Note: Sending signals to C programs

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+---
+title: "Sending signals to C programs"
+url: sending-signals-to-c-program
+date: 2024-06-17T16:13:13+02:00
+type: note
+draft: false
+---
+
+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 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     |               |