This is pgsjc/handling_SIGTSTP.c (Listing 34-6, page 724), 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.

This page shows the "distribution" or "book" version of the file (why are there two versions?), or the differences between the two versions. You can switch between the views using the tabs below.

In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.


Download pgsjc/handling_SIGTSTP.c

  Cover of The Linux Programming Interface

Function list (Bold in this list means a function is not static)

/* handling_SIGTSTP.c

   Demonstrate the correct way to catch SIGTSTP and raise it again (so that a
   parent process that is monitoring this program can see that it was stopped
   by SIGTSTP).
#include <signal.h>
#include "tlpi_hdr.h"
static void                             /* Handler for SIGTSTP */
tstpHandler(int sig)
    sigset_t tstpMask, prevMask;
    int savedErrno;
    struct sigaction sa;

    savedErrno = errno;                 /* In case we change 'errno' here */

    printf("Caught SIGTSTP\n");         /* UNSAFE (see Section 21.1.2) */

    if (signal(SIGTSTP, SIG_DFL) == SIG_ERR)
        errExit("signal");              /* Set handling to default */

    raise(SIGTSTP);                     /* Generate a further SIGTSTP */

    /* Unblock SIGTSTP; the pending SIGTSTP immediately suspends the program */

    sigaddset(&tstpMask, SIGTSTP);
    if (sigprocmask(SIG_UNBLOCK, &tstpMask, &prevMask) == -1)

    /* Execution resumes here after SIGCONT */

    if (sigprocmask(SIG_SETMASK, &prevMask, NULL) == -1)
        errExit("sigprocmask");         /* Reblock SIGTSTP */

    sigemptyset(&sa.sa_mask);           /* Reestablish handler */
    sa.sa_flags = SA_RESTART;
    sa.sa_handler = tstpHandler;
    if (sigaction(SIGTSTP, &sa, NULL) == -1)

    printf("Exiting SIGTSTP handler\n");
    errno = savedErrno;
main(int argc, char *argv[])
    struct sigaction sa;

    /* Only establish handler for SIGTSTP if it is not being ignored */

    if (sigaction(SIGTSTP, NULL, &sa) == -1)

    if (sa.sa_handler != SIG_IGN) {
        sa.sa_flags = SA_RESTART;
        sa.sa_handler = tstpHandler;
        if (sigaction(SIGTSTP, &sa, NULL) == -1)

    for (;;) {                          /* Wait for signals */


Download pgsjc/handling_SIGTSTP.c

Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.

Valid XHTML 1.1