xref: /freebsd/crypto/openssh/ssh-agent.1 (revision 271c3a9060f2ee55607ebe146523f888e1db2654)
1.\" $OpenBSD: ssh-agent.1,v 1.46 2007/09/09 11:38:01 sobrado 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,
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35.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36.\"
37.Dd $Mdocdate: June 5 2007 $
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 c Li | Fl s
46.Op Fl d
47.Op Fl a Ar bind_address
48.Op Fl t Ar life
49.Op Ar command Op Ar arg ...
50.Nm ssh-agent
51.Op Fl c Li | Fl s
52.Fl k
53.Sh DESCRIPTION
54.Nm
55is a program to hold private keys used for public key authentication
56(RSA, DSA).
57The idea is that
58.Nm
59is started in the beginning of an X-session or a login session, and
60all other windows or programs are started as clients to the ssh-agent
61program.
62Through use of environment variables the agent can be located
63and automatically used for authentication when logging in to other
64machines using
65.Xr ssh 1 .
66.Pp
67The options are as follows:
68.Bl -tag -width Ds
69.It Fl a Ar bind_address
70Bind the agent to the unix-domain socket
71.Ar bind_address .
72The default is
73.Pa /tmp/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
74.It Fl c
75Generate C-shell commands on
76.Dv stdout .
77This is the default if
78.Ev SHELL
79looks like it's a csh style of shell.
80.It Fl d
81Debug mode.
82When this option is specified
83.Nm
84will not fork.
85.It Fl k
86Kill the current agent (given by the
87.Ev SSH_AGENT_PID
88environment variable).
89.It Fl s
90Generate Bourne shell commands on
91.Dv stdout .
92This is the default if
93.Ev SHELL
94does not look like it's a csh style of shell.
95.It Fl t Ar life
96Set a default value for the maximum lifetime of identities added to the agent.
97The lifetime may be specified in seconds or in a time format specified in
98.Xr sshd_config 5 .
99A lifetime specified for an identity with
100.Xr ssh-add 1
101overrides this value.
102Without this option the default maximum lifetime is forever.
103.El
104.Pp
105If a commandline is given, this is executed as a subprocess of the agent.
106When the command dies, so does the agent.
107.Pp
108The agent initially does not have any private keys.
109Keys are added using
110.Xr ssh-add 1 .
111When executed without arguments,
112.Xr ssh-add 1
113adds the files
114.Pa ~/.ssh/id_rsa ,
115.Pa ~/.ssh/id_dsa
116and
117.Pa ~/.ssh/identity .
118If the identity has a passphrase,
119.Xr ssh-add 1
120asks for the passphrase (using a small X11 application if running
121under X11, or from the terminal if running without X).
122It then sends the identity to the agent.
123Several identities can be stored in the
124agent; the agent can automatically use any of these identities.
125.Ic ssh-add -l
126displays the identities currently held by the agent.
127.Pp
128The idea is that the agent is run in the user's local PC, laptop, or
129terminal.
130Authentication data need not be stored on any other
131machine, and authentication passphrases never go over the network.
132However, the connection to the agent is forwarded over SSH
133remote logins, and the user can thus use the privileges given by the
134identities anywhere in the network in a secure way.
135.Pp
136There are two main ways to get an agent set up:
137The first is that the agent starts a new subcommand into which some environment
138variables are exported, eg
139.Cm ssh-agent xterm & .
140The second is that the agent prints the needed shell commands (either
141.Xr sh 1
142or
143.Xr csh 1
144syntax can be generated) which can be evalled in the calling shell, eg
145.Cm eval `ssh-agent -s`
146for Bourne-type shells such as
147.Xr sh 1
148or
149.Xr ksh 1
150and
151.Cm eval `ssh-agent -c`
152for
153.Xr csh 1
154and derivatives.
155.Pp
156Later
157.Xr ssh 1
158looks at these variables and uses them to establish a connection to the agent.
159.Pp
160The agent will never send a private key over its request channel.
161Instead, operations that require a private key will be performed
162by the agent, and the result will be returned to the requester.
163This way, private keys are not exposed to clients using the agent.
164.Pp
165A unix-domain socket is created
166and the name of this socket is stored in the
167.Ev SSH_AUTH_SOCK
168environment
169variable.
170The socket is made accessible only to the current user.
171This method is easily abused by root or another instance of the same
172user.
173.Pp
174The
175.Ev SSH_AGENT_PID
176environment variable holds the agent's process ID.
177.Pp
178The agent exits automatically when the command given on the command
179line terminates.
180.Sh FILES
181.Bl -tag -width Ds
182.It Pa ~/.ssh/identity
183Contains the protocol version 1 RSA authentication identity of the user.
184.It Pa ~/.ssh/id_dsa
185Contains the protocol version 2 DSA authentication identity of the user.
186.It Pa ~/.ssh/id_rsa
187Contains the protocol version 2 RSA authentication identity of the user.
188.It Pa /tmp/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt
189Unix-domain sockets used to contain the connection to the
190authentication agent.
191These sockets should only be readable by the owner.
192The 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
200OpenSSH is a derivative of the original and free
201ssh 1.2.12 release by Tatu Ylonen.
202Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
203Theo de Raadt and Dug Song
204removed many bugs, re-added newer features and
205created OpenSSH.
206Markus Friedl contributed the support for SSH
207protocol versions 1.5 and 2.0.
208