ssh-agent

SSH-AGENT(1)		 BSD General Commands Manual		 SSH-AGENT(1)

NAME
     ssh-agent - authentication agent

SYNOPSIS
     ssh-agent [-a bind_address] [-c | -s] [-t life] [-d]
	       [command [args ...]]
     ssh-agent [-c | -s] -k

DESCRIPTION
     ssh-agent is a program to hold private keys used for public key authen-
     tication (RSA, DSA).  The idea is that ssh-agent 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 authentication when logging in to other machines using ssh(1).

     The options are as follows:

     -a bind_address
	     Bind the agent to the unix-domain socket bind_address.  The
	     default is /tmp/ssh-XXXXXXXX/agent.<ppid>.

     -c	     Generate C-shell commands on stdout.  This is the default if
	     SHELL looks like it’s a csh style of shell.

     -s	     Generate Bourne shell commands on stdout.	This is the default
	     if SHELL does not look like it’s a csh style of shell.

     -k	     Kill the current agent (given by the SSH_AGENT_PID environment
	     variable).

     -t life
	     Set a default value for the maximum lifetime of identities added
	     to the agent.  The lifetime may be specified in seconds or in a
	     time format specified in sshd(8).	A lifetime specified for an
	     identity with ssh-add(1) overrides this value.  Without this
	     option the default maximum lifetime is forever.

     -d	     Debug mode.  When this option is specified ssh-agent will not
	     fork.

     If a commandline is given, this is executed as a subprocess of the
     agent.  When the command dies, so does the agent.

     The agent initially does not have any private keys.  Keys are added
     using ssh-add(1).	When executed without arguments, ssh-add(1) adds the
     files $HOME/.ssh/id_rsa, $HOME/.ssh/id_dsa and $HOME/.ssh/identity.  If
     the identity has a passphrase, 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.  ssh-add -l displays the identities currently
     held by the agent.

     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.

     There are two main ways to get an agent set up: The first is that the
     agent starts a new subcommand into which some environment variables are
     exported, eg ssh-agent xterm &.  The second is that the agent prints the
     needed shell commands (either sh(1) or csh(1) syntax can be generated)
     which can be evalled in the calling shell, eg eval ‘ssh-agent -s‘ for
     Bourne-type shells such as sh(1) or ksh(1) and eval ‘ssh-agent -c‘ for
     csh(1) and derivatives.

     Later ssh(1) looks at these variables and uses them to establish a con-
     nection to the agent.

     The agent will never send a private key over its request channel.
     Instead, operations that require a private key will be performed by the
     agent, and the result will be returned to the requester.  This way, pri-
     vate keys are not exposed to clients using the agent.

     A unix-domain socket is created and the name of this socket is stored in
     the 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.

     The SSH_AGENT_PID environment variable holds the agent’s process ID.

     The agent exits automatically when the command given on the command line
     terminates.

FILES
     $HOME/.ssh/identity
	     Contains the protocol version 1 RSA authentication identity of
	     the user.

     $HOME/.ssh/id_dsa
	     Contains the protocol version 2 DSA authentication identity of
	     the user.

     $HOME/.ssh/id_rsa
	     Contains the protocol version 2 RSA authentication identity of
	     the user.

     /tmp/ssh-XXXXXXXX/agent.<ppid>
	     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.

SEE ALSO
     ssh(1), ssh-add(1), ssh-keygen(1), sshd(8)

AUTHORS
     OpenSSH is a derivative of the original and free ssh 1.2.12 release by
     Tatu Ylonen.  Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
     Theo de Raadt and Dug Song removed many bugs, re-added newer features
     and created OpenSSH.  Markus Friedl contributed the support for SSH pro-
     tocol versions 1.5 and 2.0.

BSD			      September 25, 1999			  BSD