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

NAME
     dhcpcd -- an RFC 2131 compliant DHCP client

SYNOPSIS
     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 -U, --dumplease interface
     dhcpcd -x, --exit [interface]
     dhcpcd -v, --version

DESCRIPTION
     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
     951.

     dhcpcd is also an implementation of an IPv6 Router Solicitor as specified
     in RFC 6106 with regard to the RDNSS and DNSSL options.

   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
     patterns.

   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 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
             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.

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

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

     -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]
             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 DISCOVER/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 run-
             ning and pretends it has an infinite lease.  dhcpcd will not de-
             configure the interface when it exits.  If dhcpcd fails to con-
             tact 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 members 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 01,192.168.0.2 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,\"192.168.0.2\" eth0
             Set un-encapsulated vendor option to hello world.
                   dhcpcd -v ,"hello world" eth0

     -v, --version
             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 back-
             ground.

     -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.

     -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
             IPv4LL.

     -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
             dns.
                   dhcpcd -S ip_address=192.168.0.10/24 \
                   -S routers=192.168.0.1 \
                   -S domain_name_servers=192.168.0.1 \
                   eth0

     -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 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.

     -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).

3RDPARTY LINK MANAGEMENT
     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 is
     configured for INFORM, then dhcpcd unicasts INFORM to the destination,
     otherwise it defaults to STATIC.

NOTES
     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.

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

     /etc/dhcpcd.duid
     Text file that holds the DUID used to identify the host.

     /libexec/dhcpcd-run-hooks
     Bourne shell script that is run to configure or de-configure an inter-
     face.

     /libexec/dhcpcd-hooks
     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.

     /var/db/dhcpcd-interface.lease
     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.

     /var/run/dhcpcd.pid
     Stores the PID of dhcpcd running on all interfaces.

     /var/run/dhcpcd-interface.pid
     Stores the PID of dhcpcd running on the interface.

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

STANDARDS
     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
     5969, RFC 6106.

AUTHORS
     Roy Marples <roy@marples.name>

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

NetBSD 6.0                     December 15, 2011                    NetBSD 6.0

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