DEBUG: if this flag is activated the module will write to the debug
console every command line it executes. This flag is reserved to
developers: activating it may slow down the module or interfere with serial
trasmissions.
LEVELS DESCRIPTION
VERBOSITY: default: progress indicator
1: quiet
COMPRESSION: default: normal
1: no compression
2: fast
3: normal
4: high
5: best
NOTES
This module requires the registered version of the archiver command. Users
who didn't register, can download the freely-distributable generic keyfile.