Block is a segment of data that contains data for the file, binary, dll, metadata, etc. Block is used to store information about files. Some blocks hold metadata about file system and called superblock.
The superblock is a segment of metadata that contains information about the file system on a block device. Superblock provides the following information about a file, binary, dll, metadata, etc.
- size of the file system
- block size of the file system
- empty or filled blocks of the file system
- size and allocation of inode tables
To access a file in a file system requires access to the superblock to get information about the file. The superblock is backed up into multiple areas of a disk.
List Super Block and Backups
We can list super block backups with
dumpe2fs command. Backup superblocks will list with the group descriptors.
$ sudo dumpe2fs /dev/sda1 | grep -i superblock
- The primary superblock is at 0
- Backup superblocks are separated to the different locations of the disk
List Details Of Blocks
We can use dumpe2fs tool to list all block information. But this will create a lot of output.
$ sudo dumpe2fs /dev/vda1
- `Last mounted on` provides the last path the given file system is mounted which is `/` in this example.
- `Filesystem UID` is the unique identifier about the file system
- `Filesystem magic number` is the number which numbers the file system type
- `Filesystem revision`
- `Filesystem features` are the features provided by the filesystem
- `Filesystem flags`
- `Default mount options`
- `Filesystem state` show the health of the file system which is clean in this example.
- `Errors behavior` will specify what will be done if some error occurs during mount
- `Filesystem OS type` shows the file system OS which is `Linux` in this case.