BTRFS-QGROUP(8)			     BTRFS		       BTRFS-QGROUP(8)

NAME
       btrfs-qgroup - control the quota group of a btrfs filesystem

SYNOPSIS
       btrfs qgroup <subcommand> <args>

DESCRIPTION
       btrfs qgroup is used to control quota group (qgroup) of a btrfs
       filesystem.

       NOTE:
	  To use qgroup you need to enable quota first using btrfs quota
	  enable command, see btrfs-quota(8).

QGROUP
       Quota groups or qgroup in btrfs make a tree hierarchy, the leaf qgroups
       are attached to subvolumes. The size limits are set per qgroup and
       apply when any limit is reached in tree that contains a given
       subvolume.

       The limits are separated between shared and exclusive and reflect the
       extent ownership. For example a fresh snapshot shares almost all the
       blocks with the original subvolume, new writes to either subvolume will
       raise towards the exclusive limit. Extent sharing is also result of
       reflink or deduplication.

       NOTE:
	  Qgroup limit only works when qgroup is in a consistent state.	 If
	  some workload marks qgroup inconsistent (like assigning a qgroup to
	  another qgroup), the limit will no longer work until the
	  inconsistent flag is cleared by btrfs quota rescan.

       The qgroup identifiers conform to level/id where level 0 is reserved to
       the qgroups associated with subvolumes. Such qgroups are created
       automatically.

       The qgroup hierarchy is built by commands btrfs qgroup create and btrfs
       qgroup assign.

       NOTE:
	  If the qgroup of a subvolume is destroyed, quota related to the
	  subvolume will not be functional until qgroup 0/<subvolume id> is
	  created again.

SUBCOMMAND

       assign [options] <src> <dst> <path>
	      Assign qgroup src as the child qgroup of dst in the btrfs
	      filesystem identified by path.

	      Options

	      --rescan
		     (default since: 4.19) Automatically schedule quota rescan
		     if the new qgroup assignment would lead to quota
		     inconsistency. See QUOTA RESCAN for more information.

	      --no-rescan
		     Explicitly ask not to do a rescan, even if the assignment
		     will make the quotas inconsistent. This may be useful for
		     repeated calls where the rescan would add unnecessary
		     overhead.

       create <qgroupid> <path>
	      Create a subvolume quota group.

	      For the 0/<subvolume id> qgroup, a qgroup can be created even
	      before the subvolume is created.

       destroy <qgroupid> <path>
	      Destroy a qgroup.

	      If a qgroup is not isolated, meaning it is a parent or child
	      qgroup, then it can only be destroyed after the relationship is
	      removed.

       clear-stale <path>
	      Clear all stale qgroups whose subvolume does not exist anymore,
	      this is the level 0 qgroup like 0/subvolid. Higher level qgroups
	      are not deleted even if they don't have any child qgroups as
	      they are always created by the user and their deletion should be
	      verified first.

       limit [options] <size>|none [<qgroupid>] <path>
	      Limit the size of a qgroup to size or no limit in the btrfs
	      filesystem identified by path.

	      If qgroupid is not given, qgroup of the subvolume identified by
	      path is used if possible.

	      Options

	      -c     limit amount of data after compression. This is the
		     default, it is currently not possible to turn off this
		     option.

	      -e     limit space exclusively assigned to this qgroup.

       remove <src> <dst> <path>
	      Remove the relationship between child qgroup src and parent
	      qgroup dst in the btrfs filesystem identified by path.

	      Options

	      --rescan
		     (default since: 4.19) Automatically schedule quota rescan
		     if the removed qgroup relation would lead to quota
		     inconsistency. See QUOTA RESCAN for more information.

	      --no-rescan
		     Explicitly ask not to do a rescan, even if the removal
		     will make the quotas inconsistent. This may be useful for
		     repeated calls where the rescan would add unnecessary
		     overhead.

       show [options] <path>
	      Show all qgroups in the btrfs filesystem identified by <path>.

	      Options

	      -p     print parent qgroup id.

	      -c     print child qgroup id.

	      -r     print limit of referenced size of qgroup.

	      -e     print limit of exclusive size of qgroup.

	      -F     list all qgroups which impact the given path(include
		     ancestral qgroups)

	      -f     list all qgroups which impact the given path(exclude
		     ancestral qgroups)

	      --raw  raw numbers in bytes, without the B suffix.

	      --human-readable
		     print human friendly numbers, base 1024, this is the
		     default

	      --iec  select the 1024 base for the following options, according
		     to the IEC standard.

	      --si   select the 1000 base for the following options, according
		     to the SI standard.

	      --kbytes
		     show sizes in KiB, or kB with --si.

	      --mbytes
		     show sizes in MiB, or MB with --si.

	      --gbytes
		     show sizes in GiB, or GB with --si.

	      --tbytes
		     show sizes in TiB, or TB with --si.

	      --sort=[+/-]<attr>[,[+/-]<attr>]...
		     list qgroups in order of <attr>.

		     <attr> can be one or more of
		     qgroupid,rfer,excl,max_rfer,max_excl.

		     Prefix + means ascending order and - means descending
		     order of attr.  If no prefix is given, use ascending
		     order by default.

		     If multiple attr values are given, use comma to separate.

	      --sync To retrieve information after updating the state of
		     qgroups, force sync of the filesystem identified by path
		     before getting information.

SPECIAL PATHS
       For btrfs qgroup show command, the path column can print special
       values:

       <toplevel>
	      The toplevel subvolume.

       <under deletion>
	      The subvolume has been deleted (its directory removed), but the
	      subvolume metadata not not yet fully cleaned.

       <squota space holder>
	      For simple quota mode only.  By its design, a fully deleted
	      subvolume may still have accounting on it, so even if the
	      subvolume is gone, the numbers are still here for future
	      accounting.

       <stale>
	      The qgroup has no corresponding subvolume anymore, and the
	      qgroup can be cleaned up under most cases.  The only exception
	      is that, if the qgroup numbers are inconsistent and the qgroup
	      numbers are not all zeros, some older kernels may refuse to
	      delete such qgroups until a full rescan.

QUOTA RESCAN
       The rescan reads all extent sharing metadata and updates the respective
       qgroups accordingly.

       The information consists of bytes owned exclusively (excl) or
       shared/referenced to (rfer). There's no explicit information about
       which extents are shared or owned exclusively.  This means when qgroup
       relationship changes, extent owners change and qgroup numbers are no
       longer consistent unless we do a full rescan.

       However there are cases where we can avoid a full rescan, if a
       subvolume whose rfer number equals its excl number, which means all
       bytes are exclusively owned, then assigning/removing this subvolume
       only needs to add/subtract rfer number from its parent qgroup. This can
       speed up the rescan.

EXAMPLES
   Make a parent group that has two quota group children
       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

EXIT STATUS
       btrfs qgroup returns a zero exit status if it succeeds. Non zero is
       returned in case of failure.

AVAILABILITY
       btrfs is part of btrfs-progs.  Please refer to the documentation at
       https://btrfs.readthedocs.io.

SEE ALSO
       btrfs-quota(8), btrfs-subvolume(8), mkfs.btrfs(8)

6.16.1			      September 10, 2025	       BTRFS-QGROUP(8)