systemd is like the service manager for your Centos and other modern Linux distributions (including Debian/Mint/Ubuntu) allows you to enable services, stop them, restart them, check their status and even reboot your system.
The key commands or arguments you will use with systemctl are the following:
list-units [PATTERN...] List loaded units
Convert MBOX Mail files into Maildir using Linux
*You need perl an the TimeDate module
Get the free Perl script mb2md from the project/author's site:
#remember you need timedate or you'll get this error: