DHCPCD(8)                   System Manager's Manual                  DHCPCD(8)

     dhcpcd -- an RFC 2131 compliant DHCP client

     dhcpcd [-bdknpqABDEGKLTV] [-c, --script script] [-f, --config file]
            [-h, --hostname hostname] [-i, --vendorclassid vendorclassid]
            [-l, --leasetime seconds] [-m, --metric metric]
            [-o, --option option] [-r, --request address]
            [-s, --inform address[/cidr]] [-t, --timeout seconds]
            [-u, --userclass class] [-v, --vendor code, value]
            [-C, --nohook hook] [-F, --fqdn FQDN] [-I, --clientid clientid]
            [-O, --nooption option] [-Q, --require option]
            [-X, --blacklist address] interface
     dhcpcd -k, --release interface
     dhcpcd -x, --exit interface

     dhcpcd is an implementation of the DHCP client specified in RFC 2131.
     dhcpcd gets the host information (IP address, routes, etc) from a DHCP
     server and configures the network interface of the machine on which it is
     running.  dhcpcd then runs the configuration script which writes DNS
     information to resolvconf(8), if available, otherwise directly to
     /etc/resolv.conf.  If the hostname is currenly blank, (null) or localhost
     then dhcpcd sets the hostname to the one supplied by the DHCP server.
     dhcpcd then daemonises and waits for the lease renewal time to lapse.
     Then it attempts to renew its lease and reconfigure if the new lease

   Local Link configuration
     If dhcpcd failed to obtain a lease, it probes for a valid IPv4LL address
     (aka ZeroConf, aka APIPA).  Once obtained it restarts the process of
     looking for a DHCP server to get a proper address.

     When using IPv4LL, dhcpcd nearly always succeeds and returns an exit code
     of 0.  In the rare case it fails, it normally means that there is a
     reverse ARP proxy installed which always defeats IPv4LL probing.  To dis-
     able this behaviour, you can use the -L, --noipv4ll option.

   Hooking into DHCP events
     dhcpcd runs /libexec/dhcpcd-run-hooks, or the script specified by the -c,
     --script option.  This script runs each script found in
     /libexec/dhcpcd-hooks in a lexical order.  The default installation sup-
     plies the scripts 01-test, 10-mtu, 20-resolv.conf and 30-hostname.  You
     can disable each script by using the -C, --nohook option.  See
     dhcpcd-run-hooks(8) for details on how these scripts work.  dhcpcd cur-
     rently ignores the exit code of the script.

   Fine tuning
     You can fine tune the behaviour of dhcpcd with the following options:

     -b, --background
             Background immediately.  This is useful for startup scripts which
             don't disable link messages for carrier status.

     -c, --script script
             Use this script instead of the default /libexec/dhcpcd-run-hooks.

     -d, --debug
             Echo debug and informational messages to the console.  Subsequent
             debug options stop dhcpcd from daemonising.

     -f, --config file
             Specify a config to load instead of /etc/dhcpcd.conf.  dhcpcd
             always processes the config file before any command line options.

     -h, --hostname hostname
             By default, dhcpcd sends the current hostname to the DHCP server
             so it can register in DNS.  You can use this option to specify
             the hostname sent, or an empty string to stop any hostname from
             being sent.

     -i, --vendorclassid vendorclassid
             Override the vendorclassid field sent. The default is dhcpcd
             <version>.  If not set then none is sent.

     -k, --release
             This causes an existing dhcpcd process running on the interface
             to release its lease, deconfigure the interface and then exit.
             dhcpcd then waits until this process has exited.

     -l, --leasetime seconds
             Request a specific lease time in seconds.  By default dhcpcd does
             not request any lease time and leaves the it in the hands of the
             DHCP server.

     -m, --metric metric
             Added routes will use the metric on systems where this is sup-
             ported (presently only Linux).  Route metrics allow the addition
             of routes to the same destination across different interfaces,
             the lower the metric the more it is preferred.

     -o, --option option
             Request the DHCP option variable for use in

     -n, --rebind
             Notifies an existing dhcpcd process running on the interface to
             rebind it's lease.  dhcpcd will not re-configure itself or use
             any other command line arguments.  dhcpcd will timeout the rebind
             after 30 seconds at which point the lease will be expired and
             dhcpcd will enter the discovery state to obtain a new lease.  Use
             the -t, --timeout option to change this.  If dhcpcd is not run-
             ning, then it starts up as normal.  This option used to be renew,
             but rebind is more accurate as we need to broadcast the request
             instead of unicasting.

     -p, --persistent
             dhcpcd normally deconfigures the interface and configuration when
             it exits.  Sometimes, this isn't desirable if for example you
             have root mounted over NFS.  You can use this option to stop this
             from happening.

     -r, --request [address]
             dhcpcd normally sends a DHCP DISCOVER to find servers to offer an
             address.  dhcpcd then requests the address used.  You can use
             this option to skip the BROADCAST step and just request the
             address.  The downside is if you request an address the DHCP
             server does not know about or the DHCP server is not authorative,
             it will remain silent.  In this situation, we go back to the init
             state and DISCOVER again.  If no address is given then the first
             address currently assigned to the interface is used.

     -s, --inform [address[/cidr]]
             Behaves like -r, --request as above, but sends a DHCP INFORM
             instead of a REQUEST.  This does not get a lease as such, just
             notifies the DHCP server of the address in use.  You should also
             include the optional cidr network number in-case the address is
             not already configured on the interface.  dhcpcd remains running
             and pretends it has an infinite lease.  dhcpcd will not de-con-
             figure the interface when it exits.  If dhcpcd fails to contact a
             DHCP server then it returns a failure instead of falling back on

     -t, --timeout seconds
             Timeout after seconds, instead of the default 30.  A setting of 0
             seconds causes dhcpcd to wait forever to get a lease.

     -u, --userclass class
             Tags the DHCP message with the userclass class.  DHCP servers use
             this give members of the class DHCP options other than the
             default, without having to know things like hardware address or

     -v, --vendor code,value
             Add an enscapulated vendor option.  code should be between 1 and
             254 inclusive.  Examples.

             Set the vendor option 01 with an IP address.
                   dhcpcd -v 01, eth0
             Set the vendor option 02 with a hex code.
                   dhcpcd -v 02,01:02:03:04:05 eth0
             Do the above and set a third option with a string and not an IP
                   dhcpcd -v 01, -v 02,01:02:03:04:05 -v
                   03,\"\" eth0

     -x, --exit
             This will signal an existing dhcpcd process running on the
             interface to deconfigure the interface and exit.  dhcpcd then
             waits until this process has exited.

     -D, --duid
             Generate an RFC 4361 compliant clientid.  This requires persis-
             tent storage and not all DHCP servers work with it so it's not
             enabled by default.  dhcpcd generates the DUID and stores in it
             /etc/dhcpcd.duid This file should not be copied to other hosts.

     -E, --lastlease
             If dhcpcd cannot obtain a lease, then try to use the last lease
             acquired for the interface.  If the -p, --persistent option is
             not given then the lease is used if it hasn't expired.

     -F, --fqdn fqdn
             Requests that the DHCP server updates DNS using FQDN instead of
             just a hostname.  Valid values for fqdn are disable, none, ptr
             and both.  The current hostname or the hostname specified using
             the -h, --hostname option must be a FQDN.  dhcpcd itself never
             does any DNS updates.  dhcpcd encodes the FQDN hostname as speci-
             fied in RFC1035.

     -I, --clientid clientid
             Send the clientid.  If the string is of the format 01:02:03 then
             it is encoded as hex.  For interfaces whose hardware address is
             longer than 8 bytes, or if the clientid is an empty string then
             dhcpcd sends a default clientid of the hardware family and the
             hardware address.

   Restriciting behaviour
     dhcpcd will try to do as much as it can by default.  However, there are
     sometimes situations where you don't want the things to be configured
     exactly how the the DHCP server wants.  Here are some options that deal
     with turning these bits off.

     -q, --quiet
             Quiet dhcpcd on the command line, only warnings and errors will
             be displayed.  The messages are still logged though.

     -A, --noarp
             Don't request or claim the address by ARP.  This also disables

     -B, --nobackground
             Don't run in the background when we acquire a lease.  This is
             mainly useful for running under the control of another process,
             such as a debugger or a network manager.

     -C, --nohook script
             Don't run this hook script.  Matches full name, or prefixed with
             2 numbers optionally ending with .sh.

             So to stop dhcpcd from touching your DNS or MTU settings you
             would do:-
                   dhcpcd -C resolv.conf -C mtu eth0

     -G, --nogateway
             Don't set any default routes.

     -K, --nolink
             Don't receive link messages for carrier status.  You should only
             have to use this with buggy device drivers or running dhcpcd
             through a network manager.

     -L, --noipv4ll
             Don't use IPv4LL (aka APIPA, aka Bonjour, aka ZeroConf).

     -O, --nooption option
             Don't request the specified option.  If no option given, then
             don't request any options other than those to configure the
             interface and routing.

     -Q, --require option
             Requires the option to be present in all DHCP messages, otherwise
             the message is ignored.

     -T, --test
             On receipt of OFFER messages just call /libexec/dhcpcd-run-hooks
             with the reason of TEST which echo's the DHCP variables found in
             the message to the console.  The interface configuration isn't
             touched and neither are any configuration files.

     -V, --variables
             Display a list of option codes and the associated variable for
             use in dhcpcd-run-hooks(8).

     -X, --blacklist address
             Ignores all DHCP messages which have this address as the server
             ID.  This may be expanded in future releases to ignore all pack-
             ets matching either the IP or hardware address.

     dhcpcd requires a Berkley Packet Filter, or BPF device on BSD based sys-
     tems and a Linux Socket Filter, or LPF device on Linux based systems.

     Configuration file for dhcpcd.  If you always use the same options, put
     them here.

     Text file that holds the DUID used to identify the host.

     Bourne shell script that is run to configure or deconfigure an interface.

     A directory containing bourne shell scripts that are run by the above
     script.  Each script can be disabled by using the -C, --nohook option
     described above.

     The actual DHCP message send by the server. We use this when reading the
     last lease and use the files mtime as when it was issued.

     Stores the PID of dhcpcd running on the interface.

     dhcpcd.conf(5), dhcpcd-run-hooks(8), resolv.conf(5), resolvconf(8),

     RFC 2131, RFC 2132, RFC 2855, RFC 3004, RFC 3361, RFC 3396, RFC 3397, RFC
     3442, RFC 3927, RFC 4361, RFC 4390, RFC 4702.

     Roy Marples <roy@marples.name>

     Please report them to http://roy.marples.name/projects/dhcpcd

NetBSD 5.0_RC4                 November 18, 2008                NetBSD 5.0_RC4

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