Why process control manages running programs in Linux CLI - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the command to list all running processes.

Linux CLI

ps [1]

Drag options to blanks, or click blank then click option'

A-z

B-l

C-a

D-x

Attempts:

3 left

💡 Hint

Common Mistakes

Using -z which is not a valid option.

Using -l which shows detailed info but not all processes.

Using -a which shows processes with terminals only.

The ps -x command lists all running processes including those without a controlling terminal.

2fill in blank

medium

Complete the command to stop a running process by its PID.

Linux CLI

kill [1]

Drag options to blanks, or click blank then click option'

A1234

B-1

C-9

D-5

Attempts:

3 left

💡 Hint

Common Mistakes

Using a signal option like -9 without a PID.

Using a signal option instead of the PID.

Not providing any argument.

The kill command followed by the process ID (PID) stops that process. Here, 1234 is an example PID.

3fill in blank

hard

Fix the error in the command to run a program in the background.

Linux CLI

[1]myscript.sh &

Drag options to blanks, or click blank then click option'

Astart

B./

Crun

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'run' or 'start' which are not valid commands.

Omitting the ./ prefix causing 'command not found'.

To run a script in the background, prefix it with ./ if it's in the current directory.

4fill in blank

hard

Fill both blanks to show the process tree with all processes.

Linux CLI

pstree [1] [2]

Drag options to blanks, or click blank then click option'

A-p

B-a

C-A

D-u

Attempts:

3 left

💡 Hint

Common Mistakes

Using options that don't show PIDs or arguments.

Using only one option instead of both.

The pstree -p -a command shows the process tree with PIDs and command line arguments.

5fill in blank

hard

Fill all three blanks to create a dictionary of running processes with PID as key and command as value.

Linux CLI

processes = [1]: [2] for [3] in $(ps -e -o pid=,comm=)}}

Drag options to blanks, or click blank then click option'

Apid

Bline

Cline.split()[0]

Dline.split()[1]

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names not defined in the loop.

Not splitting the line to separate PID and command.

This code splits each line from ps output to get PID and command, then creates a dictionary.

Practice

1. What is the main purpose of process control in Linux?

easy

A. To manage running programs by starting, stopping, or pausing them

B. To install new software packages

C. To change the screen resolution

D. To create new user accounts

Solution

1. Step 1: Understand process control basics

   Process control is about managing programs that are currently running on the system.

2. Step 2: Identify the correct purpose

   Starting, stopping, and pausing programs are key actions in process control.

3. Final Answer:

   To manage running programs by starting, stopping, or pausing them -> Option A

4. Quick Check:

   Process control = Manage running programs [OK]

Hint: Process control means managing running programs [OK]

Common Mistakes:

• Confusing process control with software installation
• Thinking it manages hardware settings
• Mixing it up with user account management

2. Which command is used to pause a running process in Linux?

easy

A. kill -9 <pid>

B. kill -STOP <pid>

C. kill -CONT <pid>

D. kill -TERM <pid>

Solution

1. Step 1: Recall kill command signals

   The kill command sends signals to processes; -STOP pauses, -CONT resumes.

2. Step 2: Identify pause signal

   Signal -STOP pauses the process without terminating it.

3. Final Answer:

   kill -STOP <pid> -> Option B

4. Quick Check:

   Pause process = kill -STOP [OK]

Hint: Use kill -STOP to pause a process [OK]

Common Mistakes:

• Using kill -9 which forcefully kills the process
• Confusing -CONT (resume) with pause
• Using kill -TERM which terminates the process

3. What will be the output of the command sequence below?

sleep 100 &
jobs
kill -STOP %1
jobs

medium

A. Shows the job stopped both times

B. Shows no jobs running

C. Shows the job running, then shows it stopped

D. Shows an error because kill -STOP is invalid

Solution

1. Step 1: Understand the commands

   sleep 100 & runs sleep in background; jobs lists jobs; kill -STOP %1 pauses job 1.

2. Step 2: Predict jobs output

   First jobs shows sleep running; after kill -STOP, jobs shows it stopped.

3. Final Answer:

   Shows the job running, then shows it stopped -> Option C

4. Quick Check:

   jobs before and after kill -STOP = running then stopped [OK]

Hint: jobs shows status; kill -STOP pauses job [OK]

Common Mistakes:

• Thinking kill -STOP kills the job
• Expecting no jobs after sleep &
• Believing kill -STOP is invalid

4. You run kill -STOP 1234 but the process does not pause. What is the most likely reason?

medium

A. You need to run the command as root

B. You used the wrong signal; should be kill -9

C. The process is already stopped

D. The process ID 1234 does not exist

Solution

1. Step 1: Check process existence

   If the process ID does not exist, kill commands have no effect.

2. Step 2: Consider other reasons

   Wrong signal or permissions cause errors, but no pause means no such process.

3. Final Answer:

   The process ID 1234 does not exist -> Option D

4. Quick Check:

   Nonexistent PID = no pause [OK]

Hint: Check if PID exists before sending signals [OK]

Common Mistakes:

• Assuming kill -9 pauses process
• Ignoring process existence
• Thinking root is always required

5. You want to temporarily pause a script running in the background, then resume it later. Which sequence of commands correctly achieves this?

hard

A. kill -STOP <pid> to pause, then kill -CONT <pid> to resume

B. kill -TERM <pid> to pause, then kill -STOP <pid> to resume

C. kill -9 <pid> to pause, then restart the script manually

D. kill -CONT <pid> to pause, then kill -STOP <pid> to resume

Solution

1. Step 1: Identify pause and resume signals

   kill -STOP pauses a process; kill -CONT resumes it.

2. Step 2: Verify command sequence

   Pause with kill -STOP, then resume with kill -CONT is correct.

3. Final Answer:

   kill -STOP <pid> to pause, then kill -CONT <pid> to resume -> Option A

4. Quick Check:

   Pause = kill -STOP, Resume = kill -CONT [OK]

Hint: Pause with STOP, resume with CONT signals [OK]

Common Mistakes:

• Using kill -9 which kills process
• Mixing up STOP and CONT signals
• Trying to resume with STOP signal