Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1 | .\" -*- nroff -*- |
| 2 | .\" |
| 3 | .\" sshd.8.in |
| 4 | .\" |
| 5 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
| 6 | .\" |
| 7 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
| 8 | .\" All rights reserved |
| 9 | .\" |
| 10 | .\" Created: Sat Apr 22 21:55:14 1995 ylo |
| 11 | .\" |
Damien Miller | cfabe86 | 2000-04-20 23:27:27 +1000 | [diff] [blame^] | 12 | .\" $Id: sshd.8,v 1.18 2000/04/20 13:27:27 damien Exp $ |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 13 | .\" |
| 14 | .Dd September 25, 1999 |
| 15 | .Dt SSHD 8 |
| 16 | .Os |
| 17 | .Sh NAME |
| 18 | .Nm sshd |
| 19 | .Nd secure shell daemon |
| 20 | .Sh SYNOPSIS |
| 21 | .Nm sshd |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 22 | .Op Fl diqQ46 |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 23 | .Op Fl b Ar bits |
| 24 | .Op Fl f Ar config_file |
| 25 | .Op Fl g Ar login_grace_time |
| 26 | .Op Fl h Ar host_key_file |
| 27 | .Op Fl k Ar key_gen_time |
| 28 | .Op Fl p Ar port |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 29 | .Op Fl V Ar client_protocol_id |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 30 | .Sh DESCRIPTION |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 31 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 32 | (Secure Shell Daemon) is the daemon program for |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 33 | .Xr ssh 1 . |
| 34 | Together these programs replace rlogin and rsh programs, and |
| 35 | provide secure encrypted communications between two untrusted hosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 36 | over an insecure network. |
| 37 | The programs are intended to be as easy to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 38 | install and use as possible. |
| 39 | .Pp |
| 40 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 41 | is the daemon that listens for connections from clients. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 42 | It is normally started at boot from |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 43 | .Pa /etc/rc . |
| 44 | It forks a new |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 45 | daemon for each incoming connection. |
| 46 | The forked daemons handle |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 47 | key exchange, encryption, authentication, command execution, |
| 48 | and data exchange. |
| 49 | .Pp |
| 50 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 51 | works as follows. |
| 52 | Each host has a host-specific RSA key |
| 53 | (normally 1024 bits) used to identify the host. |
| 54 | Additionally, when |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 55 | the daemon starts, it generates a server RSA key (normally 768 bits). |
| 56 | This key is normally regenerated every hour if it has been used, and |
| 57 | is never stored on disk. |
| 58 | .Pp |
| 59 | Whenever a client connects the daemon, the daemon sends its host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 60 | and server public keys to the client. |
| 61 | The client compares the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 62 | 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] | 63 | The client then generates a 256 bit random number. |
| 64 | It encrypts this |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 65 | 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] | 66 | the encrypted number to the server. |
| 67 | Both sides then start to use this |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 68 | 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] | 69 | communications in the session. |
| 70 | The rest of the session is encrypted |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 71 | using a conventional cipher, currently Blowfish and 3DES, with 3DES |
Damien Miller | b38eff8 | 2000-04-01 11:09:21 +1000 | [diff] [blame] | 72 | being used by default. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 73 | The client selects the encryption algorithm |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 74 | to use from those offered by the server. |
| 75 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 76 | Next, the server and the client enter an authentication dialog. |
| 77 | The client tries to authenticate itself using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 78 | .Pa .rhosts |
| 79 | authentication, |
| 80 | .Pa .rhosts |
| 81 | authentication combined with RSA host |
| 82 | authentication, RSA challenge-response authentication, or password |
| 83 | based authentication. |
| 84 | .Pp |
| 85 | Rhosts authentication is normally disabled |
| 86 | because it is fundamentally insecure, but can be enabled in the server |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 87 | configuration file if desired. |
| 88 | System security is not improved unless |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 89 | .Xr rshd 8 , |
| 90 | .Xr rlogind 8 , |
| 91 | .Xr rexecd 8 , |
| 92 | and |
| 93 | .Xr rexd 8 |
| 94 | are disabled (thus completely disabling |
| 95 | .Xr rlogin 1 |
| 96 | and |
| 97 | .Xr rsh 1 |
| 98 | into that machine). |
| 99 | .Pp |
| 100 | If the client successfully authenticates itself, a dialog for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 101 | preparing the session is entered. |
| 102 | At this time the client may request |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 103 | things like allocating a pseudo-tty, forwarding X11 connections, |
| 104 | forwarding TCP/IP connections, or forwarding the authentication agent |
| 105 | connection over the secure channel. |
| 106 | .Pp |
| 107 | Finally, the client either requests a shell or execution of a command. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 108 | The sides then enter session mode. |
| 109 | In this mode, either side may send |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 110 | data at any time, and such data is forwarded to/from the shell or |
| 111 | command on the server side, and the user terminal in the client side. |
| 112 | .Pp |
| 113 | When the user program terminates and all forwarded X11 and other |
| 114 | connections have been closed, the server sends command exit status to |
| 115 | the client, and both sides exit. |
| 116 | .Pp |
| 117 | .Nm |
| 118 | can be configured using command-line options or a configuration |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 119 | file. |
| 120 | Command-line options override values specified in the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 121 | configuration file. |
| 122 | .Pp |
Damien Miller | 6162d12 | 1999-11-21 13:23:52 +1100 | [diff] [blame] | 123 | .Nm |
| 124 | rereads its configuration file when it receives a hangup signal, |
| 125 | .Dv SIGHUP . |
| 126 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 127 | The options are as follows: |
| 128 | .Bl -tag -width Ds |
| 129 | .It Fl b Ar bits |
| 130 | Specifies the number of bits in the server key (default 768). |
| 131 | .Pp |
| 132 | .It Fl d |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 133 | Debug mode. |
| 134 | The server sends verbose debug output to the system |
| 135 | log, and does not put itself in the background. |
| 136 | The server also will not fork and will only process one connection. |
| 137 | This option is only intended for debugging for the server. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 138 | .It Fl f Ar configuration_file |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 139 | Specifies the name of the configuration file. |
| 140 | The default is |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 141 | .Pa /etc/sshd_config . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 142 | .Nm |
| 143 | refuses to start if there is no configuration file. |
| 144 | .It Fl g Ar login_grace_time |
| 145 | Gives the grace time for clients to authenticate themselves (default |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 146 | 300 seconds). |
| 147 | If the client fails to authenticate the user within |
| 148 | this many seconds, the server disconnects and exits. |
| 149 | A value of zero indicates no limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 150 | .It Fl h Ar host_key_file |
| 151 | Specifies the file from which the host key is read (default |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 152 | .Pa /etc/ssh_host_key ) . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 153 | This option must be given if |
| 154 | .Nm |
| 155 | is not run as root (as the normal |
| 156 | host file is normally not readable by anyone but root). |
| 157 | .It Fl i |
| 158 | Specifies that |
| 159 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 160 | is being run from inetd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 161 | .Nm |
| 162 | is normally not run |
| 163 | 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] | 164 | respond to the client, and this may take tens of seconds. |
| 165 | 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] | 166 | However, with small key sizes (e.g., 512) using |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 167 | .Nm |
| 168 | from inetd may |
| 169 | be feasible. |
| 170 | .It Fl k Ar key_gen_time |
| 171 | Specifies how often the server key is regenerated (default 3600 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 172 | seconds, or one hour). |
| 173 | The motivation for regenerating the key fairly |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 174 | often is that the key is not stored anywhere, and after about an hour, |
| 175 | it becomes impossible to recover the key for decrypting intercepted |
| 176 | communications even if the machine is cracked into or physically |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 177 | seized. |
| 178 | A value of zero indicates that the key will never be regenerated. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 179 | .It Fl p Ar port |
| 180 | Specifies the port on which the server listens for connections |
| 181 | (default 22). |
| 182 | .It Fl q |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 183 | Quiet mode. |
| 184 | Nothing is sent to the system log. |
| 185 | Normally the beginning, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 186 | authentication, and termination of each connection is logged. |
| 187 | .It Fl Q |
| 188 | Do not print an error message if RSA support is missing. |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 189 | .It Fl V Ar client_protocol_id |
| 190 | SSH2 compatibility mode. |
| 191 | When this options is specified |
| 192 | .Nm |
| 193 | assumes the client has sent the given version string |
| 194 | and skips the |
| 195 | Protocol Version Identification Exchange. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 196 | .It Fl 4 |
| 197 | Forces |
| 198 | .Nm |
| 199 | to use IPv4 addresses only. |
| 200 | .It Fl 6 |
| 201 | Forces |
| 202 | .Nm |
| 203 | to use IPv6 addresses only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 204 | .El |
| 205 | .Sh CONFIGURATION FILE |
| 206 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 207 | reads configuration data from |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 208 | .Pa /etc/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 209 | (or the file specified with |
| 210 | .Fl f |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 211 | on the command line). |
| 212 | The file contains keyword-value pairs, one per line. |
| 213 | Lines starting with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 214 | .Ql # |
| 215 | and empty lines are interpreted as comments. |
| 216 | .Pp |
| 217 | The following keywords are possible. |
| 218 | .Bl -tag -width Ds |
| 219 | .It Cm AFSTokenPassing |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 220 | Specifies whether an AFS token may be forwarded to the server. |
| 221 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 222 | .Dq yes . |
| 223 | .It Cm AllowGroups |
| 224 | This keyword can be followed by a number of group names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 225 | by spaces. |
| 226 | If specified, login is allowed only for users whose primary |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 227 | group matches one of the patterns. |
| 228 | .Ql \&* |
| 229 | and |
| 230 | .Ql ? |
| 231 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 232 | wildcards in the patterns. |
| 233 | Only group names are valid, a numerical group ID isn't recognized. |
| 234 | By default login is allowed regardless of the primary group. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 235 | .Pp |
| 236 | .It Cm AllowUsers |
| 237 | This keyword can be followed by a number of user names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 238 | by spaces. |
| 239 | If specified, login is allowed only for users names that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 240 | match one of the patterns. |
| 241 | .Ql \&* |
| 242 | and |
| 243 | .Ql ? |
| 244 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 245 | wildcards in the patterns. |
| 246 | Only user names are valid, a numerical user ID isn't recognized. |
| 247 | By default login is allowed regardless of the user name. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 248 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 249 | .It Cm Ciphers |
| 250 | Specifies the ciphers allowed for protocol version 2. |
| 251 | Multiple ciphers must be comma-separated. |
| 252 | The default is |
| 253 | .Dq blowfish-cbc,3des-cbc,arcfour,cast128-cbc . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 254 | .It Cm CheckMail |
| 255 | Specifies whether |
| 256 | .Nm |
| 257 | should check for new mail for interactive logins. |
| 258 | The default is |
| 259 | .Dq no . |
| 260 | .It Cm DenyGroups |
| 261 | This keyword can be followed by a number of group names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 262 | by spaces. |
| 263 | Users whose primary group matches one of the patterns |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 264 | aren't allowed to log in. |
| 265 | .Ql \&* |
| 266 | and |
| 267 | .Ql ? |
| 268 | can be used as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 269 | wildcards in the patterns. |
| 270 | Only group names are valid, a numerical group ID isn't recognized. |
| 271 | By default login is allowed regardless of the primary group. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 272 | .Pp |
| 273 | .It Cm DenyUsers |
| 274 | This keyword can be followed by a number of user names, separated |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 275 | by spaces. |
| 276 | Login is disallowed for user names that match one of the patterns. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 277 | .Ql \&* |
| 278 | and |
| 279 | .Ql ? |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 280 | can be used as wildcards in the patterns. |
| 281 | Only user names are valid, a numerical user ID isn't recognized. |
| 282 | By default login is allowed regardless of the user name. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 283 | .It Cm HostKey |
| 284 | Specifies the file containing the private host key (default |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 285 | .Pa /etc/ssh_host_key ) . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 286 | Note that |
| 287 | .Nm |
| 288 | does not start if this file is group/world-accessible. |
| 289 | .It Cm IgnoreRhosts |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 290 | Specifies that |
| 291 | .Pa .rhosts |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 292 | and |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 293 | .Pa .shosts |
| 294 | files will not be used in authentication. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 295 | .Pa /etc/hosts.equiv |
| 296 | and |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 297 | .Pa /etc/shosts.equiv |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 298 | are still used. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 299 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 300 | .Dq yes . |
Damien Miller | 3226509 | 1999-11-12 11:33:04 +1100 | [diff] [blame] | 301 | .It Cm IgnoreUserKnownHosts |
| 302 | Specifies whether |
| 303 | .Nm |
| 304 | should ignore the user's |
| 305 | .Pa $HOME/.ssh/known_hosts |
| 306 | during |
| 307 | .Cm RhostsRSAAuthentication . |
| 308 | The default is |
| 309 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 310 | .It Cm KeepAlive |
| 311 | Specifies whether the system should send keepalive messages to the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 312 | other side. |
| 313 | If they are sent, death of the connection or crash of one |
| 314 | of the machines will be properly noticed. |
| 315 | However, this means that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 316 | connections will die if the route is down temporarily, and some people |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 317 | find it annoying. |
| 318 | On the other hand, if keepalives are not send, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 319 | sessions may hang indefinitely on the server, leaving |
| 320 | .Dq ghost |
| 321 | users and consuming server resources. |
| 322 | .Pp |
| 323 | The default is |
| 324 | .Dq yes |
| 325 | (to send keepalives), and the server will notice |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 326 | if the network goes down or the client host reboots. |
| 327 | This avoids infinitely hanging sessions. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 328 | .Pp |
| 329 | To disable keepalives, the value should be set to |
| 330 | .Dq no |
| 331 | in both the server and the client configuration files. |
| 332 | .It Cm KerberosAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 333 | Specifies whether Kerberos authentication is allowed. |
| 334 | This can be in the form of a Kerberos ticket, or if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 335 | .Cm PasswordAuthentication |
| 336 | is yes, the password provided by the user will be validated through |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 337 | the Kerberos KDC. |
| 338 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 339 | .Dq yes . |
| 340 | .It Cm KerberosOrLocalPasswd |
| 341 | If set then if password authentication through Kerberos fails then |
| 342 | the password will be validated via any additional local mechanism |
| 343 | such as |
| 344 | .Pa /etc/passwd |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 345 | or SecurID. |
| 346 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 347 | .Dq yes . |
| 348 | .It Cm KerberosTgtPassing |
| 349 | Specifies whether a Kerberos TGT may be forwarded to the server. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 350 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 351 | .Dq no , |
| 352 | as this only works when the Kerberos KDC is actually an AFS kaserver. |
| 353 | .It Cm KerberosTicketCleanup |
| 354 | Specifies whether to automatically destroy the user's ticket cache |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 355 | file on logout. |
| 356 | Default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 357 | .Dq yes . |
| 358 | .It Cm KeyRegenerationInterval |
| 359 | The server key is automatically regenerated after this many seconds |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 360 | (if it has been used). |
| 361 | The purpose of regeneration is to prevent |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 362 | decrypting captured sessions by later breaking into the machine and |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 363 | stealing the keys. |
| 364 | The key is never stored anywhere. |
| 365 | If the value is 0, the key is never regenerated. |
| 366 | The default is 3600 (seconds). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 367 | .It Cm ListenAddress |
| 368 | Specifies what local address |
| 369 | .Nm |
| 370 | should listen on. |
| 371 | The default is to listen to all local addresses. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 372 | Multiple options of this type are permitted. |
| 373 | Additionally, the |
| 374 | .Cm Ports |
| 375 | options must precede this option. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 376 | .It Cm LoginGraceTime |
| 377 | The server disconnects after this time if the user has not |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 378 | successfully logged in. |
| 379 | If the value is 0, there is no time limit. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 380 | The default is 600 (seconds). |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 381 | .It Cm LogLevel |
| 382 | Gives the verbosity level that is used when logging messages from |
| 383 | .Nm sshd . |
| 384 | The possible values are: |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 385 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 386 | The default is INFO. |
| 387 | Logging with level DEBUG violates the privacy of users |
| 388 | and is not recommended. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 389 | .It Cm PasswordAuthentication |
| 390 | Specifies whether password authentication is allowed. |
| 391 | The default is |
| 392 | .Dq yes . |
| 393 | .It Cm PermitEmptyPasswords |
| 394 | When password authentication is allowed, it specifies whether the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 395 | server allows login to accounts with empty password strings. |
| 396 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 397 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 398 | .It Cm PermitRootLogin |
| 399 | Specifies whether the root can log in using |
| 400 | .Xr ssh 1 . |
| 401 | The argument must be |
| 402 | .Dq yes , |
| 403 | .Dq without-password |
| 404 | or |
| 405 | .Dq no . |
| 406 | The default is |
| 407 | .Dq yes . |
| 408 | If this options is set to |
| 409 | .Dq without-password |
| 410 | only password authentication is disabled for root. |
| 411 | .Pp |
| 412 | Root login with RSA authentication when the |
| 413 | .Ar command |
| 414 | option has been |
| 415 | specified will be allowed regardless of the value of this setting |
| 416 | (which may be useful for taking remote backups even if root login is |
| 417 | normally not allowed). |
| 418 | .It Cm Port |
| 419 | Specifies the port number that |
| 420 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 421 | listens on. |
| 422 | The default is 22. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 423 | Multiple options of this type are permitted. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 424 | .It Cm PrintMotd |
| 425 | Specifies whether |
| 426 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 427 | should print |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 428 | .Pa /etc/motd |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 429 | when a user logs in interactively. |
| 430 | (On some systems it is also printed by the shell, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 431 | .Pa /etc/profile , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 432 | or equivalent.) |
| 433 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 434 | .Dq yes . |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 435 | .It Cm Protocol |
| 436 | Specifies the protocol versions |
| 437 | .Nm |
| 438 | should support. |
| 439 | The possible values are |
| 440 | .Dq 1 |
| 441 | and |
| 442 | .Dq 2 . |
| 443 | Multiple versions must be comma-separated. |
| 444 | The default is |
| 445 | .Dq 1 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 446 | .It Cm RandomSeed |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 447 | Obsolete. |
| 448 | Random number generation uses other techniques. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 449 | .It Cm RhostsAuthentication |
| 450 | Specifies whether authentication using rhosts or /etc/hosts.equiv |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 451 | files is sufficient. |
| 452 | Normally, this method should not be permitted because it is insecure. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 453 | .Cm RhostsRSAAuthentication |
| 454 | should be used |
| 455 | instead, because it performs RSA-based host authentication in addition |
| 456 | to normal rhosts or /etc/hosts.equiv authentication. |
| 457 | The default is |
| 458 | .Dq no . |
| 459 | .It Cm RhostsRSAAuthentication |
| 460 | Specifies whether rhosts or /etc/hosts.equiv authentication together |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 461 | with successful RSA host authentication is allowed. |
| 462 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 463 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 464 | .It Cm RSAAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 465 | Specifies whether pure RSA authentication is allowed. |
| 466 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 467 | .Dq yes . |
| 468 | .It Cm ServerKeyBits |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 469 | Defines the number of bits in the server key. |
| 470 | The minimum value is 512, and the default is 768. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 471 | .It Cm SkeyAuthentication |
| 472 | Specifies whether |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 473 | .Xr skey 1 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 474 | authentication is allowed. |
| 475 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 476 | .Dq yes . |
| 477 | Note that s/key authentication is enabled only if |
| 478 | .Cm PasswordAuthentication |
| 479 | is allowed, too. |
| 480 | .It Cm StrictModes |
| 481 | Specifies whether |
| 482 | .Nm |
| 483 | should check file modes and ownership of the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 484 | user's files and home directory before accepting login. |
| 485 | This is normally desirable because novices sometimes accidentally leave their |
| 486 | directory or files world-writable. |
| 487 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 488 | .Dq yes . |
| 489 | .It Cm SyslogFacility |
| 490 | Gives the facility code that is used when logging messages from |
| 491 | .Nm sshd . |
| 492 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 493 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. |
| 494 | The default is AUTH. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 495 | .It Cm UseLogin |
| 496 | Specifies whether |
| 497 | .Xr login 1 |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 498 | is used. |
| 499 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 500 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 501 | .It Cm X11DisplayOffset |
| 502 | Specifies the first display number available for |
| 503 | .Nm sshd Ns 's |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 504 | X11 forwarding. |
| 505 | This prevents |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 506 | .Nm |
| 507 | from interfering with real X11 servers. |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 508 | The default is 10. |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 509 | .It Cm X11Forwarding |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 510 | Specifies whether X11 forwarding is permitted. |
| 511 | The default is |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 512 | .Dq no . |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 513 | Note that disabling X11 forwarding does not improve security in any |
| 514 | way, as users can always install their own forwarders. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 515 | .El |
| 516 | .Sh LOGIN PROCESS |
| 517 | When a user successfully logs in, |
| 518 | .Nm |
| 519 | does the following: |
| 520 | .Bl -enum -offset indent |
| 521 | .It |
| 522 | 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] | 523 | prints last login time and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 524 | .Pa /etc/motd |
| 525 | (unless prevented in the configuration file or by |
| 526 | .Pa $HOME/.hushlogin ; |
| 527 | see the |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 528 | .Sx FILES |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 529 | section). |
| 530 | .It |
| 531 | If the login is on a tty, records login time. |
| 532 | .It |
| 533 | Checks |
| 534 | .Pa /etc/nologin ; |
| 535 | if it exists, prints contents and quits |
| 536 | (unless root). |
| 537 | .It |
| 538 | Changes to run with normal user privileges. |
| 539 | .It |
| 540 | Sets up basic environment. |
| 541 | .It |
| 542 | Reads |
| 543 | .Pa $HOME/.ssh/environment |
| 544 | if it exists. |
| 545 | .It |
| 546 | Changes to user's home directory. |
| 547 | .It |
| 548 | If |
| 549 | .Pa $HOME/.ssh/rc |
| 550 | exists, runs it; else if |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 551 | .Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 552 | exists, runs |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 553 | it; otherwise runs xauth. |
| 554 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 555 | .Dq rc |
| 556 | files are given the X11 |
| 557 | authentication protocol and cookie in standard input. |
| 558 | .It |
| 559 | Runs user's shell or command. |
| 560 | .El |
| 561 | .Sh AUTHORIZED_KEYS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 562 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 563 | .Pa $HOME/.ssh/authorized_keys |
| 564 | file lists the RSA keys that are |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 565 | permitted for RSA authentication. |
| 566 | Each line of the file contains one |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 567 | key (empty lines and lines starting with a |
| 568 | .Ql # |
| 569 | are ignored as |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 570 | comments). |
| 571 | Each line consists of the following fields, separated by |
| 572 | spaces: options, bits, exponent, modulus, comment. |
| 573 | The options field |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 574 | is optional; its presence is determined by whether the line starts |
| 575 | with a number or not (the option field never starts with a number). |
| 576 | The bits, exponent, modulus and comment fields give the RSA key; the |
| 577 | comment field is not used for anything (but may be convenient for the |
| 578 | user to identify the key). |
| 579 | .Pp |
| 580 | Note that lines in this file are usually several hundred bytes long |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 581 | (because of the size of the RSA key modulus). |
| 582 | You don't want to type them in; instead, copy the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 583 | .Pa identity.pub |
| 584 | file and edit it. |
| 585 | .Pp |
| 586 | The options (if present) consists of comma-separated option |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 587 | specifications. |
| 588 | No spaces are permitted, except within double quotes. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 589 | The following option specifications are supported: |
| 590 | .Bl -tag -width Ds |
| 591 | .It Cm from="pattern-list" |
| 592 | Specifies that in addition to RSA authentication, the canonical name |
| 593 | 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] | 594 | patterns |
| 595 | .Pf ( Ql * |
| 596 | and |
| 597 | .Ql ? |
| 598 | serve as wildcards). |
| 599 | The list may also contain |
| 600 | patterns negated by prefixing them with |
| 601 | .Ql ! ; |
| 602 | if the canonical host name matches a negated pattern, the key is not accepted. |
| 603 | The purpose |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 604 | of this option is to optionally increase security: RSA authentication |
| 605 | by itself does not trust the network or name servers or anything (but |
| 606 | the key); however, if somebody somehow steals the key, the key |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 607 | permits an intruder to log in from anywhere in the world. |
| 608 | This additional option makes using a stolen key more difficult (name |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 609 | servers and/or routers would have to be compromised in addition to |
| 610 | just the key). |
| 611 | .It Cm command="command" |
| 612 | Specifies that the command is executed whenever this key is used for |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 613 | authentication. |
| 614 | The command supplied by the user (if any) is ignored. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 615 | 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] | 616 | otherwise it is run without a tty. |
| 617 | A quote may be included in the command by quoting it with a backslash. |
| 618 | This option might be useful |
| 619 | to restrict certain RSA keys to perform just a specific operation. |
| 620 | An example might be a key that permits remote backups but nothing else. |
| 621 | Notice that the client may specify TCP/IP and/or X11 |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 622 | forwardings unless they are explicitly prohibited. |
| 623 | .It Cm environment="NAME=value" |
| 624 | Specifies that the string is to be added to the environment when |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 625 | logging in using this key. |
| 626 | Environment variables set this way |
| 627 | override other default environment values. |
| 628 | Multiple options of this type are permitted. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 629 | .It Cm no-port-forwarding |
| 630 | Forbids TCP/IP forwarding when this key is used for authentication. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 631 | Any port forward requests by the client will return an error. |
| 632 | This might be used, e.g., in connection with the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 633 | .Cm command |
| 634 | option. |
| 635 | .It Cm no-X11-forwarding |
| 636 | Forbids X11 forwarding when this key is used for authentication. |
| 637 | Any X11 forward requests by the client will return an error. |
| 638 | .It Cm no-agent-forwarding |
| 639 | Forbids authentication agent forwarding when this key is used for |
| 640 | authentication. |
| 641 | .It Cm no-pty |
| 642 | Prevents tty allocation (a request to allocate a pty will fail). |
| 643 | .El |
| 644 | .Ss Examples |
| 645 | 1024 33 12121.\|.\|.\|312314325 ylo@foo.bar |
| 646 | .Pp |
| 647 | from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23.\|.\|.\|2334 ylo@niksula |
| 648 | .Pp |
| 649 | command="dump /home",no-pty,no-port-forwarding 1024 33 23.\|.\|.\|2323 backup.hut.fi |
| 650 | .Sh SSH_KNOWN_HOSTS FILE FORMAT |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 651 | The |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 652 | .Pa /etc/ssh_known_hosts |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 653 | and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 654 | .Pa $HOME/.ssh/known_hosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 655 | files contain host public keys for all known hosts. |
| 656 | The global file should |
| 657 | be prepared by the administrator (optional), and the per-user file is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 658 | maintained automatically: whenever the user connects an unknown host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 659 | its key is added to the per-user file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 660 | .Pp |
| 661 | Each line in these files contains the following fields: hostnames, |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 662 | bits, exponent, modulus, comment. |
| 663 | The fields are separated by spaces. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 664 | .Pp |
| 665 | Hostnames is a comma-separated list of patterns ('*' and '?' act as |
| 666 | wildcards); each pattern in turn is matched against the canonical host |
| 667 | name (when authenticating a client) or against the user-supplied |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 668 | name (when authenticating a server). |
| 669 | A pattern may also be preceded by |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 670 | .Ql ! |
| 671 | to indicate negation: if the host name matches a negated |
| 672 | pattern, it is not accepted (by that line) even if it matched another |
| 673 | pattern on the line. |
| 674 | .Pp |
| 675 | Bits, exponent, and modulus are taken directly from the host key; they |
| 676 | can be obtained, e.g., from |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 677 | .Pa /etc/ssh_host_key.pub . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 678 | The optional comment field continues to the end of the line, and is not used. |
| 679 | .Pp |
| 680 | Lines starting with |
| 681 | .Ql # |
| 682 | and empty lines are ignored as comments. |
| 683 | .Pp |
| 684 | When performing host authentication, authentication is accepted if any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 685 | matching line has the proper key. |
| 686 | It is thus permissible (but not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 687 | recommended) to have several lines or different host keys for the same |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 688 | names. |
| 689 | This will inevitably happen when short forms of host names |
| 690 | from different domains are put in the file. |
| 691 | It is possible |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 692 | that the files contain conflicting information; authentication is |
| 693 | accepted if valid information can be found from either file. |
| 694 | .Pp |
| 695 | Note that the lines in these files are typically hundreds of characters |
| 696 | long, and you definitely don't want to type in the host keys by hand. |
| 697 | Rather, generate them by a script |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 698 | or by taking |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 699 | .Pa /etc/ssh_host_key.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 700 | and adding the host names at the front. |
| 701 | .Ss Examples |
| 702 | closenet,closenet.hut.fi,.\|.\|.\|,130.233.208.41 1024 37 159.\|.\|.93 closenet.hut.fi |
| 703 | .Sh FILES |
| 704 | .Bl -tag -width Ds |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 705 | .It Pa /etc/sshd_config |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 706 | Contains configuration data for |
| 707 | .Nm sshd . |
| 708 | This file should be writable by root only, but it is recommended |
| 709 | (though not necessary) that it be world-readable. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 710 | .It Pa /etc/ssh_host_key |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 711 | Contains the private part of the host key. |
| 712 | This file should only be owned by root, readable only by root, and not |
| 713 | accessible to others. |
| 714 | Note that |
| 715 | .Nm |
| 716 | does not start if this file is group/world-accessible. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 717 | .It Pa /etc/ssh_host_key.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 718 | Contains the public part of the host key. |
| 719 | This file should be world-readable but writable only by |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 720 | root. |
| 721 | Its contents should match the private part. |
| 722 | This file is not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 723 | really used for anything; it is only provided for the convenience of |
| 724 | the user so its contents can be copied to known hosts files. |
| 725 | These two files are created using |
| 726 | .Xr ssh-keygen 1 . |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 727 | .It Pa /var/run/sshd.pid |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 728 | Contains the process ID of the |
| 729 | .Nm |
| 730 | listening for connections (if there are several daemons running |
| 731 | concurrently for different ports, this contains the pid of the one |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 732 | started last). |
| 733 | The contents of this file are not sensitive; it can be world-readable. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 734 | .It Pa $HOME/.ssh/authorized_keys |
| 735 | Lists the RSA keys that can be used to log into the user's account. |
| 736 | This file must be readable by root (which may on some machines imply |
| 737 | it being world-readable if the user's home directory resides on an NFS |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 738 | volume). |
| 739 | It is recommended that it not be accessible by others. |
| 740 | The format of this file is described above. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 741 | .It Pa "/etc/ssh_known_hosts" and "$HOME/.ssh/known_hosts" |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 742 | These files are consulted when using rhosts with RSA host |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 743 | authentication to check the public key of the host. |
| 744 | 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] | 745 | The client uses the same files |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 746 | to verify that the remote host is the one we intended to connect. |
| 747 | These files should be writable only by root/the owner. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 748 | .Pa /etc/ssh_known_hosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 749 | should be world-readable, and |
| 750 | .Pa $HOME/.ssh/known_hosts |
| 751 | can but need not be world-readable. |
| 752 | .It Pa /etc/nologin |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 753 | If this file exists, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 754 | .Nm |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 755 | refuses to let anyone except root log in. |
| 756 | The contents of the file |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 757 | 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] | 758 | refused. |
| 759 | The file should be world-readable. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 760 | .It Pa /etc/hosts.allow, /etc/hosts.deny |
| 761 | If compiled with |
| 762 | .Sy LIBWRAP |
| 763 | support, tcp-wrappers access controls may be defined here as described in |
| 764 | .Xr hosts_access 5 . |
| 765 | .It Pa $HOME/.rhosts |
| 766 | This file contains host-username pairs, separated by a space, one per |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 767 | line. |
| 768 | The given user on the corresponding host is permitted to log in |
| 769 | without password. |
| 770 | The same file is used by rlogind and rshd. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 771 | The file must |
| 772 | be writable only by the user; it is recommended that it not be |
| 773 | accessible by others. |
| 774 | .Pp |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 775 | If is also possible to use netgroups in the file. |
| 776 | Either host or user |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 777 | name may be of the form +@groupname to specify all hosts or all users |
| 778 | in the group. |
| 779 | .It Pa $HOME/.shosts |
| 780 | For ssh, |
| 781 | this file is exactly the same as for |
| 782 | .Pa .rhosts . |
| 783 | However, this file is |
| 784 | not used by rlogin and rshd, so using this permits access using SSH only. |
| 785 | .Pa /etc/hosts.equiv |
| 786 | This file is used during |
| 787 | .Pa .rhosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 788 | authentication. |
| 789 | In the simplest form, this file contains host names, one per line. |
| 790 | Users on |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 791 | those hosts are permitted to log in without a password, provided they |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 792 | have the same user name on both machines. |
| 793 | The host name may also be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 794 | followed by a user name; such users are permitted to log in as |
| 795 | .Em any |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 796 | user on this machine (except root). |
| 797 | Additionally, the syntax |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 798 | .Dq +@group |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 799 | can be used to specify netgroups. |
| 800 | Negated entries start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 801 | .Ql \&- . |
| 802 | .Pp |
| 803 | If the client host/user is successfully matched in this file, login is |
| 804 | automatically permitted provided the client and server user names are the |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 805 | same. |
| 806 | Additionally, successful RSA host authentication is normally required. |
| 807 | This file must be writable only by root; it is recommended |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 808 | that it be world-readable. |
| 809 | .Pp |
| 810 | .Sy "Warning: It is almost never a good idea to use user names in" |
| 811 | .Pa hosts.equiv . |
| 812 | Beware that it really means that the named user(s) can log in as |
| 813 | .Em anybody , |
| 814 | which includes bin, daemon, adm, and other accounts that own critical |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 815 | binaries and directories. |
| 816 | Using a user name practically grants the user root access. |
| 817 | The only valid use for user names that I can think |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 818 | of is in negative entries. |
| 819 | .Pp |
| 820 | Note that this warning also applies to rsh/rlogin. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 821 | .It Pa /etc/shosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 822 | This is processed exactly as |
| 823 | .Pa /etc/hosts.equiv . |
| 824 | However, this file may be useful in environments that want to run both |
| 825 | rsh/rlogin and ssh. |
| 826 | .It Pa $HOME/.ssh/environment |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 827 | This file is read into the environment at login (if it exists). |
| 828 | It can only contain empty lines, comment lines (that start with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 829 | .Ql # ) , |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 830 | and assignment lines of the form name=value. |
| 831 | The file should be writable |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 832 | only by the user; it need not be readable by anyone else. |
| 833 | .It Pa $HOME/.ssh/rc |
| 834 | 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] | 835 | environment files but before starting the user's shell or command. |
| 836 | 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] | 837 | standard input (and |
| 838 | .Ev DISPLAY |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 839 | in environment). |
| 840 | This must call |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 841 | .Xr xauth 1 |
| 842 | in that case. |
| 843 | .Pp |
| 844 | The primary purpose of this file is to run any initialization routines |
| 845 | which may be needed before the user's home directory becomes |
| 846 | accessible; AFS is a particular example of such an environment. |
| 847 | .Pp |
| 848 | This file will probably contain some initialization code followed by |
| 849 | something similar to: "if read proto cookie; then echo add $DISPLAY |
| 850 | $proto $cookie | xauth -q -; fi". |
| 851 | .Pp |
| 852 | If this file does not exist, |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 853 | .Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 854 | is run, and if that |
| 855 | does not exist either, xauth is used to store the cookie. |
| 856 | .Pp |
| 857 | This file should be writable only by the user, and need not be |
| 858 | readable by anyone else. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 859 | .It Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 860 | Like |
| 861 | .Pa $HOME/.ssh/rc . |
| 862 | This can be used to specify |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 863 | machine-specific login-time initializations globally. |
| 864 | This file should be writable only by root, and should be world-readable. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 865 | .Sh AUTHOR |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 866 | OpenSSH |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 867 | 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] | 868 | but with bugs removed and newer features re-added. |
| 869 | Rapidly after the |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 870 | 1.2.12 release, newer versions of the original ssh bore successively |
| 871 | more restrictive licenses, and thus demand for a free version was born. |
| 872 | This version of OpenSSH |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 873 | .Bl -bullet |
| 874 | .It |
Damien Miller | cfabe86 | 2000-04-20 23:27:27 +1000 | [diff] [blame^] | 875 | has all components of a restrictive nature (i.e., patents) |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 876 | directly removed from the source code; any licensed or patented components |
| 877 | are chosen from |
| 878 | external libraries. |
| 879 | .It |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 880 | has been updated to support ssh protocol 1.5, making it compatible with |
| 881 | all other ssh protocol 1 clients and servers. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 882 | .It |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 883 | contains added support for |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 884 | .Xr kerberos 8 |
| 885 | authentication and ticket passing. |
| 886 | .It |
| 887 | supports one-time password authentication with |
| 888 | .Xr skey 1 . |
| 889 | .El |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 890 | .Sh SEE ALSO |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 891 | .Xr scp 1 , |
| 892 | .Xr ssh 1 , |
| 893 | .Xr ssh-add 1 , |
| 894 | .Xr ssh-agent 1 , |
| 895 | .Xr ssh-keygen 1 , |
Damien Miller | b38eff8 | 2000-04-01 11:09:21 +1000 | [diff] [blame] | 896 | .Xr rlogin 1 , |
| 897 | .Xr rsh 1 |