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, 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 set up: The first is
              that the agent starts a new subcommand into which some  environ-
              ment  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 connection to the agent.

              The  agent  will never send a private key over its request chan-
              nel.  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.

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
       protocol versions 1.5 and 2.0.

                              September 25, 1999                  SSH-AGENT(1)