On 28/10/2010, at 9:29 AM, john skaller wrote:
>
> well, that's interesting. I do:
>
> int sout = open("mystdout.log",O_CREAT | O_WRONLY | O_TRUNC);
> int serr = open("mystderr.log",O_CREAT | O_WRONLY | O_TRUNC);
> close(0); close(1); close(2);
> dup2(sout,1);
> dup2(serr,2);
> while(1){
> FILE *f= fopen("log.log","w");
> fprintf(f,"Daemon running\n");
> fclose(f);
> printf("[stdout]Daemon running pid=%d\n",getpid());
> fprintf(stderr,"[stderr]Daemon running pid=%d\n",getpid());
> sleep(5);
> }
>
> and all the output goes into mystdout.log, mystderr.log is
> empty. what did I do wrong here?
Well, thanks to the bad documentation (see the man page to the open()
function, doesn't even *mention* the permissions argument, not
even the OpenGroup page does .. despite giving examples using it):
Now I do:
int sout = open("mystdout.log",O_CREAT | O_WRONLY | O_TRUNC, S_IRUSR |
S_IWUSR | S_IRGRP | S_IROTH);
int serr = open("mystderr.log",O_CREAT | O_WRONLY | O_TRUNC, S_IRUSR |
S_IWUSR | S_IRGRP | S_IROTH);
and the C output works. Maybe I got confused. I moved the close() calls to after
the open calls to ensure 0,1,2 stayed open long enough to ensure sout and
serr didn't get numbers 0,1, or 2 so I could dup2 onto them. I should
also open 0 onto /dev/null I guess to prevent some other open() call
using the wrong value (fd 0 will be unused so must be assigned
by the next open() call, I better use it in case I try to read from it
and get a different file .. kind of messy).
--
john skaller
[email protected]
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