btrfs-check - check or repair an unmounted btrfs filesystem
btrfs check [options] <device>
The filesystem checker is used to verify structural integrity of a filesystem and attempt to repair it if requested. The filesystem must be unmounted. By default, btrfs check will not modify the device but you can reaffirm that by the option --readonly. btrfsck is an alias of btrfs check command and is now deprecated. Warning Do not use --repair unless you are adviced to by a developer, an experienced user or accept the fact that fsck cannot possibly fix all sorts of damage that could happen to a filesystem because of software and hardware bugs. The structural integrity check verifies if internal filesystem objects or data structures satisfy the constraints, point to the right objects or are correctly connected together. There are several cross checks that can detect wrong reference counts of shared extents, backrefrences, missing extents of inodes, directory and inode connectivity etc. The amount of memory required can be high, depending on the size of the filesystem, smililarly the run time.
SAFE OR ADVISORY OPTIONS
-b|--backup use the first valid set of backup roots stored in the superblock This can be combined with --super if some of the superblocks are damaged. --check-data-csum verify checksums of data blocks This expects that the filesystem is otherwise OK, so this is basically and offline scrub but does not repair data from spare coipes. --chunk-root <bytenr> use the given offset bytenr for the chunk tree root -E|--subvol-extents <subvolid> show extent state for the given subvolume -p|--progress indicate progress at various checking phases --qgroup-report verify qgroup accounting and compare against filesystem accounting -r|--tree-root <bytenr> use the given offset bytenr for the tree root --readonly (default) run in read-only mode, this option exists to calm potential panic when users are going to run the checker -s|--super <superblock> use 'superblock'th superblock copy, valid values are 0, 1 or 2 if the respective superblock offset is within the device size This can be used to use a different starting point if some of the primary superblock is damaged.
--repair enable the repair mode and attempt to fix problems where possible --init-csum-tree create a new checksum tree and recalculate checksums in all files Note Do not blindly use this option to fix checksum mismatch problems. --init-extent-tree build the extent tree from scratch Note Do not use unless you know what you're doing. --mode=MODE select mode of operation regarding memory and IO The MODE can be one of original and lowmem. The original mode is mostly unoptimized regarding memory consumpption and can lead to out-of-memory conditions on large filesystems. The possible workaround is to export the block device over network to a machine with enough memory. The low memory mode is supposed to address the memory consumption, at the cost of increased IO when it needs to re-read blocks when needed. This may increase run time. Note lowmem mode does not work with --repair yet, and is still considered experimental.
btrfs check returns a zero exit status if it succeeds. Non zero is returned in case of failure.
btrfs is part of btrfs-progs. Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for further details.
mkfs.btrfs(8), btrfs-scrub(8), btrfs-rescue(8)
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