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https://github.com/kdave/btrfs-progs
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159 lines
4.9 KiB
Plaintext
159 lines
4.9 KiB
Plaintext
btrfs-check(8)
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==============
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NAME
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----
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btrfs-check - check or repair a btrfs filesystem
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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 '--force').
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By default, *btrfs check* will not modify the device but you can reaffirm that
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by the option '--readonly'.
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*btrfsck* is an alias of *btrfs check* command and is now deprecated.
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WARNING: 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. Eg. 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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+
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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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+
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This expects that the filesystem is otherwise OK, and is basically and offline
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'scrub' but 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 <superblock>::
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use 'superblock'th 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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+
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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 wipe all free space cache of given type
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For free space cache 'v1', the 'clear_cache' kernel mount option only rebuilds
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the free space cache for block groups that are modified while the filesystem is
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mounted with that option. Thus, using this option with 'v1' makes it possible
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to actually clear the entire free space cache.
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+
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For free space cache 'v2', the 'clear_cache' kernel mount option destroys
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the entire free space cache. This option, with 'v2' provides an alternative
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method of clearing the free space cache that doesn't require mounting the
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filesystem.
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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: 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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+
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NOTE: 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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+
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NOTE: 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: 'lowmem' mode does not work with '--repair' yet, and is still considered
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experimental.
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--force::
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allow work on a mounted filesystem. Note that this should work fine on a
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quiescent or read-only mounted filesystem but may crash if the device is
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changed externally, eg. by the kernel module. Repair without mount checks is
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not supported right now.
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+
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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.
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Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for
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further details.
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SEE ALSO
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--------
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`mkfs.btrfs`(8),
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`btrfs-scrub`(8),
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`btrfs-rescue`(8)
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