Linux

Question 1

How to check g++ version in system?

Answer 1

dpkg –list | grep compiler

Question 2

how to update the Ubuntu package list?

Answer 2

sudo apt-get update

Question 3

How to find location of command?

Answer 3

whereis For example: whereis g++

Question 4

How to show current path?

Answer 4

pwd

Question 5

how to completely disabling Touchpad

Answer 5

xinput list xinput set-prop 12 “Device Enabled” 0 Virtual core pointer id=2 [master pointer (3)] ⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)] ⎜ ↳ Logitech USB-PS/2 Optical Mouse id=13 [slave pointer (2)] ⎜ ↳ ImExPS/2 Generic Explorer Mouse id=12 [slave pointer (2)]

Question 6

What command to show ID, group etc

Answer 6

id

Question 7

$ ls -l show file attributes, what does the first symbol mean?

Answer 7

• Regular file d Directory l Symbolic link

Question 8

Read permission of directory allow to ?

Answer 8

Allows file names in the directory to be read

Question 9

Write permission of directory allow to ?

Answer 9

Allow entries to be modified within the directory like add new file

Question 10

Execute permission of directory allow to?

Answer 10

Allows access to contents and metadata for entries like the owner, modified date etc..

Question 11

how to show all users in the system?

Answer 11

less /etc/passwd or getent passwd

Question 12

How to list all users only for username?

Answer 12

awk -F: ‘{ print $1 }’ /etc/passwd

Question 13

how to display the list of recent commands in Linux?

Answer 13

history

Question 14

what is default separator in awk

Answer 14

White-space character which is space or tab

Question 15

What is the option value to set separator in “awk” command?

Answer 15

-F For example: awk -F: ‘{print $1}’ /etc/passwd

Question 16

What is $0 in awk?

Answer 16

that repersent the whole line

Question 17

what is statement control in awk?

Answer 17

if else while do for continue break Example if ( expr ) statement if ( expr ) statement else statement while ( expr ) statement do statement while ( expr ) for ( opt_expr ; opt_expr ; opt_expr ) statement for ( var in array ) statement continue break

awk ‘{if($3 != 0) {a = ($3/$4); print $0, a;} else if($3==0) print $0, “-“ }’ file_name

Question 18

How “statement” structure in awk?

Answer 18

Group of statement are blocked via {…} and can be separated by semi-colons or new line For example: awk -F: ‘{if ($3 > 100) { x=x+1; print x, $1, $3} }’ /etc/passwd

Question 19

What is permission categories?

Answer 19

u:User, g:Group, o:Other and a:All

Question 20

command ls -l, what is the first column mean?

Answer 20

1st char: type, file, dir or link next 3: user permission rwx next 3: group permission rwx next 3: other permission rwx

Question 21

How to change permission of file?

Answer 21

chmod and provide u=rwx,g=rwx,o=rwx or we can use u+ or u- or we can use 777

Question 22

What is the command to list file in directory that include file that start name with dot (.)?

Answer 22

ls -a

Question 23

How to change directory to Home?

Answer 23

cd ~

Question 24

How to find file name that start wiht utp* from current directory and under?

Answer 24

find . -name utp*

Question 25

how to display the execute of ls -l on file that start with uta\* from current directory and under?

Answer 25

find . -name utp\* -exec ls -l {} \; We need {}, find will subsitute {} filename they found. also it need ";" (put \ escape to prevent shell to interpret it)

Question 26

How to list file that size \> 10 Megabite and perform ls -l

Answer 26

find -size +10M -exec ls -l {} \;

Question 27

What command to find executable file?

Answer 27

find . -executable -type f

Question 28

How to unzip zip file from Windows

Answer 28

unzip zip\_file

Question 29

How to grep recursively?

Answer 29

grep -r whatever ./

Question 30

Grep to show line before & after

Answer 30

grep -C5 "xxx"

Question 31

what is default /bin/sh in Ubuntu

Answer 31

dash and in RedHat is bash

Question 32

What is link on linux

Answer 32

Hard link and Soft link ln // this is hard link ln -s this is soft linke we can remove it by rm or --- unlink

Question 33

To create environment variable

Answer 33

export TEST=1234 to show it --- echo $TEST to remove it --- unset $TEST

Question 34

How to list files by newest date?

Answer 34

ls -lt

Question 35

To display host IP address

Answer 35

ifconfig

Question 36

To check ubuntu version

Answer 36

lsb\_release -a

Question 37

How to create short-cut command line?

Answer 37

alias alias ena\_serv = "systemctl list-unit-files | grep enabled" to make it permanent, add those line in ~/.bash\_aliases

Question 38

How to display process in linux

Answer 38

ps aux or top command to display top 5 usage ps aux | ort -nrk s3,3 | head -n 5 to refresh every 2 seconds watch "ps aux | ort -nrk s3,3 | head -n 5"

Question 39

How to kill process

Answer 39

kill -9 "id"

Question 40

How to display all socket

Answer 40

ss -a netstat --listen netstat -ratn

Question 41

How to check memory

Answer 41

free /proc/meminfo top

Question 42

What is the max size of file name?

Answer 42

255

Question 43

How many mode in vi?

Answer 43

3 modes command mode, edit mode and replace mode

Question 44

What commands to see content of file?

Answer 44

cat, head, tail, cat, more, less

Question 45

List of most use network command

Answer 45

netstat -tulpn ping, telnet, tracerout ifconfig -a host www.google.com ip address show

Question 46

How to check disk usage of directory?

Answer 46

du -sh "directory name"

Question 47

show disk usage

Answer 47

df -ah

Question 48

how to check system infomation

Answer 48

uname -a

Question 49

How to check disk mount at boot time

Answer 49

check file /etc/fstab we pronouce "file system tab"

Question 50

How to search contain of file and show 5 lines before & after

Answer 50

grep -C5 "Whatever"

Question 51

What is systemd?

Answer 51

it is stand for "system-deamons" ## Footnote - It work like Window Services. - It is used with sysctrl command.

Question 52

What is /bin/sh

Answer 52

In Unbuntu it is "dash". In RedHat is bash