System Call

Question 1

What is a System Call?

Answer 1

A system call is a programmatic way for a user application to request a service from the operating system (OS). It acts as an interface between user programs and the kernel.

Question 2

Why are System Calls Needed?

Answer 2

System calls are needed to allow user programs to perform tasks that require privileged access to hardware or kernel resources, enforce security, and provide a consistent interface for applications.

Question 3

How do System Calls Work?

Answer 3

1) The user program invokes a system call using a library function. 2) A software interrupt (trap) switches the CPU from user mode to kernel mode. 3) The kernel executes the requested operation. 4) The kernel returns the result to the user program.

Question 4

What are the Types of System Calls?

Answer 4

1) Process Control, 2) File Management, 3) Device Management, 4) Information Maintenance, 5) Communication, 6) Protection.

Question 5

What is Process Control in System Calls?

Answer 5

Process control system calls manage processes, such as creating, terminating, or executing them. Examples: fork(), exec(), exit(), wait().

Question 6

What is File Management in System Calls?

Answer 6

File management system calls manipulate files, such as creating, reading, writing, or deleting them. Examples: open(), read(), write(), close(), unlink().

Question 7

What is Device Management in System Calls?

Answer 7

Device management system calls manage hardware devices, such as printers or disks. Examples: ioctl(), read(), write().

Question 8

What is Information Maintenance in System Calls?

Answer 8

Information maintenance system calls retrieve or set system information. Examples: getpid(), time(), sysinfo().

Question 9

What is Communication in System Calls?

Answer 9

Communication system calls facilitate inter-process communication (IPC). Examples: pipe(), shmget(), msgget().

Question 10

What is Protection in System Calls?

Answer 10

Protection system calls manage access control and permissions. Examples: chmod(), chown().

Question 11

What is a System Call Number?

Answer 11

A system call number is a unique identifier assigned to each system call. The kernel uses this number to identify the requested service.

Question 12

What is a System Call Table?

Answer 12

A system call table is a data structure in the kernel that maps system call numbers to their corresponding functions.

Question 13

What is a Software Interrupt?

Answer 13

A software interrupt (e.g., int 0x80 on x86) triggers a switch from user mode to kernel mode to execute a system call.

Question 14

What is Context Switching in System Calls?

Answer 14

Context switching is the process of saving the current state of a process (registers, program counter) and switching to kernel mode to execute a system call.

Question 15

What is the Overhead of a System Call?

Answer 15

The overhead of a system call includes context switching, kernel mode execution, and potential delays due to hardware access.

Question 16

How can System Call Overhead be Reduced?

Answer 16

System call overhead can be reduced by using buffered I/O, batching operations, or minimizing the number of system calls.

Question 17

What is the Role of the Kernel in System Calls?

Answer 17

The kernel executes system calls, manages hardware resources, and ensures security and isolation between processes.

Question 18

What is the Difference Between a System Call and a Library Function?

Answer 18

A system call interacts with the kernel, while a library function runs in user space. Library functions may internally use system calls.

Question 19

What is the Purpose of the fork() System Call?

Answer 19

The fork() system call creates a new process by duplicating the current process. The new process is called the child process.

Question 20

What is the Purpose of the exec() System Call?

Answer 20

The exec() system call replaces the current process with a new program. It loads the new program into memory and starts its execution.

Question 21

What is the Purpose of the wait() System Call?

Answer 21

The wait() system call allows a parent process to wait for a child process to terminate and retrieve its exit status.

Question 22

What is the Purpose of the pipe() System Call?

Answer 22

The pipe() system call creates a pipe, which is a unidirectional communication channel between two processes.

Question 23

What is the Purpose of the open() System Call?

Answer 23

The open() system call opens a file and returns a file descriptor, which is used for subsequent file operations.

Question 24

What is the Purpose of the read() System Call?

Answer 24

The read() system call reads data from a file or device into a buffer.

Question 25

What is the Purpose of the `write()` System Call?

Answer 25

The `write()` system call writes data from a buffer to a file or device.

Question 26

What is the Purpose of the `close()` System Call?

Answer 26

The `close()` system call closes a file descriptor, releasing associated resources.

Question 27

What is the Purpose of the `ioctl()` System Call?

Answer 27

The `ioctl()` system call sends control commands to a device, such as configuring its settings.

Question 28

What is the Purpose of the `getpid()` System Call?

Answer 28

The `getpid()` system call returns the process ID of the current process.

Question 29

What is the Purpose of the `time()` System Call?

Answer 29

The `time()` system call returns the current time in seconds since the Unix epoch (January 1, 1970).

Question 30

What is the Purpose of the `chmod()` System Call?

Answer 30

The `chmod()` system call changes the permissions of a file or directory.

Question 31

What is the Purpose of the `chown()` System Call?

Answer 31

The `chown()` system call changes the ownership of a file or directory.

Question 32

What is the Difference Between `fork()` and `exec()`?

Answer 32

`fork()` creates a new process by duplicating the current process, while `exec()` replaces the current process with a new program.

Question 33

What is the Difference Between User Mode and Kernel Mode?

Answer 33

User mode restricts direct hardware access for applications, while kernel mode allows privileged access to hardware and critical operations.

Question 34

What is the Role of the System Call Table?

Answer 34

The system call table maps system call numbers to their corresponding kernel functions, enabling the kernel to execute the requested service.

Question 35

What is the Role of the `init` Process in System Calls?

Answer 35

The `init` process (PID 1) is the first process started by the kernel and manages all other processes, including handling orphaned processes.

Question 36

What is a Zombie Process?

Answer 36

A zombie process is a terminated process that remains in the process table until its parent reads its exit status.

Question 37

What is an Orphan Process?

Answer 37

An orphan process is a child process whose parent has terminated, and it is adopted by the `init` process (PID 1).

Question 38

What is a Daemon Process?

Answer 38

A daemon process is a background process that provides services, such as a web server or print spooler. It has no controlling terminal.

Question 39

What is the Purpose of the `kill()` System Call?

Answer 39

The `kill()` system call sends a signal to a process, such as terminating it (`SIGKILL`) or interrupting it (`SIGINT`).

Question 40

What is the Purpose of the `pipe()` System Call?

Answer 40

The `pipe()` system call creates a unidirectional communication channel between two processes, allowing them to exchange data.

Question 41

What is the Purpose of the `shmget()` System Call?

Answer 41

The `shmget()` system call allocates a shared memory segment, which can be accessed by multiple processes.

Question 42

What is the Purpose of the `msgget()` System Call?

Answer 42

The `msgget()` system call creates a message queue, which allows processes to exchange messages.

Question 43

What is the Purpose of the `sysinfo()` System Call?

Answer 43

The `sysinfo()` system call retrieves system statistics, such as memory usage, CPU load, and uptime.