Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1 | .\" -*- nroff -*- |
| 2 | .\" |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
| 5 | .\" All rights reserved |
| 6 | .\" |
Damien Miller | e4340be | 2000-09-16 13:29:08 +1100 | [diff] [blame] | 7 | .\" As far as I am concerned, the code I have written for this software |
| 8 | .\" can be used freely for any purpose. Any derived versions of this |
| 9 | .\" software must be clearly marked as such, and if the derived work is |
| 10 | .\" incompatible with the protocol description in the RFC file, it must be |
| 11 | .\" called by a name other than "ssh" or "Secure Shell". |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 12 | .\" |
Ben Lindstrom | 92a2e38 | 2001-03-05 06:59:27 +0000 | [diff] [blame] | 13 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. |
| 14 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. |
| 15 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. |
Damien Miller | e4340be | 2000-09-16 13:29:08 +1100 | [diff] [blame] | 16 | .\" |
| 17 | .\" Redistribution and use in source and binary forms, with or without |
| 18 | .\" modification, are permitted provided that the following conditions |
| 19 | .\" are met: |
| 20 | .\" 1. Redistributions of source code must retain the above copyright |
| 21 | .\" notice, this list of conditions and the following disclaimer. |
| 22 | .\" 2. Redistributions in binary form must reproduce the above copyright |
| 23 | .\" notice, this list of conditions and the following disclaimer in the |
| 24 | .\" documentation and/or other materials provided with the distribution. |
| 25 | .\" |
| 26 | .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
| 27 | .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
| 28 | .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
| 29 | .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
| 30 | .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
| 31 | .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| 32 | .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| 33 | .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| 34 | .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
| 35 | .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 36 | .\" |
Damien Miller | c27f83a | 2006-01-06 14:50:26 +1100 | [diff] [blame] | 37 | .\" $OpenBSD: ssh.1,v 1.243 2006/01/04 19:50:09 jmc Exp $ |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 38 | .Dd September 25, 1999 |
| 39 | .Dt SSH 1 |
| 40 | .Os |
| 41 | .Sh NAME |
| 42 | .Nm ssh |
Ben Lindstrom | d58eb5f | 2001-03-07 06:07:22 +0000 | [diff] [blame] | 43 | .Nd OpenSSH SSH client (remote login program) |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 44 | .Sh SYNOPSIS |
| 45 | .Nm ssh |
Darren Tucker | ba5c592 | 2004-06-18 16:22:39 +1000 | [diff] [blame] | 46 | .Op Fl 1246AaCfgkMNnqsTtVvXxY |
Ben Lindstrom | e0f8804 | 2001-04-30 13:06:24 +0000 | [diff] [blame] | 47 | .Op Fl b Ar bind_address |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 48 | .Op Fl c Ar cipher_spec |
Darren Tucker | c8d6421 | 2005-10-03 18:13:42 +1000 | [diff] [blame] | 49 | .Oo Fl D\ \& |
| 50 | .Sm off |
| 51 | .Oo Ar bind_address : Oc |
| 52 | .Ar port |
| 53 | .Sm on |
| 54 | .Oc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 55 | .Op Fl e Ar escape_char |
Ben Lindstrom | 14f31ab | 2001-09-12 17:48:04 +0000 | [diff] [blame] | 56 | .Op Fl F Ar configfile |
Darren Tucker | 05d4dfe | 2005-10-03 18:17:38 +1000 | [diff] [blame] | 57 | .Bk -words |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 58 | .Op Fl i Ar identity_file |
Darren Tucker | 05d4dfe | 2005-10-03 18:17:38 +1000 | [diff] [blame] | 59 | .Ek |
Damien Miller | 36bf7dd | 2005-03-02 12:02:47 +1100 | [diff] [blame] | 60 | .Oo Fl L\ \& |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 61 | .Sm off |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 62 | .Oo Ar bind_address : Oc |
Damien Miller | 36bf7dd | 2005-03-02 12:02:47 +1100 | [diff] [blame] | 63 | .Ar port : host : hostport |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 64 | .Sm on |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 65 | .Oc |
Darren Tucker | 05d4dfe | 2005-10-03 18:17:38 +1000 | [diff] [blame] | 66 | .Bk -words |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 67 | .Op Fl l Ar login_name |
Darren Tucker | 05d4dfe | 2005-10-03 18:17:38 +1000 | [diff] [blame] | 68 | .Ek |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 69 | .Op Fl m Ar mac_spec |
Darren Tucker | 7ebfc10 | 2004-11-07 20:06:19 +1100 | [diff] [blame] | 70 | .Op Fl O Ar ctl_cmd |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 71 | .Op Fl o Ar option |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 72 | .Op Fl p Ar port |
Damien Miller | 36bf7dd | 2005-03-02 12:02:47 +1100 | [diff] [blame] | 73 | .Oo Fl R\ \& |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 74 | .Sm off |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 75 | .Oo Ar bind_address : Oc |
Damien Miller | 36bf7dd | 2005-03-02 12:02:47 +1100 | [diff] [blame] | 76 | .Ar port : host : hostport |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 77 | .Sm on |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 78 | .Oc |
Darren Tucker | 7ebfc10 | 2004-11-07 20:06:19 +1100 | [diff] [blame] | 79 | .Op Fl S Ar ctl_path |
Damien Miller | f0c8c15 | 2005-12-13 19:29:58 +1100 | [diff] [blame] | 80 | .Bk -words |
| 81 | .Op Fl w Ar tunnel : Ns Ar tunnel |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 82 | .Oo Ar user Ns @ Oc Ns Ar hostname |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 83 | .Op Ar command |
Damien Miller | f0c8c15 | 2005-12-13 19:29:58 +1100 | [diff] [blame] | 84 | .Ek |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 85 | .Sh DESCRIPTION |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 86 | .Nm |
Ben Lindstrom | d58eb5f | 2001-03-07 06:07:22 +0000 | [diff] [blame] | 87 | (SSH client) is a program for logging into a remote machine and for |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 88 | executing commands on a remote machine. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 89 | It is intended to replace rlogin and rsh, |
| 90 | and provide secure encrypted communications between |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 91 | two untrusted hosts over an insecure network. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 92 | X11 connections and arbitrary TCP/IP ports |
| 93 | can also be forwarded over the secure channel. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 94 | .Pp |
| 95 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 96 | connects and logs into the specified |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 97 | .Ar hostname |
| 98 | (with optional |
| 99 | .Ar user |
| 100 | name). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 101 | The user must prove |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 102 | his/her identity to the remote machine using one of several methods |
Darren Tucker | 5434cfe | 2005-12-20 16:11:35 +1100 | [diff] [blame] | 103 | depending on the protocol version used (see below). |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 104 | .Pp |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 105 | If |
| 106 | .Ar command |
| 107 | is specified, |
Darren Tucker | b18c867 | 2005-12-20 16:10:09 +1100 | [diff] [blame] | 108 | it is executed on the remote host instead of a login shell. |
Darren Tucker | 0b42e6d | 2004-08-13 21:22:40 +1000 | [diff] [blame] | 109 | .Pp |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 110 | The options are as follows: |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 111 | .Bl -tag -width Ds |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 112 | .It Fl 1 |
| 113 | Forces |
| 114 | .Nm |
| 115 | to try protocol version 1 only. |
| 116 | .It Fl 2 |
| 117 | Forces |
| 118 | .Nm |
| 119 | to try protocol version 2 only. |
| 120 | .It Fl 4 |
| 121 | Forces |
| 122 | .Nm |
| 123 | to use IPv4 addresses only. |
| 124 | .It Fl 6 |
| 125 | Forces |
| 126 | .Nm |
| 127 | to use IPv6 addresses only. |
Damien Miller | b1715dc | 2000-05-30 13:44:51 +1000 | [diff] [blame] | 128 | .It Fl A |
| 129 | Enables forwarding of the authentication agent connection. |
| 130 | This can also be specified on a per-host basis in a configuration file. |
Damien Miller | b5fdfaa | 2002-09-12 09:52:03 +1000 | [diff] [blame] | 131 | .Pp |
Damien Miller | 495dca3 | 2003-04-01 21:42:14 +1000 | [diff] [blame] | 132 | Agent forwarding should be enabled with caution. |
| 133 | Users with the ability to bypass file permissions on the remote host |
| 134 | (for the agent's Unix-domain socket) |
| 135 | can access the local agent through the forwarded connection. |
| 136 | An attacker cannot obtain key material from the agent, |
Damien Miller | b5fdfaa | 2002-09-12 09:52:03 +1000 | [diff] [blame] | 137 | however they can perform operations on the keys that enable them to |
| 138 | authenticate using the identities loaded into the agent. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 139 | .It Fl a |
| 140 | Disables forwarding of the authentication agent connection. |
Ben Lindstrom | e0f8804 | 2001-04-30 13:06:24 +0000 | [diff] [blame] | 141 | .It Fl b Ar bind_address |
Darren Tucker | a5cf855 | 2005-07-14 17:04:18 +1000 | [diff] [blame] | 142 | Use |
| 143 | .Ar bind_address |
| 144 | on the local machine as the source address |
| 145 | of the connection. |
| 146 | Only useful on systems with more than one address. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 147 | .It Fl C |
| 148 | Requests compression of all data (including stdin, stdout, stderr, and |
| 149 | data for forwarded X11 and TCP/IP connections). |
| 150 | The compression algorithm is the same used by |
| 151 | .Xr gzip 1 , |
| 152 | and the |
| 153 | .Dq level |
| 154 | can be controlled by the |
| 155 | .Cm CompressionLevel |
| 156 | option for protocol version 1. |
| 157 | Compression is desirable on modem lines and other |
| 158 | slow connections, but will only slow down things on fast networks. |
| 159 | The default value can be set on a host-by-host basis in the |
| 160 | configuration files; see the |
| 161 | .Cm Compression |
| 162 | option. |
Damien Miller | 05202ff | 2004-06-15 10:30:39 +1000 | [diff] [blame] | 163 | .It Fl c Ar cipher_spec |
| 164 | Selects the cipher specification for encrypting the session. |
| 165 | .Pp |
| 166 | Protocol version 1 allows specification of a single cipher. |
Darren Tucker | 1e4308e | 2005-10-03 18:18:40 +1000 | [diff] [blame] | 167 | The supported values are |
Damien Miller | 05202ff | 2004-06-15 10:30:39 +1000 | [diff] [blame] | 168 | .Dq 3des , |
Darren Tucker | ff9f484 | 2005-12-20 16:10:45 +1100 | [diff] [blame] | 169 | .Dq blowfish , |
Damien Miller | 05202ff | 2004-06-15 10:30:39 +1000 | [diff] [blame] | 170 | and |
| 171 | .Dq des . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 172 | .Ar 3des |
| 173 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. |
Damien Miller | 05202ff | 2004-06-15 10:30:39 +1000 | [diff] [blame] | 174 | It is believed to be secure. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 175 | .Ar blowfish |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 176 | is a fast block cipher; it appears very secure and is much faster than |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 177 | .Ar 3des . |
Ben Lindstrom | ffa1dd6 | 2001-09-12 16:52:28 +0000 | [diff] [blame] | 178 | .Ar des |
| 179 | is only supported in the |
| 180 | .Nm |
| 181 | client for interoperability with legacy protocol 1 implementations |
| 182 | that do not support the |
| 183 | .Ar 3des |
Damien Miller | 495dca3 | 2003-04-01 21:42:14 +1000 | [diff] [blame] | 184 | cipher. |
| 185 | Its use is strongly discouraged due to cryptographic weaknesses. |
Damien Miller | 05202ff | 2004-06-15 10:30:39 +1000 | [diff] [blame] | 186 | The default is |
| 187 | .Dq 3des . |
| 188 | .Pp |
Damien Miller | 3597821 | 2005-12-24 14:56:47 +1100 | [diff] [blame] | 189 | For protocol version 2, |
Damien Miller | 05202ff | 2004-06-15 10:30:39 +1000 | [diff] [blame] | 190 | .Ar cipher_spec |
| 191 | is a comma-separated list of ciphers |
| 192 | listed in order of preference. |
Damien Miller | 3597821 | 2005-12-24 14:56:47 +1100 | [diff] [blame] | 193 | The supported ciphers are: |
| 194 | 3des-cbc, |
| 195 | aes128-cbc, |
| 196 | aes192-cbc, |
| 197 | aes256-cbc, |
| 198 | aes128-ctr, |
| 199 | aes192-ctr, |
| 200 | aes256-ctr, |
| 201 | arcfour128, |
| 202 | arcfour256, |
| 203 | arcfour, |
| 204 | blowfish-cbc, |
Damien Miller | 05202ff | 2004-06-15 10:30:39 +1000 | [diff] [blame] | 205 | and |
Damien Miller | 3597821 | 2005-12-24 14:56:47 +1100 | [diff] [blame] | 206 | cast128-cbc. |
Darren Tucker | ff9f484 | 2005-12-20 16:10:45 +1100 | [diff] [blame] | 207 | The default is: |
| 208 | .Bd -literal -offset indent |
| 209 | aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, |
| 210 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, |
| 211 | aes192-ctr,aes256-ctr |
Damien Miller | 05202ff | 2004-06-15 10:30:39 +1000 | [diff] [blame] | 212 | .Ed |
Darren Tucker | c8d6421 | 2005-10-03 18:13:42 +1000 | [diff] [blame] | 213 | .It Fl D Xo |
| 214 | .Sm off |
| 215 | .Oo Ar bind_address : Oc |
| 216 | .Ar port |
| 217 | .Sm on |
| 218 | .Xc |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 219 | Specifies a local |
| 220 | .Dq dynamic |
| 221 | application-level port forwarding. |
| 222 | This works by allocating a socket to listen to |
| 223 | .Ar port |
Darren Tucker | c8d6421 | 2005-10-03 18:13:42 +1000 | [diff] [blame] | 224 | on the local side, optionally bound to the specified |
| 225 | .Ar bind_address . |
| 226 | Whenever a connection is made to this port, the |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 227 | connection is forwarded over the secure channel, and the application |
| 228 | protocol is then used to determine where to connect to from the |
| 229 | remote machine. |
| 230 | Currently the SOCKS4 and SOCKS5 protocols are supported, and |
| 231 | .Nm |
| 232 | will act as a SOCKS server. |
| 233 | Only root can forward privileged ports. |
| 234 | Dynamic port forwardings can also be specified in the configuration file. |
Darren Tucker | c8d6421 | 2005-10-03 18:13:42 +1000 | [diff] [blame] | 235 | .Pp |
| 236 | IPv6 addresses can be specified with an alternative syntax: |
| 237 | .Sm off |
| 238 | .Xo |
| 239 | .Op Ar bind_address No / |
| 240 | .Ar port |
| 241 | .Xc |
| 242 | .Sm on |
| 243 | or by enclosing the address in square brackets. |
| 244 | Only the superuser can forward privileged ports. |
| 245 | By default, the local port is bound in accordance with the |
| 246 | .Cm GatewayPorts |
| 247 | setting. |
| 248 | However, an explicit |
| 249 | .Ar bind_address |
| 250 | may be used to bind the connection to a specific address. |
| 251 | The |
| 252 | .Ar bind_address |
| 253 | of |
| 254 | .Dq localhost |
| 255 | indicates that the listening port be bound for local use only, while an |
| 256 | empty address or |
| 257 | .Sq * |
| 258 | indicates that the port should be available from all interfaces. |
Damien Miller | 2142ba0 | 2005-12-24 14:56:29 +1100 | [diff] [blame] | 259 | .It Fl e Ar escape_char |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 260 | Sets the escape character for sessions with a pty (default: |
| 261 | .Ql ~ ) . |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 262 | The escape character is only recognized at the beginning of a line. |
| 263 | The escape character followed by a dot |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 264 | .Pq Ql \&. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 265 | closes the connection; |
| 266 | followed by control-Z suspends the connection; |
| 267 | and followed by itself sends the escape character once. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 268 | Setting the character to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 269 | .Dq none |
| 270 | disables any escapes and makes the session fully transparent. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 271 | .It Fl F Ar configfile |
| 272 | Specifies an alternative per-user configuration file. |
| 273 | If a configuration file is given on the command line, |
| 274 | the system-wide configuration file |
| 275 | .Pq Pa /etc/ssh/ssh_config |
| 276 | will be ignored. |
| 277 | The default for the per-user configuration file is |
Damien Miller | 167ea5d | 2005-05-26 12:04:02 +1000 | [diff] [blame] | 278 | .Pa ~/.ssh/config . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 279 | .It Fl f |
| 280 | Requests |
| 281 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 282 | to go to background just before command execution. |
| 283 | This is useful if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 284 | .Nm |
| 285 | is going to ask for passwords or passphrases, but the user |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 286 | wants it in the background. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 287 | This implies |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 288 | .Fl n . |
| 289 | The recommended way to start X11 programs at a remote site is with |
| 290 | something like |
| 291 | .Ic ssh -f host xterm . |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 292 | .It Fl g |
| 293 | Allows remote hosts to connect to local forwarded ports. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 294 | .It Fl I Ar smartcard_device |
Damien Miller | 2142ba0 | 2005-12-24 14:56:29 +1100 | [diff] [blame] | 295 | Specify the device |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 296 | .Nm |
| 297 | should use to communicate with a smartcard used for storing the user's |
| 298 | private RSA key. |
Damien Miller | 2142ba0 | 2005-12-24 14:56:29 +1100 | [diff] [blame] | 299 | This option is only available if support for smartcard devices |
| 300 | is compiled in (default is no support). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 301 | .It Fl i Ar identity_file |
Damien Miller | fae2386 | 2002-01-22 23:32:26 +1100 | [diff] [blame] | 302 | Selects a file from which the identity (private key) for |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 303 | RSA or DSA authentication is read. |
Damien Miller | fae2386 | 2002-01-22 23:32:26 +1100 | [diff] [blame] | 304 | The default is |
Damien Miller | 167ea5d | 2005-05-26 12:04:02 +1000 | [diff] [blame] | 305 | .Pa ~/.ssh/identity |
Damien Miller | fae2386 | 2002-01-22 23:32:26 +1100 | [diff] [blame] | 306 | for protocol version 1, and |
Damien Miller | 167ea5d | 2005-05-26 12:04:02 +1000 | [diff] [blame] | 307 | .Pa ~/.ssh/id_rsa |
Damien Miller | fae2386 | 2002-01-22 23:32:26 +1100 | [diff] [blame] | 308 | and |
Damien Miller | 167ea5d | 2005-05-26 12:04:02 +1000 | [diff] [blame] | 309 | .Pa ~/.ssh/id_dsa |
Damien Miller | fae2386 | 2002-01-22 23:32:26 +1100 | [diff] [blame] | 310 | for protocol version 2. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 311 | Identity files may also be specified on |
| 312 | a per-host basis in the configuration file. |
| 313 | It is possible to have multiple |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 314 | .Fl i |
| 315 | options (and multiple identities specified in |
| 316 | configuration files). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 317 | .It Fl k |
Damien Miller | e0113cc | 2003-11-24 13:10:09 +1100 | [diff] [blame] | 318 | Disables forwarding (delegation) of GSSAPI credentials to the server. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 319 | .It Fl L Xo |
| 320 | .Sm off |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 321 | .Oo Ar bind_address : Oc |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 322 | .Ar port : host : hostport |
| 323 | .Sm on |
| 324 | .Xc |
| 325 | Specifies that the given port on the local (client) host is to be |
| 326 | forwarded to the given host and port on the remote side. |
| 327 | This works by allocating a socket to listen to |
| 328 | .Ar port |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 329 | on the local side, optionally bound to the specified |
| 330 | .Ar bind_address . |
| 331 | Whenever a connection is made to this port, the |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 332 | connection is forwarded over the secure channel, and a connection is |
| 333 | made to |
| 334 | .Ar host |
| 335 | port |
| 336 | .Ar hostport |
| 337 | from the remote machine. |
| 338 | Port forwardings can also be specified in the configuration file. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 339 | IPv6 addresses can be specified with an alternative syntax: |
| 340 | .Sm off |
| 341 | .Xo |
Damien Miller | b096ac4 | 2005-03-09 11:00:05 +1100 | [diff] [blame] | 342 | .Op Ar bind_address No / |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 343 | .Ar port No / Ar host No / |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 344 | .Ar hostport |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 345 | .Xc |
| 346 | .Sm on |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 347 | or by enclosing the address in square brackets. |
| 348 | Only the superuser can forward privileged ports. |
| 349 | By default, the local port is bound in accordance with the |
| 350 | .Cm GatewayPorts |
| 351 | setting. |
| 352 | However, an explicit |
| 353 | .Ar bind_address |
| 354 | may be used to bind the connection to a specific address. |
| 355 | The |
| 356 | .Ar bind_address |
| 357 | of |
| 358 | .Dq localhost |
Damien Miller | 36bf7dd | 2005-03-02 12:02:47 +1100 | [diff] [blame] | 359 | indicates that the listening port be bound for local use only, while an |
| 360 | empty address or |
| 361 | .Sq * |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 362 | indicates that the port should be available from all interfaces. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 363 | .It Fl l Ar login_name |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 364 | Specifies the user to log in as on the remote machine. |
| 365 | This also may be specified on a per-host basis in the configuration file. |
Damien Miller | 0e220db | 2004-06-15 10:34:08 +1000 | [diff] [blame] | 366 | .It Fl M |
| 367 | Places the |
| 368 | .Nm |
| 369 | client into |
| 370 | .Dq master |
| 371 | mode for connection sharing. |
Damien Miller | 88b2552 | 2005-12-31 16:23:15 +1100 | [diff] [blame] | 372 | Multiple |
| 373 | .Fl M |
| 374 | options places |
| 375 | .Nm |
| 376 | into |
| 377 | .Dq master |
| 378 | mode with confirmation required before slave connections are accepted. |
Damien Miller | 0e220db | 2004-06-15 10:34:08 +1000 | [diff] [blame] | 379 | Refer to the description of |
| 380 | .Cm ControlMaster |
| 381 | in |
| 382 | .Xr ssh_config 5 |
| 383 | for details. |
Damien Miller | 5d1eceb | 2004-06-30 22:37:57 +1000 | [diff] [blame] | 384 | .It Fl m Ar mac_spec |
| 385 | Additionally, for protocol version 2 a comma-separated list of MAC |
| 386 | (message authentication code) algorithms can |
| 387 | be specified in order of preference. |
| 388 | See the |
| 389 | .Cm MACs |
| 390 | keyword for more information. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 391 | .It Fl N |
| 392 | Do not execute a remote command. |
| 393 | This is useful for just forwarding ports |
| 394 | (protocol version 2 only). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 395 | .It Fl n |
| 396 | Redirects stdin from |
| 397 | .Pa /dev/null |
| 398 | (actually, prevents reading from stdin). |
| 399 | This must be used when |
| 400 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 401 | is run in the background. |
| 402 | A common trick is to use this to run X11 programs on a remote machine. |
| 403 | For example, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 404 | .Ic ssh -n shadows.cs.hut.fi emacs & |
| 405 | will start an emacs on shadows.cs.hut.fi, and the X11 |
| 406 | connection will be automatically forwarded over an encrypted channel. |
| 407 | The |
| 408 | .Nm |
| 409 | program will be put in the background. |
| 410 | (This does not work if |
| 411 | .Nm |
| 412 | needs to ask for a password or passphrase; see also the |
| 413 | .Fl f |
| 414 | option.) |
Darren Tucker | e04644c | 2004-12-03 14:08:45 +1100 | [diff] [blame] | 415 | .It Fl O Ar ctl_cmd |
| 416 | Control an active connection multiplexing master process. |
| 417 | When the |
| 418 | .Fl O |
| 419 | option is specified, the |
| 420 | .Ar ctl_cmd |
| 421 | argument is interpreted and passed to the master process. |
| 422 | Valid commands are: |
| 423 | .Dq check |
| 424 | (check that the master process is running) and |
| 425 | .Dq exit |
| 426 | (request the master to exit). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 427 | .It Fl o Ar option |
Ben Lindstrom | 14c62eb | 2001-08-15 23:25:46 +0000 | [diff] [blame] | 428 | Can be used to give options in the format used in the configuration file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 429 | This is useful for specifying options for which there is no separate |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 430 | command-line flag. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 431 | For full details of the options listed below, and their possible values, see |
| 432 | .Xr ssh_config 5 . |
| 433 | .Pp |
| 434 | .Bl -tag -width Ds -offset indent -compact |
| 435 | .It AddressFamily |
| 436 | .It BatchMode |
| 437 | .It BindAddress |
| 438 | .It ChallengeResponseAuthentication |
| 439 | .It CheckHostIP |
| 440 | .It Cipher |
| 441 | .It Ciphers |
| 442 | .It ClearAllForwardings |
| 443 | .It Compression |
| 444 | .It CompressionLevel |
| 445 | .It ConnectionAttempts |
Darren Tucker | edae0ec | 2004-05-02 22:15:52 +1000 | [diff] [blame] | 446 | .It ConnectTimeout |
Damien Miller | 0e220db | 2004-06-15 10:34:08 +1000 | [diff] [blame] | 447 | .It ControlMaster |
| 448 | .It ControlPath |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 449 | .It DynamicForward |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 450 | .It EscapeChar |
| 451 | .It ForwardAgent |
| 452 | .It ForwardX11 |
Darren Tucker | 0a118da | 2003-10-15 15:54:32 +1000 | [diff] [blame] | 453 | .It ForwardX11Trusted |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 454 | .It GatewayPorts |
| 455 | .It GlobalKnownHostsFile |
| 456 | .It GSSAPIAuthentication |
| 457 | .It GSSAPIDelegateCredentials |
Damien Miller | e177615 | 2005-03-01 21:47:37 +1100 | [diff] [blame] | 458 | .It HashKnownHosts |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 459 | .It Host |
| 460 | .It HostbasedAuthentication |
| 461 | .It HostKeyAlgorithms |
| 462 | .It HostKeyAlias |
| 463 | .It HostName |
| 464 | .It IdentityFile |
Damien Miller | bd394c3 | 2004-03-08 23:12:36 +1100 | [diff] [blame] | 465 | .It IdentitiesOnly |
Darren Tucker | 636ca90 | 2004-11-05 20:22:00 +1100 | [diff] [blame] | 466 | .It KbdInteractiveDevices |
Damien Miller | d27b947 | 2005-12-13 19:29:02 +1100 | [diff] [blame] | 467 | .It LocalCommand |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 468 | .It LocalForward |
| 469 | .It LogLevel |
| 470 | .It MACs |
| 471 | .It NoHostAuthenticationForLocalhost |
| 472 | .It NumberOfPasswordPrompts |
| 473 | .It PasswordAuthentication |
Damien Miller | d27b947 | 2005-12-13 19:29:02 +1100 | [diff] [blame] | 474 | .It PermitLocalCommand |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 475 | .It Port |
| 476 | .It PreferredAuthentications |
| 477 | .It Protocol |
| 478 | .It ProxyCommand |
| 479 | .It PubkeyAuthentication |
| 480 | .It RemoteForward |
| 481 | .It RhostsRSAAuthentication |
| 482 | .It RSAAuthentication |
Darren Tucker | 7a6c066 | 2004-05-02 22:14:03 +1000 | [diff] [blame] | 483 | .It SendEnv |
Damien Miller | 509b010 | 2003-12-17 16:33:10 +1100 | [diff] [blame] | 484 | .It ServerAliveInterval |
| 485 | .It ServerAliveCountMax |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 486 | .It SmartcardDevice |
| 487 | .It StrictHostKeyChecking |
Damien Miller | 12c150e | 2003-12-17 16:31:10 +1100 | [diff] [blame] | 488 | .It TCPKeepAlive |
Damien Miller | d27b947 | 2005-12-13 19:29:02 +1100 | [diff] [blame] | 489 | .It Tunnel |
| 490 | .It TunnelDevice |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 491 | .It UsePrivilegedPort |
| 492 | .It User |
| 493 | .It UserKnownHostsFile |
| 494 | .It VerifyHostKeyDNS |
| 495 | .It XAuthLocation |
| 496 | .El |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 497 | .It Fl p Ar port |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 498 | Port to connect to on the remote host. |
| 499 | This can be specified on a |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 500 | per-host basis in the configuration file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 501 | .It Fl q |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 502 | Quiet mode. |
| 503 | Causes all warning and diagnostic messages to be suppressed. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 504 | .It Fl R Xo |
| 505 | .Sm off |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 506 | .Oo Ar bind_address : Oc |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 507 | .Ar port : host : hostport |
| 508 | .Sm on |
| 509 | .Xc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 510 | Specifies that the given port on the remote (server) host is to be |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 511 | forwarded to the given host and port on the local side. |
| 512 | This works by allocating a socket to listen to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 513 | .Ar port |
| 514 | on the remote side, and whenever a connection is made to this port, the |
| 515 | connection is forwarded over the secure channel, and a connection is |
| 516 | made to |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 517 | .Ar host |
| 518 | port |
| 519 | .Ar hostport |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 520 | from the local machine. |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 521 | .Pp |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 522 | Port forwardings can also be specified in the configuration file. |
| 523 | Privileged ports can be forwarded only when |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 524 | logging in as root on the remote machine. |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 525 | IPv6 addresses can be specified by enclosing the address in square braces or |
| 526 | using an alternative syntax: |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 527 | .Sm off |
Damien Miller | 36bf7dd | 2005-03-02 12:02:47 +1100 | [diff] [blame] | 528 | .Xo |
Damien Miller | b096ac4 | 2005-03-09 11:00:05 +1100 | [diff] [blame] | 529 | .Op Ar bind_address No / |
Damien Miller | 36bf7dd | 2005-03-02 12:02:47 +1100 | [diff] [blame] | 530 | .Ar host No / Ar port No / |
| 531 | .Ar hostport |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 532 | .Xc . |
Damien Miller | 36bf7dd | 2005-03-02 12:02:47 +1100 | [diff] [blame] | 533 | .Sm on |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 534 | .Pp |
| 535 | By default, the listening socket on the server will be bound to the loopback |
| 536 | interface only. |
| 537 | This may be overriden by specifying a |
| 538 | .Ar bind_address . |
Damien Miller | 36bf7dd | 2005-03-02 12:02:47 +1100 | [diff] [blame] | 539 | An empty |
| 540 | .Ar bind_address , |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 541 | or the address |
Damien Miller | 36bf7dd | 2005-03-02 12:02:47 +1100 | [diff] [blame] | 542 | .Ql * , |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 543 | indicates that the remote socket should listen on all interfaces. |
| 544 | Specifying a remote |
| 545 | .Ar bind_address |
Damien Miller | 36bf7dd | 2005-03-02 12:02:47 +1100 | [diff] [blame] | 546 | will only succeed if the server's |
| 547 | .Cm GatewayPorts |
Damien Miller | f91ee4c | 2005-03-01 21:24:33 +1100 | [diff] [blame] | 548 | option is enabled (see |
Damien Miller | 36bf7dd | 2005-03-02 12:02:47 +1100 | [diff] [blame] | 549 | .Xr sshd_config 5 ) . |
Darren Tucker | 7ebfc10 | 2004-11-07 20:06:19 +1100 | [diff] [blame] | 550 | .It Fl S Ar ctl_path |
Damien Miller | 5d1eceb | 2004-06-30 22:37:57 +1000 | [diff] [blame] | 551 | Specifies the location of a control socket for connection sharing. |
Damien Miller | 0e220db | 2004-06-15 10:34:08 +1000 | [diff] [blame] | 552 | Refer to the description of |
Darren Tucker | ba5c592 | 2004-06-18 16:22:39 +1000 | [diff] [blame] | 553 | .Cm ControlPath |
| 554 | and |
Damien Miller | 0e220db | 2004-06-15 10:34:08 +1000 | [diff] [blame] | 555 | .Cm ControlMaster |
| 556 | in |
| 557 | .Xr ssh_config 5 |
| 558 | for details. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 559 | .It Fl s |
| 560 | May be used to request invocation of a subsystem on the remote system. |
| 561 | Subsystems are a feature of the SSH2 protocol which facilitate the use |
| 562 | of SSH as a secure transport for other applications (eg.\& |
| 563 | .Xr sftp 1 ) . |
| 564 | The subsystem is specified as the remote command. |
| 565 | .It Fl T |
| 566 | Disable pseudo-tty allocation. |
| 567 | .It Fl t |
| 568 | Force pseudo-tty allocation. |
| 569 | This can be used to execute arbitrary |
| 570 | screen-based programs on a remote machine, which can be very useful, |
| 571 | e.g., when implementing menu services. |
| 572 | Multiple |
| 573 | .Fl t |
| 574 | options force tty allocation, even if |
Ben Lindstrom | 19ceb17 | 2001-09-12 17:54:24 +0000 | [diff] [blame] | 575 | .Nm |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 576 | has no local tty. |
| 577 | .It Fl V |
| 578 | Display the version number and exit. |
| 579 | .It Fl v |
| 580 | Verbose mode. |
| 581 | Causes |
Ben Lindstrom | 5ab6ae1 | 2001-02-10 22:08:03 +0000 | [diff] [blame] | 582 | .Nm |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 583 | to print debugging messages about its progress. |
| 584 | This is helpful in |
| 585 | debugging connection, authentication, and configuration problems. |
| 586 | Multiple |
| 587 | .Fl v |
| 588 | options increase the verbosity. |
| 589 | The maximum is 3. |
Damien Miller | f0c8c15 | 2005-12-13 19:29:58 +1100 | [diff] [blame] | 590 | .It Fl w Ar tunnel : Ns Ar tunnel |
Damien Miller | d27b947 | 2005-12-13 19:29:02 +1100 | [diff] [blame] | 591 | Requests a |
| 592 | .Xr tun 4 |
Damien Miller | cf1e342 | 2005-12-24 14:56:04 +1100 | [diff] [blame] | 593 | device on the client |
| 594 | (first |
| 595 | .Ar tunnel |
| 596 | arg) |
| 597 | and server |
| 598 | (second |
| 599 | .Ar tunnel |
| 600 | arg). |
| 601 | The devices may be specified by numerical ID or the keyword |
| 602 | .Dq any , |
| 603 | which uses the next available tunnel device. |
| 604 | See also the |
Damien Miller | d27b947 | 2005-12-13 19:29:02 +1100 | [diff] [blame] | 605 | .Cm Tunnel |
| 606 | directive in |
| 607 | .Xr ssh_config 5 . |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 608 | .It Fl X |
| 609 | Enables X11 forwarding. |
| 610 | This can also be specified on a per-host basis in a configuration file. |
| 611 | .Pp |
| 612 | X11 forwarding should be enabled with caution. |
| 613 | Users with the ability to bypass file permissions on the remote host |
| 614 | (for the user's X authorization database) |
| 615 | can access the local X11 display through the forwarded connection. |
| 616 | An attacker may then be able to perform activities such as keystroke monitoring. |
Damien Miller | 947219e | 2005-03-02 13:22:30 +1100 | [diff] [blame] | 617 | .Pp |
Damien Miller | b022b23 | 2005-03-05 11:22:36 +1100 | [diff] [blame] | 618 | For this reason, X11 forwarding is subjected to X11 SECURITY extension |
Damien Miller | 947219e | 2005-03-02 13:22:30 +1100 | [diff] [blame] | 619 | restrictions by default. |
| 620 | Please refer to the |
| 621 | .Nm |
| 622 | .Fl Y |
| 623 | option and the |
| 624 | .Cm ForwardX11Trusted |
| 625 | directive in |
| 626 | .Xr ssh_config 5 |
| 627 | for more information. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 628 | .It Fl x |
| 629 | Disables X11 forwarding. |
Darren Tucker | 0a118da | 2003-10-15 15:54:32 +1000 | [diff] [blame] | 630 | .It Fl Y |
| 631 | Enables trusted X11 forwarding. |
Damien Miller | 947219e | 2005-03-02 13:22:30 +1100 | [diff] [blame] | 632 | Trusted X11 forwardings are not subjected to the X11 SECURITY extension |
| 633 | controls. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 634 | .El |
Damien Miller | e9b333a | 2005-12-24 14:53:04 +1100 | [diff] [blame] | 635 | .Pp |
| 636 | .Nm |
| 637 | may additionally obtain configuration data from |
| 638 | a per-user configuration file and a system-wide configuration file. |
| 639 | The file format and configuration options are described in |
| 640 | .Xr ssh_config 5 . |
| 641 | .Pp |
| 642 | .Nm |
| 643 | exits with the exit status of the remote command or with 255 |
| 644 | if an error occurred. |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 645 | .Sh AUTHENTICATION |
| 646 | The OpenSSH SSH client supports OpenSSH protocols 1 and 2. |
| 647 | Protocol 2 is the default, with |
| 648 | .Nm |
| 649 | falling back to protocol 1 if it detects protocol 2 is unsupported. |
| 650 | These settings may be altered using the |
| 651 | .Cm Protocol |
| 652 | option in |
| 653 | .Xr ssh_config 5 , |
| 654 | or enforced using the |
| 655 | .Fl 1 |
| 656 | and |
| 657 | .Fl 2 |
| 658 | options (see above). |
| 659 | Both protocols support similar authentication methods, |
| 660 | but protocol 2 is preferred since |
| 661 | it provides additional mechanisms for confidentiality |
| 662 | (the traffic is encrypted using AES, 3DES, Blowfish, CAST128, or Arcfour) |
| 663 | and integrity (hmac-md5, hmac-sha1, hmac-ripemd160). |
| 664 | Protocol 1 lacks a strong mechanism for ensuring the |
| 665 | integrity of the connection. |
| 666 | .Pp |
| 667 | The methods available for authentication are: |
| 668 | host-based authentication, |
| 669 | public key authentication, |
| 670 | challenge-response authentication, |
| 671 | and password authentication. |
| 672 | Authentication methods are tried in the order specified above, |
| 673 | though protocol 2 has a configuration option to change the default order: |
| 674 | .Cm PreferredAuthentications . |
| 675 | .Pp |
| 676 | Host-based authentication works as follows: |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 677 | If the machine the user logs in from is listed in |
| 678 | .Pa /etc/hosts.equiv |
| 679 | or |
| 680 | .Pa /etc/shosts.equiv |
| 681 | on the remote machine, and the user names are |
| 682 | the same on both sides, or if the files |
| 683 | .Pa ~/.rhosts |
| 684 | or |
| 685 | .Pa ~/.shosts |
| 686 | exist in the user's home directory on the |
| 687 | remote machine and contain a line containing the name of the client |
| 688 | machine and the name of the user on that machine, the user is |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 689 | considered for login. |
| 690 | Additionally, the server |
| 691 | .Em must |
| 692 | be able to verify the client's |
| 693 | host key (see the description of |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 694 | .Pa /etc/ssh/ssh_known_hosts |
| 695 | and |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 696 | .Pa ~/.ssh/known_hosts , |
| 697 | below) |
| 698 | for login to be permitted. |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 699 | This authentication method closes security holes due to IP |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 700 | spoofing, DNS spoofing, and routing spoofing. |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 701 | [Note to the administrator: |
| 702 | .Pa /etc/hosts.equiv , |
| 703 | .Pa ~/.rhosts , |
| 704 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
| 705 | disabled if security is desired.] |
| 706 | .Pp |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 707 | Public key authentication works as follows: |
| 708 | The scheme is based on public-key cryptography, |
| 709 | using cryptosystems |
| 710 | where encryption and decryption are done using separate keys, |
| 711 | and it is unfeasible to derive the decryption key from the encryption key. |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 712 | The idea is that each user creates a public/private |
| 713 | key pair for authentication purposes. |
| 714 | The server knows the public key, and only the user knows the private key. |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 715 | .Nm |
| 716 | implements public key authentication protocol automatically, |
| 717 | using either the RSA or DSA algorithms. |
| 718 | Protocol 1 is restricted to using only RSA keys, |
| 719 | but protocol 2 may use either. |
| 720 | The |
| 721 | .Sx HISTORY |
| 722 | section of |
| 723 | .Xr ssl 8 |
| 724 | contains a brief discussion of the two algorithms. |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 725 | .Pp |
| 726 | The file |
| 727 | .Pa ~/.ssh/authorized_keys |
| 728 | lists the public keys that are permitted for logging in. |
| 729 | When the user logs in, the |
| 730 | .Nm |
| 731 | program tells the server which key pair it would like to use for |
| 732 | authentication. |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 733 | The client proves that it has access to the private key |
| 734 | and the server checks that the corresponding public key |
| 735 | is authorized to accept the account. |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 736 | .Pp |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 737 | The user creates his/her key pair by running |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 738 | .Xr ssh-keygen 1 . |
| 739 | This stores the private key in |
| 740 | .Pa ~/.ssh/identity |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 741 | (protocol 1), |
| 742 | .Pa ~/.ssh/id_dsa |
| 743 | (protocol 2 DSA), |
| 744 | or |
| 745 | .Pa ~/.ssh/id_rsa |
| 746 | (protocol 2 RSA) |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 747 | and stores the public key in |
| 748 | .Pa ~/.ssh/identity.pub |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 749 | (protocol 1), |
| 750 | .Pa ~/.ssh/id_dsa.pub |
| 751 | (protocol 2 DSA), |
| 752 | or |
| 753 | .Pa ~/.ssh/id_rsa.pub |
| 754 | (protocol 2 RSA) |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 755 | in the user's home directory. |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 756 | The user should then copy the public key |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 757 | to |
| 758 | .Pa ~/.ssh/authorized_keys |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 759 | in his/her home directory on the remote machine. |
| 760 | The |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 761 | .Pa authorized_keys |
| 762 | file corresponds to the conventional |
| 763 | .Pa ~/.rhosts |
| 764 | file, and has one key |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 765 | per line, though the lines can be very long. |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 766 | After this, the user can log in without giving the password. |
| 767 | .Pp |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 768 | The most convenient way to use public key authentication may be with an |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 769 | authentication agent. |
| 770 | See |
| 771 | .Xr ssh-agent 1 |
| 772 | for more information. |
| 773 | .Pp |
Damien Miller | c93a813 | 2005-12-24 14:52:13 +1100 | [diff] [blame] | 774 | Challenge-response authentication works as follows: |
| 775 | The server sends an arbitrary |
| 776 | .Qq challenge |
| 777 | text, and prompts for a response. |
| 778 | Protocol 2 allows multiple challenges and responses; |
| 779 | protocol 1 is restricted to just one challenge/response. |
| 780 | Examples of challenge-response authentication include |
| 781 | BSD Authentication (see |
| 782 | .Xr login.conf 5 ) |
| 783 | and PAM (some non-OpenBSD systems). |
| 784 | .Pp |
| 785 | Finally, if other authentication methods fail, |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 786 | .Nm |
| 787 | prompts the user for a password. |
| 788 | The password is sent to the remote |
| 789 | host for checking; however, since all communications are encrypted, |
| 790 | the password cannot be seen by someone listening on the network. |
Damien Miller | 48c94ab | 2006-01-02 23:38:00 +1100 | [diff] [blame] | 791 | .Pp |
| 792 | .Nm |
| 793 | automatically maintains and checks a database containing |
| 794 | identification for all hosts it has ever been used with. |
| 795 | Host keys are stored in |
| 796 | .Pa ~/.ssh/known_hosts |
| 797 | in the user's home directory. |
| 798 | Additionally, the file |
| 799 | .Pa /etc/ssh/ssh_known_hosts |
| 800 | is automatically checked for known hosts. |
| 801 | Any new hosts are automatically added to the user's file. |
| 802 | If a host's identification ever changes, |
| 803 | .Nm |
| 804 | warns about this and disables password authentication to prevent |
| 805 | server spoofing or man-in-the-middle attacks, |
| 806 | which could otherwise be used to circumvent the encryption. |
| 807 | The |
| 808 | .Cm StrictHostKeyChecking |
| 809 | option can be used to control logins to machines whose |
| 810 | host key is not known or has changed. |
| 811 | .Pp |
| 812 | .Nm |
| 813 | can be configured to verify host identification using fingerprint resource |
| 814 | records (SSHFP) published in DNS. |
| 815 | The |
| 816 | .Cm VerifyHostKeyDNS |
| 817 | option can be used to control how DNS lookups are performed. |
| 818 | SSHFP resource records can be generated using |
| 819 | .Xr ssh-keygen 1 . |
| 820 | .Pp |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 821 | When the user's identity has been accepted by the server, the server |
| 822 | either executes the given command, or logs into the machine and gives |
| 823 | the user a normal shell on the remote machine. |
| 824 | All communication with |
| 825 | the remote command or shell will be automatically encrypted. |
| 826 | .Pp |
| 827 | If a pseudo-terminal has been allocated (normal login session), the |
| 828 | user may use the escape characters noted below. |
| 829 | .Pp |
| 830 | If no pseudo-tty has been allocated, |
| 831 | the session is transparent and can be used to reliably transfer binary data. |
| 832 | On most systems, setting the escape character to |
| 833 | .Dq none |
| 834 | will also make the session transparent even if a tty is used. |
| 835 | .Pp |
| 836 | The session terminates when the command or shell on the remote |
| 837 | machine exits and all X11 and TCP/IP connections have been closed. |
Damien Miller | 52d2061 | 2005-12-24 14:52:36 +1100 | [diff] [blame] | 838 | .Sh ESCAPE CHARACTERS |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 839 | When a pseudo-terminal has been requested, |
| 840 | .Nm |
| 841 | supports a number of functions through the use of an escape character. |
| 842 | .Pp |
| 843 | A single tilde character can be sent as |
| 844 | .Ic ~~ |
| 845 | or by following the tilde by a character other than those described below. |
| 846 | The escape character must always follow a newline to be interpreted as |
| 847 | special. |
| 848 | The escape character can be changed in configuration files using the |
| 849 | .Cm EscapeChar |
| 850 | configuration directive or on the command line by the |
| 851 | .Fl e |
| 852 | option. |
| 853 | .Pp |
| 854 | The supported escapes (assuming the default |
| 855 | .Ql ~ ) |
| 856 | are: |
| 857 | .Bl -tag -width Ds |
| 858 | .It Cm ~. |
| 859 | Disconnect. |
| 860 | .It Cm ~^Z |
| 861 | Background |
Damien Miller | 1164c29 | 2006-01-02 23:38:37 +1100 | [diff] [blame] | 862 | .Nm . |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 863 | .It Cm ~# |
| 864 | List forwarded connections. |
| 865 | .It Cm ~& |
| 866 | Background |
| 867 | .Nm |
| 868 | at logout when waiting for forwarded connection / X11 sessions to terminate. |
| 869 | .It Cm ~? |
| 870 | Display a list of escape characters. |
| 871 | .It Cm ~B |
| 872 | Send a BREAK to the remote system |
| 873 | (only useful for SSH protocol version 2 and if the peer supports it). |
| 874 | .It Cm ~C |
| 875 | Open command line. |
| 876 | Currently this allows the addition of port forwardings using the |
| 877 | .Fl L |
| 878 | and |
| 879 | .Fl R |
Damien Miller | 329cb01 | 2005-12-24 14:53:23 +1100 | [diff] [blame] | 880 | options (see above). |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 881 | It also allows the cancellation of existing remote port-forwardings |
| 882 | using |
| 883 | .Fl KR Ar hostport . |
| 884 | .Ic !\& Ns Ar command |
| 885 | allows the user to execute a local command if the |
| 886 | .Ic PermitLocalCommand |
| 887 | option is enabled in |
| 888 | .Xr ssh_config 5 . |
| 889 | Basic help is available, using the |
| 890 | .Fl h |
| 891 | option. |
| 892 | .It Cm ~R |
| 893 | Request rekeying of the connection |
| 894 | (only useful for SSH protocol version 2 and if the peer supports it). |
| 895 | .El |
Damien Miller | 52d2061 | 2005-12-24 14:52:36 +1100 | [diff] [blame] | 896 | .Sh X11 AND TCP FORWARDING |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 897 | If the |
| 898 | .Cm ForwardX11 |
| 899 | variable is set to |
| 900 | .Dq yes |
| 901 | (or see the description of the |
Damien Miller | d7f308f | 2005-12-24 14:55:16 +1100 | [diff] [blame] | 902 | .Fl X , |
| 903 | .Fl x , |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 904 | and |
Damien Miller | d7f308f | 2005-12-24 14:55:16 +1100 | [diff] [blame] | 905 | .Fl Y |
Damien Miller | 9a765b2 | 2005-12-24 14:53:44 +1100 | [diff] [blame] | 906 | options above) |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 907 | and the user is using X11 (the |
| 908 | .Ev DISPLAY |
| 909 | environment variable is set), the connection to the X11 display is |
| 910 | automatically forwarded to the remote side in such a way that any X11 |
| 911 | programs started from the shell (or command) will go through the |
| 912 | encrypted channel, and the connection to the real X server will be made |
| 913 | from the local machine. |
| 914 | The user should not manually set |
| 915 | .Ev DISPLAY . |
| 916 | Forwarding of X11 connections can be |
| 917 | configured on the command line or in configuration files. |
| 918 | .Pp |
| 919 | The |
| 920 | .Ev DISPLAY |
| 921 | value set by |
| 922 | .Nm |
| 923 | will point to the server machine, but with a display number greater than zero. |
| 924 | This is normal, and happens because |
| 925 | .Nm |
| 926 | creates a |
| 927 | .Dq proxy |
| 928 | X server on the server machine for forwarding the |
| 929 | connections over the encrypted channel. |
| 930 | .Pp |
| 931 | .Nm |
| 932 | will also automatically set up Xauthority data on the server machine. |
| 933 | For this purpose, it will generate a random authorization cookie, |
| 934 | store it in Xauthority on the server, and verify that any forwarded |
| 935 | connections carry this cookie and replace it by the real cookie when |
| 936 | the connection is opened. |
| 937 | The real authentication cookie is never |
| 938 | sent to the server machine (and no cookies are sent in the plain). |
| 939 | .Pp |
| 940 | If the |
| 941 | .Cm ForwardAgent |
| 942 | variable is set to |
| 943 | .Dq yes |
| 944 | (or see the description of the |
| 945 | .Fl A |
| 946 | and |
| 947 | .Fl a |
Damien Miller | 9a765b2 | 2005-12-24 14:53:44 +1100 | [diff] [blame] | 948 | options above) and |
Darren Tucker | d3877b9 | 2005-12-20 16:09:36 +1100 | [diff] [blame] | 949 | the user is using an authentication agent, the connection to the agent |
| 950 | is automatically forwarded to the remote side. |
| 951 | .Pp |
| 952 | Forwarding of arbitrary TCP/IP connections over the secure channel can |
| 953 | be specified either on the command line or in a configuration file. |
| 954 | One possible application of TCP/IP forwarding is a secure connection to an |
| 955 | electronic purse; another is going through firewalls. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 956 | .Sh ENVIRONMENT |
| 957 | .Nm |
| 958 | will normally set the following environment variables: |
Damien Miller | 6aa2290 | 2006-01-06 14:48:34 +1100 | [diff] [blame] | 959 | .Bl -tag -width "SSH_ORIGINAL_COMMAND" |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 960 | .It Ev DISPLAY |
| 961 | The |
| 962 | .Ev DISPLAY |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 963 | variable indicates the location of the X11 server. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 964 | It is automatically set by |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 965 | .Nm |
| 966 | to point to a value of the form |
Damien Miller | 14af93e | 2006-01-02 23:38:21 +1100 | [diff] [blame] | 967 | .Dq hostname:n , |
| 968 | where |
| 969 | .Dq hostname |
| 970 | indicates the host where the shell runs, and |
| 971 | .Sq n |
| 972 | is an integer \*(Ge 1. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 973 | .Nm |
| 974 | uses this special value to forward X11 connections over the secure |
| 975 | channel. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 976 | The user should normally not set |
| 977 | .Ev DISPLAY |
| 978 | explicitly, as that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 979 | will render the X11 connection insecure (and will require the user to |
| 980 | manually copy any required authorization cookies). |
| 981 | .It Ev HOME |
| 982 | Set to the path of the user's home directory. |
| 983 | .It Ev LOGNAME |
| 984 | Synonym for |
| 985 | .Ev USER ; |
| 986 | set for compatibility with systems that use this variable. |
| 987 | .It Ev MAIL |
Ben Lindstrom | e59433d | 2001-09-12 16:41:37 +0000 | [diff] [blame] | 988 | Set to the path of the user's mailbox. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 989 | .It Ev PATH |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 990 | Set to the default |
| 991 | .Ev PATH , |
| 992 | as specified when compiling |
Damien Miller | 1164c29 | 2006-01-02 23:38:37 +1100 | [diff] [blame] | 993 | .Nm . |
Ben Lindstrom | 5bf5d67 | 2001-07-04 04:31:38 +0000 | [diff] [blame] | 994 | .It Ev SSH_ASKPASS |
| 995 | If |
| 996 | .Nm |
| 997 | needs a passphrase, it will read the passphrase from the current |
| 998 | terminal if it was run from a terminal. |
| 999 | If |
| 1000 | .Nm |
| 1001 | does not have a terminal associated with it but |
| 1002 | .Ev DISPLAY |
| 1003 | and |
| 1004 | .Ev SSH_ASKPASS |
| 1005 | are set, it will execute the program specified by |
| 1006 | .Ev SSH_ASKPASS |
| 1007 | and open an X11 window to read the passphrase. |
| 1008 | This is particularly useful when calling |
| 1009 | .Nm |
| 1010 | from a |
Darren Tucker | 4e4fe00 | 2004-11-05 20:01:03 +1100 | [diff] [blame] | 1011 | .Pa .xsession |
Ben Lindstrom | 5bf5d67 | 2001-07-04 04:31:38 +0000 | [diff] [blame] | 1012 | or related script. |
| 1013 | (Note that on some machines it |
| 1014 | may be necessary to redirect the input from |
| 1015 | .Pa /dev/null |
| 1016 | to make this work.) |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1017 | .It Ev SSH_AUTH_SOCK |
Damien Miller | 14af93e | 2006-01-02 23:38:21 +1100 | [diff] [blame] | 1018 | Identifies the path of a |
| 1019 | .Ux Ns -domain |
| 1020 | socket used to communicate with the agent. |
Damien Miller | f37e246 | 2002-09-19 11:47:55 +1000 | [diff] [blame] | 1021 | .It Ev SSH_CONNECTION |
| 1022 | Identifies the client and server ends of the connection. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1023 | The variable contains |
Damien Miller | 14af93e | 2006-01-02 23:38:21 +1100 | [diff] [blame] | 1024 | four space-separated values: client IP address, client port number, |
| 1025 | server IP address, and server port number. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 1026 | .It Ev SSH_ORIGINAL_COMMAND |
Damien Miller | 14af93e | 2006-01-02 23:38:21 +1100 | [diff] [blame] | 1027 | This variable contains the original command line if a forced command |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 1028 | is executed. |
| 1029 | It can be used to extract the original arguments. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1030 | .It Ev SSH_TTY |
| 1031 | This is set to the name of the tty (path to the device) associated |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1032 | with the current shell or command. |
| 1033 | If the current session has no tty, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1034 | this variable is not set. |
| 1035 | .It Ev TZ |
Damien Miller | 6dbdb6a | 2005-12-13 19:25:43 +1100 | [diff] [blame] | 1036 | This variable is set to indicate the present time zone if it |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 1037 | was set when the daemon was started (i.e., the daemon passes the value |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1038 | on to new connections). |
| 1039 | .It Ev USER |
| 1040 | Set to the name of the user logging in. |
| 1041 | .El |
| 1042 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1043 | Additionally, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1044 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1045 | reads |
Damien Miller | 167ea5d | 2005-05-26 12:04:02 +1000 | [diff] [blame] | 1046 | .Pa ~/.ssh/environment , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1047 | and adds lines of the format |
| 1048 | .Dq VARNAME=value |
Damien Miller | 14af93e | 2006-01-02 23:38:21 +1100 | [diff] [blame] | 1049 | to the environment if the file exists and users are allowed to |
Ben Lindstrom | dc7adf2 | 2002-08-20 18:38:02 +0000 | [diff] [blame] | 1050 | change their environment. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 1051 | For more information, see the |
Ben Lindstrom | dc7adf2 | 2002-08-20 18:38:02 +0000 | [diff] [blame] | 1052 | .Cm PermitUserEnvironment |
Ben Lindstrom | bd9bf38 | 2002-08-20 18:54:20 +0000 | [diff] [blame] | 1053 | option in |
Ben Lindstrom | dc7adf2 | 2002-08-20 18:38:02 +0000 | [diff] [blame] | 1054 | .Xr sshd_config 5 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1055 | .Sh FILES |
Damien Miller | 7655f5c | 2006-01-06 14:48:18 +1100 | [diff] [blame] | 1056 | .Bl -tag -width Ds -compact |
Damien Miller | 7655f5c | 2006-01-06 14:48:18 +1100 | [diff] [blame] | 1057 | .It ~/.rhosts |
Damien Miller | 1bcdb50 | 2006-01-06 14:49:38 +1100 | [diff] [blame] | 1058 | This file is used for host-based authentication (see above). |
Ben Lindstrom | ebd888d | 2001-03-05 05:49:29 +0000 | [diff] [blame] | 1059 | On some machines this file may need to be |
Damien Miller | 1bcdb50 | 2006-01-06 14:49:38 +1100 | [diff] [blame] | 1060 | world-readable if the user's home directory is on an NFS partition, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1061 | because |
| 1062 | .Xr sshd 8 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1063 | reads it as root. |
| 1064 | Additionally, this file must be owned by the user, |
| 1065 | and must not have write permissions for anyone else. |
| 1066 | The recommended |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1067 | permission for most machines is read/write for the user, and not |
| 1068 | accessible by others. |
| 1069 | .Pp |
Damien Miller | 7655f5c | 2006-01-06 14:48:18 +1100 | [diff] [blame] | 1070 | .It ~/.shosts |
Damien Miller | 1bcdb50 | 2006-01-06 14:49:38 +1100 | [diff] [blame] | 1071 | This file is used in exactly the same way as |
| 1072 | .Pa .rhosts , |
| 1073 | but allows host-based authentication without permitting login with |
| 1074 | rlogin/rsh. |
Damien Miller | 7655f5c | 2006-01-06 14:48:18 +1100 | [diff] [blame] | 1075 | .Pp |
Damien Miller | fb8ea74 | 2006-01-06 14:48:52 +1100 | [diff] [blame] | 1076 | .It ~/.ssh/authorized_keys |
| 1077 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. |
| 1078 | The format of this file is described in the |
| 1079 | .Xr sshd 8 |
| 1080 | manual page. |
| 1081 | In the simplest form the format is the same as the |
| 1082 | .Pa .pub |
| 1083 | identity files. |
| 1084 | This file is not highly sensitive, but the recommended |
| 1085 | permissions are read/write for the user, and not accessible by others. |
| 1086 | .Pp |
| 1087 | .It ~/.ssh/config |
| 1088 | This is the per-user configuration file. |
| 1089 | The file format and configuration options are described in |
| 1090 | .Xr ssh_config 5 . |
| 1091 | Because of the potential for abuse, this file must have strict permissions: |
| 1092 | read/write for the user, and not accessible by others. |
| 1093 | .Pp |
| 1094 | .It ~/.ssh/environment |
Damien Miller | 4c102ee | 2006-01-06 14:49:17 +1100 | [diff] [blame] | 1095 | Contains additional definitions for environment variables; see |
| 1096 | .Sx ENVIRONMENT , |
Damien Miller | fb8ea74 | 2006-01-06 14:48:52 +1100 | [diff] [blame] | 1097 | above. |
| 1098 | .Pp |
| 1099 | .It ~/.ssh/identity |
| 1100 | .It ~/.ssh/id_dsa |
| 1101 | .It ~/.ssh/id_rsa |
| 1102 | Contains the private key for authentication. |
| 1103 | These files |
| 1104 | contain sensitive data and should be readable by the user but not |
| 1105 | accessible by others (read/write/execute). |
| 1106 | .Nm |
| 1107 | will simply ignore a private key file if it is accessible by others. |
| 1108 | It is possible to specify a passphrase when |
| 1109 | generating the key which will be used to encrypt the |
| 1110 | sensitive part of this file using 3DES. |
| 1111 | .Pp |
| 1112 | .It ~/.ssh/identity.pub |
| 1113 | .It ~/.ssh/id_dsa.pub |
| 1114 | .It ~/.ssh/id_rsa.pub |
| 1115 | Contains the public key for authentication. |
| 1116 | These files are not |
| 1117 | sensitive and can (but need not) be readable by anyone. |
| 1118 | They are |
| 1119 | never used automatically and are not necessary: they are only provided for |
| 1120 | the convenience of the user. |
| 1121 | .Pp |
| 1122 | .It ~/.ssh/known_hosts |
| 1123 | Records host keys for all hosts the user has logged into that are not |
| 1124 | in |
| 1125 | .Pa /etc/ssh/ssh_known_hosts . |
| 1126 | See |
| 1127 | .Xr sshd 8 . |
| 1128 | .Pp |
| 1129 | .It ~/.ssh/rc |
| 1130 | Commands in this file are executed by |
| 1131 | .Nm |
| 1132 | when the user logs in just before the user's shell (or command) is |
| 1133 | started. |
| 1134 | See the |
| 1135 | .Xr sshd 8 |
| 1136 | manual page for more information. |
| 1137 | .Pp |
Damien Miller | 7655f5c | 2006-01-06 14:48:18 +1100 | [diff] [blame] | 1138 | .It /etc/hosts.equiv |
Damien Miller | 1bcdb50 | 2006-01-06 14:49:38 +1100 | [diff] [blame] | 1139 | This file is for host-based authentication (see above). |
| 1140 | It should only be writable by root. |
Damien Miller | 7655f5c | 2006-01-06 14:48:18 +1100 | [diff] [blame] | 1141 | .Pp |
| 1142 | .It /etc/shosts.equiv |
Damien Miller | 1bcdb50 | 2006-01-06 14:49:38 +1100 | [diff] [blame] | 1143 | This file is used in exactly the same way as |
| 1144 | .Pa hosts.equiv , |
| 1145 | but allows host-based authentication without permitting login with |
| 1146 | rlogin/rsh. |
Damien Miller | 7655f5c | 2006-01-06 14:48:18 +1100 | [diff] [blame] | 1147 | .Pp |
Damien Miller | fb8ea74 | 2006-01-06 14:48:52 +1100 | [diff] [blame] | 1148 | .It Pa /etc/ssh/ssh_config |
| 1149 | Systemwide configuration file. |
| 1150 | The file format and configuration options are described in |
| 1151 | .Xr ssh_config 5 . |
| 1152 | .Pp |
| 1153 | .It /etc/ssh/ssh_host_key |
| 1154 | .It /etc/ssh/ssh_host_dsa_key |
| 1155 | .It /etc/ssh/ssh_host_rsa_key |
| 1156 | These three files contain the private parts of the host keys |
| 1157 | and are used for |
| 1158 | .Cm RhostsRSAAuthentication |
| 1159 | and |
| 1160 | .Cm HostbasedAuthentication . |
| 1161 | If the protocol version 1 |
| 1162 | .Cm RhostsRSAAuthentication |
| 1163 | method is used, |
| 1164 | .Nm |
| 1165 | must be setuid root, since the host key is readable only by root. |
| 1166 | For protocol version 2, |
| 1167 | .Nm |
| 1168 | uses |
| 1169 | .Xr ssh-keysign 8 |
| 1170 | to access the host keys for |
| 1171 | .Cm HostbasedAuthentication . |
| 1172 | This eliminates the requirement that |
| 1173 | .Nm |
| 1174 | be setuid root when that authentication method is used. |
| 1175 | By default |
| 1176 | .Nm |
| 1177 | is not setuid root. |
| 1178 | .Pp |
| 1179 | .It /etc/ssh/ssh_known_hosts |
| 1180 | Systemwide list of known host keys. |
| 1181 | This file should be prepared by the |
| 1182 | system administrator to contain the public host keys of all machines in the |
| 1183 | organization. |
| 1184 | This file should be world-readable. |
| 1185 | This file contains |
| 1186 | public keys, one per line, in the following format (fields separated |
| 1187 | by spaces): system name, public key and optional comment field. |
| 1188 | When different names are used |
| 1189 | for the same machine, all such names should be listed, separated by |
| 1190 | commas. |
| 1191 | The format is described in the |
| 1192 | .Xr sshd 8 |
| 1193 | manual page. |
| 1194 | .Pp |
| 1195 | The canonical system name (as returned by name servers) is used by |
| 1196 | .Xr sshd 8 |
| 1197 | to verify the client host when logging in; other names are needed because |
| 1198 | .Nm |
| 1199 | does not convert the user-supplied name to a canonical name before |
| 1200 | checking the key, because someone with access to the name servers |
| 1201 | would then be able to fool host authentication. |
| 1202 | .Pp |
Damien Miller | 7655f5c | 2006-01-06 14:48:18 +1100 | [diff] [blame] | 1203 | .It /etc/ssh/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1204 | Commands in this file are executed by |
| 1205 | .Nm |
| 1206 | when the user logs in just before the user's shell (or command) is started. |
| 1207 | See the |
| 1208 | .Xr sshd 8 |
| 1209 | manual page for more information. |
Damien Miller | 7b28dc5 | 2000-09-05 13:34:53 +1100 | [diff] [blame] | 1210 | .El |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1211 | .Sh SEE ALSO |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1212 | .Xr scp 1 , |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 1213 | .Xr sftp 1 , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1214 | .Xr ssh-add 1 , |
| 1215 | .Xr ssh-agent 1 , |
| 1216 | .Xr ssh-keygen 1 , |
Damien Miller | 128a0f1 | 2006-01-06 14:50:11 +1100 | [diff] [blame] | 1217 | .Xr ssh-keyscan 1 , |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 1218 | .Xr hosts.equiv 5 , |
Ben Lindstrom | bf69e3b | 2002-06-23 00:31:24 +0000 | [diff] [blame] | 1219 | .Xr ssh_config 5 , |
Ben Lindstrom | c001cd3 | 2002-06-23 00:32:11 +0000 | [diff] [blame] | 1220 | .Xr ssh-keysign 8 , |
Ben Lindstrom | 5ab6ae1 | 2001-02-10 22:08:03 +0000 | [diff] [blame] | 1221 | .Xr sshd 8 |
Ben Lindstrom | 160ec62 | 2001-04-22 17:17:46 +0000 | [diff] [blame] | 1222 | .Rs |
| 1223 | .%A T. Ylonen |
| 1224 | .%A T. Kivinen |
| 1225 | .%A M. Saarinen |
| 1226 | .%A T. Rinne |
| 1227 | .%A S. Lehtinen |
| 1228 | .%T "SSH Protocol Architecture" |
Ben Lindstrom | f181384 | 2002-03-27 17:18:31 +0000 | [diff] [blame] | 1229 | .%N draft-ietf-secsh-architecture-12.txt |
| 1230 | .%D January 2002 |
Ben Lindstrom | 160ec62 | 2001-04-22 17:17:46 +0000 | [diff] [blame] | 1231 | .%O work in progress material |
| 1232 | .Re |
Damien Miller | f1ce505 | 2003-06-11 22:04:39 +1000 | [diff] [blame] | 1233 | .Sh AUTHORS |
| 1234 | OpenSSH is a derivative of the original and free |
| 1235 | ssh 1.2.12 release by Tatu Ylonen. |
| 1236 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, |
| 1237 | Theo de Raadt and Dug Song |
| 1238 | removed many bugs, re-added newer features and |
| 1239 | created OpenSSH. |
| 1240 | Markus Friedl contributed the support for SSH |
| 1241 | protocol versions 1.5 and 2.0. |