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+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
+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.
+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.
+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
+indicate progress at various checking phases
+verify qgroup accounting and compare against filesystem accounting
+-r|--tree-root <bytenr>::
+use the given offset 'bytenr' for the tree root
+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.
+enable the repair mode and attempt to fix problems where possible
+create a new checksum tree and recalculate checksums in all files
+NOTE: Do not blindly use this option to fix checksum mismatch problems.
+build the extent tree from scratch
+NOTE: Do not use unless you know what you're doing.
+*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 for
+further details.