Category: Operating System Objective Questions

Tough Operating System Questions and Answers on “Protection – Revocation of Access Rights”.

1. What are the incorrect methods of revocation of access rights?
a) Immediate/Delayed
b) Selective/General
c) Partial/total
d) Crucial

Answer: d
Clarification: None.

2. Why is it difficult to revoke capabilities?
a) They are too many
b) They are not defined precicely
c) They are distributed throughout the system
d) None of the mentioned

Answer: c
Clarification: None.

3. What is the reacquisition scheme to revoke capability?
a) When a process capability is revoked then it won’t be able to reacquire it
b) Pointers are maintained for each object which can be used to revoke
c) Indirect pointing is done to revoke object’s capabilities
d) Master key can be used compare and revoke.

Answer: a
Clarification: None.

4. What is false regarding Back-Pointers scheme to revoke capability?
a) List of pointers is maintained with each object
b) When revocation is required these pointers are followed
c) This scheme is not adopted in MULTICS system
d) These point to all capabilities associated with that object

Answer: c
Clarification: None.

5. What is true about Indirection to revoke capability?
a) Capabilities point indirectly to the objects
b) Each capability will not have a unique entry in global
c) Table entries cannot be reused for other capabilities
d) This system was adopted in MULTICS system

Answer: a
Clarification: None.

6. How can Keys be defined or replaced?
a) create [keyname] [bits]
b) set-key
c) Key
d) MAKE [Key Name]

Answer: b
Clarification: None.

7. What are the characteristics of the Hydra system?
a) It consists of known access rights and interpreted by the system
b) A user can of protection system can declare other rights
c) Hydra system is not flexible
d) Hydra doesn’t provide rights amplification

Answer: a
Clarification: None.

8. What are the characteristics of rights amplification in Hydra?
a) This scheme allows a procedure to be certified as trustworthy
b) Amplification of rights cannot be stated explicitly in declaration
c) It includes kernel rights such as read
d) All of the mentioned

Answer: a
Clarification: None.

9. What is the problem of mutually suspicious subsystem?
a) Service program can steal users data
b) Service program can malfunction and retain some rights of data provided by user
c) Calling program can get access to restricted portion from service program
d) Calling program gets unrestricted access

Answer: b
Clarification: Both calling program and service program are vulnerable to access each others private data/rights.

10. What are the characteristics of Cambridge CAP system as compared to Hydra system?
a) It is simpler and less powerful than hydra system
b) It is more powerful than hydra system
c) It is powerful than hydra system
d) It is not as secure as Hydra system

Answer: a
Clarification: None.

11. What are the two capabilities defined in CAP system?
a) data & software capability
b) address & data capability
c) hardware & software capability
d) software capability

Answer: a
Clarification: None.

Operating System Multiple Choice Questions on “Semaphores”.

1. An un-interruptible unit is known as ____________
a) single
b) atomic
c) static
d) none of the mentioned

Answer: b
Clarification: None.

2. TestAndSet instruction is executed ____________
a) after a particular process
b) periodically
c) atomically
d) none of the mentioned

Answer: c
Clarification: None.

3. Semaphore is a/an _______ to solve the critical section problem.
a) hardware for a system
b) special program for a system
c) integer variable
d) none of the mentioned

Answer: c
Clarification: None.

4. What are the two atomic operations permissible on semaphores?
a) wait
b) stop
c) hold
d) none of the mentioned

Answer: a
Clarification: None.

5. What are Spinlocks?
a) CPU cycles wasting locks over critical sections of programs
b) Locks that avoid time wastage in context switches
c) Locks that work better on multiprocessor systems
d) All of the mentioned

Answer: d
Clarification: None.

6. What is the main disadvantage of spinlocks?
a) they are not sufficient for many process
b) they require busy waiting
c) they are unreliable sometimes
d) they are too complex for programmers

Answer: b
Clarification: None.

7. The wait operation of the semaphore basically works on the basic _______ system call.
a) stop()
b) block()
c) hold()
d) wait()

Answer: b
Clarification: None.

8. The signal operation of the semaphore basically works on the basic _______ system call.
a) continue()
b) wakeup()
c) getup()
d) start()

Answer: b
Clarification: None.

9. If the semaphore value is negative ____________
a) its magnitude is the number of processes waiting on that semaphore
b) it is invalid
c) no operation can be further performed on it until the signal operation is performed on it
d) none of the mentioned

Answer: a
Clarification: None.

10. The code that changes the value of the semaphore is ____________
a) remainder section code
b) non – critical section code
c) critical section code
d) none of the mentioned

Answer: c
Clarification: None.

11. The following program consists of 3 concurrent processes and 3 binary semaphores. The semaphores are initialized as S0 = 1, S1 = 0, S2 = 0.

Process P0
while(true)
{
    wait(S0);
    print '0';
    release(S1);
    release(S2);
}
 
Process P1
wait(S1);
release(S0);
 
Process P2
wait(S2);
release(S0);

How many times will P0 print ‘0’?
a) At least twice
b) Exactly twice
c) Exactly thrice
d) Exactly once

Answer: a
Clarification: None.

12. Each process Pi, i = 0,1,2,3,……,9 is coded as follows.

repeat
 P(mutex)
 {Critical Section}
 V(mutex)
 forever

The code for P10 is identical except that it uses V(mutex) instead of P(mutex). What is the largest number of processes that can be inside the critical section at any moment (the mutex being initialized to 1)?
a) 1
b) 2
c) 3
d) None of the mentioned

Answer: c
Clarification: Any one of the 9 processes can get into critical section after executing P(mutex) which decrements the mutex value to 0. At this time P10 can enter critical section by incrementing the value to 1. Now any of the 9 processes can enter the critical section by again decrementing the mutex value to 0. None of the remaining processes can get into their critical sections.

13. Two processes, P1 and P2, need to access a critical section of code. Consider the following synchronization construct used by the processes.

Process P1 :
while(true)
{
w1 = true;
while(w2 == true);
Critical section
w1 = false;
}
Remainder Section
 
Process P2 :
while(true)
{
w2 = true;
while(w1 == true);
Critical section
w2 = false;
}
Remainder Section

Here, w1 and w2 have shared variables, which are initialized to false. Which one of the following statements is TRUE about the above construct?
a) It does not ensure mutual exclusion
b) It does not ensure bounded waiting
c) It requires that processes enter the critical section in strict alternation
d) It does not prevent deadlocks but ensures mutual exclusion

Answer: d

Operating System Quiz on “Paging”.

1. Each entry in a translation lookaside buffer (TLB) consists of ____________
a) key
b) value
c) bit value
d) constant

Answer: a
Clarification: None.

2. If a page number is not found in the TLB, then it is known as a ____________
a) TLB miss
b) Buffer miss
c) TLB hit
d) All of the mentioned

Answer: a
Clarification: None.

3. An ______ uniquely identifies processes and is used to provide address space protection for that process.
a) address space locator
b) address space identifier
c) address process identifier
d) none of the mentioned

Answer: b
Clarification: None.

4. The percentage of times a page number is found in the TLB is known as ____________
a) miss ratio
b) hit ratio
c) miss percent
d) none of the mentioned

Answer: b
Clarification: None.

5. Memory protection in a paged environment is accomplished by ____________
a) protection algorithm with each page
b) restricted access rights to users
c) restriction on page visibility
d) protection bit with each page

Answer: d
Clarification: None.

6. When the valid – invalid bit is set to valid, it means that the associated page ____________
a) is in the TLB
b) has data in it
c) is in the process’s logical address space
d) is the system’s physical address space

Answer: c
Clarification: None.

7. Illegal addresses are trapped using the _____ bit.
a) error
b) protection
c) valid – invalid
d) access

Answer: c
Clarification: None.

8. When there is a large logical address space, the best way of paging would be ____________
a) not to page
b) a two level paging algorithm
c) the page table itself
d) all of the mentioned

Answer: b
Clarification: None.

9. In a paged memory, the page hit ratio is 0.35. The required to access a page in secondary memory is equal to 100 ns. The time required to access a page in primary memory is 10 ns. The average time required to access a page is?
a) 3.0 ns
b) 68.0 ns
c) 68.5 ns
d) 78.5 ns

Answer: c
Clarification: None.

10. To obtain better memory utilization, dynamic loading is used. With dynamic loading, a routine is not loaded until it is called. For implementing dynamic loading ____________
a) special support from hardware is required
b) special support from operating system is essential
c) special support from both hardware and operating system is essential
d) user programs can implement dynamic loading without any special support from hardware or operating system

Answer: d
Clarification: None.

11. In paged memory systems, if the page size is increased, then the internal fragmentation generally ____________
a) becomes less
b) becomes more
c) remains constant
d) none of the mentioned

Answer: b

Operating System Multiple Choice Questions on “Security – User Authentication”.

1. Which of the following are forms of malicious attack?
a) Theft of information
b) Modification of data
c) Wiping of information
d) All of the mentioned

Answer: d
Clarification: None.

2. What are the common security threats?
a) File Shredding
b) File sharing and permission
c) File corrupting
d) File integrity

Answer: b
Clarification: Sharing and associated permissions are usual exploits which can compromise the system.

3. From the following, which is not a common file permission?
a) Write
b) Execute
c) Stop
d) Read

Answer: c
Clarification: None.

4. Which of the following is a good practice?
a) Give full permission for remote transferring
b) Grant read only permission
c) Grant limited permission to specified account
d) Give both read and write permission but not execute

Answer: c
Clarification: Limited access is a key method to circumvent unauthorized access and exploits.

5. What is not a good practice for user administration?
a) Isolating a system after a compromise
b) Perform random auditing procedures
c) Granting privileges on a per host basis
d) Using telnet and FTP for remote access

Answer: d
Clarification: Telnet and FTP are not encrypted and can be compromised.

6. Which of the following is the least secure method of authentication?
a) Key card
b) fingerprint
c) retina pattern
d) Password

Answer: d
Clarification: Passwords can be compromised more easily than to replicate a physical thing like key card, fingerprint or retina.

7. Which of the following is a strong password?
a) 19thAugust88
b) Delhi88
c) P@assw0rd
d) !augustdelhi

Answer: c
Clarification: It has a combination of Alphabet both capital and small along with number and special character. Thus always use complex password with a combination of all these.

8. Why is one time password safe?
a) It is easy to generated
b) It cannot be shared
c) It is different for every access
d) It is a complex encrypted password

Answer: c
Clarification: One time password is safe since it is generated per access and thus cannot be brute forced or deduced.

9. What does Light Directory Access Protocol (LDAP) doesn’t store?
a) Users
b) Address
c) Passwords
d) Security Keys

Answer: b
Clarification: None.

10. What is characteristic of RADIUS system?
a) It is essential for centralized encryption and authentication
b) It works on Network layer to deny access to unauthorized people
c) It provides centralized authentication mechanism via network devices
d) It’s a strong File access system

Answer: c
Clarification: None.

11. Which happens first authorization or authentication?
a) Authorization
b) Authentication
c) Authorization & Authentication are same
d) None of the mentioned

Answer: a
Clarification: None.

12. What are the characteristics of Authorization?
a) RADIUS and RSA
b) 3 way handshaking with syn and fin
c) Multilayered protection for securing resources
d) Deals with privileges and rights

Answer: d
Clarification: None.

13. What forces the user to change password at first login?
a) Default behavior of OS
b) Part of AES encryption practice
c) Devices being accessed forces the user
d) Account administrator

Answer: d
Clarification: Its administrator’s job to ensure that password of the user remains private and is known only to user. But while making a new user account he assigns a random general password to give it to user. Thus even administrator cannot access a particular users account.

14. What is not a best practice for password policy?
a) Deciding maximum age of password
b) Restriction on password reuse and history
c) Password encryption
d) Having change password every 2 years

Answer: d
Clarification: Old passwords are more vulnerable to being misplaced or compromised. Passwords should be changed periodically to enhance security.

Operating System Multiple Choice Questions on “Virtual Memory – Page Replacement Algorithms”.

1. Which of the following page replacement algorithms suffers from Belady’s Anomaly?
a) Optimal replacement
b) LRU
c) FIFO
d) Both optimal replacement and FIFO

Answer: c
Clarification: None.

2. A process refers to 5 pages, A, B, C, D, E in the order : A, B, C, D, A, B, E, A, B, C, D, E. If the page replacement algorithm is FIFO, the number of page transfers with an empty internal store of 3 frames is?
a) 8
b) 10
c) 9
d) 7

Answer: c
Clarification: None.

3. In question 2, if the number of page frames is increased to 4, then the number of page transfers ____________
a) decreases
b) increases
c) remains the same
d) none of the mentioned

Answer: b
Clarification: None.

4. A memory page containing a heavily used variable that was initialized very early and is in constant use is removed, then the page replacement algorithm used is ____________
a) LRU
b) LFU
c) FIFO
d) None of the mentioned

Answer: c
Clarification: None.

5. A virtual memory system uses First In First Out (FIFO) page replacement policy and allocates a fixed number of frames to a process. Consider the following statements.
P : Increasing the number of page frames allocated to a process sometimes increases the page fault rate
Q : Some programs do not exhibit locality of reference
Which of the following is TRUE?
a) Both P and Q are true, and Q is the reason for P
b) Both P and Q are true, but Q is not the reason for P
c) P is false but Q is true
d) Both P and Q are false

Answer: c
Clarification: None.

6. Users _______ that their processes are running on a paged system.
a) are aware
b) are unaware
c) may unaware
d) none of the mentioned

Answer: b
Clarification: None.

7. If no frames are free, _____ page transfer(s) is/are required.
a) one
b) two
c) three
d) four

Answer: b
Clarification: None.

8. When a page is selected for replacement, and its modify bit is set ____________
a) the page is clean
b) the page has been modified since it was read in from the disk
c) the page is dirty
d) the page has been modified since it was read in from the disk & page is dirty

Answer: d
Clarification: None.

9. The aim of creating page replacement algorithms is to ____________
a) replace pages faster
b) increase the page fault rate
c) decrease the page fault rate
d) to allocate multiple pages to processes

Answer: c
Clarification: None.

10. A FIFO replacement algorithm associates with each page the _______
a) time it was brought into memory
b) size of the page in memory
c) page after and before it
d) all of the mentioned

Answer: a
Clarification: None.

11. What is the Optimal page – replacement algorithm?
a) Replace the page that has not been used for a long time
b) Replace the page that has been used for a long time
c) Replace the page that will not be used for a long time
d) None of the mentioned

Answer: c
Clarification: None.

12. Optimal page – replacement algorithm is difficult to implement, because ____________
a) it requires a lot of information
b) it requires future knowledge of the reference string
c) it is too complex
d) it is extremely expensive

Answer: b
Clarification: None.

13. LRU page – replacement algorithm associates with each page the ______
a) time it was brought into memory
b) the time of that page’s last use
c) page after and before it
d) all of the mentioned

Answer: b
Clarification: None.

14. For 3 page frames, the following is the reference string:
7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1
How many page faults does the LRU page replacement algorithm produce?
a) 10
b) 15
c) 11
d) 12

Answer: d
Clarification: None.

15. What are the two methods of the LRU page replacement policy that can be implemented in hardware?
a) Counters
b) RAM & Registers
c) Stack & Counters
d) Registers

Answer: c

Operating System Multiple Choice Questions on “File System Implementation – Recovery”.

1. Some directory information is kept in main memory or cache to ___________
a) fill up the cache
b) increase free space in secondary storage
c) decrease free space in secondary storage
d) speed up access

Answer: d
Clarification: None.

2. A systems program such as fsck in ______ is a consistency checker.
a) UNIX
b) Windows
c) Macintosh
d) Solaris

Answer: a
Clarification: None.

3. A consistency checker __________________ and tries to fix any inconsistencies it finds.
a) compares the data in the secondary storage with the data in the cache
b) compares the data in the directory structure with the data blocks on disk
c) compares the system generated output and user required output
d) all of the mentioned

Answer: b
Clarification: None.

4. Each set of operations for performing a specific task is a _________
a) program
b) code
c) transaction
d) all of the mentioned

Answer: c
Clarification: None.

5. Once the changes are written to the log, they are considered to be ________
a) committed
b) aborted
c) completed
d) none of the mentioned

Answer: a
Clarification: None.

6. When an entire committed transaction is completed, ___________
a) it is stored in the memory
b) it is removed from the log file
c) it is redone
d) none of the mentioned

Answer: b
Clarification: None.

7. What is a circular buffer?
a) writes to the end of its space and then continues at the beginning
b) overwrites older values as it goes
c) all of the mentioned
d) none of the mentioned

Answer: a
Clarification: None.

8. All the changes that were done from a transaction that did not commit before the system crashed, have to be _________
a) saved
b) saved and the transaction redone
c) undone
d) none of the mentioned

Answer: c