c daemon() for unix doesnt work with sleep()

Question

I have very simple code that should run on background and at 1 am shut down the computer:

#include <ctime>
#include <cstdlib>
#include <unistd.h>

int main() {
    time_t t;struct tm * now;
    daemon(0,0);
    while(1){
        t = time(0);
        now = localtime( & t );
        if(now->tm_hour==1){
           system("shutdown -P");
           break;
        }
        sleep(10);
    }
    return 0;
}

The code works without sleep(10) but uses whole free memory so I need sleep function there to stop loop and recheck time each ten seconds, but with sleep function program stops immediately after I run it.

How do you know it stops ? You call daemon() so it'll put itself in the background, and not consume any noticeable resources/CPU. — nos, Jan 03 '14 at 14:05
As a side note, did you know that `shutdown` already has the feature you are implementing? (`shutdown -P 01:00`) — rodrigo, Jan 03 '14 at 14:14

score 1 · Accepted Answer · answered Jan 03 '14 at 14:01

1

If you are writing C code, don't use C++ headers (ctime, cstdlib). Replace those #includes with #include <stdlib.h> and #include <time.h>. If the behavior of this code is really as you describe (which I would find surprising), then this is probably the source of the error.

answered Jan 03 '14 at 14:01

Andrey Mishchenko

3,986
2
19
37

Sure this had to cause the problem because now it runs, thanks. – Ruli Jan 03 '14 at 14:11

score 1 · Answer 2 · answered Jan 03 '14 at 14:07

1

Of course it immediately exits. Thats the whole point of using daemon. Check with ps and you will see that your proram is still running as a seperate process now.

Check the man page for a desription how daemon works.

answered Jan 03 '14 at 14:07

Devolus

21,661
13
66
113

c daemon() for unix doesnt work with sleep()

2 Answers2