| blob | f1b877790949d32fd4a5f68c85820a6c15355f89 |
1 .\" $OpenBSD: ssh-agent.1,v 1.44 2006/07/18 08:03:09 jmc Exp $
2 .\"
3 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 .\" All rights reserved
6 .\"
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".
12 .\"
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.
16 .\"
17 .\" Redistribution and use in source and binary forms, with or without
18 .\" modification, are permitted provided that the following conditions
19 .\" are met:
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.
25 .\"
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.
36 .\"
37 .Dd September 25, 1999
38 .Dt SSH-AGENT 1
39 .Os
40 .Sh NAME
41 .Nm ssh-agent
42 .Nd authentication agent
43 .Sh SYNOPSIS
44 .Nm ssh-agent
45 .Op Fl a Ar bind_address
46 .Op Fl c Li | Fl s
47 .Op Fl t Ar life
48 .Op Fl d
49 .Op Ar command Op Ar args ...
50 .Nm ssh-agent
51 .Op Fl c Li | Fl s
52 .Fl k
53 .Sh DESCRIPTION
54 .Nm
55 is a program to hold private keys used for public key authentication
56 (RSA, DSA).
57 The idea is that
58 .Nm
59 is started in the beginning of an X-session or a login session, and
60 all other windows or programs are started as clients to the ssh-agent
61 program.
62 Through use of environment variables the agent can be located
63 and automatically used for authentication when logging in to other
64 machines using
65 .Xr ssh 1 .
66 .Pp
67 The options are as follows:
68 .Bl -tag -width Ds
69 .It Fl a Ar bind_address
70 Bind the agent to the unix-domain socket
71 .Ar bind_address .
72 The default is
73 .Pa /tmp/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
74 .It Fl c
75 Generate C-shell commands on
76 .Dv stdout .
77 This is the default if
78 .Ev SHELL
79 looks like it's a csh style of shell.
80 .It Fl s
81 Generate Bourne shell commands on
82 .Dv stdout .
83 This is the default if
84 .Ev SHELL
85 does not look like it's a csh style of shell.
86 .It Fl k
87 Kill the current agent (given by the
88 .Ev SSH_AGENT_PID
89 environment variable).
90 .It Fl t Ar life
91 Set a default value for the maximum lifetime of identities added to the agent.
92 The lifetime may be specified in seconds or in a time format specified in
93 .Xr sshd_config 5 .
94 A lifetime specified for an identity with
95 .Xr ssh-add 1
96 overrides this value.
97 Without this option the default maximum lifetime is forever.
98 .It Fl d
99 Debug mode.
100 When this option is specified
101 .Nm
102 will not fork.
103 .El
104 .Pp
105 If a commandline is given, this is executed as a subprocess of the agent.
106 When the command dies, so does the agent.
107 .Pp
108 The agent initially does not have any private keys.
109 Keys are added using
110 .Xr ssh-add 1 .
111 When executed without arguments,
112 .Xr ssh-add 1
113 adds the files
114 .Pa ~/.ssh/id_rsa ,
115 .Pa ~/.ssh/id_dsa
116 and
117 .Pa ~/.ssh/identity .
118 If the identity has a passphrase,
119 .Xr ssh-add 1
120 asks for the passphrase (using a small X11 application if running
121 under X11, or from the terminal if running without X).
122 It then sends the identity to the agent.
123 Several identities can be stored in the
124 agent; the agent can automatically use any of these identities.
125 .Ic ssh-add -l
126 displays the identities currently held by the agent.
127 .Pp
128 The idea is that the agent is run in the user's local PC, laptop, or
129 terminal.
130 Authentication data need not be stored on any other
131 machine, and authentication passphrases never go over the network.
132 However, the connection to the agent is forwarded over SSH
133 remote logins, and the user can thus use the privileges given by the
134 identities anywhere in the network in a secure way.
135 .Pp
136 There are two main ways to get an agent set up:
137 The first is that the agent starts a new subcommand into which some environment
138 variables are exported, eg
139 .Cm ssh-agent xterm & .
140 The second is that the agent prints the needed shell commands (either
141 .Xr sh 1
142 or
143 .Xr csh 1
144 syntax can be generated) which can be evalled in the calling shell, eg
145 .Cm eval `ssh-agent -s`
146 for Bourne-type shells such as
147 .Xr sh 1
148 or
149 .Xr ksh 1
150 and
151 .Cm eval `ssh-agent -c`
152 for
153 .Xr csh 1
154 and derivatives.
155 .Pp
156 Later
157 .Xr ssh 1
158 looks at these variables and uses them to establish a connection to the agent.
159 .Pp
160 The agent will never send a private key over its request channel.
161 Instead, operations that require a private key will be performed
162 by the agent, and the result will be returned to the requester.
163 This way, private keys are not exposed to clients using the agent.
164 .Pp
165 A unix-domain socket is created
166 and the name of this socket is stored in the
167 .Ev SSH_AUTH_SOCK
168 environment
169 variable.
170 The socket is made accessible only to the current user.
171 This method is easily abused by root or another instance of the same
172 user.
173 .Pp
174 The
175 .Ev SSH_AGENT_PID
176 environment variable holds the agent's process ID.
177 .Pp
178 The agent exits automatically when the command given on the command
179 line terminates.
180 .Sh FILES
181 .Bl -tag -width Ds
182 .It Pa ~/.ssh/identity
183 Contains the protocol version 1 RSA authentication identity of the user.
184 .It Pa ~/.ssh/id_dsa
185 Contains the protocol version 2 DSA authentication identity of the user.
186 .It Pa ~/.ssh/id_rsa
187 Contains the protocol version 2 RSA authentication identity of the user.
188 .It Pa /tmp/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt
189 Unix-domain sockets used to contain the connection to the
190 authentication agent.
191 These sockets should only be readable by the owner.
192 The sockets should get automatically removed when the agent exits.
193 .El
194 .Sh SEE ALSO
195 .Xr ssh 1 ,
196 .Xr ssh-add 1 ,
197 .Xr ssh-keygen 1 ,
198 .Xr sshd 8
199 .Sh AUTHORS
200 OpenSSH is a derivative of the original and free
201 ssh 1.2.12 release by Tatu Ylonen.
202 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
203 Theo de Raadt and Dug Song
204 removed many bugs, re-added newer features and
205 created OpenSSH.
206 Markus Friedl contributed the support for SSH
207 protocol versions 1.5 and 2.0.