The /etc/dhcp/dhclient.d directory allows other packages and system

administrators to create application-specific option handlers for dhclient.

When dhclient is run, any option listed in the dhcp-options(5) man page can

be requested.  dhclient-script does not handle every option available

because doing so would make the script unmaintainable as the components

using those options might change over time.  The knowledge of how to handle

those options should be under the responsibility of the package maintainer

for that component (e.g., NTP options belong in a handler in the ntp

package).

To make maintenance easier, application specific DHCP options can be handled

by creating a bash script with two functions and placing it in /etc/dhcp/dhclient.d

The script must follow a specific form:

(1) The script must be named NAME.sh.  NAME can be anything, but it makes

    sense to name it for the service it handles.  e.g., ntp.sh

(2) The script must provide a NAME_config() function to read the options and

    do whatever it takes to put those options in place.

(3) The script must provide a NAME_restore() function to restore original

    configuration state when dhclient stops.

(4) The script must be 'chmod +x' or dhclient-script will ignore it.

The scripts execute in the same environment as dhclient-script.  That means

all of the functions and variables available to it are available to your

NAME.sh script.  Things of note:

    ${SAVEDIR} is where original configuration files are saved.  Save your

    original configuration files here before you take the DHCP provided

    values and generate new files.

    Variables set in /etc/sysconfig/network, /etc/sysconfig/networking/network,

    and /etc/sysconfig/network-scripts/ifcfg-$interface are available to

    you.

See the scripts in /etc/dhcp/dhclient.d for examples.

NOTE:  Do not use functions defined in /usr/sbin/dhclient-script.  Consider

dhclient-script a black box.  This script may change over time, so the

dhclient.d scripts should not be using functions defined in it.

-- 

David Cantrell <dcantrell@redhat.com>