procesid

Procesid, or process identifier, is a numeric value assigned by the operating system to a running process. It uniquely identifies the process within the host system and is used by the kernel and user-space tools to manage and monitor the process during its lifetime.

Allocation and lifetime: When a process is created, the kernel allocates a new PID from a pool of available numbers. PIDs are unique at a given time but may be reused after a process terminates. The maximum value and reuse policy vary by operating system; some systems provide separate namespaces to isolate groups of processes, such as those in containers.

Usage: The PID is used to refer to a process for resource accounting, scheduling decisions, and inter-process communication. It is required for sending signals in Unix-like systems, for attaching debuggers, and for monitoring tools to display process information such as CPU usage, memory consumption, and state.

Relationship to threads: A process may comprise multiple threads; the PID generally identifies the process as a unit, while individual threads may have their own identifiers depending on the OS. In some systems, all threads of a process share the same PID; in others, each thread has its own ID.

Lifecycle considerations: When a process ends, its PID can be reused for new processes. If the parent process does not reap the child, the child becomes a zombie briefly until the system reclaims resources. In containerized environments, PID namespaces provide isolation so that PIDs restart within the container context.

Examples: In Unix-like systems, tools such as ps, top, and pgrep display PIDs; on Windows, Task Manager and Get-Process show process IDs.