is an implementation of the DHCP client specified in
RFC 2131
gets the host information
Po IP address, routes, etc
Pc from a DHCP server and configures the network
interface
of the
machine on which it is running.
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
sets the hostname to the one supplied by the DHCP server.
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.
is also an implementation of the BOOTP client specified in
RFC 951
Local Link configuration
If
failed to obtain a lease, it probes for a valid IPv4LL address
Po aka ZeroConf, aka APIPA
Pc .
Once obtained it restarts the process of looking for a DHCP server to get a
proper address.
When using IPv4LL,
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
only works with those interfaces, otherwise
discovers available Ethernet interfaces.
If any interface reports a working carrier then
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
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
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
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-hooks8
for details on how these scripts work.
currently ignores the exit code of the script.
Fine tuning
You can fine-tune the behaviour of
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 , -debug
Echo debug messages to the stderr and syslog.
-e , -env value
Push
value
to the environment for use in
dhcpcd-run-hooks8.
For example, you can force the hostname hook to always set the hostname with
-eforce_hostname=YES
-g , -reconfigure
will re-apply IP address, routing and run
dhcpcd-run-hooks8
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
to put things back afterwards.
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
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
process running on the
interface
to release its lease, de-configure the
interface
and then exit.
then waits until this process has exited.
-l , -leasetime seconds
Request a specific lease time in
seconds
By default
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.
will supply a default metic of 200 +
if_nametoindex3.
An extra 100 will be added for wireless interfaces.
-o , -option option
Request the DHCP
option
variable for use in
/lib/dhcpcd/dhcpcd-run-hooks
-n , -rebind
Notifies
to reload its configuration and rebind its interfaces.
If
is not running, then it starts up as normal.
-p , -persistent
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
]
normally sends a DHCP DISCOVER to find servers to offer an address.
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
authoritative, 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.
remains running and pretends it has an infinite lease.
will not de-configure the interface when it exits.
If
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
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.
Set the vendor option 02 with a hex code.
Set the vendor option 03 with an IP address as a string.
Set un-encapsulated vendor option to hello world.
-v , -version
Display both program version and copyright information.
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
process running on the
interface
to de-configure the
interface
and exit.
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
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.
generates the DUID and stores it in
/etc/dhcpcd.duid
This file should not be copied to other hosts.
-E , -lastlease
If
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.
itself never does any DNS updates.
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
sends a default
clientid
of the hardware family and the hardware address.
Restricting behaviour
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
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
from touching your DNS or MTU settings you would do:-
-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,
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
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
only responds to DHCP servers and not BOOTP servers, you can
-Qdhcp_message_type
-S, -static value
Configures a static
value
If you set
ip_address
then
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.
-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
.
-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-hooks8.
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
is marked as STATIC or INFORM without an address then
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
unicasts INFORM to the destination, otherwise it defaults to STATIC.
NOTES
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.