Overview: Linux and Unix

1. Overview: Linux and Unix (OS comparison) Credit: Cailan Hao (Lancy) Instructor: Mort Anvari Date: 11/3/1999 Southeastern University The symbol of Linux

2. SECTION I: LINUX OVERVIEW Basic Linux Information Slide 2 • FREE (GPL Licensed), based heavily on the POSIX and UNIX API's. • Supports both 32 and 64 bit hardware; Provide a stable multi-user Internet ready OS. Note: The word “Linux” throughout the presentation refers to Red Hat Linux 6.0 – the most popular type of Linux.

3. SECTION I: LINUX OVERVIEW Memory Management Slide 3 • Linux uses the Buddy algorithm to effectively allocate and de-allocate blocks of pages. (Left Figure) • Linux assumes that there are three levels of page tables. (Right Figure)

4. SECTION I: LINUX OVERVIEW Cache Management Slide 4 • The role of the Linux page cache is to speed up access to files on disk. • When swapping pages out to the swap files, Linux avoids writing pages if it does not have to.

5. Linux is a multiprocessing operating system Its objective is to have a process running on each CPU in the system at all times -maximize CPU utilization. Linux supports a number of different executable file formats. EX: ELF and Java Linux can manage the processes in the system, each process is represented by a task_struct data structure Some common function areas: State Running: ready to run Waiting: waiting for an event Stopped: process stopped Zombie: halted Scheduling Information: which program most deserve to run Identifiers: used to control this processes access to the files and devices in the system Times and Timers: Each clock tick, the kernel updates the amount of time in jiffies that the current process has spent in system and in user mode SECTION I: LINUX OVERVIEW How Linux Processes Slide 5

6. Linux implements the internet protocol address family as a series of connected layers of software: Linux supports the following socket address families or domains: UNIX - Unix domain sockets, INET TCP/IP protocols AX25 - Amateur radio X25 IPX - Novell IPX APPLETALK – AppleTalk DDP X25 - X25 SECTION I: LINUX OVERVIEW Linux Networking Slide 6

7. The PCI initialization code in Linux is broken into three logical parts: PCI Device Driver searches the PCI system; starting at Bus 0 and locates all PCI devices and bridges in the system; builds a linked list of data PCI BIOS provides the services described in bib-pci-bios-specification PCI Fix-up tidies up the system specific loose ends of PCI initialization. SECTION I: LINUX OVERVIEW Linux PCI Initialization Slide 7

8. Unix is a layered operating system User programs interact with the kernel through a set of standard system calls Unix is a multi-user, multi-tasking operating system SECTION 2 – UNIX OVERVIEW Unix OS Structure Slide 8

9. SECTION 2 – UNIX OVERVIEW Unix File System Slide 9 • You start with the root directory, denoted by /, at the top and work down through sub-directories underneath it.

10. SECTION 2 – UNIX OVERVIEW Unix Directories Structure Slide 10 • Every directory and file is listed in its parent directory. • An inode is a special file designed to be read by the kernel to learn the information about each file. – function: specifies the permissions on the file, ownership, date of creation and of last access and change. • The system – does not require particular structure for the data in the file itself. • There's no header, trailer, label information or EOF character as part of the file.

11. SECTION 2 – UNIX OVERVIEW Unix Common Control Keys Slide 11 • Control keys - used to perform special functions on the command line or within an editor in Unix • ^S, With control keys upper and lower case are the same, so ^S is the same as ^s. This particular example is a stop signal and tells the terminal to stop accepting input • EX: Control-U is normally the "line-kill" signal for your terminal. It erases the entire input file.

12. SECTION 2 – UNIX OVERVIEW Unix Shell Slide 12 • The shell - acting as a command interpreter - reads your terminal input and translates the commands into actions taken by the system. • The shell is analogous to command.com in DOS. The original shell was the Bourne shell, sh. Every Unix platform will either have the Bourne shell, or a Bourne compatible shell available. • The default prompt for the Bourne shell is $ (or #, for the root user). The default prompt for the C shell is %.

13. For both OS: Separate filesystems that the system may use are not accessed by device identifiers (such as a drive number or a drive name) but instead they are combined into a single hierarchical tree structure that represents the filesystem as a single entity. Unix and Linux transparently supports many different filesystems (for example MS-DOS and EXT2) and presents all of the mounted files and filesystems as one integrated virtual filesystem. SECTION 3 - COMPARISON Similarity - File System Slide 13

14. SECTION 3 - COMPARISON Similarity – Memory Management Slide 14 • Linux supports the Unix TM System V shared memory IPC.

15. SECTION 3 - COMPARISON Similarity - IPC Slide 15 • Inter-Process Communication • Linux supports the classic Unix TM IPC mechanisms of signals, pipes and semaphores and also the System V IPC mechanisms of shared memory, semaphores and message queues.

16. SECTION 3 - COMPARISON Similarity – Identifiers Slide 16 • Linux and Unix - uses user and group identifiers to check for access rights to files and images in the system. • All of the files in a Linux system have ownerships and permissions, these permissions describe what access the system's users have to that file or directory.

17. SECTION 3 - COMPARISON Similarity – Executing Programs Slide 17 • In both OS - programs and commands are normally executed by a command interpreter. (A command interpreter is a user process like any other process and is called a shell 2) • Shells - searches the directories in the process's search path, held in the PATH environment variable, for an executable image with a matching name.

18. SECTION 3 - COMPARISON Similarity - EXT2 File System Slide 18 • A Linux filename has the same format as all Unix TM filenames have. It is a series of directory names separated by forward slashes (``/'') and ending in the file's name. • EX: /home/rusling/.cshrc where /home and /rusling are directory names and the file's name is .cshrc. • Like Unix TM systems, Linux does not care about the format of the filename itself; it can be any length and consist of any of the printable characters.

19. END NOTE: THE MAJOR DIFFERENCE DIFFERENCE Slide 19 • Although Linux share a lot of similarities with Unix, It is not Unix. • Many people think Linux is a kind of Unix but actually, they do not come from the same source code base.

20. Presentation designer: Cailan Hao (Lancy) Presentation Instructor: Mort Anvari Presentation content: Overview Linux and Unix – Comparison Presentation Slides #: 20 Contact Me Lannee@zdnetmail.com Name: Lancy *OS Comparison Presentation 11/3/1999 Presentation Info