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+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. An 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
+For more details about quota design, see the documentation in quota-tools package
+Quota netlink interface
+When user exceeds a softlimit, runs out of grace time or reaches hardlimit,
+quota subsystem traditionally printed a message to the controlling terminal of
+the process which caused the excess. This method has the disadvantage that
+when user is using a graphical desktop he usually cannot see the message.
+Thus quota netlink interface has been designed to pass information about
+the above events to userspace. There they can be captured by an application
+and processed accordingly.
+The interface uses generic netlink framework (see
+http://lwn.net/Articles/208755/ and http://people.suug.ch/~tgr/libnl/ for more
+details about this layer). The name of the quota generic netlink interface
+is "VFS_DQUOT". Definitions of constants below are in <linux/quota.h>.
+ Currently, the interface supports only one message type QUOTA_NL_C_WARNING.
+This command is used to send a notification about any of the above mentioned
+events. Each message has six attributes. These are (type of the argument is
+in parentheses):
+ - type of quota being exceeded (one of USRQUOTA, GRPQUOTA)
+ - UID/GID (depends on quota type) of user / group whose limit
+ is being exceeded.
+ - UID of a user who caused the event
+ - what kind of limit is exceeded:
+ QUOTA_NL_IHARDWARN - inode hardlimit
+ QUOTA_NL_ISOFTLONGWARN - inode softlimit is exceeded longer
+ than given grace period
+ QUOTA_NL_ISOFTWARN - inode softlimit
+ QUOTA_NL_BHARDWARN - space (block) hardlimit
+ QUOTA_NL_BSOFTLONGWARN - space (block) softlimit is exceeded
+ longer than given grace period.
+ QUOTA_NL_BSOFTWARN - space (block) softlimit
+ - four warnings are also defined for the event when user stops
+ exceeding some limit:
+ QUOTA_NL_IHARDBELOW - inode hardlimit
+ QUOTA_NL_ISOFTBELOW - inode softlimit
+ QUOTA_NL_BHARDBELOW - space (block) hardlimit
+ QUOTA_NL_BSOFTBELOW - space (block) softlimit
+ - major number of a device with the affected filesystem
+ - minor number of a device with the affected filesystem