1 .\" $OpenBSD: ssh-agent.1,v 1.54 2013/12/07 11:58:46 naddy 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.
43 .Nd authentication agent
48 .Op Fl a Ar bind_address
50 .Op Ar command Op Ar arg ...
56 is a program to hold private keys used for public key authentication
57 (RSA, DSA, ECDSA, ED25519).
60 is 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 options are as follows:
70 .It Fl a Ar bind_address
76 .Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
78 Generate C-shell commands on
80 This is the default if
82 looks like it's a csh style of shell.
85 When this option is specified
89 Kill the current agent (given by the
91 environment variable).
93 Generate Bourne shell commands on
95 This is the default if
97 does not look like it's a csh style of shell.
99 Set a default value for the maximum lifetime of identities added to the agent.
100 The lifetime may be specified in seconds or in a time format specified in
102 A lifetime specified for an identity with
104 overrides this value.
105 Without this option the default maximum lifetime is forever.
107 Exit after the last client has disconnected.
110 If a commandline is given, this is executed as a subprocess of the agent.
111 When the command dies, so does the agent.
113 The agent initially does not have any private keys.
116 When executed without arguments,
121 .Pa ~/.ssh/id_ecdsa ,
122 .Pa ~/.ssh/id_ed25519
124 .Pa ~/.ssh/identity .
125 If the identity has a passphrase,
127 asks for the passphrase on the terminal if it has one or from a small X11
128 program if running under X11.
129 If neither of these is the case then the authentication will fail.
130 It then sends the identity to the agent.
131 Several identities can be stored in the
132 agent; the agent can automatically use any of these identities.
134 displays the identities currently held by the agent.
136 The idea is that the agent is run in the user's local PC, laptop, or
138 Authentication data need not be stored on any other
139 machine, and authentication passphrases never go over the network.
140 However, the connection to the agent is forwarded over SSH
141 remote logins, and the user can thus use the privileges given by the
142 identities anywhere in the network in a secure way.
144 There are two main ways to get an agent set up:
145 The first is that the agent starts a new subcommand into which some environment
146 variables are exported, eg
147 .Cm ssh-agent xterm & .
148 The second is that the agent prints the needed shell commands (either
152 syntax can be generated) which can be evaluated in the calling shell, eg
153 .Cm eval `ssh-agent -s`
154 for Bourne-type shells such as
159 .Cm eval `ssh-agent -c`
166 looks at these variables and uses them to establish a connection to the agent.
168 The agent will never send a private key over its request channel.
169 Instead, operations that require a private key will be performed
170 by the agent, and the result will be returned to the requester.
171 This way, private keys are not exposed to clients using the agent.
175 socket is created and the name of this socket is stored in the
179 The socket is made accessible only to the current user.
180 This method is easily abused by root or another instance of the same
185 environment variable holds the agent's process ID.
187 The agent exits automatically when the command given on the command
191 .It Pa ~/.ssh/identity
192 Contains the protocol version 1 RSA authentication identity of the user.
194 Contains the protocol version 2 DSA authentication identity of the user.
195 .It Pa ~/.ssh/id_ecdsa
196 Contains the protocol version 2 ECDSA authentication identity of the user.
197 .It Pa ~/.ssh/id_ed25519
198 Contains the protocol version 2 ED25519 authentication identity of the user.
200 Contains the protocol version 2 RSA authentication identity of the user.
201 .It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt
203 sockets used to contain the connection to the authentication agent.
204 These sockets should only be readable by the owner.
205 The sockets should get automatically removed when the agent exits.
213 OpenSSH is a derivative of the original and free
214 ssh 1.2.12 release by Tatu Ylonen.
215 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
216 Theo de Raadt and Dug Song
217 removed many bugs, re-added newer features and
219 Markus Friedl contributed the support for SSH
220 protocol versions 1.5 and 2.0.