process

A Process/Task is an instance of a program which is currently being executed

• when running: program in action or program in execution It is the Kernel’s responsibility for Process Scheduling
• The Kernel decides which Process gets to run on which CPU / core and when
• Pre-emption is used, allows the Kernel to forcefully interrupt a running process and replace it with another task The process control block contains metadata which describes a process, including a:
• numerical ID of the process (pid)
• its parent (ppid)
• links to open files
• and a snapshot of the CPU state
• Other attributes: owner, permissions, etc. The virtual memory contents includes:
• A copy of the program
• The contents of variables and constants
• Program state, such as the functions which have been called and their parameters

Forking

A process is created by Forking(duplicating) an existing process, creating a parent-child relationship

Redirection

A process has Three I/O streams:

• stdin to pass a list of typed commands into a program
• stdout to save the output of a program to be processed later
• stderr to save a copy of any error messages in order to debug a program

Transclude of linux_commands#process-process