Linux_CASESTUDY.ppt
- 2. 2 Reference S.M. Sarwar, R. Koretsky and S.A. Sarwar, Linux – The Textbook, Addison Wesley, 1st ed, 2002
- 3. 3 Provide a user interface Organize files on disk Allocating resource to different users with security control Co-ordinate programs to work with devices and other programs Features of modern OS
- 4. 4 Case study: Linux A. Development of Linux
- 5. 5 Before Linux – In 80’s, Microsoft’s DOS was the dominated OS for PC – Apple MAC is better, but expensive – UNIX is much better, but much much expensive. Only for minicomputer for commercial applications – People was looking for a UNIX based system, which is cheaper and can run on PC – Both DOS, MAC and UNIX are proprietary, i.e., the source code of their kernel is protected – No modification is possible without paying high license fees
- 6. 6 GNU project – Established in 1984 by Richard Stallman, who believes that software should be free from restrictions against copying or modification in order to make better and efficient computer programs – GNU is a recursive acronym for “GNU's Not Unix” – Aim at developing a complete Unix-like operating system which is free for copying and modification – Companies make their money by maintaining and distributing the software, e.g. optimally packaging the software with different tools (Redhat, Slackware, Mandrake, SuSE, etc) – Stallman built the first free GNU C Compiler in 1991. But still, an OS was yet to be developed
- 7. 7 Beginning of Linux – A famous professor Andrew Tanenbaum developed Minix, a simplified version of UNIX that runs on PC – Minix is for class teaching only. No intention for commercial use – In Sept 1991, Linus Torvalds, a second year student of Computer Science at the University of Helsinki, developed the preliminary kernel of Linux, known as Linux version 0.0.1 – It was put to the Internet and received enormous response from worldwide software developers – By December came version 0.10. Still Linux was little more than in skeletal form.
- 8. 8 Confrontation and Development – Message from Professor Andrew Tanenbaum – " I still maintain the point that designing a monolithic kernel in 1991 is a fundamental error. Be thankful you are not my student. You would not get a high grade for such a design :-)" (Andrew Tanenbaum to Linus Torvalds) – "Linux is obsolete". (Remark made by Andrew Tanenbaum) – But work went on. Soon more than a hundred people joined the Linux camp. Then thousands. Then hundreds of thousands – It was licensed under GNU General Public License, thus ensuring that the source codes will be free for all to copy, study and to change.
- 9. 9 Linux Today – Linux has been used for many computing platforms – PC, PDA, Supercomputer,… – Current kernel version 2.4.20. 2.5 is coming – Not only character user interface but graphical user interface, thanks to the X-Window technology – Commercial vendors moved in Linix itself to provide freely distributed code. They make their money by compiling up various software and gathering them in a distributable format – Red Hat, Slackware, etc – Chinese distribution of Linux also appeared in Taiwan and China - CLE, Red Flag Linux
- 10. 10 Linux Pros and Cons Advantages over Windows – It's almost free to relatively inexpensive – Source code is included – Bugs are fixed quickly and help is readily available through the vast support in Internet – Linux is more stable than Windows – Linux is truly multi-user and multi-tasking – multiuser: OS that can simultaneously serve a number of users – multitasking: OS that can simultaneously execute a number of programs – Linux runs on equipment that other operating systems consider too underpowered, e.g. 386 systems, PDA, etc
- 11. 11 Linux Pros and Cons (Cont) Disadvantages compared with Windows – My program cannot run on Linux – Isn't as popular as Windows – No one commercial company is responsible for Linux – Linux is relatively hard to install, learn and use Hence currently, Linux is mainly used in commercial applications, server implementation More than 75% current network servers are developed based on Linux or Unix systems – Due to the relatively high reliability
- 12. 12 Case study: Linux B. Linux System Architecture
- 13. 13 Computer Hardware System call interface Applications: Compilers, word processors, X-based GUI API AUI BIOS LINUX Shell: Bourne Again (bash), TC, Z, etc. Language libraries Device Drives Kernel File management Memory management Process Management
- 14. 14 Kernel – The part of an OS where the real work is done System call interface – Comprise a set of functions (often known as API) that can be used by the applications and library routines to use the services provided by the kernel Application User’s Interface – Interface between the kernel and user – Allow user to make commands to the system – Divided into text based and graphical based
- 15. 15 File Management – Control the creation, removal of files and provide directory maintenance – For a multiuser system, every user should have its own right to access files and directories Process Management – For a multitask system, multiple programs can be executed simultaneously in the system – When a program starts to execute, it becomes a process – The same program executing at two different times will become two different processes – Kernel manages processes in terms of creating, suspending, and terminating them – A process is protected from other processes and can communicate with the others
- 16. 16 Memory management – Memory in a computer is divided into main memory (RAM) and secondary storage (usually refer to hard disk) – Memory is small in capacity but fast in speed, and hard disk is vice versa – Data that are not currently used should be saved to hard disk first, while data that are urgently needed should be retrieved and stored in RAM – The mechanism is referred as memory management Device drivers – Interfaces between the kernel and the BIOS – Different device has different driver
- 17. 17 Case study: Linux B.1 User interface
- 18. 18 : Linux User Login Linux is a multiuser OS Allow multiple users to use the resource of a computer at the same time Every user needs to login the system with the password provided to identify their right in using the resource Require for both client-server based system or desktop Linux Server Client-server based system PeterMary Paul Peter: admin Paul : general Mary : intruder
- 19. 19 Linux User Interface Traditional Linux (Unix also) uses command- driven interface (or text-based interface) – User needs to type lines of command to instruct the computer to work, similar to DOS – Advantage: fast in speed. Very few resource is required for its implementation – Disadvantages: user needs to type, hence can easily make error. Besides, user needs to memorize all commands – Suitable for expert users and for the systems that interaction with user is not frequent, such as servers
- 20. 20 By adopting the X-Window technology, graphical user interface (GUI) is available for Linux: – Uses pointing devices (e.g. mouse) to control the system, similar to Microsoft’s Windows – Provide menu-driven and/or icon-driven interfaces – menu-driven: user is provided with a menu of choices. Each choice refers to a particular task – icon-driven: tasks are represented by pictures (icon) and shown to user. Click on an icon invokes one task – Advantages: No need to memorize commands. Always select task from menus or icons – Disadvantages: Slow and require certain resource for its implementation – Suitable for general users and systems, such as PC
- 21. 21 • A typical Linux GUI based on GNOME • Similar to Microsoft’s Windows, however, different window systems can be chosen (e.g. GNOME, KDE, etc)
- 22. 22 Linux text-based interface command to show the content of current directory command to show the content of current directory with option -al The prompt $ shows that bash shell is using
- 23. 23 Kernel Bash, Tcsh, Zsh ls pwd whoami Shell interprets the command and request service from kernel Similar to DOS but DOS has only one set of interface while Linux can select different shell – Bourne Again shell (Bash), TC shell (Tcsh), Z shell (Zsh) Linux Shell Different shell has similar but different functionality Bash is the default for Linux Graphical user interface of Linux is in fact an application program work on the shell
- 24. 24 Frequently used commands available in most shells: – ls : to show the names of the file in the current directory – cd : change directory, – e.g. cd / change to the root directory cd .. change to the parent of that directory – cp : copy one file to another – e.g. cp abc.txt xyz.txt copy abc.txt to xyz.txt – rm : remove a file – man : ask for the manual (or help) of a command – e.g. man cd ask for the manual of the command cd – pwd : show the name of the current directory – cat : to show the content of a text file – e.g. cat abc.txt show the content of abc.txt – whoami : to show the username of the current user
- 25. 25 Case study: Linux B.2 File management
- 26. 26 Linux File Management In Linux, file is defined as simply the thing that deals with a sequence of bytes Hence everything are files – An ordinary file is a file; a directory is also file; a network card, a hard disk, any device are also files since they deal with a sequence of bytes Linux supports five types of files – simple/ordinary file (text file, c++ file, etc) – directory – symbolic (soft) link – special file (device) – named pipe (FIFO)
- 27. 27 Names in blue are directories, indicated by a letter d at the beginning of the line The concept of simple file and directory is similar to DOS
- 28. 28 Symbolic (soft) link – Not a real file, just a link to another file – Allow giving another name to a file without actually duplicates it – hence save memory space Special file (device) – Each hardware device, e.g. keyboard, hard disk, CD-ROM, etc is associated with at least one file – Usually store in /dev directory – Applications can read and write any devices by reading and writing their associate file – hence the access method is known as device independent – Divide into two types: character special files, e.g. keyboard, and block special files, e.g. disk
- 29. 29 ENG224 INFORMATION TECHNOLOGY – Part I 2. Operating System Case Study: Linux Command that sets a symbolic link to a file called CUI to anotherCUI A symbolic link begins with a letter l File size is only 6 bytes
- 30. 30 ENG224 INFORMATION TECHNOLOGY – Part I 2. Operating System Case Study: Linux Some of the special device files in /dev fd0 – floppy disk md0 – CD-Rom Both of them are block devices, hence start with a letter b Some are character devices, hence start with a letter c
- 31. 31 Linux File System Structure root / bin boot dev etc home lib lost+found mnt opt proc root sbin tmp usr var fd hd hd … group passwd dlun guest bin lib local According to the File System Standard (FSSTND) proposed in 1994, every LINUX system should contain a set of standard files and directories file directories
- 32. 32 Root Directory ( / ) – Top of the file system. Similar to in DOS /bin – Contain the binary (executable code) of most essential Linux commands, e.g. bash, cat, cp, ln, ls, etc. /boot – Contain all the files needed to boot the Linux system, including the binary of the Linux kernel. E.g., on Red Hat Linux 6.1, the kernel is in /boot/vmlinux-2.2.5-15 file /dev – Contain the special files for devices, e.g. fd0, hd0, etc.
- 33. 33 /etc – Contain host-specific files and directories, e.g. information about system configuration – /etc/passwd – This file contains login information of users in the system – For every user, one line of record is stored in the following format: login_name : dummy_or_encrypted_password : user_ID : group_ID : user_info : home_directory : login_shell
- 34. 34 /home – Contain the home directories of every user in the system, e.g. dlun, guest, etc /lib – Store all essential libraries for different language compilers /lost+found – Contain all the files on the system not connected to any directory. – System administrator should determine the fate of the files in this directory
- 35. 35 /mnt – Use by system administrator to mount file systems temporarily by using the mount command – Before using any devices, they have to be mounted to the system for registration – For example, after mounting a CD-ROM, the file system in it will be mapped to /mnt/cdrom directory – User can then read and write files in the CD-ROM by accessing this directory – Similar to mapping a drive letter to a CD-ROM in Windows – Different from the special file in /dev. Special file is only a place where data of the CD-ROM is transferred or stored. No file system concept
- 36. 36 /opt – Use to install add-on software packages, e.g. star office, etc. /proc – Contain process and system information /root – Home directory of the user root, usually the administrator /sbin – The directories /sbin, /usr/sbin, and /usr/local/sbin contain system administration tools, utilities and general root only commands, such as halt, reboot and shutdown
- 37. 37 /tmp – Contain temporary files. Usually files in this directory will be deleted from time to time to avoid the system fills with temp files /usr – One of the largest sections of the Linux file system – Contain read-only data that are shared between various users, e.g. the manual pages needed for the command man. Stored in /usr/man direcrtory /var – Contain data that keeps on changing as the system is running. E.g. /var/spool/mail directory keeps the mail of user
- 38. 38 Linux File Access Privilege Linux is a multiuser system, the files of all users are stored in a single file structure Mechanism is required to restrict one user to access the files of another user, if he is not supposed to User can impose access permission to each file to restrict its access The term “access permission” refers to – read permission – write permission – execute permission
- 39. 39 The file access permission can be seen by using the command ls –l or ls -al
- 40. Access permission can also be assigned to a directory Directory is also a file that contains the attributes of the files inside it If read permission is not given to a directory – cannot show the structure of this directory – e.g. cannot use ls If write permission is not given to a directory – cannot modify anything of the directory structure – e.g. cannot copy a file into this directory since it will modify the directory structure by adding one more file If execute permission is not given to a directory – nearly nothing can be done with this directory, even cd
- 41. The access permission of a file or directory can be changed by using the command chmod xyz filename/directory name xyz refers 3 digit in octal form E.g. 660 : 110 110 000 rw- rw- --- 545 : 101 100 101 r-x r-- r-x
- 42. 42 temp does not have execution right even cd is not workable execution right is added now we can change the directory to temp
- 43. 43 File Storage in Linux Data storage on hard disk – Data in a hard disk are stored on a magnetic flat plate – Disk’s surface needs to be partitioned and labeled so that computer can go directly to a specific point on it – Achieve by low level formatting the disk Create magnetic concentric circles called tracks Each track is split into smaller parts called sectors and numbered Each sector: hold 512 bytes data E.g. 80 tracks (from outer to inner 0 .. 79), 18 sectors disk can store 80x18x512 bytes data.
- 44. 44 Formatted Disk Sector Track Density of data is higher for inner tracks than outer tracks
- 45. 45 Must read or write whole sector at a time OS allocates groups of sectors called cluster to files Files smaller than the cluster will still be allocated the whole cluster, but the rest left unused In Linux, every file is associated with an inode that records its location in the disk The inode of all files are put together in a data structure called inode table In the directory, every file is associated with a inode number that points to an entry of the inode table
- 46. 46 Case study: Linux B.3 Process management
- 47. 47 Linux Process Management Linux is a multitasking system Multiple programs can be executed at the same time Ultimately, a program needs to be executed by a CPU If there is only one CPU, how multiple programs can be executed at the same time? By time sharing That is, all programs are claimed to be executing. In fact, most of them are waiting for the CPU