CSNB334 Advanced Operating Systems 1. Introduction to Linux Lecturer: Abdul Rahim Ahmad

Contents Unix vs Linux What is Linux Open Source OS Linux History Linux Kernel

Unix vs Linux Architecture of Modern OSs ◦ Kernel: OS core running in privileged mode ◦ User-space: compiler, editor, GUI, …, system and other application programs running in user mode. A good example is Unix ◦ Many flavors (most not “free”) ◦ Many different versions ◦ Not open – proprietary source code Linux look and feel like UNIX ◦ But with totally different code and free.

What is Linux? Full featured, Unix-like OS Open source: entire kernel source available free Community: created by a loose worldwide community of programmers collaborating mainly through the internet Portable : from mainframe to hand-helds Estimated users: over 29 million (see counter.li.org)

GNU: Open Source OS before Linux The concept of “free” software ◦ Through 70s: Richard Stallman advocates “free” software ◦ “ free” as in “free speech” not “free beer” (not zero cost) - free to use, distribute (for a profit), and modify. 1984: Richard Stallman founded GNU ◦ Goal: to produce free software GPL: ensure software freedom by copyright terms ◦ GNU software: Unix-like programs (no kernel)

Linux History 1991: Finnish student Linus Torvalds started working on an update of Minix (released in 1987 by Andrew S Tanenbaum). From the start, Linus asked volunteers on the Internet to help him develop Linux ◦ People started using and publicizing Linux ◦ A number of programmers joined the project From the start, the source code has been freely available on the Internet Linux provides a kernel for GNU software ◦ GNU has lots of user-space programs (like libraries, compilers, text editors and a Windowing System) but no kernel ◦ Linux kernel + GNU software = Linux distribution

The Linux Kernel Linux kernel is written in C programming language It implements POSIX standards in terms of interface, commands etc, but the source code implementation is not UNIX Linux kernel just provides the bare necessity. GNU software provides the bell and whistles.

Linux Kernel Evolution Linux kernel has undergone massive development in the last one and a half decade : ◦ 0 (Apr 1991): First from Linus about his new OS. ◦ 0.01 (Sept 1991) ◦ 1.0 (March 94), user: 100,000 ◦ 1.2 (March 95), user: 500,000 ◦ 2.0 (June 96), user: 1,500,000 ◦ 2.2 (January 99) ◦ 2.4 (January 2001) ◦ 2.6 (December 2003) Odd/Even versioning system ◦ 2.4.x: stable kernels ◦ 2.5.x: development kernels ◦ Starting with the Linux 2.6.x series,  there is no significance to even or odd numbers, with new feature development going on in the same kernel series. Linus Torvalds has stated that this will be the model for the foreseeable future.  The version number of the Linux kernel has changed from a three-number versioning scheme to a four-number one. A.B.C[.D] (e.g ).

Linux Kernel History (wikipedia) April 1991, First version. Started by Linus Torvalds, just 21 years old then (only task switcher and a terminal driver).task switcherterminal driver September 1991, Linux version 0.01 was released (10,239 lines of code). October 1991, Linux version 0.02 was released. December 1991, Linux 0.11 was released. (self-hosted - could be compiled on a computer running Linux 0.11itself)self-hosted February 1992 version 0.12 (use GNU General Public License)GNU General Public License 19 January 1992, A newsgroup alt.os.linux was startednewsgroup March 1992, Linux version 0.95 was released (Able to run GUI based X Window System )X Window System 14 March 1994, Linux was released (176,250 lines of code). March 1995, Linux was released (310,950 lines of code). 9 June 1996 version 2 of Linux released. 25 January Linux was released (1,800,847 lines of code). 18 December 1999 becoming enterprise-class machines in IBM mainframe (using modified release).IBM mainframe 4 January Linux was released (3,377,902 lines of code). 17 December Linux was released (5,929,913 lines of code). 9 June Linux was released (11,637,173 lines of code).

The Kernel of Our Study Version ◦ Latest Stable version Linux distribution used is Xandross Linux The entire kernel source code is available and downloadable from the internet ( For study purpose, you can download the source code into windows directories.

Using Linux on Windows ◦ Most organizations use Windows. In order to use Linux in this kind of environment, we need to install multiple OS in a single computer  By using partitioning and a dual boot system  By running Linux in a virtual machine on a Windows system. For our purpose, we will use Xandros Linux using a dual boot system. You can also use Ubuntu Linux.

Linux - Fun reading ◦ If you can, Read the whole book.  Otherwise ◦ Read part II (pp : “Birth of an Operating System”)  Or ◦ Read part II section X (pp : “Minix vs Linux”)

Linux and Systems Programming What is System Programming? ◦ Dealing with large complex and usually monolithic system software (e.g., OS kernel) Why large, complex, and monolithic software? ◦ Structure often limits flexibility and performance ◦ Working such system requires extraordinary skill ◦ It is often an art more than a science or an engineering In industry ◦ System programmers usually have more “respect” than application programmers.