Kill a hanged disk i/o process...
nvass at teledomenet.gr
Fri Mar 9 14:07:33 UTC 2007
On Friday 09 March 2007 15:28, Modulok wrote:
> Thank you for your reply, it was quite informative and very much
> appreciated, but the underlying question remains un-answered:
> How do you kill a hanged process that (seemingly) cannot be killed because
> of the two conditions below?
> -It's hanged, so it's not ever going to self terminate.
> -It's a disk i/o process so not even root can kill it.
As I said before disk I/O is irrelevant.
> The gentle shutdown solution doesn't work: Even during shutdown the process
> cannot be killed: it's hanged, it's disk i/o.
> How do you kill an un-killable process?
What makes you believe there is another official way
to kill a process?
Perhaps you should ask "How do I work-around a situation
where my rm, cp, whatever hang forever?", if that's what
you are looking for.
> On 3/9/07, Nikos Vassiliadis <nvass at teledomenet.gr> wrote:
> > On Thursday 08 March 2007 13:49, Modulok wrote:
> > > To the best of my knowledge, most processes can be killed explicitly
> > > by "kill -s KILL;" There are a few which cannot, such as disk i/o
> > > processes. The idea here is data integrity.
> > A process might be in cannot-be-killed condition while
> > in kernel e.g. during a system call. That has to do with
> > the completion of the system call, not with data integrity.
> > The kernel tries to complete what was asked for.
> > Also, Killing a process with SIGKILL is far from safe. To put
> > it in another way "data integrity" can be guaranteed only
> > by the program itself. For example it could have a defined
> > behavior when it is signaled by e.g. SIGTERM, for example
> > clean up data and exit. Or not. It's up to the programmer.
> > Sending a SIGKILL will not give that chance. SIGKILL can
> > not be handled. It will be terminated as soon as possible.
> > Also, separate the meanings "data integrity" and "filesystem
> > data integrity". The filesystem will be in fine condition when
> > a process gets killed by SIGKILL during file I/O, the data in
> > the file most probably not.
> > >
> > > On the rare occasion however, (when attempting to recover data from
> > > corrupt disks for example), I've had a process invoked by the "cp"
> > > command, hang. This poses a significant problem as these processes are
> > > disk i/o processes, and as such cannot be terminated (even by root).
> > > So, other than physically hitting the reset button on the case, is
> > > there a more eloquent method of forcefully halting a hanged disk i/o
> > > process? The idea of "you don't want to terminate a disk i/o process,
> > > it could corrupt the data" isn't really a good argument, because if
> > > the process hangs and I have to punch the reset button anyway what's
> > > the difference?
> > "Pressing the button" will leave your filesystem in a undefined state,
> > you are risking filesystem integrity. Keep in mind that while in use
> > (open files etc) a filesystem cannot be unmounted. Anyway, try to shut
> > the computer down, it's far more gentle than pressing the button. At
> > least the rest of the filesystems will be cleanly unmounted.
> > Is there something in particular you want to achieve?
> > Nikos
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