Filesystem, Disk I/O, & Kernel Internals

Question 1

What is the Virtual File System (VFS)?

Answer 1

A kernel abstraction layer that provides a uniform interface for all filesystem types.

Question 2

What are the main VFS objects?

Answer 2

Superblock, Inode, Dentry, and File objects.

Question 3

What does a Superblock represent?

Answer 3

A mounted filesystem, containing metadata and pointers to filesystem operations.

Question 4

What does an Inode represent?

Answer 4

A file or directory with metadata such as permissions, owner, timestamps, and data pointers.

Question 5

What is a Dentry object used for?

Answer 5

Represents a directory entry; links a filename to an inode and speeds up path lookups.

Question 6

What is the purpose of the dentry cache (dcache)?

Answer 6

Speeds up file path resolution by caching directory lookups.

Question 7

What is a File object in VFS?

Answer 7

Represents an open file instance for a process, including position and access mode.

Question 8

What is the relationship between File, Dentry, and Inode objects?

Answer 8

File → Dentry → Inode → Data Blocks.

Question 9

What command shows mounted filesystems?

Answer 9

mount or cat /proc/mounts

Question 10

What does /etc/fstab store?

Answer 10

Persistent mount configuration for filesystems.

Question 11

What is the function of mkfs.ext4?

Answer 11

Creates an ext4 filesystem on a partition or disk.

Question 12

What are common ext4 features?

Answer 12

Extents, journaling, delayed allocation, multiblock allocation, and checksumming.

Question 13

What is journaling in filesystems?

Answer 13

Records metadata (and optionally data) updates before committing to prevent corruption.

Question 14

What are block devices?

Answer 14

Devices that transfer data in fixed-size blocks, e.g., hard drives and SSDs.

Question 15

What is the typical block size in Linux?

Answer 15

Usually 4KB, must be a multiple of the sector size.

Question 16

What is a buffer cache for filesystems?

Answer 16

Stores metadata and file system structure data for block devices.

Question 17

What is the page cache?

Answer 17

Caches file data in memory to minimize disk I/O.

Question 18

What are write-through and write-back policies?

Answer 18

Write-through: immediately write to disk; Write-back: defer writes, mark pages dirty.

Question 19

How does Linux decide which pages to evict from cache?

Answer 19

Uses an active and inactive LRU list algorithm.

Question 20

What command forces all dirty pages to disk?

Answer 20

sync

Question 21

How do you drop page cache manually?

Answer 21

echo 1 > /proc/sys/vm/drop_caches

Question 22

What are hard and soft links?

Answer 22

Hard link: same inode; Soft link: separate inode pointing to a path.

Question 23

What command creates a hard link?

Answer 23

ln existing_file new_link

Question 24

What command creates a soft (symbolic) link?

Answer 24

ln -s target link_name

Question 25

What is RAID used for?

Answer 25

Combines multiple disks for redundancy or performance.

Question 26

What is the default I/O scheduler for modern Linux systems?

Answer 26

BFQ or Deadline, depending on the kernel version.

Question 27

What is a kernel panic?

Answer 27

A fatal kernel error that halts the system to prevent data corruption.

Question 28

How do you determine if a drive is full?

Answer 28

run df -h to see which mount is full lsblk or mount to map to an underlying device Check for inodes with df -i

Question 29

What is the role of the Virtual File System (VFS) in the Linux kernel?

Answer 29

The virtual file system is an abstraction layer on top of a filesystem like ext4. Provides uniform API and allows Linux to support multiple filesystems inodes, dentries, superblocks, etc. syscall -> VFS -> FS Caching to speed up lookups

Question 30

What's the difference between a filesystem driver and the block layer?

Answer 30

Filesystem driver = what to read/write (structured data view) Block layer = how to read/write (raw storage I/O)

Question 31

Explain the process of mounting and unmounting filesystems in Linux.

Answer 31

Use mount or umount cmds Associates a filesystem with a directory path Kernel reads super block, initializes in-memory structures and adds to VFS mount table Unmounting flushes caches, ensure no open file remains, and detaches Can't unmount busy filesystem

Question 32

What are inodes in Linux?

Answer 32

Store metadata (permissions, size, timestamps, links, pointers to data blocks) Each file has a unique inode numbers Directory entries map filesnames to inode number

Question 33

What is a Linux file descriptor?

Answer 33

Integer that process use to refer to open file socket or pipe open() or sockert() creates file objects in kernel space and create pointer to file object 0 = stdin, 1 = stdout, 2 = stderr