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Bug#3038: SOLVED: can't remove print jobs

Package: lpr
Version: 5.9-11

Ian Jackson (ian@chiark.chu.cam.ac.uk) wrote on 17 May 1996 14:24:
 >Rick Macdonald writes ("Bug#3038: SOLVED: can't remove print jobs"):
 >> On Thu, 16 May 1996, Carlos Carvalho wrote:
 >> > I also found that lockchk in line 156 of rmjob.c is doing a
 >> >
 >> >         if (kill(cur_daemon, 0) < 0) {
 >> >
 >> > I don't think it's right to send a signal number 0, at least it's not
 >> > documented. Also it has no effect at all, though it returns 0.
 >> It's not in the Linux man page but it is in others (like Solaris). The 0
 >> signal can be used to tell if the process is still valid (running).
 >> I've used it a few times. I assumed it was pretty standard.
 >If lpr is doing this then it is almost certainly broken.  You see,
 >pids are be reused, so that it's never safe to store a pid in a
 >variable and then use it for something later unless you're the
 >process's parent (in which case kill(,0) is redundant) or can do some
 >other check to see that the process is the same as the one it used to
 >This means that kill(,0) is almost always a mistake.
 >Could you check to see whether lpr is failing to check this, and if so
 >report it as a bug ?

It's lpd in the case of a remote printer, but it's certainly doing it.
I think the point is that it's going to remove the files, so it should
kill any process that has them open. How can it determine the pid's of
the processes?


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