What are the permissions?​

998pl.maintenance.reload: Allows to reload the config with the command
998pl.maintenance.on : Allows to turn on the mode with the command
998pl.maintenance.off : Allows to turn off the mode with the command
998pl.maintenance.modify: Allows to add/remove players from the maintenance mode list, also required to view said list
998pl.maintenance.* : You can use this only permission to give the 4 others at the same time​

How do I use it?
Download the plugin, put it in your plugins folder, then restart your server.
Afterwards;
You can use config.yml to allow players and toggle the mode,
Or you can use the commands from in game or the console. [easier]

What are the commands?
/maintenanceallow <uuid> <remove/add>: Remove/Add a player to the whitelist by its uuid
/maintenancelist: See which players are allowed to join while maintenance mode is on
/998maintenance <reload|on|off> Manage plugin

Command examples:

/maintenanceallow 069a79f4-44e9-4726-a5be-fca90e38aaf5 add
^ Allow notch to join while maintenance mode
^ If your server is cracked, you must use the cracked UUIDs

/maintenanceallow 069a79f4-44e9-4726-a5be-fca90e38aaf5 remove
^ Remove notch from the maintenance most list

/998maintenance reload
^ Reload the configuration

/998maintenance on
^ Enable maintenance mode

/998maintenance off
^ Disable maintenance mode

/maintenancelist
^ See who is allowed to join while maintenance is on​