235 lines
7.2 KiB
Groff
235 lines
7.2 KiB
Groff
.\" $OpenBSD: ssh-agent.1,v 1.64 2016/11/30 06:54:26 jmc Exp $
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.\" $FreeBSD$
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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: November 30 2016 $
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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 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 \&Ddx
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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 P Ar pkcs11_whitelist
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.Op Fl t Ar life
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.Op 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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(RSA, DSA, ECDSA, Ed25519).
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.Nm
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is usually started in the beginning of an X-session or a login session, and
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all other windows or programs are started as clients to the ssh-agent
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program.
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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 agent initially does not have any private keys.
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Keys are added using
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.Xr ssh 1
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(see
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.Cm AddKeysToAgent
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in
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.Xr ssh_config 5
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for details)
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or
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.Xr ssh-add 1 .
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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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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 P Ar pkcs11_whitelist
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Specify a pattern-list of acceptable paths for PKCS#11 shared libraries
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that may be added using the
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.Fl s
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option to
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.Xr ssh-add 1 .
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The default is to allow loading PKCS#11 libraries from
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.Dq /usr/lib/*,/usr/local/lib/* .
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PKCS#11 libraries that do not match the whitelist 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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.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 Fl x
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Exit after the last client has disconnected.
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.El
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.Pp
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If a command line is given, this is executed as a subprocess of the agent.
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When the command dies, so does the agent.
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.Pp
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The idea is that the agent is run in the user's local PC, laptop, or
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terminal.
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Authentication data need not be stored on any other
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machine, and authentication passphrases never go over the network.
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However, the connection to the agent is forwarded over SSH
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remote logins, and the user can thus use the privileges given by the
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identities anywhere in the network in a secure way.
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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 that the agent starts a new subcommand into which some environment
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variables are exported, eg
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.Cm ssh-agent xterm & .
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The second is that the agent prints the needed shell commands (either
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.Xr sh 1
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or
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.Xr csh 1
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syntax can be generated) which can be evaluated in the calling shell, eg
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.Cm eval `ssh-agent -s`
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for Bourne-type shells such as
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.Xr sh 1
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or
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.Xr ksh 1
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and
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.Cm eval `ssh-agent -c`
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for
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.Xr csh 1
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and derivatives.
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.Pp
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Later
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.Xr ssh 1
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looks at these variables and uses them to establish a connection to the agent.
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.Pp
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The agent will never send a private key over its request channel.
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Instead, operations that require a private key will be performed
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by the agent, and the result will be returned to the requester.
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This way, private keys are not exposed to clients using the agent.
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.Pp
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A
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.Ux Ns -domain
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socket is created and the name of this socket is stored in the
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.Ev SSH_AUTH_SOCK
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environment
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variable.
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The socket is made accessible only to the current user.
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This method is easily abused by root or another instance of the same
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user.
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.Pp
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The
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.Ev SSH_AGENT_PID
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environment variable holds the agent's process ID.
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.Pp
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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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.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 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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