What is UNIX?

1. What is UNIX? • UNIX is an Operating System (OS). • An operating system is a control program that helps the user communicate with the computer hardware. • UNIX was developed long before Windows, about 30 years ago at AT&T Bell Labs in the US (95% written in “C” programming language). • UNIX was designed as an operating system for experts, used on high-end workstations, servers and hosts.

2. What is UNIX? UNIX provides some powerful features: • Security - private and shared files • Multi-user support • Inter-process communication • Extensive network support • Data sent to display, files, or printers in same way • Windows NT was developed by Microsoft to try to replace UNIX as the “OS for experts”.

3. Most Important Feature of UNIX • Most important feature of UNIX:STABILITY • 30 years to get the bugs out • Important in shared environments and critical applications • Shared Environments Example: University • Windows98/NT crashes at least once a day in labs • UNIX servers crash about once a semester (usually due to hard disk failure) • UNIX more than 100 times more reliable than Windows! • Critical Applications • Hospital - Don’t want to wait for reboot during operation! • Airport - Air traffic control landing planes. • Telecom - Don’t want phone system going down!

4. UNIX Versions • There are two main types of UNIX: • BSD (Berkeley Software Distribution) • System V (developed at AT&T) • There are many different versions of UNIX for different hardware: • Sun Microsystem’s Solaris (and SunOS) • Hewlett-Packard’s HP-UX • IBM’s AIX • SGI’s IRIX • Many UNIX dialects for PCs • “Free”: Linux (distributions such as Red Hat, Caldera,Corel, SuSE, TurboLinux, WinLinux), FreeBSD(see http://www.linux.org/; http://www.linux.org/dist/index.html) • Commercial: SCO UNIX (Xenix), Sun OS

5. PC UNIX • Linux basically free • Also runs well on older PCs • Many free, reliable software & development tools with source code e.g.,Web/Mail Server, Database Server, File Server (NFS for UNIX, Samba for Windows clients), Firewall, Dialup • Extremely fast PC for hosts and servers • Multiple (2,4,8) CPUs in one PC – Symmetric Multi-Processing (SMP) • PC clusters for scientific computingMore powerful than and therefore alternative for older expensive mini/mainframe & some super computers, especially if they are running UNIX

6. Who Uses UNIX? • Computer manufacturers such as Sun, SGI, IBM, and HP • Computer chip manufacturers like Motorola & Intel • Software companies • Banks • Hospital Authority • Universities • Internet Service Providers (ISP) • Web Companies • Web servers of many organization and for personal use

7. UNIX BSD • Berkeley Standard Distribution(univ at CA) • Tools: • C shell • VI editor • File managers • Network applications

8. Unix System V • “Standard” unix • AT&T version • Improved file sharing in the network • Version 4.0 developed by AT&T and Sun Microsystems

9. X-Windows • GUI for Unix • Many tools • Standard for every system • Provides: windows, menus, buttons, dialog boxes etc…

10. Applications • File Managers • Shells • Editors • Databases • Web Servers • Mail server • Network applications and utilities

11. Programming • Many tools: compilers, debuggers etc.. • Supports: C, C++, Fortran, Pascal, Java, Basic, Cobol, Lisp, APL, Logo, RPG • Easy Connection between Application with the standard input and output. • Shell Programming

12. General UNIX Architecture • Hardware • Kernel • System Call Interface • Unix applications/commands

13. Unix File System • What is a file system? A means of organizing information on the computer. A file system is a logical view, not necessarily a physical view. • What does the file system provide: • Ways to create, move, and remove files • Ways to order files • Security • Examples of file systems: • DOS, Macintosh, CD-ROM, UNIX, NFS (networked file system)

14. / bin homes lib . . . horner jbond . . . .mailrc 111 top10 . . . UNIX File Systems • Hierarchical Organization • Single root of tree is at top denoted by ‘/’ • Kinds of files: • Directory files (the branches in the tree) • Regular files (leaves in the tree)

15. Home and Working Directories • Home directory • The directory you are in when you first login in • This is your space; you control security • Place to put your personalized ,startup files • Your working directory after typing cd with no arguments • Working directory • Can access files in your working directory by simply typing the filename • To access files in other directories, must use a pathname • pwd command prints the working directory • cd command changes the working directory

16. Directory Shorthands • “.” is the directory itself • “..” is the parent directory • In most shells “~” means your home directory • ~user means user’s home directory, so: ~jbond/.plan • looks at the file .plan in /home/jbond, which is jbond’s home directory.

17. Special Directories • “/” (pronounced “slash” and also called “the “root”) is the ancestor of all files in the file system • /bin and /usr/bin contain UNIX utilities (e.g., cat) • /dev contains special files which describe “devices” such as terminals and printers • /etc has administrative programs like password files • /tmp is for temporary files; periodically deleted • Every directory has at least two entries: “.” is the directory itself, and “..” is the directory’s parent

18. Naming Files • Files in the same directory can’t have the same name • Case sensitive: secret and Secret are different • Files are sometimes named with an extension (e.g., bond.cpp, 007.html) to show the file’s content. • You cannot create a file named “.” or “..” • “Invisible” files and directories (those that don’t appear using ls) have a period as the first character (e.g., .plan, .xinitrc). Some programs use invisible files to store information.