Defining Custom Signal

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# 1  
Old 07-27-2009
Defining Custom Signal

Is it possible to send a custom signal to a process?

e.g. Send signal 9999 to my process, which handles it with some custom handler.

How would one do this?
# 2  
Old 07-27-2009
SIGUSR1 and SIGUSR2 and "custom" signals. Nothing else but your code will raise or send those signals to your app.

SIGHUP is traditionally used to cause a daemon to close the logfiles it has open, and reread the initfile, if there is one.
# 3  
Old 07-27-2009
Is it possible to have more than 2 user-defined signals?
# 4  
Old 07-28-2009
You might check out the "real time" signals, whose numbers are defined as a range from SIGRTMIN to SIGRTMAX. Not all systems support them however. POSIX compliant ones should, but OSX for one does not last time I checked... Also, the first three realtime signals (SIGRTMIN+0, ..., SIGRTMIN+2) are reserved on some versions of Linux.

Last edited by Corona688; 07-28-2009 at 11:56 AM..
# 5  
Old 07-29-2009
OK, I have decided to just send SIGUSR1 and read instructions from a file.

However, once receiving SIGUSR1, I can no longer send SIGINT to stop the process. It breaks out of my sleep or pause call, but it doesn't stop execution. I have to create a special handler for SIGINT in order for it to work. However, SIGSEGV stops the process as usual. But this worries me - am I doing something wrong, and are there any other signals which will need special attention?
# 6  
Old 07-29-2009
We can't read your code from here unless you post it. I wonder if there are problems with your signal mask.
# 7  
Old 07-29-2009
Here is the code:

#include <Python.h>
#include <stdio.h>
#include <sys/types.h>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>

#define MAX_STR_LEN 255

void catch_int(int sig_num);
void catch_usr1(int sig_num);
void write_run_file();
void run_action(char *line);
void run_script_function(char *fname, char *func);

int main(int argc, char *argv[]) {

  signal(SIGUSR1, catch_usr1);
  /*signal(SIGINT, catch_int);*/



  while(1) {
    printf("Still Alive!\n");


  return 0;


void write_run_file() {

  FILE *fh;

  fh = fopen("test.RUN", "w");
  if(fh == NULL) {
    printf("Could not open .RUN file.\n");

  fprintf(fh, "%i", getpid());



void catch_int(int sig_num) {



void catch_usr1(int sig_num) {

  FILE *fh;
  char line[MAX_STR_LEN];

  sigset_t mask_set, old_set;

  /* reset for next time */
  signal(SIGUSR1, catch_usr1);

  /* mask any further signals */
  sigprocmask(SIG_SETMASK, &mask_set, &old_set);

  printf("Caught SIGUSR1\n");

  fh = fopen("action", "r");
  if(fh == NULL) {
    printf("Could not open file.\n");
  while(fgets(line, MAX_STR_LEN, fh)) {
    printf("Running %s\n", line);
    printf("Finished action\n");


  /* restore old signal mask */
  sigprocmask(SIG_SETMASK, &old_set, NULL);


void run_action(char *line) {

  char *action, *fname, *func;
  char py_fun[] = "PYFUN";

  action = strtok(line, " ");

  if(strlen(action) == 0) {

  if(strcmp(action, py_fun) == 0) {
    fname = strtok(NULL, " ");
    func = strtok(NULL, " ");
    run_script_function(fname, func);


void run_script_function(char *fname, char *func) {

  FILE *fh;
  char call[MAX_STR_LEN];

  fh = fopen(fname, "r");
  if(fh == NULL) {
    printf("Could not open file %s\n", fname);

  PyRun_SimpleFile(fh, fname);


  strcpy(call, func);
  strcat(call, "()");



It actually happens both before and after receiving the first SIGUSR1. It also happens both with and without the mask.
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