btrfs-select-super(8)

overwrite primary superblock with a backup copy

Section 8 btrfs-progs bookworm source

Description

BTRFS-SELECT-SUPER

NAME

btrfs-select-super - overwrite primary superblock with a backup copy

SYNOPSIS

btrfs-select-super -s number <device>

DESCRIPTION

Destructively overwrite all copies of the superblock with a specified copy. This helps in certain cases, for example when write barriers were disabled during a power failure and not all superblocks were written, or if the primary superblock is damaged, e.g. accidentally overwritten.

The filesystem specified by device must not be mounted.

NOTE:

Prior to overwriting the primary superblock, please make sure that the backup copies are valid!

To dump a superblock use the btrfs inspect-internal dump-super command.

Then run the check (in the non-repair mode) using the command btrfs check -s where -s specifies the superblock copy to use.

Superblock copies exist in the following offsets on the device:

	•		primary: 64KiB (65536)
	•		1st copy: 64MiB (67108864)
	•		2nd copy: 256GiB (274877906944)

A superblock size is 4KiB (4096).

OPTIONS

-s|--super <N>

use Nth superblock copy, valid values are 0 1 or 2 if the respective superblock offset is within the device size