Understanding Linux: Kernel, Memory, Processes, and File Systems Explained

Linux System Overview

Linux systems are composed of four main parts: the kernel, the shell, the file system, and applications. Together they enable users to run programs, manage files, and interact with the operating system.

1. Linux Kernel

The kernel is the core of the OS, handling process, memory, device driver, file system, and network management. Its source code resides in ./linux/kernel, with architecture‑specific code in ./linux/arch. System call interfaces (SCI) provide user‑space to kernel transitions.

2. Memory Management

Linux uses virtual memory, dividing memory into 4 KB pages and employing mechanisms such as the slab allocator, swapping pages to disk, and managing page allocation. Source code is located in ./linux/mm.

3. Process Management

Processes are execution entities; Linux achieves multitasking by time‑slicing and a priority‑based scheduler. It supports inter‑process communication via signals, pipes, shared memory, semaphores, and sockets. Process creation and control use APIs like fork, exec, kill, and exit.

4. File System

Linux adopts a unified hierarchical tree, mounting individual file systems at directories. The Virtual File System (VFS) abstracts hardware details, offering a common API for operations such as open, close, read, and write. Source code resides in ./linux/fs.

Key directories include /bin, /dev, /etc, /home, /lib, /sbin, /tmp, /root, /mnt, /proc, /var, and /usr (with subdirectories like /usr/bin, /usr/lib, /usr/include, etc.).

5. Device Drivers

Device drivers run in privileged mode, providing abstract interfaces to hardware. Errors in drivers can crash the system.

6. Network Interface (NET)

Linux supports BSD sockets and the full TCP/IP stack, with separate protocol and driver layers.

7. Linux Shell

The shell is the user interface for command execution. Common shells are Bourne Shell, Bash (Bourne Again Shell), Korn Shell, and C Shell.

8. File System Types and Partitioning

Supported file systems include Ext2/Ext3, FAT/FAT32/VFAT, NTFS, ISO9660, XFS, JFS, ReiserFS, and many others. Partitions are identified as primary, extended, or logical and are accessed via device nodes such as /dev/hda1, /dev/sda2, etc.

Mounting attaches a file system to a directory (the mount point) using the mount command, e.g., mount -t vfat /dev/hda5 /mnt/winc. Automatic mounting at boot is configured in /etc/fstab.

9. Links

Hard links share the same inode, while symbolic (soft) links point to a pathname. Hard links cannot cross file‑system boundaries; soft links can.

10. Core Kernel Structures

Key structures include file (open file descriptor), dentry (directory entry cache), inode (metadata), and super_block (file‑system-wide information). These structures interconnect to implement VFS operations.