Unix Operating System Overview

Unix

• Unix is the most popular operating system developed in AT&T laboratories.
• Unix source code is currently owned by THE OPEN GROUP.
• The operating system has been used as a base by many vendors, who developed their own value-added versions.
• Two distinct flavors (strains) of Unix emerged from its beginnings at AT&T Bell Laboratories: SYSTEM V and BSD (BERKELEY SOFTWARE DISTRIBUTION).
• There was considerable cross-influence between them.

Unix Genealogy

• Fig. 1 illustrates the Unix genealogy based on the family.
• A detailed Unix family tree can be found at http://perso.wanadoo.fr/levenez/unix/.
• The opening chapters of Life with UNIX, by Don Libes and Sandy Ressler, provide an entertaining overview of the history of Unix.
• A Quarter Century of UNIX, by Peter Salus, offers a detailed written history.

Linux

• Linux is an open-source system kernel that forms the basis of various distributions designed to serve different purposes and environments.
• Linux originated in 1991 as a personal project of Linus Torvalds, a Finnish graduate student.
• The kernel was initially conceived as a modest offshoot of Minix, a model operating system written by Andrew S. Tanenbaum.
• By exploiting the power of cooperative development, Linus was able to tackle a more ambitious agenda.
• Kernel version 1.0 was released in 1994.

POSIX

• POSIX (PORTABLE OPERATING SYSTEM INTERFACE) is a family of standards specified by the IEEE for maintaining compatibility between operating systems.

Linux Distributions

• Examples of Linux distributions include:
  • Ubuntu
  • Debian
  • Fedora
  • CentOS
  • RHEL
  • OpenSUSE
  • Arch Linux
  • Linux Mint
  • Slackware
  • Kali Linux
  • Elementary OS

System Management

• System management involves a range of activities and requires both people skills and computer skills.
• Table 1 shows personal experience of Æleen Frisch in Linux system administration.

System Administration Tasks

• Creating a new directory using the terminal: mkdir
• Uniquely identifying a process: ps aux | grep

SWAP

• SWAP is a space on a hard drive used as virtual memory when the physical RAM is full.
• It allows the system to continue running applications by swapping out less frequently used data from RAM to SWAP space.
• Windows OS has a similar concept known as the page file or virtual memory (located in C:\PAGEFILE.SYS).
• The key difference between Linux and Windows SWAP is that Linux SWAP is usually a separate partition on the file system, defined and managed by the user/system administrator, whereas the Windows page file is located on the system drive and is managed automatically by the Windows OS.