Linux Basic commands

 

Date:  Display the System date.

                Date +  <formatspecifier>

Formatspecifiers:

                %D  – Date

                %T   ­– Time

                %d   – Date in the month

                %m  – month

                %Y   – Year

[root@Hemanth ~]#  date +%d-%m-%Y

14-september-2020

2.       Cal :  Displays the calendar

Cal -3    :  shows the 3 months calendar(previous,current,coming).

Cal –y    :  Displays Complete year calendar.

Cal –j     :  Displays the Julian calendar ( count of days in a year)

Cal –m  :  Calendar starts from Monday.

Cal mm year : Display the given month in the given year calendar.

3.       Clear : clear the screen  or  (ctrl+l)

4.       Scroll the Screen  (Shift + pageup/pagedown).

5.       dmidecode :  Displays the system Hardware information.

Dmidecode –t <no> : Displays the given no type device information.

Numbers:

1 : System Bios

2 : Mother Board Information

4 : Processor information

6 : RAM Information.

6.       Fdisk –l : displays the secondary storage device information

(storage sige / no of partitions)

7.       Lsusb : displays the  list of USB devices connected.

8.       Free : Get the RAM and swap memory information.

                Free –m/-g : Displays informstion in mega and gega bytes.

9.       Df : Display the information of the partitions used by the Linux operating system (mounted device information).

Df –h : Display the size in mega and giga bytes.

10.   Hostname : Display the Linux System Name.

11.   Uname : Display the name of the unix system.

Uname –r : Display the kernel version.

Uname –a : All the daetails about OS and architecture.

12.   Arch : useful to know the machine architecture.

13.   Uptime : Display the system boot tome information.

14.   Runlevel : Display the prev and current Run level information.

15.   Who : Display the list of terminals and users working in the linux system

Who –r : Display the RUN level information.

16.   Who am I / who I am : Current working terminal information.

17.    whoami : Display the username of the current terminal.

18.   Tty : current terminal information.

19.   W : Detailed information of the terminal and Login users.

20.   Lastlog : Display all the users  with the last login information.

21.   Last : Detailed Login and logout information of the current users.

Last username : Display the information of the given user.

22.   Ifconfig : Display the all Ethernet devices and IP Address

Ifconfig –a : Display all devices along with inactive devices.

23.   Ping <ipaddress> : Display the given IP addressdevice can  e access from the machine or not?

Ctrl + c ->  Stop the ping operation.

Ping –c <no> <ipaddress> : send the ping request for the given number of times.

24.   Traceroute <url / ipaddress> : Provide the route information with the HOP count

25.   Cat / etc / resolv.conf : DNS server information.

26.   Dig <url> : DNS response information for the given url (domaine information grouper)

27.   Nslookup <url> : Complete information for the given url in the Name Server.

28.   Netstat : Get the running port information in the current system.

Netstat –a : All the open ports information.

Netstat –nat/u :  Information of the ports working with the given protocol.

29.   Daemon : The process which is running in the background.

 

 

 

30.   Ps : display the information of the processes running in the current terminal.

Ps –A: Display all the processes r4unning in the system.

Ps –A –l : Long list information.

31.   Top : Display the dynamic view of the running processes.

</>  :  Scroll the pages

q : close

k : close any application.

Short cut keys:

Ctrl + d : End of the file

Ctrl + z : Send the process to back ground.

Ctrl + c : Kill the process

32.   Kill <processed> : Kill the process of the given process id

Note: By default kill uses the signal no 15.

Kill –l : view the list of signals.

33.   Jobs : useful to view the list of applications running in the background

34.   Bg : Display the recent background process information

35.   Fg <jobid> : bringback the given jobid process to Foreground(default will bring back the recent process).

36.    <command> & : Run the given command in the background.

37.   History : Display the list of executed commands.

!historyid : Execute the command of the history id.

History <no> : Display given no of commands from history

History –c : clear the history

Note : up arrow and down arrow is useful to get the used command one by one.

38.   Id : Display user id and group id of current Login user

Id username : Display the information of the given user.

II.                  Help commands:

1.       <Command> --help :

Display the information about the given command

2.       Info <commandname> :

It is like a chain usefulto provide other information along with the required information.

q -> quit

u -> up

 p -> prev

n -> next

3.       Whatis <commandname> :

Display the purpose of the given command.

4.       Man <commandname> :

Display the detail information of the command.

q -> quit

man <cno> <command> : display the given command information from the given chapter

man –f <command> : Display the information of the chapters where this command exists.

5.       Which <command> :

Display the location of the command.

6.       Whereis <command> :

Display the location of the command and the manual information of the command.

Whereis –m <command> : provides only manual information

7.       Env : Display all the linux environment variables information. ( This information useful for the application in the various cases)

8.       Echo $variablename : print the value in the given variable

Echo $PATH

9.       Print $variablename : Print the value in the given variable

Print $HISTSIZE

10.   Alias : Display all the alias commands

Alias aliasname=”command” - > create the alias command for the given command.

11.   Unalias aliasname : remove the alias command.

12.   Pwd : Display the absolute path of the current working directory.