1.4 Given a scenario, configure and use the appropriate processes and services

Question 1

Command to start daemon/service

Answer 1

systemctl start [service]

Question 2

Command to stop daemon/service

Answer 2

systemctl stop [service]

Question 3

Command to restart daemon/service

Answer 3

systemctl restart [service]

Question 4

Command to get status of daemon/service

Answer 4

systemctl status [service]

Question 5

Command to automatically start service on system boot

Answer 5

systemctl enable [service]

Question 6

Command to remove service from automatically starting on system boot

Answer 6

systemctl disable [service]

Question 7

Command to stop a service from being started at all, either manually or automatically

Answer 7

systemctl mask [service]

Question 8

What does the top command do?

Answer 8

Shows an abbreviated, dynamic list of processes and their mem & cpu usage

Question 9

What does the ps command do? What is the default if no options are added to it?

Answer 9

1. Shows a static list of processes
2. Default behavior only shows active “user” processes for the current shell

Question 10

What does ps command option “A” or “e” do?

Answer 10

Shows all processes

Question 11

What 2 ps command options show more detailed info about processes?

Answer 11

-l and -f

Question 12

What ps command option shows the state (i.e. running, sleeping, zombie, etc) of processes?

Answer 12

-l

Question 13

What ps command option shows processes for a specific user?

Answer 13

-u

Question 14

What ps command option shows processes that are started during system boot?

Answer 14

-x

Question 15

What are the 4 state letter codes for processes?

Answer 15

1. “R” running
2. “S” sleeping
3. “T” traced
4. “Z” zombie

Question 16

What does the pgrep command do?

Answer 16

Combines functionality of ps & grep command into an easier to use command

Question 17

What are the 3 most common pgrep options and what do they do?

Answer 17

1. -f search for the specified process name
2. -u show all processes owned by a specific user
3. -p show all processes with PPID specified

Question 18

How can a process be started to run in the background?

Answer 18

[command] followed by [space] &

Question 19

What does the jobs command do?

Answer 19

Lists the processes running in the background with JobID and state (i.e. running, stopped)

Question 20

In the shell, how can a process running in the foreground be moved to the background? (3)

Answer 20

1. Press Ctrl + z to stop the current process and assign it a JobID
2. Run jobs command to see a list of the processes and JobIDs
3. To start the job in the background, use command: bg [JobID]

Question 21

In the shell, how can a process be moved from running in the background to the foreground? (2)

Answer 21

1. Use jobs command to list the processes running in the background
2. command fg [JobID] to move the program to the foreground

Question 22

What does Ctrl + z do?

Answer 22

Stops the currently running (foreground) app/process/command and assigns JobID for it as a background process

Question 23

How does the priority value affect a process’ access to CPU time?

Answer 23

Inversely, The higher the value, the less CPU time the process gets

Question 24

How can the priority of a process be changed?

Answer 24

Although the priority can’t be directly modified, a nice level can be set which adjusts the priority assigned by the system

Question 25

What does the nice command do? What is the syntax?

Answer 25

1. Starts a process and specifies the nice level which affects the priority the process will run with
2. nice -n [nice_level] [command]

Question 26

What does the renice command do? What is the syntax?

Answer 26

1. Modifies the nice level, or priority, of a currently running process
2. renice -n [nice_level] [PID]

Question 27

What is the range that can be specified for a nice level?

Answer 27

-20 to 19

Question 28

What restriction exists when setting nice level?

Answer 28

Unless executed with root privilege, user can only be values from 0 to 19
Only root can assign a negative nice level

Question 29

What 3 commands can be used to terminate a process?

Answer 29

1. kill
2. killall
3. pkill

Question 30

What does Ctrl+c do?

Answer 30

Interrupts and stops a process by sending the SIGINT signal

Question 31

What does the SIGHUP signal do?

Answer 31

Shuts down and restarts a process

Question 32

What does the SIGKILL signal do?

Answer 32

Forces a process to stop, without releasing resources allocated to it, when it is unresponsive all other options to stop it fail

Question 33

What does the SIGTERM signal do?

Answer 33

Stops a process cleanly and releases resources allocated to it

Question 34

In what order should signals be sent to try to kill a process?

Answer 34

1. SIGINT (Ctrl+c)
2. SIGTERM
3. SIGKILL

Question 35

What are the alternative numeric values for the 4 signal types sent with kill command(s)?

Answer 35

SIGHUP - 1
SIGINT - 2
SIGKILL - 9
SIGTERM - 15

Question 36

Syntax of kill command

Answer 36

kill [signal] [PID]

Question 37

Syntax of killall command

Answer 37

killall [signal] [process name]

Question 38

Syntax of pkill command

Answer 38

pkill [signal] -f [search term for proc name]

Question 39

What is the default signal, if none is specified, for all 3 kill commands?

Answer 39

SIGTERM

Question 40

What does htop command do?

Answer 40

Shows a graphical view of system processes and real-time memory & cpu usage, kind of like task manager does in Windows