1 .\" $OpenBSD: ssh-agent.1,v 1.70 2019/12/21 20:22:34 naddy 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 2019 $
42 .Nd OpenSSH authentication agent
47 .Op Fl a Ar bind_address
48 .Op Fl E Ar fingerprint_hash
49 .Op Fl P Ar provider_whitelist
51 .Op Ar command Op Ar arg ...
57 is a program to hold private keys used for public key authentication.
58 Through use of environment variables the agent can be located
59 and automatically used for authentication when logging in to other
63 The options are as follows:
65 .It Fl a Ar bind_address
71 .Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
73 Generate C-shell commands on
75 This is the default if
77 looks like it's a csh style of shell.
80 When this option is specified
85 When this option is specified
87 will not fork and will write debug information to standard error.
88 .It Fl E Ar fingerprint_hash
89 Specifies the hash algorithm used when displaying key fingerprints.
97 Kill the current agent (given by the
99 environment variable).
100 .It Fl P Ar provider_whitelist
101 Specify a pattern-list of acceptable paths for PKCS#11 and FIDO authenticator
102 shared libraries that may be used with the
108 Libraries that do not match the whitelist will be refused.
111 for a description of pattern-list syntax.
112 The default whitelist is
113 .Dq /usr/lib/*,/usr/local/lib/* .
115 Generate Bourne shell commands on
117 This is the default if
119 does not look like it's a csh style of shell.
121 Set a default value for the maximum lifetime of identities added to the agent.
122 The lifetime may be specified in seconds or in a time format specified in
124 A lifetime specified for an identity with
126 overrides this value.
127 Without this option the default maximum lifetime is forever.
128 .It Ar command Op Ar arg ...
129 If a command (and optional arguments) is given,
130 this is executed as a subprocess of the agent.
131 The agent exits automatically when the command given on the command
135 There are two main ways to get an agent set up.
136 The first is at the start of an X session,
137 where all other windows or programs are started as children of the
140 The agent starts a command under which its environment
141 variables are exported, for example
142 .Cm ssh-agent xterm & .
143 When the command terminates, so does the agent.
145 The second method is used for a login session.
149 it prints the shell commands required to set its environment variables,
150 which in turn can be evaluated in the calling shell, for example
151 .Cm eval `ssh-agent -s` .
155 looks at these environment variables and uses them to establish a connection to the agent.
157 The agent initially does not have any private keys.
166 Multiple identities may be stored in
170 will automatically use them if present.
172 is also used to remove keys from
174 and to query the keys that are held in one.
178 may be forwarded from further remote hosts using the
182 (but see the caveats documented therein),
183 avoiding the need for authentication data to be stored on other machines.
184 Authentication passphrases and private keys never go over the network:
185 the connection to the agent is forwarded over SSH remote connections
186 and the result is returned to the requester,
187 allowing the user access to their identities anywhere in the network
190 .Bl -tag -width "SSH_AGENT_PID"
194 starts, it stores the name of the agent's process ID (PID) in this variable.
200 socket and stores its pathname in this variable.
201 It is accessible only to the current user,
202 but is easily abused by root or another instance of the same user.
206 .It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>
208 sockets used to contain the connection to the authentication agent.
209 These sockets should only be readable by the owner.
210 The sockets should get automatically removed when the agent exits.
220 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
222 .An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos , Theo de Raadt
225 removed many bugs, re-added newer features and created OpenSSH.
227 contributed the support for SSH protocol versions 1.5 and 2.0.