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 | .\" |
Darren Tucker | 1973c88 | 2004-05-24 10:34:36 +1000 | [diff] [blame^] | 37 | .\" $OpenBSD: ssh.1,v 1.187 2004/05/22 06:32:12 djm 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 | 0a118da | 2003-10-15 15:54:32 +1000 | [diff] [blame] | 46 | .Op Fl 1246AaCfgkNnqsTtVvXxY |
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 | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 49 | .Op Fl D Ar port |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 50 | .Op Fl e Ar escape_char |
Ben Lindstrom | 14f31ab | 2001-09-12 17:48:04 +0000 | [diff] [blame] | 51 | .Op Fl F Ar configfile |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 52 | .Op Fl i Ar identity_file |
| 53 | .Bk -words |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 54 | .Oo Fl L Xo |
| 55 | .Sm off |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 56 | .Ar port : |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 57 | .Ar host : |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 58 | .Ar hostport |
| 59 | .Sm on |
| 60 | .Xc |
| 61 | .Oc |
Damien Miller | 495dca3 | 2003-04-01 21:42:14 +1000 | [diff] [blame] | 62 | .Ek |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 63 | .Op Fl l Ar login_name |
| 64 | .Op Fl m Ar mac_spec |
| 65 | .Op Fl o Ar option |
Damien Miller | 495dca3 | 2003-04-01 21:42:14 +1000 | [diff] [blame] | 66 | .Bk -words |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 67 | .Op Fl p Ar port |
| 68 | .Ek |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 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 |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 77 | .Oo Ar user Ns @ Oc Ns Ar hostname |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 78 | .Op Ar command |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 79 | .Sh DESCRIPTION |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 80 | .Nm |
Ben Lindstrom | d58eb5f | 2001-03-07 06:07:22 +0000 | [diff] [blame] | 81 | (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] | 82 | executing commands on a remote machine. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 83 | It is intended to replace rlogin and rsh, |
| 84 | and provide secure encrypted communications between |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 85 | two untrusted hosts over an insecure network. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 86 | X11 connections and arbitrary TCP/IP ports |
| 87 | can also be forwarded over the secure channel. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 88 | .Pp |
| 89 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 90 | connects and logs into the specified |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 91 | .Ar hostname |
| 92 | (with optional |
| 93 | .Ar user |
| 94 | name). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 95 | The user must prove |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 96 | his/her identity to the remote machine using one of several methods |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 97 | depending on the protocol version used. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 98 | .Pp |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 99 | If |
| 100 | .Ar command |
| 101 | is specified, |
| 102 | .Ar command |
| 103 | is executed on the remote host instead of a login shell. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 104 | .Ss SSH protocol version 1 |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 105 | First, if the machine the user logs in from is listed in |
| 106 | .Pa /etc/hosts.equiv |
| 107 | or |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 108 | .Pa /etc/shosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 109 | on the remote machine, and the user names are |
| 110 | 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] | 111 | Second, if |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 112 | .Pa .rhosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 113 | or |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 114 | .Pa .shosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 115 | exists in the user's home directory on the |
| 116 | remote machine and contains a line containing the name of the client |
| 117 | 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] | 118 | permitted to log in. |
| 119 | This form of authentication alone is normally not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 120 | allowed by the server because it is not secure. |
| 121 | .Pp |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 122 | The second authentication method is the |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 123 | .Em rhosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 124 | or |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 125 | .Em hosts.equiv |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 126 | method combined with RSA-based host authentication. |
| 127 | It means that if the login would be permitted by |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 128 | .Pa $HOME/.rhosts , |
| 129 | .Pa $HOME/.shosts , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 130 | .Pa /etc/hosts.equiv , |
| 131 | or |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 132 | .Pa /etc/shosts.equiv , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 133 | and if additionally the server can verify the client's |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 134 | host key (see |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 135 | .Pa /etc/ssh/ssh_known_hosts |
Damien Miller | 33e511e | 1999-11-11 11:43:13 +1100 | [diff] [blame] | 136 | and |
| 137 | .Pa $HOME/.ssh/known_hosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 138 | in the |
| 139 | .Sx FILES |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 140 | section), only then is login permitted. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 141 | This authentication method closes security holes due to IP |
| 142 | spoofing, DNS spoofing and routing spoofing. |
| 143 | [Note to the administrator: |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 144 | .Pa /etc/hosts.equiv , |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 145 | .Pa $HOME/.rhosts , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 146 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
| 147 | disabled if security is desired.] |
| 148 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 149 | As a third authentication method, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 150 | .Nm |
| 151 | supports RSA based authentication. |
| 152 | The scheme is based on public-key cryptography: there are cryptosystems |
| 153 | where encryption and decryption are done using separate keys, and it |
| 154 | is not possible to derive the decryption key from the encryption key. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 155 | RSA is one such system. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 156 | The idea is that each user creates a public/private |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 157 | key pair for authentication purposes. |
| 158 | The server knows the public key, and only the user knows the private key. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 159 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 160 | The file |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 161 | .Pa $HOME/.ssh/authorized_keys |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 162 | lists the public keys that are permitted for logging in. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 163 | When the user logs in, the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 164 | .Nm |
| 165 | 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] | 166 | authentication. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 167 | The server checks if this key is permitted, and if so, |
| 168 | sends the user (actually the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 169 | .Nm |
| 170 | program running on behalf of the user) a challenge, a random number, |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 171 | encrypted by the user's public key. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 172 | The challenge can only be decrypted using the proper private key. |
| 173 | The user's client then decrypts the challenge using the private key, |
| 174 | proving that he/she knows the private key |
| 175 | but without disclosing it to the server. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 176 | .Pp |
| 177 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 178 | implements the RSA authentication protocol automatically. |
| 179 | The user creates his/her RSA key pair by running |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 180 | .Xr ssh-keygen 1 . |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 181 | This stores the private key in |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 182 | .Pa $HOME/.ssh/identity |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 183 | and stores the public key in |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 184 | .Pa $HOME/.ssh/identity.pub |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 185 | in the user's home directory. |
| 186 | The user should then copy the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 187 | .Pa identity.pub |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 188 | to |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 189 | .Pa $HOME/.ssh/authorized_keys |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 190 | in his/her home directory on the remote machine (the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 191 | .Pa authorized_keys |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 192 | file corresponds to the conventional |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 193 | .Pa $HOME/.rhosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 194 | file, and has one key |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 195 | per line, though the lines can be very long). |
| 196 | After this, the user can log in without giving the password. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 197 | RSA authentication is much more secure than |
| 198 | .Em rhosts |
| 199 | authentication. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 200 | .Pp |
| 201 | The most convenient way to use RSA authentication may be with an |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 202 | authentication agent. |
| 203 | See |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 204 | .Xr ssh-agent 1 |
| 205 | for more information. |
| 206 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 207 | If other authentication methods fail, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 208 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 209 | prompts the user for a password. |
| 210 | The password is sent to the remote |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 211 | host for checking; however, since all communications are encrypted, |
| 212 | the password cannot be seen by someone listening on the network. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 213 | .Ss SSH protocol version 2 |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 214 | When a user connects using protocol version 2, |
Damien Miller | 07a2d42 | 2002-02-05 12:16:15 +1100 | [diff] [blame] | 215 | similar authentication methods are available. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 216 | Using the default values for |
| 217 | .Cm PreferredAuthentications , |
Ben Lindstrom | a9086a1 | 2001-08-06 20:58:51 +0000 | [diff] [blame] | 218 | the client will try to authenticate first using the hostbased method; |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 219 | if this method fails, public key authentication is attempted, |
| 220 | and finally if this method fails, keyboard-interactive and |
Ben Lindstrom | a9086a1 | 2001-08-06 20:58:51 +0000 | [diff] [blame] | 221 | password authentication are tried. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 222 | .Pp |
| 223 | The public key method is similar to RSA authentication described |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 224 | 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] | 225 | The client uses his private key, |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 226 | .Pa $HOME/.ssh/id_dsa |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 227 | or |
| 228 | .Pa $HOME/.ssh/id_rsa , |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 229 | to sign the session identifier and sends the result to the server. |
| 230 | The server checks whether the matching public key is listed in |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 231 | .Pa $HOME/.ssh/authorized_keys |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 232 | and grants access if both the key is found and the signature is correct. |
| 233 | The session identifier is derived from a shared Diffie-Hellman value |
| 234 | and is only known to the client and the server. |
| 235 | .Pp |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 236 | If public key authentication fails or is not available, a password |
| 237 | can be sent encrypted to the remote host to prove the user's identity. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 238 | .Pp |
| 239 | Additionally, |
| 240 | .Nm |
| 241 | supports hostbased or challenge response authentication. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 242 | .Pp |
| 243 | Protocol 2 provides additional mechanisms for confidentiality |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 244 | (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour) |
Ben Lindstrom | ec26fb1 | 2001-03-06 01:05:23 +0000 | [diff] [blame] | 245 | and integrity (hmac-md5, hmac-sha1). |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 246 | Note that protocol 1 lacks a strong mechanism for ensuring the |
| 247 | integrity of the connection. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 248 | .Ss Login session and remote execution |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 249 | When the user's identity has been accepted by the server, the server |
| 250 | either executes the given command, or logs into the machine and gives |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 251 | the user a normal shell on the remote machine. |
| 252 | All communication with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 253 | the remote command or shell will be automatically encrypted. |
| 254 | .Pp |
| 255 | If a pseudo-terminal has been allocated (normal login session), the |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 256 | user may use the escape characters noted below. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 257 | .Pp |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 258 | If no pseudo-tty has been allocated, |
| 259 | the session is transparent and can be used to reliably transfer binary data. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 260 | On most systems, setting the escape character to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 261 | .Dq none |
| 262 | will also make the session transparent even if a tty is used. |
| 263 | .Pp |
Ben Lindstrom | a688561 | 2000-12-09 03:45:32 +0000 | [diff] [blame] | 264 | The session terminates when the command or shell on the remote |
Ben Lindstrom | ebd888d | 2001-03-05 05:49:29 +0000 | [diff] [blame] | 265 | machine exits and all X11 and TCP/IP connections have been closed. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 266 | The exit status of the remote program is returned as the exit status of |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 267 | .Nm ssh . |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 268 | .Ss Escape Characters |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 269 | When a pseudo-terminal has been requested, |
| 270 | .Nm |
| 271 | supports a number of functions through the use of an escape character. |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 272 | .Pp |
| 273 | A single tilde character can be sent as |
| 274 | .Ic ~~ |
Ben Lindstrom | 6600769 | 2001-07-22 20:41:59 +0000 | [diff] [blame] | 275 | 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] | 276 | The escape character must always follow a newline to be interpreted as |
| 277 | special. |
| 278 | The escape character can be changed in configuration files using the |
| 279 | .Cm EscapeChar |
Ben Lindstrom | 2464322 | 2001-06-25 05:08:11 +0000 | [diff] [blame] | 280 | configuration directive or on the command line by the |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 281 | .Fl e |
| 282 | option. |
| 283 | .Pp |
| 284 | The supported escapes (assuming the default |
| 285 | .Ql ~ ) |
| 286 | are: |
| 287 | .Bl -tag -width Ds |
| 288 | .It Cm ~. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 289 | Disconnect. |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 290 | .It Cm ~^Z |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 291 | Background |
| 292 | .Nm ssh . |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 293 | .It Cm ~# |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 294 | List forwarded connections. |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 295 | .It Cm ~& |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 296 | Background |
| 297 | .Nm |
| 298 | at logout when waiting for forwarded connection / X11 sessions to terminate. |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 299 | .It Cm ~? |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 300 | Display a list of escape characters. |
Damien Miller | 54c4598 | 2003-05-15 10:20:13 +1000 | [diff] [blame] | 301 | .It Cm ~B |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 302 | Send a BREAK to the remote system |
| 303 | (only useful for SSH protocol version 2 and if the peer supports it). |
Ben Lindstrom | 5589f4b | 2002-03-22 03:24:32 +0000 | [diff] [blame] | 304 | .It Cm ~C |
Darren Tucker | e7066df | 2004-05-24 10:18:05 +1000 | [diff] [blame] | 305 | Open command line. |
| 306 | Currently this allows the addition of port forwardings using the |
Ben Lindstrom | 5589f4b | 2002-03-22 03:24:32 +0000 | [diff] [blame] | 307 | .Fl L |
| 308 | and |
| 309 | .Fl R |
Darren Tucker | e7066df | 2004-05-24 10:18:05 +1000 | [diff] [blame] | 310 | options (see below). |
| 311 | It also allows the cancellation of existing remote port-forwardings |
| 312 | using |
| 313 | .Fl KR Ar hostport . |
Darren Tucker | 1973c88 | 2004-05-24 10:34:36 +1000 | [diff] [blame^] | 314 | Basic help is available, using the |
| 315 | .Fl h |
Darren Tucker | e7066df | 2004-05-24 10:18:05 +1000 | [diff] [blame] | 316 | option. |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 317 | .It Cm ~R |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 318 | Request rekeying of the connection |
| 319 | (only useful for SSH protocol version 2 and if the peer supports it). |
Ben Lindstrom | 9ffdcb5 | 2001-04-20 12:50:51 +0000 | [diff] [blame] | 320 | .El |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 321 | .Ss X11 and TCP forwarding |
Ben Lindstrom | 7121507 | 2001-05-17 03:16:18 +0000 | [diff] [blame] | 322 | If the |
| 323 | .Cm ForwardX11 |
| 324 | variable is set to |
| 325 | .Dq yes |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 326 | (or see the description of the |
Ben Lindstrom | 7121507 | 2001-05-17 03:16:18 +0000 | [diff] [blame] | 327 | .Fl X |
| 328 | and |
| 329 | .Fl x |
| 330 | options described later) |
| 331 | and the user is using X11 (the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 332 | .Ev DISPLAY |
| 333 | environment variable is set), the connection to the X11 display is |
| 334 | automatically forwarded to the remote side in such a way that any X11 |
| 335 | programs started from the shell (or command) will go through the |
| 336 | 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] | 337 | from the local machine. |
| 338 | The user should not manually set |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 339 | .Ev DISPLAY . |
| 340 | Forwarding of X11 connections can be |
| 341 | configured on the command line or in configuration files. |
| 342 | .Pp |
| 343 | The |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 344 | .Ev DISPLAY |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 345 | value set by |
| 346 | .Nm |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 347 | will point to the server machine, but with a display number greater than zero. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 348 | This is normal, and happens because |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 349 | .Nm |
| 350 | creates a |
| 351 | .Dq proxy |
| 352 | X server on the server machine for forwarding the |
| 353 | connections over the encrypted channel. |
| 354 | .Pp |
| 355 | .Nm |
| 356 | will also automatically set up Xauthority data on the server machine. |
| 357 | For this purpose, it will generate a random authorization cookie, |
| 358 | store it in Xauthority on the server, and verify that any forwarded |
| 359 | connections carry this cookie and replace it by the real cookie when |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 360 | the connection is opened. |
| 361 | The real authentication cookie is never |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 362 | sent to the server machine (and no cookies are sent in the plain). |
| 363 | .Pp |
Ben Lindstrom | 3541f18 | 2002-08-20 19:03:20 +0000 | [diff] [blame] | 364 | If the |
| 365 | .Cm ForwardAgent |
| 366 | variable is set to |
| 367 | .Dq yes |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 368 | (or see the description of the |
Ben Lindstrom | 3541f18 | 2002-08-20 19:03:20 +0000 | [diff] [blame] | 369 | .Fl A |
| 370 | and |
| 371 | .Fl a |
Damien Miller | 495dca3 | 2003-04-01 21:42:14 +1000 | [diff] [blame] | 372 | options described later) and |
Ben Lindstrom | 3541f18 | 2002-08-20 19:03:20 +0000 | [diff] [blame] | 373 | the user is using an authentication agent, the connection to the agent |
| 374 | is automatically forwarded to the remote side. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 375 | .Pp |
| 376 | Forwarding of arbitrary TCP/IP connections over the secure channel can |
Ben Lindstrom | 979c981 | 2001-07-22 20:45:39 +0000 | [diff] [blame] | 377 | be specified either on the command line or in a configuration file. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 378 | 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] | 379 | electronic purse; another is going through firewalls. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 380 | .Ss Server authentication |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 381 | .Nm |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 382 | automatically maintains and checks a database containing |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 383 | identifications for all hosts it has ever been used with. |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 384 | Host keys are stored in |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 385 | .Pa $HOME/.ssh/known_hosts |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 386 | in the user's home directory. |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 387 | Additionally, the file |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 388 | .Pa /etc/ssh/ssh_known_hosts |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 389 | is automatically checked for known hosts. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 390 | Any new hosts are automatically added to the user's file. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 391 | If a host's identification ever changes, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 392 | .Nm |
| 393 | warns about this and disables password authentication to prevent a |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 394 | trojan horse from getting the user's password. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 395 | Another purpose of this mechanism is to prevent man-in-the-middle attacks |
| 396 | which could otherwise be used to circumvent the encryption. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 397 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 398 | .Cm StrictHostKeyChecking |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 399 | option can be used to prevent logins to machines whose |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 400 | host key is not known or has changed. |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 401 | .Pp |
| 402 | The options are as follows: |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 403 | .Bl -tag -width Ds |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 404 | .It Fl 1 |
| 405 | Forces |
| 406 | .Nm |
| 407 | to try protocol version 1 only. |
| 408 | .It Fl 2 |
| 409 | Forces |
| 410 | .Nm |
| 411 | to try protocol version 2 only. |
| 412 | .It Fl 4 |
| 413 | Forces |
| 414 | .Nm |
| 415 | to use IPv4 addresses only. |
| 416 | .It Fl 6 |
| 417 | Forces |
| 418 | .Nm |
| 419 | to use IPv6 addresses only. |
Damien Miller | b1715dc | 2000-05-30 13:44:51 +1000 | [diff] [blame] | 420 | .It Fl A |
| 421 | Enables forwarding of the authentication agent connection. |
| 422 | 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] | 423 | .Pp |
Damien Miller | 495dca3 | 2003-04-01 21:42:14 +1000 | [diff] [blame] | 424 | Agent forwarding should be enabled with caution. |
| 425 | Users with the ability to bypass file permissions on the remote host |
| 426 | (for the agent's Unix-domain socket) |
| 427 | can access the local agent through the forwarded connection. |
| 428 | An attacker cannot obtain key material from the agent, |
Damien Miller | b5fdfaa | 2002-09-12 09:52:03 +1000 | [diff] [blame] | 429 | however they can perform operations on the keys that enable them to |
| 430 | authenticate using the identities loaded into the agent. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 431 | .It Fl a |
| 432 | Disables forwarding of the authentication agent connection. |
Ben Lindstrom | e0f8804 | 2001-04-30 13:06:24 +0000 | [diff] [blame] | 433 | .It Fl b Ar bind_address |
| 434 | Specify the interface to transmit from on machines with multiple |
| 435 | interfaces or aliased addresses. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 436 | .It Fl C |
| 437 | Requests compression of all data (including stdin, stdout, stderr, and |
| 438 | data for forwarded X11 and TCP/IP connections). |
| 439 | The compression algorithm is the same used by |
| 440 | .Xr gzip 1 , |
| 441 | and the |
| 442 | .Dq level |
| 443 | can be controlled by the |
| 444 | .Cm CompressionLevel |
| 445 | option for protocol version 1. |
| 446 | Compression is desirable on modem lines and other |
| 447 | slow connections, but will only slow down things on fast networks. |
| 448 | The default value can be set on a host-by-host basis in the |
| 449 | configuration files; see the |
| 450 | .Cm Compression |
| 451 | option. |
| 452 | .It Fl c Ar blowfish | 3des | des |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 453 | Selects the cipher to use for encrypting the session. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 454 | .Ar 3des |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 455 | is used by default. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 456 | It is believed to be secure. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 457 | .Ar 3des |
| 458 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 459 | .Ar blowfish |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 460 | 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] | 461 | .Ar 3des . |
Ben Lindstrom | ffa1dd6 | 2001-09-12 16:52:28 +0000 | [diff] [blame] | 462 | .Ar des |
| 463 | is only supported in the |
| 464 | .Nm |
| 465 | client for interoperability with legacy protocol 1 implementations |
| 466 | that do not support the |
| 467 | .Ar 3des |
Damien Miller | 495dca3 | 2003-04-01 21:42:14 +1000 | [diff] [blame] | 468 | cipher. |
| 469 | Its use is strongly discouraged due to cryptographic weaknesses. |
Ben Lindstrom | 5ab6ae1 | 2001-02-10 22:08:03 +0000 | [diff] [blame] | 470 | .It Fl c Ar cipher_spec |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 471 | Additionally, for protocol version 2 a comma-separated list of ciphers can |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 472 | be specified in order of preference. |
Ben Lindstrom | 5ab6ae1 | 2001-02-10 22:08:03 +0000 | [diff] [blame] | 473 | See |
| 474 | .Cm Ciphers |
| 475 | for more information. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 476 | .It Fl D Ar port |
| 477 | Specifies a local |
| 478 | .Dq dynamic |
| 479 | application-level port forwarding. |
| 480 | This works by allocating a socket to listen to |
| 481 | .Ar port |
| 482 | on the local side, and whenever a connection is made to this port, the |
| 483 | connection is forwarded over the secure channel, and the application |
| 484 | protocol is then used to determine where to connect to from the |
| 485 | remote machine. |
| 486 | Currently the SOCKS4 and SOCKS5 protocols are supported, and |
| 487 | .Nm |
| 488 | will act as a SOCKS server. |
| 489 | Only root can forward privileged ports. |
| 490 | Dynamic port forwardings can also be specified in the configuration file. |
| 491 | .It Fl e Ar ch | ^ch | none |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 492 | Sets the escape character for sessions with a pty (default: |
| 493 | .Ql ~ ) . |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 494 | The escape character is only recognized at the beginning of a line. |
| 495 | The escape character followed by a dot |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 496 | .Pq Ql \&. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 497 | closes the connection; |
| 498 | followed by control-Z suspends the connection; |
| 499 | and followed by itself sends the escape character once. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 500 | Setting the character to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 501 | .Dq none |
| 502 | disables any escapes and makes the session fully transparent. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 503 | .It Fl F Ar configfile |
| 504 | Specifies an alternative per-user configuration file. |
| 505 | If a configuration file is given on the command line, |
| 506 | the system-wide configuration file |
| 507 | .Pq Pa /etc/ssh/ssh_config |
| 508 | will be ignored. |
| 509 | The default for the per-user configuration file is |
| 510 | .Pa $HOME/.ssh/config . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 511 | .It Fl f |
| 512 | Requests |
| 513 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 514 | to go to background just before command execution. |
| 515 | This is useful if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 516 | .Nm |
| 517 | is going to ask for passwords or passphrases, but the user |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 518 | wants it in the background. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 519 | This implies |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 520 | .Fl n . |
| 521 | The recommended way to start X11 programs at a remote site is with |
| 522 | something like |
| 523 | .Ic ssh -f host xterm . |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 524 | .It Fl g |
| 525 | Allows remote hosts to connect to local forwarded ports. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 526 | .It Fl I Ar smartcard_device |
| 527 | Specifies which smartcard device to use. |
| 528 | The argument is the device |
| 529 | .Nm |
| 530 | should use to communicate with a smartcard used for storing the user's |
| 531 | private RSA key. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 532 | .It Fl i Ar identity_file |
Damien Miller | fae2386 | 2002-01-22 23:32:26 +1100 | [diff] [blame] | 533 | Selects a file from which the identity (private key) for |
Damien Miller | 0bc1bd8 | 2000-11-13 22:57:25 +1100 | [diff] [blame] | 534 | RSA or DSA authentication is read. |
Damien Miller | fae2386 | 2002-01-22 23:32:26 +1100 | [diff] [blame] | 535 | The default is |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 536 | .Pa $HOME/.ssh/identity |
Damien Miller | fae2386 | 2002-01-22 23:32:26 +1100 | [diff] [blame] | 537 | for protocol version 1, and |
| 538 | .Pa $HOME/.ssh/id_rsa |
| 539 | and |
| 540 | .Pa $HOME/.ssh/id_dsa |
| 541 | for protocol version 2. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 542 | Identity files may also be specified on |
| 543 | a per-host basis in the configuration file. |
| 544 | It is possible to have multiple |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 545 | .Fl i |
| 546 | options (and multiple identities specified in |
| 547 | configuration files). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 548 | .It Fl k |
Damien Miller | e0113cc | 2003-11-24 13:10:09 +1100 | [diff] [blame] | 549 | Disables forwarding (delegation) of GSSAPI credentials to the server. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 550 | .It Fl L Xo |
| 551 | .Sm off |
| 552 | .Ar port : host : hostport |
| 553 | .Sm on |
| 554 | .Xc |
| 555 | Specifies that the given port on the local (client) host is to be |
| 556 | forwarded to the given host and port on the remote side. |
| 557 | This works by allocating a socket to listen to |
| 558 | .Ar port |
| 559 | on the local side, and whenever a connection is made to this port, the |
| 560 | connection is forwarded over the secure channel, and a connection is |
| 561 | made to |
| 562 | .Ar host |
| 563 | port |
| 564 | .Ar hostport |
| 565 | from the remote machine. |
| 566 | Port forwardings can also be specified in the configuration file. |
| 567 | Only root can forward privileged ports. |
| 568 | IPv6 addresses can be specified with an alternative syntax: |
| 569 | .Sm off |
| 570 | .Xo |
| 571 | .Ar port No / Ar host No / |
| 572 | .Ar hostport . |
| 573 | .Xc |
| 574 | .Sm on |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 575 | .It Fl l Ar login_name |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 576 | Specifies the user to log in as on the remote machine. |
| 577 | 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] | 578 | .It Fl m Ar mac_spec |
| 579 | Additionally, for protocol version 2 a comma-separated list of MAC |
| 580 | (message authentication code) algorithms can |
| 581 | be specified in order of preference. |
| 582 | See the |
| 583 | .Cm MACs |
| 584 | keyword for more information. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 585 | .It Fl N |
| 586 | Do not execute a remote command. |
| 587 | This is useful for just forwarding ports |
| 588 | (protocol version 2 only). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 589 | .It Fl n |
| 590 | Redirects stdin from |
| 591 | .Pa /dev/null |
| 592 | (actually, prevents reading from stdin). |
| 593 | This must be used when |
| 594 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 595 | is run in the background. |
| 596 | A common trick is to use this to run X11 programs on a remote machine. |
| 597 | For example, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 598 | .Ic ssh -n shadows.cs.hut.fi emacs & |
| 599 | will start an emacs on shadows.cs.hut.fi, and the X11 |
| 600 | connection will be automatically forwarded over an encrypted channel. |
| 601 | The |
| 602 | .Nm |
| 603 | program will be put in the background. |
| 604 | (This does not work if |
| 605 | .Nm |
| 606 | needs to ask for a password or passphrase; see also the |
| 607 | .Fl f |
| 608 | option.) |
| 609 | .It Fl o Ar option |
Ben Lindstrom | 14c62eb | 2001-08-15 23:25:46 +0000 | [diff] [blame] | 610 | 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] | 611 | This is useful for specifying options for which there is no separate |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 612 | command-line flag. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 613 | For full details of the options listed below, and their possible values, see |
| 614 | .Xr ssh_config 5 . |
| 615 | .Pp |
| 616 | .Bl -tag -width Ds -offset indent -compact |
| 617 | .It AddressFamily |
| 618 | .It BatchMode |
| 619 | .It BindAddress |
| 620 | .It ChallengeResponseAuthentication |
| 621 | .It CheckHostIP |
| 622 | .It Cipher |
| 623 | .It Ciphers |
| 624 | .It ClearAllForwardings |
| 625 | .It Compression |
| 626 | .It CompressionLevel |
| 627 | .It ConnectionAttempts |
Darren Tucker | edae0ec | 2004-05-02 22:15:52 +1000 | [diff] [blame] | 628 | .It ConnectTimeout |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 629 | .It DynamicForward |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 630 | .It EscapeChar |
| 631 | .It ForwardAgent |
| 632 | .It ForwardX11 |
Darren Tucker | 0a118da | 2003-10-15 15:54:32 +1000 | [diff] [blame] | 633 | .It ForwardX11Trusted |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 634 | .It GatewayPorts |
| 635 | .It GlobalKnownHostsFile |
| 636 | .It GSSAPIAuthentication |
| 637 | .It GSSAPIDelegateCredentials |
| 638 | .It Host |
| 639 | .It HostbasedAuthentication |
| 640 | .It HostKeyAlgorithms |
| 641 | .It HostKeyAlias |
| 642 | .It HostName |
| 643 | .It IdentityFile |
Damien Miller | bd394c3 | 2004-03-08 23:12:36 +1100 | [diff] [blame] | 644 | .It IdentitiesOnly |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 645 | .It LocalForward |
| 646 | .It LogLevel |
| 647 | .It MACs |
| 648 | .It NoHostAuthenticationForLocalhost |
| 649 | .It NumberOfPasswordPrompts |
| 650 | .It PasswordAuthentication |
| 651 | .It Port |
| 652 | .It PreferredAuthentications |
| 653 | .It Protocol |
| 654 | .It ProxyCommand |
| 655 | .It PubkeyAuthentication |
| 656 | .It RemoteForward |
| 657 | .It RhostsRSAAuthentication |
| 658 | .It RSAAuthentication |
Darren Tucker | 7a6c066 | 2004-05-02 22:14:03 +1000 | [diff] [blame] | 659 | .It SendEnv |
Damien Miller | 509b010 | 2003-12-17 16:33:10 +1100 | [diff] [blame] | 660 | .It ServerAliveInterval |
| 661 | .It ServerAliveCountMax |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 662 | .It SmartcardDevice |
| 663 | .It StrictHostKeyChecking |
Damien Miller | 12c150e | 2003-12-17 16:31:10 +1100 | [diff] [blame] | 664 | .It TCPKeepAlive |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 665 | .It UsePrivilegedPort |
| 666 | .It User |
| 667 | .It UserKnownHostsFile |
| 668 | .It VerifyHostKeyDNS |
| 669 | .It XAuthLocation |
| 670 | .El |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 671 | .It Fl p Ar port |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 672 | Port to connect to on the remote host. |
| 673 | This can be specified on a |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 674 | per-host basis in the configuration file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 675 | .It Fl q |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 676 | Quiet mode. |
| 677 | Causes all warning and diagnostic messages to be suppressed. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 678 | .It Fl R Xo |
| 679 | .Sm off |
| 680 | .Ar port : host : hostport |
| 681 | .Sm on |
| 682 | .Xc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 683 | 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] | 684 | forwarded to the given host and port on the local side. |
| 685 | This works by allocating a socket to listen to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 686 | .Ar port |
| 687 | on the remote side, and whenever a connection is made to this port, the |
| 688 | connection is forwarded over the secure channel, and a connection is |
| 689 | made to |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 690 | .Ar host |
| 691 | port |
| 692 | .Ar hostport |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 693 | from the local machine. |
| 694 | Port forwardings can also be specified in the configuration file. |
| 695 | Privileged ports can be forwarded only when |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 696 | logging in as root on the remote machine. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 697 | IPv6 addresses can be specified with an alternative syntax: |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 698 | .Sm off |
| 699 | .Xo |
| 700 | .Ar port No / Ar host No / |
| 701 | .Ar hostport . |
| 702 | .Xc |
| 703 | .Sm on |
| 704 | .It Fl s |
| 705 | May be used to request invocation of a subsystem on the remote system. |
| 706 | Subsystems are a feature of the SSH2 protocol which facilitate the use |
| 707 | of SSH as a secure transport for other applications (eg.\& |
| 708 | .Xr sftp 1 ) . |
| 709 | The subsystem is specified as the remote command. |
| 710 | .It Fl T |
| 711 | Disable pseudo-tty allocation. |
| 712 | .It Fl t |
| 713 | Force pseudo-tty allocation. |
| 714 | This can be used to execute arbitrary |
| 715 | screen-based programs on a remote machine, which can be very useful, |
| 716 | e.g., when implementing menu services. |
| 717 | Multiple |
| 718 | .Fl t |
| 719 | options force tty allocation, even if |
Ben Lindstrom | 19ceb17 | 2001-09-12 17:54:24 +0000 | [diff] [blame] | 720 | .Nm |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 721 | has no local tty. |
| 722 | .It Fl V |
| 723 | Display the version number and exit. |
| 724 | .It Fl v |
| 725 | Verbose mode. |
| 726 | Causes |
Ben Lindstrom | 5ab6ae1 | 2001-02-10 22:08:03 +0000 | [diff] [blame] | 727 | .Nm |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 728 | to print debugging messages about its progress. |
| 729 | This is helpful in |
| 730 | debugging connection, authentication, and configuration problems. |
| 731 | Multiple |
| 732 | .Fl v |
| 733 | options increase the verbosity. |
| 734 | The maximum is 3. |
| 735 | .It Fl X |
| 736 | Enables X11 forwarding. |
| 737 | This can also be specified on a per-host basis in a configuration file. |
| 738 | .Pp |
| 739 | X11 forwarding should be enabled with caution. |
| 740 | Users with the ability to bypass file permissions on the remote host |
| 741 | (for the user's X authorization database) |
| 742 | can access the local X11 display through the forwarded connection. |
| 743 | An attacker may then be able to perform activities such as keystroke monitoring. |
| 744 | .It Fl x |
| 745 | Disables X11 forwarding. |
Darren Tucker | 0a118da | 2003-10-15 15:54:32 +1000 | [diff] [blame] | 746 | .It Fl Y |
| 747 | Enables trusted X11 forwarding. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 748 | .El |
| 749 | .Sh CONFIGURATION FILES |
| 750 | .Nm |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 751 | may additionally obtain configuration data from |
| 752 | a per-user configuration file and a system-wide configuration file. |
| 753 | The file format and configuration options are described in |
| 754 | .Xr ssh_config 5 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 755 | .Sh ENVIRONMENT |
| 756 | .Nm |
| 757 | will normally set the following environment variables: |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 758 | .Bl -tag -width LOGNAME |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 759 | .It Ev DISPLAY |
| 760 | The |
| 761 | .Ev DISPLAY |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 762 | variable indicates the location of the X11 server. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 763 | It is automatically set by |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 764 | .Nm |
| 765 | to point to a value of the form |
| 766 | .Dq hostname:n |
| 767 | where hostname indicates |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 768 | the host where the shell runs, and n is an integer \*(Ge 1. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 769 | .Nm |
| 770 | uses this special value to forward X11 connections over the secure |
| 771 | channel. |
Ben Lindstrom | c65e6a0 | 2001-04-23 13:02:16 +0000 | [diff] [blame] | 772 | The user should normally not set |
| 773 | .Ev DISPLAY |
| 774 | explicitly, as that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 775 | will render the X11 connection insecure (and will require the user to |
| 776 | manually copy any required authorization cookies). |
| 777 | .It Ev HOME |
| 778 | Set to the path of the user's home directory. |
| 779 | .It Ev LOGNAME |
| 780 | Synonym for |
| 781 | .Ev USER ; |
| 782 | set for compatibility with systems that use this variable. |
| 783 | .It Ev MAIL |
Ben Lindstrom | e59433d | 2001-09-12 16:41:37 +0000 | [diff] [blame] | 784 | Set to the path of the user's mailbox. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 785 | .It Ev PATH |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 786 | Set to the default |
| 787 | .Ev PATH , |
| 788 | as specified when compiling |
| 789 | .Nm ssh . |
Ben Lindstrom | 5bf5d67 | 2001-07-04 04:31:38 +0000 | [diff] [blame] | 790 | .It Ev SSH_ASKPASS |
| 791 | If |
| 792 | .Nm |
| 793 | needs a passphrase, it will read the passphrase from the current |
| 794 | terminal if it was run from a terminal. |
| 795 | If |
| 796 | .Nm |
| 797 | does not have a terminal associated with it but |
| 798 | .Ev DISPLAY |
| 799 | and |
| 800 | .Ev SSH_ASKPASS |
| 801 | are set, it will execute the program specified by |
| 802 | .Ev SSH_ASKPASS |
| 803 | and open an X11 window to read the passphrase. |
| 804 | This is particularly useful when calling |
| 805 | .Nm |
| 806 | from a |
| 807 | .Pa .Xsession |
| 808 | or related script. |
| 809 | (Note that on some machines it |
| 810 | may be necessary to redirect the input from |
| 811 | .Pa /dev/null |
| 812 | to make this work.) |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 813 | .It Ev SSH_AUTH_SOCK |
Ben Lindstrom | e59433d | 2001-09-12 16:41:37 +0000 | [diff] [blame] | 814 | 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] | 815 | agent. |
Damien Miller | f37e246 | 2002-09-19 11:47:55 +1000 | [diff] [blame] | 816 | .It Ev SSH_CONNECTION |
| 817 | Identifies the client and server ends of the connection. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 818 | The variable contains |
Damien Miller | f37e246 | 2002-09-19 11:47:55 +1000 | [diff] [blame] | 819 | four space-separated values: client ip-address, client port number, |
| 820 | server ip-address and server port number. |
Ben Lindstrom | 4dccfa5 | 2000-12-28 16:40:05 +0000 | [diff] [blame] | 821 | .It Ev SSH_ORIGINAL_COMMAND |
| 822 | The variable contains the original command line if a forced command |
| 823 | is executed. |
| 824 | It can be used to extract the original arguments. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 825 | .It Ev SSH_TTY |
| 826 | 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] | 827 | with the current shell or command. |
| 828 | If the current session has no tty, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 829 | this variable is not set. |
| 830 | .It Ev TZ |
| 831 | The timezone variable is set to indicate the present timezone if it |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 832 | 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] | 833 | on to new connections). |
| 834 | .It Ev USER |
| 835 | Set to the name of the user logging in. |
| 836 | .El |
| 837 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 838 | Additionally, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 839 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 840 | reads |
| 841 | .Pa $HOME/.ssh/environment , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 842 | and adds lines of the format |
| 843 | .Dq VARNAME=value |
Ben Lindstrom | dc7adf2 | 2002-08-20 18:38:02 +0000 | [diff] [blame] | 844 | to the environment if the file exists and if users are allowed to |
| 845 | change their environment. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 846 | For more information, see the |
Ben Lindstrom | dc7adf2 | 2002-08-20 18:38:02 +0000 | [diff] [blame] | 847 | .Cm PermitUserEnvironment |
Ben Lindstrom | bd9bf38 | 2002-08-20 18:54:20 +0000 | [diff] [blame] | 848 | option in |
Ben Lindstrom | dc7adf2 | 2002-08-20 18:38:02 +0000 | [diff] [blame] | 849 | .Xr sshd_config 5 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 850 | .Sh FILES |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 851 | .Bl -tag -width Ds |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 852 | .It Pa $HOME/.ssh/known_hosts |
Ben Lindstrom | e59433d | 2001-09-12 16:41:37 +0000 | [diff] [blame] | 853 | 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] | 854 | in |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 855 | .Pa /etc/ssh/ssh_known_hosts . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 856 | See |
| 857 | .Xr sshd 8 . |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 858 | .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa |
| 859 | Contains the authentication identity of the user. |
| 860 | 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] | 861 | These files |
| 862 | contain sensitive data and should be readable by the user but not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 863 | accessible by others (read/write/execute). |
| 864 | Note that |
| 865 | .Nm |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 866 | ignores a private key file if it is accessible by others. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 867 | It is possible to specify a passphrase when |
| 868 | generating the key; the passphrase will be used to encrypt the |
| 869 | sensitive part of this file using 3DES. |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 870 | .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] | 871 | Contains the public key for authentication (public part of the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 872 | identity file in human-readable form). |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 873 | The contents of the |
| 874 | .Pa $HOME/.ssh/identity.pub |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 875 | file should be added to the file |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 876 | .Pa $HOME/.ssh/authorized_keys |
| 877 | on all machines |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 878 | 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] | 879 | The contents of the |
| 880 | .Pa $HOME/.ssh/id_dsa.pub |
Ben Lindstrom | 18a82ac | 2001-04-11 15:59:35 +0000 | [diff] [blame] | 881 | and |
| 882 | .Pa $HOME/.ssh/id_rsa.pub |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 883 | file should be added to |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 884 | .Pa $HOME/.ssh/authorized_keys |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 885 | on all machines |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 886 | 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] | 887 | These files are not |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 888 | sensitive and can (but need not) be readable by anyone. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 889 | These files are |
Kevin Steves | 3c034ae | 2001-02-05 13:47:11 +0000 | [diff] [blame] | 890 | never used automatically and are not necessary; they are only provided for |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 891 | the convenience of the user. |
| 892 | .It Pa $HOME/.ssh/config |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 893 | This is the per-user configuration file. |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 894 | The file format and configuration options are described in |
| 895 | .Xr ssh_config 5 . |
Damien Miller | c970cb9 | 2004-04-20 20:12:53 +1000 | [diff] [blame] | 896 | Because of the potential for abuse, this file must have strict permissions: |
| 897 | read/write for the user, and not accessible by others. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 898 | .It Pa $HOME/.ssh/authorized_keys |
Ben Lindstrom | f96704d | 2001-06-25 04:17:12 +0000 | [diff] [blame] | 899 | 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] | 900 | The format of this file is described in the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 901 | .Xr sshd 8 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 902 | manual page. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 903 | In the simplest form the format is the same as the |
| 904 | .Pa .pub |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 905 | identity files. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 906 | This file is not highly sensitive, but the recommended |
| 907 | permissions are read/write for the user, and not accessible by others. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 908 | .It Pa /etc/ssh/ssh_known_hosts |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 909 | Systemwide list of known host keys. |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 910 | This file should be prepared by the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 911 | 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] | 912 | organization. |
| 913 | This file should be world-readable. |
| 914 | This file contains |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 915 | public keys, one per line, in the following format (fields separated |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 916 | by spaces): system name, public key and optional comment field. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 917 | When different names are used |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 918 | for the same machine, all such names should be listed, separated by |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 919 | commas. |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 920 | The format is described in the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 921 | .Xr sshd 8 |
| 922 | manual page. |
| 923 | .Pp |
| 924 | The canonical system name (as returned by name servers) is used by |
| 925 | .Xr sshd 8 |
| 926 | to verify the client host when logging in; other names are needed because |
| 927 | .Nm |
| 928 | does not convert the user-supplied name to a canonical name before |
| 929 | checking the key, because someone with access to the name servers |
| 930 | would then be able to fool host authentication. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 931 | .It Pa /etc/ssh/ssh_config |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 932 | Systemwide configuration file. |
Ben Lindstrom | 9f04903 | 2002-06-21 00:59:05 +0000 | [diff] [blame] | 933 | The file format and configuration options are described in |
| 934 | .Xr ssh_config 5 . |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 935 | .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] | 936 | These three files contain the private parts of the host keys |
| 937 | and are used for |
| 938 | .Cm RhostsRSAAuthentication |
| 939 | and |
| 940 | .Cm HostbasedAuthentication . |
Ben Lindstrom | 5cac423 | 2002-06-11 15:45:02 +0000 | [diff] [blame] | 941 | If the protocol version 1 |
| 942 | .Cm RhostsRSAAuthentication |
Ben Lindstrom | cb72e4f | 2002-06-21 00:41:51 +0000 | [diff] [blame] | 943 | method is used, |
Damien Miller | 705499b | 2001-11-12 11:05:38 +1100 | [diff] [blame] | 944 | .Nm |
Ben Lindstrom | 5cac423 | 2002-06-11 15:45:02 +0000 | [diff] [blame] | 945 | must be setuid root, since the host key is readable only by root. |
| 946 | For protocol version 2, |
| 947 | .Nm |
| 948 | uses |
| 949 | .Xr ssh-keysign 8 |
| 950 | to access the host keys for |
| 951 | .Cm HostbasedAuthentication . |
| 952 | This eliminates the requirement that |
| 953 | .Nm |
| 954 | be setuid root when that authentication method is used. |
| 955 | By default |
| 956 | .Nm |
| 957 | is not setuid root. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 958 | .It Pa $HOME/.rhosts |
| 959 | This file is used in |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 960 | .Em rhosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 961 | authentication to list the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 962 | host/user pairs that are permitted to log in. |
| 963 | (Note that this file is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 964 | also used by rlogin and rsh, which makes using this file insecure.) |
| 965 | Each line of the file contains a host name (in the canonical form |
| 966 | returned by name servers), and then a user name on that host, |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 967 | separated by a space. |
Ben Lindstrom | ebd888d | 2001-03-05 05:49:29 +0000 | [diff] [blame] | 968 | On some machines this file may need to be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 969 | world-readable if the user's home directory is on a NFS partition, |
| 970 | because |
| 971 | .Xr sshd 8 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 972 | reads it as root. |
| 973 | Additionally, this file must be owned by the user, |
| 974 | and must not have write permissions for anyone else. |
| 975 | The recommended |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 976 | permission for most machines is read/write for the user, and not |
| 977 | accessible by others. |
| 978 | .Pp |
| 979 | Note that by default |
| 980 | .Xr sshd 8 |
| 981 | will be installed so that it requires successful RSA host |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 982 | authentication before permitting |
| 983 | .Em rhosts |
| 984 | authentication. |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 985 | 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] | 986 | .Pa /etc/ssh/ssh_known_hosts , |
Ben Lindstrom | 594e203 | 2001-09-12 18:35:30 +0000 | [diff] [blame] | 987 | it can be stored in |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 988 | .Pa $HOME/.ssh/known_hosts . |
| 989 | The easiest way to do this is to |
| 990 | connect back to the client from the server machine using ssh; this |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 991 | will automatically add the host key to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 992 | .Pa $HOME/.ssh/known_hosts . |
| 993 | .It Pa $HOME/.shosts |
| 994 | This file is used exactly the same way as |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 995 | .Pa .rhosts . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 996 | The purpose for |
| 997 | having this file is to be able to use rhosts authentication with |
| 998 | .Nm |
| 999 | without permitting login with |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 1000 | .Xr rlogin |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1001 | or |
| 1002 | .Xr rsh 1 . |
| 1003 | .It Pa /etc/hosts.equiv |
| 1004 | This file is used during |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 1005 | .Em rhosts |
Damien Miller | f1ce505 | 2003-06-11 22:04:39 +1000 | [diff] [blame] | 1006 | authentication. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1007 | It contains |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 1008 | canonical hosts names, one per line (the full format is described in the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1009 | .Xr sshd 8 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1010 | manual page). |
| 1011 | If the client host is found in this file, login is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1012 | automatically permitted provided client and server user names are the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1013 | same. |
| 1014 | Additionally, successful RSA host authentication is normally |
| 1015 | required. |
| 1016 | This file should only be writable by root. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1017 | .It Pa /etc/shosts.equiv |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1018 | This file is processed exactly as |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1019 | .Pa /etc/hosts.equiv . |
| 1020 | This file may be useful to permit logins using |
| 1021 | .Nm |
| 1022 | but not using rsh/rlogin. |
Damien Miller | 05eda43 | 2002-02-10 18:32:28 +1100 | [diff] [blame] | 1023 | .It Pa /etc/ssh/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1024 | Commands in this file are executed by |
| 1025 | .Nm |
| 1026 | when the user logs in just before the user's shell (or command) is started. |
| 1027 | See the |
| 1028 | .Xr sshd 8 |
| 1029 | manual page for more information. |
| 1030 | .It Pa $HOME/.ssh/rc |
| 1031 | Commands in this file are executed by |
| 1032 | .Nm |
| 1033 | when the user logs in just before the user's shell (or command) is |
| 1034 | started. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1035 | See the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1036 | .Xr sshd 8 |
| 1037 | manual page for more information. |
Damien Miller | 4f0fa56 | 1999-12-26 14:24:41 +1100 | [diff] [blame] | 1038 | .It Pa $HOME/.ssh/environment |
| 1039 | Contains additional definitions for environment variables, see section |
| 1040 | .Sx ENVIRONMENT |
| 1041 | above. |
Damien Miller | 7b28dc5 | 2000-09-05 13:34:53 +1100 | [diff] [blame] | 1042 | .El |
Damien Miller | 07a2d42 | 2002-02-05 12:16:15 +1100 | [diff] [blame] | 1043 | .Sh DIAGNOSTICS |
| 1044 | .Nm |
| 1045 | exits with the exit status of the remote command or with 255 |
| 1046 | if an error occurred. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1047 | .Sh SEE ALSO |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 1048 | .Xr gzip 1 , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1049 | .Xr rsh 1 , |
| 1050 | .Xr scp 1 , |
Damien Miller | 3380426 | 2001-02-04 23:20:18 +1100 | [diff] [blame] | 1051 | .Xr sftp 1 , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1052 | .Xr ssh-add 1 , |
| 1053 | .Xr ssh-agent 1 , |
| 1054 | .Xr ssh-keygen 1 , |
| 1055 | .Xr telnet 1 , |
Darren Tucker | 6177695 | 2003-10-02 16:19:47 +1000 | [diff] [blame] | 1056 | .Xr hosts.equiv 5 , |
Ben Lindstrom | bf69e3b | 2002-06-23 00:31:24 +0000 | [diff] [blame] | 1057 | .Xr ssh_config 5 , |
Ben Lindstrom | c001cd3 | 2002-06-23 00:32:11 +0000 | [diff] [blame] | 1058 | .Xr ssh-keysign 8 , |
Ben Lindstrom | 5ab6ae1 | 2001-02-10 22:08:03 +0000 | [diff] [blame] | 1059 | .Xr sshd 8 |
Ben Lindstrom | 160ec62 | 2001-04-22 17:17:46 +0000 | [diff] [blame] | 1060 | .Rs |
| 1061 | .%A T. Ylonen |
| 1062 | .%A T. Kivinen |
| 1063 | .%A M. Saarinen |
| 1064 | .%A T. Rinne |
| 1065 | .%A S. Lehtinen |
| 1066 | .%T "SSH Protocol Architecture" |
Ben Lindstrom | f181384 | 2002-03-27 17:18:31 +0000 | [diff] [blame] | 1067 | .%N draft-ietf-secsh-architecture-12.txt |
| 1068 | .%D January 2002 |
Ben Lindstrom | 160ec62 | 2001-04-22 17:17:46 +0000 | [diff] [blame] | 1069 | .%O work in progress material |
| 1070 | .Re |
Damien Miller | f1ce505 | 2003-06-11 22:04:39 +1000 | [diff] [blame] | 1071 | .Sh AUTHORS |
| 1072 | OpenSSH is a derivative of the original and free |
| 1073 | ssh 1.2.12 release by Tatu Ylonen. |
| 1074 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, |
| 1075 | Theo de Raadt and Dug Song |
| 1076 | removed many bugs, re-added newer features and |
| 1077 | created OpenSSH. |
| 1078 | Markus Friedl contributed the support for SSH |
| 1079 | protocol versions 1.5 and 2.0. |