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

NAME         top

     ssh-agent — authentication agent

SYNOPSIS         top

     ssh-agent [-c | -s] [-Dd] [-a bind_address] [-E fingerprint_hash]
               [-P pkcs11_whitelist] [-t life] [command [arg ...]]
     ssh-agent [-c | -s] -k

DESCRIPTION         top

     ssh-agent is a program to hold private keys used for public key authen‐
     tication (RSA, DSA, ECDSA, Ed25519).  ssh-agent is usually 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 agent initially does not have any private keys.  Keys are added
     using ssh(1) (see AddKeysToAgent in ssh_config(5) for details) or
     ssh-add(1).  Multiple identities may be stored in ssh-agent concur‐
     rently and ssh(1) will automatically use them if present.  ssh-add(1)
     is also used to remove keys from ssh-agent and to query the keys that
     are held in one.

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

     -d      Debug mode.  When this option is specified ssh-agent will not
             fork and will write debug information to standard error.

     -E fingerprint_hash
             Specifies the hash algorithm used when displaying key finger‐
             prints.  Valid options are: “md5” and “sha256”.  The default is

     -k      Kill the current agent (given by the SSH_AGENT_PID environment

     -P pkcs11_whitelist
             Specify a pattern-list of acceptable paths for PKCS#11 shared
             libraries that may be added using the -s option to ssh-add(1).
             The default is to allow loading PKCS#11 libraries from
             “/usr/lib/*,/usr/local/lib/*”.  PKCS#11 libraries that do not
             match the whitelist will be refused.  See PATTERNS in
             ssh_config(5) for a description of pattern-list syntax.

     -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 command line is given, this is executed as a subprocess of the
     agent.  When the command dies, so does 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 gener‐
     ated) 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 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,
     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 accessi‐
     ble 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         top

             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         top

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

AUTHORS         top

     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.

COLOPHON         top

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BSD                           November 30, 2016                          BSD