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---
title: "Sending signals to C programs"
url: sending-signals-to-c-program.html
date: 2024-06-17T16:13:13+02:00
type: note
draft: false
tags: [c]
---
For simple and easy IPC to the C program we can use signals.
https://www.man7.org/linux/man-pages/man7/signal.7.html
Only two user defined signals are available (`SIGUSR1` and `SIGUSR2`) but you
can hijack other ones even though this is really not advisable.
```c
// signal.c
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
void handle_signal(int signal) {
printf("Signal received: %d\n", signal);
}
int main() {
signal(SIGUSR1, handle_signal); // is equal to 10
signal(SIGUSR2, handle_signal); // is equal to 12
while(1) {
sleep(1);
}
return 0;
}
```
Compile with `gcc -o signal signal.c` and run the program with `./signal` and
then from another terminal send the signal to the program with `kill -10
$(pidof signal)` which should print out `Signal received: 10`.
| Signal | x86/ARM | Alpha/ | MIPS | PARISC | Notes |
|-------------|---------|--------|--------|--------|---------------|
| SIGHUP | 1 | 1 | 1 | 1 | |
| SIGINT | 2 | 2 | 2 | 2 | |
| SIGQUIT | 3 | 3 | 3 | 3 | |
| SIGILL | 4 | 4 | 4 | 4 | |
| SIGTRAP | 5 | 5 | 5 | 5 | |
| SIGABRT | 6 | 6 | 6 | 6 | |
| SIGIOT | 6 | 6 | 6 | 6 | |
| SIGBUS | 7 | 10 | 10 | 10 | |
| SIGEMT | - | 7 | 7 | - | |
| SIGFPE | 8 | 8 | 8 | 8 | |
| SIGKILL | 9 | 9 | 9 | 9 | |
| **SIGUSR1** | **10** | **30** | **16** | **16** | |
| SIGSEGV | 11 | 11 | 11 | 11 | |
| **SIGUSR2** | **12** | **31** | **17** | **17** | |
| SIGPIPE | 13 | 13 | 13 | 13 | |
| SIGALRM | 14 | 14 | 14 | 14 | |
| SIGTERM | 15 | 15 | 15 | 15 | |
| SIGSTKFLT | 16 | - | - | 7 | |
| SIGCHLD | 17 | 20 | 18 | 18 | |
| SIGCLD | - | - | 18 | - | |
| SIGCONT | 18 | 19 | 25 | 26 | |
| SIGSTOP | 19 | 17 | 23 | 24 | |
| SIGTSTP | 20 | 18 | 24 | 25 | |
| SIGTTIN | 21 | 21 | 26 | 27 | |
| SIGTTOU | 22 | 22 | 27 | 28 | |
| SIGURG | 23 | 16 | 21 | 29 | |
| SIGXCPU | 24 | 24 | 30 | 12 | |
| SIGXFSZ | 25 | 25 | 31 | 30 | |
| SIGVTALRM | 26 | 26 | 28 | 20 | |
| SIGPROF | 27 | 27 | 29 | 21 | |
| SIGWINCH | 28 | 28 | 20 | 23 | |
| SIGIO | 29 | 23 | 22 | 22 | |
| SIGPOLL | | | | | Same as SIGIO |
| SIGPWR | 30 | 29/- | 19 | 19 | |
| SIGINFO | - | 29/- | - | - | |
| SIGLOST | - | -/29 | - | - | |
| SIGSYS | 31 | 12 | 12 | 31 | |
| SIGUNUSED | 31 | - | - | 31 | |
|
