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Introduction to UNIX. Ke Liu [email protected] Topics. Logging in. Unix Shells and useful shell commands. File System in Unix. Program, Process and Process control. Inter-process communication. Compiling and debugging C programs. Editors.

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Introduction to UNIX

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Introduction to unix l.jpg

Introduction to UNIX

Ke Liu

[email protected]

Topics l.jpg


  • Logging in.

  • Unix Shells and useful shell commands.

  • File System in Unix.

  • Program, Process and Process control.

  • Inter-process communication.

  • Compiling and debugging C programs.

  • Editors.

Slide3 l.jpg


  • UNIX is multi-user and multi-tasking operating system.

  • Multi-tasking: Multiple processes can run concurrently.

  • Example, different users can read mails, copy files, and print all at once.

Logging in l.jpg

Logging In

  • Enter login name and password !

  • System password file: /etc/passwd (usually).

  • You can change password using the command: passwd.

Shell l.jpg


  • After a successful login, the shell program is run. The default shell of bingsuns: tcsh

  • bingsun2% ps


    2159 pts/2 0:00 tcsh

  • Shell is a command line interpreter that reads user commands and executes them.

Unix shells l.jpg

Unix Shells

  • Common Shells: Bourne shell, the C shell, and the Korn shell.

  • The shell on bingsuns is tcsh (tc shell).

  • Users can switch between shells, using the commands bash, csh, ksh, sh.

  • Control D (^d) to return back to original shell, or just use the command: exit.

Some shell commands l.jpg

Some shell commands

  • Most Important command: man (manual pages).

  • Help: unix commands, C functions.

  • Usage: man <command/function>

  • Try “man man” !

  • Example:

    man ls, man passwd, man printf.

Some shell commands cont l.jpg

Some shell commands (cont’)

  • pwd: working directory (/u0/users/2/kliu1).

  • ls: list contents of directory

  • mkdir <dir-name>: make directory

  • rmdir <dir-name>: remove an empty directory

  • rm –r <dir-name>: remove a directory with all the contents

  • cd <directory>: change directory, ~/ means your home directory

  • cp <source> <target>: copy command.

Some shell commands cont9 l.jpg

Some shell commands (cont’)

  • chmod <mode> <filename>: change mode of a file/directory

  • ls –l <directory or filename>: long list with details

  • 9 permission bits: d r w x r w x r w x

  • 3 categories: user/group/all.

  • Permissions: read/write/execute (r/w/x).

  • E.g.: mode= 644 means r w _ r_ _ r _ _

    command: chmod 644 <filename>

  • first 3 bits for user. Next group. Next all others.

Some shell commands cont10 l.jpg

Some shell commands (cont’)

  • rm <option> <filename>: remove files

    e.g.: rm –fr directory/filename

  • mv <old> <new>: change the name of a file

  • Pipes: Connect the stdout of one command with the stdin of another command

    e.g.: ls -l | more or ls –l | less

File system l.jpg

File System

  • Hierarchical arrangement of files and directories.

  • Top level: root or /

    e.g.: cd /

  • . Current directory, .. One level higher directory

    e.g.: cd . No change for it is current directory

    or cd .. Change to parent directory.

File system cont l.jpg

File System (cont’)

  • Pathname: absolute and relative.

  • Absolute pathname: /u0/users/2/kliu1

  • Relative pathname: abc.

Editors l.jpg


  • Different editors: emacs, pico, vi

  • emacs <filename>

  • pico <filename>

  • vi <filename>

The easiest editor pico or nano l.jpg

The easiest editor: pico or nano

  • pico <filename>

  • Full screen editor

  • Help on the bottom of the screen

  • The nano is an extension to the pico

Basic operations in pico l.jpg

Basic operations in pico

  • Ctrl + v : to move page down

  • Ctrl + y : to move page up

  • Ctrl + o : to save the current buffer

  • Ctrl + x : to exit with or without saving

  • Ctrl + g : to get help

  • Ctrl + r : to open a file

  • Ctrl + w : to find a string in the current buffer

  • Ctrl + c : to get the current position in the buffer

Program process l.jpg

Program & Process

  • Program is an executable file that resides on the disk.

  • Process is an executing instance of a program.

  • A Unix process is identified by a unique non-negative integer called the process ID.

  • Check process status using the “ps” command.

Foreground background processes l.jpg

Foreground/background processes

  • A program run using the ampersand operator “&” creates a background process.

  • E.g.:

    bingsun2% back &

  • otherwise it creates a foreground process.

  • E.g.:

    bingsun2% back

Foreground background processes18 l.jpg

Foreground/background processes

  • Only 1 foreground process for each session. Multiple background processes.

  • Where are background processes used?

  • All system daemons, long user processes, etc.

    e.g. printer-daemon process or mailer-daemon process.

  • These processes are always running in background.

  • Pine is foreground process.

Process status l.jpg

Process Status

bingsun2% back &

[1] 16488 the process id assigned by system

bingsun2% ps


1973 pts/39 0:01 tcsh

16488 pts/39 0:00 back

How to stop a process l.jpg

How to stop a process?

  • Foreground processes can generally be stopped by pressing CONTROL C (^C).

  • Background processes can be stopped using the kill command.

  • Usage: kill SIGNAL <process id list>

  • kill -9 <process id list> (-9 means no blocked)

    Or kill <process id list>.

  • If a foreground process is not stopping by ^C, you can open another session and use the kill command.

  • Login