NAME¶
dhcpcd —
an RFC 2131 compliant DHCP
client
SYNOPSIS¶
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 |
-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 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 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 DHCP 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,
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>. 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.
- -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 /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.
- -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.
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 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