In This Tutorial, we will Learn About top Linux commands for interview which are always use in Linux, Ubuntu, CentOS, Debian. These commands are used in all Linux Distributions Linux/Ubuntu/UNIX/CentOS, Fedora, Debian, etc. These commands are required to work in the Terminal of Linux. these commands are used daily basis for every system administrator and Linux user.
Table of Contents
Display System Calender
With this command, you can see the calendar of any year.
Syntax: cal [option] [year]
[root@simitech ~]# cal -y
OR
[root@simitech ~]cal 2020
| Options | Descriptions |
|---|---|
| cal | Display month’s calendar will be a show |
| cal month year | Display a specific month Calendar |
Check and Modify System Date
more tutorial about system Change system date and time, Click Here
system timezone
Check system time zone execute bellow command
change system time zone
List of time zones
Create Files
touch: when you want to create more than one empty file use the touch command.
[root@simitech ~]# touch data
[root@simitech ~]# touch data1 data2 data3
| touch data_{1..100} | To create 100 or more files in one command |
Nano: Create a new file and modify the existing file
[root@simitech ~]# nano data
to save and exit from the Current file press ctrl +x from the keyboard.
cat: cat is a most Important Commands In Linux It is used to create new data files. to save and exit from the file press ctrl +x from the keyboard.
[root@simitech ~] cat > data
show the content of the file .
[root@simitech ~]# cat data
it use to add new content in the file
[root@simitech ~] cat >> data
vim: vim is a most important command in Linux/Ubuntu/Centos etc. from this command we can create, modify the file, vim is an improved version of vi. Click here for a complete tutorial on the vim.
[root@simitech ~]# vim data
Create And Delete Directory
mkdir is a most Important Commands In Linux. it Create the specified Directory
[root@simitech ~]# mkdir data
Remove or delete file and Directory from the system use bellow command
rm -rf DirectoryName { Delete Directory without confirmation }.
rm -f FileName { delete file without confirmation}.
[root@simitech ~]# rm -rf LinuxData
[root@simitech ~]# rm -rf data
cd (Change Directory)
Change the Current Directory. if you type the cd command without any option, this command changes to the current user’s home DIrectory. To enter or exit any directory, use this command.
[root@simitech ~]# cd LinuxData
| Options | Descriptions |
|---|---|
| cd | enter and exit to user home Directory |
| cd /var/www/html | switch to the specific Directory by path name |
| cd .. | switch to parent Directory |
Copy File And Directory
cp: [option] [source] [destination]
Copies one source file to a Destination file or copies multiple source files to a destination file that must be an exiting Directory.
The following command used to copy file source to Destination.
the command used to copy Directory from Source To Destination.
The bellow command use to copy Directory from Source To Destination.
it’s use to copy file and Directory from source to Destination with Rename
move File And Directory
mv: Move one source file or Directory to a Destination file or move multiple source files and Directory to a destination file that must be an exiting Directory.
mv [option] [source] [destination]
[root@simitech ~]# mv data /var/www/html/NewData # move file
[root@simitech ~]# mv LinuxData /var/www/html # move dir
Getting Help
man
man is a system manual pager. it provide a quick way to get information most of the utility installed on the system.
[root@simitech ~]# man date [root@simitech ~]# man mkdir
info
Similar to man command but it is more depth.run info without page urges to list all pages. info page provides information like website.
[root@simitech ~]# info cal
whatis
display short Description of command
[root@simitech ~]# whatis df
[root@simitech ~]# whatis ls
The Help option:
Displays brief summaries of built-in commands. If PATTERN is specified, give detailed help on all commands matching PATTERN, otherwise, the list of help topics is printed.
[root@simitech ~]# help cal
[root@simitech ~]# help time
logout Command
Exits From the current session and display login screen. this command use only in text mode session. do not use it when GUI is running.
[root@simitech ~] logout
shutdown
the shutdown is the most Important Commands In Linux. This command is used to shut down the system. You can do this command only in text mode. You must have root privileges to run this command.
[root@simtech ~]# shutdown
| options | Description |
|---|---|
| shutdown -r now | restart the system without delay |
| shutdown -s now | |
| shutdown -h +2 | halts the system in two minutes |
startx
This shell scripts,typically supplied with X11 distributions, enable you to start an X Session from the Current User Account.
[root@simitech ~]# startx
Su,sudo (Switch User)
Create a new shell session with a different User’s id and Privileges. if you run su command without specifying a username, you create a shell for the superuser ( root) . that is a user who has gained the root user’s privileges
[root@simitech ~]$ su
Switch to another user
[root@ simtech ~]# su siya
tty (teletypewrite)
The use of this command gives information about which terminal it is logged from.tty stand for teletypewriter. But it is popular with the user in the name of the terminal.
[root@simitech ~]# tty /dev/pts/0
chfn (Change Finger)
chfn stand for change finger, This command is used to add and modify the user’s finger information. This information is stored in the file /etc/passwd.including full name, office phone number, address
hwclock
Display Or set the system ‘s hardware clock . hardware clock are different from system clock , a time keeping routine that is the part of the Linux Kernel although the two are synchronized when you start the system
Syntax hwclock –set –date=’MM/DD/YYYY hh:mm:ss’
[root#simitech ~]# hwclock –set –date=’10/10/2020 11:40:10
id command
This command Displays the User’s own ID information, including User ID and Group ID and number.
uname
print certain system information including system architecture, kernel release , kernel version,print processor, os Information etc.
[root@simitech ~]# uname -a # or uname –all
| option | Description |
|---|---|
| uname -n, –nodename | print the network node hostname |
| -r, –kernel-release | print the kernel release |
| -v, –kernel-version | print the kernel version |
| uname –p, –processor | print the processor type |
| uname –help | list all options |
| -o, –operating-system | print the operating system |
| uname -m | print the machine hardware name |
uptime
Display the current time, amount of time the system has been running in the current login session, the number of users logged in the system, and average CPU Load.
Display brief list of the current user login to the system
w or who command
With the help of this command, how many users are logged in the system and including which terminal are they using, when they logged on, information about CPU Usage.
whoami
With the help of this command, display the username of the user currently login in the system.
[root@simitech ~]# whoami root
pwd
PWD stands for print working Directory, With the help of this command, we can find out which directory is currently in it.
[root@simitech ~]#pwd root
history
the shell keeps track of the command you have entered, it shows a history list in which each command is given a unique number. delete history from the system use history -c.
[root@simtech ~]# history
bc command
With the help of this command you can use your system calculator
jobs
With the help of this command, you can find out how many jobs are running in the system and suspended jobs.
[root@simitech ~]# jobs
ps command
With this command, we can find out how many processes are running in the system. more details about ps use man helping command.
kill command
Terminate the process specified ID. to kill the process, you must be the owner or have a superuser privileges
[root@simitech ~]# kill 2445
top command
Display all running Process in the system, count number of running task , cpu usage,Users login Details, and PID etc.
adduser
user creation is a most important command in Linux, With this command, a user can be created in the system, All information of the user is stored in the /etc/passwd file. At the same time of creating a user, his home directory is also created /home/ location.
add group and set passwd
With this command, a group can be created in the system, All information of the group is stored in the /etc/group file. bellow command we are creating a sales group
[root@simitech ~]#groupadd sales
set password to the group
To delete a group from the system from bellow command.
[root@simitech ~]# groupdel sales
delete user
this command delete user from the system but don’t delete his home directory
[root@simitech ~]# userdel siya
Remove user as well as his home Directory
[root@simitech ~]# userdel -R siya
Add user in Group
syntax usermod -G [groupname] [username]
You can add a common user to the Specify group
[root@simitech ~] usermod -G sales siya
Lock system User
usermod -L [username]
[root@simitech ~]#usermod -L siya
Unlock or enable system user
usermod -U [username]
[root@simitech ~]# usermod -U siya
The command name ‘chage’ stands for ‘change age’ This command can be used to change the user’s password aging/expiry information.
syntax: chage -l [username]
You can change information of particular user
administrator can set password expiry date for a specific user
syntax: chage -d [year]-[month]-[date] username
[root@simitech ~]# chage -d 2020-10-05 siya
wc (word count)
With the help of this command, you can display the word, character, line number, and byte of any file.
syntax: wc [option] [filename]
[root@simitech ~]# wc -l data1 356 data
| Option | Descriptions |
|---|---|
| wc -l | only line count |
| wc -c | for only byte count |
| wc -w | only word count |
| wc -m | for only charector count |
ls command
List the content of the current Directory and file OR Specific Directoryand file .
ls [option] [file or Directory]
[root@simitech ~]# ls -la
| option | Description |
|---|---|
| ls -R | list subdirectories recursively |
| ls -a | list included hidden file |
| ls -l | Display Extra Information |
rmdir
Syntax : rmdir [empty Directory Name]
this command use to Delete Empty Directory
[root@simitech ~]# rmdir data
Network tools
ifconfig
With the help of this command, you can see the information of the system Ethernet, such as IP address netmask, broadcast Address, MTU status attached network Card, It is used at boot time to set up interfaces as necessary.
| ip addr show | Display ethernet Configuration |
| ifdown [ethernet device name] nmcli connection down [device name] | Ethernet disable |
| ifup [ethernet device name] nmcli connection up [device name] | Ethernet enable |
df commad
df shows the all mounted partition.df displays the amount of disk space available on the file system containing each file name argument. If no filename is given, the space available on all currently mounted file systems is shown. Disk space is shown in 1K. df -h show mount partition in Human Readable format,
du command
With the help of this command, you can see the report of the disk usage of the system, which files and directories have taken how much disk.
lscpu
Display all System Cpu Architacture Related Information.
clear
Using this command, you can clear the content being displayed in the system.or Use Short Cut key ctrl+l.
[root@simitech ~]# clear # Clear system Screen
last
last, lastb – show a listing of last logged in users.
lsusb
lsusb is a utility for displaying information about USB buses in the system and the devices connected to them.
[root@simitech ~]# lsusb
ps
pstree shows running processes as a tree.
[root@simkitech ~]# pstree
hdparm
hdparm display hard drive related parameter and test performance.
[root@simitech ~]# hdparm
vmstat
vmstat displays information about processes, memory, paging, block IO, traps, disks, and CPU activity.
In this Tutorials, we learned About top Linux commands for interview. I hope that now you are comfortable in Any open-source operating system. If your problem is still not solved share your Problem via comments.
