1 .\" $OpenBSD: ssh-agent.1,v 1.59 2015/04/24 06:26:49 jmc Exp $
4 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
5 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
6 .\" All rights reserved
8 .\" As far as I am concerned, the code I have written for this software
9 .\" can be used freely for any purpose. Any derived versions of this
10 .\" software must be clearly marked as such, and if the derived work is
11 .\" incompatible with the protocol description in the RFC file, it must be
12 .\" called by a name other than "ssh" or "Secure Shell".
14 .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
15 .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
16 .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
18 .\" Redistribution and use in source and binary forms, with or without
19 .\" modification, are permitted provided that the following conditions
21 .\" 1. Redistributions of source code must retain the above copyright
22 .\" notice, this list of conditions and the following disclaimer.
23 .\" 2. Redistributions in binary form must reproduce the above copyright
24 .\" notice, this list of conditions and the following disclaimer in the
25 .\" documentation and/or other materials provided with the distribution.
27 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
28 .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
29 .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
30 .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
31 .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
32 .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
33 .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
34 .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
35 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
36 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
38 .Dd $Mdocdate: April 24 2015 $
43 .Nd authentication agent
48 .Op Fl a Ar bind_address
49 .Op Fl E Ar fingerprint_hash
51 .Op Ar command Op Ar arg ...
57 is a program to hold private keys used for public key authentication
58 (RSA, DSA, ECDSA, Ed25519).
60 is usually started in the beginning of an X-session or a login session, and
61 all other windows or programs are started as clients to the ssh-agent
63 Through use of environment variables the agent can be located
64 and automatically used for authentication when logging in to other
68 The agent initially does not have any private keys.
71 Multiple identities may be stored in
75 will automatically use them if present.
77 is also used to remove keys from
79 and to query the keys that are held in one.
81 The options are as follows:
83 .It Fl a Ar bind_address
89 .Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
91 Generate C-shell commands on
93 This is the default if
95 looks like it's a csh style of shell.
98 When this option is specified
103 When this option is specified
105 will not fork and will write debug information to standard error.
106 .It Fl E Ar fingerprint_hash
107 Specifies the hash algorithm used when displaying key fingerprints.
115 Kill the current agent (given by the
117 environment variable).
119 Generate Bourne shell commands on
121 This is the default if
123 does not look like it's a csh style of shell.
125 Set a default value for the maximum lifetime of identities added to the agent.
126 The lifetime may be specified in seconds or in a time format specified in
128 A lifetime specified for an identity with
130 overrides this value.
131 Without this option the default maximum lifetime is forever.
133 Exit after the last client has disconnected.
136 If a commandline is given, this is executed as a subprocess of the agent.
137 When the command dies, so does the agent.
139 The idea is that the agent is run in the user's local PC, laptop, or
141 Authentication data need not be stored on any other
142 machine, and authentication passphrases never go over the network.
143 However, the connection to the agent is forwarded over SSH
144 remote logins, and the user can thus use the privileges given by the
145 identities anywhere in the network in a secure way.
147 There are two main ways to get an agent set up:
148 The first is that the agent starts a new subcommand into which some environment
149 variables are exported, eg
150 .Cm ssh-agent xterm & .
151 The second is that the agent prints the needed shell commands (either
155 syntax can be generated) which can be evaluated in the calling shell, eg
156 .Cm eval `ssh-agent -s`
157 for Bourne-type shells such as
162 .Cm eval `ssh-agent -c`
169 looks at these variables and uses them to establish a connection to the agent.
171 The agent will never send a private key over its request channel.
172 Instead, operations that require a private key will be performed
173 by the agent, and the result will be returned to the requester.
174 This way, private keys are not exposed to clients using the agent.
178 socket is created and the name of this socket is stored in the
182 The socket is made accessible only to the current user.
183 This method is easily abused by root or another instance of the same
188 environment variable holds the agent's process ID.
190 The agent exits automatically when the command given on the command
194 .It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt
196 sockets used to contain the connection to the authentication agent.
197 These sockets should only be readable by the owner.
198 The sockets should get automatically removed when the agent exits.
206 OpenSSH is a derivative of the original and free
207 ssh 1.2.12 release by Tatu Ylonen.
208 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
209 Theo de Raadt and Dug Song
210 removed many bugs, re-added newer features and
212 Markus Friedl contributed the support for SSH
213 protocol versions 1.5 and 2.0.