Annotation of src/usr.bin/ssh/ssh-agent.1, Revision 1.61
1.61 ! jcs 1: .\" $OpenBSD: ssh-agent.1,v 1.60 2015/11/05 09:48:05 jmc 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: .\"
1.61 ! jcs 37: .Dd $Mdocdate: November 5 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
1.61 ! jcs 69: .Xr ssh 1
! 70: (see
! 71: .Cm AddKeysToAgent
! 72: in
! 73: .Xr ssh_config 5
! 74: for details)
! 75: or
1.55 djm 76: .Xr ssh-add 1 .
77: Multiple identities may be stored in
78: .Nm
79: concurrently and
80: .Xr ssh 1
81: will automatically use them if present.
82: .Xr ssh-add 1
83: is also used to remove keys from
84: .Nm
85: and to query the keys that are held in one.
86: .Pp
1.7 markus 87: The options are as follows:
88: .Bl -tag -width Ds
1.32 markus 89: .It Fl a Ar bind_address
1.48 sobrado 90: Bind the agent to the
1.49 sobrado 91: .Ux Ns -domain
92: socket
1.32 markus 93: .Ar bind_address .
94: The default is
1.53 djm 95: .Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
1.7 markus 96: .It Fl c
97: Generate C-shell commands on
98: .Dv stdout .
99: This is the default if
100: .Ev SHELL
101: looks like it's a csh style of shell.
1.58 djm 102: .It Fl D
103: Foreground mode.
104: When this option is specified
105: .Nm
106: will not fork.
1.46 sobrado 107: .It Fl d
108: Debug mode.
109: When this option is specified
110: .Nm
1.58 djm 111: will not fork and will write debug information to standard error.
1.57 djm 112: .It Fl E Ar fingerprint_hash
113: Specifies the hash algorithm used when displaying key fingerprints.
114: Valid options are:
115: .Dq md5
116: and
117: .Dq sha256 .
118: The default is
119: .Dq sha256 .
1.46 sobrado 120: .It Fl k
121: Kill the current agent (given by the
122: .Ev SSH_AGENT_PID
123: environment variable).
1.7 markus 124: .It Fl s
125: Generate Bourne shell commands on
126: .Dv stdout .
127: This is the default if
128: .Ev SHELL
129: does not look like it's a csh style of shell.
1.36 marc 130: .It Fl t Ar life
1.37 jmc 131: Set a default value for the maximum lifetime of identities added to the agent.
1.36 marc 132: The lifetime may be specified in seconds or in a time format specified in
1.43 dtucker 133: .Xr sshd_config 5 .
1.36 marc 134: A lifetime specified for an identity with
135: .Xr ssh-add 1
136: overrides this value.
137: Without this option the default maximum lifetime is forever.
1.7 markus 138: .El
139: .Pp
1.60 jmc 140: If a command line is given, this is executed as a subprocess of the agent.
1.7 markus 141: When the command dies, so does the agent.
142: .Pp
1.1 deraadt 143: The idea is that the agent is run in the user's local PC, laptop, or
1.10 aaron 144: terminal.
145: Authentication data need not be stored on any other
1.1 deraadt 146: machine, and authentication passphrases never go over the network.
1.2 deraadt 147: However, the connection to the agent is forwarded over SSH
1.1 deraadt 148: remote logins, and the user can thus use the privileges given by the
149: identities anywhere in the network in a secure way.
1.2 deraadt 150: .Pp
1.38 jmc 151: There are two main ways to get an agent set up:
1.40 dtucker 152: The first is that the agent starts a new subcommand into which some environment
153: variables are exported, eg
154: .Cm ssh-agent xterm & .
155: The second is that the agent prints the needed shell commands (either
1.7 markus 156: .Xr sh 1
157: or
158: .Xr csh 1
1.47 sobrado 159: syntax can be generated) which can be evaluated in the calling shell, eg
1.40 dtucker 160: .Cm eval `ssh-agent -s`
161: for Bourne-type shells such as
162: .Xr sh 1
163: or
164: .Xr ksh 1
165: and
1.41 deraadt 166: .Cm eval `ssh-agent -c`
1.40 dtucker 167: for
168: .Xr csh 1
169: and derivatives.
170: .Pp
1.7 markus 171: Later
172: .Xr ssh 1
1.23 deraadt 173: looks at these variables and uses them to establish a connection to the agent.
1.29 stevesk 174: .Pp
175: The agent will never send a private key over its request channel.
176: Instead, operations that require a private key will be performed
177: by the agent, and the result will be returned to the requester.
178: This way, private keys are not exposed to clients using the agent.
1.7 markus 179: .Pp
1.48 sobrado 180: A
1.49 sobrado 181: .Ux Ns -domain
182: socket is created and the name of this socket is stored in the
1.5 markus 183: .Ev SSH_AUTH_SOCK
1.1 deraadt 184: environment
1.10 aaron 185: variable.
186: The socket is made accessible only to the current user.
1.1 deraadt 187: This method is easily abused by root or another instance of the same
1.4 markus 188: user.
1.7 markus 189: .Pp
190: The
191: .Ev SSH_AGENT_PID
1.34 stevesk 192: environment variable holds the agent's process ID.
1.2 deraadt 193: .Pp
1.1 deraadt 194: The agent exits automatically when the command given on the command
195: line terminates.
1.2 deraadt 196: .Sh FILES
197: .Bl -tag -width Ds
1.53 djm 198: .It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt
1.49 sobrado 199: .Ux Ns -domain
200: sockets used to contain the connection to the authentication agent.
1.10 aaron 201: These sockets should only be readable by the owner.
202: The sockets should get automatically removed when the agent exits.
1.13 aaron 203: .El
1.39 jmc 204: .Sh SEE ALSO
205: .Xr ssh 1 ,
206: .Xr ssh-add 1 ,
207: .Xr ssh-keygen 1 ,
208: .Xr sshd 8
1.17 aaron 209: .Sh AUTHORS
1.20 markus 210: OpenSSH is a derivative of the original and free
211: ssh 1.2.12 release by Tatu Ylonen.
212: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
213: Theo de Raadt and Dug Song
214: removed many bugs, re-added newer features and
215: created OpenSSH.
216: Markus Friedl contributed the support for SSH
217: protocol versions 1.5 and 2.0.
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