signals

I wrote a very simple c program: #include<stdio.h> int main(){ int a=2; int b=0; printf("%d\n", a/b); } and run it with strace: strace ./a.out and get below output (only paste tail part) ... ... mprotect(0x600000, 4096, PROT_READ) = 0 mprotect(0x7f04c7fb8000, 4096, PROT_READ) = 0 munmap(0x7f04c7f96000, 127640) = 0 --- SIGFPE (Floating point exception) @ 0 (0) --- +++ killed by SIGFPE +++ Floating point exception The output matches my expectation, as it was killed by SIGFPE signal. However, the same program written in Java, doesn't get SIGFPE signal, does anybody know how java processes "divide

I am using my android phone as Access Point. Now I want to find the distance and direction of the wifi devices connected with my phone. Please help me through suitable example and code. Thanks in advance. I downloaded Wifi Radar that you mentioned and tried it. There's an important step there - it asks you to rotate on the spot for a bit while holding the device to your body. So my guess is that it uses the internal compass to figure out which direction you're pointing to, and then measures the signal. When the signal gets stronger, it figures that you're pointing toward the AP. Since the app

I am still a little confused as to why exactly it is unsafe to receive a signal and call a non async safe function from within that signal handler. Could someone explain the reasoning behind this and possibly try and give me some references that I can follow to read up more on this myself? In other words I am asking why it is unsafe to say call printf from within a signal handler. Is it because of intra-process issues and possible race conditions resulting from two possible calls to printf without protection or is it because of inter process races to the same resource (in this example stdout).

Well, at least a mystery to me. Consider the following: import time import signal def catcher(signum, _): print "beat!" signal.signal(signal.SIGALRM, catcher) signal.setitimer(signal.ITIMER_REAL, 2, 2) while True: time.sleep(5) Works as expected i.e. delivers a "beat!" message every 2 seconds. Next, no output is produced: import time import signal def catcher(signum, _): print "beat!" signal.signal(signal.SIGVTALRM, catcher) signal.setitimer(signal.ITIMER_VIRTUAL, 2, 2) while True: time.sleep(5) Where is the issue? From my system's man setitimer (emphasis mine): The system provides each

I am newbie on the Linux signals, please help. The following code get core dump when run in Linux 2.6 gcc. $ ./a.out Floating point exception (core dumped) The questions: 1. Since a process signal mask is installed, shouldn't the "SIGFPGE" generated by line 40 volatile int z = x/y; be blocked? 2. If it is not blocked, since a signal handler has been installed, shouldn't the "SIGFPE" be captured by the signal handler, instead of a core dump? 3. If I commented out line 40 volatile int z = x/y; , and use line 42 raise(SIGFPE); instead, then everything works as I expected. What is the difference

I'm writing a very simple server that loops forever until Ctrl-C is pressed. I'd like to have the signal handler for ctrl-c close the open sockets and shut down the server, but I don't know what the scope is for a signal handler, and I don't like the idea of declaring the socket(s) I would need to close to be global. Can someone offer suggestions? Is there some standard way to do this? Well, since you have signal handlers, I'm going to assume you're on a Unix variant. If so: A socket is identified to the kernel by the file number, which is an int. See socket(2) . That int is valid for your

I have a server application which I want to protect from being stopped by any signal which I can ignore. Is there a way to ignore all possible signals at once, without setting them one by one? Yes: #include <signal.h> sigset_t mask; sigfillset(&mask); sigprocmask(SIG_SETMASK, &mask, NULL); This does not exactly ignore the signals, but blocks them; which in practice is the same effect. I guess there's no need to mention that SIGKILL and SIGSTOP cannot be blocked nor ignored in any way. For more detailed semantics, like mask inheritance rules and the like, check the man page Blocking signals is