BCE-C712 Linux System Administration

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Managing Unix File Systems

Superblock and I-nodes

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1. Superblock:

  • What is the Superblock?
    • The superblock is like the blueprint of a file system. It contains essential details about the file system’s structure and status.
  • Key Information in the Superblock:
    • File system type, block size, total number of inodes, available free blocks, and more. Think of it as the file system’s identity card.
  • Why is it Important?
    • Imagine trying to use a building without knowing its layout. The superblock provides the necessary information for the system to understand and navigate the file system.
  • Example:bashCopy codesudo dumpe2fs /dev/sda1 | grep "Superblock" Output:csharpCopy codeSuperblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208

2. Inodes (Index Nodes):

  • What are Inodes?
    • Inodes are like the DNA of files and directories. Each file or directory has a corresponding inode that holds crucial information about it.
  • Contents of an Inode:
    • Permissions, ownership, timestamps (when the file was created, modified, and accessed), and pointers to the actual data blocks.
  • How Inodes Work:
    • When you access a file, the system uses the inode number to locate the corresponding inode. From there, it finds the actual data blocks containing the file’s content.
  • Example:bashCopy codels -i Output:Copy code1234567 file.txt

3. Inode Number (i-number):

  • What is an Inode Number?
    • Think of it as a unique serial number for each file or directory. It’s how the file system keeps track of them.
  • Using Inode Numbers:
    • When you request a file, the system uses the inode number to find the right inode, which then guides it to the actual data.

4. Inode Table:

  • What is the Inode Table?
    • Picture a directory that lists all the residents in an apartment building. The inode table is a list of all inodes in the file system.
  • Why Does it Matter?
    • It helps the system know which inodes are in use and which are available for new files and directories.
  • Example:bashCopy codedf -i Output:bashCopy codeFilesystem Inodes IUsed IFree IUse% Mounted on /dev/sda1 256000 60000 196000 24% /

5. Inode Attributes:

  • What Information is Stored?
    • Permissions (who can read, write, and execute the file), ownership (who owns the file), and timestamps (when it was created, modified, and accessed).
  • Why are These Attributes Important?
    • They determine who can do what with a file, and they track its history.
  • Example:bashCopy codels -l Output:csharpCopy code-rw-r--r-- 1 user group 1024 Mar 1 14:30 file.txt

6. File System Integrity (fsck):

  • Ensuring File System Health:
    • Sometimes, a file system may encounter issues. Tools like fsck use the superblock and inode information to identify and fix these problems, ensuring everything runs smoothly.
  • Example:bashCopy codesudo fsck /dev/sda1

7. File System Resizing (Optional):

  • Adapting to Change:
    • Superblocks and inodes play a crucial role when resizing file systems. Understanding their intricacies helps ensure a smooth transition.