Module 4

Question 1

4 Linux Process States

Answer 1

1) Running (R)
2) Sleeping (S, D, K, & I)
3) Stopped (T, T)
4) Zombie (Z, x)

Question 2

Linux Process - Running State (R)

Answer 2

R - TASK_RUNNING: The process is either executing on a CPU or waiting to run. The process can be executing user routines or kernel routines (system calls), or be queued & ready when in the “Running” (or Runnable) state.

Question 3

Linux Process - Sleeping State (S)

Answer 3

TASK_INTERRUPTIBLE: The process is waiting for some condition: a hardware request, system resource access, or a signal. When an event or signals satisfies the condition, the process returns to Running.

Question 4

Linux Process - Sleeping State (D)

Answer 4

TASK_INTERRUPTIBLE: This process is also sleeping, but unlike the “s” state, does not respond to signals. It is used only wen process interruption might cause an unpredictable device state.

Question 5

Linux Process - Sleeping State (K)

Answer 5

TASK_KILLABLE: Same as the interruptible “D” state, but modified to allow a waiting task to respond to the signal to kill it (exit completely). Utilities often display “Killable” processes as the “D” state.

Question 6

Linux Process - Sleeping State (I)

Answer 6

TASK_REPORT_IDLE: A subset of state “D”. The kernel does not count these processes when calculating the load average. It is used for kernel threads. The TASK_INTERRUPTIBLE & TASK_NOLOAD flags are set.

It is similar to TASK_KILLABLE, & is also a subset of state “D”. It accepts fatal signals.

Question 7

Linux Process - Stopped State (T1)

Answer 7

TASK_STOPPED: The process is stopped (suspended), usually by being signaled by a user or another process. The process can be continued (resumed) by another signal to return to running.

Question 8

Linux Process - Stopped State (T2)

Answer 8

TASK_TRACED: A process that is being debugged is also temporarily stopped & shares the “T” state flag

Question 9

Linux Process - Zombie State (Z)

Answer 9

EXIT_ZOMBIE: A child process signals to its parents as it exits. All resources except for the process identity (PID) are released.

Question 10

Linux Process - Zombie State (x)

Answer 10

EXIT_DEAD: When the parents cleans up (reaps) the remaining child process structure, the process is not released completely. This state cannot be observed in process-listing utilities.

Question 11

What are the Fundamental Process Management Signals?

Answer 11

1) 1
2) 2
3) 3
4) 9
5) 15 (default)
6) 18
7) 19
8) 20

Question 12

Signal 1

Answer 12

HUP

Hangup: Reports termination of the controlling process of a terminal. Also requests process re-initialization (configuration reload) w/o termination.

Question 13

Signal 2

Answer 13

INT

Keyboard interrupt: Causes program termination. It can be blocked or handled. Sent by pressing the INTR (interrupt) key sequence (Ctrl+c)

Question 14

Signal 3

Answer 14

QUIT

Keyboard quit: Similar to SIGINT; adds a process dump at termination. Send by pressing the QUIT key sequence (Ctrl+)

Question 15

Signal 9

Answer 15

KILL

Kill, unblockable: Causes abrupt program termination. It cannot be blocked, ignored, or handled; consistently fatal.

Question 16

Signal 15 (default)

Answer 16

TERM

Terminate: Causes program termination. Unlike SIGKILL, it can be blocked, ignored, or handled. The “clean” way to ask a program to terminate; it allows the program to complete essential operations & self-cleanup before termination

Question 17

Signal 18

Answer 17

CONT

Continue: Sent to a process to resume if stopped. It cannot be blocked. Even if handled, it always resumes the process.

Question 18

Signal 19

Answer 18

STOP

Stop, unblockable: Suspends the process. It cannot be blocked or handled

Question 19

Signal 20

Answer 19

TSTP

Keyboard stop: Unlike SIGSTOP, it can be blocked, ignored, or handled. Sent by pressing the suspend key sequence (Ctrl+z)

Question 20

Keyboard Control sequence to Suspend

Answer 20

Ctrl+z

Question 21

Keyboard Control sequence to Kill

Answer 21

Ctrl+c

Question 22

Keyboard Control sequence to Core Dump

Answer 22

Ctrl+\

Question 23

Default action - Term

Answer 23

Terminate a program (exit) immediately

Question 24

Default action - Core

Answer 24

Save a program’s memory image (core dump), & then terminate

Question 25

Default action - Stop

Answer 25

Stop a running program (suspend) & wait to continue (resume)

Question 26

Fundamental Keystroke in “top” Command - “?” or “h”

Answer 26

Help for interactive keystrokes

Question 27

Fundamental Keystroke in “top” Command - “l, t, m”

Answer 27

Toggles for load, threads, & memory header lines

Question 28

Fundamental Keystroke in “top” Command - “I” (capital “eye”)

Answer 28

Toggle for individual CPUs or a summary for all CPUs in the header

Question 29

Fundamental Keystroke in “top” Command - “s”

Answer 29

Change the refresh (screen) rate, in decimal seconds (0.5, 1, 5)

Question 30

Fundamental Keystroke in “top” Command - “b”

Answer 30

Toggle reverse highlighting for “Running” processes; the default is bold only

Question 31

Fundamental Keystroke in “top” Command - Shift+b

Answer 31

Enables bold use in display, in the header, & for “Running” processes

Question 32

Fundamental Keystroke in “top” Command - Shift+h

Answer 32

Toggle threads; show process summmary or individual threads

Question 33

Fundamental Keystroke in “top” Command - “u”, Shift+u

Answer 33

Filter for any username (effective, real)

Question 34

Fundamental Keystroke in “top” Command - Shift+m

Answer 34

Sort process listing by memory usage; in descending order