System calls

Resource Management

System calls happen between the application and operating system layer part of this diagram.

This diagram shows a simplified representation of a system call.

In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the kernel of the operating system on which it is executed. This may include hardware-related services (for example, accessing a hard disk drive), creation and execution of new processes, and communication with integral kernel services such as process scheduling. System calls provide an essential interface between a process and the operating system.

Categories of system calls can be grouped as noted below:

1. Process control
   • create process (for example, fork (operating system)|fork on Unix-like systems, or NtCreateProcess in the Windows NT, Native API)
   • Kill (command)|terminate process
   • Loader (computing)|load, Exec (operating system)|execute
   • get/set process attributes
   • Wait (operating system)|wait for time, wait event, Signal (computing)|signal event
   • Dynamic memory allocation|allocate and Garbage collection (computer science)|free memory
2. File management
   • create file, delete file
   • open, close
   • read, write, reposition
   • get/set file attributes
3. Device management
   • request device, release device
   • read, write, reposition
   • get/set device attributes
   • logically attach or detach devices
4. Information maintenance
   • get/set time or date
   • get/set system data
   • get/set process, file, or device attributes
5. Communication
   • create, delete communication connection
   • send, receive messages
   • transfer status information
   • attach or detach remote devices
6. Protection
   • get/set file permissions