Types of System Calls
Since an user needs to attach many resources, the type of system calls depends on the user of these resources.
Basically there are 5 broad categories of system calls-
1) Process Control System Calls- A process - A basic entity in the system. The processes in the system need to be created, deleted and aborted. Besides this many operations are required on the processes for their management.
There are some examples
- fork()- create a process
- Exit()- terminate a process
- Kill()- terminate a process abnormally
- Nice ()- increase a Priority of a process
2) File Management System Calls -Creation, Deletion, Opening, Closing, Reading, and Writing are some general operations on files. Similarly for organizing files, there is a directory system and thereby system calls for managing them
- Create()- to create a new file
- Open ()- to open a file
- Close ()- to close a file
- read()- to read a file
- write()- to write a file
- LSeek()- change the position of the read write pointer
- Link()- give another name to a file
- Unlink()- delete a file in the directory
- Mkdir()- create a new directory.
3) Device management system calls -The general commands are:
- request off device,
- release of device,
- read and write operation and so on.
4) Information Maintenance System Calls-Many system calls exist simply for the purpose of transferring information between the user program and the operating system. Like -
- Return current time and date,
- Number of current user,
- The version of the operating system,
- Amount of free memory.
|Get time ()||set time()||get processor()|
|get date()||get system data()||set process()|
|Set time()||set custom data()||get file()|
5) Communication System Calls-There is a need for communication among the processes in the system. General operations are-
opening and closing the connection,
sending and receiving the messages,
reading and writing messages and so on.
msgsnd() sending a message
msgrcv() receiving a message
The system calls may be related to communication between processes either on the same machine or between processes on different nodes of a network. Thus inter process communication is provided by the operating system through these communication related system calls.