Annotation of src/usr.bin/ssh/ssh-agent.1, Revision 1.59
1.59 ! jmc 1: .\" $OpenBSD: ssh-agent.1,v 1.58 2015/04/24 05:26:44 djm Exp $
1.7 markus 2: .\"
1.16 deraadt 3: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5: .\" All rights reserved
1.1 deraadt 6: .\"
1.16 deraadt 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".
1.1 deraadt 12: .\"
1.22 deraadt 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.
1.8 deraadt 16: .\"
1.16 deraadt 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.
1.1 deraadt 25: .\"
1.16 deraadt 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.
1.1 deraadt 36: .\"
1.59 ! jmc 37: .Dd $Mdocdate: April 24 2015 $
1.2 deraadt 38: .Dt SSH-AGENT 1
39: .Os
40: .Sh NAME
41: .Nm ssh-agent
42: .Nd authentication agent
43: .Sh SYNOPSIS
1.11 aaron 44: .Nm ssh-agent
1.52 jmc 45: .Op Fl c | s
1.59 ! jmc 46: .Op Fl Dd
1.32 markus 47: .Op Fl a Ar bind_address
1.57 djm 48: .Op Fl E Ar fingerprint_hash
1.36 marc 49: .Op Fl t Ar life
1.46 sobrado 50: .Op Ar command Op Ar arg ...
1.18 markus 51: .Nm ssh-agent
1.52 jmc 52: .Op Fl c | s
1.18 markus 53: .Fl k
1.11 aaron 54: .Sh DESCRIPTION
1.2 deraadt 55: .Nm
1.14 markus 56: is a program to hold private keys used for public key authentication
1.56 sobrado 57: (RSA, DSA, ECDSA, Ed25519).
1.2 deraadt 58: .Nm
1.55 djm 59: is usually started in the beginning of an X-session or a login session, and
1.7 markus 60: all other windows or programs are started as clients to the ssh-agent
1.10 aaron 61: program.
62: Through use of environment variables the agent can be located
1.14 markus 63: and automatically used for authentication when logging in to other
1.1 deraadt 64: machines using
1.2 deraadt 65: .Xr ssh 1 .
66: .Pp
1.55 djm 67: The agent initially does not have any private keys.
68: Keys are added using
69: .Xr ssh-add 1 .
70: Multiple identities may be stored in
71: .Nm
72: concurrently and
73: .Xr ssh 1
74: will automatically use them if present.
75: .Xr ssh-add 1
76: is also used to remove keys from
77: .Nm
78: and to query the keys that are held in one.
79: .Pp
1.7 markus 80: The options are as follows:
81: .Bl -tag -width Ds
1.32 markus 82: .It Fl a Ar bind_address
1.48 sobrado 83: Bind the agent to the
1.49 sobrado 84: .Ux Ns -domain
85: socket
1.32 markus 86: .Ar bind_address .
87: The default is
1.53 djm 88: .Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
1.7 markus 89: .It Fl c
90: Generate C-shell commands on
91: .Dv stdout .
92: This is the default if
93: .Ev SHELL
94: looks like it's a csh style of shell.
1.58 djm 95: .It Fl D
96: Foreground mode.
97: When this option is specified
98: .Nm
99: will not fork.
1.46 sobrado 100: .It Fl d
101: Debug mode.
102: When this option is specified
103: .Nm
1.58 djm 104: will not fork and will write debug information to standard error.
1.57 djm 105: .It Fl E Ar fingerprint_hash
106: Specifies the hash algorithm used when displaying key fingerprints.
107: Valid options are:
108: .Dq md5
109: and
110: .Dq sha256 .
111: The default is
112: .Dq sha256 .
1.46 sobrado 113: .It Fl k
114: Kill the current agent (given by the
115: .Ev SSH_AGENT_PID
116: environment variable).
1.7 markus 117: .It Fl s
118: Generate Bourne shell commands on
119: .Dv stdout .
120: This is the default if
121: .Ev SHELL
122: does not look like it's a csh style of shell.
1.36 marc 123: .It Fl t Ar life
1.37 jmc 124: Set a default value for the maximum lifetime of identities added to the agent.
1.36 marc 125: The lifetime may be specified in seconds or in a time format specified in
1.43 dtucker 126: .Xr sshd_config 5 .
1.36 marc 127: A lifetime specified for an identity with
128: .Xr ssh-add 1
129: overrides this value.
130: Without this option the default maximum lifetime is forever.
1.7 markus 131: .El
132: .Pp
133: If a commandline is given, this is executed as a subprocess of the agent.
134: When the command dies, so does the agent.
135: .Pp
1.1 deraadt 136: The idea is that the agent is run in the user's local PC, laptop, or
1.10 aaron 137: terminal.
138: Authentication data need not be stored on any other
1.1 deraadt 139: machine, and authentication passphrases never go over the network.
1.2 deraadt 140: However, the connection to the agent is forwarded over SSH
1.1 deraadt 141: remote logins, and the user can thus use the privileges given by the
142: identities anywhere in the network in a secure way.
1.2 deraadt 143: .Pp
1.38 jmc 144: There are two main ways to get an agent set up:
1.40 dtucker 145: The first is that the agent starts a new subcommand into which some environment
146: variables are exported, eg
147: .Cm ssh-agent xterm & .
148: The second is that the agent prints the needed shell commands (either
1.7 markus 149: .Xr sh 1
150: or
151: .Xr csh 1
1.47 sobrado 152: syntax can be generated) which can be evaluated in the calling shell, eg
1.40 dtucker 153: .Cm eval `ssh-agent -s`
154: for Bourne-type shells such as
155: .Xr sh 1
156: or
157: .Xr ksh 1
158: and
1.41 deraadt 159: .Cm eval `ssh-agent -c`
1.40 dtucker 160: for
161: .Xr csh 1
162: and derivatives.
163: .Pp
1.7 markus 164: Later
165: .Xr ssh 1
1.23 deraadt 166: looks at these variables and uses them to establish a connection to the agent.
1.29 stevesk 167: .Pp
168: The agent will never send a private key over its request channel.
169: Instead, operations that require a private key will be performed
170: by the agent, and the result will be returned to the requester.
171: This way, private keys are not exposed to clients using the agent.
1.7 markus 172: .Pp
1.48 sobrado 173: A
1.49 sobrado 174: .Ux Ns -domain
175: socket is created and the name of this socket is stored in the
1.5 markus 176: .Ev SSH_AUTH_SOCK
1.1 deraadt 177: environment
1.10 aaron 178: variable.
179: The socket is made accessible only to the current user.
1.1 deraadt 180: This method is easily abused by root or another instance of the same
1.4 markus 181: user.
1.7 markus 182: .Pp
183: The
184: .Ev SSH_AGENT_PID
1.34 stevesk 185: environment variable holds the agent's process ID.
1.2 deraadt 186: .Pp
1.1 deraadt 187: The agent exits automatically when the command given on the command
188: line terminates.
1.2 deraadt 189: .Sh FILES
190: .Bl -tag -width Ds
1.53 djm 191: .It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt
1.49 sobrado 192: .Ux Ns -domain
193: sockets used to contain the connection to the authentication agent.
1.10 aaron 194: These sockets should only be readable by the owner.
195: The sockets should get automatically removed when the agent exits.
1.13 aaron 196: .El
1.39 jmc 197: .Sh SEE ALSO
198: .Xr ssh 1 ,
199: .Xr ssh-add 1 ,
200: .Xr ssh-keygen 1 ,
201: .Xr sshd 8
1.17 aaron 202: .Sh AUTHORS
1.20 markus 203: OpenSSH is a derivative of the original and free
204: ssh 1.2.12 release by Tatu Ylonen.
205: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
206: Theo de Raadt and Dug Song
207: removed many bugs, re-added newer features and
208: created OpenSSH.
209: Markus Friedl contributed the support for SSH
210: protocol versions 1.5 and 2.0.
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