Local Link configuration

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 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

Fine tuning

-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, --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 DHCPv4 vendorclassid field sent. The default is dhcpcd-<version>:<os>:<machine>:<platform>. For example

dhcpcd-5.5.6:NetBSD-6.99.5:i386:i386

If 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 [interface]

This causes an existing dhcpcd process running on the interface to release its lease and de-configure the interface. If no interface is specified then this applies to all interfaces. If no interfaces are left running, dhcpcd will exit.

-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, --master

Start dhcpcd in master mode even if only one interface specified on the command line. See the Multiple Interfaces section above.

-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 [interface]

Notifies dhcpcd to reload its configuration and rebind the specified interface. If no interface is specified then this applies to all interfaces. If dhcpcd 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 /libexec/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 or SSH clients connect to this host and they need to be notified of the host shutting down. 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.

-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, --timeout seconds

Timeout after seconds, instead of the default 30. A setting of 0 seconds causes dhcpcd to wait forever to get a lease. If dhcpcd is working on a single interface then dhcpcd will exit when a timeout occurs, otherwise dhcpcd will fork into the background.

-u, --userclass class

Tags the DHCPv4 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 [4 | 6]

Wait for an address to be assigned before forking to the background. 4 means wait for an IPv4 address to be assigned. 6 means wait for an IPv6 address to be assigned. If no argument is given, dhcpcd will wait for any address protocol to be assigned. It is possible to wait for more than one address protocol and dhcpcd will only fork to the background when all waiting conditions are satisfied.

-x, --exit [interface]

This will signal an existing dhcpcd process running on the interface to de-configure the interface and exit. If no interface is specified, then the above is applied to all interfaces. 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. Allow reboot seconds before starting fallback states from the discover phase. IPv4LL is started when the first reboot timeout is reached. The default is 5 seconds. A setting of 0 seconds causes dhcpcd to skip the reboot phase and go straight into discover. This has no effect on DHCPv6 other than skipping the reboot phase.

Restricting behaviour

-4, --ipv4only

Configure IPv4 only.

-6, --ipv6only

Configure IPv6 only.

-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.

-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. The rapid_commit option is not sent in TEST mode so that the server does not lease an address. 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. Use the -4 or -6 flags to specify an address family. Pass a 2nd -U, --dumplease -option -to -dump -a -secondary -lease, -such -as DHCPv6 Prefix Delegation when not being mixed with another IA type.

-V, --variables

Display a list of option codes, the associated variable and encoding 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.

--nodev

Don't load any /dev management modules.