dhclient(8)                                           dhclient(8)

       dhclient  -  Dynamic  Host  Configuration  Protocol (DHCP)

       dhclient [ -p port ] [ -d ] [ -q ] [ -1 ] [  -r  ]  [  -lf
       lease-file  ]  [  -pf pid-file ] [ -cf config-file ] [ -sf
       script-file ] [ -s server ] [ -g relay ] [ -n ] [ -nw ]  [
       -w ] [ 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.

       You  must have the Berkeley Packet Filter (bpf) configured
       in your NetBSD  kernel.    You  must  have  at  least  one
       /dev/bpf*  file  for each broadcast network interface that
       is attached to your system.

       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.

       On startup, dhclient reads the dhclient.conf for  configu-
       ration instructions.   It then gets a list of all the net-
       work 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
       dhclient.leases~ until the next time dhclient rewrites the


dhclient(8)                                           dhclient(8)


       Old leases are kept around in  case  the  DHCP  server  is
       unavailable when dhclient is first invoked (generally dur-
       ing 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  normally  identify all network interfaces,
       elimininating non-broadcast interfaces  if  possible,  and
       attempt to configure each interface.

       It  is  also possible to specify interfaces by name in the
       dhclient.conf(5) file.   If interfaces  are  specified  in
       this  way,  then the client will only configure interfaces
       that are either specified in the configuration file or  on
       the command line, and will ignore all other interfaces.

       If  the  DHCP  client 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  a different port is specified for the client to listen
       on and transmit on, the client will also use  a  different
       destination port - one greater than the specified destina-
       tion port.

       The DHCP client normally transmits any  protocol  messages
       it    sends   before   acquiring   an   IP   address   to,, the IP limited broadcast  address.    For
       debugging  purposes,  it  may be useful to have the server
       transmit these messages to some other address.   This  can
       be  specified with the -s flag, followed by the IP address
       or domain name of the destination.


dhclient(8)                                           dhclient(8)

       For testing purposes, the giaddr field of all packets that
       the client sends can be set using the -g flag, followed by
       the IP address to send.   This is only useful for testing,
       and  should  not  be expected to work in any consistent or
       useful way.

       The DHCP client 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 the client under a
       debugger,  or  when  running it out of inittab on System V

       The client normally prints a startup message and  displays
       the  protocol  sequence  to  the standard error descriptor
       until it has acquired an address, and then only logs  mes-
       sages  using  the  syslog (3) facility.   The -q flag pre-
       vents any messages other than errors from being printed to
       the standard error descriptor.

       The  client  normally doesn't release the current lease as
       it is not required by the DHCP protocol.  Some cable  ISPs
       require their clients to notify the server if they wish to
       release an assigned IP address.  The  -r  flag  explicitly
       releases  the  current  lease, and once the lease has been
       released, the client exits.

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

       The  DHCP  client normally gets its configuration informa-
       tion from  /etc/dhclient.conf,  its  lease  database  from
       /var/db/dhclient.leases,  stores  its process ID in a file
       called /var/run/dhclient.pid, and configures  the  network
       interface using /sbin/dhclient-script To specify different
       names and/or locations for these files, use the -cf,  -lf,
       -pf  and  -sf flags, respectively, followed by the name of
       the file.   This can be particularly useful if, for  exam-
       ple, /var/db or /var/run has not yet been mounted when the
       DHCP client is started.

       The DHCP client normally exits if it isn't able  to  iden-
       tify any network interfaces to configure.   On laptop com-
       puters and other computers with hot-swappable  I/O  buses,
       it  is  possible  that  a broadcast interface may be added
       after system startup.   The -w flag can be used  to  cause
       the  client  not  to  exit  when  it doesn't find any such
       interfaces.   The omshell (8) 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.

       The  DHCP  client  can  be  directed  not  to  attempt  to


dhclient(8)                                           dhclient(8)

       configure any interfaces using the -n flag.   This is most
       likely to be useful in combination with the -w flag.

       The client can also be instructed to become a daemon imme-
       diately, rather than waiting until it has acquired  an  IP
       address.   This can be done by supplying the -nw flag.

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

       The DHCP client provides some ability to control it  while
       it  is  running,  without stopping it.  This capability is
       provided using  OMAPI,  an  API  for  manipulating  remote
       objects.   OMAPI  clients  connect  to  the  client  using
       TCP/IP, authenticate, and can then  examine  the  client's
       current status and make changes to it.

       Rather  than  implementing  the  underlying OMAPI protocol
       directly, user programs should  use  the  dhcpctl  API  or
       OMAPI  itself.   Dhcpctl is a wrapper that handles some of
       the housekeeping chores that OMAPI does not  do  automati-
       cally.    Dhcpctl  and  OMAPI are documented in dhcpctl(3)
       and omapi(3).   Most things you'd  want  to  do  with  the
       client  can be done directly using the omshell(1) command,
       rather than having to write a special program.

       The control object allows you to  shut  the  client  down,
       releasing  all  leases  that it holds and deleting any DNS
       records it may have added.  It also allows  you  to  pause
       the  client  - this unconfigures any interfaces the client
       is using.   You can then restart it, which  causes  it  to
       reconfigure  those  interfaces.   You would normally pause
       the client prior to going into hibernation or sleep  on  a
       laptop  computer.    You  would  then  resume it after the
       power comes back.  This allows PC cards to  be  shut  down
       while  the  computer  is hibernating or sleeping, and then
       reinitialized to their previous state  once  the  computer
       comes out of hibernation or sleep.

       The   control   object  has  one  attribute  -  the  state
       attribute.   To  shut  the  client  down,  set  its  state
       attribute  to 2.   It will automatically do a DHCPRELEASE.
       To pause it, set its state attribute to 3.   To resume it,
       set its state attribute to 4.

       /sbin/dhclient-script,                 /etc/dhclient.conf,
       /var/db/dhclient.leases,            /var/run/dhclient.pid,


dhclient(8)                                           dhclient(8)

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

       dhclient(8) has been written  for  the  Internet  Software
       Consortium  by Ted Lemon <mellon@fugue.com> in cooperation
       with Vixie Enterprises.  To learn more about the  Internet
       Software Consortium, see http://www.vix.com/isc.  To learn
       more about Vixie Enterprises, see http://www.vix.com.

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

       The current version owes much to Elliot's  Linux  enhance-
       ments,  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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