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NetBSD 6.1.5 - man page for dhcpcd (netbsd section 8)

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

     dhcpcd -- an RFC 2131 compliant DHCP client

     dhcpcd [-ABbDdEGgHJKkLnpqTVw] [-C, --nohook hook] [-c, --script script] [-e, --env value]
	    [-F, --fqdn FQDN] [-f, --config file] [-h, --hostname hostname]
	    [-I, --clientid clientid] [-i, --vendorclassid vendorclassid]
	    [-l, --leasetime seconds] [-m, --metric metric] [-O, --nooption option]
	    [-o, --option option] [-Q, --require option] [-r, --request address]
	    [-S, --static value] [-s, --inform address[/cidr]] [-t, --timeout seconds]
	    [-u, --userclass class] [-v, --vendor code, value] [-W, --whitelist address[/cidr]]
	    [-y, --reboot seconds] [-X, --blacklist address[/cidr]]
	    [-Z, --denyinterfaces pattern] [-z, --allowinterfaces pattern] [interface] [...]
     dhcpcd -k, --release [interface]
     dhcpcd -U, --dumplease interface
     dhcpcd --version
     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 currently blank, (null) or localhost, or
     force_hostname is YES or TRUE or 1 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.  It will
     then attempt to renew its lease and reconfigure if the new lease changes.

     dhcpcd is also an implementation of the BOOTP client specified in RFC 951.

     dhcpcd is also an implementation of an IPv6 Router Solicitor as specified in RFC 4861 and
     RFC 6106.	dhcpcd can optionally handle address and route management itself, and will do so
     by default if Router Solicitation is disabled in the kernel.  If dhcpcd is managing routes,
     dhcpcd sends Neighbor Solicitions to each advertising router periodically and will expire
     the ones that do not respond.

   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

     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 disable this behaviour, you can use the -L, --noipv4ll option.

   Multiple interfaces
     If a list of interfaces are given on the command line, then dhcpcd only works with those
     interfaces, otherwise dhcpcd discovers available Ethernet interfaces.  If any interface
     reports a working carrier then dhcpcd will try and obtain a lease before forking to the
     background, otherwise it will fork right away.  This behaviour can be modified with the -b,
     --background and -w, --waitip options.

     If a single interface is given then dhcpcd only works for that interface and runs as a sepa-
     rate instance.  The -w, --waitip option is enabled in this instance to maintain compatibil-
     ity with older versions.

     Interfaces are preferred by carrier, DHCP lease/IPv4LL and then lowest metric.  For systems
     that support route metrics, each route will be tagged with the metric, otherwise dhcpcd
     changes the routes to use the interface with the same route and the lowest metric.  See
     options below for controlling which interfaces we allow and deny through the use of pat-

   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 supplies 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 currently 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, --duid
	     Generate an RFC 4361 compliant clientid.  This requires persistent storage and not
	     all DHCP servers work with it so it is not enabled by default.  dhcpcd generates the
	     DUID and stores it in /etc/dhcpcd.duid.  This file should not be copied to other

     -d, --debug
	     Echo debug messages to the stderr and syslog.

     -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.

     -e, --env value
	     Push value to the environment for use in dhcpcd-run-hooks(8).  For example, you can
	     force the hostname hook to always set the hostname with -e force_hostname=YES.

     -g, --reconfigure
	     dhcpcd will re-apply IP address, routing and run dhcpcd-run-hooks(8) for each inter-
	     face.  This is useful so that a 3rd party such as PPP or VPN can change the routing
	     table and / or DNS, etc and then instruct dhcpcd to put things back afterwards.
	     dhcpcd does not read a new configuration when this happens - you should rebind if
	     you need that functionality.

     -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.  dhcpcd itself never does any
	     DNS updates.  dhcpcd encodes the FQDN hostname as specified in RFC1035.

     -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
	     Sends hostname to the DHCP server so it can be registered in DNS.	If hostname is an
	     empty string then the current system hostname is sent.  If hostname is a FQDN (ie,
	     contains a .) then it will be encoded as such.

     -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.

     -i, --vendorclassid vendorclassid
	     Override the vendorclassid field sent.  The default is dhcpcd-<ver-
	     sion>:<os>:<machine>:<platform>.  For example
	     If not set then none is sent.  Some badly configured DHCP servers reject unknown
	     vendorclassids.  To work around it, try and impersonate Windows by using the MSFT

     -k, --release
	     This causes an existing dhcpcd process running on the interface to release its
	     lease, de-configure 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 it in the hands of the DHCP server.

     -m, --metric metric
	     Metrics are used to prefer an interface over another one, lowest wins.  dhcpcd will
	     supply a default metic of 200 + if_nametoindex(3).  An extra 100 will be added for
	     wireless interfaces.

     -n, --rebind
	     Notifies dhcpcd to reload its configuration and rebind its interfaces.  If dhcpcd is
	     not running, then it starts up as normal.

     -o, --option option
	     Request the DHCP option variable for use in /libexec/dhcpcd-run-hooks.

     -p, --persistent
	     dhcpcd normally de-configures the interface and configuration when it exits.  Some-
	     times, 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]
	     Request the address in the DHCP DISCOVER message.	There is no guarantee this is the
	     address the DHCP server will actually give.  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 DIS-
	     COVER/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-configure the interface
	     when it exits.  If dhcpcd fails to contact a DHCP server then it returns a failure
	     instead of falling back on IPv4LL.

     -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 to give mem-
	     bers of the class DHCP options other than the default, without having to know things
	     like hardware address or hostname.

     -v, --vendor code,value
	     Add an encapsulated vendor option.  code should be between 1 and 254 inclusive.  To
	     add a raw vendor string, omit code but keep the comma.  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
	     Set the vendor option 03 with an IP address as a string.
		   dhcpcd -v 03,\"\" eth0
	     Set un-encapsulated vendor option to hello world.
		   dhcpcd -v ,"hello world" eth0

	     Display both program version and copyright information.  dhcpcd then exits before
	     doing any configuration.

     -w, --waitip
	     Wait for an address to be assigned before forking to the background.

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

     -y, --reboot seconds
	     Allow reboot seconds before moving to the discover phase if we have an old lease to
	     use.  The default is 5 seconds.  A setting of 0 seconds causes dhcpcd to skip the
	     reboot phase and go straight into discover.

   Restricting 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.

     -A, --noarp
	     Don't request or claim the address by ARP.  This also disables IPv4LL.

     -B, --nobackground
	     Don't run in the background when we acquire a lease.  This is mainly useful for run-
	     ning 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 option-
	     ally 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.

     -H, --xidhwaddr
	     Use the last four bytes of the hardware address as the DHCP xid instead of a ran-
	     domly generated number.

     -J, --broadcast
	     Instructs the DHCP server to broadcast replies back to the client.  Normally this is
	     only set for non Ethernet interfaces, such as FireWire and InfiniBand.  In most
	     instances, dhcpcd will set this automatically.

     -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.  To enforce that dhcpcd only responds to DHCP servers and not BOOTP
	     servers, you can -Q dhcp_message_type.

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

     -S, --static value
	     Configures a static value.  If you set ip_address then dhcpcd will not attempt to
	     obtain a lease and just use the value for the address with an infinite lease time.

	     Here is an example which configures a static address, routes and dns.
		   dhcpcd -S ip_address= \
		   -S routers= \
		   -S domain_name_servers= \

     -T, --test
	     On receipt of DHCP messages just call /libexec/dhcpcd-run-hooks with the reason of
	     TEST which echos the DHCP variables found in the message to the console.  The inter-
	     face configuration isn't touched and neither are any configuration files.	To test
	     INFORM the interface needs to be configured with the desired address before starting

     -U, --dumplease interface
	     Dumps the last lease for the interface to stdout.	interface could also be a path to
	     a DHCP wire formatted file.

     -V, --variables
	     Display a list of option codes and the associated variable for use in
	     dhcpcd-run-hooks(8).  Variables are prefixed with new_ and old_ unless the option
	     number is -.  Variables without an option are part of the DHCP message and cannot be
	     directly requested.

     -W, --whitelist address[/cidr]
	     Only accept packets from address[/cidr].  -X, --blacklist is ignored if -W,
	     --whitelist is set.

     -X, --blacklist address[/cidr]
	     Ignore all packets from address[/cidr].

     -Z, --denyinterfaces pattern
	     When discovering interfaces, the interface name must not match pattern which is a
	     space or comma separated list of patterns passed to fnmatch(3).

     -z, --allowinterfaces pattern
	     When discovering interfaces, the interface name must match pattern which is a space
	     or comma separated list of patterns passed to fnmatch(3).	If the same interface is
	     matched in -Z, --denyinterfaces then it is still denied.

     Some interfaces require configuration by 3rd parties, such as PPP or VPN.	When an interface
     configuration in dhcpcd is marked as STATIC or INFORM without an address then dhcpcd will
     monitor the interface until an address is added or removed from it and act accordingly.  For
     point to point interfaces (like PPP), a default route to its destination is automatically
     added to the configuration.  If the point to point interface is configured for INFORM, then
     dhcpcd unicasts INFORM to the destination, otherwise it defaults to STATIC.

     dhcpcd requires a Berkley Packet Filter, or BPF device on BSD based systems 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 de-configure 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 all interfaces.

     Stores the PID of dhcpcd running on the interface.

     fnmatch(3), if_nametoindex(3), dhcpcd.conf(5), resolv.conf(5), dhcpcd-run-hooks(8),

     RFC 951, RFC 1534, RFC 2131, RFC 2132, RFC 2855, RFC 3004, RFC 3361, RFC 3396, RFC 3397, RFC
     3442, RFC 3927, RFC 4361, RFC 4390, RFC 4702, RFC 4861, RFC 5969, RFC 6106.

     Roy Marples <roy@marples.name>

     Please report them to

BSD					   June 7, 2012 				      BSD

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