Terminal Processes

Question 1

Foreground

Answer 1

Processes executed on terminal run in foreground by default (recieve input from keyboard, send output to screen)

Question 2

Background

Answer 2

For processes that don’t require keyboard input, can send to background to run in parallel with & (or ^Z, then bg)

Question 3

&

Answer 3

symbol/character represents “execution in the background”

./program &

Question 4

nohup

Answer 4

(no hang up): used as a prefix when starting a background process so you can log off and the process keeps executing

Question 5

nice

Answer 5

used as a prefix for command to modify niceness(scheduling priority) , -20 (most favorable) and +19 (least favorable)

Gary’s Analogy: you don’t expect nice to be something to be a command, if you’re nice you’ll let other people go ahead of you.

Question 6

SIGCHILD

Answer 6

death of a child signal

Parent reaps

Question 7

What is a PPID?

Answer 7

Parent Process ID: Every process has a parent that started it, tracked using PPID

Question 8

init or launchd

Answer 8

Processes are heirarchial. init or launchd can be thought of as the root of the process tree

Question 9

pstree

Answer 9

pstree: this command shows the relationship of all processes in a tree-like structure

Question 10

UID (Process ID)

Answer 10

UID: user ID that this process belongs to (the person running it)

Question 11

C (Process ID)

Answer 11

CPU utilization of processor

Question 12

TTY

Answer 12

Terminal type associated with the process

Question 13

TIME

Answer 13

CPU time taken by the process

Question 14

CMD

Answer 14

The command that started this process

Question 15

Child Process: fork( )

Answer 15

In unix a child process is created when the parent process invoke the fork ( )

Question 16

Piping v. Redirecting

Piping is redirecting ouput from one command to another command
Extracting and analyzing data from large files

Redirecting
Redirecting output of one command to a file
> redirects standard output overwriting over a file.
2> for just stderrr
» appends from stdout
< redirects stand input

Answer 16

ex. : $ who | wc -l -> lists users and pipes the word count

Question 17

echo cat v. cat echo

echo cat : will print cat on the screen

cat echo : will look for file named echo, and if it doesn’t find it , it throw error

Answer 17

What happens when a file exists/doesn’t exists?

Question 18

Processes : ready, blocked, running

ready :

blocked :

running : running in the background and running in foreground

Answer 18

What is a process? A program in execution

How to start a process? execute a utility, program or script

Question 19

Child Process: fork()
fork() in a unix child process created with the parent process invoke the fork() system call.
Child process are initially identical copies of their parent until they execute their command!

Answer 19

child process : fork returns 0

parent process : fork returns PID of child

Question 20

Daemon Process: a program run it he background process without being controlled by an active user.

Answer 20

Sometimes daemon processes are adopted by init

Question 21

Zombie processes: process that has completed execution, memory and resources are deallocated, but still has an entry in the process table (z)

Answer 21

A zombie is not an orphan!

Resource leak: PID is unusable until parent process reads child’s exit status (wait() system call)

Question 22

Foreground: processes executed on terminal run in the foreground by default (recieve input from keyboard, send output to screen )

Answer 22

Cannot run another command until previous command finishes