1 .\" $OpenBSD: ssh-agent.1,v 1.64 2016/11/30 06:54:26 jmc 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: November 30 2016 $
42 .Nd authentication agent
47 .Op Fl a Ar bind_address
48 .Op Fl E Ar fingerprint_hash
49 .Op Fl P Ar pkcs11_whitelist
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.
78 Multiple identities may be stored in
82 will automatically use them if present.
84 is also used to remove keys from
86 and to query the keys that are held in one.
88 The options are as follows:
90 .It Fl a Ar bind_address
96 .Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
98 Generate C-shell commands on
100 This is the default if
102 looks like it's a csh style of shell.
105 When this option is specified
110 When this option is specified
112 will not fork and will write debug information to standard error.
113 .It Fl E Ar fingerprint_hash
114 Specifies the hash algorithm used when displaying key fingerprints.
122 Kill the current agent (given by the
124 environment variable).
125 .It Fl P Ar pkcs11_whitelist
126 Specify a pattern-list of acceptable paths for PKCS#11 shared libraries
127 that may be added using the
131 The default is to allow loading PKCS#11 libraries from
132 .Dq /usr/lib/*,/usr/local/lib/* .
133 PKCS#11 libraries that do not match the whitelist will be refused.
136 for a description of pattern-list syntax.
138 Generate Bourne shell commands on
140 This is the default if
142 does not look like it's a csh style of shell.
144 Set a default value for the maximum lifetime of identities added to the agent.
145 The lifetime may be specified in seconds or in a time format specified in
147 A lifetime specified for an identity with
149 overrides this value.
150 Without this option the default maximum lifetime is forever.
153 If a command line is given, this is executed as a subprocess of the agent.
154 When the command dies, so does the agent.
156 The idea is that the agent is run in the user's local PC, laptop, or
158 Authentication data need not be stored on any other
159 machine, and authentication passphrases never go over the network.
160 However, the connection to the agent is forwarded over SSH
161 remote logins, and the user can thus use the privileges given by the
162 identities anywhere in the network in a secure way.
164 There are two main ways to get an agent set up:
165 The first is that the agent starts a new subcommand into which some environment
166 variables are exported, eg
167 .Cm ssh-agent xterm & .
168 The second is that the agent prints the needed shell commands (either
172 syntax can be generated) which can be evaluated in the calling shell, eg
173 .Cm eval `ssh-agent -s`
174 for Bourne-type shells such as
179 .Cm eval `ssh-agent -c`
186 looks at these variables and uses them to establish a connection to the agent.
188 The agent will never send a private key over its request channel.
189 Instead, operations that require a private key will be performed
190 by the agent, and the result will be returned to the requester.
191 This way, private keys are not exposed to clients using the agent.
195 socket is created and the name of this socket is stored in the
199 The socket is made accessible only to the current user.
200 This method is easily abused by root or another instance of the same
205 environment variable holds the agent's process ID.
207 The agent exits automatically when the command given on the command
211 .It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>
213 sockets used to contain the connection to the authentication agent.
214 These sockets should only be readable by the owner.
215 The sockets should get automatically removed when the agent exits.
224 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
226 .An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos , Theo de Raadt
229 removed many bugs, re-added newer features and created OpenSSH.
231 contributed the support for SSH protocol versions 1.5 and 2.0.