Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1 | .\" -*- nroff -*- |
| 2 | .\" |
| 3 | .\" ssh.1.in |
| 4 | .\" |
| 5 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> |
| 6 | .\" |
| 7 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
| 8 | .\" All rights reserved |
| 9 | .\" |
| 10 | .\" Created: Sat Apr 22 21:55:14 1995 ylo |
| 11 | .\" |
Damien Miller | caf6dd6 | 2000-08-29 11:33:50 +1100 | [diff] [blame] | 12 | .\" $Id: ssh.1,v 1.30 2000/08/29 00:33:51 djm Exp $ |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 13 | .\" |
| 14 | .Dd September 25, 1999 |
| 15 | .Dt SSH 1 |
| 16 | .Os |
| 17 | .Sh NAME |
| 18 | .Nm ssh |
| 19 | .Nd OpenSSH secure shell client (remote login program) |
| 20 | .Sh SYNOPSIS |
| 21 | .Nm ssh |
| 22 | .Op Fl l Ar login_name |
| 23 | .Op Ar hostname | user@hostname |
| 24 | .Op Ar command |
| 25 | .Pp |
| 26 | .Nm ssh |
Damien Miller | b1715dc | 2000-05-30 13:44:51 +1000 | [diff] [blame] | 27 | .Op Fl afgknqtvxACNPTX246 |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 28 | .Op Fl c Ar cipher_spec |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 29 | .Op Fl e Ar escape_char |
| 30 | .Op Fl i Ar identity_file |
| 31 | .Op Fl l Ar login_name |
| 32 | .Op Fl o Ar option |
| 33 | .Op Fl p Ar port |
| 34 | .Oo Fl L Xo |
| 35 | .Sm off |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 36 | .Ar port : |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 37 | .Ar host : |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 38 | .Ar hostport |
| 39 | .Sm on |
| 40 | .Xc |
| 41 | .Oc |
| 42 | .Oo Fl R Xo |
| 43 | .Sm off |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 44 | .Ar port : |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 45 | .Ar host : |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 46 | .Ar hostport |
| 47 | .Sm on |
| 48 | .Xc |
| 49 | .Oc |
| 50 | .Op Ar hostname | user@hostname |
| 51 | .Op Ar command |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 52 | .Sh DESCRIPTION |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 53 | .Nm |
| 54 | (Secure Shell) is a program for logging into a remote machine and for |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 55 | executing commands on a remote machine. |
| 56 | It is intended to replace |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 57 | rlogin and rsh, and provide secure encrypted communications between |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 58 | two untrusted hosts over an insecure network. |
| 59 | X11 connections and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 60 | arbitrary TCP/IP ports can also be forwarded over the secure channel. |
| 61 | .Pp |
| 62 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 63 | connects and logs into the specified |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 64 | .Ar hostname . |
| 65 | The user must prove |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 66 | his/her identity to the remote machine using one of several methods |
| 67 | depending on the protocol version used: |
| 68 | .Pp |
| 69 | .Ss SSH protocol version 1 |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 70 | .Pp |
| 71 | First, if the machine the user logs in from is listed in |
| 72 | .Pa /etc/hosts.equiv |
| 73 | or |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 74 | .Pa /etc/shosts.equiv |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 75 | on the remote machine, and the user names are |
| 76 | 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] | 77 | Second, if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 78 | .Pa \&.rhosts |
| 79 | or |
| 80 | .Pa \&.shosts |
| 81 | exists in the user's home directory on the |
| 82 | remote machine and contains a line containing the name of the client |
| 83 | 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] | 84 | permitted to log in. |
| 85 | This form of authentication alone is normally not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 86 | allowed by the server because it is not secure. |
| 87 | .Pp |
| 88 | The second (and primary) authentication method is the |
| 89 | .Pa rhosts |
| 90 | or |
| 91 | .Pa hosts.equiv |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 92 | method combined with RSA-based host authentication. |
| 93 | It means that if the login would be permitted by |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 94 | .Pa $HOME/.rhosts , |
| 95 | .Pa $HOME/.shosts , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 96 | .Pa /etc/hosts.equiv , |
| 97 | or |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 98 | .Pa /etc/shosts.equiv , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 99 | and if additionally the server can verify the client's |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 100 | host key (see |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 101 | .Pa /etc/ssh_known_hosts |
Damien Miller | 33e511e | 1999-11-11 11:43:13 +1100 | [diff] [blame] | 102 | and |
| 103 | .Pa $HOME/.ssh/known_hosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 104 | in the |
| 105 | .Sx FILES |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 106 | section), only then login is permitted. |
| 107 | This authentication method closes security holes due to IP |
| 108 | spoofing, DNS spoofing and routing spoofing. |
| 109 | [Note to the administrator: |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 110 | .Pa /etc/hosts.equiv , |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 111 | .Pa $HOME/.rhosts , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 112 | and the rlogin/rsh protocol in general, are inherently insecure and should be |
| 113 | disabled if security is desired.] |
| 114 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 115 | As a third authentication method, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 116 | .Nm |
| 117 | supports RSA based authentication. |
| 118 | The scheme is based on public-key cryptography: there are cryptosystems |
| 119 | where encryption and decryption are done using separate keys, and it |
| 120 | is not possible to derive the decryption key from the encryption key. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 121 | RSA is one such system. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 122 | The idea is that each user creates a public/private |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 123 | key pair for authentication purposes. |
| 124 | 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] | 125 | The file |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 126 | .Pa $HOME/.ssh/authorized_keys |
| 127 | lists the public keys that are permitted for logging |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 128 | in. |
| 129 | When the user logs in, the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 130 | .Nm |
| 131 | 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] | 132 | authentication. |
| 133 | The server checks if this key is permitted, and if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 134 | so, sends the user (actually the |
| 135 | .Nm |
| 136 | program running on behalf of the user) a challenge, a random number, |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 137 | encrypted by the user's public key. |
| 138 | The challenge can only be |
| 139 | decrypted using the proper private key. |
| 140 | The user's client then decrypts the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 141 | challenge using the private key, proving that he/she knows the private |
| 142 | key but without disclosing it to the server. |
| 143 | .Pp |
| 144 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 145 | implements the RSA authentication protocol automatically. |
| 146 | The user creates his/her RSA key pair by running |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 147 | .Xr ssh-keygen 1 . |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 148 | This stores the private key in |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 149 | .Pa $HOME/.ssh/identity |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 150 | and the public key in |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 151 | .Pa $HOME/.ssh/identity.pub |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 152 | in the user's home directory. |
| 153 | The user should then copy the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 154 | .Pa identity.pub |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 155 | to |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 156 | .Pa $HOME/.ssh/authorized_keys |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 157 | in his/her home directory on the remote machine (the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 158 | .Pa authorized_keys |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 159 | file corresponds to the conventional |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 160 | .Pa $HOME/.rhosts |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 161 | file, and has one key |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 162 | per line, though the lines can be very long). |
| 163 | After this, the user can log in without giving the password. |
| 164 | RSA authentication is much |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 165 | more secure than rhosts authentication. |
| 166 | .Pp |
| 167 | The most convenient way to use RSA authentication may be with an |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 168 | authentication agent. |
| 169 | See |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 170 | .Xr ssh-agent 1 |
| 171 | for more information. |
| 172 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 173 | If other authentication methods fail, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 174 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 175 | prompts the user for a password. |
| 176 | The password is sent to the remote |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 177 | host for checking; however, since all communications are encrypted, |
| 178 | the password cannot be seen by someone listening on the network. |
| 179 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 180 | .Ss SSH protocol version 2 |
| 181 | .Pp |
| 182 | When a user connects using the protocol version 2 |
| 183 | different authentication methods are available: |
| 184 | At first, the client attempts to authenticate using the public key method. |
| 185 | If this method fails password authentication is tried. |
| 186 | .Pp |
| 187 | The public key method is similar to RSA authentication described |
| 188 | in the previous section except that the DSA algorithm is used |
| 189 | instead of the patented RSA algorithm. |
| 190 | The client uses his private DSA key |
| 191 | .Pa $HOME/.ssh/id_dsa |
| 192 | to sign the session identifier and sends the result to the server. |
| 193 | The server checks whether the matching public key is listed in |
| 194 | .Pa $HOME/.ssh/authorized_keys2 |
| 195 | and grants access if both the key is found and the signature is correct. |
| 196 | The session identifier is derived from a shared Diffie-Hellman value |
| 197 | and is only known to the client and the server. |
| 198 | .Pp |
| 199 | If public key authentication fails or is not available a password |
| 200 | can be sent encrypted to the remote host for proving the user's identity. |
| 201 | This protocol 2 implementation does not yet support Kerberos or |
| 202 | S/Key authentication. |
| 203 | .Pp |
| 204 | Protocol 2 provides additional mechanisms for confidentiality |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 205 | (the traffic is encrypted using 3DES, Blowfish, CAST128 or Arcfour) |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 206 | and integrity (hmac-sha1, hmac-md5). |
| 207 | Note that protocol 1 lacks a strong mechanism for ensuring the |
| 208 | integrity of the connection. |
| 209 | .Pp |
| 210 | .Ss Login session and remote execution |
| 211 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 212 | When the user's identity has been accepted by the server, the server |
| 213 | either executes the given command, or logs into the machine and gives |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 214 | the user a normal shell on the remote machine. |
| 215 | All communication with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 216 | the remote command or shell will be automatically encrypted. |
| 217 | .Pp |
| 218 | If a pseudo-terminal has been allocated (normal login session), the |
| 219 | user can disconnect with |
| 220 | .Ic ~. , |
| 221 | and suspend |
| 222 | .Nm |
| 223 | with |
| 224 | .Ic ~^Z . |
| 225 | All forwarded connections can be listed with |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 226 | .Ic ~# |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 227 | and if |
| 228 | the session blocks waiting for forwarded X11 or TCP/IP |
| 229 | connections to terminate, it can be backgrounded with |
| 230 | .Ic ~& |
| 231 | (this should not be used while the user shell is active, as it can cause the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 232 | shell to hang). |
| 233 | All available escapes can be listed with |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 234 | .Ic ~? . |
| 235 | .Pp |
| 236 | A single tilde character can be sent as |
| 237 | .Ic ~~ |
| 238 | (or by following the tilde by a character other than those described above). |
| 239 | The escape character must always follow a newline to be interpreted as |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 240 | special. |
| 241 | The escape character can be changed in configuration files |
| 242 | or on the command line. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 243 | .Pp |
| 244 | If no pseudo tty has been allocated, the |
| 245 | session is transparent and can be used to reliably transfer binary |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 246 | data. |
| 247 | On most systems, setting the escape character to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 248 | .Dq none |
| 249 | will also make the session transparent even if a tty is used. |
| 250 | .Pp |
| 251 | The session terminates when the command or shell in on the remote |
| 252 | machine exists and all X11 and TCP/IP connections have been closed. |
| 253 | The exit status of the remote program is returned as the exit status |
| 254 | of |
| 255 | .Nm ssh . |
| 256 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 257 | .Ss X11 and TCP forwarding |
| 258 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 259 | If the user is using X11 (the |
| 260 | .Ev DISPLAY |
| 261 | environment variable is set), the connection to the X11 display is |
| 262 | automatically forwarded to the remote side in such a way that any X11 |
| 263 | programs started from the shell (or command) will go through the |
| 264 | 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] | 265 | from the local machine. |
| 266 | The user should not manually set |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 267 | .Ev DISPLAY . |
| 268 | Forwarding of X11 connections can be |
| 269 | configured on the command line or in configuration files. |
| 270 | .Pp |
| 271 | The |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 272 | .Ev DISPLAY |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 273 | value set by |
| 274 | .Nm |
| 275 | will point to the server machine, but with a display number greater |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 276 | than zero. |
| 277 | This is normal, and happens because |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 278 | .Nm |
| 279 | creates a |
| 280 | .Dq proxy |
| 281 | X server on the server machine for forwarding the |
| 282 | connections over the encrypted channel. |
| 283 | .Pp |
| 284 | .Nm |
| 285 | will also automatically set up Xauthority data on the server machine. |
| 286 | For this purpose, it will generate a random authorization cookie, |
| 287 | store it in Xauthority on the server, and verify that any forwarded |
| 288 | connections carry this cookie and replace it by the real cookie when |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 289 | the connection is opened. |
| 290 | The real authentication cookie is never |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 291 | sent to the server machine (and no cookies are sent in the plain). |
| 292 | .Pp |
| 293 | If the user is using an authentication agent, the connection to the agent |
| 294 | is automatically forwarded to the remote side unless disabled on |
| 295 | command line or in a configuration file. |
| 296 | .Pp |
| 297 | Forwarding of arbitrary TCP/IP connections over the secure channel can |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 298 | be specified either on command line or in a configuration file. |
| 299 | One possible application of TCP/IP forwarding is a secure connection to an |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 300 | electronic purse; another is going trough firewalls. |
| 301 | .Pp |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 302 | .Ss Server authentication |
| 303 | .Pp |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 304 | .Nm |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 305 | automatically maintains and checks a database containing |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 306 | identifications for all hosts it has ever been used with. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 307 | RSA host keys are stored in |
| 308 | .Pa $HOME/.ssh/known_hosts |
| 309 | and |
| 310 | DSA host keys are stored in |
| 311 | .Pa $HOME/.ssh/known_hosts2 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 312 | in the user's home directory. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 313 | Additionally, the files |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 314 | .Pa /etc/ssh_known_hosts |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 315 | and |
| 316 | .Pa /etc/ssh_known_hosts2 |
| 317 | are automatically checked for known hosts. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 318 | Any new hosts are automatically added to the user's file. |
| 319 | If a host's identification |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 320 | ever changes, |
| 321 | .Nm |
| 322 | warns about this and disables password authentication to prevent a |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 323 | trojan horse from getting the user's password. |
| 324 | Another purpose of |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 325 | this mechanism is to prevent man-in-the-middle attacks which could |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 326 | otherwise be used to circumvent the encryption. |
| 327 | The |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 328 | .Cm StrictHostKeyChecking |
| 329 | option (see below) can be used to prevent logins to machines whose |
| 330 | host key is not known or has changed. |
| 331 | .Sh OPTIONS |
| 332 | .Bl -tag -width Ds |
| 333 | .It Fl a |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 334 | Disables forwarding of the authentication agent connection. |
Damien Miller | b1715dc | 2000-05-30 13:44:51 +1000 | [diff] [blame] | 335 | .It Fl A |
| 336 | Enables forwarding of the authentication agent connection. |
| 337 | This can also be specified on a per-host basis in a configuration file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 338 | .It Fl c Ar blowfish|3des |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 339 | Selects the cipher to use for encrypting the session. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 340 | .Ar 3des |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 341 | is used by default. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 342 | It is believed to be secure. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 343 | .Ar 3des |
| 344 | (triple-des) is an encrypt-decrypt-encrypt triple with three different keys. |
| 345 | It is presumably more secure than the |
| 346 | .Ar des |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 347 | cipher which is no longer supported in |
| 348 | .Nm ssh . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 349 | .Ar blowfish |
| 350 | 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] | 351 | .Ar 3des . |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 352 | .It Fl c Ar "3des-cbc,blowfish-cbc,arcfour,cast128-cbc" |
| 353 | Additionally, for protocol version 2 a comma-separated list of ciphers can |
| 354 | be specified in order of preference. Protocol version 2 supports |
| 355 | 3DES, Blowfish and CAST128 in CBC mode and Arcfour. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 356 | .It Fl e Ar ch|^ch|none |
| 357 | Sets the escape character for sessions with a pty (default: |
| 358 | .Ql ~ ) . |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 359 | The escape character is only recognized at the beginning of a line. |
| 360 | The escape character followed by a dot |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 361 | .Pq Ql \&. |
| 362 | closes the connection, followed |
| 363 | by control-Z suspends the connection, and followed by itself sends the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 364 | escape character once. |
| 365 | Setting the character to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 366 | .Dq none |
| 367 | disables any escapes and makes the session fully transparent. |
| 368 | .It Fl f |
| 369 | Requests |
| 370 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 371 | to go to background just before command execution. |
| 372 | This is useful if |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 373 | .Nm |
| 374 | is going to ask for passwords or passphrases, but the user |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 375 | wants it in the background. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 376 | This implies |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 377 | .Fl n . |
| 378 | The recommended way to start X11 programs at a remote site is with |
| 379 | something like |
| 380 | .Ic ssh -f host xterm . |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 381 | .It Fl g |
| 382 | Allows remote hosts to connect to local forwarded ports. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 383 | .It Fl i Ar identity_file |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 384 | Selects the file from which the identity (private key) for |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 385 | RSA authentication is read. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 386 | Default is |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 387 | .Pa $HOME/.ssh/identity |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 388 | in the user's home directory. |
| 389 | Identity files may also be specified on |
| 390 | a per-host basis in the configuration file. |
| 391 | It is possible to have multiple |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 392 | .Fl i |
| 393 | options (and multiple identities specified in |
| 394 | configuration files). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 395 | .It Fl k |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 396 | Disables forwarding of Kerberos tickets and AFS tokens. |
| 397 | 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] | 398 | .It Fl l Ar login_name |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 399 | Specifies the user to log in as on the remote machine. |
| 400 | This also may be specified on a per-host basis in the configuration file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 401 | .It Fl n |
| 402 | Redirects stdin from |
| 403 | .Pa /dev/null |
| 404 | (actually, prevents reading from stdin). |
| 405 | This must be used when |
| 406 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 407 | is run in the background. |
| 408 | A common trick is to use this to run X11 programs on a remote machine. |
| 409 | For example, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 410 | .Ic ssh -n shadows.cs.hut.fi emacs & |
| 411 | will start an emacs on shadows.cs.hut.fi, and the X11 |
| 412 | connection will be automatically forwarded over an encrypted channel. |
| 413 | The |
| 414 | .Nm |
| 415 | program will be put in the background. |
| 416 | (This does not work if |
| 417 | .Nm |
| 418 | needs to ask for a password or passphrase; see also the |
| 419 | .Fl f |
| 420 | option.) |
Damien Miller | dcb6ecd | 2000-05-17 22:34:22 +1000 | [diff] [blame] | 421 | .It Fl N |
| 422 | Do not execute a remote command. |
| 423 | This is usefull if you just want to forward ports |
| 424 | (protocol version 2 only). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 425 | .It Fl o Ar option |
| 426 | Can be used to give options in the format used in the config file. |
| 427 | This is useful for specifying options for which there is no separate |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 428 | command-line flag. |
| 429 | The option has the same format as a line in the configuration file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 430 | .It Fl p Ar port |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 431 | Port to connect to on the remote host. |
| 432 | This can be specified on a |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 433 | per-host basis in the configuration file. |
| 434 | .It Fl P |
| 435 | Use a non-privileged port for outgoing connections. |
| 436 | This can be used if your firewall does |
| 437 | not permit connections from privileged ports. |
Damien Miller | a34a28b | 1999-12-14 10:47:15 +1100 | [diff] [blame] | 438 | Note that this option turns off |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 439 | .Cm RhostsAuthentication |
| 440 | and |
| 441 | .Cm RhostsRSAAuthentication . |
| 442 | .It Fl q |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 443 | Quiet mode. |
| 444 | Causes all warning and diagnostic messages to be suppressed. |
| 445 | Only fatal errors are displayed. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 446 | .It Fl t |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 447 | Force pseudo-tty allocation. |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 448 | This can be used to execute arbitrary |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 449 | screen-based programs on a remote machine, which can be very useful, |
| 450 | e.g., when implementing menu services. |
Damien Miller | dcb6ecd | 2000-05-17 22:34:22 +1000 | [diff] [blame] | 451 | .It Fl T |
| 452 | Disable pseudo-tty allocation (protocol version 2 only). |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 453 | .It Fl v |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 454 | Verbose mode. |
| 455 | Causes |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 456 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 457 | to print debugging messages about its progress. |
| 458 | This is helpful in |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 459 | debugging connection, authentication, and configuration problems. |
| 460 | The verbose mode is also used to display |
| 461 | .Xr skey 1 |
| 462 | challenges, if the user entered "s/key" as password. |
| 463 | .It Fl x |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 464 | Disables X11 forwarding. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 465 | .It Fl X |
| 466 | Enables X11 forwarding. |
Damien Miller | b1715dc | 2000-05-30 13:44:51 +1000 | [diff] [blame] | 467 | This can also be specified on a per-host basis in a configuration file. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 468 | .It Fl C |
| 469 | Requests compression of all data (including stdin, stdout, stderr, and |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 470 | data for forwarded X11 and TCP/IP connections). |
| 471 | The compression algorithm is the same used by |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 472 | .Xr gzip 1 , |
| 473 | and the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 474 | .Dq level |
| 475 | can be controlled by the |
| 476 | .Cm CompressionLevel |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 477 | option (see below). |
| 478 | Compression is desirable on modem lines and other |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 479 | slow connections, but will only slow down things on fast networks. |
| 480 | The default value can be set on a host-by-host basis in the |
| 481 | configuration files; see the |
| 482 | .Cm Compress |
| 483 | option below. |
| 484 | .It Fl L Ar port:host:hostport |
| 485 | 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] | 486 | forwarded to the given host and port on the remote side. |
| 487 | This works by allocating a socket to listen to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 488 | .Ar port |
| 489 | on the local side, and whenever a connection is made to this port, the |
| 490 | connection is forwarded over the secure channel, and a connection is |
| 491 | made to |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 492 | .Ar host |
| 493 | port |
| 494 | .Ar hostport |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 495 | from the remote machine. |
| 496 | Port forwardings can also be specified in the configuration file. |
| 497 | Only root can forward privileged ports. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 498 | IPv6 addresses can be specified with an alternative syntax: |
| 499 | .Ar port/host/hostport |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 500 | .It Fl R Ar port:host:hostport |
| 501 | 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] | 502 | forwarded to the given host and port on the local side. |
| 503 | This works by allocating a socket to listen to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 504 | .Ar port |
| 505 | on the remote side, and whenever a connection is made to this port, the |
| 506 | connection is forwarded over the secure channel, and a connection is |
| 507 | made to |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 508 | .Ar host |
| 509 | port |
| 510 | .Ar hostport |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 511 | from the local machine. |
| 512 | Port forwardings can also be specified in the configuration file. |
| 513 | Privileged ports can be forwarded only when |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 514 | logging in as root on the remote machine. |
Damien Miller | 4af5130 | 2000-04-16 11:18:38 +1000 | [diff] [blame] | 515 | .It Fl 2 |
| 516 | Forces |
| 517 | .Nm |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 518 | to try protocol version 2 only. |
Damien Miller | 34132e5 | 2000-01-14 15:45:46 +1100 | [diff] [blame] | 519 | .It Fl 4 |
| 520 | Forces |
| 521 | .Nm |
| 522 | to use IPv4 addresses only. |
| 523 | .It Fl 6 |
| 524 | Forces |
| 525 | .Nm |
| 526 | to use IPv6 addresses only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 527 | .El |
| 528 | .Sh CONFIGURATION FILES |
| 529 | .Nm |
| 530 | obtains configuration data from the following sources (in this order): |
| 531 | command line options, user's configuration file |
| 532 | .Pq Pa $HOME/.ssh/config , |
| 533 | and system-wide configuration file |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 534 | .Pq Pa /etc/ssh_config . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 535 | For each parameter, the first obtained value |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 536 | will be used. |
| 537 | The configuration files contain sections bracketed by |
| 538 | .Dq Host |
| 539 | specifications, and that section is only applied for hosts that |
| 540 | match one of the patterns given in the specification. |
| 541 | The matched host name is the one given on the command line. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 542 | .Pp |
| 543 | Since the first obtained value for each parameter is used, more |
| 544 | host-specific declarations should be given near the beginning of the |
| 545 | file, and general defaults at the end. |
| 546 | .Pp |
| 547 | The configuration file has the following format: |
| 548 | .Pp |
| 549 | Empty lines and lines starting with |
| 550 | .Ql # |
| 551 | are comments. |
| 552 | .Pp |
| 553 | Otherwise a line is of the format |
| 554 | .Dq keyword arguments . |
| 555 | The possible |
| 556 | keywords and their meanings are as follows (note that the |
| 557 | configuration files are case-sensitive): |
| 558 | .Bl -tag -width Ds |
| 559 | .It Cm Host |
| 560 | Restricts the following declarations (up to the next |
| 561 | .Cm Host |
| 562 | keyword) to be only for those hosts that match one of the patterns |
| 563 | given after the keyword. |
| 564 | .Ql \&* |
| 565 | and |
| 566 | .Ql ? |
| 567 | can be used as wildcards in the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 568 | patterns. |
| 569 | A single |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 570 | .Ql \&* |
| 571 | as a pattern can be used to provide global |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 572 | defaults for all hosts. |
| 573 | The host is the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 574 | .Ar hostname |
| 575 | argument given on the command line (i.e., the name is not converted to |
| 576 | a canonicalized host name before matching). |
| 577 | .It Cm AFSTokenPassing |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 578 | Specifies whether to pass AFS tokens to remote host. |
| 579 | The argument to this keyword must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 580 | .Dq yes |
| 581 | or |
| 582 | .Dq no . |
| 583 | .It Cm BatchMode |
| 584 | If set to |
| 585 | .Dq yes , |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 586 | passphrase/password querying will be disabled. |
| 587 | This option is useful in scripts and other batch jobs where you have no |
| 588 | user to supply the password. |
| 589 | The argument must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 590 | .Dq yes |
| 591 | or |
| 592 | .Dq no . |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 593 | .It Cm CheckHostIP |
| 594 | If this flag is set to |
| 595 | .Dq yes , |
| 596 | ssh will additionally check the host ip address in the |
| 597 | .Pa known_hosts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 598 | file. |
| 599 | This allows ssh to detect if a host key changed due to DNS spoofing. |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 600 | If the option is set to |
| 601 | .Dq no , |
| 602 | the check will not be executed. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 603 | .It Cm Cipher |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 604 | Specifies the cipher to use for encrypting the session. |
| 605 | Currently, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 606 | .Dq blowfish , |
| 607 | and |
| 608 | .Dq 3des |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 609 | are supported. |
| 610 | The default is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 611 | .Dq 3des . |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 612 | .It Cm Ciphers |
| 613 | Specifies the ciphers allowed for protocol version 2 |
| 614 | in order of preference. |
| 615 | Multiple ciphers must be comma-separated. |
| 616 | The default is |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 617 | .Dq 3des-cbc,blowfish-cbc,arcfour,cast128-cbc . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 618 | .It Cm Compression |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 619 | Specifies whether to use compression. |
| 620 | The argument must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 621 | .Dq yes |
| 622 | or |
| 623 | .Dq no . |
| 624 | .It Cm CompressionLevel |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 625 | Specifies the compression level to use if compression is enable. |
| 626 | The argument must be an integer from 1 (fast) to 9 (slow, best). |
| 627 | The default level is 6, which is good for most applications. |
| 628 | The meaning of the values is the same as in |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 629 | .Xr gzip 1 . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 630 | .It Cm ConnectionAttempts |
| 631 | Specifies the number of tries (one per second) to make before falling |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 632 | back to rsh or exiting. |
| 633 | The argument must be an integer. |
| 634 | This may be useful in scripts if the connection sometimes fails. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 635 | .It Cm DSAAuthentication |
| 636 | Specifies whether to try DSA authentication. |
| 637 | The argument to this keyword must be |
| 638 | .Dq yes |
| 639 | or |
| 640 | .Dq no . |
| 641 | DSA authentication will only be |
| 642 | attempted if a DSA identity file exists. |
| 643 | Note that this option applies to protocol version 2 only. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 644 | .It Cm EscapeChar |
| 645 | Sets the escape character (default: |
| 646 | .Ql ~ ) . |
| 647 | The escape character can also |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 648 | be set on the command line. |
| 649 | The argument should be a single character, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 650 | .Ql ^ |
| 651 | followed by a letter, or |
| 652 | .Dq none |
| 653 | to disable the escape |
| 654 | character entirely (making the connection transparent for binary |
| 655 | data). |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 656 | .It Cm FallBackToRsh |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 657 | Specifies that if connecting via |
| 658 | .Nm |
| 659 | fails due to a connection refused error (there is no |
| 660 | .Xr sshd 8 |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 661 | listening on the remote host), |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 662 | .Xr rsh 1 |
| 663 | should automatically be used instead (after a suitable warning about |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 664 | the session being unencrypted). |
| 665 | The argument must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 666 | .Dq yes |
| 667 | or |
| 668 | .Dq no . |
| 669 | .It Cm ForwardAgent |
| 670 | Specifies whether the connection to the authentication agent (if any) |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 671 | will be forwarded to the remote machine. |
| 672 | The argument must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 673 | .Dq yes |
| 674 | or |
| 675 | .Dq no . |
Damien Miller | b1715dc | 2000-05-30 13:44:51 +1000 | [diff] [blame] | 676 | The default is |
| 677 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 678 | .It Cm ForwardX11 |
| 679 | Specifies whether X11 connections will be automatically redirected |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 680 | over the secure channel and |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 681 | .Ev DISPLAY |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 682 | set. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 683 | The argument must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 684 | .Dq yes |
| 685 | or |
| 686 | .Dq no . |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 687 | The default is |
| 688 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 689 | .It Cm GatewayPorts |
| 690 | Specifies whether remote hosts are allowed to connect to local |
| 691 | forwarded ports. |
| 692 | The argument must be |
| 693 | .Dq yes |
| 694 | or |
| 695 | .Dq no . |
| 696 | The default is |
| 697 | .Dq no . |
| 698 | .It Cm GlobalKnownHostsFile |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 699 | Specifies a file to use instead of |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 700 | .Pa /etc/ssh_known_hosts . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 701 | .It Cm HostName |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 702 | Specifies the real host name to log into. |
| 703 | This can be used to specify nicknames or abbreviations for hosts. |
| 704 | Default is the name given on the command line. |
| 705 | Numeric IP addresses are also permitted (both on the command line and in |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 706 | .Cm HostName |
| 707 | specifications). |
| 708 | .It Cm IdentityFile |
| 709 | Specifies the file from which the user's RSA authentication identity |
| 710 | is read (default |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 711 | .Pa $HOME/.ssh/identity |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 712 | in the user's home directory). |
| 713 | Additionally, any identities represented by the authentication agent |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 714 | will be used for authentication. |
| 715 | The file name may use the tilde |
| 716 | syntax to refer to a user's home directory. |
| 717 | It is possible to have |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 718 | multiple identity files specified in configuration files; all these |
| 719 | identities will be tried in sequence. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 720 | .It Cm IdentityFile2 |
| 721 | Specifies the file from which the user's DSA authentication identity |
| 722 | is read (default |
| 723 | .Pa $HOME/.ssh/id_dsa |
| 724 | in the user's home directory). |
| 725 | The file name may use the tilde |
| 726 | syntax to refer to a user's home directory. |
| 727 | It is possible to have |
| 728 | multiple identity files specified in configuration files; all these |
| 729 | identities will be tried in sequence. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 730 | .It Cm KeepAlive |
| 731 | Specifies whether the system should send keepalive messages to the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 732 | other side. |
| 733 | If they are sent, death of the connection or crash of one |
| 734 | of the machines will be properly noticed. |
| 735 | However, this means that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 736 | connections will die if the route is down temporarily, and some people |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 737 | find it annoying. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 738 | .Pp |
| 739 | The default is |
| 740 | .Dq yes |
| 741 | (to send keepalives), and the client will notice |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 742 | if the network goes down or the remote host dies. |
| 743 | This is important in scripts, and many users want it too. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 744 | .Pp |
| 745 | To disable keepalives, the value should be set to |
| 746 | .Dq no |
| 747 | in both the server and the client configuration files. |
| 748 | .It Cm KerberosAuthentication |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 749 | Specifies whether Kerberos authentication will be used. |
| 750 | The argument to this keyword must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 751 | .Dq yes |
| 752 | or |
| 753 | .Dq no . |
| 754 | .It Cm KerberosTgtPassing |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 755 | Specifies whether a Kerberos TGT will be forwarded to the server. |
| 756 | This will only work if the Kerberos server is actually an AFS kaserver. |
| 757 | The argument to this keyword must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 758 | .Dq yes |
| 759 | or |
| 760 | .Dq no . |
| 761 | .It Cm LocalForward |
| 762 | Specifies that a TCP/IP port on the local machine be forwarded over |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 763 | the secure channel to given host:port from the remote machine. |
| 764 | The first argument must be a port number, and the second must be |
| 765 | host:port. |
| 766 | Multiple forwardings may be specified, and additional |
| 767 | forwardings can be given on the command line. |
| 768 | Only the superuser can forward privileged ports. |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 769 | .It Cm LogLevel |
| 770 | Gives the verbosity level that is used when logging messages from |
| 771 | .Nm ssh . |
| 772 | The possible values are: |
Damien Miller | 00d4bb1 | 2000-03-03 22:48:49 +1100 | [diff] [blame] | 773 | QUIET, FATAL, ERROR, INFO, VERBOSE and DEBUG. |
Damien Miller | 5ce662a | 1999-11-11 17:57:39 +1100 | [diff] [blame] | 774 | The default is INFO. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 775 | .It Cm NumberOfPasswordPrompts |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 776 | Specifies the number of password prompts before giving up. |
| 777 | The argument to this keyword must be an integer. |
| 778 | Default is 3. |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 779 | .It Cm PasswordAuthentication |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 780 | Specifies whether to use password authentication. |
| 781 | The argument to this keyword must be |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 782 | .Dq yes |
| 783 | or |
| 784 | .Dq no . |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 785 | Note that this option applies to both protocol version 1 and 2. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 786 | .It Cm Port |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 787 | Specifies the port number to connect on the remote host. |
| 788 | Default is 22. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 789 | .It Cm Protocol |
| 790 | Specifies the protocol versions |
| 791 | .Nm |
| 792 | should support in order of preference. |
| 793 | The possible values are |
| 794 | .Dq 1 |
| 795 | and |
| 796 | .Dq 2 . |
| 797 | Multiple versions must be comma-separated. |
| 798 | The default is |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 799 | .Dq 1,2 . |
| 800 | This means that |
| 801 | .Nm |
| 802 | tries version 1 and falls back to version 2 |
Damien Miller | 30c3d42 | 2000-05-09 11:02:59 +1000 | [diff] [blame] | 803 | if version 1 is not available. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 804 | .It Cm ProxyCommand |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 805 | Specifies the command to use to connect to the server. |
| 806 | The command |
| 807 | string extends to the end of the line, and is executed with |
| 808 | .Pa /bin/sh . |
| 809 | In the command string, |
| 810 | .Ql %h |
| 811 | will be substituted by the host name to |
| 812 | connect and |
| 813 | .Ql %p |
| 814 | by the port. |
| 815 | The command can be basically anything, |
| 816 | and should read from its standard input and write to its standard output. |
| 817 | It should eventually connect an |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 818 | .Xr sshd 8 |
| 819 | server running on some machine, or execute |
| 820 | .Ic sshd -i |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 821 | somewhere. |
| 822 | Host key management will be done using the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 823 | HostName of the host being connected (defaulting to the name typed by |
| 824 | the user). |
Damien Miller | aae6c61 | 1999-12-06 11:47:28 +1100 | [diff] [blame] | 825 | Note that |
| 826 | .Cm CheckHostIP |
| 827 | is not available for connects with a proxy command. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 828 | .Pp |
| 829 | .It Cm RemoteForward |
| 830 | Specifies that a TCP/IP port on the remote machine be forwarded over |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 831 | the secure channel to given host:port from the local machine. |
| 832 | The first argument must be a port number, and the second must be |
| 833 | host:port. |
| 834 | Multiple forwardings may be specified, and additional |
| 835 | forwardings can be given on the command line. |
| 836 | Only the superuser can forward privileged ports. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 837 | .It Cm RhostsAuthentication |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 838 | Specifies whether to try rhosts based authentication. |
| 839 | Note that this |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 840 | declaration only affects the client side and has no effect whatsoever |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 841 | on security. |
| 842 | Disabling rhosts authentication may reduce |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 843 | authentication time on slow connections when rhosts authentication is |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 844 | not used. |
| 845 | Most servers do not permit RhostsAuthentication because it |
| 846 | is not secure (see RhostsRSAAuthentication). |
| 847 | The argument to this keyword must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 848 | .Dq yes |
| 849 | or |
| 850 | .Dq no . |
| 851 | .It Cm RhostsRSAAuthentication |
| 852 | Specifies whether to try rhosts based authentication with RSA host |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 853 | authentication. |
| 854 | This is the primary authentication method for most sites. |
| 855 | The argument must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 856 | .Dq yes |
| 857 | or |
| 858 | .Dq no . |
| 859 | .It Cm RSAAuthentication |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 860 | Specifies whether to try RSA authentication. |
| 861 | The argument to this keyword must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 862 | .Dq yes |
| 863 | or |
| 864 | .Dq no . |
| 865 | RSA authentication will only be |
| 866 | attempted if the identity file exists, or an authentication agent is |
| 867 | running. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 868 | Note that this option applies to protocol version 1 only. |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 869 | .It Cm SkeyAuthentication |
| 870 | Specifies whether to use |
| 871 | .Xr skey 1 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 872 | authentication. |
| 873 | The argument to this keyword must be |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 874 | .Dq yes |
| 875 | or |
| 876 | .Dq no . |
| 877 | The default is |
| 878 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 879 | .It Cm StrictHostKeyChecking |
| 880 | If this flag is set to |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 881 | .Dq yes , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 882 | .Nm |
| 883 | ssh will never automatically add host keys to the |
| 884 | .Pa $HOME/.ssh/known_hosts |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 885 | and |
| 886 | .Pa $HOME/.ssh/known_hosts2 |
| 887 | files, and refuses to connect hosts whose host key has changed. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 888 | This provides maximum protection against trojan horse attacks. |
| 889 | However, it can be somewhat annoying if you don't have good |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 890 | .Pa /etc/ssh_known_hosts |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 891 | and |
| 892 | .Pa /etc/ssh_known_hosts2 |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 893 | files installed and frequently |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 894 | connect new hosts. |
| 895 | Basically this option forces the user to manually |
| 896 | add any new hosts. |
| 897 | Normally this option is disabled, and new hosts |
| 898 | will automatically be added to the known host files. |
| 899 | The host keys of |
| 900 | known hosts will be verified automatically in either case. |
| 901 | The argument must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 902 | .Dq yes |
| 903 | or |
| 904 | .Dq no . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 905 | .It Cm UsePrivilegedPort |
| 906 | Specifies whether to use a privileged port for outgoing connections. |
| 907 | The argument must be |
| 908 | .Dq yes |
| 909 | or |
| 910 | .Dq no . |
| 911 | The default is |
| 912 | .Dq yes . |
| 913 | Note that setting this option to |
| 914 | .Dq no |
Damien Miller | a34a28b | 1999-12-14 10:47:15 +1100 | [diff] [blame] | 915 | turns off |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 916 | .Cm RhostsAuthentication |
| 917 | and |
| 918 | .Cm RhostsRSAAuthentication . |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 919 | .It Cm User |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 920 | Specifies the user to log in as. |
| 921 | This can be useful if you have a different user name on different machines. |
| 922 | This saves the trouble of |
Damien Miller | 396691a | 2000-01-20 22:44:08 +1100 | [diff] [blame] | 923 | having to remember to give the user name on the command line. |
| 924 | .It Cm UserKnownHostsFile |
| 925 | Specifies a file to use instead of |
| 926 | .Pa $HOME/.ssh/known_hosts . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 927 | .It Cm UseRsh |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 928 | Specifies that rlogin/rsh should be used for this host. |
| 929 | It is possible that the host does not at all support the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 930 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 931 | protocol. |
| 932 | This causes |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 933 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 934 | to immediately execute |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 935 | .Xr rsh 1 . |
| 936 | All other options (except |
| 937 | .Cm HostName ) |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 938 | are ignored if this has been specified. |
| 939 | The argument must be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 940 | .Dq yes |
| 941 | or |
| 942 | .Dq no . |
Damien Miller | d3a1857 | 2000-06-07 19:55:44 +1000 | [diff] [blame] | 943 | .It Cm XAuthLocation |
| 944 | Specifies the location of the |
| 945 | .Xr xauth 1 |
| 946 | program. |
| 947 | The default is |
| 948 | .Pa /usr/X11R6/bin/xauth . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 949 | .Sh ENVIRONMENT |
| 950 | .Nm |
| 951 | will normally set the following environment variables: |
| 952 | .Bl -tag -width Ds |
| 953 | .It Ev DISPLAY |
| 954 | The |
| 955 | .Ev DISPLAY |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 956 | variable indicates the location of the X11 server. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 957 | It is automatically set by |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 958 | .Nm |
| 959 | to point to a value of the form |
| 960 | .Dq hostname:n |
| 961 | where hostname indicates |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 962 | the host where the shell runs, and n is an integer >= 1. |
| 963 | .Nm |
| 964 | uses this special value to forward X11 connections over the secure |
| 965 | channel. |
| 966 | The user should normally not set DISPLAY explicitly, as that |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 967 | will render the X11 connection insecure (and will require the user to |
| 968 | manually copy any required authorization cookies). |
| 969 | .It Ev HOME |
| 970 | Set to the path of the user's home directory. |
| 971 | .It Ev LOGNAME |
| 972 | Synonym for |
| 973 | .Ev USER ; |
| 974 | set for compatibility with systems that use this variable. |
| 975 | .It Ev MAIL |
| 976 | Set to point the user's mailbox. |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 977 | .It Ev PATH |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 978 | Set to the default |
| 979 | .Ev PATH , |
| 980 | as specified when compiling |
| 981 | .Nm ssh . |
| 982 | .It Ev SSH_AUTH_SOCK |
| 983 | indicates the path of a unix-domain socket used to communicate with the |
| 984 | agent. |
| 985 | .It Ev SSH_CLIENT |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 986 | Identifies the client end of the connection. |
| 987 | The variable contains |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 988 | three space-separated values: client ip-address, client port number, |
| 989 | and server port number. |
| 990 | .It Ev SSH_TTY |
| 991 | 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] | 992 | with the current shell or command. |
| 993 | If the current session has no tty, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 994 | this variable is not set. |
| 995 | .It Ev TZ |
| 996 | The timezone variable is set to indicate the present timezone if it |
Damien Miller | 942da03 | 2000-08-18 13:59:06 +1000 | [diff] [blame] | 997 | 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] | 998 | on to new connections). |
| 999 | .It Ev USER |
| 1000 | Set to the name of the user logging in. |
| 1001 | .El |
| 1002 | .Pp |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1003 | Additionally, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1004 | .Nm |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1005 | reads |
| 1006 | .Pa $HOME/.ssh/environment , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1007 | and adds lines of the format |
| 1008 | .Dq VARNAME=value |
| 1009 | to the environment. |
| 1010 | .Sh FILES |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 1011 | .Bl -tag -width Ds |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1012 | .It Pa $HOME/.ssh/known_hosts |
| 1013 | Records host keys for all hosts the user has logged into (that are not |
| 1014 | in |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1015 | .Pa /etc/ssh_known_hosts ) . |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1016 | See |
| 1017 | .Xr sshd 8 . |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1018 | .It Pa $HOME/.ssh/identity, $HOME/.ssh/id_dsa |
| 1019 | Contains the RSA and the DSA authentication identity of the user. |
| 1020 | These files |
| 1021 | contain sensitive data and should be readable by the user but not |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1022 | accessible by others (read/write/execute). |
| 1023 | Note that |
| 1024 | .Nm |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1025 | ignores a private key file if it is accessible by others. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1026 | It is possible to specify a passphrase when |
| 1027 | generating the key; the passphrase will be used to encrypt the |
| 1028 | sensitive part of this file using 3DES. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1029 | .It Pa $HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1030 | Contains the public key for authentication (public part of the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1031 | identity file in human-readable form). |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1032 | The contents of the |
| 1033 | .Pa $HOME/.ssh/identity.pub |
| 1034 | file should be added to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1035 | .Pa $HOME/.ssh/authorized_keys |
| 1036 | on all machines |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1037 | where you wish to log in using RSA authentication. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1038 | The contents of the |
| 1039 | .Pa $HOME/.ssh/id_dsa.pub |
| 1040 | file should be added to |
| 1041 | .Pa $HOME/.ssh/authorized_keys2 |
| 1042 | on all machines |
| 1043 | where you wish to log in using DSA authentication. |
| 1044 | These files are not |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1045 | sensitive and can (but need not) be readable by anyone. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1046 | These files are |
| 1047 | never used automatically and are not necessary; they is only provided for |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1048 | the convenience of the user. |
| 1049 | .It Pa $HOME/.ssh/config |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1050 | This is the per-user configuration file. |
| 1051 | The format of this file is described above. |
| 1052 | This file is used by the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1053 | .Nm |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1054 | client. |
| 1055 | This file does not usually contain any sensitive information, |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1056 | but the recommended permissions are read/write for the user, and not |
| 1057 | accessible by others. |
| 1058 | .It Pa $HOME/.ssh/authorized_keys |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1059 | Lists the RSA keys that can be used for logging in as this user. |
| 1060 | The format of this file is described in the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1061 | .Xr sshd 8 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1062 | manual page. |
| 1063 | In the simplest form the format is the same as the .pub |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1064 | identity files (that is, each line contains the number of bits in |
| 1065 | modulus, public exponent, modulus, and comment fields, separated by |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1066 | spaces). |
| 1067 | This file is not highly sensitive, but the recommended |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1068 | permissions are read/write for the user, and not accessible by others. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1069 | .It Pa $HOME/.ssh/authorized_keys2 |
| 1070 | Lists the DSA keys that can be used for logging in as this user. |
| 1071 | This file is not highly sensitive, but the recommended |
| 1072 | permissions are read/write for the user, and not accessible by others. |
| 1073 | .It Pa /etc/ssh_known_hosts, /etc/ssh_known_hosts2 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1074 | Systemwide list of known host keys. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1075 | .Pa /etc/ssh_known_hosts |
| 1076 | contains RSA and |
| 1077 | .Pa /etc/ssh_known_hosts2 |
| 1078 | contains DSA keys. |
| 1079 | These files should be prepared by the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1080 | 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] | 1081 | organization. |
| 1082 | This file should be world-readable. |
| 1083 | This file contains |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1084 | public keys, one per line, in the following format (fields separated |
| 1085 | by spaces): system name, number of bits in modulus, public exponent, |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1086 | modulus, and optional comment field. |
| 1087 | When different names are used |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1088 | for the same machine, all such names should be listed, separated by |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1089 | commas. |
| 1090 | The format is described on the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1091 | .Xr sshd 8 |
| 1092 | manual page. |
| 1093 | .Pp |
| 1094 | The canonical system name (as returned by name servers) is used by |
| 1095 | .Xr sshd 8 |
| 1096 | to verify the client host when logging in; other names are needed because |
| 1097 | .Nm |
| 1098 | does not convert the user-supplied name to a canonical name before |
| 1099 | checking the key, because someone with access to the name servers |
| 1100 | would then be able to fool host authentication. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1101 | .It Pa /etc/ssh_config |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1102 | Systemwide configuration file. |
| 1103 | This file provides defaults for those |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1104 | values that are not specified in the user's configuration file, and |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1105 | for those users who do not have a configuration file. |
| 1106 | This file must be world-readable. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1107 | .It Pa $HOME/.rhosts |
| 1108 | This file is used in |
| 1109 | .Pa \&.rhosts |
| 1110 | authentication to list the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1111 | host/user pairs that are permitted to log in. |
| 1112 | (Note that this file is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1113 | also used by rlogin and rsh, which makes using this file insecure.) |
| 1114 | Each line of the file contains a host name (in the canonical form |
| 1115 | returned by name servers), and then a user name on that host, |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1116 | separated by a space. |
| 1117 | One some machines this file may need to be |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1118 | world-readable if the user's home directory is on a NFS partition, |
| 1119 | because |
| 1120 | .Xr sshd 8 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1121 | reads it as root. |
| 1122 | Additionally, this file must be owned by the user, |
| 1123 | and must not have write permissions for anyone else. |
| 1124 | The recommended |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1125 | permission for most machines is read/write for the user, and not |
| 1126 | accessible by others. |
| 1127 | .Pp |
| 1128 | Note that by default |
| 1129 | .Xr sshd 8 |
| 1130 | will be installed so that it requires successful RSA host |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1131 | authentication before permitting \s+2.\s0rhosts authentication. |
| 1132 | If your server machine does not have the client's host key in |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1133 | .Pa /etc/ssh_known_hosts , |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1134 | you can store it in |
| 1135 | .Pa $HOME/.ssh/known_hosts . |
| 1136 | The easiest way to do this is to |
| 1137 | connect back to the client from the server machine using ssh; this |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1138 | will automatically add the host key to |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1139 | .Pa $HOME/.ssh/known_hosts . |
| 1140 | .It Pa $HOME/.shosts |
| 1141 | This file is used exactly the same way as |
| 1142 | .Pa \&.rhosts . |
| 1143 | The purpose for |
| 1144 | having this file is to be able to use rhosts authentication with |
| 1145 | .Nm |
| 1146 | without permitting login with |
| 1147 | .Xr rlogin 1 |
| 1148 | or |
| 1149 | .Xr rsh 1 . |
| 1150 | .It Pa /etc/hosts.equiv |
| 1151 | This file is used during |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1152 | .Pa \&.rhosts authentication. |
| 1153 | It contains |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1154 | canonical hosts names, one per line (the full format is described on |
| 1155 | the |
| 1156 | .Xr sshd 8 |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1157 | manual page). |
| 1158 | If the client host is found in this file, login is |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1159 | automatically permitted provided client and server user names are the |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1160 | same. |
| 1161 | Additionally, successful RSA host authentication is normally |
| 1162 | required. |
| 1163 | This file should only be writable by root. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1164 | .It Pa /etc/shosts.equiv |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1165 | This file is processed exactly as |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1166 | .Pa /etc/hosts.equiv . |
| 1167 | This file may be useful to permit logins using |
| 1168 | .Nm |
| 1169 | but not using rsh/rlogin. |
Damien Miller | 886c63a | 2000-01-20 23:13:36 +1100 | [diff] [blame] | 1170 | .It Pa /etc/sshrc |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1171 | Commands in this file are executed by |
| 1172 | .Nm |
| 1173 | when the user logs in just before the user's shell (or command) is started. |
| 1174 | See the |
| 1175 | .Xr sshd 8 |
| 1176 | manual page for more information. |
| 1177 | .It Pa $HOME/.ssh/rc |
| 1178 | Commands in this file are executed by |
| 1179 | .Nm |
| 1180 | when the user logs in just before the user's shell (or command) is |
| 1181 | started. |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1182 | See the |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1183 | .Xr sshd 8 |
| 1184 | manual page for more information. |
Damien Miller | 4f0fa56 | 1999-12-26 14:24:41 +1100 | [diff] [blame] | 1185 | .It Pa $HOME/.ssh/environment |
| 1186 | Contains additional definitions for environment variables, see section |
| 1187 | .Sx ENVIRONMENT |
| 1188 | above. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1189 | .It Pa libcrypto.so.X.1 |
| 1190 | A version of this library which includes support for the RSA algorithm |
| 1191 | is required for proper operation. |
| 1192 | .Sh AUTHOR |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1193 | OpenSSH |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 1194 | is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen, |
Damien Miller | 7684ee1 | 2000-03-17 23:40:15 +1100 | [diff] [blame] | 1195 | but with bugs removed and newer features re-added. |
| 1196 | Rapidly after the |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 1197 | 1.2.12 release, newer versions of the original ssh bore successively |
| 1198 | more restrictive licenses, and thus demand for a free version was born. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1199 | .Pp |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 1200 | This version of OpenSSH |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1201 | .Bl -bullet |
| 1202 | .It |
Damien Miller | cfabe86 | 2000-04-20 23:27:27 +1000 | [diff] [blame] | 1203 | has all components of a restrictive nature (i.e., patents) |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1204 | directly removed from the source code; any licensed or patented components |
| 1205 | are chosen from |
| 1206 | external libraries. |
| 1207 | .It |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1208 | has been updated to support SSH protocol 1.5 and 2, making it compatible with |
| 1209 | all other SSH clients and servers. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1210 | .It |
Damien Miller | 22c7726 | 2000-04-13 12:26:34 +1000 | [diff] [blame] | 1211 | contains added support for |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1212 | .Xr kerberos 8 |
| 1213 | authentication and ticket passing. |
| 1214 | .It |
| 1215 | supports one-time password authentication with |
| 1216 | .Xr skey 1 . |
| 1217 | .El |
| 1218 | .Pp |
Damien Miller | 6ee9564 | 1999-11-18 11:35:13 +1100 | [diff] [blame] | 1219 | OpenSSH has been created by Aaron Campbell, Bob Beck, Markus Friedl, |
Damien Miller | 10f6f6b | 1999-11-17 17:29:08 +1100 | [diff] [blame] | 1220 | Niels Provos, Theo de Raadt, and Dug Song. |
Damien Miller | e247cc4 | 2000-05-07 12:03:14 +1000 | [diff] [blame] | 1221 | .Pp |
| 1222 | The support for SSH protocol 2 was written by Markus Friedl. |
Damien Miller | 32aa144 | 1999-10-29 09:15:49 +1000 | [diff] [blame] | 1223 | .Sh SEE ALSO |
| 1224 | .Xr rlogin 1 , |
| 1225 | .Xr rsh 1 , |
| 1226 | .Xr scp 1 , |
| 1227 | .Xr ssh-add 1 , |
| 1228 | .Xr ssh-agent 1 , |
| 1229 | .Xr ssh-keygen 1 , |
| 1230 | .Xr telnet 1 , |
| 1231 | .Xr sshd 8 , |