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jmc@openbsd.orgb7ca2762015-04-24 06:26:49 +00001.\" $OpenBSD: ssh-agent.1,v 1.59 2015/04/24 06:26:49 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.\"
djm@openbsd.org2ea97462015-04-24 05:26:44 +000037.Dd $Mdocdate: April 24 2015 $
Damien Miller32aa1441999-10-29 09:15:49 +100038.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
Damien Millerde735ea2010-09-10 11:12:38 +100045.Op Fl c | s
jmc@openbsd.orgb7ca2762015-04-24 06:26:49 +000046.Op Fl Dd
Damien Miller5cbe7ca2007-09-17 16:05:50 +100047.Op Fl a Ar bind_address
djm@openbsd.org56d1c832014-12-21 22:27:55 +000048.Op Fl E Ar fingerprint_hash
Damien Miller5cbe7ca2007-09-17 16:05:50 +100049.Op Fl t Ar life
50.Op Ar command Op Ar arg ...
Ben Lindstrom14920292000-11-21 21:24:55 +000051.Nm ssh-agent
Damien Millerde735ea2010-09-10 11:12:38 +100052.Op Fl c | s
Ben Lindstrom14920292000-11-21 21:24:55 +000053.Fl k
Damien Miller22c77262000-04-13 12:26:34 +100054.Sh DESCRIPTION
Damien Miller32aa1441999-10-29 09:15:49 +100055.Nm
Damien Millerad833b32000-08-23 10:46:23 +100056is a program to hold private keys used for public key authentication
sobrado@openbsd.orgf70b22b2014-08-30 15:33:50 +000057(RSA, DSA, ECDSA, Ed25519).
Damien Miller32aa1441999-10-29 09:15:49 +100058.Nm
Damien Miller8c492da2014-04-20 13:25:09 +100059is usually started in the beginning of an X-session or a login session, and
Damien Miller32aa1441999-10-29 09:15:49 +100060all 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
Damien Miller8c492da2014-04-20 13:25:09 +100067The agent initially does not have any private keys.
68Keys are added using
69.Xr ssh-add 1 .
70Multiple identities may be stored in
71.Nm
72concurrently and
73.Xr ssh 1
74will automatically use them if present.
75.Xr ssh-add 1
76is also used to remove keys from
77.Nm
78and to query the keys that are held in one.
79.Pp
Damien Miller32aa1441999-10-29 09:15:49 +100080The options are as follows:
81.Bl -tag -width Ds
Ben Lindstromb7788f32002-06-06 21:46:08 +000082.It Fl a Ar bind_address
Darren Tuckerae69e1d2009-10-24 11:41:34 +110083Bind the agent to the
Darren Tucker98c9aec2009-10-24 11:42:44 +110084.Ux Ns -domain
85socket
Ben Lindstromb7788f32002-06-06 21:46:08 +000086.Ar bind_address .
87The default is
Damien Miller2cd62932010-12-01 11:50:35 +110088.Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
Damien Miller32aa1441999-10-29 09:15:49 +100089.It Fl c
90Generate C-shell commands on
91.Dv stdout .
92This is the default if
93.Ev SHELL
94looks like it's a csh style of shell.
djm@openbsd.org2ea97462015-04-24 05:26:44 +000095.It Fl D
96Foreground mode.
97When this option is specified
98.Nm
99will not fork.
Damien Miller5cbe7ca2007-09-17 16:05:50 +1000100.It Fl d
101Debug mode.
102When this option is specified
103.Nm
djm@openbsd.org2ea97462015-04-24 05:26:44 +0000104will not fork and will write debug information to standard error.
djm@openbsd.org56d1c832014-12-21 22:27:55 +0000105.It Fl E Ar fingerprint_hash
106Specifies the hash algorithm used when displaying key fingerprints.
107Valid options are:
108.Dq md5
109and
110.Dq sha256 .
111The default is
112.Dq sha256 .
Damien Miller5cbe7ca2007-09-17 16:05:50 +1000113.It Fl k
114Kill the current agent (given by the
115.Ev SSH_AGENT_PID
116environment variable).
Damien Miller32aa1441999-10-29 09:15:49 +1000117.It Fl s
118Generate Bourne shell commands on
119.Dv stdout .
120This is the default if
121.Ev SHELL
122does not look like it's a csh style of shell.
Damien Miller53d81482003-01-22 11:47:19 +1100123.It Fl t Ar life
Damien Miller495dca32003-04-01 21:42:14 +1000124Set a default value for the maximum lifetime of identities added to the agent.
Damien Miller53d81482003-01-22 11:47:19 +1100125The lifetime may be specified in seconds or in a time format specified in
Darren Tucker3a4634f2005-11-28 17:05:40 +1100126.Xr sshd_config 5 .
Damien Miller53d81482003-01-22 11:47:19 +1100127A lifetime specified for an identity with
128.Xr ssh-add 1
129overrides this value.
130Without this option the default maximum lifetime is forever.
Damien Miller32aa1441999-10-29 09:15:49 +1000131.El
132.Pp
133If a commandline is given, this is executed as a subprocess of the agent.
134When the command dies, so does the agent.
135.Pp
Damien Miller32aa1441999-10-29 09:15:49 +1000136The idea is that the agent is run in the user's local PC, laptop, or
Damien Miller450a7a12000-03-26 13:04:51 +1000137terminal.
138Authentication data need not be stored on any other
Damien Miller32aa1441999-10-29 09:15:49 +1000139machine, and authentication passphrases never go over the network.
140However, the connection to the agent is forwarded over SSH
141remote logins, and the user can thus use the privileges given by the
142identities anywhere in the network in a secure way.
143.Pp
Damien Millerabbae982003-05-15 10:16:21 +1000144There are two main ways to get an agent set up:
Darren Tuckera86b4532004-05-13 16:45:46 +1000145The first is that the agent starts a new subcommand into which some environment
146variables are exported, eg
147.Cm ssh-agent xterm & .
148The second is that the agent prints the needed shell commands (either
Damien Miller32aa1441999-10-29 09:15:49 +1000149.Xr sh 1
150or
151.Xr csh 1
Darren Tucker5837b512009-06-21 17:52:27 +1000152syntax can be generated) which can be evaluated in the calling shell, eg
Darren Tuckera86b4532004-05-13 16:45:46 +1000153.Cm eval `ssh-agent -s`
154for Bourne-type shells such as
155.Xr sh 1
156or
157.Xr ksh 1
158and
Darren Tuckerfc959702004-07-17 16:12:08 +1000159.Cm eval `ssh-agent -c`
Darren Tuckera86b4532004-05-13 16:45:46 +1000160for
161.Xr csh 1
162and derivatives.
163.Pp
Damien Miller32aa1441999-10-29 09:15:49 +1000164Later
165.Xr ssh 1
Ben Lindstrom0d3e8fa2001-04-04 01:51:25 +0000166looks at these variables and uses them to establish a connection to the agent.
Damien Miller32aa1441999-10-29 09:15:49 +1000167.Pp
Ben Lindstrom11f790b2001-12-06 16:37:51 +0000168The agent will never send a private key over its request channel.
169Instead, operations that require a private key will be performed
170by the agent, and the result will be returned to the requester.
171This way, private keys are not exposed to clients using the agent.
172.Pp
Darren Tuckerae69e1d2009-10-24 11:41:34 +1100173A
Darren Tucker98c9aec2009-10-24 11:42:44 +1100174.Ux Ns -domain
175socket is created and the name of this socket is stored in the
Damien Miller32aa1441999-10-29 09:15:49 +1000176.Ev SSH_AUTH_SOCK
177environment
Damien Miller450a7a12000-03-26 13:04:51 +1000178variable.
179The socket is made accessible only to the current user.
Damien Miller32aa1441999-10-29 09:15:49 +1000180This method is easily abused by root or another instance of the same
181user.
182.Pp
183The
184.Ev SSH_AGENT_PID
Ben Lindstrom959de992002-06-23 00:35:25 +0000185environment variable holds the agent's process ID.
Damien Miller32aa1441999-10-29 09:15:49 +1000186.Pp
187The agent exits automatically when the command given on the command
188line terminates.
Damien Miller32aa1441999-10-29 09:15:49 +1000189.Sh FILES
190.Bl -tag -width Ds
Damien Miller2cd62932010-12-01 11:50:35 +1100191.It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt
Darren Tucker98c9aec2009-10-24 11:42:44 +1100192.Ux Ns -domain
193sockets used to contain the connection to the authentication agent.
Damien Miller450a7a12000-03-26 13:04:51 +1000194These sockets should only be readable by the owner.
195The sockets should get automatically removed when the agent exits.
Damien Miller37023962000-07-11 17:31:38 +1000196.El
Damien Millerf1ce5052003-06-11 22:04:39 +1000197.Sh SEE ALSO
198.Xr ssh 1 ,
199.Xr ssh-add 1 ,
200.Xr ssh-keygen 1 ,
201.Xr sshd 8
Damien Miller0bc1bd82000-11-13 22:57:25 +1100202.Sh AUTHORS
Ben Lindstrom035782e2001-01-29 08:34:16 +0000203OpenSSH is a derivative of the original and free
204ssh 1.2.12 release by Tatu Ylonen.
205Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
206Theo de Raadt and Dug Song
207removed many bugs, re-added newer features and
208created OpenSSH.
209Markus Friedl contributed the support for SSH
210protocol versions 1.5 and 2.0.