Process ID

Question 1

What is a PID in Linux?

Answer 1

A unique non-repeating integer assigned to every running program.

Question 2

What is the purpose of PID?

Answer 2

Used to allocate CPU time, memory pages, file-descriptor tables, and scheduling priorities.

Question 3

What is PPID?

Answer 3

Parent Process ID that identifies the process which spawned the current process.

Question 4

Why is PPID important?

Answer 4

Enables tracing of process lineage and understanding of process trees.

Question 5

How can you view PIDs?

Answer 5

Using commands like ps aux, ps -eo pid,stat,cmd, top, htop.

Question 6

How to access live kernel statistics for a PID?

Answer 6

cat /proc/<PID>/</PID>

Question 7

How to send a signal to a process?

Answer 7

kill -9 <PID> or use SIGKILL for forceful termination.</PID>

Question 8

How to change process priority?

Answer 8

renice -n 10 -p <PID></PID>

Question 9

How to trace system calls of a process?

Answer 9

strace -p <PID></PID>

Question 10

What is PID 1?

Answer 10

systemd, the first process started and never exited.

Question 11

What happens if PID 1 is terminated?

Answer 11

The system crashes.

Question 12

Do PIDs recycle?

Answer 12

Yes, after a process ends.

Question 13

What should you confirm before sending commands to a PID?

Answer 13

Confirm the current PID.

Question 14

How to view process hierarchy?

Answer 14

ps -e –forest -o pid,ppid,cmd or pstree -p.

Question 15

What happens if you stop a parent process?

Answer 15

It affects all its child processes.

Question 16

How to kill a parent process and its children?

Answer 16

kill <PPID>, pkill -P <PPID> <signal>, or systemctl kill --kill-who=all <service>.service.</service></signal></PPID></PPID>

Question 17

What are orphaned processes?

Answer 17

Processes whose parent has terminated; they are adopted by PID 1.

Question 18

What are zombie processes?

Answer 18

Defunct processes not reaped by parent.

Question 19

What does reaping mean?

Answer 19

Parent performs a wait operation to free child’s resources and remove its entry from the process table.