When a child process terminates, it becomes a
zombie process, and continues to exist as an entry in the system
process table even though it is no longer an actively executing program. Under normal operation it will typically be immediately waited on by its parent, and then reaped by the system, reclaiming the resource (the process table entry). If a child is not waited on by its parent, it continues to consume this resource indefinitely, and thus is a
resource leak. Such situations are typically handled with a special "reaper" process that locates zombies and retrieves their exit status, allowing the operating system to then deallocate their resources. Conversely, a child process whose parent process terminates before it does becomes an
orphan process. Such situations are typically handled with a special "root" (or "init") process, which is assigned as the new parent of a process when its parent process exits. This special process detects when an orphan process terminates and then retrieves its exit status, allowing the system to deallocate the terminated child process. If a child process receives a signal, a waiting parent will then continue execution leaving an orphan process behind. Hence it is sometimes needed to check the argument set by wait, waitpid or waitid and, in the case that WIFSIGNALED is true, wait for the child process again to deallocate resources. == See also ==