I Belive this matter is most useful by Linux tutorial course....For more updates coming soon....

1. LINUX IMPORTANT COMMANDS
1. top : Show Process
2. su : Sudo for enter as root (or) administrator
3. date : Current date and time
4. cal : Month’s calender
5. uptime : Current uptime
6. w : Who is online
7. whoami : Who you are logged in as
8. uname -a : Kernel information
9. free : Memory and Swap usage
10. touch : Create new file
11. cp : Copy
12. mv : Move
13. rm : Remove
14. ls -ls ll : List all
15. pwd : Current directory
16. man : Manual
17. ifconfig,ifconfig -s : Show IP address
18. hostname : Display hostname
19. wget : Download file from terminal
20. history : Command history
21. clear : Clear the command prompt
(I) DIRECTORY STRUCTURE
/
ROOT BIN SBIN ETC HOME LIB MNT PROC TMP USR VAR
PASSWD SHADOW BIN MAN SBIN LOG
1. ROOT : Root Accout’s Home Dir.
2. BIN & SBIN : Executable Programs are stored in BIN & SBIN.
3. ETC : There are two types.
1. PASSWD 2. SHADOW
Contains conf items like account information and hashed password.
4. HOME : Contains User’s Home Dir.
5. LIB : Contains Common Libraries.
6. MNT : Temp file systems are attached like CD-ROM (OR) USB Drive.
7. PROC : Virtual file system stores kernal information.
8. TMP : Contains Temporary Data.
9. USR : There are three types.
1. BIN : Contains USR program and other data.
2. MAN : Contains USR program and other data.
3. SBIN : Contains USR program and other data.
10. VAR -----> LOG : Variable data where system must be able to write during operation.

2. (II) ACCOUNTS
1. $ and #
2. su (or) su[Login Name]
3. whoami
4. passwd
5. id
(III) FILE SYSTEMS
1. cd [Dir Name] (or) cd ~
2. pwd
3. locate [File Name]
4. ls with -l (or) -a
5. mount CD-ROM and Eject
6. mkdir
7. rm
8. cp [Source Destination]
9. gedit [File Name]
10. cat [File Name]
11. less [File Name]
12. | [Piping]
(IV) RUNNING A PROGRAM
1. $PATH
2. ./program
3. PS aux
4. CTRL+C AND CTRL+Z
5. bg
6. jobs
7. fg job number
(V) LINUX BASIC NETWORKING COMMANDS
1. hostname : Host/Domain name and IP address.
2. netstat : Network connections, routing tables.
3. ping : Test network connections.
4. ifconfig : Getting network configuration.
5. nslookup : Query DNS lookup name.
6. telnet : Communicate with other host name.
7. traceroute : Outing steps that packets take to get to network host.
HOSTNAME
1. hostname : Displays the machines hostname.
2. hostname -d : Displays the domain name the machine belongs to.
3. hostname -f : Displays the fully qualified host and domain name.
4. hostname -i : Displays the IP address for the current machine.

3. NETSTAT
1. netstat -nap | grep port : Display process id of application which is using that port.
2. netstat -a (or) netstat -all : Display all connections including TCP and UDP.
3. netstat -tcp (or) netstat -t : Display only TCP connection.
4. netstat -udp (or) netstat -u : Display only UDP connection.
5. netstat -g : Display all multicast network suscribed by this host.
6. netstat -l : List only listening ports.
IFCONFIG
1. $> ifconfig -a : View all network configuration and settings.
2. $> ifconfig ethO : view specific network settings.
3. $> ifconfig ethO up (or) ifup ethO : Enabling ethO interface.
4. $> ifconfig ethO down (or) ifdown ethO : Disabling ethO interface.
NSLOOKUP
1. Discovers Hostname from IP address.
2. Discovers IP address from Hostname.
EX : $> nslookup google.com
TRACEROUTE
A Handy utility to view the number of hops and response time to get to a remote system (or)
website is traceroute. Again you need an internet connection to make use of this tool.
EX : $> traceroute google.com