{ "mode": "man", "parameter": "btrfs-qgroup", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/btrfs-qgroup/8/json", "generated": "2026-09-17T05:49:23Z", "synopsis": "btrfs qgroup ", "sections": { "NAME": { "content": "btrfs-qgroup - control the quota group of a btrfs filesystem\n", "subsections": [] }, "SYNOPSIS": { "content": "btrfs qgroup \n", "subsections": [] }, "DESCRIPTION": { "content": "btrfs qgroup is used to control quota group (qgroup) of a btrfs filesystem.\n", "subsections": [ { "name": "NOTE:", "content": "To use qgroup you need to enable quota first using btrfs quota enable command.\n" }, { "name": "WARNING:", "content": "Qgroup is not stable yet and will impact performance in current mainline kernel (v4.14).\n" } ] }, "QGROUP": { "content": "Quota groups or qgroup in btrfs make a tree hierarchy, the leaf qgroups are attached to sub‐\nvolumes. The size limits are set per qgroup and apply when any limit is reached in tree that\ncontains a given subvolume.\n\nThe limits are separated between shared and exclusive and reflect the extent ownership. For\nexample a fresh snapshot shares almost all the blocks with the original subvolume, new writes\nto either subvolume will raise towards the exclusive limit.\n\nThe qgroup identifiers conform to level/id where level 0 is reserved to the qgroups associ‐\nated with subvolumes. Such qgroups are created automatically.\n\nThe qgroup hierarchy is built by commands create and assign.\n", "subsections": [ { "name": "NOTE:", "content": "If the qgroup of a subvolume is destroyed, quota about the subvolume will not be func‐\ntional until qgroup 0/ is created again.\n" } ] }, "SUBCOMMAND": { "content": "", "subsections": [ { "name": "assign [options] ", "content": "Assign qgroup src as the child qgroup of dst in the btrfs filesystem identified by\npath.\n\nOptions\n\n--rescan\n(default since: 4.19) Automatically schedule quota rescan if the new qgroup as‐\nsignment would lead to quota inconsistency. See QUOTA RESCAN for more informa‐\ntion.\n\n--no-rescan\nExplicitly ask not to do a rescan, even if the assignment will make the quotas\ninconsistent. This may be useful for repeated calls where the rescan would add\nunnecessary overhead.\n" }, { "name": "create ", "content": "Create a subvolume quota group.\n\nFor the 0/ qgroup, a qgroup can be created even before the subvolume is\ncreated.\n" }, { "name": "destroy ", "content": "Destroy a qgroup.\n\nIf a qgroup is not isolated, meaning it is a parent or child qgroup, then it can only\nbe destroyed after the relationship is removed.\n" }, { "name": "clear-stale ", "content": "Clear all stale qgroups whose subvolume does not exist anymore, this is the level 0\nqgroup like 0/subvolid. Higher level qgroups are not deleted even if they don't have\nany child qgroups.\n" }, { "name": "limit [options] |none [] ", "content": "Limit the size of a qgroup to size or no limit in the btrfs filesystem identified by\npath.\n\nIf qgroupid is not given, qgroup of the subvolume identified by path is used if possi‐\nble.\n\nOptions\n\n-c limit amount of data after compression. This is the default, it is currently\nnot possible to turn off this option.\n\n-e limit space exclusively assigned to this qgroup.\n" }, { "name": "remove ", "content": "Remove the relationship between child qgroup src and parent qgroup dst in the btrfs\nfilesystem identified by path.\n\nOptions\n\n--rescan\n(default since: 4.19) Automatically schedule quota rescan if the removed qgroup\nrelation would lead to quota inconsistency. See QUOTA RESCAN for more informa‐\ntion.\n\n--no-rescan\nExplicitly ask not to do a rescan, even if the removal will make the quotas in‐\nconsistent. This may be useful for repeated calls where the rescan would add\nunnecessary overhead.\n" }, { "name": "show [options] ", "content": "Show all qgroups in the btrfs filesystem identified by .\n\nOptions\n\n-p print parent qgroup id.\n\n-c print child qgroup id.\n\n-r print limit of referenced size of qgroup.\n\n-e print limit of exclusive size of qgroup.\n\n-F list all qgroups which impact the given path(include ancestral qgroups)\n\n-f list all qgroups which impact the given path(exclude ancestral qgroups)\n\n--raw raw numbers in bytes, without the B suffix.\n\n--human-readable\nprint human friendly numbers, base 1024, this is the default\n\n--iec select the 1024 base for the following options, according to the IEC standard.\n\n--si select the 1000 base for the following options, according to the SI standard.\n\n--kbytes\nshow sizes in KiB, or kB with --si.\n\n--mbytes\nshow sizes in MiB, or MB with --si.\n\n--gbytes\nshow sizes in GiB, or GB with --si.\n\n--tbytes\nshow sizes in TiB, or TB with --si.\n\n--sort=[+/-][,[+/-]]...\nlist qgroups in order of .\n\n can be one or more of qgroupid,rfer,excl,maxrfer,maxexcl.\n\nPrefix + means ascending order and - means descending order of attr. If no\nprefix is given, use ascending order by default.\n\nIf multiple attr values are given, use comma to separate.\n\n--sync To retrieve information after updating the state of qgroups, force sync of the\nfilesystem identified by path before getting information.\n" } ] }, "QUOTA RESCAN": { "content": "The rescan reads all extent sharing metadata and updates the respective qgroups accordingly.\n\nThe information consists of bytes owned exclusively (excl) or shared/referred to (rfer).\nThere's no explicit information about which extents are shared or owned exclusively. This\nmeans when qgroup relationship changes, extent owners change and qgroup numbers are no longer\nconsistent unless we do a full rescan.\n\nHowever there are cases where we can avoid a full rescan, if a subvolume whose rfer number\nequals its excl number, which means all bytes are exclusively owned, then assigning/removing\nthis subvolume only needs to add/subtract rfer number from its parent qgroup. This can speed\nup the rescan.\n", "subsections": [] }, "EXAMPLES": { "content": "", "subsections": [ { "name": "Make a parent group that has two quota group children", "content": "Given the following filesystem mounted at /mnt/my-vault\n\nLabel: none uuid: 60d2ab3b-941a-4f22-8d1a-315f329797b2\nTotal devices 1 FS bytes used 128.00KiB\ndevid 1 size 5.00GiB used 536.00MiB path /dev/vdb\n\nEnable quota and create subvolumes. Check subvolume ids.\n\n$ cd /mnt/my-vault\n$ btrfs quota enable .\n$ btrfs subvolume create a\n$ btrfs subvolume create b\n$ btrfs subvolume list .\n\nID 261 gen 61 top level 5 path a\nID 262 gen 62 top level 5 path b\n\nCreate qgroup and set limit to 10MiB.\n\n$ btrfs qgroup create 1/100 .\n$ btrfs qgroup limit 10M 1/100 .\n$ btrfs qgroup assign 0/261 1/100 .\n$ btrfs qgroup assign 0/262 1/100 .\n\nAnd check qgroups.\n\n$ btrfs qgroup show .\n\nqgroupid rfer excl\n-------- ---- ----\n0/5 16.00KiB 16.00KiB\n0/261 16.00KiB 16.00KiB\n0/262 16.00KiB 16.00KiB\n1/100 32.00KiB 32.00KiB\n" } ] }, "EXIT STATUS": { "content": "btrfs qgroup returns a zero exit status if it succeeds. Non zero is returned in case of fail‐\nure.\n", "subsections": [] }, "AVAILABILITY": { "content": "btrfs is part of btrfs-progs. Please refer to the documentation at\nhttps://btrfs.readthedocs.io.\n", "subsections": [] }, "SEE ALSO": { "content": "btrfs-quota(8), btrfs-subvolume(8), mkfs.btrfs(8)\n\n\n6.6.3 Mar 31, 2024 BTRFS-QGROUP(8)", "subsections": [] } }, "summary": "btrfs-qgroup - control the quota group of a btrfs filesystem", "flags": [], "examples": [ "Given the following filesystem mounted at /mnt/my-vault", "Label: none uuid: 60d2ab3b-941a-4f22-8d1a-315f329797b2", "Total devices 1 FS bytes used 128.00KiB", "devid 1 size 5.00GiB used 536.00MiB path /dev/vdb", "Enable quota and create subvolumes. Check subvolume ids.", "$ cd /mnt/my-vault", "$ btrfs quota enable .", "$ btrfs subvolume create a", "$ btrfs subvolume create b", "$ btrfs subvolume list .", "ID 261 gen 61 top level 5 path a", "ID 262 gen 62 top level 5 path b", "Create qgroup and set limit to 10MiB.", "$ btrfs qgroup create 1/100 .", "$ btrfs qgroup limit 10M 1/100 .", "$ btrfs qgroup assign 0/261 1/100 .", "$ btrfs qgroup assign 0/262 1/100 .", "And check qgroups.", "$ btrfs qgroup show .", "qgroupid rfer excl", "-------- ---- ----", "0/5 16.00KiB 16.00KiB", "0/261 16.00KiB 16.00KiB", "0/262 16.00KiB 16.00KiB", "1/100 32.00KiB 32.00KiB" ], "see_also": [ { "name": "btrfs-quota", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/btrfs-quota/8/json" }, { "name": "btrfs-subvolume", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/btrfs-subvolume/8/json" }, { "name": "mkfs.btrfs", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/mkfs.btrfs/8/json" }, { "name": "BTRFS-QGROUP", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/BTRFS-QGROUP/8/json" } ] }