1. Introduction to UNIX
CS208

2. What is UNIX? UNIX is an Operating System (OS).
An operating system is a control program that allocates the computer's resources, schedules tasks, and helps the user communicate with the computer.
Most popular PC operating systems: Windows 95/98/2000/XP -- proprietary, single-user OS
UNIX was developed long before Windows, about 30 years ago at AT&T Bell Labs (95% written in “C” programming language).

3. UNIX Compared with other OS
Mature and stable OS
Large user community
Vendor-independent OS
Network-portable window system (X)
Runs on range of hardware (PC - Cray)
Common Open System Environment (COSE)
Source code is available to view and modify

4. Multi-user, Multi-tasking
More than one user can run at the same time and each user can run more than one task at the same time
In Unix, each program is started as a process.
A process is a program in execution.
Usually only one copy of a program, but there may be many processes running the same program.
Each interactive user may have:
only one process in foreground
may have several processes in background

5. 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
Windows 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!

6. UNIX Versions Two main types of UNIX:
BSD (Berkeley Software Distribution)/OSF
System V (developed at AT&T)
Different versions of UNIX for different hardware:
Sun Microsystem’s Solaris (and SunOS)
Hewlett-Packard’s HP-UX
IBM’s AIX
SGI’s IRIX

7. Unix Operating System Structure
OS mediates between the user and the computer
User
Application Programs
Kernel
Shell
Shell - Whenever you log in,you get placed in a program called a shell.
You can see the shell prompt.
Enter commands at the prompt.
Shell acts as a command interpreter,
taking commands and passing them on to the kernel.
Kernel: At the core of the Unix system,
loaded whenever the system is started up (booted).
Manages computer resources (memory, processes, file system)
manages memory and allocates it to each process
schedules work done by the CPU
organizes transfer of data from one part of machine to another
accepts instructions from shell and carries them out
enforces access permission on the file system
Hardware

8. Why has Unix been successful?
 UNIX is portable, because it was written in C.
Provides hardware independence.
Open System
Underlying operating system source code is available
 Provides a productive environment
Allows multi-tasking and sharing of data
Excellent C development environment is built-in
Networking capabilities are built in

9. Unix Disadvantages
UNIX is not as user-friendly as some operating systems
Command names are often cryptic
User help is not great
UNIX does not error check user commands to protect users from hurting themselves or the system
Example: Request to copy a file over an existing file will overwrite the existing file with no warning.

10. Unix Disadvantages UNIX is less secure than some operating systems
Developed to be used as a software development environment, in which all users are working together cooperatively. Security was traded for more convenience and flexibility.
Well-documented open code makes hacking easier.
UNIX's portability also makes it less efficient on any particular hardware.
Proprietary operating systems are optimized for that hardware.

11. Basic UNIX Commands

12. The Unix Prompt
After you log in, and the startup files have been run, the shell will display a prompt $
Different shells and different systems have different prompts.
Two common prompts are $ and #.
Your prompt can be changed.
A prompt (plus a cursor) tells you that the system is ready for your commands.
F 1-7 PD 1-7

13. Standard Command Format
Format: command [options] <arguments>
stuff in brackets is optional
boldface words are literals (must be typed as is)
<> enclosed words are args (replace appropriately)
Commands are case sensitive (mostly lowercase)
Spaces must be inserted between commands, options, arguments

14. Standard Command Format
Options (also called flags) modify how the command works (command behavior)
single letters prefixed with a dash “-”
combined or separated (e.g., -al = -a -l)
come before arguments
Arguments define the command scope
Optional for some commands, mandatory for others
Some commands assume a default argument if none is supplied
Usually files or directories

15. Basic Commands date - Print the date and time
Wed Feb 3 12:13:07 MDT 2003 $
echo - Display command line input to screen
$ echo Hi, I am your instructor!
Hi, I am your instructor!

16. Commands to Manipulate Files
ls lists files in a directory (names, not the contents of files)
cat, head, tail, more display files
rm removes files (and directories)
cp copies files (and directories)
mv moves (renames) files (and directories)

17. List Files in a Directory
Format: ls [-alRF…] <file-list>
-a list all files including the dot files
-l long format (show file type, permissions, #links, owner, etc)
-R recursive list subdirectories
-F list directories with file type (trailing / *)

18. Listing Files in a Directory
BLOCK
SIZE
# DIRECTORIES
FILE SIZE
GROUP
1 drwxr-xr-x 180 root admin Oct 1 ../
2 -rw-r--r smith fac Oct 3 file
PERMISSIONS
MODIFY DATE
FILE
TYPE
FILE NAME
OWNER
Permission settings will be covered in a later section. For now just remember that Unix is multi-user, and with any multi-user system you need security to prevent one person from changing another person’s file space.

19. Getting Help Check the manual pages! Format: man <command>
For shell command, system programs, and library functions.
Format: man <command>
man –k <keywords>
Man(ual) page format
Name
Synopsis
Description (options, defaults, detail desc., examples)
Files
See Also
Bugs

20. man Examples $ man man Displays help on the man command $ man who
Displays help on the who command
$ man -k mail
Checks all man pages for keyword “mail”

21. man Output Example spacebar - move forward one page
$ man ls
Reformatting page. Wait... done
User Commands ls(1)
NAME
ls - list contents of directory
SYNOPSIS
/usr/bin/ls [ -aAbcCdfFgilLmnopqrRstux1 ] [ file... ]
/usr/xpg4/bin/ls [ -aAbcCdfFgilLmnopqrRstux1 ] [ file... ]
--More--(11%)
spacebar - move forward one page
b – move back one page
h – more commands q – quit

22. Viewing Files
cat concatonate and print to screen (ctrl-s and ctrl-q to stop/start)
head display first x lines of file
tail display last x lines of file
(both default to 10 lines)
more display part of file to screen

23. Example: cat, head, tail $ cat letter Mr. Jones,
It is getting late. Please order some pizza and stop
by my office. We’ll tidy up a few more things before
calling it a night.
Thanks!
Ben
$ head –2 letter
$ tail –1 letter

24. Copying Files Format: cp [-ir…] file1 file2
cp [-ir…] file-list directory
cp [-ir…] directory directory
i for interactive. Prompt whenever a file will be overwritten.
r for recursive. copy a whole directory tree.

25. cp Examples $ ls letter1 secret $ cp letter1 letter2 $ ls -F
letter1 letter2 secret/
$ cp letter1 letter2 secret
$ ls secret
letter1 letter2

26. Moving /Renaming Files
Format:
mv [-i…] file1 file2
- Renames file1 to file2
mv [-i…] file-list directory
- Moves files from current location to new directory
mv [-i…] directory directory
- Renames a directory

27. mv Examples $ ls letter memo saved $ mv memo memo1 $ ls -F
$ mv saved trash
letter memo1 trash/

28. Deleting Files Format: rm file-list - Deletes files rm -r directory
- Deletes directory and all files and directories within it
- Use with CAUTION!

29. rm Examples $ ls -F letter1 letter2 secret/ $ rm letter1
$ ls –F secret
memo morestuff/
$ rm –r secret
$ ls
letter2