openssh/ssh-agent.1.in

.\" $OpenBSD: ssh-agent.1,v 1.8 1999/11/16 23:59:21 deraadt Exp $
.\"
.\"  -*- nroff -*-
.\"
.\" ssh-agent.1
.\"
.\" Author: Tatu Ylonen <ylo@cs.hut.fi>
.\"
.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
.\"                    All rights reserved
.\"
.\" Created: Sat Apr 23 20:10:43 1995 ylo
.\"
.Dd September 25, 1999
.Dt SSH-AGENT 1
.Os
.Sh NAME
.Nm ssh-agent
.Nd authentication agent
.Sh SYNOPSIS
.Nm ssh-agent 
.Op Fl c Li | Fl s
.Op Fl k
.Oo
.Ar command
.Op Ar args ...
.Oc
.Sh DESCRIPTION 
.Nm
is a program to hold authentication private keys.  The
idea is that
.Nm
is started in the beginning of an X-session or a login session, and
all other windows or programs are started as clients to the ssh-agent
program.  Through use of environment variables the agent can be located
and automatically used for RSA authentication when logging in to other
machines using
.Xr ssh 1 .
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl c
Generate C-shell commands on
.Dv stdout .
This is the default if
.Ev SHELL
looks like it's a csh style of shell.
.It Fl s
Generate Bourne shell commands on
.Dv stdout .
This is the default if
.Ev SHELL
does not look like it's a csh style of shell.
.It Fl k
Kill the current agent (given by the
.Ev SSH_AGENT_PID
environment variable).
.El
.Pp
If a commandline is given, this is executed as a subprocess of the agent.
When the command dies, so does the agent.
.Pp
The agent initially does not have any private keys.  Keys are added
using
.Xr ssh-add 1 .
When executed without arguments, 
.Xr ssh-add 1
adds the 
.Pa $HOME/.ssh/identity
file.  If the identity has a passphrase, 
.Xr ssh-add 1
asks for the passphrase (using a small X11 application if running
under X11, or from the terminal if running without X).  It then sends
the identity to the agent.  Several identities can be stored in the
agent; the agent can automatically use any of these identities.
.Ic ssh-add -l
displays the identities currently held by the agent.
.Pp
The idea is that the agent is run in the user's local PC, laptop, or
terminal.  Authentication data need not be stored on any other
machine, and authentication passphrases never go over the network.
However, the connection to the agent is forwarded over SSH
remote logins, and the user can thus use the privileges given by the
identities anywhere in the network in a secure way.
.Pp
There are two main ways to get an agent setup:  Either you let the agent
start a new subcommand into which some environment variables are exported, or
you let the agent print the needed shell commands (either
.Xr sh 1
or
.Xr csh 1
syntax can be generated) which can be evalled in the calling shell.
Later
.Xr ssh 1
look at these variables and use them to establish a connection to the agent.
.Pp
A unix-domain socket is created
.Pq Pa /tmp/ssh-XXXXXXXX/agent.<pid> ,
and the name of this socket is stored in the
.Ev SSH_AUTH_SOCK
environment
variable.  The socket is made accessible only to the current user.
This method is easily abused by root or another instance of the same
user.
.Pp
The
.Ev SSH_AGENT_PID
environment variable holds the agent's PID.
.Pp
The agent exits automatically when the command given on the command
line terminates.
.Pp
Here's a trick that will allow you to start this up from your .bash_profile (just put it in as the first thing that happens):
.Sp
.Vb 1

\&	[ ! "$SSH_AGENT_PID" ] && exec ssh-agent -- bash --login
\&	ssh-add
.Ve
.Sh FILES
.Bl -tag -width Ds
.It Pa $HOME/.ssh/identity
Contains the RSA authentication identity of the user.  This file
should not be readable by anyone but the user.  It is possible to
specify a passphrase when generating the key; that passphrase will be
used to encrypt the private part of this file.  This file
is not used by
.Nm
but is normally added to the agent using
.Xr ssh-add 1
at login time.
.It Pa /tmp/ssh-XXXX/agent.<pid> ,
Unix-domain sockets used to contain the connection to the
authentication agent.  These sockets should only be readable by the
owner.  The sockets should get automatically removed when the agent
exits.
.Sh AUTHOR
Tatu Ylonen <ylo@cs.hut.fi>
.Pp
OpenSSH
is a derivative of the original (free) ssh 1.2.12 release, but with bugs
removed and newer features re-added.   Rapidly after the 1.2.12 release,
newer versions bore successively more restrictive licenses.  This version
of OpenSSH
.Bl -bullet
.It
has all components of a restrictive nature (ie. patents, see
.Xr ssl 8 )
directly removed from the source code; any licensed or patented components
are chosen from
external libraries.
.It
has been updated to support ssh protocol 1.5.
.It
contains added support for 
.Xr kerberos 8
authentication and ticket passing.
.It
supports one-time password authentication with
.Xr skey 1 .
.El
.Pp
The libraries described in
.Xr ssl 8
are required for proper operation.
.Sh SEE ALSO
.Xr ssh 1 ,
.Xr ssh-add 1 ,
.Xr ssh-keygen 1 ,
.Xr sshd 8 ,
.Xr ssl 8
- Merged OpenBSD CVS changes - [ChangeLog.Ylonen] noone needs this anymore - [authfd.c] close-on-exec for auth-socket, ok deraadt - [hostfile.c] in known_hosts key lookup the entry for the bits does not need to match, all the information is contained in n and e. This solves the problem with buggy servers announcing the wrong modulus length. markus and me. - [serverloop.c] bugfix: check for space if child has terminated, from: iedowse@maths.tcd.ie - [ssh-add.1 ssh-add.c ssh-keygen.1 ssh-keygen.c sshconnect.c] [fingerprint.c fingerprint.h] rsa key fingerprints, idea from Bjoern Groenvall <bg@sics.se> - [ssh-agent.1] typo - [ssh.1] add OpenSSH information to AUTHOR section. okay markus@ - [sshd.c] force logging to stderr while loading private key file (lost while converting to new log-levels) 1999-11-17 06:29:08 +00:00			`.\" $OpenBSD: ssh-agent.1,v 1.8 1999/11/16 23:59:21 deraadt Exp $`
Re-imported OpenBSD manpages 1999-10-28 23:15:49 +00:00			`.\"`
			`.\" -- nroff --`
			`.\"`
			`.\" ssh-agent.1`
			`.\"`
			`.\" Author: Tatu Ylonen <ylo@cs.hut.fi>`
- Merged OpenBSD CVS changes - [ChangeLog.Ylonen] noone needs this anymore - [authfd.c] close-on-exec for auth-socket, ok deraadt - [hostfile.c] in known_hosts key lookup the entry for the bits does not need to match, all the information is contained in n and e. This solves the problem with buggy servers announcing the wrong modulus length. markus and me. - [serverloop.c] bugfix: check for space if child has terminated, from: iedowse@maths.tcd.ie - [ssh-add.1 ssh-add.c ssh-keygen.1 ssh-keygen.c sshconnect.c] [fingerprint.c fingerprint.h] rsa key fingerprints, idea from Bjoern Groenvall <bg@sics.se> - [ssh-agent.1] typo - [ssh.1] add OpenSSH information to AUTHOR section. okay markus@ - [sshd.c] force logging to stderr while loading private key file (lost while converting to new log-levels) 1999-11-17 06:29:08 +00:00			`.\"`
Re-imported OpenBSD manpages 1999-10-28 23:15:49 +00:00			`.\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland`
			`.\" All rights reserved`
			`.\"`
			`.\" Created: Sat Apr 23 20:10:43 1995 ylo`
			`.\"`
			`.Dd September 25, 1999`
			`.Dt SSH-AGENT 1`
			`.Os`
			`.Sh NAME`
			`.Nm ssh-agent`
			`.Nd authentication agent`
			`.Sh SYNOPSIS`
			`.Nm ssh-agent`
			`.Op Fl c Li \| Fl s`
			`.Op Fl k`
			`.Oo`
			`.Ar command`
			`.Op Ar args ...`
			`.Oc`
			`.Sh DESCRIPTION`
			`.Nm`
			`is a program to hold authentication private keys. The`
			`idea is that`
			`.Nm`
			`is started in the beginning of an X-session or a login session, and`
			`all other windows or programs are started as clients to the ssh-agent`
			`program. Through use of environment variables the agent can be located`
			`and automatically used for RSA authentication when logging in to other`
			`machines using`
			`.Xr ssh 1 .`
			`.Pp`
			`The options are as follows:`
			`.Bl -tag -width Ds`
			`.It Fl c`
			`Generate C-shell commands on`
			`.Dv stdout .`
			`This is the default if`
			`.Ev SHELL`
			`looks like it's a csh style of shell.`
			`.It Fl s`
			`Generate Bourne shell commands on`
			`.Dv stdout .`
			`This is the default if`
			`.Ev SHELL`
			`does not look like it's a csh style of shell.`
			`.It Fl k`
			`Kill the current agent (given by the`
			`.Ev SSH_AGENT_PID`
			`environment variable).`
			`.El`
			`.Pp`
			`If a commandline is given, this is executed as a subprocess of the agent.`
			`When the command dies, so does the agent.`
			`.Pp`
			`The agent initially does not have any private keys. Keys are added`
			`using`
			`.Xr ssh-add 1 .`
			`When executed without arguments,`
			`.Xr ssh-add 1`
			`adds the`
			`.Pa $HOME/.ssh/identity`
			`file. If the identity has a passphrase,`
			`.Xr ssh-add 1`
			`asks for the passphrase (using a small X11 application if running`
			`under X11, or from the terminal if running without X). It then sends`
			`the identity to the agent. Several identities can be stored in the`
			`agent; the agent can automatically use any of these identities.`
			`.Ic ssh-add -l`
			`displays the identities currently held by the agent.`
			`.Pp`
			`The idea is that the agent is run in the user's local PC, laptop, or`
			`terminal. Authentication data need not be stored on any other`
			`machine, and authentication passphrases never go over the network.`
			`However, the connection to the agent is forwarded over SSH`
			`remote logins, and the user can thus use the privileges given by the`
			`identities anywhere in the network in a secure way.`
			`.Pp`
			`There are two main ways to get an agent setup: Either you let the agent`
			`start a new subcommand into which some environment variables are exported, or`
			`you let the agent print the needed shell commands (either`
			`.Xr sh 1`
			`or`
			`.Xr csh 1`
			`syntax can be generated) which can be evalled in the calling shell.`
			`Later`
			`.Xr ssh 1`
			`look at these variables and use them to establish a connection to the agent.`
			`.Pp`
			`A unix-domain socket is created`
			`.Pq Pa /tmp/ssh-XXXXXXXX/agent.<pid> ,`
			`and the name of this socket is stored in the`
			`.Ev SSH_AUTH_SOCK`
			`environment`
			`variable. The socket is made accessible only to the current user.`
			`This method is easily abused by root or another instance of the same`
			`user.`
			`.Pp`
			`The`
			`.Ev SSH_AGENT_PID`
			`environment variable holds the agent's PID.`
			`.Pp`
			`The agent exits automatically when the command given on the command`
			`line terminates.`
Lots of changes: - Removed lots of unnecessary checks from autoconf - Added support and autoconf test for openpty() function (Unix98 pty support) - Fix for scp not finding ssh if not installed as /usr/bin/ssh - Added TODO file - Merged parts of Debian patch From Phil Hands <phil@hands.com>: - Added ssh-askpass program - Added ssh-askpass support to ssh-add.c - Create symlinks for slogin on install - Fix "distclean" target in makefile - Added example for ssh-agent to manpage - Added support for PAM_TEXT_INFO messages - Disable internal /etc/nologin support if PAM enabled - Merged latest OpenBSD CVS changes: - [sshd.c] don't send fail-msg but disconnect if too many authentication failures - [sshd.c] replace assert() with error, fatal or packet_disconnect - [sshd.c] remove unused argument. ok dugsong - [sshd.c] typo - [rsa.c] clear buffers used for encryption. ok: niels - [rsa.c] replace assert() with error, fatal or packet_disconnect - Fixed coredump after merge of OpenBSD rsa.c patch 1999-11-08 04:30:59 +00:00			`.Pp`
			`Here's a trick that will allow you to start this up from your .bash_profile (just put it in as the first thing that happens):`
			`.Sp`
			`.Vb 1`

			`\& [ ! "$SSH_AGENT_PID" ] && exec ssh-agent -- bash --login`
			`\& ssh-add`
			`.Ve`
Re-imported OpenBSD manpages 1999-10-28 23:15:49 +00:00			`.Sh FILES`
			`.Bl -tag -width Ds`
			`.It Pa $HOME/.ssh/identity`
			`Contains the RSA authentication identity of the user. This file`
			`should not be readable by anyone but the user. It is possible to`
			`specify a passphrase when generating the key; that passphrase will be`
			`used to encrypt the private part of this file. This file`
			`is not used by`
			`.Nm`
			`but is normally added to the agent using`
			`.Xr ssh-add 1`
			`at login time.`
			`.It Pa /tmp/ssh-XXXX/agent.<pid> ,`
			`Unix-domain sockets used to contain the connection to the`
			`authentication agent. These sockets should only be readable by the`
			`owner. The sockets should get automatically removed when the agent`
			`exits.`
			`.Sh AUTHOR`
			`Tatu Ylonen <ylo@cs.hut.fi>`
			`.Pp`
			`OpenSSH`
			`is a derivative of the original (free) ssh 1.2.12 release, but with bugs`
			`removed and newer features re-added. Rapidly after the 1.2.12 release,`
			`newer versions bore successively more restrictive licenses. This version`
			`of OpenSSH`
			`.Bl -bullet`
			`.It`
			`has all components of a restrictive nature (ie. patents, see`
			`.Xr ssl 8 )`
			`directly removed from the source code; any licensed or patented components`
			`are chosen from`
			`external libraries.`
			`.It`
			`has been updated to support ssh protocol 1.5.`
			`.It`
			`contains added support for`
			`.Xr kerberos 8`
			`authentication and ticket passing.`
			`.It`
			`supports one-time password authentication with`
			`.Xr skey 1 .`
			`.El`
			`.Pp`
			`The libraries described in`
			`.Xr ssl 8`
			`are required for proper operation.`
			`.Sh SEE ALSO`
			`.Xr ssh 1 ,`
			`.Xr ssh-add 1 ,`
			`.Xr ssh-keygen 1 ,`
			`.Xr sshd 8 ,`
			`.Xr ssl 8`