Verziószám: isc-dhclient-4.3.5
Fejlesztő/tulajdonos: Internet Systems Consortium



Man oldal kimenet

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

       dhclient - Dynamic Host Configuration Protocol Client

       dhclient  [ -4 | -6 ] [ -S ] [ -N [ -N...  ] ] [ -T [ -T...  ] ] [ -P [ -P...  ] ] -R
       ] [ -i ] [ -I ] [ -4o6 port ] [ -D LL|LLT ] [ -p port-number ] [ -d  ]  [  -df  duid-
       lease-file ] [ -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 ] ]

       The Internet Systems Consortium DHCP Client, dhclient, provides a means for configur‐
       ing 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.

       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 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  adminis‐
       trator  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,  eliminating  non-broad‐
       cast 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.

       -4     Use  the  DHCPv4  protocol to obtain an IPv4 address and configuration parame‐
              ters.  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
              -N and -D arguments provide more control over aspects of the  DHCPv6  process‐
              ing.   Note:  it is not recommended to mix queries of different types together
              or even to share the lease file between them.

       -4o6 port
              Participate in the DHCPv4 over DHCPv6 protocol specified by  RFC  7341.   This
              associates  a  DHCPv4  and  a  DHCPv6 client to allow the v4 client to send v4
              requests encapsulated in a v6 packet.  Communication between the  two  clients
              is  done on a pair of UDP sockets bound to ::1 port and port + 1. Both clients
              must be launched using the same port argument.

       -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
              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  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  con‐
              figure.  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 combina‐
              tion with the -w flag.

       -e VAR=value
              Define  additional  environment  variables for the environment where dhclient-
              script 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 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  shut‐
              down via this method dhclient-script will be executed with the specific reason
              for calling the script set.

       -p port-number
              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  des‐
              tination  for  DHCP  protocol  messages  before  dhclient  has  acquired an IP
              address.  Normally, dhclient transmits these messages to  (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 purposes only and should not be expected to work
              in any consistent or useful way.

       -i     Use a DUID with DHCPv4 clients.  If no DUID is available in the lease file one
              will  be  constructed and saved.  The DUID will be used to construct a RFC4361
              style client id that will be included in the client's messages.   This  client
              id  can be overridden by setting a client id in the configuration file.  Over‐
              ridding the client id in this fashion is discouraged.

       -I     Use the standard DDNS scheme from RFCs 4701 & 4702.

              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 data‐

       -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.  Multiple prefixes can be requested with
              multiple -P flags.  Note only one requested interface is allowed.

       -R     Require that responses include all of the items requested by any -N, -T, or -P
              options.  Normally even if the command line includes a  number  of  these  the
              client  will  be  willing  to  accept  the best lease it can even if the lease
              doesn't include all of the requested items.  This option causes the client  to
              only accept leases that include all of the requested items.

              Note  well:  enabling  this  may  prevent  the client from using any leases it
              receives if the servers aren't configured to supply all of the items.

       -D LL or LLT
              Override the default when selecting the type of  DUID  to  use.   By  default,
              DHCPv6  dhclient  creates an identifier based on the link-layer address (DUID-
              LL) if it is running in stateless mode (with -S, not requesting  an  address),
              or  it  creates an identifier based on the link-layer address plus a timestamp
              (DUID-LLT) if it is running  in  stateful  mode  (without  -S,  requesting  an
              address).  When DHCPv4 is configured to use a DUID using -i option the default
              is to use a DUID-LLT.  -D overrides these default, with a value of  either  LL
              or LLT.

       -N     Restore normal address query for IPv6. This implies -6.  It is used to restore
              normal operation after using -T or -P.  Multiple addresses  can  be  requested
              with multiple -N flags.

       Modifying  default  file  locations:  The following options can be used to modify the
       locations a client uses for its files.  They can be particularly useful if, for exam‐
       ple, /var/lib/dhcp or /var/run have not been mounted when the DHCP client is started.

       -cf config-file
              Path   to   the  client  configuration  file.   If  unspecified,  the  default
              /etc/dhcp/dhclient.conf is used.  See dhclient.conf(5) for  a  description  of
              this file.

       -df duid-lease-file
              Path  to  a secondary lease file.  If the primary lease file doesn't contain a
              DUID this file will be searched.  The DUID read from  the  secondary  will  be
              written  to the primary.  This option can be used to allow an IPv4 instance of
              the client to share a DUID with an IPv6 instance.  After starting one  of  the
              instances  the  second  can  be started with this option pointing to the lease
              file of the first instance.  There is no default.  If no file is specified  no
              search is made for a DUID should one not be found in the main lease file.

       -lf lease-file
              Path   to   the   lease   database   file.    If   unspecified,   the  default
              /var/lib/dhcp/dhclient.leases is used.  See dhclient.leases(5) for a  descrip‐
              tion of this file.

       -pf pid-file
              Path    to    the    process   ID   file.    If   unspecified,   the   default
              /var/run/dhclient.pid is used.

              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  /sbin/dhclient-script  is  used.  See
              dhclient-script(8) for a description of this file.

       During operations the client may use multiple UDP ports to  provide  different  func‐
       tions.  Which ports are opened depends on both the way you compiled your code and the
       configuration you supply.  The following should provide you an idea of what ports may
       be in use.

       Normally  a  DHCPv4 client will open a raw UDP socket to receive and send most DHCPv4
       packets.  It also opens a fallback UDP socket for use  in  sending  unicast  packets.
       Normally these will both use the well known port number for BOOTPC.

       For DHCPv6 the client opens a UDP socket on the well known client port and a fallback
       UDP socket on a random port for use in sending unicast messages.  Unlike  DHCPv4  the
       well known socket doesn't need to be opened in raw mode.

       If  you  have  included  an  omapi port statement in your configuration file then the
       client will open a TCP socket on that port to listen  for  OMPAI  connections.   When
       something connects another port will be used for the established connection.

       When  DDNS is enabled at compile time (see includes/site.h) the client will open both
       a v4 and a v6 UDP socket on random ports.  These ports are opened  even  if  DDNS  is
       disabled in the configuration file.

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

       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 doc‐
       umented 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

       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.

       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.

              The dhclient.conf configuration file.

              The dhclient.leases database.

              The dhclient PID file.

              The dhclient-script file.

       /sbin/dhclient-script,    /etc/dhcp/dhclient.conf,     /var/lib/dhcp/dhclient.leases,
       /var/run/dhclient.pid, /var/lib/dhcp/dhclient.leases~.

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

       dhclient(8) To learn more about Internet Systems Consortium, see https://www.isc.org

       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-spe‐
       cific 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-spe‐
       cific configuration code to these operating systems - instead, the shell  script  can
       invoke the native tools to accomplish the same purpose.




Súgó kimenet

dhclient --help
Internet Systems Consortium DHCP Client 4.3.5
Copyright 2004-2016 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/
Unknown command: --help
Usage: dhclient [-4|-6] [-SNTPRI1dvrxi] [-nw] [-p <port>] [-D LL|LLT] 
                [-s server-addr] [-cf config-file]
                [-df duid-file] [-lf lease-file]
                [-pf pid-file] [--no-pid] [-e VAR=val]
                [-sf script-file] [interface]*

If you think you have received this message due to a bug rather
than a configuration issue please read the section on submitting
bugs on either our web page at www.isc.org or in the README file
before submitting a bug.  These pages explain the proper
process and the information we find helpful for debugging..



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