ssh-agent

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

NAME
     ssh-agent — OpenSSH authentication agent

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

DESCRIPTION
     ssh-agent is a program to hold private keys used for public key
     authentication.  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      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 fingerprints.
             Valid options are: “md5” and “sha256”.  The default is “sha256”.

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

     -P allowed_providers
             Specify a pattern-list of acceptable paths for PKCS#11 provider and
             FIDO authenticator middleware shared libraries that may be used
             with the -S or -s options to ssh-add(1).  Libraries that do not
             match the pattern list will be refused.  See PATTERNS in
             ssh_config(5) for a description of pattern-list syntax.  The
             default list is “/usr/lib/*,/usr/local/lib/*”.

     -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.

     command [arg ...]
             If a command (and optional arguments) is given, this is executed as
             a subprocess of the agent.  The agent exits automatically when the
             command given on the command line terminates.

     There are two main ways to get an agent set up.  The first is at the start
     of an X session, where all other windows or programs are started as
     children of the ssh-agent program.  The agent starts a command under which
     its environment variables are exported, for example ssh-agent xterm &.
     When the command terminates, so does the agent.

     The second method is used for a login session.  When ssh-agent is started,
     it prints the shell commands required to set its environment variables,
     which in turn can be evaluated in the calling shell, for example eval
     `ssh-agent -s`.

     In both cases, ssh(1) looks at these environment variables and uses them to
     establish a connection to the agent.

     The agent initially does not have any private keys.  Keys are added using
     ssh-add(1) or by ssh(1) when AddKeysToAgent is set in ssh_config(5).
     Multiple identities may be stored in ssh-agent concurrently 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.

     Connections to ssh-agent may be forwarded from further remote hosts using
     the -A option to ssh(1) (but see the caveats documented therein), avoiding
     the need for authentication data to be stored on other machines.
     Authentication passphrases and private keys never go over the network: the
     connection to the agent is forwarded over SSH remote connections and the
     result is returned to the requester, allowing the user access to their
     identities anywhere in the network in a secure fashion.

ENVIRONMENT
     SSH_AGENT_PID  When ssh-agent starts, it stores the name of the agent's
                    process ID (PID) in this variable.

     SSH_AUTH_SOCK  When ssh-agent starts, it creates a UNIX-domain socket and
                    stores its pathname in this variable.  It is accessible only
                    to the current user, but is easily abused by root or another
                    instance of the same user.

FILES
     $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), ssh_config(5), 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.

BSD                               June 22, 2020                              BSD