ssh-agent — OpenSSH authentication agent

       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                                           August 10, 2023                                    SSH-AGENT(1)

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:

       -abind_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.

       -Efingerprint_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).

       -Ooption
               Specify   an   option   when   starting   ssh-agent.    Currently   two  options  are  supported:
               allow-remote-pkcs11 and no-restrict-websafe.

               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 a ssh(1) user authentication request or  a  ssh-keygen(1)  signature.   The
               default  behaviour  prevents  forwarded  access to a FIDO key from also implicitly forwarding the
               ability to authenticate to websites.

       -Pallowed_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 “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.

       -tlife
               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-agentxterm&.  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.

       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.

$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.

       ssh-agent — OpenSSH authentication agent

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

ssh-agent  [-c  |  -s]  [-Dd]  [-abind_address] [-Efingerprint_hash] [-Ooption] [-Pallowed_providers]
                 [-tlife]
       ssh-agent [-abind_address] [-Efingerprint_hash] [-Ooption] [-Pallowed_providers]  [-tlife]  command
                 [arg...]
       ssh-agent [-c | -s] -k