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btrfs-progs: docs: update btrfs-select-super

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Signed-off-by: David Sterba <dsterba@suse.com>
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David Sterba 2016-05-06 13:28:17 +02:00
parent ae213f7633
commit ce69f8c36e
1 changed files with 27 additions and 9 deletions
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Documentation/btrfs-select-super.asciidoc
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@ -3,27 +3,45 @@ btrfs-select-super(8)
NAME
----
btrfs-select-super - overwrite superblock with a backup
btrfs-select-super - overwrite primary superblock with a backup copy
SYNOPSIS
--------
*btrfs-select-super* -s number dev
*btrfs-select-super* -s number <device>
DESCRIPTION
-----------
*btrfs-select-super* destructively overwrites all copies of the superblock
with a specified copy. This helps with certain cases of damage, especially
when barriers were disabled during a power failure. You can find a valid
copy of the superblock with *btrfs check -s*.
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, eg. accidentally overwritten.
The filesystem specified by `dev` must not be mounted.
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, or the obsolete command *btrfs-show-super*.
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 <superblock>::
use <superblock>th superblock copy, valid values are 0 up to 2 if the
respective superblock offset is within the filesystem
use 'superblock'th superblock copy, valid values are 0 1 or 2 if the
respective superblock offset is within the device size
SEE ALSO
--------
`btrfs-inspect-internal`(8),
`btrfsck check`(8)