System Calls

System Call:

In computing, a system call is the programmatic way in which a computer program requests a service from the kernel of the operating system it is executed on. A system call is a way for programs to interact with the operating system.

System calls provide an interface between the process and the operating system.

System calls allow user-level processes to request some services from the operating system which itself is not allowed to do.

System call provides the services of the operating system to the user programs via Application Program Interface(API).

System calls are the only entry points into the kernel system. All programs needing resources must use system calls.

For example, for I/O a process involves a system call telling the operating system to read or write particular area and this request is satisfied by the operating system.

The following different types of system calls provided by an operating system:

Process control

• end, abort

• load, execute

• create process, terminate process

• get process attributes, set process attributes

• wait for time

• wait event, signal event

• allocate and free memory

File management

• create file, delete file

• open, close

• read, write, reposition

• get file attributes, set file attributes

Device management

• request device, release device

• read, write, reposition

• get device attributes, set device attributes

• logically attach or detach devices

Information maintenance

• get time or date, set time or date

• get system data, set system data

• get process, file, or device attributes

• set process, file, or device attributes

Communications

• create, delete communication connection

• send, receive messages

• transfer status information

• attach or detach remote devices

Protection

. set permissions and get permissions

. allow user and deny user.