164 lines
4.6 KiB
Groff
164 lines
4.6 KiB
Groff
.\" $OpenBSD: ssh-agent.1,v 1.9 2000/01/22 02:17:50 aaron Exp $
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.\"
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.\" -*- nroff -*-
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.\"
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.\" ssh-agent.1
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.\"
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.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
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.\"
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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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.\" Created: Sat Apr 23 20:10:43 1995 ylo
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.\"
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.Dd September 25, 1999
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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 Li | Fl s
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.Op Fl k
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.Oo
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.Ar command
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.Op Ar args ...
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.Oc
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.Sh DESCRIPTION
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.Nm
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is a program to hold authentication private keys. The
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idea is that
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.Nm
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is 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. Through use of environment variables the agent can be located
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and automatically used for RSA 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 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 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 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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.El
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.Pp
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If a commandline 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 agent initially does not have any private keys. Keys are added
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using
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.Xr ssh-add 1 .
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When executed without arguments,
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.Xr ssh-add 1
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adds the
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.Pa $HOME/.ssh/identity
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file. If the identity has a passphrase,
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.Xr ssh-add 1
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asks for the passphrase (using a small X11 application if running
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under X11, or from the terminal if running without X). It then sends
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the identity to the agent. Several identities can be stored in the
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agent; the agent can automatically use any of these identities.
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.Ic ssh-add -l
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displays the identities currently held by 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. 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 setup: Either you let the agent
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start a new subcommand into which some environment variables are exported, or
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you let the agent print 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 evalled in the calling shell.
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Later
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.Xr ssh 1
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look at these variables and use them to establish a connection to the agent.
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.Pp
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A unix-domain socket is created
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.Pq Pa /tmp/ssh-XXXXXXXX/agent.<pid> ,
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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. 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 PID.
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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 $HOME/.ssh/identity
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Contains the RSA authentication identity of the user. This file
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should not be readable by anyone but the user. It is possible to
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specify a passphrase when generating the key; that passphrase will be
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used to encrypt the private part of this file. This file
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is not used by
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.Nm
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but is normally added to the agent using
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.Xr ssh-add 1
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at login time.
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.It Pa /tmp/ssh-XXXX/agent.<pid> ,
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Unix-domain sockets used to contain the connection to the
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authentication agent. These sockets should only be readable by the
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owner. The sockets should get automatically removed when the agent
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exits.
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.Sh AUTHOR
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Tatu Ylonen <ylo@cs.hut.fi>
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.Pp
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OpenSSH
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is a derivative of the original (free) ssh 1.2.12 release, but with bugs
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removed and newer features re-added. Rapidly after the 1.2.12 release,
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newer versions bore successively more restrictive licenses. This version
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of OpenSSH
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.Bl -bullet
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.It
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has all components of a restrictive nature (i.e., patents, see
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.Xr ssl 8 )
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directly removed from the source code; any licensed or patented components
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are chosen from
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external libraries.
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.It
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has been updated to support ssh protocol 1.5.
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.It
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contains added support for
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.Xr kerberos 8
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authentication and ticket passing.
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.It
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supports one-time password authentication with
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.Xr skey 1 .
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.El
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.Pp
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The libraries described in
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.Xr ssl 8
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are required for proper operation.
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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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.Xr ssl 8
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