Linux

Question 1

Find current kernel version ?

Answer 1

(sudo) uname -a for full, -r for just version

Question 2

Find list of kernels available

Answer 2

(sudo) ls /boot

Question 3

Install packages on the box

Answer 3

(sudo) apt install

Question 4

Remove a file forever

Answer 4

shred <filename></filename>

Question 5

Find your own username

Answer 5

whoami

Question 6

Add a new user

Answer 6

(sudo) useradd john . Note: he has no password, so use passwd to set the password before login.

Question 7

Add a new user who will not have login access

Answer 7

(sudo) useradd -s /sbin/nologin john OR
(sudo) useradd -s /bin/false

Question 8

Open a shell as different user

Answer 8

su john

Question 9

Get a list of all users authorized to this box

Answer 9

ls /etc/passwd

Question 10

Change a password

Answer 10

passwd

Question 11

Find information about a user

Answer 11

finger john

Question 12

Find what an executable is and the path where it is located

Answer 12

whatis , whereis

Question 13

Do an HTTP GET

Answer 13

wget https://… or curl 172.45.23.2

Question 14

Compare see difference between files

Answer 14

cmp , diff

Question 15

Make a file executable

Answer 15

chmod

Question 16

Make someone owner of a file

Answer 16

chown

Question 17

Find the IP address of current box

Answer 17

ip addr , ifconfig

Question 18

Search using a regex expression

Answer 18

awk

Question 19

Get the DNS configuration for the server

Answer 19

resolvectl status , cat /etc/resolv.conf

Question 20

Determine reachability and network routing

Answer 20

ping -n 172.3.4.5 , traceroute

Question 21

Find the open ports, ports being used by specific protocols

Answer 21

netstat -tulpn , ss

Question 22

(Dis) Allow traffic on specific ports

Answer 22

iptables, ufw status/allow/enable/disable..

Question 23

Find available memory

Answer 23

free

Question 24

Find available disk space

Answer 24

df -H

Question 25

Pull a list of processes running on the system

Answer 25

(sudo) ps -aux

Question 26

Find processes consuming most resources

Answer 26

top, htop

Question 27

Terminate a process

Answer 27

kill -9 , first find pid using ps -aux | grep name

Question 28

List services running on box

Answer 28

systemctl list-units

Question 29

Start / Stop / Restart services

Answer 29

systemctl start / stop / restart

Question 30

Find the recursively total space under a folder

Answer 30

du -sh /etc/abc

Question 31

See current mounts on startup

Answer 31

ls /etc/fstab

Question 32

See all current mounts

Answer 32

mount

Question 33

What does ip 0.0.0.0 denote

Answer 33

All public addresses

Question 34

A service keeps restarting, how to debug

Answer 34

journalctl -f -u servicename (then systemctl restart)

Question 35

How do you check and ensure the linux server is synchronizing its clock (time) correctly

Answer 35

ntpq -p reports on the NTP servers it is synching with Install and configure ntpd or chrony to fix Also make sure timezone is set right with timezonectl

Question 36

How do you implement disk quotas by user

Answer 36

Enable them in /etc/fstab edquota to edit them quotaon to switch them on

Question 37

A service needs to start on booting up. How to configure ?

Answer 37

systemctl enable svcname

Question 38

How would you clean files from a temp folder periodically

Answer 38

#/bin/bash \n rm -rf /tmp/* chmod +x script crontab -e 0 0 * * * /path/to/script

Question 39

Kill all processes by a certain user

Answer 39

ps -u ubuntu | grep -v PID | awk '{print $1}' | xargs kill -9

Question 40

How do you generate a core file file (dump) of a running process in linux

Answer 40

gcore [-o filename] pid