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

     ssh-agent -- OpenSSH authentication agent

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

     ssh-agent is a program to hold private keys used for public key authenti-
     cation.  Through use of environment variables the agent can be located
     and automatically used for authentication when logging in to other ma-
     chines using ssh(1).

     The options are as follows:

     -a bind_address
             Bind the agent to the UNIX-domain socket bind_address.  The de-
             fault 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 provider_whitelist
             Specify a pattern-list of acceptable paths for PKCS#11 and FIDO
             authenticator shared libraries that may be used with the -S or -s
             options to ssh-add(1).  Libraries that do not match the whitelist
             will be refused.  See PATTERNS in ssh_config(5) for a description
             of pattern-list syntax.  The default whitelist is

     -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 exam-
     ple 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 re-
     move 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), avoid-
     ing the need for authentication data to be stored on other machines.  Au-
     thentication 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.

     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.

     In Debian, ssh-agent is installed with the set-group-id bit set, to pre-
     vent ptrace(2) attacks retrieving private key material.  This has the
     side-effect of causing the run-time linker to remove certain environment
     variables which might have security implications for set-id programs, in-
     cluding LD_PRELOAD, LD_LIBRARY_PATH, and TMPDIR.  If you need to set any
     of these environment variables, you will need to do so in the program ex-
     ecuted by ssh-agent.

             UNIX-domain sockets used to contain the connection to the authen-
             tication agent.  These sockets should only be readable by the
             owner.  The sockets should get automatically removed when the
             agent exits.

     ssh(1), ssh-add(1), ssh-keygen(1), ssh_config(5), sshd(8)

     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 cre-
     ated OpenSSH.  Markus Friedl contributed the support for SSH protocol
     versions 1.5 and 2.0.

BSD                            December 21, 2019                           BSD
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