Processes

Question 1

What are the different process states?

Answer 1

R: running
Z: Zombie (including Z, X)
T: Stopped
S: Sleeping (including S, D, K, I)

Question 2

ps aux

Answer 2

displays all processes including processes without a controlling terminal

Question 3

ps lax

Answer 3

long listing (lax options) provides more detail, and gives faster results by avoiding username lookup

Question 4

display the processes in a tree format

Answer 4

ps –forest

Question 5

display the list of jobs for the shell’s session

Answer 5

jobs

Question 6

bring a background job to the foreground

Answer 6

fg %1

Question 7

displays information about jobs.

Answer 7

ps j

Question 8

when running the “ps j” command, one job has the + sign. explain

Answer 8

sign indicates that this job is the current default

Question 9

when running the “ps j” command, one job has the - sign. explain

Answer 9

The - sign indicates the previous job that will become the default job when the current default job finishes.

Question 10

List the signals available

Answer 10

kill -l

Question 11

Common signals

Answer 11

1: HUP
3: QUIT
9: KILL
15: TERM (default)
18: CONT
19: STOP

Question 12

List all processes related to user bob

Answer 12

pgrep -l -u bob

Question 13

Kill all processes related to user bob

Answer 13

pkill -SIGKILL -u bob

Question 14

Find all terminals that bob is logged in from

Answer 14

w -u

Question 15

Kill all processes related to a given terminal

Answer 15

pkill -SIGKILL -t tty2

Question 16

Which signals are recommended and in which order?

Answer 16

SIGTERM
SIGINT
SIGKILL

Question 17

kill multiple processes, based on their command name

Answer 17

killall

Question 18

To terminate background job

Answer 18

kill -SIGTERM %1

Question 19

What is pts/1

Answer 19

1) pseudo-terminals
2) emulated terminals: xterm, Gnome, SSH etc.

Question 20

What is tty/2

Answer 20

1) TTY: direct interfaces with the kernel.
2) Traditionally physical terminals,
3) Originally teletypewriters, connected directly to the system.
4) Nowadays, virtual consoles accessed typically through key combinations like Ctrl+Alt+F1 to F6.
5) multi-user.target, rescue.target, emergency.target

Question 21

display the current load average

Answer 21

uptime, top

Question 22

Show cpus

Answer 22

lscpu

Question 23

lists active currently loaded service units

Answer 23

systemctl list-units --type=service

Question 24

lists all currently loaded service units

Answer 24

systemctl list-units --type=service --all

Question 25

lists units that are both loaded and active

Answer 25

systemctl

Question 26

View a unit's status with the systemctl

Answer 26

```systemctl status sshd.service```

Question 27

verify whether a service unit is active

Answer 27

systemctl is-active sshd.service

Question 28

verify whether a service unit is enabled to start automatically during system boot

Answer 28

systemctl is-enabled sshd.service

Question 29

verify whether the unit failed during startup,

Answer 29

systemctl is-failed sshd.service

Question 30

list all failed services

Answer 30

`systemctl --failed --type=service`

Question 31

List all socket units, active and inactive

Answer 31

```systemctl list-units --type=socket --all```

Question 32

Start service

Answer 32

systemctl start sshd

Question 33

Stop service

Answer 33

systemctl stop sshd

Question 34

Restart service

Answer 34

systemctl restart sshd

Question 34

Reload service

Answer 34

systemctl reload sshd

Question 35

Start or reload service

Answer 35

systemctl restart-or-reload service

Question 36

displays the hierarchy of dependencies to start a service unit

Answer 36

systemctl list-dependencies sshd.service

Question 37

Mask sendmail service

Answer 37

systemctl mask sendmail.service

Question 38

Unmask a service

Answer 38

systemctl unmask sendmail

Question 39

Configure a service to start at boot

Answer 39

systemctl enable sshd

Question 40

Configure a service to start now and at boot

Answer 40

systemctl enable --now sshd

Question 41

display a list of users that are currently logged in to the system

Answer 41

w

Question 42

Where do you set StrictHostKeyChecking

Answer 42

in ~./ssh/config. or /etc/ssh/ssh_config

Question 43

display a list of users that are currently logged in to the system while showing where user is logged in from

Answer 43

w --from

Question 44

configure your account for passwordless access

Answer 44

```ssh-copy-id -i .ssh/key-with-pass.pub user@remotehost```

Question 45

start ssh-agent

Answer 45

eval $(ssh-agent)

Question 46

What is the use of ssh-agent

Answer 46

cache ssh keys passwords

Question 47

How do you add keys to ssh-agent?

Answer 47

ssh-add

Question 48

Trubleshoot ssh

Answer 48

ssh -v -i key user@remoteserver

Question 49

risks of allowing direct login as the root user

Answer 49

1) root user exists on every Linux system, so attacker needs only to guess the password 2) root user has unrestricted privileges, so its compromise can lead to maximum damage 3) From an auditing perspective, it is hard to track which authorized user logged in as the root user

Question 50

prohibit root user to ssh in

Answer 50

`echo 'PermitRootLogin no' >> /etc/ssh/sshd_config`

Question 51

prevent password-based authentication but to allow private key-based authentication for root

Answer 51

`echo 'PermitRootLogin without-password' >> /etc/ssh/sshd_config`

Question 52

Advantages of disabling password authentication

Answer 52

1) Prevent password-guessing attacks 2) Attacker needs both the passphrase and a c private key.

Question 53

Disable password bassed login

Answer 53

`echo 'PasswordAuthentication no' > /etc/ssh/sshd_config`

Question 54

Enable ssh authentication for user

Answer 54

ensure that the user's ssh key is in ~/.ssh/authorized_keys