trying to erase only 1st superblock and two other backup superblocks (on ext4 fs), excluding MBR (seek=1) using dd cmd:
here is info about fs: sector=512bytes; block size=4096; Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912
Superblock is of 1 block size (which is 4k ) Superblock starts right after boot block MBR (512 bytes)
man dd says:
seek=N: skip N obs-sized blocks at start of output (obs is 512bytes default)
I'm not quite sure what number should be 'seek' parameter: 1st superblock
dd if=/dev/zero of=/path/to/partition count=1 seek=1 bs=4096
2nd superblock - seek will equal to 64 (32768 / 512 ) ?
dd if=/dev/zero of=/path/to/partition count=1 seek=64 bs=4096
3rd superblock - seek will equal to 192 (98304 / 512 )?
dd if=/dev/zero of=/path/to/partition count=1 seek=192 bs=4096
dumpe2fs output:
Filesystem volume name: <none>
Last mounted on: <not available>
Filesystem UUID: 8eca40e7-fc3c-43b0-b480-4e96aab5068c
Filesystem magic number: 0xEF53
Filesystem revision #: 1 (dynamic)
Filesystem features: has_journal ext_attr resize_inode dir_index filetype extent 64bit flex_bg sparse_super large_file huge_file dir_nlink extra_isize metadata_csum
Filesystem flags: signed_directory_hash
Default mount options: user_xattr acl
Filesystem state: clean
Errors behavior: Continue
Filesystem OS type: Linux
Inode count: 131072
Block count: 524032
Reserved block count: 26201
Free blocks: 506067
Free inodes: 131060
First block: 0
Block size: 4096
Fragment size: 4096
Group descriptor size: 64
Reserved GDT blocks: 255
Blocks per group: 32768
Fragments per group: 32768
Inodes per group: 8192
Inode blocks per group: 512
Flex block group size: 16
Filesystem created: Tue Aug 22 08:55:26 2023
Last mount time: n/a
Last write time: Tue Aug 22 12:05:35 2023
Mount count: 0
Maximum mount count: -1
Last checked: Tue Aug 22 10:26:26 2023
Check interval: 0 (<none>)
Lifetime writes: 2138 kB
Reserved blocks uid: 0 (user root)
Reserved blocks gid: 0 (group root)
First inode: 11
Inode size: 256
Required extra isize: 32
Desired extra isize: 32
Journal inode: 8
Default directory hash: half_md4
Directory Hash Seed: d76982f6-3c1b-42aa-a227-c0b3f594c687
Journal backup: inode blocks
Checksum type: crc32c
Checksum: 0xdf9552a4
dumpe2fs: A block group is missing an inode table while reading journal inode
when trying to mount:
mount: /mnt: mount(2) system call failed: Structure needs cleaning.
so to recover the fs, using for example 2sd (erased) backup superblock, it should not work:
e2fsck -b 98304 /path/to/paritition
output is:
e2fsck 1.45.5 (07-Jan-2020)
/dev/sdb1 was not cleanly unmounted, check forced.
Resize inode not valid. Recreate<y>? yes
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
Free blocks count wrong for group #0 (24280, counted=24281).
Fix<y>? yes
Free blocks count wrong for group #1 (32511, counted=32510).
Fix<y>? yes
Free inodes count wrong for group #0 (8181, counted=8179).
Fix<y>? yes
Free inodes count wrong (131061, counted=131059).
Fix<y>? yes
Padding at end of inode bitmap is not set. Fix<y>? yes
/dev/sdb1: ***** FILE SYSTEM WAS MODIFIED *****
/dev/sdb1: 13/131072 files (0.0% non-contiguous), 17965/524032 blocks
But I can mount fs and fsck gives me this:
fsck from util-linux 2.34
e2fsck 1.45.5 (07-Jan-2020)
/dev/sdb1: clean, 13/131072 files, 17965/524032 blocks
Are above calculations right? Thanks for suggestions
