Common Signals

Signal Handling in C (POSIX)

• kill -l: List all signal names and their numbers
• kill -s SIGNAL <pid>: Send the specified SIGNAL to process <pid>

kill(pid_t pid, int sig)

• Sends a signal to a process.
• Use getpid() for current process.
• Common signals: SIGTERM, SIGKILL, SIGUSR1.

signal(int sig, void (*handler)(int))

• Sets a handler for signal sig.
• Returns previous handler or SIG_ERR on failure.
• Common handler: SIG_DFL, SIG_IGN
• On modern systems, a handler set with signal() typically remains in effect across multiple signals and does not revert to the default after a single execution.

void handler(int sig) {
    printf("Received signal %d\\n", sig);
}
signal(SIGINT, handler);

Limitations

• Cannot catch SIGKILL, SIGSTOP.
• Obsolete for advanced use; use sigaction() instead.

sigaction(int signum, const struct sigaction *act, struct sigaction *oldact)