1 .\" $OpenBSD: ssh-agent.1,v 1.79 2023/08/10 14:37:32 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: August 10 2023 $
42 .Nd OpenSSH authentication agent
47 .Op Fl a Ar bind_address
48 .Op Fl E Ar fingerprint_hash
50 .Op Fl P Ar allowed_providers
53 .Op Fl a Ar bind_address
54 .Op Fl E Ar fingerprint_hash
56 .Op Fl P Ar allowed_providers
58 .Ar command Op Ar arg ...
64 is a program to hold private keys used for public key authentication.
65 Through use of environment variables the agent can be located
66 and automatically used for authentication when logging in to other
70 The options are as follows:
72 .It Fl a Ar bind_address
78 .Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
80 Generate C-shell commands on
82 This is the default if
84 looks like it's a csh style of shell.
87 When this option is specified,
92 When this option is specified,
94 will not fork and will write debug information to standard error.
95 .It Fl E Ar fingerprint_hash
96 Specifies the hash algorithm used when displaying key fingerprints.
104 Kill the current agent (given by the
106 environment variable).
108 Specify an option when starting
110 Currently two options are supported:
111 .Cm allow-remote-pkcs11
113 .Cm no-restrict-websafe .
116 .Cm allow-remote-pkcs11
117 option allows clients of a forwarded
119 to load PKCS#11 or FIDO provider libraries.
120 By default only local clients may perform this operation.
121 Note that signalling that an
123 client is remote is performed by
125 and use of other tools to forward access to the agent socket may circumvent
129 .Cm no-restrict-websafe
132 to permit signatures using FIDO keys that might be web authentication
136 refuses signature requests for FIDO keys where the key application string
139 and when the data to be signed does not appear to be a
141 user authentication request or a
144 The default behaviour prevents forwarded access to a FIDO key from also
145 implicitly forwarding the ability to authenticate to websites.
146 .It Fl P Ar allowed_providers
147 Specify a pattern-list of acceptable paths for PKCS#11 provider and FIDO
148 authenticator middleware shared libraries that may be used with the
154 Libraries that do not match the pattern list will be refused.
157 for a description of pattern-list syntax.
159 .Dq usr/lib*/*,/usr/local/lib*/* .
161 Generate Bourne shell commands on
163 This is the default if
165 does not look like it's a csh style of shell.
167 Set a default value for the maximum lifetime of identities added to the agent.
168 The lifetime may be specified in seconds or in a time format specified in
170 A lifetime specified for an identity with
172 overrides this value.
173 Without this option the default maximum lifetime is forever.
174 .It Ar command Op Ar arg ...
175 If a command (and optional arguments) is given,
176 this is executed as a subprocess of the agent.
177 The agent exits automatically when the command given on the command
181 There are two main ways to get an agent set up.
182 The first is at the start of an X session,
183 where all other windows or programs are started as children of the
186 The agent starts a command under which its environment
187 variables are exported, for example
188 .Cm ssh-agent xterm & .
189 When the command terminates, so does the agent.
191 The second method is used for a login session.
195 it prints the shell commands required to set its environment variables,
196 which in turn can be evaluated in the calling shell, for example
197 .Cm eval `ssh-agent -s` .
201 looks at these environment variables
202 and uses them to establish a connection to the agent.
204 The agent initially does not have any private keys.
213 Multiple identities may be stored in
217 will automatically use them if present.
219 is also used to remove keys from
221 and to query the keys that are held in one.
225 may be forwarded from further remote hosts using the
229 (but see the caveats documented therein),
230 avoiding the need for authentication data to be stored on other machines.
231 Authentication passphrases and private keys never go over the network:
232 the connection to the agent is forwarded over SSH remote connections
233 and the result is returned to the requester,
234 allowing the user access to their identities anywhere in the network
237 .Bl -tag -width "SSH_AGENT_PID"
241 starts, it stores the name of the agent's process ID (PID) in this variable.
247 socket and stores its pathname in this variable.
248 It is accessible only to the current user,
249 but is easily abused by root or another instance of the same user.
253 .It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>
255 sockets used to contain the connection to the authentication agent.
256 These sockets should only be readable by the owner.
257 The sockets should get automatically removed when the agent exits.
267 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
269 .An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos , Theo de Raadt
272 removed many bugs, re-added newer features and created OpenSSH.
274 contributed the support for SSH protocol versions 1.5 and 2.0.