Based on kernel version 3.12. Page generated on 2013-11-13 21:58 EST.
1 2 Quota subsystem 3 =============== 4 5 Quota subsystem allows system administrator to set limits on used space and 6 number of used inodes (inode is a filesystem structure which is associated with 7 each file or directory) for users and/or groups. For both used space and number 8 of used inodes there are actually two limits. The first one is called softlimit 9 and the second one hardlimit. An user can never exceed a hardlimit for any 10 resource (unless he has CAP_SYS_RESOURCE capability). User is allowed to exceed 11 softlimit but only for limited period of time. This period is called "grace 12 period" or "grace time". When grace time is over, user is not able to allocate 13 more space/inodes until he frees enough of them to get below softlimit. 14 15 Quota limits (and amount of grace time) are set independently for each 16 filesystem. 17 18 For more details about quota design, see the documentation in quota-tools package 19 (http://sourceforge.net/projects/linuxquota). 20 21 Quota netlink interface 22 ======================= 23 When user exceeds a softlimit, runs out of grace time or reaches hardlimit, 24 quota subsystem traditionally printed a message to the controlling terminal of 25 the process which caused the excess. This method has the disadvantage that 26 when user is using a graphical desktop he usually cannot see the message. 27 Thus quota netlink interface has been designed to pass information about 28 the above events to userspace. There they can be captured by an application 29 and processed accordingly. 30 31 The interface uses generic netlink framework (see 32 http://lwn.net/Articles/208755/ and http://people.suug.ch/~tgr/libnl/ for more 33 details about this layer). The name of the quota generic netlink interface 34 is "VFS_DQUOT". Definitions of constants below are in <linux/quota.h>. 35 Currently, the interface supports only one message type QUOTA_NL_C_WARNING. 36 This command is used to send a notification about any of the above mentioned 37 events. Each message has six attributes. These are (type of the argument is 38 in parentheses): 39 QUOTA_NL_A_QTYPE (u32) 40 - type of quota being exceeded (one of USRQUOTA, GRPQUOTA) 41 QUOTA_NL_A_EXCESS_ID (u64) 42 - UID/GID (depends on quota type) of user / group whose limit 43 is being exceeded. 44 QUOTA_NL_A_CAUSED_ID (u64) 45 - UID of a user who caused the event 46 QUOTA_NL_A_WARNING (u32) 47 - what kind of limit is exceeded: 48 QUOTA_NL_IHARDWARN - inode hardlimit 49 QUOTA_NL_ISOFTLONGWARN - inode softlimit is exceeded longer 50 than given grace period 51 QUOTA_NL_ISOFTWARN - inode softlimit 52 QUOTA_NL_BHARDWARN - space (block) hardlimit 53 QUOTA_NL_BSOFTLONGWARN - space (block) softlimit is exceeded 54 longer than given grace period. 55 QUOTA_NL_BSOFTWARN - space (block) softlimit 56 - four warnings are also defined for the event when user stops 57 exceeding some limit: 58 QUOTA_NL_IHARDBELOW - inode hardlimit 59 QUOTA_NL_ISOFTBELOW - inode softlimit 60 QUOTA_NL_BHARDBELOW - space (block) hardlimit 61 QUOTA_NL_BSOFTBELOW - space (block) softlimit 62 QUOTA_NL_A_DEV_MAJOR (u32) 63 - major number of a device with the affected filesystem 64 QUOTA_NL_A_DEV_MINOR (u32) 65 - minor number of a device with the affected filesystem