1 .\" $OpenBSD: ssh-agent.1,v 1.55 2014/04/16 23:28:12 djm 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 $Mdocdate: April 16 2014 $
42 .Nd authentication agent
47 .Op Fl a Ar bind_address
49 .Op Ar command Op Ar arg ...
55 is a program to hold private keys used for public key authentication
56 (RSA, DSA, ECDSA, ED25519).
58 is usually started in the beginning of an X-session or a login session, and
59 all other windows or programs are started as clients to the ssh-agent
61 Through use of environment variables the agent can be located
62 and automatically used for authentication when logging in to other
66 The agent initially does not have any private keys.
69 Multiple identities may be stored in
73 will automatically use them if present.
75 is also used to remove keys from
77 and to query the keys that are held in one.
79 The options are as follows:
81 .It Fl a Ar bind_address
87 .Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
89 Generate C-shell commands on
91 This is the default if
93 looks like it's a csh style of shell.
96 When this option is specified
100 Kill the current agent (given by the
102 environment variable).
104 Generate Bourne shell commands on
106 This is the default if
108 does not look like it's a csh style of shell.
110 Set a default value for the maximum lifetime of identities added to the agent.
111 The lifetime may be specified in seconds or in a time format specified in
113 A lifetime specified for an identity with
115 overrides this value.
116 Without this option the default maximum lifetime is forever.
119 If a commandline is given, this is executed as a subprocess of the agent.
120 When the command dies, so does the agent.
122 The idea is that the agent is run in the user's local PC, laptop, or
124 Authentication data need not be stored on any other
125 machine, and authentication passphrases never go over the network.
126 However, the connection to the agent is forwarded over SSH
127 remote logins, and the user can thus use the privileges given by the
128 identities anywhere in the network in a secure way.
130 There are two main ways to get an agent set up:
131 The first is that the agent starts a new subcommand into which some environment
132 variables are exported, eg
133 .Cm ssh-agent xterm & .
134 The second is that the agent prints the needed shell commands (either
138 syntax can be generated) which can be evaluated in the calling shell, eg
139 .Cm eval `ssh-agent -s`
140 for Bourne-type shells such as
145 .Cm eval `ssh-agent -c`
152 looks at these variables and uses them to establish a connection to the agent.
154 The agent will never send a private key over its request channel.
155 Instead, operations that require a private key will be performed
156 by the agent, and the result will be returned to the requester.
157 This way, private keys are not exposed to clients using the agent.
161 socket is created and the name of this socket is stored in the
165 The socket is made accessible only to the current user.
166 This method is easily abused by root or another instance of the same
171 environment variable holds the agent's process ID.
173 The agent exits automatically when the command given on the command
177 .It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt
179 sockets used to contain the connection to the authentication agent.
180 These sockets should only be readable by the owner.
181 The sockets should get automatically removed when the agent exits.
189 OpenSSH is a derivative of the original and free
190 ssh 1.2.12 release by Tatu Ylonen.
191 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
192 Theo de Raadt and Dug Song
193 removed many bugs, re-added newer features and
195 Markus Friedl contributed the support for SSH
196 protocol versions 1.5 and 2.0.