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dhclient(8)             FreeBSD System Manager's Manual            dhclient(8)

       dhclient - Dynamic Host Configuration Protocol Client

       dhclient [ -Ddq1 ] [ -cf config-file ] [ -lf lease-file ] [ -p port ] [
       -pf pidfile ] [ if0 [ ...ifN ] ]

       The Internet Software Consortium DHCP Client, dhclient, provides a
       means for configuring one or more network interfaces using the Dynamic
       Host Configuration Protocol, BOOTP protocol, or if these protocols
       fail, by statically assigning an address.

       The DHCP protocol allows a host to contact a central server which
       maintains a list of IP addresses which may be assigned on one or more
       subnets.   A DHCP client may request an address from this pool, and
       then use it on a temporary basis for communication on network.   The
       DHCP protocol also provides a mechanism whereby a client can learn
       important details 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 startup, dhclient reads the dhclient.conf for configuration
       instructions.   It then gets a list of all the network interfaces that
       are configured in the current system.   For each interface, it attempts
       to configure the interface using the DHCP protocol.

       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
       dhclient.leases(5) file.   On startup, after reading the dhclient.conf
       file, dhclient reads the dhclient.leases file to refresh its memory
       about what leases it has been assigned.

       When a new lease is acquired, it is appended to the end of the
       dhclient.leases file.   In order to prevent the file from becoming
       arbitrarily large, from time to time dhclient creates a new
       dhclient.leases file from its in-core lease database.  The old version
       of the dhclient.leases file is retained under the name dhcpd.leases~
       until the next time dhclient rewrites the database.

       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 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 available.

       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,
       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.

       The names of the network interfaces that dhclient should attempt to
       configure may be specified on the command line.  If no interface names
       are specified on the command line dhclient will identify all network
       interfaces, elimininating non-broadcast interfaces if possible, and
       attempt to configure each interface.

       The -D flag causes dhclient to save the script it creates for use in
       conjunction with dhclient-script in /tmp.

       Dhclient will normally run in the foreground until it has configured an
       interface, and then will revert to running in the background.  To run
       force dhclient to always run as a foreground process, the -d flag
       should be specified.  This is useful when running dhclient under a
       debugger, or when running it out of inittab on System V systems.

       If dhclient should listen and transmit on a port other than the
       standard (port 68), the -p flag may used.  It should be followed by the
       udp port number that dhclient should use.  This is mostly useful for
       debugging purposes.  If the -p flag is specified, the client will
       transmit responses to servers at a port number that is one less than
       the one specified - i.e., if you specify -p 68, then the client will
       listen on port 68 and transmit to port 67.  Datagrams that must go
       through relay agents are sent to the port number specified with the -p
       flag - if you wish to use alternate port numbers, you must configure
       any relay agents you are using to use the same alternate port numbers.

       The -cf flag may be used to change the shell script from the default of

       The -lf flag may be used to change the lease output file from the
       default of /var/db/dhclient.leases.

       The -pf flag may be used to change the PID file from the default of

       The -q flag may be used to reduce the amount of screen output from

       The -1 flag cause dhclient to try once to get a lease.  If it fails,
       dhclient exits with exit code two.

       The syntax of the dhclient.conf(5) file is discussed separately.

       /etc/dhclient.conf, /var/db/dhclient.leases, /var/db/dhclient.leases~.

       dhclient.conf(5), dhclient.leases(5), dhclient-script(8)

       dhclient(8) has been written for the Internet Software Consortium by
       Ted Lemon <> in cooperation with Vixie Enterprises.  To
       learn more about the Internet Software Consortium, see  To learn more about Vixie Enterprises, see

       This client was substantially modified and enhanced by Elliot Poger for
       use on Linux while he was working on the MosquitoNet project at

       The current version owes much to Elliot's Linux enhancements, but was
       substantially reorganized and partially rewritten by Ted Lemon so as to
       use the same networking framework that the Internet Software Consortium
       DHCP server uses.   Much system-specific configuration code was moved
       into a shell script so that as support for more operating systems is
       added, it will not be necessary to port and maintain system-specific
       configuration code to these operating systems - instead, the shell
       script can invoke the native tools to accomplish the same purpose.



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