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DHCPCD(8) System Manager's Manual DHCPCD(8)
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dhcpcd -- an RFC 2131 compliant DHCP client
dhcpcd [-bdgknpqwABDEGKLTV] [-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]
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.
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 compatability 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 /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.
You can fine-tune the behaviour of dhcpcd with the following options:
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.
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.
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.
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
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.
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 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 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 enscapulated 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-encapulated vendor option to hello world.
dhcpcd -v ,"hello world" eth0
Wait for an address to be assigned before forking to the back-
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.
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.
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
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.
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.
Don't request or claim the address by ARP. This also disables
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
dhcpcd -C resolv.conf -C mtu eth0
Don't set any default routes.
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.
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=192.168.0.10/24 \
-S routers=192.168.0.1 \
-S domain_name_servers=192.168.0.1 \
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.
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 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
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
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),
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 <firstname.lastname@example.org>
Please report them to http://roy.marples.name/projects/dhcpcd
NetBSD 5.1 October 25, 2009 NetBSD 5.1