dhclient(8) - Dynamic Host Configuration Protocol Client
-4     Use  the  DHCPv4  protocol  to  obtain  an IPv4 address and configuration parameters.  This is the
       default and cannot be combined with -6.
-6     Use the DHCPv6 protocol to obtain whatever IPv6 addresses are available along  with  configuration
       parameters.   It  cannot  be combined with -4.  The -S -T -P and -N arguments provide more control
       over aspects of the DHCPv6 processing.  Note: it is not recommended to mix  queries  of  different
       types together or even to share the lease file between them.
-1     Try  to  get a lease once.  On failure exit with code 2.  In DHCPv6 this sets the maximum duration
       of the initial exchange to timeout (from dhclient.conf(5) with a default of sixty seconds).
-d     Force dhclient to run as a  foreground  process.   Normally  the  DHCP  client  will  run  in  the
       foreground  until  is  has  configured an interface at which time it will revert to running in the
       background.  This option is useful when running the client under a debugger, or  when  running  it
       out of inittab on System V systems.  This implies -v.
-nw    Become a daemon immediately (nowait) rather than waiting until an an IP address has been acquired.
-q     Be quiet at startup, this is the default.
-v     Enable verbose log messages.
-w     Continue running even if no broadcast interfaces were found.  Normally DHCP client will exit if it
       isn't able to identify any network  interfaces  to  configure.   On  laptop  computers  and  other
       computers  with  hot-swappable  I/O  buses, it is possible that a broadcast interface may be added
       after system startup.  This flag can be used to cause the client not to exit when it doesn't  find
       any such interfaces.   The omshell(1) program can then be used to notify the client when a network
       interface has been added or removed, so that the client can attempt to configure an IP address  on
       that interface.
-n     Do  not  configure  any  interfaces.   This is most likely to be useful in combination with the -w
       flag.
-e VAR=val
       Define additional environment variables for the  environment  where  dhclient-script(8)  executes.
       You may specify multiple -e options on the command line.
-r     Release the current lease and stop the running DHCP client as previously recorded in the PID file.
       When shutdown via this method dhclient-script(8) will be executed with  the  specific  reason  for
       calling  the  script  set.   The  client normally doesn't release the current lease as this is not
       required by the DHCP protocol but some cable ISPs require their clients to notify  the  server  if
       they wish to release an assigned IP address.
-x     Stop the running DHCP client without releasing the current lease.  Kills existing dhclient process
       as previously recorded in the PID file.  When shutdown via this method dhclient-script(8) will  be
       executed with the specific reason for calling the script set.
-p port
       The UDP port number on which the DHCP client should listen and transmit.  If unspecified, dhclient
       uses the default port of 68.  This is mostly useful for debugging purposes.  If a  different  port
       is  specified on which the client should listen and transmit, the client will also use a different
       destination port - one less than the specified port.
-s server-addr
       Specify the server IP address or fully qualified domain name to use  as  a  destination  for  DHCP
       protocol  messages before dhclient has acquired an IP address.  Normally, dhclient transmits these
       messages to 255.255.255.255 (the IP limited broadcast address).  Overriding this is mostly  useful
       for debugging purposes.  This feature is not supported in DHCPv6 (-6) mode.
-g relay
       Set the giaddr field of all packets to the relay IP address simulating a relay agent.  This is for
       testing pruposes only and should not be expected to work in any consistent or useful way.
--version
       Print version number and exit.

Options available for DHCPv6 mode:
-S     Use Information-request to get only stateless configuration parameters  (i.e.,  without  address).
       This implies -6.  It also doesn't rewrite the lease database.
-T     Ask  for  IPv6  temporary  addresses,  one set per -T flag.  This implies -6 and also disables the
       normal address query.  See -N to restore it.
-P     Enable IPv6 prefix delegation.  This implies -6 and also disables the normal address  query.   See
       -N to restore it.  Note only one requested interface is allowed.
-N     Restore  normal  address  query for IPv6. This implies -6.  It is used to restore normal operation
       after using -T or -P.

Modifying default file locations: The following options can be used to modify the locations a client uses
for  it's  files.  They can be particularly useful if, for example, DBDIR or RUNDIR have not been mounted
when the DHCP client is started.
-cf config-file
       Path to the client configuration file.  If unspecified, the default ETCDIR/dhclient.conf is  used.
       See dhclient.conf(5) for a description of this file.
-lf lease-file
       Path  to the lease database file.  If unspecified, the default DBDIR/dhclient.leases is used.  See
       dhclient.leases(5) for a descriptionof this file.
-pf pid-file
       Path to the process ID file.  If unspecified, the default RUNDIR/dhclient.pid is used.
--no-pid
       Option to disable writing pid files.  By default the program  will  write  a  pid  file.   If  the
       program is invoked with this option it will not attempt to kill any existing client processes even
       if invoked with -r or -x.
-sf script-file
       Path to the  network  configuration  script  invoked  by  dhclient  when  it  gets  a  lease.   If
       unspecified,  the  default  CLIENTBINDIR/dhclient-script  is  used.   See dhclient-script(8) for a
       description of this file.