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

     dhcpcd — an RFC 2131 compliant DHCP client

     dhcpcd [-bdgknpqwABDEGHJKLTV] [-c, --script script] [-e, --env value]
	    [-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] [-y, --reboot seconds]
	    [-z, --allowinterfaces pattern] [-C, --nohook hook]
	    [-F, --fqdn FQDN] [-I, --clientid clientid]
	    [-O, --nooption option] [-Q, --require option]
	    [-S, --static value] [-W, --whitelist address[/cidr]]
	    [-X, --blacklist address[/cidr]] [-Z, --denyinterfaces pattern]
	    [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 currently blank, (null) or local‐
     host, 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

   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.

   Multiple interfaces
     If a list of interfaces are given on the command line, then dhcpcd only
     works with those interfaces, otherwise dhcpcd discovers available Ether‐
     net 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 separate instance.  The -w, --waitip option is enabled in
     this instance to maintain compatibility 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

   Hooking into DHCP events
     dhcpcd runs /lib/dhcpcd-run-hooks, or the script specified by the -c,
     --script option.  This script runs each script found in /lib/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 /lib/dhcpcd-run-hooks.

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

     -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 interface.  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 after‐
	     wards.  dhcpcd does not read a new configuration when this hap‐
	     pens - you should rebind if you need that functionality.

     -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, --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, 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

     -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

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

     -n, --rebind
	     Notifies an existing dhcpcd process running on the interface to
	     rebind its 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 de-configures 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 DISCOVER phase 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 authorita‐
	     tive, 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 to 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 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

     -w, --waitip
	     Wait for an address to be assigned before forking to the back‐

     -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 10 seconds.  A setting
	     of 0 seconds causes dhcpcd to skip the reboot phase and go
	     straight into discover.

     -D, --duid
	     Generate an RFC 4361 compliant clientid.  This requires persis‐
	     tent 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 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.	dhcpcd itself never does any DNS updates.  dhcpcd
	     encodes the FQDN hostname as specified 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.

   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.

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

     -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.

     -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.

     -H, --xidhwaddr
	     Use the last four bytes of the hardware address as the DHCP xid
	     instead of a randomly 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.

     -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
		   dhcpcd -S ip_address= \
		   -S routers= \
		   -S domain_name_servers= \

     -T, --test
	     On receipt of DHCP messages just call /lib/dhcpcd-run-hooks with
	     the reason of TEST which echos the DHCP variables found in the
	     message to the console.  The interface 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 dhcpcd.

     -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).

     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 auto‐
     matically added to the configuration.  If the point to point interface if
     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 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 de-configure an inter‐

     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.

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

     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.

     Roy Marples ⟨roy@marples.name⟩

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

BSD			       January 18, 2010				   BSD

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