Process identifier
number to identify each process running on a computer
In computing, the process identifier (a.k.a. process ID or PID) is a number used by most operating system kernels—such as those of Unix, macOS and Windows—to uniquely identify an active process. This number may be used as a parameter in various function calls, allowing processes to be manipulated, such as adjusting the process's priority or killing it altogether.
Unix-like
In Unix-like operating systems, new processes are created by the fork() system call. The PID is returned to the parent process, enabling it to refer to the child in further function calls. The parent may, for example, wait for the child to terminate with the waitpid() function, or terminate the process with kill().
There are two tasks with specially distinguished process IDs: PID 0 is used for swapper or sched, which is part of the kernel and is a process that runs on a CPU core whenever that CPU core has nothing else to do. Linux also calls the threads of this process idle tasks. In some APIs, PID 0 is also used as a special value that always refers to the calling thread, process, or process group. Process ID 1 is usually the init process primarily responsible for starting and shutting down the system.
“Process identifier” enters the record as number to identify each process running on a computer. Crown Archives preserves that source wording while asking what Process, identifier and number can confirm, complicate or overturn.
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“Process identifier” is worth following because a concise public description often conceals a longer documentary argument. Here, Process, identifier and number provides the most credible route into that argument.
Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Jun 29, 2026. The linked authority identifier is Q1541645. None of the 0 selected statements returned an explicit reference.
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This entry incorporates text from “Process identifier” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.