ssh-agent manpage

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

     ssh-agent -- authentication agent

     ssh-agent [-c | -s] [-Dd] [-a bind_address] [-E fingerprint_hash]
	       [-P pkcs11_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 (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 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.

     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 ``sha256''.

     -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 ter-
     minal.  Authentication data need not be stored on any other machine, and
     authentication passphrases never go over the network.  However, the con-
     nection to the agent is forwarded over SSH remote logins, and the user
     can thus use the privileges given by the identities anywhere in the net-
     work 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 generated)
     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, pri-
     vate 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 accessible
     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

	     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.

	     The reseeding of the OpenSSL random generator is usually done
	     from /dev/urandom.	 If the SSH_USE_STRONG_RNG environment vari-
	     able is set to value other than 0 the OpenSSL random generator is
	     reseeded from /dev/random.	 The number of bytes read is defined
	     by the SSH_USE_STRONG_RNG value.  Minimum is 14 bytes.  This set-
	     ting is not recommended on the computers without the hardware
	     random generator because insufficient entropy causes the connec-
	     tion to be blocked until enough entropy is available.

     ssh(1), ssh-add(1), ssh-keygen(1), 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				 June 25, 2019				   BSD