sigprocmask

/* To ignore the signal. Sometimes we don't want a process *
 * to receive some certain signal(s). We can ignore those  *
 * signal(s). For instance, SIGINT (ctrl-C), which is used *
 * to stop the process and the process can't continue. But *
 * SIGINT differs from SIGKILL and SIGSTOP as SIGINT can   *
 * be caught or ignored.                                   *
 * The following code, simply ignores SIGINT.              */
#include <signal.h>
signal(SIGINT, SIG_IGN);
/* After this code is reached any ctrl-C keyboard hit      *
 * can't terminate the process.                            */

/* ------------------------------------------------------- */

/* To block signal. In case we want to defer or postpone   *
 * delivery of some signals. We can simply do ...          */

    /* variables are the set of signals i.e. oldmask & newmask */
    sigset_t oldmask, newmask; /* sigset_t is type of the set. */

    /* Make the set empty. */
    sigemptyset(&newmask);

    /* Add SIGINT to the set 'newmask'. */
    sigaddset(&newmask, SIGINT);

    /* Add SIGQUIT to the set 'newmask'. */
    sigaddset(&newmask, SIGQUIT);

    /* Add SIGTSTP to the set 'newmask'. */
    sigaddset(&newmask, SIGTSTP);

    /* Call sigprocmask(2) to defer those signals in 'newmask'. *
     * The 1st arg can be either SIG_BLOCK, SIG_UNBLOCK or      *
     * SIG_SETMASK. In this example we want to block signals    *
     * (actually defer or postpone delivery of the signal to    *
     * the process). This example will block signals listed in  *
     * 'newmask' and save the previous mask in 'oldmask'.       */
    sigprocmask(SIG_BLOCK, &newmask, &oldmask);
    /* Do some stuff here. */
    /* All signals in the set, if any, are temporarily blocked. */

    /* We new restore 'oldmask' and allow all pending signals   *
     * to deliver to the process. The 3rd arg is simply NULL.   */
    sigprocmask(SIG_SETMASK, &oldmask, NULL);
    /* After this code is reached, the signals in the set are   *
     * unblocked. All pending signals are delivered to the      *
     * process.                                                 */