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NAME | SYNOPSIS | DESCRIPTION | SUBCOMMAND | EXAMPLES | EXIT STATUS | AVAILABILITY | SEE ALSO | COLOPHON |
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BTRFS-FILESYSTEM(8) Btrfs Manual BTRFS-FILESYSTEM(8)
btrfs-filesystem - command group that primarily does work on the
whole filesystems
btrfs filesystem <subcommand> <args>
btrfs filesystem is used to perform several whole filesystem level
tasks, including all the regular filesystem operations like
resizing, space stats, label setting/getting, and defragmentation.
There are other whole filesystem tasks like scrub or balance that
are grouped in separate commands.
df [options] <path>
Show a terse summary information about allocation of block
group types of a given mount point. The original purpose of
this command was a debugging helper. The output needs to be
further interpreted and is not suitable for quick overview.
An example with description:
• device size: 1.9TiB, one device, no RAID
• filesystem size: 1.9TiB
• created with: mkfs.btrfs -d single -m single
$ btrfs filesystem df /path
Data, single: total=1.15TiB, used=1.13TiB
System, single: total=32.00MiB, used=144.00KiB
Metadata, single: total=12.00GiB, used=6.45GiB
GlobalReserve, single: total=512.00MiB, used=0.00B
• Data, System and Metadata are separate block group types.
GlobalReserve is an artificial and internal emergency
space, see below.
• single — the allocation profile, defined at mkfs time
• total — sum of space reserved for all allocation profiles
of the given type, ie. all Data/single. Note that it’s not
total size of filesystem.
• used — sum of used space of the above, ie. file extents,
metadata blocks
GlobalReserve is an artificial and internal emergency space.
It is used eg. when the filesystem is full. Its total size is
dynamic based on the filesystem size, usually not larger than
512MiB, used may fluctuate.
The GlobalReserve is a portion of Metadata. In case the
filesystem metadata is exhausted, GlobalReserve/total +
Metadata/used = Metadata/total. Otherwise there appears to be
some unused space of Metadata.
Options
-b|--raw
raw numbers in bytes, without the B suffix
-h|--human-readable
print human friendly numbers, base 1024, this is the
default
-H
print human friendly numbers, base 1000
--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
-k|--kbytes
show sizes in KiB, or kB with --si
-m|--mbytes
show sizes in MiB, or MB with --si
-g|--gbytes
show sizes in GiB, or GB with --si
-t|--tbytes
show sizes in TiB, or TB with --si
If conflicting options are passed, the last one takes
precedence.
defragment [options] <file>|<dir> [<file>|<dir>...]
Defragment file data on a mounted filesystem. Requires kernel
2.6.33 and newer.
If -r is passed, files in dir will be defragmented recursively
(not descending to subvolumes, mount points and directory
symlinks). The start position and the number of bytes to
defragment can be specified by start and length using -s and
-l options below. Extents bigger than value given by -t will
be skipped, otherwise this value is used as a target extent
size, but is only advisory and may not be reached if the free
space is too fragmented. Use 0 to take the kernel default,
which is 256kB but may change in the future. You can also turn
on compression in defragment operations.
Warning
Defragmenting with Linux kernel versions < 3.9 or ≥
3.14-rc2 as well as with Linux stable kernel versions ≥
3.10.31, ≥ 3.12.12 or ≥ 3.13.4 will break up the reflinks
of COW data (for example files copied with cp --reflink,
snapshots or de-duplicated data). This may cause
considerable increase of space usage depending on the
broken up reflinks.
Note
Directory arguments without -r do not defragment files
recursively but will defragment certain internal trees
(extent tree and the subvolume tree). This has been
confusing and could be removed in the future.
For start, len, size it is possible to append units
designator: 'K', 'M', 'G', 'T', 'P', or 'E', which represent
KiB, MiB, GiB, TiB, PiB, or EiB, respectively (case does not
matter).
Options
-c[<algo>]
compress file contents while defragmenting. Optional
argument selects the compression algorithm, zlib
(default), lzo or zstd. Currently it’s not possible to
select no compression. See also section EXAMPLES.
-r
defragment files recursively in given directories, does
not descend to subvolumes or mount points
-f
flush data for each file before going to the next file.
This will limit the amount of dirty data to current file,
otherwise the amount accumulates from several files and
will increase system load. This can also lead to ENOSPC if
there’s too much dirty data to write and it’s not possible
to make the reservations for the new data (ie. how the COW
design works).
-s <start>[kKmMgGtTpPeE]
defragmentation will start from the given offset, default
is beginning of a file
-l <len>[kKmMgGtTpPeE]
defragment only up to len bytes, default is the file size
-t <size>[kKmMgGtTpPeE]
target extent size, do not touch extents bigger than size,
default: 32M
The value is only advisory and the final size of the
extents may differ, depending on the state of the free
space and fragmentation or other internal logic.
Reasonable values are from tens to hundreds of megabytes.
-v
(deprecated) alias for global -v option
du [options] <path> [<path>..]
Calculate disk usage of the target files using FIEMAP. For
individual files, it will report a count of total bytes, and
exclusive (not shared) bytes. We also calculate a set shared
value which is described below.
Each argument to btrfs filesystem du will have a set shared
value calculated for it. We define each set as those files
found by a recursive search of an argument (recursion descends
to subvolumes but not mount points). The set shared value then
is a sum of all shared space referenced by the set.
set shared takes into account overlapping shared extents,
hence it isn’t as simple as adding up shared extents.
Options
-s|--summarize
display only a total for each argument
--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.
label [<device>|<mountpoint>] [<newlabel>]
Show or update the label of a filesystem. This works on a
mounted filesystem or a filesystem image.
The newlabel argument is optional. Current label is printed if
the argument is omitted.
Note
the maximum allowable length shall be less than 256 chars
and must not contain a newline. The trailing newline is
stripped automatically.
resize [options] [<devid>:][+/-]<size>[kKmMgGtTpPeE]|[<devid>:]max
<path>
Resize a mounted filesystem identified by path. A particular
device can be resized by specifying a devid.
Warning
If path is a file containing a BTRFS image then resize
does not work as expected and does not resize the image.
This would resize the underlying filesystem instead.
The devid can be found in the output of btrfs filesystem show
and defaults to 1 if not specified. The size parameter
specifies the new size of the filesystem. If the prefix + or -
is present the size is increased or decreased by the quantity
size. If no units are specified, bytes are assumed for size.
Optionally, the size parameter may be suffixed by one of the
following unit designators: 'K', 'M', 'G', 'T', 'P', or 'E',
which represent KiB, MiB, GiB, TiB, PiB, or EiB, respectively
(case does not matter).
If max is passed, the filesystem will occupy all available
space on the device respecting devid (remember, devid 1 by
default).
The resize command does not manipulate the size of underlying
partition. If you wish to enlarge/reduce a filesystem, you
must make sure you can expand the partition before enlarging
the filesystem and shrink the partition after reducing the
size of the filesystem. This can done using fdisk(8) or
parted(8) to delete the existing partition and recreate it
with the new desired size. When recreating the partition make
sure to use the same starting partition offset as before.
Growing is usually instant as it only updates the size.
However, shrinking could take a long time if there are data in
the device area that’s beyond the new end. Relocation of the
data takes time.
See also section EXAMPLES.
Options
--enqueue
wait if there’s another exclusive operation running,
otherwise continue
show [options] [<path>|<uuid>|<device>|<label>]
Show the btrfs filesystem with some additional info about
devices and space allocation.
If no option none of path/uuid/device/label is passed,
information about all the BTRFS filesystems is shown, both
mounted and unmounted.
Options
-m|--mounted
probe kernel for mounted BTRFS filesystems
-d|--all-devices
scan all devices under /dev, otherwise the devices list is
extracted from the /proc/partitions file. This is a
fallback option if there’s no device node manager (like
udev) available in the system.
--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
sync <path>
Force a sync of the filesystem at path, similar to the sync(1)
command. In addition, it starts cleaning of deleted
subvolumes. To wait for the subvolume deletion to complete use
the btrfs subvolume sync command.
usage [options] <path> [<path>...]
Show detailed information about internal filesystem usage.
This is supposed to replace the btrfs filesystem df command in
the long run.
The level of detail can differ if the command is run under a
regular or the root user (due to use of restricted ioctl). For
both there’s a summary section with information about space
usage:
$ btrfs filesystem usage /path
WARNING: cannot read detailed chunk info, RAID5/6 numbers will be incorrect, run as root
Overall:
Device size: 1.82TiB
Device allocated: 1.17TiB
Device unallocated: 669.99GiB
Device missing: 0.00B
Used: 1.14TiB
Free (estimated): 692.57GiB (min: 692.57GiB)
Free (statfs, df) 692.57GiB
Data ratio: 1.00
Metadata ratio: 1.00
Global reserve: 512.00MiB (used: 0.00B)
Multiple profiles: no
• Device size — sum of raw device capacity available to the
filesystem
• Device allocated — sum of total space allocated for
data/metadata/system profiles, this also accounts space
reserved but not yet used for extents
• Device unallocated — the remaining unallocated space for
future allocations (difference of the above two numbers)
• Device missing — sum of capacity of all missing devices
• Used — sum of the used space of data/metadata/system
profiles, not including the reserved space
• Free (estimated) — approximate size of the remaining free
space usable for data, including currently allocated space
and estimating the usage of the unallocated space based on
the block group profiles, the min is the lower bound of
the estimate in case multiple profiles are present
• Free (statfs, df) — the amount of space available for data
as reported by the statfs syscall, also returned as Avail
in the output of df. The value is calculated in a
different way and may not match the estimate in some cases
(eg. multiple profiles).
• Data ratio — ratio of total space for data including
redundancy or parity to the effectively usable data space,
eg. single is 1.0, RAID1 is 2.0 and for RAID5/6 it depends
on the number of devices
• Metadata ratio — dtto, for metadata
• Global reserve — portion of metadata currently used for
global block reserve, used for emergency purposes (like
deletion on a full filesystem)
• Multiple profiles — what block group types (data,
metadata) have more than one profile (single, raid1, ...),
see btrfs(5) section FILESYSTEMS WITH MULTIPLE BLOCK GROUP
PROFILES.
And on a zoned filesystem there are two more lines in the
Device section:
Device zone unusable: 5.13GiB
Device zone size: 256.00MiB
• Device zone unusable — sum of of space that’s been used in
the past but now is not due to COW and not referenced
anymory, the chunks have to be reclaimed and zones reset
to make it usable again
• Device zone size — the reported zone size of the
host-managed device, same for all devices
The root user will also see stats broken down by block group
types:
Data,single: Size:1.15TiB, Used:1.13TiB (98.26%)
/dev/sdb 1.15TiB
Metadata,single: Size:12.00GiB, Used:6.45GiB (53.75%)
/dev/sdb 12.00GiB
System,single: Size:32.00MiB, Used:144.00KiB (0.44%)
/dev/sdb 32.00MiB
Unallocated:
/dev/sdb 669.99GiB
Data is block group type, single is block group profile, Size
is total size occupied by this type, Used is the actually used
space, the percent is ratio of Used/Size. The Unallocated is
remaining space.
Options
-b|--raw
raw numbers in bytes, without the B suffix
-h|--human-readable
print human friendly numbers, base 1024, this is the
default
-H
print human friendly numbers, base 1000
--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
-k|--kbytes
show sizes in KiB, or kB with --si
-m|--mbytes
show sizes in MiB, or MB with --si
-g|--gbytes
show sizes in GiB, or GB with --si
-t|--tbytes
show sizes in TiB, or TB with --si
-T
show data in tabular format
If conflicting options are passed, the last one takes
precedence.
$ btrfs filesystem defrag -v -r dir/
Recursively defragment files under dir/, print files as they are
processed. The file names will be printed in batches, similarly
the amount of data triggered by defragmentation will be
proportional to last N printed files. The system dirty memory
throttling will slow down the defragmentation but there can still
be a lot of IO load and the system may stall for a moment.
$ btrfs filesystem defrag -v -r -f dir/
Recursively defragment files under dir/, be verbose and wait until
all blocks are flushed before processing next file. You can note
slower progress of the output and lower IO load (proportional to
currently defragmented file).
$ btrfs filesystem defrag -v -r -f -clzo dir/
Recursively defragment files under dir/, be verbose, wait until
all blocks are flushed and force file compression.
$ btrfs filesystem defrag -v -r -t 64M dir/
Recursively defragment files under dir/, be verbose and try to
merge extents to be about 64MiB. As stated above, the success rate
depends on actual free space fragmentation and the final result is
not guaranteed to meet the target even if run repeatedly.
$ btrfs filesystem resize -1G /path
$ btrfs filesystem resize 1:-1G /path
Shrink size of the filesystem’s device id 1 by 1GiB. The first
syntax expects a device with id 1 to exist, otherwise fails. The
second is equivalent and more explicit. For a single-device
filesystem it’s typically not necessary to specify the devid
though.
$ btrfs filesystem resize max /path
$ btrfs filesystem resize 1:max /path
Let’s assume that devid 1 exists and the filesystem does not
occupy the whole block device, eg. it has been enlarged and we
want to grow the filesystem. By simply using max as size we will
achieve that.
Note
There are two ways to minimize the filesystem on a given
device. The btrfs inspect-internal min-dev-size command, or
iteratively shrink in steps.
btrfs filesystem returns a zero exit status if it succeeds. Non
zero is returned in case of failure.
btrfs is part of btrfs-progs. Please refer to the btrfs wiki
http://btrfs.wiki.kernel.org for further details.
btrfs-subvolume(8), mkfs.btrfs(8),
This page is part of the btrfs-progs (btrfs filesystem tools)
project. Information about the project can be found at
⟨https://btrfs.wiki.kernel.org/index.php/Btrfs_source_repositories⟩.
If you have a bug report for this manual page, see
⟨https://btrfs.wiki.kernel.org/index.php/Problem_FAQ#How_do_I_report_bugs_and_issues.3F⟩.
This page was obtained from the project's upstream Git repository
⟨git://git.kernel.org/pub/scm/linux/kernel/git/kdave/btrfs-progs.git⟩
on 2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-06-23.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to [email protected]
Btrfs v5.16.1 02/06/2022 BTRFS-FILESYSTEM(8)
Pages that refer to this page: btrfs(8), btrfs-replace(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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