xref: /freebsd/crypto/openssh/ssh-agent.1 (revision 7aa383846770374466b1dcb2cefd71bde9acf463)
1.\" $OpenBSD: ssh-agent.1,v 1.50 2010/01/17 21:49:09 tedu Exp $
2.\" $FreeBSD$
3.\"
4.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
5.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
6.\"                    All rights reserved
7.\"
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".
13.\"
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.
17.\"
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38.Dd January 17, 2010
39.Dt SSH-AGENT 1
40.Os
41.Sh NAME
42.Nm ssh-agent
43.Nd authentication agent
44.Sh SYNOPSIS
45.Nm ssh-agent
46.Op Fl c Li | Fl s
47.Op Fl d
48.Op Fl a Ar bind_address
49.Op Fl t Ar life
50.Op Ar command Op Ar arg ...
51.Nm ssh-agent
52.Op Fl c Li | Fl s
53.Fl k
54.Sh DESCRIPTION
55.Nm
56is a program to hold private keys used for public key authentication
57(RSA, DSA).
58The idea is that
59.Nm
60is started in the beginning of an X-session or a login session, and
61all other windows or programs are started as clients to the ssh-agent
62program.
63Through use of environment variables the agent can be located
64and automatically used for authentication when logging in to other
65machines using
66.Xr ssh 1 .
67.Pp
68The options are as follows:
69.Bl -tag -width Ds
70.It Fl a Ar bind_address
71Bind the agent to the
72.Ux Ns -domain
73socket
74.Ar bind_address .
75The default is
76.Pa /tmp/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
77.It Fl c
78Generate C-shell commands on
79.Dv stdout .
80This is the default if
81.Ev SHELL
82looks like it's a csh style of shell.
83.It Fl d
84Debug mode.
85When this option is specified
86.Nm
87will not fork.
88.It Fl k
89Kill the current agent (given by the
90.Ev SSH_AGENT_PID
91environment variable).
92.It Fl s
93Generate Bourne shell commands on
94.Dv stdout .
95This is the default if
96.Ev SHELL
97does not look like it's a csh style of shell.
98.It Fl t Ar life
99Set a default value for the maximum lifetime of identities added to the agent.
100The lifetime may be specified in seconds or in a time format specified in
101.Xr sshd_config 5 .
102A lifetime specified for an identity with
103.Xr ssh-add 1
104overrides this value.
105Without this option the default maximum lifetime is forever.
106.El
107.Pp
108If a commandline is given, this is executed as a subprocess of the agent.
109When the command dies, so does the agent.
110.Pp
111The agent initially does not have any private keys.
112Keys are added using
113.Xr ssh-add 1 .
114When executed without arguments,
115.Xr ssh-add 1
116adds the files
117.Pa ~/.ssh/id_rsa ,
118.Pa ~/.ssh/id_dsa
119and
120.Pa ~/.ssh/identity .
121If the identity has a passphrase,
122.Xr ssh-add 1
123asks for the passphrase on the terminal if it has one or from a small X11
124program if running under X11.
125If neither of these is the case then the authentication will fail.
126It then sends the identity to the agent.
127Several identities can be stored in the
128agent; the agent can automatically use any of these identities.
129.Ic ssh-add -l
130displays the identities currently held by the agent.
131.Pp
132The idea is that the agent is run in the user's local PC, laptop, or
133terminal.
134Authentication data need not be stored on any other
135machine, and authentication passphrases never go over the network.
136However, the connection to the agent is forwarded over SSH
137remote logins, and the user can thus use the privileges given by the
138identities anywhere in the network in a secure way.
139.Pp
140There are two main ways to get an agent set up:
141The first is that the agent starts a new subcommand into which some environment
142variables are exported, eg
143.Cm ssh-agent xterm & .
144The second is that the agent prints the needed shell commands (either
145.Xr sh 1
146or
147.Xr csh 1
148syntax can be generated) which can be evaluated in the calling shell, eg
149.Cm eval `ssh-agent -s`
150for Bourne-type shells such as
151.Xr sh 1
152or
153.Xr ksh 1
154and
155.Cm eval `ssh-agent -c`
156for
157.Xr csh 1
158and derivatives.
159.Pp
160Later
161.Xr ssh 1
162looks at these variables and uses them to establish a connection to the agent.
163.Pp
164The agent will never send a private key over its request channel.
165Instead, operations that require a private key will be performed
166by the agent, and the result will be returned to the requester.
167This way, private keys are not exposed to clients using the agent.
168.Pp
169A
170.Ux Ns -domain
171socket is created and the name of this socket is stored in the
172.Ev SSH_AUTH_SOCK
173environment
174variable.
175The socket is made accessible only to the current user.
176This method is easily abused by root or another instance of the same
177user.
178.Pp
179The
180.Ev SSH_AGENT_PID
181environment variable holds the agent's process ID.
182.Pp
183The agent exits automatically when the command given on the command
184line terminates.
185.Sh FILES
186.Bl -tag -width Ds
187.It Pa ~/.ssh/identity
188Contains the protocol version 1 RSA authentication identity of the user.
189.It Pa ~/.ssh/id_dsa
190Contains the protocol version 2 DSA authentication identity of the user.
191.It Pa ~/.ssh/id_rsa
192Contains the protocol version 2 RSA authentication identity of the user.
193.It Pa /tmp/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt
194.Ux Ns -domain
195sockets used to contain the connection to the authentication agent.
196These sockets should only be readable by the owner.
197The sockets should get automatically removed when the agent exits.
198.El
199.Sh SEE ALSO
200.Xr ssh 1 ,
201.Xr ssh-add 1 ,
202.Xr ssh-keygen 1 ,
203.Xr sshd 8
204.Sh AUTHORS
205OpenSSH is a derivative of the original and free
206ssh 1.2.12 release by Tatu Ylonen.
207Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
208Theo de Raadt and Dug Song
209removed many bugs, re-added newer features and
210created OpenSSH.
211Markus Friedl contributed the support for SSH
212protocol versions 1.5 and 2.0.
213