Unlock Linux: A Deep Dive into Kernel, Memory, Processes, and Filesystems

Linux Kernel

The kernel is the heart of the operating system, managing processes, memory, device drivers, the file system, and networking, which directly affect system performance and stability. Its source code resides in ./linux/kernel, and architecture‑specific parts are under ./linux/arch.

Memory Management

Linux uses virtual memory to abstract physical RAM, dividing memory into 4 KB pages. The slab allocator builds on these pages to allocate structures and track usage. When RAM is exhausted, pages are swapped to disk. Source code for memory management is located in ./linux/mm.

Process Management

Linux supports multitasking by giving each process a time slice and using a priority‑based scheduler to select the next runnable process. Inter‑process communication mechanisms include signals, pipes, shared memory, semaphores, and sockets. System calls such as fork, exec, kill, and exit are provided via the SCI (System Call Interface) layer.

File System Architecture

Unlike DOS, Linux organizes file systems into a single hierarchical tree. The Virtual File System (VFS) abstracts hardware details, offering a uniform API for over 50 supported file systems. VFS sits between user space and concrete file‑system drivers, while a buffer cache optimises block access.

Common Linux file‑system types include Ext2/Ext3, FAT, VFAT, NTFS, XFS, JFS, ReiserFS, and many others. Each file system consists of a superblock (metadata), inode tables (file attributes), and data blocks (file contents). Ext2, for example, uses indexed allocation, allowing the OS to read all blocks of a file in one operation.

Device Drivers

Device drivers run in kernel mode and provide the hardware‑specific implementation of the abstract interfaces exposed by VFS and other subsystems. Errors in drivers can crash the entire system.

Network Interface (NET)

Linux implements the BSD socket API and supports the full TCP/IP stack. Network drivers handle hardware communication, while protocol layers implement transmission standards.

Shell

The shell is the user interface for issuing commands to the kernel. Common shells are Bourne, Bash, Korn, and C‑Shell.

Linux Directory Structure and Partitions

Linux uses a single root directory (/) with sub‑directories such as /bin, /etc, /home, /usr, /var, /dev, and others. Partitions are identified as /dev/hdaX or /dev/sdX, with primary, extended, and logical partitions. The fdisk -l command lists partition details.

Every partition must be mounted to a directory before it can be accessed.

Mount points are ordinary directories; mounting hides the original contents of the mount point.

Mounting Filesystems

Use the mount command: mount [-t fstype] [-o options] device mount_point. Common options include ro, rw, user, nouser, codepage=, and iocharset=. Example to mount a Windows FAT32 partition:

sudo mkdir /mnt/winc
sudo mount -t vfat /dev/hda5 /mnt/winc

Automatic mounting at boot is configured in /etc/fstab, where each line specifies device, mount point, file‑system type, and options.

Links

Linux supports hard links and symbolic (soft) links. Hard links share the same inode, cannot cross file‑system boundaries, and persist after the original name is removed. Symbolic links contain a pathname to the target and can span file systems; they become dangling if the target is deleted.

Create links with the ln command:

ln source_file hard_link
ln -s source_file soft_link

Key Commands

Disk/space: fdisk, df, du File navigation: cd, pwd, mkdir, rmdir, ls File manipulation: cp, mv, rm Viewing files: cat, more, less, head, tail Permissions: chmod, chown, chgrp, umask Search: which, whereis, locate,

find

Illustrative Diagrams

<code># fdisk -l Disk /dev/hda: 80.0 GB, 80026361856 bytes 255 heads, 63 sectors/track, 9729 cylinders</code>