This is signals/signalfd_sigval.c (Listing 22-7, page 473), 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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/* signalfd_sigval.c

   Usage: signalfd_sigval sig-num...

   Demonstrate the use of signalfd() to receive signals via a file descriptor.

   This program is Linux-specific. The signalfd API is supported since kernel
#include <sys/signalfd.h>
#include <signal.h>
#include "tlpi_hdr.h"
main(int argc, char *argv[])
    sigset_t mask;
    int sfd, j;
    struct signalfd_siginfo fdsi;
    ssize_t s;

    if (argc < 2 || strcmp(argv[1], "--help") == 0)
        usageErr("%s sig-num...\n", argv[0]);

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

    for (j = 1; j < argc; j++)
        sigaddset(&mask, atoi(argv[j]));

    if (sigprocmask(SIG_BLOCK, &mask, NULL) == -1)

    sfd = signalfd(-1, &mask, 0);
    if (sfd == -1)

    for (;;) {
        s = read(sfd, &fdsi, sizeof(struct signalfd_siginfo));
        if (s != sizeof(struct signalfd_siginfo))

        printf("%s: got signal %d", argv[0], fdsi.ssi_signo);
        if (fdsi.ssi_code == SI_QUEUE) {
            printf("; ssi_pid = %d; ", fdsi.ssi_pid);
            printf("ssi_int = %d", fdsi.ssi_int);


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