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NAME

       ssh-agent — OpenSSH authentication agent

SYNOPSIS

       ssh-agent  [-c  |  -s]  [-Dd]  [-a  bind_address] [-E fingerprint_hash] [-P provider_whitelist] [-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 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 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 provider_whitelist
               Specify a pattern-list of acceptable paths for PKCS#11 and FIDO  authenticator  shared  libraries
               that  may  be  used  with  the  -S  or -s options to ssh-add(1).  Libraries that do not match the
               whitelist will be refused.  See PATTERNS in  ssh_config(5)  for  a  description  of  pattern-list
               syntax.  The default whitelist is “/usr/lib/*,/usr/local/lib/*”.

       -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.

       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  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

       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.

       In  Debian, ssh-agent is installed with the set-group-id bit set, to prevent ptrace(2) attacks retrieving
       private key material.  This has the  side-effect  of  causing  the  run-time  linker  to  remove  certain
       environment  variables  which might have security implications for set-id programs, including LD_PRELOAD,
       LD_LIBRARY_PATH, and TMPDIR.  If you need to set any of these environment variables, you will need to  do
       so in the program executed by ssh-agent.

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.

Debian                                          December 21, 2019                                   SSH-AGENT(1)