1 .\" $OpenBSD: ssh-agent.1,v 1.57 2014/12/21 22:27:56 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: December 21 2014 $
42 .Nd authentication agent
47 .Op Fl a Ar bind_address
48 .Op Fl E Ar fingerprint_hash
50 .Op Ar command Op Ar arg ...
56 is a program to hold private keys used for public key authentication
57 (RSA, DSA, ECDSA, Ed25519).
59 is usually started in the beginning of an X-session or a login session, and
60 all other windows or programs are started as clients to the ssh-agent
62 Through use of environment variables the agent can be located
63 and automatically used for authentication when logging in to other
67 The agent initially does not have any private keys.
70 Multiple identities may be stored in
74 will automatically use them if present.
76 is also used to remove keys from
78 and to query the keys that are held in one.
80 The options are as follows:
82 .It Fl a Ar bind_address
88 .Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
90 Generate C-shell commands on
92 This is the default if
94 looks like it's a csh style of shell.
97 When this option is specified
100 .It Fl E Ar fingerprint_hash
101 Specifies the hash algorithm used when displaying key fingerprints.
109 Kill the current agent (given by the
111 environment variable).
113 Generate Bourne shell commands on
115 This is the default if
117 does not look like it's a csh style of shell.
119 Set a default value for the maximum lifetime of identities added to the agent.
120 The lifetime may be specified in seconds or in a time format specified in
122 A lifetime specified for an identity with
124 overrides this value.
125 Without this option the default maximum lifetime is forever.
128 If a commandline is given, this is executed as a subprocess of the agent.
129 When the command dies, so does the agent.
131 The idea is that the agent is run in the user's local PC, laptop, or
133 Authentication data need not be stored on any other
134 machine, and authentication passphrases never go over the network.
135 However, the connection to the agent is forwarded over SSH
136 remote logins, and the user can thus use the privileges given by the
137 identities anywhere in the network in a secure way.
139 There are two main ways to get an agent set up:
140 The first is that the agent starts a new subcommand into which some environment
141 variables are exported, eg
142 .Cm ssh-agent xterm & .
143 The second is that the agent prints the needed shell commands (either
147 syntax can be generated) which can be evaluated in the calling shell, eg
148 .Cm eval `ssh-agent -s`
149 for Bourne-type shells such as
154 .Cm eval `ssh-agent -c`
161 looks at these variables and uses them to establish a connection to the agent.
163 The agent will never send a private key over its request channel.
164 Instead, operations that require a private key will be performed
165 by the agent, and the result will be returned to the requester.
166 This way, private keys are not exposed to clients using the agent.
170 socket is created and the name of this socket is stored in the
174 The socket is made accessible only to the current user.
175 This method is easily abused by root or another instance of the same
180 environment variable holds the agent's process ID.
182 The agent exits automatically when the command given on the command
186 .It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt
188 sockets used to contain the connection to the authentication agent.
189 These sockets should only be readable by the owner.
190 The sockets should get automatically removed when the agent exits.
198 OpenSSH is a derivative of the original and free
199 ssh 1.2.12 release by Tatu Ylonen.
200 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
201 Theo de Raadt and Dug Song
202 removed many bugs, re-added newer features and
204 Markus Friedl contributed the support for SSH
205 protocol versions 1.5 and 2.0.