For processes and threads created by a parent, it might be functionally useful for the parent to know the execution status of the child process/thread. This can be achieved using the wait family of system calls:

#include <sys/types.h>
#include <sys/wait.h>
pid_t wait(int *status);
pid_t waitpid(pid_t pid, int *status, intoptions);
int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options)

These system calls update the calling process with the state change events of a child. The following state change events are notified:

• Termination of child
• Stopped by a signal
• Resumed by a signal

In addition to reporting the status, these APIs allow the parent process to reap a terminated child. A process on termination is put into zombie state until the immediate parent engages the wait call to reap it.