dhclient(8)                                                                                                                        dhclient(8)

NAME

       dhclient - Dynamic Host Configuration Protocol Client

SYNOPSIS

       dhclient  [  -4 | -6 ] [ -S ] [ -N [ -N...  ] ] [ -T [ -T...  ] ] [ -P [ -P...  ] ] [ -p port ] [ -d ] [ -e VAR=value ] [ -q ] [ -1 ] [
       -r | -x ] [ -lf lease-file ] [ -pf pid-file ] [ --no-pid ] [ -cf config-file ] [ -sf script-file ] [ -s server-addr ] [ -g relay ] [ -n
       ] [ -nw ] [ -w ] [ -v ] [ --version ] [ if0 [ ...ifN ] ]

DESCRIPTION

       The  Internet  Systems  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.

OPERATION

       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.

       There are two versions of the DHCP protocol DHCPv4 and DHCPv6.  At startup the client may be started for one or the other via the -4 or
       -6 options.

       On startup, dhclient reads the dhclient.conf 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 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 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.

COMMAND LINE

       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, eliminating non-broadcast interfaces if
       possible, and attempt to configure each interface.

       It is also possible to specify interfaces by name in the dhclient.conf 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.

       The client normally prints no output during its startup sequence.  It can be made to  emit  verbose  messages  displaying  the  startup
       sequence  events  until it has acquired an address by supplying the -v command line argument.  In either case, the client logs messages
       using the syslog(3) facility.

OPTIONS

       -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.

CONFIGURATION

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

OMAPI

       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 automatically.   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

       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.

ENVIRONMENT VARIABLES

       The  following  environment variables may be defined to override the builtin defaults for file locations.  Note that use of the related
       command-line options will ignore the corresponding environment variable settings.

       PATH_DHCLIENT_CONF
              The dhclient.conf configuration file.

       PATH_DHCLIENT_DB
              The dhclient.leases database.

       PATH_DHCLIENT_PID
              The dhclient PID file.

       PATH_DHCLIENT_SCRIPT
              The dhclient-script file.

FILES

       CLIENTBINDIR/dhclient-script, ETCDIR/dhclient.conf, DBDIR/dhclient.leases, RUNDIR/dhclient.pid, DBDIR/dhclient.leases~.

SEE ALSO

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

AUTHOR

       dhclient(8) has been written for Internet Systems Consortium by Ted Lemon in cooperation with Vixie Enterprises.  To learn  more  about
       Internet Systems Consortium, see https://www.isc.org 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 enhancements, but was substantially reorganized and partially rewritten by Ted Lemon so
       as  to  use  the  same networking framework that the Internet Systems 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.

                                                                                                                                   dhclient(8)
 

Hi, Guest!

This is a manual page collection for Linux and Unix-like operating system.

Features

  • Works with all browsers and mobile phones.
  • The HTML in this layout validates as XHTML 1.0 strict.

Links

Search this site