table of contents
DHCPCD(8) | System Manager's Manual | DHCPCD(8) |
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
patterninterface ] [... ] |
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¶
Ifdhcpcd
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, thendhcpcd
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 ofdhcpcd
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 instructdhcpcd
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 inRFC1035
. -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:i386If 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. Ifdhcpcd
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. Ifdhcpcd
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 eth0Set the vendor option 02 with a hex code.dhcpcd -v 02,01:02:03:04:05 eth0Set the vendor option 03 with an IP address as a string.dhcpcd -v 03,\"192.168.0.2\" eth0Set 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
thendhcpcd
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 indhcpcd
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/dhcpcdJune 6, 2013 | Debian |