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DHCLIENT(8)		  BSD System Manager's Manual		   DHCLIENT(8)

     dhclient -- Dynamic Host Configuration Protocol (DHCP) client

     dhclient [-dqu] [-c file] [-l file] interface

     The dhclient utility provides a means for configuring network interfaces
     using DHCP, BOOTP,	or if these protocols fail, by statically assigning an

     The name of the network interface that dhclient should attempt to config-
     ure must be specified on the command line.

     The options are as	follows:

     -b	      Forces dhclient to immediately move to the background.

     -c	file  Specify an alternate location, file, for the configuration file.

     -d	      Forces dhclient to always	run as a foreground process.  By de-
	      fault, dhclient runs in the foreground until it has configured
	      the interface, and then will revert to running in	the back-

     -l	file  Specify an alternate location, file, for the leases file.

     -q	      Forces dhclient to be less verbose on startup.

     -u	      Forces dhclient to reject	leases with unknown options in them.
	      The default behaviour is to accept such lease offers.

     The DHCP protocol allows a	host to	contact	a central server which main-
     tains a list of IP	addresses which	may be assigned	on one or more sub-
     nets.  A DHCP client may request an address from this pool, and then use
     it	on a temporary basis for communication on the network.	The DHCP pro-
     tocol also	provides a mechanism whereby a client can learn	important de-
     tails about the network to	which it is attached, such as the location of
     a default router, the location of a name server, and so on.

     On	startup, dhclient reads	/etc/dhclient.conf for configuration instruc-
     tions.  It	then gets a list of all	the network interfaces that are	con-
     figured in	the current system.  It	then attempts to configure each	inter-
     face with DHCP.

     In	order to keep track of leases across system reboots and	server
     restarts, dhclient	keeps a	list of	leases it has been assigned in the
     /var/db/dhclient.leases.IFNAME file.  IFNAME represents the network in-
     terface of	the DHCP client	(e.g., em0), one for each interface.  On
     startup, after reading the	dhclient.conf(5) file, dhclient	reads the
     leases file to refresh its	memory about what leases it has	been assigned.

     Old leases	are kept around	in case	the DHCP server	is unavailable when
     dhclient is first invoked (generally during the initial system boot
     process).	In that	event, old leases from the dhclient.leases.IFNAME file
     which have	not yet	expired	are tested, and	if they	are determined to be
     valid, they are used until	either they expire or the DHCP server becomes

     A mobile host which may sometimes need to access a	network	on which no
     DHCP server exists	may be preloaded with a	lease for a fixed address on
     that network.  When all attempts to contact a DHCP	server have failed,
     dhclient will try to validate the static lease, and if it succeeds, it
     will use that lease until it is restarted.

     A mobile host may also travel to some networks on which DHCP is not
     available but BOOTP is.  In that case, it may be advantageous to arrange
     with the network administrator for	an entry on the	BOOTP database,	so
     that the host can boot quickly on that network rather than	cycling
     through the list of old leases.

     You must have the Berkeley	Packet Filter (BPF) configured in your kernel.
     The dhclient utility requires at least one	/dev/bpf* device for each
     broadcast network interface that is attached to your system.  See bpf(4)
     for more information.

     /etc/dhclient.conf		     DHCP client configuration file
     /var/db/dhclient.leases.IFNAME  database of acquired leases

     dhclient.conf(5), dhclient.leases(5), dhclient-script(8), dhcp(8),
     dhcpd(8), dhcrelay(8)

     The dhclient utility was written by Ted Lemon <> and
     Elliot Poger <>.

     The current implementation	was reworked by	Henning	Brauer

BSD				 July 22, 2005				   BSD


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