Solid-state drives (SSDs) are an alternative to hard disk drives using flash memory instead of spinning platters. This greatly improves read speeds but doesn't do quite as much for write speeds. One reason is that each sector on a solid-state drive can only be erased a finite number of times before it starts failing. For this reason, the microcontroller in an SSD perform
wear leveling to spread writes across more physical sectors.
TRIM is a feature that an operating system can use to notify a drive that a range of sectors has become unused, which helps wear leveling run more efficiently. A
cron job is a program that runs periodically in the background, and Canonical (the publisher of Ubuntu, a distribution of the GNU/Linux operating system) wants to add a cron job that scans attached drives for unused sectors and sends TRIM commands for these sectors. It's possible for an operating system kernel to send a TRIM command for multiple ranges of sectors, but the current version of Linux doesn't know this and instead sends one range at a time. This slows down deleting files because the kernel has to notify the drive of each sector range as the file is deleted. To work around this missing feature of Linux, the cron job will TRIM when a drive isn't busy doing something else.