DHCPCD(8)

NAME
dhcpcd - an RFC 2131 compliant DHCP client

SYNOPSIS
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]

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 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 disable 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 patterns. 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 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 and informational messages to the console. Subsequent debug options stop dhcpcd from daemonising.

-e, --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
    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 <version>. If not set then none is sent.

-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 + 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 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 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 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-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 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 persistent 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 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 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 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.

-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 it's 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 deconfigure 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-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

dhcpcd does not wait for commands to complete when sending them to the master dhcpcd process, nor does it echo its progress to stderr. This is a behaviour change from dhcpcd-4 and may need to be addressed if there is sufficient need.