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.TH "BTRFS-SELECT-SUPER" "8" "Nov 07, 2025" "6.17.1" "BTRFS"
.SH NAME
btrfs-select-super \- overwrite primary superblock with a backup copy
.SH SYNOPSIS
.sp
\fBbtrfs\-select\-super\fP \-s number <device>
.SH DESCRIPTION
.sp
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.
.sp
The filesystem specified by \fIdevice\fP must not be mounted.
.sp
\fBNOTE:\fP
.INDENT 0.0
.INDENT 3.5
Prior to overwriting the primary superblock, please make sure that the
backup copies are valid!
.UNINDENT
.UNINDENT
.sp
To dump a superblock use the \fBbtrfs inspect\-internal dump\-super\fP command.
.sp
Then run the check (in the non\-repair mode) using the command \fBbtrfs check \-s\fP
where \fI\-s\fP specifies the superblock copy to use.
.sp
Superblock copies exist in the following offsets on the device:
.INDENT 0.0
.IP \(bu 2
primary: 64KiB (65536)
.IP \(bu 2
1st copy: 64MiB (67108864)
.IP \(bu 2
2nd copy: 256GiB (274877906944)
.UNINDENT
.sp
A superblock size is 4KiB (4096).
.SH OPTIONS
.INDENT 0.0
.TP
.B \-s|\-\-super <N>
use Nth superblock copy, valid values are 0 1 or 2 if the
respective superblock offset is within the device size
.UNINDENT
.SH SEE ALSO
.sp
\fI\%btrfs(8)\fP
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