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Damien Miller393821a2006-07-24 14:04:53 +10001.\" $OpenBSD: ssh-agent.1,v 1.44 2006/07/18 08:03:09 jmc Exp $
Damien Miller32aa1441999-10-29 09:15:49 +10002.\"
3.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
Damien Miller32aa1441999-10-29 09:15:49 +10004.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5.\" All rights reserved
6.\"
Damien Millere4340be2000-09-16 13:29:08 +11007.\" 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.\"
Ben Lindstrom92a2e382001-03-05 06:59:27 +000013.\" 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.
Damien Millere4340be2000-09-16 13:29:08 +110016.\"
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.
Damien Miller32aa1441999-10-29 09:15:49 +100036.\"
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
Damien Miller22c77262000-04-13 12:26:34 +100044.Nm ssh-agent
Ben Lindstromb7788f32002-06-06 21:46:08 +000045.Op Fl a Ar bind_address
Ben Lindstromba1fa1d2001-09-12 17:02:49 +000046.Op Fl c Li | Fl s
Damien Miller53d81482003-01-22 11:47:19 +110047.Op Fl t Ar life
Ben Lindstromba1fa1d2001-09-12 17:02:49 +000048.Op Fl d
49.Op Ar command Op Ar args ...
Ben Lindstrom14920292000-11-21 21:24:55 +000050.Nm ssh-agent
51.Op Fl c Li | Fl s
Ben Lindstrom14920292000-11-21 21:24:55 +000052.Fl k
Damien Miller22c77262000-04-13 12:26:34 +100053.Sh DESCRIPTION
Damien Miller32aa1441999-10-29 09:15:49 +100054.Nm
Damien Millerad833b32000-08-23 10:46:23 +100055is a program to hold private keys used for public key authentication
56(RSA, DSA).
Damien Miller450a7a12000-03-26 13:04:51 +100057The idea is that
Damien Miller32aa1441999-10-29 09:15:49 +100058.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
Damien Miller450a7a12000-03-26 13:04:51 +100061program.
62Through use of environment variables the agent can be located
Damien Millerad833b32000-08-23 10:46:23 +100063and automatically used for authentication when logging in to other
Damien Miller32aa1441999-10-29 09:15:49 +100064machines using
65.Xr ssh 1 .
66.Pp
67The options are as follows:
68.Bl -tag -width Ds
Ben Lindstromb7788f32002-06-06 21:46:08 +000069.It Fl a Ar bind_address
70Bind the agent to the unix-domain socket
71.Ar bind_address .
72The default is
Damien Miller393821a2006-07-24 14:04:53 +100073.Pa /tmp/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
Damien Miller32aa1441999-10-29 09:15:49 +100074.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 s
81Generate Bourne shell commands on
82.Dv stdout .
83This is the default if
84.Ev SHELL
85does not look like it's a csh style of shell.
86.It Fl k
87Kill the current agent (given by the
88.Ev SSH_AGENT_PID
89environment variable).
Damien Miller53d81482003-01-22 11:47:19 +110090.It Fl t Ar life
Damien Miller495dca32003-04-01 21:42:14 +100091Set a default value for the maximum lifetime of identities added to the agent.
Damien Miller53d81482003-01-22 11:47:19 +110092The lifetime may be specified in seconds or in a time format specified in
Darren Tucker3a4634f2005-11-28 17:05:40 +110093.Xr sshd_config 5 .
Damien Miller53d81482003-01-22 11:47:19 +110094A lifetime specified for an identity with
95.Xr ssh-add 1
96overrides this value.
97Without this option the default maximum lifetime is forever.
Ben Lindstromd94580c2001-07-04 03:48:02 +000098.It Fl d
Damien Miller495dca32003-04-01 21:42:14 +100099Debug mode.
100When this option is specified
Ben Lindstromd94580c2001-07-04 03:48:02 +0000101.Nm
Ben Lindstroma4a53232001-07-18 15:51:00 +0000102will not fork.
Damien Miller32aa1441999-10-29 09:15:49 +1000103.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
Damien Miller450a7a12000-03-26 13:04:51 +1000108The agent initially does not have any private keys.
109Keys are added using
Damien Miller32aa1441999-10-29 09:15:49 +1000110.Xr ssh-add 1 .
Damien Miller22c77262000-04-13 12:26:34 +1000111When executed without arguments,
Damien Miller32aa1441999-10-29 09:15:49 +1000112.Xr ssh-add 1
Damien Millerd2b8f162002-02-05 12:24:19 +1100113adds the files
Damien Miller167ea5d2005-05-26 12:04:02 +1000114.Pa ~/.ssh/id_rsa ,
115.Pa ~/.ssh/id_dsa
Damien Millerd2b8f162002-02-05 12:24:19 +1100116and
Damien Miller167ea5d2005-05-26 12:04:02 +1000117.Pa ~/.ssh/identity .
Damien Miller22c77262000-04-13 12:26:34 +1000118If the identity has a passphrase,
Damien Miller32aa1441999-10-29 09:15:49 +1000119.Xr ssh-add 1
120asks for the passphrase (using a small X11 application if running
Damien Miller450a7a12000-03-26 13:04:51 +1000121under X11, or from the terminal if running without X).
122It then sends the identity to the agent.
123Several identities can be stored in the
Damien Miller32aa1441999-10-29 09:15:49 +1000124agent; 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
Damien Miller450a7a12000-03-26 13:04:51 +1000129terminal.
130Authentication data need not be stored on any other
Damien Miller32aa1441999-10-29 09:15:49 +1000131machine, 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
Damien Millerabbae982003-05-15 10:16:21 +1000136There are two main ways to get an agent set up:
Darren Tuckera86b4532004-05-13 16:45:46 +1000137The 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
Damien Miller32aa1441999-10-29 09:15:49 +1000141.Xr sh 1
142or
143.Xr csh 1
Darren Tuckera86b4532004-05-13 16:45:46 +1000144syntax 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
Darren Tuckerfc959702004-07-17 16:12:08 +1000151.Cm eval `ssh-agent -c`
Darren Tuckera86b4532004-05-13 16:45:46 +1000152for
153.Xr csh 1
154and derivatives.
155.Pp
Damien Miller32aa1441999-10-29 09:15:49 +1000156Later
157.Xr ssh 1
Ben Lindstrom0d3e8fa2001-04-04 01:51:25 +0000158looks at these variables and uses them to establish a connection to the agent.
Damien Miller32aa1441999-10-29 09:15:49 +1000159.Pp
Ben Lindstrom11f790b2001-12-06 16:37:51 +0000160The 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
Damien Miller32aa1441999-10-29 09:15:49 +1000165A unix-domain socket is created
Damien Miller32aa1441999-10-29 09:15:49 +1000166and the name of this socket is stored in the
167.Ev SSH_AUTH_SOCK
168environment
Damien Miller450a7a12000-03-26 13:04:51 +1000169variable.
170The socket is made accessible only to the current user.
Damien Miller32aa1441999-10-29 09:15:49 +1000171This method is easily abused by root or another instance of the same
172user.
173.Pp
174The
175.Ev SSH_AGENT_PID
Ben Lindstrom959de992002-06-23 00:35:25 +0000176environment variable holds the agent's process ID.
Damien Miller32aa1441999-10-29 09:15:49 +1000177.Pp
178The agent exits automatically when the command given on the command
179line terminates.
Damien Miller32aa1441999-10-29 09:15:49 +1000180.Sh FILES
181.Bl -tag -width Ds
Damien Miller167ea5d2005-05-26 12:04:02 +1000182.It Pa ~/.ssh/identity
Ben Lindstrom18a82ac2001-04-11 15:59:35 +0000183Contains the protocol version 1 RSA authentication identity of the user.
Damien Miller167ea5d2005-05-26 12:04:02 +1000184.It Pa ~/.ssh/id_dsa
Ben Lindstrom18a82ac2001-04-11 15:59:35 +0000185Contains the protocol version 2 DSA authentication identity of the user.
Damien Miller167ea5d2005-05-26 12:04:02 +1000186.It Pa ~/.ssh/id_rsa
Ben Lindstrom18a82ac2001-04-11 15:59:35 +0000187Contains the protocol version 2 RSA authentication identity of the user.
Damien Miller393821a2006-07-24 14:04:53 +1000188.It Pa /tmp/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt
Damien Miller32aa1441999-10-29 09:15:49 +1000189Unix-domain sockets used to contain the connection to the
Damien Miller450a7a12000-03-26 13:04:51 +1000190authentication agent.
191These sockets should only be readable by the owner.
192The sockets should get automatically removed when the agent exits.
Damien Miller37023962000-07-11 17:31:38 +1000193.El
Damien Millerf1ce5052003-06-11 22:04:39 +1000194.Sh SEE ALSO
195.Xr ssh 1 ,
196.Xr ssh-add 1 ,
197.Xr ssh-keygen 1 ,
198.Xr sshd 8
Damien Miller0bc1bd82000-11-13 22:57:25 +1100199.Sh AUTHORS
Ben Lindstrom035782e2001-01-29 08:34:16 +0000200OpenSSH 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.