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btrfs-progs/Documentation/btrfs-filesystem.rst
David Sterba 02ffc977be btrfs-progs: docs: don't use wiki links in manual pages and package 
The wiki has been archived so remove the links from manual page
footers. Also replace the wiki link by RTD site in configure and
libbtrfsutil.

Signed-off-by: David Sterba <dsterba@suse.com>
2023-03-16 22:38:21 +01:00

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btrfs-filesystem(8)
===================
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.
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**
.. code-block:: none
$ 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*.
-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.
-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 :doc:`Swapfile feature<Swapfile>` 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
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:
.. code-block:: none
$ 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** 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 :doc:`btrfs(5)<btrfs-man5>` section
*FILESYSTEMS WITH MULTIPLE BLOCK GROUP PROFILES*.
And on a zoned filesystem there are two more lines in the *Device* section:
.. code-block:: none
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:
.. code-block:: none
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 <https://btrfs.readthedocs.io>`_.
SEE ALSO
--------
:doc:`btrfs-subvolume(8)<btrfs-subvolume>`,
:doc:`mkfs.btrfs(8)<mkfs.btrfs>`
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