Quota subsystem

Quota subsystem allows system administrator to set limits on used space and number of used inodes (inode is a filesystem structure which is associated with each file or directory) for users and/or groups. For both used space and number of used inodes there are actually two limits. The first one is called softlimit and the second one hardlimit. A user can never exceed a hardlimit for any resource (unless he has CAP_SYS_RESOURCE capability). User is allowed to exceed softlimit but only for limited period of time. This period is called "grace period" or "grace time". When grace time is over, user is not able to allocate more space/inodes until he frees enough of them to get below softlimit.

Quota limits (and amount of grace time) are set independently for each filesystem.

For more details about quota design, see the documentation in quota-tools package (https://sourceforge.net/projects/linuxquota).