Provided by: dhcpcd5_6.0.5-2build0.14.04.1_amd64 
NAME
dhcpcd — a DHCP client
SYNOPSIS
dhcpcd [-46ABbDdEGgHJKkLnpqTVw] [-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]
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
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 the 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.
dhcpcd is also an implemenation of the DHCPv6 client as specified in RFC 3315. By default, dhcpcd only
starts DHCPv6 when instructed to do so by an IPV6 Router Advertisement.
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 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 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 events
dhcpcd runs /lib/dhcpcd/dhcpcd-run-hooks, or the script specified by the -c, --script option. This
script runs each script found in /lib/dhcpcd/dhcpcd-hooks in a lexical order. The default installation
supplies the scripts 01-test, 10-mtu, 10-wpa_supplicant, 15-timezone, 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/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 hosts.
-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 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 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-<version>:<os>:<machine>:<platform>. For example
dhcpcd-5.5.6:NetBSD-6.99.5:i386:i386
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 vendorclassid.
-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. This may also cause wpa_supplicant(8) to reload its configuration
for each interface as well.
-o, --option option
Request the DHCP option variable for use in /lib/dhcpcd/dhcpcd-run-hooks.
-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 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 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
--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 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.
-4, --ipv4only
Only configure IPv4.
-6, --ipv6only
Only confgiure IPv6.
-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.
-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=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 /lib/dhcpcd/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).
-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.
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 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.
NOTES
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 for all IPv4 configuration.
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.
/lib/dhcpcd/dhcpcd-run-hooks
Bourne shell script that is run to configure or de-configure an interface.
/lib/dhcpcd/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/lib/dhcpcd5/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
fnmatch(3), if_nametoindex(3), dhcpcd.conf(5), resolv.conf(5), dhcpcd-run-hooks(8), resolvconf(8)
STANDARDS
RFC 951 RFC 1534 RFC 2131, RFC 2132, RFC 2855, RFC 3004, RFC 3315, RFC 3361, RFC 3633, RFC 3396,
RFC 3397, RFC 3442, RFC 3927, RFC 4039 RFC 4075, RFC 4361, RFC 4390, RFC 4702, RFC 4704, RFC 4861,
RFC 4833, RFC 5227, RFC 5969, RFC 6106.
AUTHORS
Roy Marples <roy@marples.name>
BUGS
Please report them to http://roy.marples.name/projects/dhcpcd
Debian June 6, 2013 DHCPCD(8)