ssh-agent(1)

NAME

       ssh-agent - authentication agent

SYNOPSIS

       ssh-agent [-a bind_address] [-c | -s] [-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).

       -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,  lap-
              top, 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 setup: Either the  agent
              starts  a  new  subcommand into which some environment variables
              are exported, or 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.  Later ssh(1) looks at these vari-
              ables and uses them to establish a connection 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, private 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 com-
              mand 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.

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
       protocol versions 1.5 and 2.0.

SEE ALSO

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

                              September 25, 1999                  SSH-AGENT(1)