分类： LINUX
2009-09-11 01:37:57
dhcpcd -- an RFC 2131 compliant DHCP client
dhcpcd [-bdeknpqABDEGKLTV] [-c, --script script] [-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] [-X, --blacklist address[/cidr]]
[-Z, --denyinterfaces pattern] [interface] [...]
dhcpcd -k, --release [interface]
dhcpcd -x, --exit [interface]
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 , if available, otherwise directly to
/etc/resolv.conf. If the hostname is currenly blank, (null) or localhost
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.
Then it attempts 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 dis-
able this behaviour, you can use the -L, --noipv4ll option.
Multiple interfaces
dhcpcd can be run per interface or as a single instance to manage all
interfaces. If a list of interfaces are given on the command line, then
dhcpcd only works with those interfaces, otherwise dhcpcd discovers
available interfaces. If link management is enabled and no interfaces
are given on the command line, dhcpcd forks to the background right away.
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 what interfaces we allow and deny through the use of pat-
terns. Also, see the BUGS section if dhcpcd runs on a BSD system.
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 sup-
plies the scripts 01-test, 10-mtu, 20-resolv.conf and 30-hostname. You
can disable each script by using the -C, --nohook option. See
for details on how these scripts work. dhcpcd cur-
rently 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 and informational messages to the console. Subsequent
debug options stop dhcpcd from daemonising.
-e, --reconfigure
dhcpcd will re-apply IP address, routing and run
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 after-
wards. dhcpcd does not read a new configuration when this hap-
pens - 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
By default, dhcpcd sends the current hostname to the DHCP server
so it can register in DNS. You can use this option to specify
the hostname sent, or an empty string to stop any hostname from
being sent.
-i, --vendorclassid vendorclassid
Override the vendorclassid field sent. The default is dhcpcd
-k, --release
This causes an existing dhcpcd process running on the interface
to release its lease, deconfigure 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 the 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 +
. 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 it's 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 run-
ning, 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 deconfigures 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 BROADCAST step 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-con-
figure 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 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. 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
Do the above and set a third option with a string and not an IP
address.
dhcpcd -v 01,192.168.0.2 -v 02,01:02:03:04:05 -v
03,\"192.168.0.2\" eth0
-x, --exit
This will signal an existing dhcpcd process running on the
interface to deconfigure 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
if 0 seconds causes dhcpcd to skip the reboot phase and go
straight into discover.
-D, --duid
Generate an RFC 4361 compliant clientid. This requires persis-
tent storage and not all DHCP servers work with it so it's not
enabled by default. dhcpcd generates the DUID and stores in it
/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 . 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 OFFER messages just call /libexec/dhcpcd-run-hooks
with the reason of TEST which echo's the DHCP variables found in
the message to the console. The interface configuration isn't
touched and neither are any configuration files.
-V, --variables
Display a list of option codes and the associated variable for
use in . 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.
-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 .
You should read the and put your options into /etc/dhcpcd.conf. The default configuration file should work for most people just fine. Here it is, in case you lose it.
# A sample configuration for dhcpcd. # See dhcpcd.conf(5) for details. # We normally want to inform the DHCP server of our hostname for DDNS. hostname # A list of options we should request from the DHCP server. option domain_name_servers, domain_name, domain_search, host_name # Most distros have ntp support. option ntp_servers # We should behave nicely on networks and respect their MTU. # However, a lot of buggy DHCP servers set invalid MTUs so this is not # enabled by default. #option interface_mtu # We provide a hook script to lookup the hostname if not set by the DHCP # server, but we should not run it by default. nohook lookup-hostname
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