Interfaces

Question 1

whats the purpose of OS?

Answer 1

Provide reliable and efficient concurrent execution of multiple
processes

Question 2

whats the purpose of OS?

Answer 2

Provide mechanisms for inter-process communication to facilitate cooperation between process.

Question 3

whats the purpose of OS?

Answer 3

Simplify application development by hiding hardware complexity and differences between computer systems behind a clean set of abstractions and corresponding application programming interface(s)

Question 4

What are sme popularized concepts by UNIX

Answer 4

Unix system calls API
File system as a way of organising system resources
Unix shell language

Question 5

What is a Process?

Answer 5

An instance of a running program including all system resources
used for that purpose.

Question 6

How do process interact with each other or the outside world?

Answer 6

Processes interact with each-other and the outside world using only system calls (using ecall instruction). No direct access to MMIO registers is allowed for processes.

Question 7

what is process “forking” ?

Answer 7

fork() system call creates a copy of the
calling process and assigns it a new PID
* Both the parent and the child processes
continue from the same fork() call, but
– In the parent process, the fork() call returns
the new process PID ≠ 0.
– In the child process fork() returns 0

Question 8

what does wait(int *status) system call do?

Answer 8

Puts the calling process to sleep until one
of its children processes terminates.

Question 9

what does exec (prog, arguments) system call do?

Answer 9

Replaces the running program in the calling process
with the program from the file prog.
If the prog file does not exist or cannot be read, exec()
returns an error code, otherwise, exec() never returns

Question 10

chdir(char *dir) system call

Question 11

Whats a “relative pathname”?

Answer 11

A path name without the leading “/” is called
relative pathname and it is assumed to
belong in the current working directory.

Question 12

What is a device driver?

Answer 12

A piece of kernel software that implements device-specific input/output functions is called device driver (e.g. see console.c & uart.c in xv6 /kernel code)

Question 13

How does “opening” a file work?

Answer 13

open() system call prepares internal OS data
structures for interacting with the file and returns a
reference number (called file descriptor) for the
“opened” file. This reference number is used in all
subsequent system calls.

Question 14

how does “closing” a file work?

Answer 14

close(fd) “closes” an open file by saving
all outstanding data into the file and
releasing OS data structures allocated for
the file for other uses.

Question 15

What is a pipe?

Answer 15

Pipe is a communication channel between
two processes.

Question 16

What are “shell scripts” ?

Answer 16

– when takes commands from a file
– such files are called shell scripts

Question 17

Dual role of UNIX SHELL

Answer 17

Interactive user interface
– Consumes commands typed by the user,
starts new processes that run executable files
* Programming language
– when takes commands from a file
– such files are called shell scripts

Question 18

what is bash?

Answer 18

is a type of unix shell called; “Bourne-Again Shell” - default shell in Ubuntu, backwards compatible
with the original Unix shell

Question 19

form of bash command line?

Answer 19

Bash command # comment

Question 20

A simple command syntax

Answer 20

command arg1 arg2 … argN
* Elements of the command are separated from
each other by blanks

Question 21

what do this “pwd” command mean?

Answer 21

print the full name of the working
directory

Question 22

what do this “cd” command mean?

Answer 22

change working directory to your
home directory

Question 23

what do this “cd ..” command mean?

Answer 23

change working directory by going one
level up in the directory tree

Question 24

what do this “cd directory” command mean?

Answer 24

change working directory to the
directory with the specified pathname
(directory)

Question 25

what do this “./program” command mean?

Answer 25

Run the executable file program from
the working directory

Question 26

what do this “pico” command mean?

Answer 26

Start a text editor

Question 27

what do this “cat file” command mean?

Answer 27

display the contents of the file with
the name file

Question 28

what do this “co foo bar” command mean?

Answer 28

copy the contents of the file with the
name foo into the file with the name bar
(create new file bar if it does not exist)

Question 29

what do this “mv foo bar” command mean?

Answer 29

move the file foo into bar

Question 30

what do this “ln foo bar” command mean?

Answer 30

create a link bar to the file foo

Question 31

what do this “rm foo” command mean?

Answer 31

delete (remove) file named foo

Question 32

what do this “mkdir dirname” command mean?

Answer 32

Create (make) directory with the name
dirname

Question 33

what do this “rmkdir dirname” command mean?

Answer 33

Delete (remove) directory with the name
dirname

Question 34

what do this “man command” command mean?

Answer 34

Displays manual page for the command
command

Question 35

what do this “apropos keywords” command mean?

Answer 35

Lists commands whose brief description
contains keywords

Question 36

What is the unix “Philosophy” ?

Answer 36

Write programs that do one thing and do it well
Write programs to work together
Write programs to handle text streams, because that is a universal interface