Annotation of src/usr.bin/ssh/ssh-agent.1, Revision 1.58
1.58 ! djm 1: .\" $OpenBSD: ssh-agent.1,v 1.57 2014/12/21 22:27:56 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: .\"
1.58 ! djm 37: .Dd $Mdocdate: December 21 2014 $
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
1.58 ! djm 46: .Op Fl D
1.46 sobrado 47: .Op Fl d
1.32 markus 48: .Op Fl a Ar bind_address
1.57 djm 49: .Op Fl E Ar fingerprint_hash
1.36 marc 50: .Op Fl t Ar life
1.46 sobrado 51: .Op Ar command Op Ar arg ...
1.18 markus 52: .Nm ssh-agent
1.52 jmc 53: .Op Fl c | s
1.18 markus 54: .Fl k
1.11 aaron 55: .Sh DESCRIPTION
1.2 deraadt 56: .Nm
1.14 markus 57: is a program to hold private keys used for public key authentication
1.56 sobrado 58: (RSA, DSA, ECDSA, Ed25519).
1.2 deraadt 59: .Nm
1.55 djm 60: is usually started in the beginning of an X-session or a login session, and
1.7 markus 61: all other windows or programs are started as clients to the ssh-agent
1.10 aaron 62: program.
63: Through use of environment variables the agent can be located
1.14 markus 64: and automatically used for authentication when logging in to other
1.1 deraadt 65: machines using
1.2 deraadt 66: .Xr ssh 1 .
67: .Pp
1.55 djm 68: The agent initially does not have any private keys.
69: Keys are added using
70: .Xr ssh-add 1 .
71: Multiple identities may be stored in
72: .Nm
73: concurrently and
74: .Xr ssh 1
75: will automatically use them if present.
76: .Xr ssh-add 1
77: is also used to remove keys from
78: .Nm
79: and to query the keys that are held in one.
80: .Pp
1.7 markus 81: The options are as follows:
82: .Bl -tag -width Ds
1.32 markus 83: .It Fl a Ar bind_address
1.48 sobrado 84: Bind the agent to the
1.49 sobrado 85: .Ux Ns -domain
86: socket
1.32 markus 87: .Ar bind_address .
88: The default is
1.53 djm 89: .Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
1.7 markus 90: .It Fl c
91: Generate C-shell commands on
92: .Dv stdout .
93: This is the default if
94: .Ev SHELL
95: looks like it's a csh style of shell.
1.58 ! djm 96: .It Fl D
! 97: Foreground mode.
! 98: When this option is specified
! 99: .Nm
! 100: will not fork.
1.46 sobrado 101: .It Fl d
102: Debug mode.
103: When this option is specified
104: .Nm
1.58 ! djm 105: will not fork and will write debug information to standard error.
1.57 djm 106: .It Fl E Ar fingerprint_hash
107: Specifies the hash algorithm used when displaying key fingerprints.
108: Valid options are:
109: .Dq md5
110: and
111: .Dq sha256 .
112: The default is
113: .Dq sha256 .
1.46 sobrado 114: .It Fl k
115: Kill the current agent (given by the
116: .Ev SSH_AGENT_PID
117: environment variable).
1.7 markus 118: .It Fl s
119: Generate Bourne shell commands on
120: .Dv stdout .
121: This is the default if
122: .Ev SHELL
123: does not look like it's a csh style of shell.
1.36 marc 124: .It Fl t Ar life
1.37 jmc 125: Set a default value for the maximum lifetime of identities added to the agent.
1.36 marc 126: The lifetime may be specified in seconds or in a time format specified in
1.43 dtucker 127: .Xr sshd_config 5 .
1.36 marc 128: A lifetime specified for an identity with
129: .Xr ssh-add 1
130: overrides this value.
131: Without this option the default maximum lifetime is forever.
1.7 markus 132: .El
133: .Pp
134: If a commandline is given, this is executed as a subprocess of the agent.
135: When the command dies, so does the agent.
136: .Pp
1.1 deraadt 137: The idea is that the agent is run in the user's local PC, laptop, or
1.10 aaron 138: terminal.
139: Authentication data need not be stored on any other
1.1 deraadt 140: machine, and authentication passphrases never go over the network.
1.2 deraadt 141: However, the connection to the agent is forwarded over SSH
1.1 deraadt 142: remote logins, and the user can thus use the privileges given by the
143: identities anywhere in the network in a secure way.
1.2 deraadt 144: .Pp
1.38 jmc 145: There are two main ways to get an agent set up:
1.40 dtucker 146: The first is that the agent starts a new subcommand into which some environment
147: variables are exported, eg
148: .Cm ssh-agent xterm & .
149: The second is that the agent prints the needed shell commands (either
1.7 markus 150: .Xr sh 1
151: or
152: .Xr csh 1
1.47 sobrado 153: syntax can be generated) which can be evaluated in the calling shell, eg
1.40 dtucker 154: .Cm eval `ssh-agent -s`
155: for Bourne-type shells such as
156: .Xr sh 1
157: or
158: .Xr ksh 1
159: and
1.41 deraadt 160: .Cm eval `ssh-agent -c`
1.40 dtucker 161: for
162: .Xr csh 1
163: and derivatives.
164: .Pp
1.7 markus 165: Later
166: .Xr ssh 1
1.23 deraadt 167: looks at these variables and uses them to establish a connection to the agent.
1.29 stevesk 168: .Pp
169: The agent will never send a private key over its request channel.
170: Instead, operations that require a private key will be performed
171: by the agent, and the result will be returned to the requester.
172: This way, private keys are not exposed to clients using the agent.
1.7 markus 173: .Pp
1.48 sobrado 174: A
1.49 sobrado 175: .Ux Ns -domain
176: socket is created and the name of this socket is stored in the
1.5 markus 177: .Ev SSH_AUTH_SOCK
1.1 deraadt 178: environment
1.10 aaron 179: variable.
180: The socket is made accessible only to the current user.
1.1 deraadt 181: This method is easily abused by root or another instance of the same
1.4 markus 182: user.
1.7 markus 183: .Pp
184: The
185: .Ev SSH_AGENT_PID
1.34 stevesk 186: environment variable holds the agent's process ID.
1.2 deraadt 187: .Pp
1.1 deraadt 188: The agent exits automatically when the command given on the command
189: line terminates.
1.2 deraadt 190: .Sh FILES
191: .Bl -tag -width Ds
1.53 djm 192: .It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt
1.49 sobrado 193: .Ux Ns -domain
194: sockets used to contain the connection to the authentication agent.
1.10 aaron 195: These sockets should only be readable by the owner.
196: The sockets should get automatically removed when the agent exits.
1.13 aaron 197: .El
1.39 jmc 198: .Sh SEE ALSO
199: .Xr ssh 1 ,
200: .Xr ssh-add 1 ,
201: .Xr ssh-keygen 1 ,
202: .Xr sshd 8
1.17 aaron 203: .Sh AUTHORS
1.20 markus 204: OpenSSH is a derivative of the original and free
205: ssh 1.2.12 release by Tatu Ylonen.
206: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
207: Theo de Raadt and Dug Song
208: removed many bugs, re-added newer features and
209: created OpenSSH.
210: Markus Friedl contributed the support for SSH
211: protocol versions 1.5 and 2.0.
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