ProsessID

ProsessID, more commonly known as a process ID (PID), is a non-negative integer assigned by an operating system to each running process. The PID serves as a unique handle that the kernel and system utilities use to reference, monitor, and manage a process during its lifetime. In some languages the term 프로세스ID or prosessID is used as a direct translation of Process Identifier.

Allocation and lifetime: When a new process starts, the kernel allocates a PID from a global pool. The PID is unique among currently active processes. Once the process terminates, its PID may be reused for new processes after a short period. PIDs are scoped to a single host and are not globally unique across different machines.

Usage and utilities: Programs reference their own PID with system calls such as getpid() (and getppid() for the parent’s PID) in POSIX-compatible systems. Windows uses a ProcessId value returned by CreateProcess and related APIs. Utilities such as ps, top, htop, tasklist, and Task Manager display PIDs to help users inspect process state, attach debuggers, or send signals or termination requests (for example, kill on Unix-like systems).

Notable aspects: Certain PIDs have special meanings, such as PID 1 often being the init system (or systemd) and, in some contexts, PID 0 being reserved. Linux systems typically expose a tunable limit pid_max to cap the maximum PID. Exhaustion of available PIDs can occur, and zombie or defunct processes may temporarily hold a PID until fully reaped. Modern systems support separate PID spaces in containers and virtualization environments.

Relation to other identifiers: A process also has a process group ID and session ID; threads may share a PID in some architectures but typically have distinct thread identifiers. The /proc filesystem provides a directory per PID to inspect process details.