grace_time |
| 198 | Gives the grace time for clients to authenticate themselves (default |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 199 | 300 seconds). |
| 200 | If the client fails to authenticate the user within |
| 201 | this many seconds, the server disconnects and exits. |
| 202 | A value of zero indicates no limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 203 | .It Fl h Ar host_key_file |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 204 | Specifies the file from which the RSA host key is read (default |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 205 | .Pa /etc/ssh_host_key ) . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 206 | This option must be given if |
| 207 | .Nm |
| 208 | is not run as root (as the normal |
| 209 | host file is normally not readable by anyone but root). |
| 210 | .It Fl i |
| 211 | Specifies that |
| 212 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 213 | is being run from inetd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 214 | .Nm |
| 215 | is normally not run |
| 216 | 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] | 217 | respond to the client, and this may take tens of seconds. |
| 218 | 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] | 219 | However, with small key sizes (e.g., 512) using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 220 | .Nm |
| 221 | from inetd may |
| 222 | be feasible. |
| 223 | .It Fl k Ar key_gen_time |
| 224 | Specifies how often the server key is regenerated (default 3600 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 225 | seconds, or one hour). |
| 226 | The motivation for regenerating the key fairly |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 227 | often is that the key is not stored anywhere, and after about an hour, |
| 228 | it becomes impossible to recover the key for decrypting intercepted |
| 229 | communications even if the machine is cracked into or physically |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 230 | seized. |
| 231 | A value of zero indicates that the key will never be regenerated. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 232 | .It Fl p Ar port |
| 233 | Specifies the port on which the server listens for connections |
| 234 | (default 22). |
| 235 | .It Fl q |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 236 | Quiet mode. |
| 237 | Nothing is sent to the system log. |
| 238 | Normally the beginning, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 239 | authentication, and termination of each connection is logged. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 240 | .It Fl u Ar len |
| 241 | This option is used to specify the size of the field |
| 242 | in the |
| 243 | .Li utmp |
| 244 | structure that holds the remote host name. |
| 245 | If the resolved host name is longer than |
| 246 | .Ar len , |
| 247 | the dotted decimal value will be used instead. |
| 248 | This allows hosts with very long host names that |
| 249 | overflow this field to still be uniquely identified. |
| 250 | Specifying |
| 251 | .Fl u0 |
| 252 | indicates that only dotted decimal addresses |
| 253 | should be put into the |
| 254 | .Pa utmp |
| 255 | file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 256 | .It Fl Q |
| 257 | Do not print an error message if RSA support is missing. |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 258 | .It Fl V Ar client_protocol_id |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 259 | SSH-2 compatibility mode. |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 260 | When this option is specified |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 261 | .Nm |
Damien Miller | 35dabd0 | 2000-05-01 21:10:33 +1000 | [diff] [blame] | 262 | assumes the client has sent the supplied version string |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 263 | and skips the |
| 264 | Protocol Version Identification Exchange. |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 265 | This option is not intended to be called directly. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 266 | .It Fl 4 |
| 267 | Forces |
| 268 | .Nm |
| 269 | to use IPv4 addresses only. |
| 270 | .It Fl 6 |
| 271 | Forces |
| 272 | .Nm |
| 273 | to use IPv6 addresses only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 274 | .El |
| 275 | .Sh CONFIGURATION FILE |
| 276 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 277 | reads configuration data from |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 278 | .Pa /etc/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 279 | (or the file specified with |
| 280 | .Fl f |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 281 | on the command line). |
| 282 | The file contains keyword-value pairs, one per line. |
| 283 | Lines starting with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 284 | .Ql # |
| 285 | and empty lines are interpreted as comments. |
| 286 | .Pp |
| 287 | The following keywords are possible. |
| 288 | .Bl -tag -width Ds |
| 289 | .It Cm AFSTokenPassing |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 290 | Specifies whether an AFS token may be forwarded to the server. |
| 291 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 292 | .Dq yes . |
| 293 | .It Cm AllowGroups |
| 294 | This keyword can be followed by a number of group names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 295 | by spaces. |
| 296 | If specified, login is allowed only for users whose primary |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 297 | group matches one of the patterns. |
| 298 | .Ql \&* |
| 299 | and |
| 300 | .Ql ? |
| 301 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 302 | wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 303 | Only group names are valid; a numerical group ID isn't recognized. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 304 | By default login is allowed regardless of the primary group. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 305 | .Pp |
Damien Miller | 50a41ed | 2000-10-16 12:14:42 +1100 | [diff] [blame] | 306 | .It Cm AllowTcpForwarding |
| 307 | Specifies whether TCP forwarding is permitted. |
| 308 | The default is |
| 309 | .Dq yes . |
| 310 | Note that disabling TCP forwarding does not improve security unless |
| 311 | users are also denied shell access, as they can always install their |
| 312 | own forwarders. |
| 313 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 314 | .It Cm AllowUsers |
| 315 | This keyword can be followed by a number of user names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 316 | by spaces. |
| 317 | If specified, login is allowed only for users names that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 318 | match one of the patterns. |
| 319 | .Ql \&* |
| 320 | and |
| 321 | .Ql ? |
| 322 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 323 | wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 324 | Only user names are valid; a numerical user ID isn't recognized. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 325 | By default login is allowed regardless of the user name. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 326 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 327 | .It Cm Ciphers |
| 328 | Specifies the ciphers allowed for protocol version 2. |
| 329 | Multiple ciphers must be comma-separated. |
| 330 | The default is |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 331 | .Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 332 | .It Cm CheckMail |
| 333 | Specifies whether |
| 334 | .Nm |
| 335 | should check for new mail for interactive logins. |
| 336 | The default is |
| 337 | .Dq no . |
| 338 | .It Cm DenyGroups |
| 339 | This keyword can be followed by a number of group names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 340 | by spaces. |
| 341 | Users whose primary group matches one of the patterns |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 342 | aren't allowed to log in. |
| 343 | .Ql \&* |
| 344 | and |
| 345 | .Ql ? |
| 346 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 347 | wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 348 | Only group names are valid; a numerical group ID isn't recognized. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 349 | By default login is allowed regardless of the primary group. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 350 | .Pp |
| 351 | .It Cm DenyUsers |
| 352 | This keyword can be followed by a number of user names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 353 | by spaces. |
| 354 | Login is disallowed for user names that match one of the patterns. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 355 | .Ql \&* |
| 356 | and |
| 357 | .Ql ? |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 358 | can be used as wildcards in the patterns. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 359 | Only user names are valid; a numerical user ID isn't recognized. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 360 | By default login is allowed regardless of the user name. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 361 | .It Cm DSAAuthentication |
| 362 | Specifies whether DSA authentication is allowed. |
| 363 | The default is |
| 364 | .Dq yes . |
| 365 | Note that this option applies to protocol version 2 only. |
| 366 | .It Cm GatewayPorts |
| 367 | Specifies whether remote hosts are allowed to connect to ports |
| 368 | forwarded for the client. |
| 369 | The argument must be |
| 370 | .Dq yes |
| 371 | or |
| 372 | .Dq no . |
| 373 | The default is |
| 374 | .Dq no . |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 375 | .It Cm HostDSAKey |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 376 | Specifies the file containing the private DSA host key (default |
| 377 | .Pa /etc/ssh_host_dsa_key ) |
| 378 | used by SSH protocol 2.0. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 379 | Note that |
| 380 | .Nm |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 381 | disables protocol 2.0 if this file is group/world-accessible. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 382 | .It Cm HostKey |
| 383 | Specifies the file containing the private RSA host key (default |
| 384 | .Pa /etc/ssh_host_key ) |
| 385 | used by SSH protocols 1.3 and 1.5. |
| 386 | Note that |
| 387 | .Nm |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 388 | disables protocols 1.3 and 1.5 if this file is group/world-accessible. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 389 | .It Cm IgnoreRhosts |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 390 | Specifies that |
| 391 | .Pa .rhosts |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 392 | and |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 393 | .Pa .shosts |
| 394 | files will not be used in authentication. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 395 | .Pa /etc/hosts.equiv |
| 396 | and |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 397 | .Pa /etc/shosts.equiv |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 398 | are still used. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 399 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 400 | .Dq yes . |
Damien Miller | 3226509 | 1999-11-12 11:33:04 +1100 | [diff] [blame] | 401 | .It Cm IgnoreUserKnownHosts |
| 402 | Specifies whether |
| 403 | .Nm |
| 404 | should ignore the user's |
| 405 | .Pa $HOME/.ssh/known_hosts |
| 406 | during |
| 407 | .Cm RhostsRSAAuthentication . |
| 408 | The default is |
| 409 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 410 | .It Cm KeepAlive |
| 411 | Specifies whether the system should send keepalive messages to the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 412 | other side. |
| 413 | If they are sent, death of the connection or crash of one |
| 414 | of the machines will be properly noticed. |
| 415 | However, this means that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 416 | connections will die if the route is down temporarily, and some people |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 417 | find it annoying. |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 418 | On the other hand, if keepalives are not sent, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 419 | sessions may hang indefinitely on the server, leaving |
| 420 | .Dq ghost |
| 421 | users and consuming server resources. |
| 422 | .Pp |
| 423 | The default is |
| 424 | .Dq yes |
| 425 | (to send keepalives), and the server will notice |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 426 | if the network goes down or the client host reboots. |
| 427 | This avoids infinitely hanging sessions. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 428 | .Pp |
| 429 | To disable keepalives, the value should be set to |
| 430 | .Dq no |
| 431 | in both the server and the client configuration files. |
| 432 | .It Cm KerberosAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 433 | Specifies whether Kerberos authentication is allowed. |
| 434 | This can be in the form of a Kerberos ticket, or if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 435 | .Cm PasswordAuthentication |
| 436 | is yes, the password provided by the user will be validated through |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 437 | the Kerberos KDC. |
| 438 | To use this option, the server needs a |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 439 | Kerberos servtab which allows the verification of the KDC's identity. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 440 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 441 | .Dq yes . |
| 442 | .It Cm KerberosOrLocalPasswd |
| 443 | If set then if password authentication through Kerberos fails then |
| 444 | the password will be validated via any additional local mechanism |
| 445 | such as |
Damien Miller | 62cee00 | 2000-09-23 17:15:56 +1100 | [diff] [blame] | 446 | .Pa /etc/passwd . |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 447 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 448 | .Dq yes . |
| 449 | .It Cm KerberosTgtPassing |
| 450 | Specifies whether a Kerberos TGT may be forwarded to the server. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 451 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 452 | .Dq no , |
| 453 | as this only works when the Kerberos KDC is actually an AFS kaserver. |
| 454 | .It Cm KerberosTicketCleanup |
| 455 | Specifies whether to automatically destroy the user's ticket cache |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 456 | file on logout. |
| 457 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 458 | .Dq yes . |
| 459 | .It Cm KeyRegenerationInterval |
| 460 | The server key is automatically regenerated after this many seconds |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 461 | (if it has been used). |
| 462 | The purpose of regeneration is to prevent |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 463 | decrypting captured sessions by later breaking into the machine and |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 464 | stealing the keys. |
| 465 | The key is never stored anywhere. |
| 466 | If the value is 0, the key is never regenerated. |
| 467 | The default is 3600 (seconds). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 468 | .It Cm ListenAddress |
| 469 | Specifies what local address |
| 470 | .Nm |
| 471 | should listen on. |
| 472 | The default is to listen to all local addresses. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 473 | Multiple options of this type are permitted. |
| 474 | Additionally, the |
| 475 | .Cm Ports |
| 476 | options must precede this option. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 477 | .It Cm LoginGraceTime |
| 478 | The server disconnects after this time if the user has not |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 479 | successfully logged in. |
| 480 | If the value is 0, there is no time limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 481 | The default is 600 (seconds). |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 482 | .It Cm LogLevel |
| 483 | Gives the verbosity level that is used when logging messages from |
| 484 | .Nm sshd . |
| 485 | The possible values are: |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 486 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 487 | The default is INFO. |
| 488 | Logging with level DEBUG violates the privacy of users |
| 489 | and is not recommended. |
Damien Miller | 3702396 | 2000-07-11 17:31:38 +1000 | [diff] [blame] | 490 | .It Cm MaxStartups |
| 491 | Specifies the maximum number of concurrent unauthenticated connections to the |
| 492 | .Nm |
| 493 | daemon. |
| 494 | Additional connections will be dropped until authentication succeeds or the |
| 495 | .Cm LoginGraceTime |
| 496 | expires for a connection. |
| 497 | The default is 10. |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 498 | .Pp |
| 499 | Alternatively, random early drop can be enabled by specifying |
| 500 | the three colon separated values |
| 501 | .Dq start:rate:full |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 502 | (e.g., "10:30:60"). |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 503 | .Nm |
| 504 | will refuse connection attempts with a probabillity of |
| 505 | .Dq rate/100 |
| 506 | (30%) |
| 507 | if there are currently |
| 508 | .Dq start |
| 509 | (10) |
| 510 | unauthenticated connections. |
| 511 | The probabillity increases linearly and all connection attempts |
| 512 | are refused if the number of unauthenticated connections reaches |
| 513 | .Dq full |
| 514 | (60). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 515 | .It Cm PasswordAuthentication |
| 516 | Specifies whether password authentication is allowed. |
| 517 | The default is |
| 518 | .Dq yes . |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 519 | Note that this option applies to both protocol versions 1 and 2. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 520 | .It Cm PermitEmptyPasswords |
| 521 | When password authentication is allowed, it specifies whether the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 522 | server allows login to accounts with empty password strings. |
| 523 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 524 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 525 | .It Cm PermitRootLogin |
| 526 | Specifies whether the root can log in using |
| 527 | .Xr ssh 1 . |
| 528 | The argument must be |
| 529 | .Dq yes , |
| 530 | .Dq without-password |
| 531 | or |
| 532 | .Dq no . |
| 533 | The default is |
| 534 | .Dq yes . |
| 535 | If this options is set to |
| 536 | .Dq without-password |
| 537 | only password authentication is disabled for root. |
| 538 | .Pp |
| 539 | Root login with RSA authentication when the |
| 540 | .Ar command |
| 541 | option has been |
| 542 | specified will be allowed regardless of the value of this setting |
| 543 | (which may be useful for taking remote backups even if root login is |
| 544 | normally not allowed). |
Damien Miller | 6f83b8e | 2000-05-02 09:23:45 +1000 | [diff] [blame] | 545 | .It Cm PidFile |
| 546 | Specifies the file that contains the process identifier of the |
| 547 | .Nm |
| 548 | daemon. |
| 549 | The default is |
| 550 | .Pa /var/run/sshd.pid . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 551 | .It Cm Port |
| 552 | Specifies the port number that |
| 553 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 554 | listens on. |
| 555 | The default is 22. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 556 | Multiple options of this type are permitted. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 557 | .It Cm PrintMotd |
| 558 | Specifies whether |
| 559 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 560 | should print |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 561 | .Pa /etc/motd |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 562 | when a user logs in interactively. |
| 563 | (On some systems it is also printed by the shell, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 564 | .Pa /etc/profile , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 565 | or equivalent.) |
| 566 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 567 | .Dq yes . |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 568 | .It Cm Protocol |
| 569 | Specifies the protocol versions |
| 570 | .Nm |
| 571 | should support. |
| 572 | The possible values are |
| 573 | .Dq 1 |
| 574 | and |
| 575 | .Dq 2 . |
| 576 | Multiple versions must be comma-separated. |
| 577 | The default is |
| 578 | .Dq 1 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 579 | .It Cm RandomSeed |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 580 | Obsolete. |
| 581 | Random number generation uses other techniques. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 582 | .It Cm RhostsAuthentication |
| 583 | Specifies whether authentication using rhosts or /etc/hosts.equiv |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 584 | files is sufficient. |
| 585 | Normally, this method should not be permitted because it is insecure. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 586 | .Cm RhostsRSAAuthentication |
| 587 | should be used |
| 588 | instead, because it performs RSA-based host authentication in addition |
| 589 | to normal rhosts or /etc/hosts.equiv authentication. |
| 590 | The default is |
| 591 | .Dq no . |
| 592 | .It Cm RhostsRSAAuthentication |
| 593 | Specifies whether rhosts or /etc/hosts.equiv authentication together |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 594 | with successful RSA host authentication is allowed. |
| 595 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 596 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 597 | .It Cm RSAAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 598 | Specifies whether pure RSA authentication is allowed. |
| 599 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 600 | .Dq yes . |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 601 | Note that this option applies to protocol version 1 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 602 | .It Cm ServerKeyBits |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 603 | Defines the number of bits in the server key. |
| 604 | The minimum value is 512, and the default is 768. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 605 | .It Cm SkeyAuthentication |
| 606 | Specifies whether |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 607 | .Xr skey 1 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 608 | authentication is allowed. |
| 609 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 610 | .Dq yes . |
| 611 | Note that s/key authentication is enabled only if |
| 612 | .Cm PasswordAuthentication |
| 613 | is allowed, too. |
| 614 | .It Cm StrictModes |
| 615 | Specifies whether |
| 616 | .Nm |
| 617 | should check file modes and ownership of the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 618 | user's files and home directory before accepting login. |
| 619 | This is normally desirable because novices sometimes accidentally leave their |
| 620 | directory or files world-writable. |
| 621 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 622 | .Dq yes . |
Damien Miller | f6d9e22 | 2000-06-18 14:50:44 +1000 | [diff] [blame] | 623 | .It Cm Subsystem |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 624 | Configures an external subsystem (e.g., file transfer daemon). |
| 625 | Arguments should be a subsystem name and a command to execute upon subsystem |
| 626 | request. |
Damien Miller | 7b28dc5 | 2000-09-05 13:34:53 +1100 | [diff] [blame] | 627 | The command |
| 628 | .Xr sftp-server 8 |
| 629 | implements the |
| 630 | .Dq sftp |
| 631 | file transfer subsystem. |
Damien Miller | f6d9e22 | 2000-06-18 14:50:44 +1000 | [diff] [blame] | 632 | By default no subsystems are defined. |
| 633 | Note that this option applies to protocol version 2 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 634 | .It Cm SyslogFacility |
| 635 | Gives the facility code that is used when logging messages from |
| 636 | .Nm sshd . |
| 637 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 638 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
| 639 | The default is AUTH. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 640 | .It Cm UseLogin |
| 641 | Specifies whether |
| 642 | .Xr login 1 |
Damien Miller | d3a1857 | 2000-06-07 19:55:44 +1000 | [diff] [blame] | 643 | is used for interactive login sessions. |
| 644 | Note that |
| 645 | .Xr login 1 |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 646 | is never used for remote command execution. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 647 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 648 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 649 | .It Cm X11DisplayOffset |
| 650 | Specifies the first display number available for |
| 651 | .Nm sshd Ns 's |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 652 | X11 forwarding. |
| 653 | This prevents |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 654 | .Nm |
| 655 | from interfering with real X11 servers. |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 656 | The default is 10. |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 657 | .It Cm X11Forwarding |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 658 | Specifies whether X11 forwarding is permitted. |
| 659 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 660 | .Dq no . |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 661 | Note that disabling X11 forwarding does not improve security in any |
| 662 | way, as users can always install their own forwarders. |
Damien Miller | d3a1857 | 2000-06-07 19:55:44 +1000 | [diff] [blame] | 663 | .It Cm XAuthLocation |
| 664 | Specifies the location of the |
| 665 | .Xr xauth 1 |
| 666 | program. |
| 667 | The default is |
| 668 | .Pa /usr/X11R6/bin/xauth . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 669 | .El |
| 670 | .Sh LOGIN PROCESS |
| 671 | When a user successfully logs in, |
| 672 | .Nm |
| 673 | does the following: |
| 674 | .Bl -enum -offset indent |
| 675 | .It |
| 676 | 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] | 677 | prints last login time and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 678 | .Pa /etc/motd |
| 679 | (unless prevented in the configuration file or by |
| 680 | .Pa $HOME/.hushlogin ; |
| 681 | see the |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 682 | .Sx FILES |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 683 | section). |
| 684 | .It |
| 685 | If the login is on a tty, records login time. |
| 686 | .It |
| 687 | Checks |
| 688 | .Pa /etc/nologin ; |
| 689 | if it exists, prints contents and quits |
| 690 | (unless root). |
| 691 | .It |
| 692 | Changes to run with normal user privileges. |
| 693 | .It |
| 694 | Sets up basic environment. |
| 695 | .It |
| 696 | Reads |
| 697 | .Pa $HOME/.ssh/environment |
| 698 | if it exists. |
| 699 | .It |
| 700 | Changes to user's home directory. |
| 701 | .It |
| 702 | If |
| 703 | .Pa $HOME/.ssh/rc |
| 704 | exists, runs it; else if |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 705 | .Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 706 | exists, runs |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 707 | it; otherwise runs xauth. |
| 708 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 709 | .Dq rc |
| 710 | files are given the X11 |
| 711 | authentication protocol and cookie in standard input. |
| 712 | .It |
| 713 | Runs user's shell or command. |
| 714 | .El |
| 715 | .Sh AUTHORIZED_KEYS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 716 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 717 | .Pa $HOME/.ssh/authorized_keys |
| 718 | file lists the RSA keys that are |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 719 | permitted for RSA authentication in SSH protocols 1.3 and 1.5 |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 720 | Similarly, the |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 721 | .Pa $HOME/.ssh/authorized_keys2 |
| 722 | file lists the DSA keys that are |
| 723 | permitted for DSA authentication in SSH protocol 2.0. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 724 | Each line of the file contains one |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 725 | key (empty lines and lines starting with a |
| 726 | .Ql # |
| 727 | are ignored as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 728 | comments). |
| 729 | Each line consists of the following fields, separated by |
| 730 | spaces: options, bits, exponent, modulus, comment. |
| 731 | The options field |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 732 | is optional; its presence is determined by whether the line starts |
| 733 | with a number or not (the option field never starts with a number). |
| 734 | The bits, exponent, modulus and comment fields give the RSA key; the |
| 735 | comment field is not used for anything (but may be convenient for the |
| 736 | user to identify the key). |
| 737 | .Pp |
| 738 | Note that lines in this file are usually several hundred bytes long |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 739 | (because of the size of the RSA key modulus). |
| 740 | You don't want to type them in; instead, copy the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 741 | .Pa identity.pub |
| 742 | file and edit it. |
| 743 | .Pp |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 744 | The options (if present) consist of comma-separated option |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 745 | specifications. |
| 746 | No spaces are permitted, except within double quotes. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 747 | The following option specifications are supported: |
| 748 | .Bl -tag -width Ds |
| 749 | .It Cm from="pattern-list" |
| 750 | Specifies that in addition to RSA authentication, the canonical name |
| 751 | 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] | 752 | patterns |
| 753 | .Pf ( Ql * |
| 754 | and |
| 755 | .Ql ? |
| 756 | serve as wildcards). |
| 757 | The list may also contain |
| 758 | patterns negated by prefixing them with |
| 759 | .Ql ! ; |
| 760 | if the canonical host name matches a negated pattern, the key is not accepted. |
| 761 | The purpose |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 762 | of this option is to optionally increase security: RSA authentication |
| 763 | by itself does not trust the network or name servers or anything (but |
| 764 | the key); however, if somebody somehow steals the key, the key |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 765 | permits an intruder to log in from anywhere in the world. |
| 766 | This additional option makes using a stolen key more difficult (name |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 767 | servers and/or routers would have to be compromised in addition to |
| 768 | just the key). |
| 769 | .It Cm command="command" |
| 770 | Specifies that the command is executed whenever this key is used for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 771 | authentication. |
| 772 | The command supplied by the user (if any) is ignored. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 773 | 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] | 774 | otherwise it is run without a tty. |
| 775 | A quote may be included in the command by quoting it with a backslash. |
| 776 | This option might be useful |
| 777 | to restrict certain RSA keys to perform just a specific operation. |
| 778 | 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] | 779 | Note that the client may specify TCP/IP and/or X11 |
| 780 | forwarding unless they are explicitly prohibited. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 781 | .It Cm environment="NAME=value" |
| 782 | Specifies that the string is to be added to the environment when |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 783 | logging in using this key. |
| 784 | Environment variables set this way |
| 785 | override other default environment values. |
| 786 | Multiple options of this type are permitted. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 787 | .It Cm no-port-forwarding |
| 788 | Forbids TCP/IP forwarding when this key is used for authentication. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 789 | Any port forward requests by the client will return an error. |
| 790 | This might be used, e.g., in connection with the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 791 | .Cm command |
| 792 | option. |
| 793 | .It Cm no-X11-forwarding |
| 794 | Forbids X11 forwarding when this key is used for authentication. |
| 795 | Any X11 forward requests by the client will return an error. |
| 796 | .It Cm no-agent-forwarding |
| 797 | Forbids authentication agent forwarding when this key is used for |
| 798 | authentication. |
| 799 | .It Cm no-pty |
| 800 | Prevents tty allocation (a request to allocate a pty will fail). |
| 801 | .El |
| 802 | .Ss Examples |
| 803 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar |
| 804 | .Pp |
| 805 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula |
| 806 | .Pp |
| 807 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi |
| 808 | .Sh SSH_KNOWN_HOSTS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 809 | The |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 810 | .Pa /etc/ssh_known_hosts , |
| 811 | .Pa /etc/ssh_known_hosts2 , |
| 812 | .Pa $HOME/.ssh/known_hosts , |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 813 | and |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 814 | .Pa $HOME/.ssh/known_hosts2 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 815 | files contain host public keys for all known hosts. |
| 816 | The global file should |
| 817 | be prepared by the administrator (optional), and the per-user file is |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 818 | maintained automatically: whenever the user connects from an unknown host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 819 | its key is added to the per-user file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 820 | .Pp |
| 821 | Each line in these files contains the following fields: hostnames, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 822 | bits, exponent, modulus, comment. |
| 823 | The fields are separated by spaces. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 824 | .Pp |
| 825 | Hostnames is a comma-separated list of patterns ('*' and '?' act as |
| 826 | wildcards); each pattern in turn is matched against the canonical host |
| 827 | name (when authenticating a client) or against the user-supplied |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 828 | name (when authenticating a server). |
| 829 | A pattern may also be preceded by |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 830 | .Ql ! |
| 831 | to indicate negation: if the host name matches a negated |
| 832 | pattern, it is not accepted (by that line) even if it matched another |
| 833 | pattern on the line. |
| 834 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 835 | 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] | 836 | can be obtained, e.g., from |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 837 | .Pa /etc/ssh_host_key.pub . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 838 | The optional comment field continues to the end of the line, and is not used. |
| 839 | .Pp |
| 840 | Lines starting with |
| 841 | .Ql # |
| 842 | and empty lines are ignored as comments. |
| 843 | .Pp |
| 844 | When performing host authentication, authentication is accepted if any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 845 | matching line has the proper key. |
| 846 | It is thus permissible (but not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 847 | recommended) to have several lines or different host keys for the same |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 848 | names. |
| 849 | This will inevitably happen when short forms of host names |
| 850 | from different domains are put in the file. |
| 851 | It is possible |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 852 | that the files contain conflicting information; authentication is |
| 853 | accepted if valid information can be found from either file. |
| 854 | .Pp |
| 855 | Note that the lines in these files are typically hundreds of characters |
| 856 | long, and you definitely don't want to type in the host keys by hand. |
| 857 | Rather, generate them by a script |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 858 | or by taking |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 859 | .Pa /etc/ssh_host_key.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 860 | and adding the host names at the front. |
| 861 | .Ss Examples |
| 862 | closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi |
| 863 | .Sh FILES |
| 864 | .Bl -tag -width Ds |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 865 | .It Pa /etc/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 866 | Contains configuration data for |
| 867 | .Nm sshd . |
| 868 | This file should be writable by root only, but it is recommended |
| 869 | (though not necessary) that it be world-readable. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 870 | .It Pa /etc/ssh_host_key |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 871 | Contains the private part of the host key. |
| 872 | This file should only be owned by root, readable only by root, and not |
| 873 | accessible to others. |
| 874 | Note that |
| 875 | .Nm |
| 876 | does not start if this file is group/world-accessible. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 877 | .It Pa /etc/ssh_host_key.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 878 | Contains the public part of the host key. |
| 879 | This file should be world-readable but writable only by |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 880 | root. |
| 881 | Its contents should match the private part. |
| 882 | This file is not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 883 | really used for anything; it is only provided for the convenience of |
| 884 | the user so its contents can be copied to known hosts files. |
| 885 | These two files are created using |
| 886 | .Xr ssh-keygen 1 . |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 887 | .It Pa /var/run/sshd.pid |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 888 | Contains the process ID of the |
| 889 | .Nm |
| 890 | listening for connections (if there are several daemons running |
| 891 | concurrently for different ports, this contains the pid of the one |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 892 | started last). |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 893 | 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] | 894 | .It Pa $HOME/.ssh/authorized_keys |
| 895 | Lists the RSA keys that can be used to log into the user's account. |
| 896 | This file must be readable by root (which may on some machines imply |
| 897 | 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] | 898 | volume). |
| 899 | It is recommended that it not be accessible by others. |
| 900 | The format of this file is described above. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 901 | Users will place the contents of their |
| 902 | .Pa identity.pub |
| 903 | files into this file, as described in |
| 904 | .Xr ssh-keygen 1 . |
| 905 | .It Pa $HOME/.ssh/authorized_keys2 |
| 906 | Lists the DSA keys that can be used to log into the user's account. |
| 907 | This file must be readable by root (which may on some machines imply |
| 908 | it being world-readable if the user's home directory resides on an NFS |
| 909 | volume). |
| 910 | It is recommended that it not be accessible by others. |
| 911 | The format of this file is described above. |
| 912 | Users will place the contents of their |
| 913 | .Pa id_dsa.pub |
| 914 | files into this file, as described in |
| 915 | .Xr ssh-keygen 1 . |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 916 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 917 | These files are consulted when using rhosts with RSA host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 918 | authentication to check the public key of the host. |
| 919 | 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] | 920 | The client uses the same files |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 921 | 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] | 922 | These files should be writable only by root/the owner. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 923 | .Pa /etc/ssh_known_hosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 924 | should be world-readable, and |
| 925 | .Pa $HOME/.ssh/known_hosts |
| 926 | can but need not be world-readable. |
| 927 | .It Pa /etc/nologin |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 928 | If this file exists, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 929 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 930 | refuses to let anyone except root log in. |
| 931 | The contents of the file |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 932 | 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] | 933 | refused. |
| 934 | The file should be world-readable. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 935 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
| 936 | If compiled with |
| 937 | .Sy LIBWRAP |
| 938 | support, tcp-wrappers access controls may be defined here as described in |
| 939 | .Xr hosts_access 5 . |
| 940 | .It Pa $HOME/.rhosts |
| 941 | This file contains host-username pairs, separated by a space, one per |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 942 | line. |
| 943 | The given user on the corresponding host is permitted to log in |
| 944 | without password. |
| 945 | The same file is used by rlogind and rshd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 946 | The file must |
| 947 | be writable only by the user; it is recommended that it not be |
| 948 | accessible by others. |
| 949 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 950 | If is also possible to use netgroups in the file. |
| 951 | Either host or user |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 952 | name may be of the form +@groupname to specify all hosts or all users |
| 953 | in the group. |
| 954 | .It Pa $HOME/.shosts |
| 955 | For ssh, |
| 956 | this file is exactly the same as for |
| 957 | .Pa .rhosts . |
| 958 | However, this file is |
| 959 | 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] | 960 | .It Pa /etc/hosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 961 | This file is used during |
| 962 | .Pa .rhosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 963 | authentication. |
| 964 | In the simplest form, this file contains host names, one per line. |
| 965 | Users on |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 966 | those hosts are permitted to log in without a password, provided they |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 967 | have the same user name on both machines. |
| 968 | The host name may also be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 969 | followed by a user name; such users are permitted to log in as |
| 970 | .Em any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 971 | user on this machine (except root). |
| 972 | Additionally, the syntax |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 973 | .Dq +@group |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 974 | can be used to specify netgroups. |
| 975 | Negated entries start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 976 | .Ql \&- . |
| 977 | .Pp |
| 978 | If the client host/user is successfully matched in this file, login is |
| 979 | automatically permitted provided the client and server user names are the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 980 | same. |
| 981 | Additionally, successful RSA host authentication is normally required. |
| 982 | This file must be writable only by root; it is recommended |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 983 | that it be world-readable. |
| 984 | .Pp |
| 985 | .Sy "Warning: It is almost never a good idea to use user names in" |
| 986 | .Pa hosts.equiv . |
| 987 | Beware that it really means that the named user(s) can log in as |
| 988 | .Em anybody , |
| 989 | which includes bin, daemon, adm, and other accounts that own critical |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 990 | binaries and directories. |
| 991 | Using a user name practically grants the user root access. |
| 992 | The only valid use for user names that I can think |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 993 | of is in negative entries. |
| 994 | .Pp |
| 995 | Note that this warning also applies to rsh/rlogin. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 996 | .It Pa /etc/shosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 997 | This is processed exactly as |
| 998 | .Pa /etc/hosts.equiv . |
| 999 | However, this file may be useful in environments that want to run both |
| 1000 | rsh/rlogin and ssh. |
| 1001 | .It Pa $HOME/.ssh/environment |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1002 | This file is read into the environment at login (if it exists). |
| 1003 | It can only contain empty lines, comment lines (that start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1004 | .Ql # ) , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1005 | and assignment lines of the form name=value. |
| 1006 | The file should be writable |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1007 | only by the user; it need not be readable by anyone else. |
| 1008 | .It Pa $HOME/.ssh/rc |
| 1009 | 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] | 1010 | environment files but before starting the user's shell or command. |
| 1011 | 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] | 1012 | standard input (and |
| 1013 | .Ev DISPLAY |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1014 | in environment). |
| 1015 | This must call |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1016 | .Xr xauth 1 |
| 1017 | in that case. |
| 1018 | .Pp |
| 1019 | The primary purpose of this file is to run any initialization routines |
| 1020 | which may be needed before the user's home directory becomes |
| 1021 | accessible; AFS is a particular example of such an environment. |
| 1022 | .Pp |
| 1023 | This file will probably contain some initialization code followed by |
| 1024 | something similar to: "if read proto cookie; then echo add $DISPLAY |
| 1025 | $proto $cookie | xauth -q -; fi". |
| 1026 | .Pp |
| 1027 | If this file does not exist, |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1028 | .Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1029 | is run, and if that |
| 1030 | does not exist either, xauth is used to store the cookie. |
| 1031 | .Pp |
| 1032 | This file should be writable only by the user, and need not be |
| 1033 | readable by anyone else. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1034 | .It Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1035 | Like |
| 1036 | .Pa $HOME/.ssh/rc . |
| 1037 | This can be used to specify |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 1038 | machine-specific login-time initializations globally. |
| 1039 | 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] | 1040 | .El |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1041 | .Sh AUTHOR |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1042 | OpenSSH |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 1043 | 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] | 1044 | but with bugs removed and newer features re-added. |
| 1045 | Rapidly after the |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 1046 | 1.2.12 release, newer versions of the original ssh bore successively |
| 1047 | more restrictive licenses, and thus demand for a free version was born. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1048 | .Pp |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 1049 | This version of OpenSSH |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1050 | .Bl -bullet |
| 1051 | .It |
Damien Miller | e4340be | 2000-09-16 13:29:08 +1100 | [diff] [blame] | 1052 | has all components of a restrictive nature (i.e., patents, see |
| 1053 | .Xr crypto 3 ) |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1054 | directly removed from the source code; any licensed or patented components |
| 1055 | are chosen from |
| 1056 | external libraries. |
| 1057 | .It |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1058 | has been updated to support SSH protocol 1.5 and 2, making it compatible with |
| 1059 | all other SSH clients and servers. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1060 | .It |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1061 | contains added support for |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1062 | .Xr kerberos 8 |
| 1063 | authentication and ticket passing. |
| 1064 | .It |
| 1065 | supports one-time password authentication with |
| 1066 | .Xr skey 1 . |
| 1067 | .El |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1068 | .Pp |
| 1069 | OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl, |
| 1070 | Niels Provos, Theo de Raadt, and Dug Song. |
| 1071 | .Pp |
| 1072 | The support for SSH protocol 2 was written by Markus Friedl. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1073 | .Sh SEE ALSO |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1074 | .Xr scp 1 , |
Damien Miller | 7b28dc5 | 2000-09-05 13:34:53 +1100 | [diff] [blame] | 1075 | .Xr sftp-server 8 , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1076 | .Xr ssh 1 , |
| 1077 | .Xr ssh-add 1 , |
| 1078 | .Xr ssh-agent 1 , |
| 1079 | .Xr ssh-keygen 1 , |
Damien Miller | e4340be | 2000-09-16 13:29:08 +1100 | [diff] [blame] | 1080 | .Xr crypto 3 , |
Damien Miller | b38eff8 | 2000-04-01 11:09:21 +1000 | [diff] [blame] | 1081 | .Xr rlogin 1 , |
| 1082 | .Xr rsh 1 |