Kill a hanged disk i/o process...

[Modulok]

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.

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?
-Modulok-


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
>