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The /etc/dhcp/dhclient.d directory allows other packages and system
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administrators to create application-specific option handlers for dhclient.
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When dhclient is run, any option listed in the dhcp-options(5) man page can
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be requested. dhclient-script does not handle every option available
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because doing so would make the script unmaintainable as the components
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using those options might change over time. The knowledge of how to handle
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those options should be under the responsibility of the package maintainer
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for that component (e.g., NTP options belong in a handler in the ntp
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package).
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To make maintenance easier, application specific DHCP options can be handled
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by creating a bash script with two functions and placing it in /etc/dhcp/dhclient.d
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The script must follow a specific form:
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(1) The script must be named NAME.sh. NAME can be anything, but it makes
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sense to name it for the service it handles. e.g., ntp.sh
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(2) The script must provide a NAME_config() function to read the options and
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do whatever it takes to put those options in place.
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(3) The script must provide a NAME_restore() function to restore original
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configuration state when dhclient stops.
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(4) The script must be 'chmod +x' or dhclient-script will ignore it.
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The scripts execute in the same environment as dhclient-script. That means
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all of the functions and variables available to it are available to your
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NAME.sh script. Things of note:
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${SAVEDIR} is where original configuration files are saved. Save your
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original configuration files here before you take the DHCP provided
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values and generate new files.
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Variables set in /etc/sysconfig/network, /etc/sysconfig/networking/network,
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and /etc/sysconfig/network-scripts/ifcfg-$interface are available to
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you.
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See the scripts in /etc/dhcp/dhclient.d for examples.
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NOTE: Do not use functions defined in /usr/sbin/dhclient-script. Consider
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dhclient-script a black box. This script may change over time, so the
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dhclient.d scripts should not be using functions defined in it.
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--
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David Cantrell <dcantrell@redhat.com>
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