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

NAME
     ssh-agent - authentication agent

SYNOPSIS
     ssh-agent [-c | -s] [-d] [-a bind_address] [-t life] [command [arg ...]]
     ssh-agent [-c | -s] -k

DESCRIPTION
     ssh-agent is a program to hold private keys used for public key authentication (RSA, DSA, ECDSA).  The idea is
     that ssh-agent is 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 options are as follows:

     -a bind_address
             Bind the agent to the unix-domain socket bind_address.  The default is /tmp/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      Debug mode.  When this option is specified ssh-agent will not fork.

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

     -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 spec-
             ified 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 commandline is given, this is executed as a subprocess of the agent.  When the command dies, so does the
     agent.

     The agent initially does not have any private keys.  Keys are added using ssh-add(1).  When executed without
     arguments, ssh-add(1) adds the files ~/.ssh/id_rsa, ~/.ssh/id_dsa, ~/.ssh/id_ecdsa and ~/.ssh/identity.  If the
     identity has a passphrase, ssh-add(1) asks for the passphrase (using a small X11 application if running under
     X11, or from the terminal if running without X).  It then sends the identity to the agent.  Several identities
     can be stored in the agent; the agent can automatically use any of these identities.  ssh-add -l displays the
     identities currently held by the agent.

     The idea is that the agent is run in the user's local PC, laptop, or terminal.  Authentication data need not be
     stored on any other machine, and authentication passphrases never go over the network.  However, the connection
     to the agent is forwarded over SSH remote logins, and the user can thus use the privileges given by the identi-
     ties anywhere in the network 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 deriva-
     tives.

     Later ssh(1) looks at these variables and uses them to establish a connection 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, private 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 terminates.

FILES
     ~/.ssh/identity
             Contains the protocol version 1 RSA authentication identity of the user.

     ~/.ssh/id_dsa
             Contains the protocol version 2 DSA authentication identity of the user.

     ~/.ssh/id_ecdsa
             Contains the protocol version 2 ECDSA authentication identity of the user.

     ~/.ssh/id_rsa
             Contains the protocol version 2 RSA authentication identity of the user.

     /tmp/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.

ENVIRONMENT
     SSH_USE_STRONG_RNG
             The reseeding of the OpenSSL random generator is usually done from /dev/urandom.  If the
             SSH_USE_STRONG_RNG environment variable 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 setting is not recommended on the computers without the hardware random generator
             because insufficient entropy causes the connection to be blocked until enough entropy is available.

SEE ALSO
     ssh(1), ssh-add(1), ssh-keygen(1), 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                            November 24, 2017                           BSD