_exit(status) int status;
All of the descriptors open in the calling process are closed. This may entail delays, for example, waiting for output to drain; a process in this state may not be killed, as it is already dying.
If the parent process of the calling process is executing a wait or is interested in the SIGCHLD signal, then it is notified of the calling process's termination and the low-order eight bits of status are made available to it; see wait(2).
The parent process ID of all of the calling process's existing child processes are also set to 1. This means that the initialization process (see intro(2)) inherits each of these processes as well. Any stopped children are restarted with a hangup signal (SIGHUP).
Most C programs call the library routine exit(3), which performs cleanup actions in the standard I/O library before calling _exit.