mirror of git://anongit.mindrot.org/openssh.git
275 lines
8.1 KiB
Groff
275 lines
8.1 KiB
Groff
.\" $OpenBSD: ssh-agent.1,v 1.79 2023/08/10 14:37:32 naddy Exp $
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.\"
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.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
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.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
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.\" All rights reserved
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.\"
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.\" As far as I am concerned, the code I have written for this software
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.\" can be used freely for any purpose. Any derived versions of this
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.\" software must be clearly marked as such, and if the derived work is
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.\" incompatible with the protocol description in the RFC file, it must be
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.\" called by a name other than "ssh" or "Secure Shell".
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.\"
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.\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
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.\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
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.\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd $Mdocdate: August 10 2023 $
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.Dt SSH-AGENT 1
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.Os
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.Sh NAME
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.Nm ssh-agent
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.Nd OpenSSH authentication agent
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.Sh SYNOPSIS
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.Nm ssh-agent
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.Op Fl c | s
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.Op Fl \&Dd
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.Op Fl a Ar bind_address
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.Op Fl E Ar fingerprint_hash
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.Op Fl O Ar option
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.Op Fl P Ar allowed_providers
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.Op Fl t Ar life
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.Nm ssh-agent
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.Op Fl a Ar bind_address
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.Op Fl E Ar fingerprint_hash
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.Op Fl O Ar option
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.Op Fl P Ar allowed_providers
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.Op Fl t Ar life
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.Ar command Op Ar arg ...
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.Nm ssh-agent
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.Op Fl c | s
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.Fl k
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.Sh DESCRIPTION
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.Nm
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is a program to hold private keys used for public key authentication.
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Through use of environment variables the agent can be located
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and automatically used for authentication when logging in to other
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machines using
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.Xr ssh 1 .
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.Pp
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The options are as follows:
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.Bl -tag -width Ds
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.It Fl a Ar bind_address
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Bind the agent to the
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.Ux Ns -domain
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socket
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.Ar bind_address .
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The default is
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.Pa $TMPDIR/ssh-XXXXXXXXXX/agent.\*(Ltppid\*(Gt .
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.It Fl c
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Generate C-shell commands on
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.Dv stdout .
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This is the default if
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.Ev SHELL
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looks like it's a csh style of shell.
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.It Fl D
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Foreground mode.
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When this option is specified,
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.Nm
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will not fork.
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.It Fl d
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Debug mode.
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When this option is specified,
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.Nm
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will not fork and will write debug information to standard error.
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.It Fl E Ar fingerprint_hash
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Specifies the hash algorithm used when displaying key fingerprints.
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Valid options are:
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.Dq md5
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and
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.Dq sha256 .
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The default is
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.Dq sha256 .
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.It Fl k
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Kill the current agent (given by the
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.Ev SSH_AGENT_PID
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environment variable).
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.It Fl O Ar option
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Specify an option when starting
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.Nm .
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Currently two options are supported:
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.Cm allow-remote-pkcs11
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and
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.Cm no-restrict-websafe .
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.Pp
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The
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.Cm allow-remote-pkcs11
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option allows clients of a forwarded
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.Nm
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to load PKCS#11 or FIDO provider libraries.
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By default only local clients may perform this operation.
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Note that signalling that an
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.Nm
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client is remote is performed by
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.Xr ssh 1 ,
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and use of other tools to forward access to the agent socket may circumvent
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this restriction.
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.Pp
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The
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.Cm no-restrict-websafe
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option instructs
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.Nm
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to permit signatures using FIDO keys that might be web authentication
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requests.
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By default,
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.Nm
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refuses signature requests for FIDO keys where the key application string
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does not start with
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.Dq ssh:
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and when the data to be signed does not appear to be a
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.Xr ssh 1
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user authentication request or a
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.Xr ssh-keygen 1
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signature.
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The default behaviour prevents forwarded access to a FIDO key from also
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implicitly forwarding the ability to authenticate to websites.
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.It Fl P Ar allowed_providers
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Specify a pattern-list of acceptable paths for PKCS#11 provider and FIDO
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authenticator middleware shared libraries that may be used with the
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.Fl S
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or
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.Fl s
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options to
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.Xr ssh-add 1 .
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Libraries that do not match the pattern list will be refused.
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See PATTERNS in
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.Xr ssh_config 5
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for a description of pattern-list syntax.
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The default list is
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.Dq usr/lib*/*,/usr/local/lib*/* .
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.It Fl s
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Generate Bourne shell commands on
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.Dv stdout .
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This is the default if
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.Ev SHELL
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does not look like it's a csh style of shell.
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.It Fl t Ar life
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Set a default value for the maximum lifetime of identities added to the agent.
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The lifetime may be specified in seconds or in a time format specified in
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.Xr sshd_config 5 .
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A lifetime specified for an identity with
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.Xr ssh-add 1
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overrides this value.
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Without this option the default maximum lifetime is forever.
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.It Ar command Op Ar arg ...
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If a command (and optional arguments) is given,
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this is executed as a subprocess of the agent.
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The agent exits automatically when the command given on the command
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line terminates.
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.El
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.Pp
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There are two main ways to get an agent set up.
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The first is at the start of an X session,
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where all other windows or programs are started as children of the
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.Nm
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program.
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The agent starts a command under which its environment
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variables are exported, for example
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.Cm ssh-agent xterm & .
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When the command terminates, so does the agent.
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.Pp
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The second method is used for a login session.
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When
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.Nm
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is started,
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it prints the shell commands required to set its environment variables,
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which in turn can be evaluated in the calling shell, for example
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.Cm eval `ssh-agent -s` .
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.Pp
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In both cases,
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.Xr ssh 1
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looks at these environment variables
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and uses them to establish a connection to the agent.
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.Pp
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The agent initially does not have any private keys.
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Keys are added using
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.Xr ssh-add 1
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or by
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.Xr ssh 1
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when
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.Cm AddKeysToAgent
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is set in
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.Xr ssh_config 5 .
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Multiple identities may be stored in
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.Nm
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concurrently and
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.Xr ssh 1
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will automatically use them if present.
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.Xr ssh-add 1
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is also used to remove keys from
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.Nm
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and to query the keys that are held in one.
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.Pp
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Connections to
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.Nm
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may be forwarded from further remote hosts using the
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.Fl A
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option to
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.Xr ssh 1
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(but see the caveats documented therein),
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avoiding the need for authentication data to be stored on other machines.
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Authentication passphrases and private keys never go over the network:
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the connection to the agent is forwarded over SSH remote connections
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and the result is returned to the requester,
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allowing the user access to their identities anywhere in the network
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in a secure fashion.
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.Sh ENVIRONMENT
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.Bl -tag -width "SSH_AGENT_PID"
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.It Ev SSH_AGENT_PID
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When
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.Nm
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starts, it stores the name of the agent's process ID (PID) in this variable.
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.It Ev SSH_AUTH_SOCK
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When
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.Nm
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starts, it creates a
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.Ux Ns -domain
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socket and stores its pathname in this variable.
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It is accessible only to the current user,
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but is easily abused by root or another instance of the same user.
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.El
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.Sh FILES
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.Bl -tag -width Ds
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.It Pa $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>
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.Ux Ns -domain
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sockets used to contain the connection to the authentication agent.
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These sockets should only be readable by the owner.
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The sockets should get automatically removed when the agent exits.
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.El
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.Sh SEE ALSO
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.Xr ssh 1 ,
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.Xr ssh-add 1 ,
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.Xr ssh-keygen 1 ,
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.Xr ssh_config 5 ,
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.Xr sshd 8
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.Sh AUTHORS
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.An -nosplit
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OpenSSH is a derivative of the original and free ssh 1.2.12 release by
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.An Tatu Ylonen .
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.An Aaron Campbell , Bob Beck , Markus Friedl , Niels Provos , Theo de Raadt
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and
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.An Dug Song
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removed many bugs, re-added newer features and created OpenSSH.
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.An Markus Friedl
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contributed the support for SSH protocol versions 1.5 and 2.0.
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