# The LFC Process

## 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 this. `kea-lfc` is run on a periodic basis by the Kea DHCP servers.

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.

## 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 will move the current lease file here and then call `kea-lfc` with this file.

- `output` — This is the temporary file where `kea-lfc` writes the leases. Upon completion of writing this file, it will be moved to the finish file (see below).

- `finish` — This is another temporary file `kea-lfc` uses for bookkeeping. When `kea-lfc` completes writing the outputfile, it moves it to this file 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, the `kea-lfc` and the DHCP server processes can determine the correct file to use even if one of the processes was 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.