Process management and interprocess communication

Question 1

What is a process in Linux?

Answer 1

An instance of a running program with its own memory, registers, and system resources.

Question 2

What data does a Process Control Block (PCB) contain?

Answer 2

PID, PPID, process state, CPU registers, memory info, open files, signals, and scheduling data.

Question 3

What are the main process states in Linux?

Answer 3

R (Running), S (Sleeping), D (Uninterruptible Sleep), T (Stopped), Z (Zombie).

Question 4

Which process states contribute to CPU load average?

Answer 4

R (Running) and D (Uninterruptible Sleep).

Question 5

What system call creates a new process?

Answer 5

fork()

Question 6

What does fork() return to parent and child?

Answer 6

Parent: PID of child. Child: 0. Returns -1 on failure.

Question 7

What optimization does Copy-on-Write provide?

Answer 7

Parent and child share memory pages until one writes, minimizing copy overhead.

Question 8

What system call replaces the current process image with a new program?

Answer 8

exec() family (e.g., execve()).

Question 9

What is the difference between fork() and vfork()?

Answer 9

vfork() shares the parent’s address space and suspends the parent until child calls exec() or exit().

Question 10

What system call underlies fork() and thread creation?

Answer 10

clone()

Question 11

What is the difference between clone() flags CLONE_VM and CLONE_FILES?

Answer 11

CLONE_VM shares memory; CLONE_FILES shares open file descriptors.

Question 12

What system call allows a parent to wait for its child process to exit?

Answer 12

wait(), waitpid(), or wait4().

Question 13

What is a zombie process?

Answer 13

A terminated process not yet reaped by its parent; remains in the process table but holds no resources.

Can’t be killed, parent must call wait() or be killed and PID reaps zombie.

Question 14

What is an orphan process?

Answer 14

A child process whose parent terminated; adopted by init (PID 1).

Question 15

What is the role of init (PID 1)?

Answer 15

First userspace process, starts services, adopts orphan processes.

Question 16

What are the main IPC (Inter-Process Communication) mechanisms?

Answer 16

Pipes, Named Pipes (FIFOs), Shared Memory, Message Queues, Sockets, Signals.

Question 17

How are anonymous pipes typically used?

Answer 17

For unidirectional communication between parent and child created with fork().

Question 18

What is a named pipe (FIFO)?

Answer 18

A filesystem object for bidirectional communication between unrelated processes.

Question 19

What is shared memory used for?

Answer 19

Fast IPC via memory regions accessible by multiple processes; requires synchronization.

Question 20

What is a message queue used for?

Answer 20

Structured message-based communication between processes.

Question 21

What is the difference between Unix Domain Sockets and TCP Sockets?

Answer 21

Unix sockets communicate locally via filesystem; TCP sockets communicate over networks.

Question 22

What are signals in Linux?

Answer 22

Asynchronous notifications sent to processes to indicate events or control actions.

Question 23

Which signals cannot be caught, blocked, or ignored?

Answer 23

SIGKILL and SIGSTOP.

Question 24

What signal is sent by Ctrl+C?

Answer 24

SIGINT (signal 2).

Question 25

What signal is used to restart a process cleanly?

Answer 25

SIGHUP.

Question 26

What command sends a signal to a process?

Answer 26

kill - (e.g., kill -HUP 1234).

Question 27

What is the nice value range and meaning?

Answer 27

-20 (highest priority) to +19 (lowest priority).

Question 28

What command runs a process with a custom nice value?

Answer 28

nice -n ./command

Question 29

What command changes the nice value of a running process?

Answer 29

renice -n -p

Question 30

What scheduling algorithm does Linux use for normal processes?

Answer 30

Completely Fair Scheduler (CFS), based on virtual runtime (vruntime).

Question 31

What's the difference between a process and a thread?

Answer 31

Process is independent unit of execution within a process, with own memory space and system resources. Thread is lightweight unit of execution within process, shares resources with other threads.

Question 32

Explain the differences between fork() and exec() in process creation

Answer 32

fork() creates new process by duplicating current process with copy of parents memory space exec() replaces current process image with new program

Question 33

What is role of proc filesystem and how does it interact with the kernel?

Answer 33

VFS that provides interface to kernel data structures. Contains information about processes, hardware and system config as files Userspace tool and programs read files to view kernel state and write to tunables to modify kernel state

Question 34

How do you kill processes in Linux?

Answer 34

Killed with signals, kill tool SIGTERM - graceful shutdown by programs (used by kill) SIGINT - graceful shutdown by user (ctrl-c) SIGKILL - force kill

Question 35

What's a signal and how is it handled by the kernel?

Answer 35

A signal is an asynchronous software interrupt that can be sent to processes. Kernel sets pending bit in process's signal bitmap, and process picks it up next time it runs

Question 36

List the ways to catch a signal for a program that you don't have the source code for.

Answer 36

strace, gdb, /proc//status

Question 37

What signal is sent to a parent process when the child process terminates?

Answer 37

SIGCHLD, tells parent to reap it

Question 38

How does the kill command work at the kernel level?

Answer 38

Runs kill() syscall looks up target PID checks permissions enqueues signal to process task struct