# 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 data base backend. This service is written to run as a stand alone 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 for input and output of the lease entries and to indicate where it is in the process in case of an interruption. Currently the caller must supply names for all of the files, in the future this requirement may be relaxed with the process getting the names from either the configuration file or from defaults.

## 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 not currently used by the process.

The `-p` argument specifies the PID file. When the `kea-lfc` process starts it attempts to determine if 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 isn't running it writes its pid into the pid file.

The other filenames specify where the `kea-lfc` process should look for input, write its output and use for 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` — The temporary file `kea-lfc` should use to write the leases. Upon completion of writing this file, it will be moved to the finish file (see below).

- `finish` — 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 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.