ssh-agent(1) — Linux manual page


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

NAME         top

     ssh-agent — OpenSSH authentication agent

SYNOPSIS         top

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

DESCRIPTION         top

     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 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

     -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).

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

     -s      Generate Bourne shell commands on stdout.  This is the
             default if SHELL does not look like it's a csh style of

     -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

     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 example 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 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.

ENVIRONMENT         top

     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         top

             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         top

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

AUTHORS         top

     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.

COLOPHON         top

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BSD                           June 22, 2020                          BSD