Basic Unix Training

8/12/2019 Basic Unix Training

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UNIX TRAINING IBASICS


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Tejas Networks Confidential6 September, 20002

What is Unix?

Manages computer resources (for example, CPUtime, memory etc.,)

Invented at AT&T Bell Labs in early 70s.Some workstation variants SunOS and Solaris (From Sun Microsystems), HP-UX

(From Hewlett Packard), AIX (from IBM)

Some PC & Mac variants NetBSD, OpenBSD, Linux


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Why Unix?

Multiple users can use it at the same time (unlikewindows where one has to logout before someoneelse can use it!)Resources are used effectivelySecureAvailable on many systems from PCs tosupercomputersUsage transparency - basic commands are same


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Using Unix

Every user has A User Name Password (a secret code) dont share this!!! A working area called home directory

One or more users are clubbed into a group. Forexample, people working on the same project.A user avails Unix services by logging in. Thiscreates a login session. Enter your login name System prompts for the password Enter your password


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Using Unix (contd)

After logging in Unix runs a program for youcalled a shell and you land up in your homedirectory.The shell displays a shell prompt where you cantype in the commands.A user can stop using unix by logging out. This

closes the login session. Type logout on the screen OR Type exit on the screen


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What is Shell?

Shell is a program that reads the commandsthat you type in, executes them and display

the results for you.Shell sets up your working environment.Different shells are available on Unix. For

example, csh and bash.


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Directories and Files

UNIX computer systems store data on disk drivesusing a structure called a filesystem . There are many different types of filesystems User accesses directories and files in the same way

irrespective of the filesystem type.

UNIX filesystems store information in a hierarchy

of directories and files.A filesystem is created when a disk is formattedwith the proper UNIX utilities/commands.


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Directories and Files (contd) - Example

Unix Root Directory/

bin dev etc home lib proc sbin tmp usr var

modules bin lib tmp


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Directories and Files (contd)

Directories are like folders in the filesystem .Users can group files together inside thedirectories.Directories are represented as files withspecial properties.The top level of the UNIX filesystem issymbolized by the " /" character. Thisdirectory has a special name - it is called the"root " directory .


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Unix Directories and Files

The directories contain data in the form offiles.

Files have a name associated with them.They are CASE SENSITIVE ! (Contrast toWindows)

In Unix all the commands are stored as filesin the directory system.


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Get a Feel for Unix Commands

At the shell prompt type cd /. This changes theworking area to the root directory of thefilesystem.

At the shell prompt type in the word ls. Thisdisplays the list of directories and files containedin the root directory.Type cd. This takes you right back to the homedirectory. Type ls again. What do you see? (Thisis an exercise for you)Type echo $HOME at your shell prompt. This

prints your home directory name.


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How do I identify Unix files and directories?

Any file (note that directory is also a file) is identified apath name. Path name basically is a list of directories separated by /

to the point where the file exists in the filesystem. Absolute path describes the path from the root of the file system.

Example: the absolute path of your home directory is/home/.

Relative path describes the path with respect to the currentdirectory. Example: relative path of the file example.txt in your bindirectory in your home directory is (assuming it exists),

bin/example.txt


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Gee! I dont know how to use this command!

If you know that a command exists in Unix forsome purpose and dont know how to use it,DONOT PANIC! Unix has an Online help system.How to use Unix help system. Type man commandname at the shell prompt. Type man man to get help on the help system.

Exercise: Type man man and find out what it says Type man cd and find out what it says


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Working with files Basic File Commands

ls (list) list files anddirectoriescat (concatenate)

print one or more filesto the screenmv (move) renamesa filecp (copy) copies thecontents of a file to anew one.

rm (remove) delete afile.less look at thecontents of a file onescreen at t time.tail look at the endof the filediff report thedifferences betweenfiles


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Working with Directories Basic Commands

mkdir (make directory) create a directoryif it doesnt exist.

rmdir (remove directory) remove adirectory (if its empty)

pwd (present working directory) display

the directory youre in.


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File Access Permissions

Since Unixs are used by multiple users, permissions areassociated with files and directories to protect them againstmodification/deletion by others.

Types of permissions For reading a file For writing a file For executing a file

Level of permissions

Owner/Creator of the files (u = user) Group in which the owner of the file belongs to (g = group) For the rest of the world (o = others) Everyone (a = all)


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File Access Permissions (contd)

Unix command to change the file access permissions at various levels: chmod

(change mode) Usage: chmod level+permission filenameLevel (u = user/owner, g=group, o=others, a=all)Permission type (r=read, w=write, x=execute)

Example, chmod g+w file.txt gives the write permission to the people belonging to file.txtsowners group.


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File Access Permissions (contd) ChangingOwner

chown (Change Owner) Usage: chown username filename

Example: chown trainee file.txt changes theowner of the file.txt to trainee. Note that theuser ID should be created in the system for thecommand to succeed.


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File Archiving/Compressing Commands

Archiving puttingtogether multiple filesinto a single one. Tar read/write data

from/to tape OR multi-file archive on disk.

Cpio read/write datafrom/to tape OR multi-file archive on disk

Compressing shrinkingthe file size. compress compression

utility (compressed fileswith suffix .Z) gzip/gunzip GNU

compression/uncompression utility. Compressed file

suffix is .gz zip/unzip public domainsoftware compatible withDOS zip.


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Unix Processes

Unix lets multiple users run commands atthe same time.

Unix lets an individual users run commandsat the same time.When a command is executing in thecomputers memory, its called a process. Each process has a unique integer toidentify it, called PID (Process ID).


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Whos running now?? The ps command!

Check the status of the processes: ps(process status)

ps optionsType ps ef or ps ax to display all processes in theUnix systemType ps fu trainee to display all processes associatedwith the user trainee


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ps command continued!

How to check if the process is running?Check the process state S Sleeping R Runnable


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View the processes interactively!

Top look at the process activity in realtime

Run the command top and see what it shows The information shown on the screen isconfigurable.

Exercise: View only selected fields. Exercise: View only selected processes.


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How to terminate processes?

If you want a process to terminate, you canuse the command kill.

Usage: kill [optional signal name] PIDUnix sends a signal to process. Process dies when it receives a signal (default

behavior).The default may be overridden.How do you ensure that a process is killed? Run the command kill KILL PID


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Jobs and Job control

You will have to wait till the command completes before you can execute the next command.Such commands are called foreground ORinteractive commands.How to save time due to foreground commands? Detach the running command from the terminal and run

it in the background.

Background commands are called jobs. Jobs can be Suspended/resumed Brought to foreground


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Know Thy Shell!

Shell gives you the working environment.Environment is a set of initializations. Theinitializations are done in: /etc/profile (DO NOT EDIT! Common for all users) ~/.profile ~/.bashrc

What can you initialize? Shell variables Shell functions Command aliases


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Know thy Shell Variables!

Strings of characters that hold values. Example, $HOMEstands for your home directory.To see all your built- in shell variables type set at yourshell prompt.Setting the value of a shell variable: At the prompt type, variablename=value

Displaying the value of a shell variable: At the prompt, type echo $variablename

Example: Type MYVAR=simple string at the shell prompt. Type echo $MYVAR at the shell prompt. What do you see?


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Know Shell Variables Of Your Environment

Some environment variables are special: $HOME (your home directory) $PATH (directories which are to be searched

for commands)Exercise: Adding current directory to your search path

$TERM (your terminal type)

$SHELL (name of your shell) $PWD (current working directory) $OLDPWD (previous working directory)


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Special Characters of Shell

Shell uses some special characters ~ denotes your home directory.

Example: cd ~harish will take you to the homedirectory of the user harish.Recap: Also denoted by $HOME.

. Denotes the current directory

.. Denotes the directory that contains thecurrent directory (also known as parentdirectory).


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Special Characters (contd) Filenamesubstitution

* substitute any character(s) at the position. Example: Type ls *.c. Displays all the C

source files in the working directory.? substitute any character at a given position. Example: Type ls file?.c. Displays files with

names file1.c file2.c . filex.c etc., Exercises


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Filename Substitution (contd)

How to specify a range of characters at a position? Enclose the range in [ and ].

Example: [A-Z], [a-z], [0-9]. Exercise: Putting things together. What wouldthe command ls [1 -3]?abcd*.* do?


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Commands - Redirecting Input and Output

Shell lets you send the output of a command to a file ofyour choice by using > for creating/overwriting or >> appending

between the command and the output filename. Type ls l / > /tmp/out.txt at your shell prompt. The directory

contents of the root directory is now in the file out.txt in the /tmpdirectory.

Shell lets you specify the input to a command using


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I/O Redirection - Pipes

How to create? command1 | command2

What does it do? To send the output from command1 as the input to

command2.

What is it used for? To build complex shell commands.

Example: Type ps aux|less. What will it do? You can see the

output of the ps command one screenful at a time.


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Programming Shell! - Scripts

Shell script A collection of Unixcommands which are executed together.

Whats the use? Combine the individual commands to perform

specialized and complex tasks.

How does the shell let me combine thecommand? Provides a simple programming language!


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Quick Diversion Editing your programswith Vi!

Vi Screen oriented editor Extremely powerful

Mapping keyboard strokes to commandsPattern substitutionCutting and pasting textAnd much more!

Addictive : Youll never leave it once you know it! Two modes Command Mode (controlling the editing) Editing Mode (enter the text)


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Editing with Vi (contd) Entering andQuitting!

Entering Vi Type vi OR vi filename. By default the Vi is in command mode when you enter.

Quitting In the quit command you can optionally provide the filename

Type :wq [optional_filename] to save and quit

Type :q to quit (the edited file should be alreadysaved) Type :q! to quit without saving


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Editing with Vi (contd) - Command Mode

How to enter? Type ESCAPE key on the key board

Enter editing mode :Press i to insert new characters at a position Press a to append characters after current position

Save the edited text : Type :w filename Find and replace text : Type %s/oldpattern/newpattern/

Navigate through lines and wordsPress h: one character left Press l: one character right Press k: one line up Press j : one line down


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Editing with Vi (Contd)

More infohttp://www.thomer.com/thomer/vi/vi.html http://www.vim.org/
http://www.thomer.com/thomer/vi/vi.htmlhttp://www.vim.org/http://www.vim.org/http://www.thomer.com/thomer/vi/vi.html


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Shell Programming Your First Program

Type vi example -1.sh at your shell prompt. Enter editing mode

Type in echo Hello world in the vi screen. Save and quitType chmod a+x example.sh at your command

prompt. Remember: You need execute permissionto execute anything in Unix.Type ./example -1.sh. What do you see?


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Basic Unix Training