Annotation of src/usr.bin/ssh/ssh-agent.1, Revision 1.66
1.66 ! jmc 1: .\" $OpenBSD: ssh-agent.1,v 1.65 2019/10/31 21:22:01 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,
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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: .\"
1.66 ! jmc 37: .Dd $Mdocdate: October 31 2019 $
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
1.66 ! jmc 46: .Op Fl Ddk
1.32 markus 47: .Op Fl a Ar bind_address
1.57 djm 48: .Op Fl E Ar fingerprint_hash
1.65 djm 49: .Op Fl P Ar provider_whitelist
1.36 marc 50: .Op Fl t Ar life
1.46 sobrado 51: .Op Ar command Op Ar arg ...
1.11 aaron 52: .Sh DESCRIPTION
1.2 deraadt 53: .Nm
1.14 markus 54: is a program to hold private keys used for public key authentication
1.56 sobrado 55: (RSA, DSA, ECDSA, Ed25519).
1.2 deraadt 56: .Nm
1.55 djm 57: is usually started in the beginning of an X-session or a login session, and
1.7 markus 58: all other windows or programs are started as clients to the ssh-agent
1.10 aaron 59: program.
60: Through use of environment variables the agent can be located
1.14 markus 61: and automatically used for authentication when logging in to other
1.1 deraadt 62: machines using
1.2 deraadt 63: .Xr ssh 1 .
64: .Pp
1.55 djm 65: The agent initially does not have any private keys.
66: Keys are added using
1.61 jcs 67: .Xr ssh 1
68: (see
69: .Cm AddKeysToAgent
70: in
71: .Xr ssh_config 5
72: for details)
73: or
1.55 djm 74: .Xr ssh-add 1 .
75: Multiple identities may be stored in
76: .Nm
77: concurrently and
78: .Xr ssh 1
79: will automatically use them if present.
80: .Xr ssh-add 1
81: is also used to remove keys from
82: .Nm
83: and to query the keys that are held in one.
84: .Pp
1.7 markus 85: The options are as follows:
86: .Bl -tag -width Ds
1.32 markus 87: .It Fl a Ar bind_address
1.48 sobrado 88: Bind the agent to the
1.49 sobrado 89: .Ux Ns -domain
90: socket
1.32 markus 91: .Ar bind_address .
92: The default is
1.53 djm 93: .Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
1.7 markus 94: .It Fl c
95: Generate C-shell commands on
96: .Dv stdout .
97: This is the default if
98: .Ev SHELL
99: looks like it's a csh style of shell.
1.58 djm 100: .It Fl D
101: Foreground mode.
102: When this option is specified
103: .Nm
104: will not fork.
1.46 sobrado 105: .It Fl d
106: Debug mode.
107: When this option is specified
108: .Nm
1.58 djm 109: will not fork and will write debug information to standard error.
1.57 djm 110: .It Fl E Ar fingerprint_hash
111: Specifies the hash algorithm used when displaying key fingerprints.
112: Valid options are:
113: .Dq md5
114: and
115: .Dq sha256 .
116: The default is
117: .Dq sha256 .
1.46 sobrado 118: .It Fl k
119: Kill the current agent (given by the
120: .Ev SSH_AGENT_PID
121: environment variable).
1.66 ! jmc 122: This option should not be used with any other options.
1.65 djm 123: .It Fl P Ar provider_whitelist
124: Specify a pattern-list of acceptable paths for PKCS#11 and security key shared
125: libraries that may be used with the
1.63 djm 126: .Fl s
1.65 djm 127: or
128: .Fl S
129: options to
1.63 djm 130: .Xr ssh-add 1 .
1.65 djm 131: The default is to allow loading libraries from
1.63 djm 132: .Dq /usr/lib/*,/usr/local/lib/* .
1.65 djm 133: Libraries that do not match the whitelist will be refused.
1.63 djm 134: See PATTERNS in
135: .Xr ssh_config 5
136: for a description of pattern-list syntax.
1.7 markus 137: .It Fl s
138: Generate Bourne shell commands on
139: .Dv stdout .
140: This is the default if
141: .Ev SHELL
142: does not look like it's a csh style of shell.
1.36 marc 143: .It Fl t Ar life
1.37 jmc 144: Set a default value for the maximum lifetime of identities added to the agent.
1.36 marc 145: The lifetime may be specified in seconds or in a time format specified in
1.43 dtucker 146: .Xr sshd_config 5 .
1.36 marc 147: A lifetime specified for an identity with
148: .Xr ssh-add 1
149: overrides this value.
150: Without this option the default maximum lifetime is forever.
1.7 markus 151: .El
152: .Pp
1.60 jmc 153: If a command line is given, this is executed as a subprocess of the agent.
1.7 markus 154: When the command dies, so does the agent.
155: .Pp
1.1 deraadt 156: The idea is that the agent is run in the user's local PC, laptop, or
1.10 aaron 157: terminal.
158: Authentication data need not be stored on any other
1.1 deraadt 159: machine, and authentication passphrases never go over the network.
1.2 deraadt 160: However, the connection to the agent is forwarded over SSH
1.1 deraadt 161: remote logins, and the user can thus use the privileges given by the
162: identities anywhere in the network in a secure way.
1.2 deraadt 163: .Pp
1.38 jmc 164: There are two main ways to get an agent set up:
1.40 dtucker 165: The first is that the agent starts a new subcommand into which some environment
166: variables are exported, eg
167: .Cm ssh-agent xterm & .
168: The second is that the agent prints the needed shell commands (either
1.7 markus 169: .Xr sh 1
170: or
171: .Xr csh 1
1.47 sobrado 172: syntax can be generated) which can be evaluated in the calling shell, eg
1.40 dtucker 173: .Cm eval `ssh-agent -s`
174: for Bourne-type shells such as
175: .Xr sh 1
176: or
177: .Xr ksh 1
178: and
1.41 deraadt 179: .Cm eval `ssh-agent -c`
1.40 dtucker 180: for
181: .Xr csh 1
182: and derivatives.
183: .Pp
1.7 markus 184: Later
185: .Xr ssh 1
1.23 deraadt 186: looks at these variables and uses them to establish a connection to the agent.
1.29 stevesk 187: .Pp
188: The agent will never send a private key over its request channel.
189: Instead, operations that require a private key will be performed
190: by the agent, and the result will be returned to the requester.
191: This way, private keys are not exposed to clients using the agent.
1.7 markus 192: .Pp
1.48 sobrado 193: A
1.49 sobrado 194: .Ux Ns -domain
195: socket is created and the name of this socket is stored in the
1.5 markus 196: .Ev SSH_AUTH_SOCK
1.1 deraadt 197: environment
1.10 aaron 198: variable.
199: The socket is made accessible only to the current user.
1.1 deraadt 200: This method is easily abused by root or another instance of the same
1.4 markus 201: user.
1.7 markus 202: .Pp
203: The
204: .Ev SSH_AGENT_PID
1.34 stevesk 205: environment variable holds the agent's process ID.
1.2 deraadt 206: .Pp
1.1 deraadt 207: The agent exits automatically when the command given on the command
208: line terminates.
1.2 deraadt 209: .Sh FILES
210: .Bl -tag -width Ds
1.64 jmc 211: .It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>
1.49 sobrado 212: .Ux Ns -domain
213: sockets used to contain the connection to the authentication agent.
1.10 aaron 214: These sockets should only be readable by the owner.
215: The sockets should get automatically removed when the agent exits.
1.13 aaron 216: .El
1.39 jmc 217: .Sh SEE ALSO
218: .Xr ssh 1 ,
219: .Xr ssh-add 1 ,
220: .Xr ssh-keygen 1 ,
221: .Xr sshd 8
1.17 aaron 222: .Sh AUTHORS
1.64 jmc 223: .An -nosplit
224: OpenSSH is a derivative of the original and free ssh 1.2.12 release by
225: .An Tatu Ylonen .
226: .An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos , Theo de Raadt
227: and
228: .An Dug Song
229: removed many bugs, re-added newer features and created OpenSSH.
230: .An Markus Friedl
231: contributed the support for SSH protocol versions 1.5 and 2.0.
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