1 .\" $OpenBSD: ssh-agent.1,v 1.64 2016/11/30 06:54:26 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: November 30 2016 $
43 .Nd authentication agent
48 .Op Fl a Ar bind_address
49 .Op Fl E Ar fingerprint_hash
50 .Op Fl P Ar pkcs11_whitelist
52 .Op Ar command Op Ar arg ...
58 is a program to hold private keys used for public key authentication
59 (RSA, DSA, ECDSA, Ed25519).
61 is usually started in the beginning of an X-session or a login session, and
62 all other windows or programs are started as clients to the ssh-agent
64 Through use of environment variables the agent can be located
65 and automatically used for authentication when logging in to other
69 The agent initially does not have any private keys.
79 Multiple identities may be stored in
83 will automatically use them if present.
85 is also used to remove keys from
87 and to query the keys that are held in one.
89 The options are as follows:
91 .It Fl a Ar bind_address
97 .Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
99 Generate C-shell commands on
101 This is the default if
103 looks like it's a csh style of shell.
106 When this option is specified
111 When this option is specified
113 will not fork and will write debug information to standard error.
114 .It Fl E Ar fingerprint_hash
115 Specifies the hash algorithm used when displaying key fingerprints.
123 Kill the current agent (given by the
125 environment variable).
126 .It Fl P Ar pkcs11_whitelist
127 Specify a pattern-list of acceptable paths for PKCS#11 shared libraries
128 that may be added using the
132 The default is to allow loading PKCS#11 libraries from
133 .Dq /usr/lib/*,/usr/local/lib/* .
134 PKCS#11 libraries that do not match the whitelist will be refused.
137 for a description of pattern-list syntax.
139 Generate Bourne shell commands on
141 This is the default if
143 does not look like it's a csh style of shell.
145 Set a default value for the maximum lifetime of identities added to the agent.
146 The lifetime may be specified in seconds or in a time format specified in
148 A lifetime specified for an identity with
150 overrides this value.
151 Without this option the default maximum lifetime is forever.
153 Exit after the last client has disconnected.
156 If a command line is given, this is executed as a subprocess of the agent.
157 When the command dies, so does the agent.
159 The idea is that the agent is run in the user's local PC, laptop, or
161 Authentication data need not be stored on any other
162 machine, and authentication passphrases never go over the network.
163 However, the connection to the agent is forwarded over SSH
164 remote logins, and the user can thus use the privileges given by the
165 identities anywhere in the network in a secure way.
167 There are two main ways to get an agent set up:
168 The first is that the agent starts a new subcommand into which some environment
169 variables are exported, eg
170 .Cm ssh-agent xterm & .
171 The second is that the agent prints the needed shell commands (either
175 syntax can be generated) which can be evaluated in the calling shell, eg
176 .Cm eval `ssh-agent -s`
177 for Bourne-type shells such as
182 .Cm eval `ssh-agent -c`
189 looks at these variables and uses them to establish a connection to the agent.
191 The agent will never send a private key over its request channel.
192 Instead, operations that require a private key will be performed
193 by the agent, and the result will be returned to the requester.
194 This way, private keys are not exposed to clients using the agent.
198 socket is created and the name of this socket is stored in the
202 The socket is made accessible only to the current user.
203 This method is easily abused by root or another instance of the same
208 environment variable holds the agent's process ID.
210 The agent exits automatically when the command given on the command
214 .It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>
216 sockets used to contain the connection to the authentication agent.
217 These sockets should only be readable by the owner.
218 The sockets should get automatically removed when the agent exits.
227 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
229 .An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos , Theo de Raadt
232 removed many bugs, re-added newer features and created OpenSSH.
234 contributed the support for SSH protocol versions 1.5 and 2.0.