This is signals/sig_receiver.c (Listing 20-7, page 414), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* sig_receiver.c

   Usage: sig_receiver [block-time]

   Catch and report statistics on signals sent by sig_sender.c.

   Note that although we use signal() to establish the signal handler in this
   program, the use of sigaction() is always preferable for this task.
#define _GNU_SOURCE
#include <signal.h>
#include "signal_functions.h"           /* Declaration of printSigset() */
#include "tlpi_hdr.h"

static int sigCnt[NSIG];                /* Counts deliveries of each signal */
static volatile sig_atomic_t gotSigint = 0;
                                        /* Set nonzero if SIGINT is delivered */
static void
handler(int sig)
    if (sig == SIGINT)
        gotSigint = 1;
main(int argc, char *argv[])
    int n, numSecs;
    sigset_t pendingMask, blockingMask, emptyMask;

    printf("%s: PID is %ld\n", argv[0], (long) getpid());

    /* Here we use the simpler signal() API to establish a signal handler,
       but for the reasons described in Section 22.7 of TLPI, sigaction()
       is the (strongly) preferred API for this task. */

    for (n = 1; n < NSIG; n++)          /* Same handler for all signals */
        (void) signal(n, handler);      /* Ignore errors */

    /* If a sleep time was specified, temporarily block all signals,
       sleep (while another process sends us signals), and then
       display the mask of pending signals and unblock all signals */

    if (argc > 1) {
        numSecs = getInt(argv[1], GN_GT_0, NULL);

        if (sigprocmask(SIG_SETMASK, &blockingMask, NULL) == -1)

        printf("%s: sleeping for %d seconds\n", argv[0], numSecs);

        if (sigpending(&pendingMask) == -1)

        printf("%s: pending signals are: \n", argv[0]);
        printSigset(stdout, "\t\t", &pendingMask);

        sigemptyset(&emptyMask);        /* Unblock all signals */
        if (sigprocmask(SIG_SETMASK, &emptyMask, NULL) == -1)

    while (!gotSigint)                  /* Loop until SIGINT caught */

    for (n = 1; n < NSIG; n++)          /* Display number of signals received */
        if (sigCnt[n] != 0)
            printf("%s: signal %d caught %d time%s\n", argv[0], n,
                    sigCnt[n], (sigCnt[n] == 1) ? "" : "s");



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