1 .\" $OpenBSD: ssh-agent.1,v 1.31 2002/02/04 20:41:16 stevesk Exp $
3 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 .\" All rights reserved
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".
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.
17 .\" Redistribution and use in source and binary forms, with or without
18 .\" modification, are permitted provided that the following conditions
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.
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.
37 .Dd September 25, 1999
42 .Nd authentication agent
47 .Op Ar command Op Ar args ...
53 is a program to hold private keys used for public key authentication
57 is started in the beginning of an X-session or a login session, and
58 all other windows or programs are started as clients to the ssh-agent
60 Through use of environment variables the agent can be located
61 and automatically used for authentication when logging in to other
65 The options are as follows:
68 Generate C-shell commands on
70 This is the default if
72 looks like it's a csh style of shell.
74 Generate Bourne shell commands on
76 This is the default if
78 does not look like it's a csh style of shell.
80 Kill the current agent (given by the
82 environment variable).
84 Debug mode. When this option is specified
89 If a commandline is given, this is executed as a subprocess of the agent.
90 When the command dies, so does the agent.
92 The agent initially does not have any private keys.
95 When executed without arguments,
98 .Pa $HOME/.ssh/id_rsa ,
101 .Pa $HOME/.ssh/identity .
102 If the identity has a passphrase,
104 asks for the passphrase (using a small X11 application if running
105 under X11, or from the terminal if running without X).
106 It then sends the identity to the agent.
107 Several identities can be stored in the
108 agent; the agent can automatically use any of these identities.
110 displays the identities currently held by the agent.
112 The idea is that the agent is run in the user's local PC, laptop, or
114 Authentication data need not be stored on any other
115 machine, and authentication passphrases never go over the network.
116 However, the connection to the agent is forwarded over SSH
117 remote logins, and the user can thus use the privileges given by the
118 identities anywhere in the network in a secure way.
120 There are two main ways to get an agent setup:
121 Either the agent starts a new subcommand into which some environment
122 variables are exported, or the agent prints the needed shell commands
127 syntax can be generated) which can be evalled in the calling shell.
130 looks at these variables and uses them to establish a connection to the agent.
132 The agent will never send a private key over its request channel.
133 Instead, operations that require a private key will be performed
134 by the agent, and the result will be returned to the requester.
135 This way, private keys are not exposed to clients using the agent.
137 A unix-domain socket is created
138 .Pq Pa /tmp/ssh-XXXXXXXX/agent.<pid> ,
139 and the name of this socket is stored in the
143 The socket is made accessible only to the current user.
144 This method is easily abused by root or another instance of the same
149 environment variable holds the agent's PID.
151 The agent exits automatically when the command given on the command
155 .It Pa $HOME/.ssh/identity
156 Contains the protocol version 1 RSA authentication identity of the user.
157 .It Pa $HOME/.ssh/id_dsa
158 Contains the protocol version 2 DSA authentication identity of the user.
159 .It Pa $HOME/.ssh/id_rsa
160 Contains the protocol version 2 RSA authentication identity of the user.
161 .It Pa /tmp/ssh-XXXXXXXX/agent.<pid>
162 Unix-domain sockets used to contain the connection to the
163 authentication agent.
164 These sockets should only be readable by the owner.
165 The sockets should get automatically removed when the agent exits.
168 OpenSSH is a derivative of the original and free
169 ssh 1.2.12 release by Tatu Ylonen.
170 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
171 Theo de Raadt and Dug Song
172 removed many bugs, re-added newer features and
174 Markus Friedl contributed the support for SSH
175 protocol versions 1.5 and 2.0.