How do I avoid creating zombies?


Zombies are child processes that have exited but because the parent process has
not handled the SIGCHLD signal (by calling wait(), for example) the process
remains in the proc table and uses a proc slot.  Zombie processes are the
processes that show up as defunct from "ps" output.

To avoid creating zombie processes in C code set the flag SA_NOCLDWAIT in the
sa_flags field of the sigaction struct then call sigaction on SIGCHLD.  The
following is a code sample that does this.

        #include <stdio.h>
        #include <signal.h>
        ...

        int
        main(int argc, char *argv[])
        {
                struct sigaction sa;
                ...

                /* prevent zombies */
                sa.sa_handler = SIG_IGN;
                sa.sa_flags = SA_NOCLDWAIT;
                if (sigaction(SIGCHLD, &sa, NULL) == -1) {
                        perror("sigaction");
                        exit(1);
                }

                ....


For more information see sigaction(2), wait(2), fork(2), signal(2), or
signal(5).