ssh-agent(1) General Commands Manual ssh-agent(1)

NAME

 ssh-agent - OpenSSH authentication agent

SYNOPSIS

 ssh-agent [-c | -s] [-DdTU] [-a bind_address] [-E fingerprint_hash]
 [-O option] [-P allowed_providers] [-t life]
 ssh-agent [-TU] [-a bind_address] [-E fingerprint_hash] [-O option]
 [-P allowed_providers] [-t life] command [arg ...]
 ssh-agent [-c | -s] -k
 ssh-agent -u

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 to create a socket at a random path matching
 $HOME/.ssh/agent/s.*.
 -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: "md5" and "sha256". The
 default is "sha256".
 -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
 "ssh:" and when the data to be signed does not appear to be an
 ssh(1)  user authentication request or an 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:
 "websafe-allow=ssh:*,example.org,*.example.com"
 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
 "usr/lib*/*,/usr/local/lib*/*".
 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 Bind the agent socket in a randomised subdirectory of the form
 $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>, instead of the default
 behaviour of using a randomised name matching
 $HOME/.ssh/agent/s.*.
 -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.
 -U Instructs ssh-agent not to clean up stale agent sockets under
 $HOME/.ssh/agent/.
 -u Instructs ssh-agent to only clean up stale agent sockets under
 $HOME/.ssh/agent/ and then exit immediately. If this option is
 given twice, ssh-agent will delete stale agent sockets regardless
 of the host name that created them.
 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

 $HOME/.ssh/agent/s.*
 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.
macOS 15.7 October 4, 2025 macOS 15.7