NAME
dhcpcd
- an RFC 2131 compliant DHCP client
SYNOPSIS
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]
[interface]
[...]
dhcpcd
-k, -release
[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
.
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 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 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 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
/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 afterwards.
dhcpcd
does not read a new configuration when this happens - 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 .
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 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 running, 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
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-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 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
- -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 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 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.
- -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.
- -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
.
- -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 automatically 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.
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.
/libexec/dhcpcd-run-hooks
-
Bourne shell script that is run to configure or de-configure an interface.
/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.
AUTHORS
Roy Marples <roy@marples.name>
BUGS
Please report them to http://roy.marples.name/projects/dhcpcd