50 Operating System MCQs with Answers (original) (raw)

Three concurrent processes X, Y, and Z execute three different code segments that access and update certain shared variables. Process X executes the P operation (i.e., wait) on semaphores a, b and c; process Y executes the P operation on semaphores b, c and d; process Z executes the P operation on semaphores c, d, and a before entering the respective code segments. After completing the execution of its code segment, each process invokes the V operation (i.e., signal) on its three semaphores. All semaphores are binary semaphores initialized to one. Which one of the following represents a deadlockfree order of invoking the P operations by the processes? (GATE CS 2013)

X: P(a)P(b)P(c) Y:P(b)P(c)P(d) Z:P(c)P(d)P(a)
X: P(b)P(a)P(c) Y:P(b)P(c)P(d) Z:P(a)P(c)P(d)
X: P(b)P(a)P(c) Y:P(c)P(b)P(d) Z:P(a)P(c)P(d)
X: P(a)P(b)P(c) Y:P(c)P(b)P(d) Z:P(c)P(d)P(a)

Processes P

and P

use critical_flag in the following routine to achieve mutual exclusion. Assume that critical_flag is initialized to FALSE in the main program.

get_exclusive_access ( ) { if (critical _flag == FALSE) { critical_flag = TRUE ; critical_region () ; critical_flag = FALSE; } }

Consider the following statements.

i. It is possible for both P

and P

to access critical_region concurrently.

ii. This may lead to a deadlock.

Which of the following holds?

(i) is false and (ii) is true
Both (i) and (ii) are false
(i) is true and (ii) is false
Both (i) and (ii) are true

A system has n resources R0,...,Rn-1,and k processes P0,....Pk-1 .The implementation of the resource request logic of each process Pi is as follows:

if (i % 2 == 0) {
if (i < n) request Ri
if (i+2 < n) request Ri+2
}
else {
if (i < n) request Rn-i
if (i+2 < n) request Rn-i-2
}

In which one of the following situations is a deadlock possible?

Consider a system with 4 types of resources R1 (3 units), R2 (2 units), R3 (3 units), R4 (2 units). A non-preemptive resource allocation policy is used. At any given instance, a request is not entertained if it cannot be completely satisfied. Three processes P1, P2, P3 request the sources as follows if executed independently.

**Process P1:
t=0: requests 2 units of R2
t=1: requests 1 unit of R3
t=3: requests 2 units of R1
t=5: releases 1 unit of R2
and 1 unit of R1.
t=7: releases 1 unit of R3
t=8: requests 2 units of R4
t=10: Finishes

**Process P2:
t=0: requests 2 units of R3
t=2: requests 1 unit of R4
t=4: requests 1 unit of R1
t=6: releases 1 unit of R3
t=8: Finishes

**Process P3:
t=0: requests 1 unit of R4
t=2: requests 2 units of R1
t=5: releases 2 units of R1
t=7: requests 1 unit of R2
t=8: requests 1 unit of R3
t=9: Finishes

Which one of the following statements is TRUE if all three processes run concurrently starting at time t=0?

All processes will finish without any deadlock
Only P1 and P2 will be in deadlock.
Only P1 and P3 will be in a deadlock.
All three processes will be in deadlock

Which of the following is NOT true of deadlock prevention and deadlock avoidance schemes?

In deadlock prevention, the request for resources is always granted if the resulting state is safe
In deadlock avoidance, the request for resources is always granted if the result state is safe
Deadlock avoidance is less restrictive than deadlock prevention
Deadlock avoidance requires knowledge of resource requirements a priori

In Unix, files can be protected by assigning each one a 9-bit mode called rights bits. Now, consider the following two statements: I. A mode of 641 (octal) means that the owner can read and write the file, other members of the owner’s group can read it, and users can execute only. II. A mode of 100 (octal) allows the owner to execute the file, but prohibits all other access. Which of the following options is correct with reference to above statements ?

Both I and II are correct.
Both I and II are incorrect.

Which of the following commands or sequences of commands will rename a file x to file y in a Unix system? I. mv y, x II. mv x, y III. cp y, x (rm x) IV. cp x, y (rm x)

The shell command

find -name passwd -print

is executed in /etc directory of a computer system running Unix. Which of the following shell commands will give the same information as the above command when executed in the same directory?

Consider the following statements :

(a) UNIX provides three types of permissions
* Read
* Write
* Execute

(b) UNIX provides three sets of permissions
* permission for owner
* permission for group
* permission for others

Which of the above statement/s is/are true?

The linux command “mknod myfifo b 4 16”

Will create a character device if the user is root
Will create a named pipe FIFO if the user is root
Will create a block device if the user is root

There are 50 questions to complete.

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