UNIX History and Development

Historical Development of UNIX

Origins at Bell Labs (Late 1960s)

• UNIX was developed by Ken Thompson, Dennis Ritchie, and others at AT&T's Bell Laboratories in 1969
• The project aimed to create a multi-user, multitasking system for the DEC PDP-7
• The goal was to facilitate software development, particularly for a game Ken Thompson was writing

C Language and UNIX Development (Early 1970s)

• C was developed specifically for UNIX, making the two highly intertwined
• UNIX was originally written in assembly language, which is specific to a particular type of hardware
• In 1973, Dennis Ritchie and Brian Kernighan rewrote the UNIX operating system in C
• C compilers were developed for various hardware platforms, allowing UNIX to be ported to different computer hardware

Berkeley Software Distribution (1970s)

• Ken Thompson introduced UNIX to the University of California, Berkeley
• The University of California, Berkeley, created the Berkeley Software Distribution (BSD)
• Bill Joy led the development of BSD with enhancements and utilities not part of the original UNIX, such as:
  • C Shell (csh)
  • vi editor
  • Networking capabilities
• BSD versions were initially designed for minicomputers like the PDP-11 and VAX systems
• The BSD Daemon, nicknamed Beastie, is the generic mascot of BSD operating systems

AT&T Commercializes UNIX (1980s)

• After deregulation, AT&T began commercializing UNIX in the early 1980s
• UNIX System V was one of the primary versions released for commercial use
• This led to various standards efforts to ensure compatibility across different UNIX versions from different vendors
• The first part of the POSIX standard, IEEE Std 1003.1-1988, was published in 1988

Rise of Standardization and Open Systems (1990s)

• UNIX influenced the creation of free UNIX-like operating systems, most notably Linux
• Linux began its development in 1991 by Linus Torvalds

File Systems Overview

• A file system is a method for storing and organizing files and directories on a storage device, such as a hard drive, SSD, or USB drive.
• File systems manage how data is stored, retrieved, and organized, ensuring that the data is accessible and can be efficiently managed.

Types of File Systems

• Local File Systems: Ext4, NTFS, FAT32, HFS+
• Network File Systems: NFS, SMB/CIFS
• Distributed File Systems: HDFS, GlusterFS
• Special-Purpose File Systems: tmpfs, sysfs, procfs

Common File Systems in Linux

Ext4

• Features: Journaling, large file and volume support, backward compatibility with Ext2/Ext3
• Usage: Default file system for many Linux distributions

Btrfs

• Features: Copy-on-write, snapshots, built-in RAID support, data integrity checks
• Usage: Advanced features for system administrators and large storage systems

XFS

• Features: High-performance, journaling, scalable to large file systems
• Usage: Suitable for systems requiring high-performance and scalability

ZFS

• Features: High storage capacity, data integrity checks, snapshots, copy-on-write, built-in RAID
• Usage: Often used in high-availability storage solutions and servers

FAT32 and exFAT

• Features: Compatibility with multiple operating systems
• Usage: External drives and USB sticks for cross-platform compatibility

NTFS

• Features: Journaling, file compression, encryption, large file support
• Usage: Default file system for Windows; limited support in Linux via ntfs-3g

Key Concepts

Journaling

• A technique used to protect the integrity of the file system by keeping a log (journal) of changes that are about to be made
• Helps in quick recovery in case of a crash or power failure

Inodes

• Data structures that store metadata about files and directories, such as permissions, ownership, timestamps, and location of data blocks
• Each file or directory has a unique inode number

Mounting

• The process of making a file system accessible at a certain point in the directory tree
• Commands: mount, umount
• Configuration: /etc/fstab for automatic mounting at boot

Permissions

• File system permissions determine who can read, write, or execute files
• Represented as rwx for owner, group, and others
• Commands: chmod, chown, chgrp

File System Hierarchy Standard (FHS)

• A standard that defines the directory structure and directory contents in Linux
• Key directories: /, /home, /etc, /var, /usr, /bin, /sbin, /lib

Advanced Features

Snapshots

• A point-in-time copy of the file system
• Supported by file systems like Btrfs and ZFS
• Useful for backups and system recovery

Copy-on-Write (CoW)

• An optimization strategy where modifications to data are not written directly to the original location but to a new location
• File systems: Btrfs, ZFS

Data Integrity

• Techniques to ensure that data is accurate and not corrupted
• File systems like ZFS use checksums to verify data integrity

RAID (Redundant Array of Independent Disks)

• Combines multiple physical disks into one or more logical units for redundancy, performance, or both
• RAID levels: RAID 0, RAID 1, RAID 5, RAID 10
• Software RAID can be managed with mdadm

Commands and Utilities

Checking and Repairing File Systems

• fsck (File System Consistency Check): Used to check and repair file system inconsistencies
• e2fsck: Specific to Ext2/Ext3/Ext4 file systems

File System Creation

• mkfs (Make File System): Used to create a file system on a partition
• Examples: mkfs.ext4, mkfs.btrfs