1.4. Processes #
A process is an instance of a program that is currently being executed.
There are several attributes attached to a process, including:
- Ownership
- Process ID (pid)
- CPU usage
- Running time
There are three types of processes:
- User process: Initiated by a regular user
- Daemon process: A process designed to run in a background
- Kernel process: Executed in kernel-mode only
Process States #
Most processes can be in one of the following states: on the CPu or off the CPU. Only one process can run at a time on a single CPU.
A process that is off the CPU can be in the following sub-states:
- Runnable state: The process has all the resources it needs except the CPU
- Sleeping state: The process needs resources that are not currently available
- Uninterruptable sleep state: The process is waiting for a particular time slot or particular event to occur
- Zombie state: The time between when the process terminates and the parent releases the child process
Threads #
A thread is the smallest unit of execution, and is a component of a process.
Processes can contain many threads.
