btrfs-filesystem(8)


NAME

   btrfs-filesystem - command group of btrfs that usually work on the
   whole filesystem

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 taks 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

           $ 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 global block reserve is accounted within Metadata. In case the
       filesystem metadata are exhausted, GlobalReserve/total +
       Metadata/used = Metadata/total.

       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.

       If -r is passed, files in dir will be defragmented recursively. 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 ref-links 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 ref-links.

           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

       -v
           be verbose, print file names as they're submitted for
           defragmentation

       -c[<algo>]
           compress file contents while defragmenting. Optional argument
           selects the compression algorithm, zlib (default) or lzo.
           Currently it's not possible to select no compression. See also
           section EXAMPLES.

       -r
           defragment files recursively in given directories

       -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 cumulates 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.

   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 fi 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. 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 [<dev>|<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
       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 [<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 units
       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.

   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. This is done via a special
       ioctl and will also trigger cleaning of deleted subvolumes. Besides
       that it's equivalent to the sync(1) 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 fi 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)
               Data ratio:                       1.00
               Metadata ratio:                   1.00
               Global reserve:              512.00MiB      (used: 0.00B)

       The root user will also see stats broken down by block group types:

           Data,single: Size:1.15TiB, Used:1.13TiB
              /dev/sdb        1.15TiB

           Metadata,single: Size:12.00GiB, Used:6.45GiB
              /dev/sdb       12.00GiB

           System,single: Size:32.00MiB, Used:144.00KiB
              /dev/sdb       32.00MiB

           Unallocated:
              /dev/sdb      669.99GiB

       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, the filesystem does not occupy the
   whole block device, eg. it has been enlarged and we wan the grow the
   filesystem. 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 btrfs wiki
   http://btrfs.wiki.kernel.org for further details.

SEE ALSO

   mkfs.btrfs(8),





Opportunity


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.





Free Software


Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.


Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.





Free Books


The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.


Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.





Education


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.


Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.