15. The LFC Process

15.1. Overview

kea-lfc is a service process that removes redundant information from the files used to provide persistent storage for the memfile database backend. This service is written to run as a standalone process.

While kea-lfc can be started externally, there is usually no need to do so. kea-lfc is run on a periodic basis by the Kea DHCP servers, and since Kea 3.1.2 can be started using the kea-lfc-start command.

The process operates on a set of files, using them to receive input and output of the lease entries and to indicate what stage the process is in, in the event of an interruption. Currently the caller must supply names for all of the files.

15.2. Command-Line Options

kea-lfc is run as follows:

kea-lfc [-4 | -6] -c config-file -p pid-file -x previous-file -i copy-file -o output-file -f finish-file

The argument -4 or -6 selects the protocol version of the lease files.

The -c argument specifies the configuration file. This is required, but is not currently used by the process.

The -p argument specifies the PID file. When the kea-lfc process starts, it attempts to determine whether another instance of the process is already running by examining the PID file. If one is already running, the new process is terminated; if one is not running, Kea writes its PID into the PID file.

The other filenames specify where the kea-lfc process should look for input, write its output, and perform its bookkeeping:

  • previous — when kea-lfc starts, this is the result of any previous run of kea-lfc. When kea-lfc finishes, it is the result of this run. If kea-lfc is interrupted before completing, this file may not exist.

  • input — before the DHCP server invokes kea-lfc, it moves the current lease file here and then calls kea-lfc with this file.

  • output — this is the temporary file where kea-lfc writes the leases. Once the file has finished writing, it is moved to the finish file (see below).

  • finish — this is another temporary file kea-lfc uses for bookkeeping. When kea-lfc completes writing the output file, it moves the contents to the file of this name. After kea-lfc finishes deleting the other files (previous and input), it moves this file to the previous lease file. By moving the files in this fashion, kea-lfc and the DHCP server processes can determine the correct file to use even if one of the processes is interrupted before completing its task.

There are several additional arguments, mostly for debugging purposes. -d sets the logging level to debug. -v and -V print out version stamps, with -V providing a longer form. -h prints out the usage string.