Process creation (fork and exec) in Operating Systems - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new process using fork.

Operating Systems

pid = [1]()

Drag options to blanks, or click blank then click option'

Aspawn

Bexec

Cfork

Dclone

Attempts:

3 left

💡 Hint

Common Mistakes

Using exec instead of fork to create a process.

Confusing spawn or clone with fork.

The fork() system call creates a new process by duplicating the calling process.

2fill in blank

medium

Complete the code to replace the current process image with a new program using exec.

Operating Systems

exec[1]("/bin/ls", "ls", "-l", NULL);

Drag options to blanks, or click blank then click option'

Afork

Bexecvp

Cexecv

Dexecl

Attempts:

3 left

💡 Hint

Common Mistakes

Using fork instead of exec to replace the process image.

Confusing execv (which takes an array) with execl (which takes a list).

The execl() function replaces the current process image with a new program, taking the program path and arguments as a list.

3fill in blank

hard

Fix the error in the code to correctly create a child process and run a new program.

Operating Systems

pid = fork();
if (pid == 0) {
    [1]("/bin/echo", "echo", "Hello", NULL);
} else {
    wait(NULL);
}

Drag options to blanks, or click blank then click option'

Aexecl

Bexecvp

Cexit

Dfork

Attempts:

3 left

💡 Hint

Common Mistakes

Calling fork again inside the child process.

Using exit instead of exec to run the new program.

Inside the child process (pid == 0), execl() replaces the process image with the new program.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps process IDs to their status if the status is 'running'.

Operating Systems

{pid: status for pid, status in processes.items() if status [1] [2]

Drag options to blanks, or click blank then click option'

A==

B"running"

C!=

D"stopped"

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' causing wrong filtering.

Using the wrong status string like 'stopped'.

The comprehension filters processes where the status is exactly "running" using the equality operator ==.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps uppercase process names to their IDs if the ID is greater than 1000.

Operating Systems

{ [1]: [2] for [3], name in process_list if [3] > 1000 }

Drag options to blanks, or click blank then click option'

Aname.upper()

Bname

Cpid

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'id' instead of 'pid' as the loop variable.

Using 'name' instead of 'name.upper()' for the key.

The comprehension maps the uppercase process name (name.upper()) to the process ID (pid) for IDs greater than 1000.

Practice

1. What does the fork() system call do in an operating system?

easy

A. Replaces the current process with a new program

B. Creates a new process by copying the current process

C. Terminates the current process immediately

D. Pauses the current process temporarily

Solution

1. Step 1: Understand the role of fork()

   The fork() call creates a new process by duplicating the current one, including its code and data.

2. Step 2: Differentiate from exec()

   Unlike exec(), which replaces the process, fork() makes a copy, so both processes continue running.

3. Final Answer:

   Creates a new process by copying the current process -> Option B

4. Quick Check:

   fork() = process copy [OK]

Hint: Remember: fork copies, exec replaces [OK]

Common Mistakes:

• Confusing fork() with exec()
• Thinking fork() replaces the process
• Believing fork() pauses the process

2. Which of the following is the correct way to use exec() in a program?

easy

A. exec("ls -l")

B. exec("/bin/ls", "-l")

C. exec("/bin/ls", ["ls", "-l"])

D. exec("ls", "-l")

Solution

1. Step 1: Recall exec() syntax

   The exec() family requires the program path and an argument list, where the first argument is the program name.

2. Step 2: Identify correct argument format

   exec("/bin/ls", ["ls", "-l"]) correctly passes the path and an array with the program name and its argument.

3. Final Answer:

   exec("/bin/ls", ["ls", "-l"]) -> Option C

4. Quick Check:

   exec() needs path + argument list [OK]

Hint: exec() needs program path and argument array [OK]

Common Mistakes:

• Passing arguments as separate strings instead of array
• Using command line string instead of path
• Omitting the program name in argument list

3. Consider this code snippet in a Unix-like system:

pid = fork()
if pid == 0:
    exec("/bin/echo", ["echo", "Hello"])
else:
    print("Parent process")

What will be printed when this code runs?

medium

A. Parent process
Hello

B. Parent process

C. Hello

D. Hello
Parent process

Solution

1. Step 1: Understand fork() behavior

   The fork() creates a child process. The child runs the exec() replacing itself with the echo program.

2. Step 2: Analyze output from parent and child

   The parent (pid > 0) prints "Parent process". The child (pid == 0) calls exec(), loading /bin/echo which prints "Hello". Both outputs appear on stdout, typically with parent first.

3. Final Answer:

   Parent process Hello -> Option A

4. Quick Check:

   fork() + child exec() = both print [OK]

Hint: fork() child exec(): both print, parent first [OK]

Common Mistakes:

• Thinking only parent prints
• Reversing the output order
• Believing exec() prevents child output

4. What is wrong with this code snippet?

pid = fork()
if pid == 0:
    exec("ls", ["ls", "-l"])
else:
    print("Parent")

medium

A. The exec call is missing the full path to the program

B. fork() should be replaced with exec()

C. The parent process should call exec() instead

D. The argument list to exec() should be a string, not a list

Solution

1. Step 1: Check exec() usage

   The exec() call requires the full path to the executable, not just the command name.

2. Step 2: Identify the missing full path

   Using "ls" without "/bin/ls" will cause exec to fail because it won't find the program.

3. Final Answer:

   The exec call is missing the full path to the program -> Option A

4. Quick Check:

   exec() needs full path [OK]

Hint: Always use full path in exec() [OK]

Common Mistakes:

• Using command name without path in exec()
• Confusing fork() and exec() roles
• Passing wrong argument types to exec()

5. A program wants to run another program safely without stopping itself. Which sequence of system calls should it use?

hard

A. Call exec() first, then fork()

B. Call exec() directly to run the new program

C. Call fork() twice, then the parent calls exec()

D. Call fork() to create a child, then the child calls exec()

Solution

1. Step 1: Understand process creation and replacement

   Calling exec() replaces the current process, so calling it directly stops the original program.

2. Step 2: Use fork() then exec() in child

   By calling fork(), the program creates a child process. The child can then call exec() to run the new program, leaving the parent running.

3. Final Answer:

   Call fork() to create a child, then the child calls exec() -> Option D

4. Quick Check:

   fork() then exec() = safe new program run [OK]

Hint: fork first, then exec in child to keep parent alive [OK]

Common Mistakes:

• Calling exec() directly and losing original process
• Calling fork() twice unnecessarily
• Calling exec() before fork()