BTRFS-FILESYSTEM(8) BTRFS BTRFS-FILESYSTEM(8)
NAME
btrfs-filesystem - command group that primarily does work on the whole
filesystems
SYNOPSIS
btrfs filesystem <subcommand> <args>
DESCRIPTION
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 (btrfs-scrub(8), btrfs-balance(8)).
SUBCOMMAND
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, i.e. all Data/single. Note that it's not total
size of filesystem.
• used -- sum of used space of the above, i.e. file extents,
metadata blocks
GlobalReserve is an artificial and internal emergency space. It
is used e.g. 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
256KiB 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.
-L|--level <level>
Since kernel 6.15 the compresison can also take the level
parameter which will be used only for the defragmentation
and overrides the eventual mount option compression
level. Valid levels depend on the compression
algorithms: zlib 1..9, lzo does not have any levels, zstd
the standard levels 1..15 and also the realtime -1..-15.
--nocomp
Do not compress while defragmenting, uncompress extents
if needed.
-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 (i.e.
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: 32MiB
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.
--step SIZE
Perform defragmentation in the range in SIZE steps and
flush (-f) after each one. The range is default (the
whole file) or given by -s and -l, split into the steps
or done in one go if the step is larger. Minimum range
size is 256KiB. With verbosity options the progress of
defragmentation will be also printed.
-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.
mkswapfile [-s size] file
Create a new file that's suitable and formatted as a swapfile.
Default size is 2GiB, fixed page size 4KiB, minimum size is
40KiB.
A swapfile must be created in a specific way: NOCOW and
preallocated. Subvolume containing a swapfile cannot be
snapshotted and blocks of an activated swapfile cannot be
balanced.
Swapfile creation can be achieved by standalone commands too.
Activation needs to be done by command swapon(8). See also
command btrfs inspect-internal map-swapfile and the Swapfile
feature description.
NOTE:
The command is a simplified version of 'mkswap', if you want
to set label, page size, or other parameters please use
'mkswap' proper.
Options
-s|--size SIZE
Create swapfile of a given size SIZE (accepting k/m/g/e/p
suffix).
-U|--uuid UUID
specify UUID to use, or a special value: clear (all
zeros), random, time (time-based random)
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 expand the partition before enlarging the
filesystem and shrink the partition after reducing the size of
the filesystem. This can be 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.
The size of the portion that the filesystem uses of an
underlying device can be determined via the btrfs filesystem
show --raw command on the filesystem’s mount point (where it’s
given for each devid after the string size or via the btrfs
inspect-internal dump-super command on the specific device
(where it’s given as the value of dev_item.total_bytes, which is
not to be confused with total_bytes). The value is also the
address of the first byte not used by the filesystem.
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.
Note that there's a lower limit on the new size (either
specified as an absolute size or difference) that is checked by
kernel and rejected eventually as invalid. Lower values will
print a warning but still pass the request to kernel. The
currently known value is 256MiB.
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
Device slack: 1.00GiB
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, note that this may not be the same as the total
device size (the difference is accounted as slack)
• 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
• Device slack -- sum of slack space on all devices (difference
between entire device size and the space occupied by
filesystem)
• 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/statvfs 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 (e.g.
multiple profiles).
• Data ratio -- ratio of total space for data including
redundancy or parity to the effectively usable data space,
e.g. single is 1.0, RAID1 is 2.0 and for RAID5/6 it depends on
the number of devices
• Metadata ratio -- ditto, 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 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 anymore,
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.
EXAMPLES
$ 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, e.g. 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.
EXIT STATUS
btrfs filesystem 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-subvolume(8), mkfs.btrfs(8)
6.16.1 September 10, 2025 BTRFS-FILESYSTEM(8)
btrfs filesystem \- command group that primarily does work on the whole filesystems