This code prints the pid and uid of a caught signal:
#include <stdio.h>#include <unistd.h>#include <string.h>#include <signal.h>static void my_handler(int signum, siginfo_t *siginfo, void *context) { FILE *f = fopen("sig_clog.txt", "a"); fprintf(f, "Got signal '%d' from process '%d' of user '%d'\n", signum, siginfo->si_pid, siginfo->si_uid); fclose(f);}int main(void) { FILE *f = fopen("sig_clog.txt", "w"); fclose(f); struct sigaction act; memset(&act, '\0', sizeof(act)); act.sa_sigaction = &my_handler; act.sa_flags = SA_SIGINFO; sigaction(SIGINT, &act, NULL); sigaction(SIGTSTP, &act, NULL); sigaction(SIGCONT, &act, NULL); sigaction(SIGHUP, &act, NULL); printf("Hi, my pid is %d\n", getpid()); printf("my parent pid is %d\n", getppid()); while(1) sleep(1000); return 0;}After running this, if I open a different terminal and use kill command to send signal to this process, it writes a pid and an uid (they are some random numbers and I'm not sure if it is correct). But instead, if I interrupt using Ctrl+C, then it writes pid and uid as 0. Isn't the process with pid 0 is the kernel process? I was expecting the pid to be that of the shell. How the shell is making kernel to send signal to the process and why?
Also, apart from int, tstp and quit, is there any way to generate signals through shell itself? or to add custom signal keycodes? like making Ctrl+K to send kill signal? I saw stty command options, I didn't find any.