btrfs-filesystem(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | SUBCOMMAND | EXAMPLES | EXIT STATUS | AVAILABILITY | SEE ALSO | COLOPHON

BTRFS-FILESYSTEM(8)           Btrfs Manual           BTRFS-FILESYSTEM(8)

NAME         top

       btrfs-filesystem - command group that primarily does work on the
       whole filesystems

SYNOPSIS         top

       btrfs filesystem <subcommand> <args>

DESCRIPTION         top

       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.

SUBCOMMAND         top

       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.

EXAMPLES         top

       $ 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.

EXIT STATUS         top

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

AVAILABILITY         top

       btrfs is part of btrfs-progs. Please refer to the btrfs wiki
       http://btrfs.wiki.kernel.org for further details.

SEE ALSO         top

       btrfs-subvolume(8), mkfs.btrfs(8),

COLOPHON         top

       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 2021-08-27.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-07-30.)  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 man-pages@man7.org

Btrfs v4.6.1                   08/19/2021            BTRFS-FILESYSTEM(8)

Pages that refer to this page: btrfs(8)btrfs-replace(8)