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 | d876962 | 2002-09-30 12:00:55 +1000 | [diff] [blame] | 37 | .\" $OpenBSD: ssh.1,v 1.167 2002/09/27 15:46:21 stevesk 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 |
| 46 | .Op Fl l Ar login_name |
Ben Lindstrom | a10aed8 | 2001-09-12 16:43:26 +0000 | [diff] [blame] | 47 | .Ar hostname | user@hostname |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 48 | .Op Ar command |
| 49 | .Pp |
| 50 | .Nm ssh |
Damien Miller | 147bba3 | 2002-09-04 16:46:06 +1000 | [diff] [blame] | 51 | .Op Fl afgknqstvxACNTX1246 |
Ben Lindstrom | e0f8804 | 2001-04-30 13:06:24 +0000 | [diff] [blame] | 52 | .Op Fl b Ar bind_address |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 53 | .Op Fl c Ar cipher_spec |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 54 | .Op Fl e Ar escape_char |
| 55 | .Op Fl i Ar identity_file |
| 56 | .Op Fl l Ar login_name |
Ben Lindstrom | 06b33aa | 2001-02-15 03:01:59 +0000 | [diff] [blame] | 57 | .Op Fl m Ar mac_spec |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 58 | .Op Fl o Ar option |
| 59 | .Op Fl p Ar port |
Ben Lindstrom | 14f31ab | 2001-09-12 17:48:04 +0000 | [diff] [blame] | 60 | .Op Fl F Ar configfile |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 61 | .Oo Fl L Xo |
| 62 | .Sm off |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 63 | .Ar port : |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 64 | .Ar host : |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 65 | .Ar hostport |
| 66 | .Sm on |
| 67 | .Xc |
| 68 | .Oc |
| 69 | .Oo Fl R Xo |
| 70 | .Sm off |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 71 | .Ar port : |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 72 | .Ar host : |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 73 | .Ar hostport |
| 74 | .Sm on |
| 75 | .Xc |
| 76 | .Oc |
Ben Lindstrom | 6e69d53 | 2001-09-12 17:59:59 +0000 | [diff] [blame] | 77 | .Op Fl D Ar port |
Ben Lindstrom | a10aed8 | 2001-09-12 16:43:26 +0000 | [diff] [blame] | 78 | .Ar hostname | user@hostname |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 79 | .Op Ar command |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 80 | .Sh DESCRIPTION |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 81 | .Nm |
Ben Lindstrom | d58eb5f | 2001-03-07 06:07:22 +0000 | [diff] [blame] | 82 | (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] | 83 | executing commands on a remote machine. |
| 84 | It is intended to replace |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 85 | rlogin and rsh, and provide secure encrypted communications between |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 86 | two untrusted hosts over an insecure network. |
| 87 | X11 connections and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 88 | arbitrary TCP/IP ports can also be forwarded over the secure channel. |
| 89 | .Pp |
| 90 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 91 | connects and logs into the specified |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 92 | .Ar hostname . |
| 93 | The user must prove |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 94 | his/her identity to the remote machine using one of several methods |
| 95 | depending on the protocol version used: |
| 96 | .Pp |
| 97 | .Ss SSH protocol version 1 |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 98 | .Pp |
| 99 | First, if the machine the user logs in from is listed in |
| 100 | .Pa /etc/hosts.equiv |
| 101 | or |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 102 | .Pa /etc/shosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 103 | on the remote machine, and the user names are |
| 104 | the same on both sides, the user is immediately permitted to log in. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 105 | Second, if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 106 | .Pa \&.rhosts |
| 107 | or |
| 108 | .Pa \&.shosts |
| 109 | exists in the user's home directory on the |
| 110 | remote machine and contains a line containing the name of the client |
| 111 | machine and the name of the user on that machine, the user is |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 112 | permitted to log in. |
| 113 | This form of authentication alone is normally not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 114 | allowed by the server because it is not secure. |
| 115 | .Pp |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 116 | The second authentication method is the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 117 | .Pa rhosts |
| 118 | or |
| 119 | .Pa hosts.equiv |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 120 | method combined with RSA-based host authentication. |
| 121 | It means that if the login would be permitted by |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 122 | .Pa $HOME/.rhosts , |
| 123 | .Pa $HOME/.shosts , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 124 | .Pa /etc/hosts.equiv , |
| 125 | or |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 126 | .Pa /etc/shosts.equiv , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 127 | and if additionally the server can verify the client's |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 128 | host key (see |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 129 | .Pa /etc/ssh/ssh_known_hosts |
Damien Miller | 33e511e | 1999-11-11 11:43:13 +1100 | [diff] [blame] | 130 | and |
| 131 | .Pa $HOME/.ssh/known_hosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 132 | in the |
| 133 | .Sx FILES |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 134 | section), only then login is permitted. |
| 135 | This authentication method closes security holes due to IP |
| 136 | spoofing, DNS spoofing and routing spoofing. |
| 137 | [Note to the administrator: |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 138 | .Pa /etc/hosts.equiv , |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 139 | .Pa $HOME/.rhosts , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 140 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
| 141 | disabled if security is desired.] |
| 142 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 143 | As a third authentication method, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 144 | .Nm |
| 145 | supports RSA based authentication. |
| 146 | The scheme is based on public-key cryptography: there are cryptosystems |
| 147 | where encryption and decryption are done using separate keys, and it |
| 148 | is not possible to derive the decryption key from the encryption key. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 149 | RSA is one such system. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 150 | The idea is that each user creates a public/private |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 151 | key pair for authentication purposes. |
| 152 | The server knows the public key, and only the user knows the private key. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 153 | The file |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 154 | .Pa $HOME/.ssh/authorized_keys |
| 155 | lists the public keys that are permitted for logging |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 156 | in. |
| 157 | When the user logs in, the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 158 | .Nm |
| 159 | program tells the server which key pair it would like to use for |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 160 | authentication. |
| 161 | The server checks if this key is permitted, and if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 162 | so, sends the user (actually the |
| 163 | .Nm |
| 164 | program running on behalf of the user) a challenge, a random number, |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 165 | encrypted by the user's public key. |
| 166 | The challenge can only be |
| 167 | decrypted using the proper private key. |
| 168 | The user's client then decrypts the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 169 | challenge using the private key, proving that he/she knows the private |
| 170 | key but without disclosing it to the server. |
| 171 | .Pp |
| 172 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 173 | implements the RSA authentication protocol automatically. |
| 174 | The user creates his/her RSA key pair by running |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 175 | .Xr ssh-keygen 1 . |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 176 | This stores the private key in |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 177 | .Pa $HOME/.ssh/identity |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 178 | and the public key in |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 179 | .Pa $HOME/.ssh/identity.pub |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 180 | in the user's home directory. |
| 181 | The user should then copy the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 182 | .Pa identity.pub |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 183 | to |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 184 | .Pa $HOME/.ssh/authorized_keys |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 185 | in his/her home directory on the remote machine (the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 186 | .Pa authorized_keys |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 187 | file corresponds to the conventional |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 188 | .Pa $HOME/.rhosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 189 | file, and has one key |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 190 | per line, though the lines can be very long). |
| 191 | After this, the user can log in without giving the password. |
| 192 | RSA authentication is much |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 193 | more secure than rhosts authentication. |
| 194 | .Pp |
| 195 | The most convenient way to use RSA authentication may be with an |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 196 | authentication agent. |
| 197 | See |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 198 | .Xr ssh-agent 1 |
| 199 | for more information. |
| 200 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 201 | If other authentication methods fail, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 202 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 203 | prompts the user for a password. |
| 204 | The password is sent to the remote |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 205 | host for checking; however, since all communications are encrypted, |
| 206 | the password cannot be seen by someone listening on the network. |
| 207 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 208 | .Ss SSH protocol version 2 |
| 209 | .Pp |
Damien Miller | 07a2d42 | 2002-02-05 12:16:15 +1100 | [diff] [blame] | 210 | When a user connects using protocol version 2 |
| 211 | similar authentication methods are available. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 212 | Using the default values for |
| 213 | .Cm PreferredAuthentications , |
Ben Lindstrom | a9086a1 | 2001-08-06 20:58:51 +0000 | [diff] [blame] | 214 | the client will try to authenticate first using the hostbased method; |
| 215 | if this method fails public key authentication is attempted, |
| 216 | and finally if this method fails keyboard-interactive and |
| 217 | password authentication are tried. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 218 | .Pp |
| 219 | The public key method is similar to RSA authentication described |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 220 | in the previous section and allows the RSA or DSA algorithm to be used: |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 221 | The client uses his private key, |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 222 | .Pa $HOME/.ssh/id_dsa |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 223 | or |
| 224 | .Pa $HOME/.ssh/id_rsa , |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 225 | to sign the session identifier and sends the result to the server. |
| 226 | The server checks whether the matching public key is listed in |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 227 | .Pa $HOME/.ssh/authorized_keys |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 228 | and grants access if both the key is found and the signature is correct. |
| 229 | The session identifier is derived from a shared Diffie-Hellman value |
| 230 | and is only known to the client and the server. |
| 231 | .Pp |
| 232 | If public key authentication fails or is not available a password |
| 233 | can be sent encrypted to the remote host for proving the user's identity. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 234 | .Pp |
| 235 | Additionally, |
| 236 | .Nm |
| 237 | supports hostbased or challenge response authentication. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 238 | .Pp |
| 239 | Protocol 2 provides additional mechanisms for confidentiality |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 240 | (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour) |
Ben Lindstrom | ec26fb1 | 2001-03-06 01:05:23 +0000 | [diff] [blame] | 241 | and integrity (hmac-md5, hmac-sha1). |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 242 | Note that protocol 1 lacks a strong mechanism for ensuring the |
| 243 | integrity of the connection. |
| 244 | .Pp |
| 245 | .Ss Login session and remote execution |
| 246 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 247 | When the user's identity has been accepted by the server, the server |
| 248 | either executes the given command, or logs into the machine and gives |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 249 | the user a normal shell on the remote machine. |
| 250 | All communication with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 251 | the remote command or shell will be automatically encrypted. |
| 252 | .Pp |
| 253 | If a pseudo-terminal has been allocated (normal login session), the |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 254 | user may use the escape characters noted below. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 255 | .Pp |
| 256 | If no pseudo tty has been allocated, the |
| 257 | session is transparent and can be used to reliably transfer binary |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 258 | data. |
| 259 | On most systems, setting the escape character to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 260 | .Dq none |
| 261 | will also make the session transparent even if a tty is used. |
| 262 | .Pp |
Ben Lindstrom | a688561 | 2000-12-09 03:45:32 +0000 | [diff] [blame] | 263 | The session terminates when the command or shell on the remote |
Ben Lindstrom | ebd888d | 2001-03-05 05:49:29 +0000 | [diff] [blame] | 264 | machine exits and all X11 and TCP/IP connections have been closed. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 265 | The exit status of the remote program is returned as the exit status |
| 266 | of |
| 267 | .Nm ssh . |
| 268 | .Pp |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 269 | .Ss Escape Characters |
| 270 | .Pp |
| 271 | When a pseudo terminal has been requested, ssh supports a number of functions |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 272 | through the use of an escape character. |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 273 | .Pp |
| 274 | A single tilde character can be sent as |
| 275 | .Ic ~~ |
Ben Lindstrom | 6600769 | 2001-07-22 20:41:59 +0000 | [diff] [blame] | 276 | or by following the tilde by a character other than those described below. |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 277 | The escape character must always follow a newline to be interpreted as |
| 278 | special. |
| 279 | The escape character can be changed in configuration files using the |
| 280 | .Cm EscapeChar |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 281 | configuration directive or on the command line by the |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 282 | .Fl e |
| 283 | option. |
| 284 | .Pp |
| 285 | The supported escapes (assuming the default |
| 286 | .Ql ~ ) |
| 287 | are: |
| 288 | .Bl -tag -width Ds |
| 289 | .It Cm ~. |
| 290 | Disconnect |
| 291 | .It Cm ~^Z |
| 292 | Background ssh |
| 293 | .It Cm ~# |
| 294 | List forwarded connections |
| 295 | .It Cm ~& |
| 296 | Background ssh at logout when waiting for forwarded connection / X11 sessions |
Damien Miller | 1f8dddc | 2001-11-12 11:02:25 +1100 | [diff] [blame] | 297 | to terminate |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 298 | .It Cm ~? |
| 299 | Display a list of escape characters |
Ben Lindstrom | 5589f4b | 2002-03-22 03:24:32 +0000 | [diff] [blame] | 300 | .It Cm ~C |
| 301 | Open command line (only useful for adding port forwardings using the |
| 302 | .Fl L |
| 303 | and |
| 304 | .Fl R |
| 305 | options) |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 306 | .It Cm ~R |
Ben Lindstrom | f8d2457 | 2001-04-22 17:11:56 +0000 | [diff] [blame] | 307 | Request rekeying of the connection (only useful for SSH protocol version 2 |
| 308 | and if the peer supports it) |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 309 | .El |
| 310 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 311 | .Ss X11 and TCP forwarding |
| 312 | .Pp |
Ben Lindstrom | 7121507 | 2001-05-17 03:16:18 +0000 | [diff] [blame] | 313 | If the |
| 314 | .Cm ForwardX11 |
| 315 | variable is set to |
| 316 | .Dq yes |
| 317 | (or, see the description of the |
| 318 | .Fl X |
| 319 | and |
| 320 | .Fl x |
| 321 | options described later) |
| 322 | and the user is using X11 (the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 323 | .Ev DISPLAY |
| 324 | environment variable is set), the connection to the X11 display is |
| 325 | automatically forwarded to the remote side in such a way that any X11 |
| 326 | programs started from the shell (or command) will go through the |
| 327 | encrypted channel, and the connection to the real X server will be made |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 328 | from the local machine. |
| 329 | The user should not manually set |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 330 | .Ev DISPLAY . |
| 331 | Forwarding of X11 connections can be |
| 332 | configured on the command line or in configuration files. |
| 333 | .Pp |
| 334 | The |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 335 | .Ev DISPLAY |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 336 | value set by |
| 337 | .Nm |
| 338 | will point to the server machine, but with a display number greater |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 339 | than zero. |
| 340 | This is normal, and happens because |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 341 | .Nm |
| 342 | creates a |
| 343 | .Dq proxy |
| 344 | X server on the server machine for forwarding the |
| 345 | connections over the encrypted channel. |
| 346 | .Pp |
| 347 | .Nm |
| 348 | will also automatically set up Xauthority data on the server machine. |
| 349 | For this purpose, it will generate a random authorization cookie, |
| 350 | store it in Xauthority on the server, and verify that any forwarded |
| 351 | connections carry this cookie and replace it by the real cookie when |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 352 | the connection is opened. |
| 353 | The real authentication cookie is never |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 354 | sent to the server machine (and no cookies are sent in the plain). |
| 355 | .Pp |
Ben Lindstrom | 3541f18 | 2002-08-20 19:03:20 +0000 | [diff] [blame] | 356 | If the |
| 357 | .Cm ForwardAgent |
| 358 | variable is set to |
| 359 | .Dq yes |
| 360 | (or, see the description of the |
| 361 | .Fl A |
| 362 | and |
| 363 | .Fl a |
| 364 | options described later) and |
| 365 | the user is using an authentication agent, the connection to the agent |
| 366 | is automatically forwarded to the remote side. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 367 | .Pp |
| 368 | Forwarding of arbitrary TCP/IP connections over the secure channel can |
Ben Lindstrom | 979c981 | 2001-07-22 20:45:39 +0000 | [diff] [blame] | 369 | be specified either on the command line or in a configuration file. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 370 | One possible application of TCP/IP forwarding is a secure connection to an |
Ben Lindstrom | ebd888d | 2001-03-05 05:49:29 +0000 | [diff] [blame] | 371 | electronic purse; another is going through firewalls. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 372 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 373 | .Ss Server authentication |
| 374 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 375 | .Nm |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 376 | automatically maintains and checks a database containing |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 377 | identifications for all hosts it has ever been used with. |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 378 | Host keys are stored in |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 379 | .Pa $HOME/.ssh/known_hosts |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 380 | in the user's home directory. |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 381 | Additionally, the file |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 382 | .Pa /etc/ssh/ssh_known_hosts |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 383 | is automatically checked for known hosts. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 384 | Any new hosts are automatically added to the user's file. |
| 385 | If a host's identification |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 386 | ever changes, |
| 387 | .Nm |
| 388 | warns about this and disables password authentication to prevent a |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 389 | trojan horse from getting the user's password. |
| 390 | Another purpose of |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 391 | this mechanism is to prevent man-in-the-middle attacks which could |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 392 | otherwise be used to circumvent the encryption. |
| 393 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 394 | .Cm StrictHostKeyChecking |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 395 | option can be used to prevent logins to machines whose |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 396 | host key is not known or has changed. |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 397 | .Pp |
| 398 | The options are as follows: |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 399 | .Bl -tag -width Ds |
| 400 | .It Fl a |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 401 | Disables forwarding of the authentication agent connection. |
Damien Miller | b1715dc | 2000-05-30 13:44:51 +1000 | [diff] [blame] | 402 | .It Fl A |
| 403 | Enables forwarding of the authentication agent connection. |
| 404 | 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] | 405 | .Pp |
| 406 | Agent forwarding should be enabled with caution. Users with the |
| 407 | ability to bypass file permissions on the remote host (for the agent's |
| 408 | Unix-domain socket) can access the local agent through the forwarded |
| 409 | connection. An attacker cannot obtain key material from the agent, |
| 410 | however they can perform operations on the keys that enable them to |
| 411 | authenticate using the identities loaded into the agent. |
Ben Lindstrom | e0f8804 | 2001-04-30 13:06:24 +0000 | [diff] [blame] | 412 | .It Fl b Ar bind_address |
| 413 | Specify the interface to transmit from on machines with multiple |
| 414 | interfaces or aliased addresses. |
Ben Lindstrom | ffa1dd6 | 2001-09-12 16:52:28 +0000 | [diff] [blame] | 415 | .It Fl c Ar blowfish|3des|des |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 416 | Selects the cipher to use for encrypting the session. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 417 | .Ar 3des |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 418 | is used by default. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 419 | It is believed to be secure. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 420 | .Ar 3des |
| 421 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 422 | .Ar blowfish |
| 423 | 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] | 424 | .Ar 3des . |
Ben Lindstrom | ffa1dd6 | 2001-09-12 16:52:28 +0000 | [diff] [blame] | 425 | .Ar des |
| 426 | is only supported in the |
| 427 | .Nm |
| 428 | client for interoperability with legacy protocol 1 implementations |
| 429 | that do not support the |
| 430 | .Ar 3des |
| 431 | cipher. Its use is strongly discouraged due to cryptographic |
| 432 | weaknesses. |
Ben Lindstrom | 5ab6ae1 | 2001-02-10 22:08:03 +0000 | [diff] [blame] | 433 | .It Fl c Ar cipher_spec |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 434 | Additionally, for protocol version 2 a comma-separated list of ciphers can |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 435 | be specified in order of preference. |
Ben Lindstrom | 5ab6ae1 | 2001-02-10 22:08:03 +0000 | [diff] [blame] | 436 | See |
| 437 | .Cm Ciphers |
| 438 | for more information. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 439 | .It Fl e Ar ch|^ch|none |
| 440 | Sets the escape character for sessions with a pty (default: |
| 441 | .Ql ~ ) . |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 442 | The escape character is only recognized at the beginning of a line. |
| 443 | The escape character followed by a dot |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 444 | .Pq Ql \&. |
| 445 | closes the connection, followed |
| 446 | by control-Z suspends the connection, and followed by itself sends the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 447 | escape character once. |
| 448 | Setting the character to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 449 | .Dq none |
| 450 | disables any escapes and makes the session fully transparent. |
| 451 | .It Fl f |
| 452 | Requests |
| 453 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 454 | to go to background just before command execution. |
| 455 | This is useful if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 456 | .Nm |
| 457 | is going to ask for passwords or passphrases, but the user |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 458 | wants it in the background. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 459 | This implies |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 460 | .Fl n . |
| 461 | The recommended way to start X11 programs at a remote site is with |
| 462 | something like |
| 463 | .Ic ssh -f host xterm . |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 464 | .It Fl g |
| 465 | Allows remote hosts to connect to local forwarded ports. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 466 | .It Fl i Ar identity_file |
Damien Miller | fae2386 | 2002-01-22 23:32:26 +1100 | [diff] [blame] | 467 | Selects a file from which the identity (private key) for |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 468 | RSA or DSA authentication is read. |
Damien Miller | fae2386 | 2002-01-22 23:32:26 +1100 | [diff] [blame] | 469 | The default is |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 470 | .Pa $HOME/.ssh/identity |
Damien Miller | fae2386 | 2002-01-22 23:32:26 +1100 | [diff] [blame] | 471 | for protocol version 1, and |
| 472 | .Pa $HOME/.ssh/id_rsa |
| 473 | and |
| 474 | .Pa $HOME/.ssh/id_dsa |
| 475 | for protocol version 2. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 476 | Identity files may also be specified on |
| 477 | a per-host basis in the configuration file. |
| 478 | It is possible to have multiple |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 479 | .Fl i |
| 480 | options (and multiple identities specified in |
| 481 | configuration files). |
Ben Lindstrom | ae996bf | 2001-08-06 21:27:53 +0000 | [diff] [blame] | 482 | .It Fl I Ar smartcard_device |
| 483 | Specifies which smartcard device to use. The argument is |
| 484 | the device |
| 485 | .Nm |
| 486 | should use to communicate with a smartcard used for storing the user's |
| 487 | private RSA key. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 488 | .It Fl k |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 489 | Disables forwarding of Kerberos tickets and AFS tokens. |
| 490 | This may also be specified on a per-host basis in the configuration file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 491 | .It Fl l Ar login_name |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 492 | Specifies the user to log in as on the remote machine. |
| 493 | This also may be specified on a per-host basis in the configuration file. |
Ben Lindstrom | 06b33aa | 2001-02-15 03:01:59 +0000 | [diff] [blame] | 494 | .It Fl m Ar mac_spec |
| 495 | Additionally, for protocol version 2 a comma-separated list of MAC |
| 496 | (message authentication code) algorithms can |
| 497 | be specified in order of preference. |
| 498 | See the |
| 499 | .Cm MACs |
| 500 | keyword for more information. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 501 | .It Fl n |
| 502 | Redirects stdin from |
| 503 | .Pa /dev/null |
| 504 | (actually, prevents reading from stdin). |
| 505 | This must be used when |
| 506 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 507 | is run in the background. |
| 508 | A common trick is to use this to run X11 programs on a remote machine. |
| 509 | For example, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 510 | .Ic ssh -n shadows.cs.hut.fi emacs & |
| 511 | will start an emacs on shadows.cs.hut.fi, and the X11 |
| 512 | connection will be automatically forwarded over an encrypted channel. |
| 513 | The |
| 514 | .Nm |
| 515 | program will be put in the background. |
| 516 | (This does not work if |
| 517 | .Nm |
| 518 | needs to ask for a password or passphrase; see also the |
| 519 | .Fl f |
| 520 | option.) |
Damien Miller | dcb6ecd | 2000-05-17 22:34:22 +1000 | [diff] [blame] | 521 | .It Fl N |
| 522 | Do not execute a remote command. |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 523 | This is useful for just forwarding ports |
Damien Miller | dcb6ecd | 2000-05-17 22:34:22 +1000 | [diff] [blame] | 524 | (protocol version 2 only). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 525 | .It Fl o Ar option |
Ben Lindstrom | 14c62eb | 2001-08-15 23:25:46 +0000 | [diff] [blame] | 526 | 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] | 527 | This is useful for specifying options for which there is no separate |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 528 | command-line flag. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 529 | .It Fl p Ar port |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 530 | Port to connect to on the remote host. |
| 531 | This can be specified on a |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 532 | per-host basis in the configuration file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 533 | .It Fl q |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 534 | Quiet mode. |
| 535 | Causes all warning and diagnostic messages to be suppressed. |
Damien Miller | 832562e | 2001-01-30 09:30:01 +1100 | [diff] [blame] | 536 | .It Fl s |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 537 | May be used to request invocation of a subsystem on the remote system. Subsystems are a feature of the SSH2 protocol which facilitate the use |
| 538 | of SSH as a secure transport for other applications (eg. sftp). The |
Damien Miller | 832562e | 2001-01-30 09:30:01 +1100 | [diff] [blame] | 539 | subsystem is specified as the remote command. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 540 | .It Fl t |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 541 | Force pseudo-tty allocation. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 542 | This can be used to execute arbitrary |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 543 | screen-based programs on a remote machine, which can be very useful, |
| 544 | e.g., when implementing menu services. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 545 | Multiple |
| 546 | .Fl t |
| 547 | options force tty allocation, even if |
| 548 | .Nm |
| 549 | has no local tty. |
Damien Miller | dcb6ecd | 2000-05-17 22:34:22 +1000 | [diff] [blame] | 550 | .It Fl T |
Ben Lindstrom | c72745a | 2000-12-02 19:03:54 +0000 | [diff] [blame] | 551 | Disable pseudo-tty allocation. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 552 | .It Fl v |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 553 | Verbose mode. |
| 554 | Causes |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 555 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 556 | to print debugging messages about its progress. |
| 557 | This is helpful in |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 558 | debugging connection, authentication, and configuration problems. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 559 | Multiple |
| 560 | .Fl v |
| 561 | options increases the verbosity. |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 562 | Maximum is 3. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 563 | .It Fl x |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 564 | Disables X11 forwarding. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 565 | .It Fl X |
| 566 | Enables X11 forwarding. |
Damien Miller | b1715dc | 2000-05-30 13:44:51 +1000 | [diff] [blame] | 567 | 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] | 568 | .Pp |
| 569 | X11 forwarding should be enabled with caution. Users with the ability |
| 570 | to bypass file permissions on the remote host (for the user's X |
| 571 | authorization database) can access the local X11 display through the |
| 572 | forwarded connection. An attacker may then be able to perform |
| 573 | activities such as keystroke monitoring. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 574 | .It Fl C |
| 575 | Requests compression of all data (including stdin, stdout, stderr, and |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 576 | data for forwarded X11 and TCP/IP connections). |
| 577 | The compression algorithm is the same used by |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 578 | .Xr gzip 1 , |
| 579 | and the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 580 | .Dq level |
| 581 | can be controlled by the |
| 582 | .Cm CompressionLevel |
Damien Miller | d876962 | 2002-09-30 12:00:55 +1000 | [diff] [blame] | 583 | option for protocol version 1. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 584 | Compression is desirable on modem lines and other |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 585 | slow connections, but will only slow down things on fast networks. |
| 586 | The default value can be set on a host-by-host basis in the |
| 587 | configuration files; see the |
Ben Lindstrom | e2b9b06 | 2001-08-06 20:50:55 +0000 | [diff] [blame] | 588 | .Cm Compression |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 589 | option. |
Ben Lindstrom | 14f31ab | 2001-09-12 17:48:04 +0000 | [diff] [blame] | 590 | .It Fl F Ar configfile |
| 591 | Specifies an alternative per-user configuration file. |
| 592 | If a configuration file is given on the command line, |
| 593 | the system-wide configuration file |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 594 | .Pq Pa /etc/ssh/ssh_config |
Ben Lindstrom | 14f31ab | 2001-09-12 17:48:04 +0000 | [diff] [blame] | 595 | will be ignored. |
| 596 | The default for the per-user configuration file is |
| 597 | .Pa $HOME/.ssh/config . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 598 | .It Fl L Ar port:host:hostport |
| 599 | Specifies that the given port on the local (client) host is to be |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 600 | forwarded to the given host and port on the remote side. |
| 601 | This works by allocating a socket to listen to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 602 | .Ar port |
| 603 | on the local side, and whenever a connection is made to this port, the |
| 604 | connection is forwarded over the secure channel, and a connection is |
| 605 | made to |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 606 | .Ar host |
| 607 | port |
| 608 | .Ar hostport |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 609 | from the remote machine. |
| 610 | Port forwardings can also be specified in the configuration file. |
| 611 | Only root can forward privileged ports. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 612 | IPv6 addresses can be specified with an alternative syntax: |
| 613 | .Ar port/host/hostport |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 614 | .It Fl R Ar port:host:hostport |
| 615 | 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] | 616 | forwarded to the given host and port on the local side. |
| 617 | This works by allocating a socket to listen to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 618 | .Ar port |
| 619 | on the remote side, and whenever a connection is made to this port, the |
| 620 | connection is forwarded over the secure channel, and a connection is |
| 621 | made to |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 622 | .Ar host |
| 623 | port |
| 624 | .Ar hostport |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 625 | from the local machine. |
| 626 | Port forwardings can also be specified in the configuration file. |
| 627 | Privileged ports can be forwarded only when |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 628 | logging in as root on the remote machine. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 629 | IPv6 addresses can be specified with an alternative syntax: |
| 630 | .Ar port/host/hostport |
Ben Lindstrom | 19ceb17 | 2001-09-12 17:54:24 +0000 | [diff] [blame] | 631 | .It Fl D Ar port |
| 632 | Specifies a local |
| 633 | .Dq dynamic |
| 634 | application-level port forwarding. |
| 635 | This works by allocating a socket to listen to |
| 636 | .Ar port |
| 637 | on the local side, and whenever a connection is made to this port, the |
| 638 | connection is forwarded over the secure channel, and the application |
| 639 | protocol is then used to determine where to connect to from the |
| 640 | remote machine. Currently the SOCKS4 protocol is supported, and |
| 641 | .Nm |
| 642 | will act as a SOCKS4 server. |
| 643 | Only root can forward privileged ports. |
| 644 | Dynamic port forwardings can also be specified in the configuration file. |
Ben Lindstrom | 5ab6ae1 | 2001-02-10 22:08:03 +0000 | [diff] [blame] | 645 | .It Fl 1 |
| 646 | Forces |
| 647 | .Nm |
| 648 | to try protocol version 1 only. |
Damien Miller | 4af5130 | 2000-04-16 11:18:38 +1000 | [diff] [blame] | 649 | .It Fl 2 |
| 650 | Forces |
| 651 | .Nm |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 652 | to try protocol version 2 only. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 653 | .It Fl 4 |
| 654 | Forces |
| 655 | .Nm |
| 656 | to use IPv4 addresses only. |
| 657 | .It Fl 6 |
| 658 | Forces |
| 659 | .Nm |
| 660 | to use IPv6 addresses only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 661 | .El |
| 662 | .Sh CONFIGURATION FILES |
| 663 | .Nm |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 664 | may additionally obtain configuration data from |
| 665 | a per-user configuration file and a system-wide configuration file. |
| 666 | The file format and configuration options are described in |
| 667 | .Xr ssh_config 5 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 668 | .Sh ENVIRONMENT |
| 669 | .Nm |
| 670 | will normally set the following environment variables: |
| 671 | .Bl -tag -width Ds |
| 672 | .It Ev DISPLAY |
| 673 | The |
| 674 | .Ev DISPLAY |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 675 | variable indicates the location of the X11 server. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 676 | It is automatically set by |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 677 | .Nm |
| 678 | to point to a value of the form |
| 679 | .Dq hostname:n |
| 680 | where hostname indicates |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 681 | the host where the shell runs, and n is an integer >= 1. |
| 682 | .Nm |
| 683 | uses this special value to forward X11 connections over the secure |
| 684 | channel. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 685 | The user should normally not set |
| 686 | .Ev DISPLAY |
| 687 | explicitly, as that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 688 | will render the X11 connection insecure (and will require the user to |
| 689 | manually copy any required authorization cookies). |
| 690 | .It Ev HOME |
| 691 | Set to the path of the user's home directory. |
| 692 | .It Ev LOGNAME |
| 693 | Synonym for |
| 694 | .Ev USER ; |
| 695 | set for compatibility with systems that use this variable. |
| 696 | .It Ev MAIL |
Ben Lindstrom | e59433d | 2001-09-12 16:41:37 +0000 | [diff] [blame] | 697 | Set to the path of the user's mailbox. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 698 | .It Ev PATH |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 699 | Set to the default |
| 700 | .Ev PATH , |
| 701 | as specified when compiling |
| 702 | .Nm ssh . |
Ben Lindstrom | 5bf5d67 | 2001-07-04 04:31:38 +0000 | [diff] [blame] | 703 | .It Ev SSH_ASKPASS |
| 704 | If |
| 705 | .Nm |
| 706 | needs a passphrase, it will read the passphrase from the current |
| 707 | terminal if it was run from a terminal. |
| 708 | If |
| 709 | .Nm |
| 710 | does not have a terminal associated with it but |
| 711 | .Ev DISPLAY |
| 712 | and |
| 713 | .Ev SSH_ASKPASS |
| 714 | are set, it will execute the program specified by |
| 715 | .Ev SSH_ASKPASS |
| 716 | and open an X11 window to read the passphrase. |
| 717 | This is particularly useful when calling |
| 718 | .Nm |
| 719 | from a |
| 720 | .Pa .Xsession |
| 721 | or related script. |
| 722 | (Note that on some machines it |
| 723 | may be necessary to redirect the input from |
| 724 | .Pa /dev/null |
| 725 | to make this work.) |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 726 | .It Ev SSH_AUTH_SOCK |
Ben Lindstrom | e59433d | 2001-09-12 16:41:37 +0000 | [diff] [blame] | 727 | Identifies the path of a unix-domain socket used to communicate with the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 728 | agent. |
Damien Miller | f37e246 | 2002-09-19 11:47:55 +1000 | [diff] [blame] | 729 | .It Ev SSH_CONNECTION |
| 730 | Identifies the client and server ends of the connection. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 731 | The variable contains |
Damien Miller | f37e246 | 2002-09-19 11:47:55 +1000 | [diff] [blame] | 732 | four space-separated values: client ip-address, client port number, |
| 733 | server ip-address and server port number. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 734 | .It Ev SSH_ORIGINAL_COMMAND |
| 735 | The variable contains the original command line if a forced command |
| 736 | is executed. |
| 737 | It can be used to extract the original arguments. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 738 | .It Ev SSH_TTY |
| 739 | 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] | 740 | with the current shell or command. |
| 741 | If the current session has no tty, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 742 | this variable is not set. |
| 743 | .It Ev TZ |
| 744 | The timezone variable is set to indicate the present timezone if it |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 745 | 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] | 746 | on to new connections). |
| 747 | .It Ev USER |
| 748 | Set to the name of the user logging in. |
| 749 | .El |
| 750 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 751 | Additionally, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 752 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 753 | reads |
| 754 | .Pa $HOME/.ssh/environment , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 755 | and adds lines of the format |
| 756 | .Dq VARNAME=value |
Ben Lindstrom | dc7adf2 | 2002-08-20 18:38:02 +0000 | [diff] [blame] | 757 | to the environment if the file exists and if users are allowed to |
| 758 | change their environment. |
Ben Lindstrom | bd9bf38 | 2002-08-20 18:54:20 +0000 | [diff] [blame] | 759 | See the |
Ben Lindstrom | dc7adf2 | 2002-08-20 18:38:02 +0000 | [diff] [blame] | 760 | .Cm PermitUserEnvironment |
Ben Lindstrom | bd9bf38 | 2002-08-20 18:54:20 +0000 | [diff] [blame] | 761 | option in |
Ben Lindstrom | dc7adf2 | 2002-08-20 18:38:02 +0000 | [diff] [blame] | 762 | .Xr sshd_config 5 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 763 | .Sh FILES |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 764 | .Bl -tag -width Ds |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 765 | .It Pa $HOME/.ssh/known_hosts |
Ben Lindstrom | e59433d | 2001-09-12 16:41:37 +0000 | [diff] [blame] | 766 | Records host keys for all hosts the user has logged into that are not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 767 | in |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 768 | .Pa /etc/ssh/ssh_known_hosts . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 769 | See |
| 770 | .Xr sshd 8 . |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 771 | .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa |
| 772 | Contains the authentication identity of the user. |
| 773 | They are for protocol 1 RSA, protocol 2 DSA, and protocol 2 RSA, respectively. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 774 | These files |
| 775 | contain sensitive data and should be readable by the user but not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 776 | accessible by others (read/write/execute). |
| 777 | Note that |
| 778 | .Nm |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 779 | ignores a private key file if it is accessible by others. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 780 | It is possible to specify a passphrase when |
| 781 | generating the key; the passphrase will be used to encrypt the |
| 782 | sensitive part of this file using 3DES. |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 783 | .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 784 | Contains the public key for authentication (public part of the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 785 | identity file in human-readable form). |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 786 | The contents of the |
| 787 | .Pa $HOME/.ssh/identity.pub |
| 788 | file should be added to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 789 | .Pa $HOME/.ssh/authorized_keys |
| 790 | on all machines |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 791 | where the user wishes to log in using protocol version 1 RSA authentication. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 792 | The contents of the |
| 793 | .Pa $HOME/.ssh/id_dsa.pub |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 794 | and |
| 795 | .Pa $HOME/.ssh/id_rsa.pub |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 796 | file should be added to |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 797 | .Pa $HOME/.ssh/authorized_keys |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 798 | on all machines |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 799 | where the user wishes to log in using protocol version 2 DSA/RSA authentication. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 800 | These files are not |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 801 | sensitive and can (but need not) be readable by anyone. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 802 | These files are |
Kevin Steves | 3c034ae | 2001-02-05 13:47:11 +0000 | [diff] [blame] | 803 | never used automatically and are not necessary; they are only provided for |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 804 | the convenience of the user. |
| 805 | .It Pa $HOME/.ssh/config |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 806 | This is the per-user configuration file. |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 807 | The file format and configuration options are described in |
| 808 | .Xr ssh_config 5 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 809 | .It Pa $HOME/.ssh/authorized_keys |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 810 | Lists the public keys (RSA/DSA) that can be used for logging in as this user. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 811 | The format of this file is described in the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 812 | .Xr sshd 8 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 813 | manual page. |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 814 | In the simplest form the format is the same as the .pub |
| 815 | identity files. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 816 | This file is not highly sensitive, but the recommended |
| 817 | permissions are read/write for the user, and not accessible by others. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 818 | .It Pa /etc/ssh/ssh_known_hosts |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 819 | Systemwide list of known host keys. |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 820 | This file should be prepared by the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 821 | system administrator to contain the public host keys of all machines in the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 822 | organization. |
| 823 | This file should be world-readable. |
| 824 | This file contains |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 825 | public keys, one per line, in the following format (fields separated |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 826 | by spaces): system name, public key and optional comment field. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 827 | When different names are used |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 828 | for the same machine, all such names should be listed, separated by |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 829 | commas. |
| 830 | The format is described on the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 831 | .Xr sshd 8 |
| 832 | manual page. |
| 833 | .Pp |
| 834 | The canonical system name (as returned by name servers) is used by |
| 835 | .Xr sshd 8 |
| 836 | to verify the client host when logging in; other names are needed because |
| 837 | .Nm |
| 838 | does not convert the user-supplied name to a canonical name before |
| 839 | checking the key, because someone with access to the name servers |
| 840 | would then be able to fool host authentication. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 841 | .It Pa /etc/ssh/ssh_config |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 842 | Systemwide configuration file. |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 843 | The file format and configuration options are described in |
| 844 | .Xr ssh_config 5 . |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 845 | .It Pa /etc/ssh/ssh_host_key, /etc/ssh/ssh_host_dsa_key, /etc/ssh/ssh_host_rsa_key |
Damien Miller | 705499b | 2001-11-12 11:05:38 +1100 | [diff] [blame] | 846 | These three files contain the private parts of the host keys |
| 847 | and are used for |
| 848 | .Cm RhostsRSAAuthentication |
| 849 | and |
| 850 | .Cm HostbasedAuthentication . |
Ben Lindstrom | 5cac423 | 2002-06-11 15:45:02 +0000 | [diff] [blame] | 851 | If the protocol version 1 |
| 852 | .Cm RhostsRSAAuthentication |
Ben Lindstrom | cb72e4f | 2002-06-21 00:41:51 +0000 | [diff] [blame] | 853 | method is used, |
Damien Miller | 705499b | 2001-11-12 11:05:38 +1100 | [diff] [blame] | 854 | .Nm |
Ben Lindstrom | 5cac423 | 2002-06-11 15:45:02 +0000 | [diff] [blame] | 855 | must be setuid root, since the host key is readable only by root. |
| 856 | For protocol version 2, |
| 857 | .Nm |
| 858 | uses |
| 859 | .Xr ssh-keysign 8 |
| 860 | to access the host keys for |
| 861 | .Cm HostbasedAuthentication . |
| 862 | This eliminates the requirement that |
| 863 | .Nm |
| 864 | be setuid root when that authentication method is used. |
| 865 | By default |
| 866 | .Nm |
| 867 | is not setuid root. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 868 | .It Pa $HOME/.rhosts |
| 869 | This file is used in |
| 870 | .Pa \&.rhosts |
| 871 | authentication to list the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 872 | host/user pairs that are permitted to log in. |
| 873 | (Note that this file is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 874 | also used by rlogin and rsh, which makes using this file insecure.) |
| 875 | Each line of the file contains a host name (in the canonical form |
| 876 | returned by name servers), and then a user name on that host, |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 877 | separated by a space. |
Ben Lindstrom | ebd888d | 2001-03-05 05:49:29 +0000 | [diff] [blame] | 878 | On some machines this file may need to be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 879 | world-readable if the user's home directory is on a NFS partition, |
| 880 | because |
| 881 | .Xr sshd 8 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 882 | reads it as root. |
| 883 | Additionally, this file must be owned by the user, |
| 884 | and must not have write permissions for anyone else. |
| 885 | The recommended |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 886 | permission for most machines is read/write for the user, and not |
| 887 | accessible by others. |
| 888 | .Pp |
| 889 | Note that by default |
| 890 | .Xr sshd 8 |
| 891 | will be installed so that it requires successful RSA host |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 892 | authentication before permitting \s+2.\s0rhosts authentication. |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 893 | If the server machine does not have the client's host key in |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 894 | .Pa /etc/ssh/ssh_known_hosts , |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 895 | it can be stored in |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 896 | .Pa $HOME/.ssh/known_hosts . |
| 897 | The easiest way to do this is to |
| 898 | connect back to the client from the server machine using ssh; this |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 899 | will automatically add the host key to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 900 | .Pa $HOME/.ssh/known_hosts . |
| 901 | .It Pa $HOME/.shosts |
| 902 | This file is used exactly the same way as |
| 903 | .Pa \&.rhosts . |
| 904 | The purpose for |
| 905 | having this file is to be able to use rhosts authentication with |
| 906 | .Nm |
| 907 | without permitting login with |
Ben Lindstrom | c57bbf1 | 2002-05-15 21:36:45 +0000 | [diff] [blame] | 908 | .Nm rlogin |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 909 | or |
| 910 | .Xr rsh 1 . |
| 911 | .It Pa /etc/hosts.equiv |
| 912 | This file is used during |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 913 | .Pa \&.rhosts authentication. |
| 914 | It contains |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 915 | canonical hosts names, one per line (the full format is described on |
| 916 | the |
| 917 | .Xr sshd 8 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 918 | manual page). |
| 919 | If the client host is found in this file, login is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 920 | automatically permitted provided client and server user names are the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 921 | same. |
| 922 | Additionally, successful RSA host authentication is normally |
| 923 | required. |
| 924 | This file should only be writable by root. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 925 | .It Pa /etc/shosts.equiv |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 926 | This file is processed exactly as |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 927 | .Pa /etc/hosts.equiv . |
| 928 | This file may be useful to permit logins using |
| 929 | .Nm |
| 930 | but not using rsh/rlogin. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 931 | .It Pa /etc/ssh/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 932 | Commands in this file are executed by |
| 933 | .Nm |
| 934 | when the user logs in just before the user's shell (or command) is started. |
| 935 | See the |
| 936 | .Xr sshd 8 |
| 937 | manual page for more information. |
| 938 | .It Pa $HOME/.ssh/rc |
| 939 | Commands in this file are executed by |
| 940 | .Nm |
| 941 | when the user logs in just before the user's shell (or command) is |
| 942 | started. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 943 | See the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 944 | .Xr sshd 8 |
| 945 | manual page for more information. |
Damien Miller | 4f0fa56 | 1999-12-26 14:24:41 +1100 | [diff] [blame] | 946 | .It Pa $HOME/.ssh/environment |
| 947 | Contains additional definitions for environment variables, see section |
| 948 | .Sx ENVIRONMENT |
| 949 | above. |
Damien Miller | 7b28dc5 | 2000-09-05 13:34:53 +1100 | [diff] [blame] | 950 | .El |
Damien Miller | 07a2d42 | 2002-02-05 12:16:15 +1100 | [diff] [blame] | 951 | .Sh DIAGNOSTICS |
| 952 | .Nm |
| 953 | exits with the exit status of the remote command or with 255 |
| 954 | if an error occurred. |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 955 | .Sh AUTHORS |
Ben Lindstrom | 035782e | 2001-01-29 08:34:16 +0000 | [diff] [blame] | 956 | OpenSSH is a derivative of the original and free |
| 957 | ssh 1.2.12 release by Tatu Ylonen. |
| 958 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, |
| 959 | Theo de Raadt and Dug Song |
| 960 | removed many bugs, re-added newer features and |
| 961 | created OpenSSH. |
| 962 | Markus Friedl contributed the support for SSH |
| 963 | protocol versions 1.5 and 2.0. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 964 | .Sh SEE ALSO |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 965 | .Xr rsh 1 , |
| 966 | .Xr scp 1 , |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 967 | .Xr sftp 1 , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 968 | .Xr ssh-add 1 , |
| 969 | .Xr ssh-agent 1 , |
| 970 | .Xr ssh-keygen 1 , |
| 971 | .Xr telnet 1 , |
Ben Lindstrom | bf69e3b | 2002-06-23 00:31:24 +0000 | [diff] [blame] | 972 | .Xr ssh_config 5 , |
Ben Lindstrom | c001cd3 | 2002-06-23 00:32:11 +0000 | [diff] [blame] | 973 | .Xr ssh-keysign 8 , |
Ben Lindstrom | 5ab6ae1 | 2001-02-10 22:08:03 +0000 | [diff] [blame] | 974 | .Xr sshd 8 |
Ben Lindstrom | 160ec62 | 2001-04-22 17:17:46 +0000 | [diff] [blame] | 975 | .Rs |
| 976 | .%A T. Ylonen |
| 977 | .%A T. Kivinen |
| 978 | .%A M. Saarinen |
| 979 | .%A T. Rinne |
| 980 | .%A S. Lehtinen |
| 981 | .%T "SSH Protocol Architecture" |
Ben Lindstrom | f181384 | 2002-03-27 17:18:31 +0000 | [diff] [blame] | 982 | .%N draft-ietf-secsh-architecture-12.txt |
| 983 | .%D January 2002 |
Ben Lindstrom | 160ec62 | 2001-04-22 17:17:46 +0000 | [diff] [blame] | 984 | .%O work in progress material |
| 985 | .Re |