Question

Kill(pid, 0) seems to not set the error code correctly…as stated in man for kill

Errors

The kill() function shall fail if:

EINVAL The value of the sig argument is an invalid or unsupported
signal number.
EPERM The process does not have permission to send the
signal to any receiving process.
ESRCH No process or process group can
be found corresponding to that specified by pid. The following
sections are informative.
1

It is returning ENOENT (no such file or directory) and then sometimes it returns EINTR (system call interrupted)…

Here is what I am doing:

kill(g_StatusInstance[i].pid, SIGTERM) == -1 && log_fatal_syscall("kill-sigterm");
kill(g_StatusInstance[i].pid, 0);

log_info_console( "Checking process for errors: %s\n", strerror(errno));

if(errno != ENOENT)
{
   kill(g_StatusInstance[i].pid, SIGKILL) == -1 && log_fatal_syscall("kill-sigkill");
}

Am I doing something wrong?

Answer 1

Kill(pid, 0) seems to not set the error code correctly …
It is returning ENOENT… EINTR

Here is what I am doing:

...
kill(g_StatusInstance[i].pid, 0);
log_info_console( "Checking process for errors: %s\n", strerror(errno));

Am I doing something wrong?

Yes. You are not checking the return value of the kill() system call. kill() does not set errno to any particular value in the successful case.

Try this:

if(kill(g_StatusInstance[i].pid, 0) == -1) {
  log_info_console( "Checking process for errors: %s\n", strerror(errno));
} else {
  log_info_console( "kill returned 0, process still alive\n" );
}

More generally, you ought to check the return value of every system call or library call, unless it is declared to return void.