signal() and kill command

#include <signal.h>
#include <stdio.h>
#include <unistd.h>

void ouch(int sig)
{
printf(" <--- OUCH ! - Got signal - %d\n", sig);
signal(SIGINT, SIG_DFL);
}

int main()
{
signal(SIGINT, ouch);

while(1) {
  printf("Hello SIGINT !\n");
  sleep(1);
}
}

signal in main(): set ouch() as the SIGINT handler signal in ouch(): set SIGINT handler to default, terminate process If you SIGINT handler is not reset to default, the process can not be interrupted by Ctrl+C. $ man signal (a good man in linux)

:
First the signals described in the original POSIX.1-1990 standard.

Signal     Value     Action   Comment
----------------------------------------------------------------------
SIGHUP        1       Term    Hangup detected on controlling terminal
                             or death of controlling process
SIGINT        2       Term    Interrupt from keyboard
SIGQUIT       3       Core    Quit from keyboard
SIGILL        4       Core    Illegal Instruction
SIGABRT       6       Core    Abort signal from abort(3)
SIGFPE        8       Core    Floating point exception
SIGKILL       9       Term    Kill signal
SIGSEGV      11       Core    Invalid memory reference
SIGPIPE      13       Term    Broken pipe: write to pipe with no
                             readers
SIGALRM      14       Term    Timer signal from alarm(2)
SIGTERM      15       Term    Termination signal
SIGUSR1   30,10,16    Term    User-defined signal 1
SIGUSR2   31,12,17    Term    User-defined signal 2
SIGCHLD   20,17,18    Ign     Child stopped or terminated
SIGCONT   19,18,25    Cont    Continue if stopped
SIGSTOP   17,19,23    Stop    Stop process
SIGTSTP   18,20,24    Stop    Stop typed at tty
SIGTTIN   21,21,26    Stop    tty input for background process
SIGTTOU   22,22,27    Stop    tty output for background process

The  signals SIGKILL and SIGSTOP cannot be caught, blocked, or ignored.

:

The  entries  in  the  "Action"  column of the tables below specify the
default disposition for each signal, as follows:

Term   Default action is to terminate the process.
Ign    Default action is to ignore the signal.
Core   Default action is to terminate the process and  dump  core  (see
      core(5)).
Stop   Default action is to stop the process.
Cont   Default  action  is  to  continue the process if it is currently
       stopped.
:

Running the program, and test

$ ./a.out
Hello SIGINT !
Hello SIGINT !
^C <--- OUCH ! - Got signal - 2
Hello SIGINT !
Hello SIGINT !
Hello SIGINT !
^C
$

Below red ones are command from other terminal. PID is got from ps ax | grep a.out.

$ kill -19 4100 (stop process)
Hello SIGINT !
Hello SIGINT !

[1]+  Stopped                 ./a.out
$

$ kill -18 4100 (continue process if stopped)
$ Hello SIGINT !
Hello SIGINT !
Hello SIGINT !
Hello SIGINT !
$ kill -2 4100 (keyboard interrupt Ctrl+C)
^C <--- OUCH ! - Got signal - 2 
Hello SIGINT !  
$ kill -2 4100 (keyboard interrupt Ctrl+C)
[1]+  中斷                  ./a.out
$


$ kill -15 4107 (terminate process)
Hello SIGINT !
Hello SIGINT !
終止 (terminated)
$

$ kill -9 4369 (kill process)
Hello SIGINT !
已砍掉 (killed)
$

.