172 lines
5.6 KiB
ReStructuredText
172 lines
5.6 KiB
ReStructuredText
btrfs-check(8)
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==============
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SYNOPSIS
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--------
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**btrfs check** [options] <device>
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DESCRIPTION
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-----------
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The filesystem checker is used to verify structural integrity of a filesystem
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and attempt to repair it if requested. It is recommended to unmount the
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filesystem prior to running the check, but it is possible to start checking a
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mounted filesystem (see :ref:`--force<man-check-option-force>`).
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By default, :command:`btrfs check` will not modify the device but you can reaffirm that
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by the option *--readonly*.
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:command:`btrfsck` is an alias of :command:`btrfs check` command and is now deprecated.
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.. warning::
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Do not use *--repair* unless you are advised to do so by a developer
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or an experienced user, and then only after having accepted that no *fsck*
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successfully repair all types of filesystem corruption. E.g. some other software
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or hardware bugs can fatally damage a volume.
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The structural integrity check verifies if internal filesystem objects or
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data structures satisfy the constraints, point to the right objects or are
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correctly connected together.
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There are several cross checks that can detect wrong reference counts of shared
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extents, backreferences, missing extents of inodes, directory and inode
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connectivity etc.
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The amount of memory required can be high, depending on the size of the
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filesystem, similarly the run time. Check the modes that can also affect that.
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SAFE OR ADVISORY OPTIONS
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------------------------
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-b|--backup
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use the first valid set of backup roots stored in the superblock
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This can be combined with *--super* if some of the superblocks are damaged.
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--check-data-csum
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verify checksums of data blocks
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This expects that the filesystem is otherwise OK, and is basically an offline
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*scrub* that does not repair data from spare copies.
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--chunk-root <bytenr>
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use the given offset *bytenr* for the chunk tree root
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-E|--subvol-extents <subvolid>
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show extent state for the given subvolume
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-p|--progress
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indicate progress at various checking phases
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-Q|--qgroup-report
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verify qgroup accounting and compare against filesystem accounting
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-r|--tree-root <bytenr>
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use the given offset 'bytenr' for the tree root
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--readonly
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(default)
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run in read-only mode, this option exists to calm potential panic when users
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are going to run the checker
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-s|--super <N>
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use Nth superblock copy, valid values are 0, 1 or 2 if the
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respective superblock offset is within the device size
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This can be used to use a different starting point if some of the primary
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superblock is damaged.
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--clear-space-cache v1|v2
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completely remove the free space cache of the given version
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See also the *clear_cache* mount option.
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.. warning::
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This option is deprecated, please use `btrfs rescue clear-space-cache`
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instead, this option would be removed in the future eventually.
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--clear-ino-cache
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remove leftover items pertaining to the deprecated `inode cache` feature
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.. warning::
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This option is deprecated, please use `btrfs rescue clear-ino-cache`
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instead, this option would be removed in the future eventually.
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DANGEROUS OPTIONS
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-----------------
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--repair
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enable the repair mode and attempt to fix problems where possible
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.. note::
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There's a warning and 10 second delay when this option is run without
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*--force* to give users a chance to think twice before running repair, the
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warnings in documentation have shown to be insufficient.
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--init-csum-tree
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create a new checksum tree and recalculate checksums in all files
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.. warning::
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Do not blindly use this option to fix checksum mismatch problems.
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--init-extent-tree
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build the extent tree from scratch
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.. warning::
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Do not use unless you know what you're doing.
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--mode <MODE>
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select mode of operation regarding memory and IO
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The *MODE* can be one of:
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original
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The metadata are read into memory and verified, thus the requirements are high
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on large filesystems and can even lead to out-of-memory conditions. The
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possible workaround is to export the block device over network to a machine
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with enough memory.
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lowmem
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This mode is supposed to address the high memory consumption at the cost of
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increased IO when it needs to re-read blocks. This may increase run time.
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.. note::
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*lowmem* mode does not work with *--repair* yet, and is still considered
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experimental.
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.. _man-check-option-force:
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--force
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allow work on a mounted filesystem and skip mount checks. Note that
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this should work fine on a quiescent or read-only mounted filesystem
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but may crash if the device is changed externally, e.g. by the kernel
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module.
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.. note::
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It is possible to run with --repair but on a mounted filesystem
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that will most likely lead to a corruption unless the filesystem
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is in a quiescent state which may not be possible to guarantee.
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This option also skips the delay and warning in the repair mode (see
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*--repair*).
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EXIT STATUS
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-----------
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**btrfs check** returns a zero exit status if it succeeds. Non zero is
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returned in case of failure.
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AVAILABILITY
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------------
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**btrfs** is part of btrfs-progs. Please refer to the documentation at
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`https://btrfs.readthedocs.io <https://btrfs.readthedocs.io>`_.
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SEE ALSO
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--------
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:doc:`mkfs.btrfs`,
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:doc:`btrfs-scrub`,
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:doc:`btrfs-rescue`
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