xref: /freebsd-10.1-release/crypto/openssh/ssh-agent.0

SSH-AGENT(1)               OpenBSD Reference Manual               SSH-AGENT(1)

NAME
     ssh-agent - authentication agent

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

DESCRIPTION
     ssh-agent is a program to hold private keys used for public key
     authentication (RSA, DSA, ECDSA, ED25519).  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 $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>.

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

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

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

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

     -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_config(5).  A lifetime specified
             for an identity with ssh-add(1) overrides this value.  Without
             this option the default maximum lifetime is forever.

     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
     ~/.ssh/id_rsa, ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 and
     ~/.ssh/identity.  If the identity has a passphrase, ssh-add(1) asks for
     the passphrase on the terminal if it has one or from a small X11 program
     if running under X11.  If neither of these is the case then the
     authentication will fail.  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 evaluated 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 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 command line
     terminates.

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

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

     ~/.ssh/id_ecdsa
             Contains the protocol version 2 ECDSA authentication identity of
             the user.

     ~/.ssh/id_ed25519
             Contains the protocol version 2 ED25519 authentication identity
             of the user.

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

     $TMPDIR/ssh-XXXXXXXXXX/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.

OpenBSD 5.5                    December 7, 2013                    OpenBSD 5.5