Types of System Calls

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Types of System Calls (Neso Academy - Operating System)

1. Summary

This video from Neso Academy explains the fundamental concept of system calls in operating systems. It categorizes system calls into five main types: Process Control, File Manipulation, Device Manipulation, Information Maintenance, and Communications. The video aims to provide a clear understanding of how user programs interact with the operating system kernel through these system call mechanisms to perform various operations.

2. Key Takeaways

* System calls are the interface between user programs and the operating system kernel.

* They allow user programs to request services from the OS, such as process creation, file operations, and device access.

* System calls are categorized into five major types for organizational purposes.

* Each category encompasses a set of specific functions that the OS provides.

3. Detailed Notes

#### Introduction to System Calls

* **Definition:** System calls are the programmatic way in which a user program requests a service from the kernel of the operating system.

* **Purpose:** To allow user-level applications to access hardware and OS resources that are normally protected by the kernel.

* **Mechanism:** Typically invoked by a software interrupt or a special instruction.

#### Types of System Calls:

##### 1. Process Control

These system calls manage the execution and state of processes.

* **Process Creation:**

* `fork()`: Creates a new process that is a duplicate of the calling process.

* `exec()`: Replaces the current process image with a new program.

* **Process Termination:**

* `exit()`: Terminates the calling process.

* `abort()`: Terminates the calling process abnormally.

* **Process Management:**

* `wait()`: Suspends the calling process until a child process terminates.

* `signal()`: Sends a signal to a process or group of processes.

* `getpid()`: Returns the process ID of the calling process.

* `getppid()`: Returns the parent process ID.

* `getpriority()` / `setpriority()`: Get/set the scheduling priority of a process.

##### 2. File Manipulation

These system calls are used to interact with files on the file system.

* **File Creation/Deletion:**

* `create()`: Creates a new file.

* `delete()`: Deletes an existing file.

* **File Opening/Closing:**

* `open()`: Opens an existing file.

* `close()`: Closes an open file.

* **File Reading/Writing:**

* `read()`: Reads data from a file.

* `write()`: Writes data to a file.

* **File Manipulation:**

* `lseek()`: Changes the file offset.

* `stat()`: Gets file status (e.g., size, permissions).

* `chmod()`: Changes file permissions.

* `chown()`: Changes file owner.

##### 3. Device Manipulation

These system calls allow processes to interact with hardware devices.

* **Device Request/Release:**

* `request_device()`: Requests access to a specific device.

* `release_device()`: Releases a device.

* **Device Input/Output:**

* `read_device()`: Reads data from a device.

* `write_device()`: Writes data to a device.

* **Device Management:**

* `get_device_parameters()`: Retrieves device configuration.

* `set_device_parameters()`: Configures device parameters.

* `eject()`: Ejects a removable device.

##### 4. Information Maintenance

These system calls are used to get or set information about the system or processes.

* **System Information:**

* `get_current_time()`: Returns the current system time.

* `get_system_info()`: Retrieves general system information (e.g., CPU type, memory size).

* **Process Information:**

* `get_process_times()`: Returns CPU time used by a process.

* `get_process_memory_info()`: Retrieves memory usage of a process.

##### 5. Communications

These system calls facilitate communication between different processes.

* **Inter-Process Communication (IPC):**

* `pipe()`: Creates a pipe for communication.

* `shm_open()` / `shm_close()`: Manages shared memory segments.

* `msg_send()` / `msg_receive()`: For message queues.

* **Network Communications:**

* `socket()`: Creates a network socket.

* `connect()`: Establishes a connection to a remote host.

* `send()` / `recv()`: Sends/receives data over a network.

* `bind()`: Associates a socket with a port.

* `listen()`: Marks a socket as passive.

* `accept()`: Accepts an incoming connection.

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