My Net Watch Press

8/3/2019 My Net Watch Press

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What Is Linux?

Linux is a clone of the Unix operating system (OS)that has been popular in academia and manybusiness environments for years. Formerly usedexclusively on large mainframes.

Unix and Linux can now run on small computerswhich are actually far more powerful than themainframes of just a few years ago.

Because of its mainframe heritage, Unix (andhence also Linux) scales well to perform todaysdemanding scientific, engineering, and networkserver tasks.


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Understanding Command-LineBasics

Linux borrows heavily from Unix, and Unixbegan as a textbased operating system (OS).Unix and Linux retain much of this heritage,which means that to understand how to useand, especially, administer Linux, you must

understand at least the basics of its command-line tools.


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Shell

If you log into Linux using a graphical userinterface (GUI) login screen, though, youllhave to start a shell manually.

Some GUIs provide a menu option to start aprogram called a terminal, xterm, Konsole, orsomething similar. These programs enable youto run textmode programs within Linux, and

by default they come up running your shell.


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Learning the Bash Shell

To change the directory use cd

cd /usr/share/doc

To show current working directory usepwd command

To list contents of a directory use ls

ls /root , ls -la /root , ls -lh /root


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Using I/O redirection

To catch certain expression use grep

grep root /etc/passwd

To send stdout to a file

ls > file1.txt

Append stdout to the end of a file

ls /etc >> file1.txt


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Cont..

To pipe stdout to command2

ls /etc | mail -s list root@localhost

To send stderr to a file

lss 2> cmdnotfound.txt

To append stderr to the end of a file

lsk 2>> cmdnotfound.txt
mailto:root@localhostmailto:root@localhost


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Environment Variables

When you log in as a user, you get a

set of environment variables that con-trol many aspects of what you see andwhat you do on your OS.


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cont..

To see the environment variable

env

echo $HOSTNAME

echo $hostname

echo $USER

The values are case sensitive


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Viewing process information

Every time the shell acts on a commandthat you type, it starts a process. The

shell itself is a process.

ps aux

ps aux |grep bash


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Terminating a process

A process can be terminated

Kill a process id

kill 3400

Kill all specific process at one time

killall firefox-bin


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Viewing the command history

To make it easy for you to repeat longcommands, Bash stores the old

commands. history

history |grep ls

history |more


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Package management

The RPM package Manager greatlysimplifies the distribution, installation,upgrading and removal of software.

Software to be installed using rpm isdistributed through rpm package file,which are essentially compressedarchives of files, associated dependency

information and instructions.


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cont..

rpm is both a command and a back-endfor other programs such as yum or pirut.

These tools provide significant

advantages such as automaticdependency resolution.

e.g to install a package

rpm -ivh zip-2.3-8.i386.rpm e.g to remove a package

rpm -e zip


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cont.. yum is the front-end to rpm

Designed to resolve packagedependencies

Can locate packages across multiplerepositories

Replacement for up2date


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cont..

To list all package from repositories

yum list all

To grep packages from repositories

yum list all |grep zip

To list group of package

yum grouplist

To install a group of package

yum groupinstall open office


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Runlevel

The idea behind operating differentservices at different runlevels revolvesaround the fact that different systemscan be used in a different ways.

Some services can not be used until thesystem is in a particular states or mode

such as being ready for more than oneuser or having networking available.


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cont..

0 Halt

1 single user mode

2 Not used (user definable) 3 Full multiuser mode with networking

4 Not used (user definable)

5 Full multiuser mode (with x windows)

6 - reboot


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cont..

To view current runlevel

runlevel

To switch to other runlevel

init 3, init 1, init 6, init 0


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Managing services

Services can be manually start or stopby accessing the scripts on /etc/init.d

chkconfig manages services definitionsin run levels

to start the apache web server oncurrent runlevel, chkconfig httpd on

to start apache on runlevel 3 and 5

chkconfig --level 35 httpd on


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Text Editor The vi text editor is a full-screen text

editor that enables you to view a fileseveral lines at a time.

Most UNIX systems including Linux comewith vi.

If you learn the basic features of vi,

therefore you can edit text files on almostany UNIX systems.


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cont..

To start the text editor just type vi

To edit or view a file, type vi filename

To start inserting or editing a file press aafter opening the file

To exit without saving press escapeshift : and q!

To save file and exit press escape : andwq!

To find a phrase press escape and /


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Network connectivity

The OS requires an IP Address to communicate Verify that the OS having correct IP Address

IP address can be set

static (manually set) dhcp (auto discover from DHCP server)

View current setting of network interface

ifconfig

Restart network service in case changes aremade

service network restart


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cont..

There are many ways you can verifyconnectivity from your host to the others

ping

ping 10.20.10.53

ping www.google.com.my

Telnet to port number

telnet www.google.com.my 80
http://www.google.com.my/http://www.google.com.my/http://www.google.com.my/http://www.google.com.my/


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cont..

Telnet can be used to verify the connectivitybetween host e.g client and server

A successful attempt to connect to a web server

telnet www.google.com.my 80

Trying 64.233.181.99...

Connected to www.google.com.my

(64.233.181.99).Escape character is '^]'.
http://www.google.com.my/http://www.google.com.my/


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cont..A failed attempt to connect to an ftp server

telnet www.oscc.org.my 21

Trying 10.20.10.52...

telnet: connect to address 10.20.10.52: Connection refused

telnet: Unable to connect to remote host: Connectionrefused

Reason

A firewall blocking the communication

There is no such service running on port 21on the server

The service is down


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Port Number

Every network service requires portnumber to operate

Http (80)

Ftp (21) Smtp (25)

Pop3 (110)

Ssh (22)

We can view list of registered port in/etc/services

cat /etc/services |grep smtp


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Help and Manual

Help and manual usually come with theinstalled program e.g to read manual forls

man ls

Also can view from the help option

ls --help Google for more advanced topics

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