Warning

Do not use --repair unless you are advised 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.

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.

use the given offset bytenr for the chunk tree root

show extent state for the given subvolume

indicate progress at various checking phases

verify qgroup accounting and compare against filesystem accounting

use the given offset bytenr for the tree root

(default) run in read-only mode, this option exists to calm potential panic when users are going to run the checker

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.

completely wipe all free space cache of given type

For free space cache v1, the clear_cache kernel mount option only rebuilds the free space cache for block groups that are modified while the filesystem is mounted with that option. Thus, using this option with v1 makes it possible to actually clear the entire free space cache.

For free space cache v2, the clear_cache kernel mount option does destroy the entire free space cache. This option with v2 provides an alternative method of clearing the free space cache that doesn’t require mounting the filesystem.

enable the repair mode and attempt to fix problems where possible

create a new checksum tree and recalculate checksums in all files

build the extent tree from scratch

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.