openssh-0bsdforeveryone/ssh-agent.0

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

NAME
     ssh-agent M-bM-^@M-^S OpenSSH authentication agent

SYNOPSIS
     ssh-agent [-c | -s] [-Dd] [-a bind_address] [-E fingerprint_hash]
               [-O option] [-P allowed_providers] [-t life]
     ssh-agent [-a bind_address] [-E fingerprint_hash] [-O option]
               [-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 standard output.  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: M-bM-^@M-^\md5M-bM-^@M-^] and M-bM-^@M-^\sha256M-bM-^@M-^].  The
             default is M-bM-^@M-^\sha256M-bM-^@M-^].

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

     -O option
             Specify an option when starting ssh-agent.  The supported options
             are: allow-remote-pkcs11, no-restrict-websafe and websafe-allow.

             The allow-remote-pkcs11 option allows clients of a forwarded
             ssh-agent to load PKCS#11 or FIDO provider libraries.  By default
             only local clients may perform this operation.  Note that
             signalling that an ssh-agent client is remote is performed by
             ssh(1), and use of other tools to forward access to the agent
             socket may circumvent this restriction.

             The no-restrict-websafe option instructs ssh-agent to permit
             signatures using FIDO keys that might be web authentication
             requests.  By default, ssh-agent refuses signature requests for
             FIDO keys where the key application string does not start with
             M-bM-^@M-^\ssh:M-bM-^@M-^] and when the data to be signed does not appear to be a
             ssh(1) user authentication request or a ssh-keygen(1) signature.
             The default behaviour prevents forwarded access to a FIDO key
             from also implicitly forwarding the ability to authenticate to
             websites.

             Alternately the websafe-allow option allows specifying a pattern-
             list of key application strings to replace the default
             application allow-list, for example:
             M-bM-^@M-^\websafe-allow=ssh:*,example.org,*.example.comM-bM-^@M-^]

             See PATTERNS in ssh_config(5) for a description of pattern-list
             syntax.

     -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.  The default list is
             M-bM-^@M-^\usr/lib*/*,/usr/local/lib*/*M-bM-^@M-^].

             See PATTERNS in ssh_config(5) for a description of pattern-list
             syntax.

     -s      Generate Bourne shell commands on standard output.  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 three 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 of these cases, ssh(1) looks at these environment variables and
     uses them to establish a connection to the agent.

     The third way to run ssh-agent is via socket activation from a
     supervising process, such as systemd.  In this mode, the supervising
     process creates the listening socket and is responsible for starting
     ssh-agent as needed, and also for communicating the location of the
     socket listener to other programs in the user's session.  Socket
     activation is used when ssh-agent is started with either of the -d or -D
     flags, no socket listening address specified by the -a flag, and both the
     LISTEN_FDS and LISTEN_PID environment variables correctly supplied by the
     supervising process.

     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.

     ssh-agent will delete all keys it has loaded upon receiving SIGUSR1.

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.

OpenBSD 7.6                    February 9, 2025                    OpenBSD 7.6