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Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!seismo!brl-adm!adm!rbj@icst-cmr.arpa
From: rbj@icst-cmr.arpa
Newsgroups: comp.unix.questions
Subject: Tu77 ate tape, then hung device.
Message-ID: <5474@brl-adm.ARPA>
Date: Mon, 23-Mar-87 18:07:01 EST
Article-I.D.: brl-adm.5474
Posted: Mon Mar 23 18:07:01 1987
Date-Received: Wed, 25-Mar-87 06:04:42 EST
Sender: news@brl-adm.ARPA
Lines: 45


   In article <1105@hoxna.UUCP> lou@hoxna.UUCP ( L. Marco ) writes:
   >	I looked around, and the original cpio was still running, so
   >I did kill -9 20279. No problem, right ?  Funny thing is, the process
   >was still alive.  I could 'kill -9' it all I wanted, and it wouldn't
   >die.  I killed the parent, && eventually it was adopted by init, 
   >(ppid was 1 ), but I *still* couldn't touch it.  And of course, *that* 
   >process was still using /dev/rmt0, so I couldn't access the device.....  
   >Anyone have any idea what happened ? Am I even right in assuming that 
   >this 'immortal' cpio was stopping me from writing to the device ?

   I've encountered similar problems on a VAX, (BSD4.2). I used "mt" to skip
   n number of fields on a tape, but the tape only contained (n-1) files, so
   the process ended up reading to the end of tape. As i couldn't CTRL-C from
   the "mt" command, i attempted to kill the process from another terminal,
   and got the same problem you did; the process wouldn't die.

   >It's a 780 running 5.2, TU77 drive.  I finally re-booted, && the problem
   >went away.  Anything less drastic I could have done ?

   I powered off, (and on), the tape drive, the "mt" process then exited and
   everything carried on as normal.

This is a better solution. An even better one is to punch the offline
button. The tape controller will give an error, terminate the I/O, allow
the system to deliver the signal, which kills it. Then you rewind the tape.

   Anyone have any ideas as to why "mt" can't be interrupted or killed while
   the device is being accessed?

My guess is that the process is sleeping at a priority greater (less than?)
the magic constant PZERO. What that means is that I/O to `fast' devices
like disks (and by extension tapes) are not interrupted by signals. I don't
know if you can ^Z it either, so you just have to learn to put all your
mt commands in background with `&'. Rewind seems to be an exception.

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(Root Boy) Jim "Just Say Yes" Cottrell	<rbj@icst-cmr.arpa>
I want to kill everyone here with a cute colorful Hydrogen Bomb!!

P.S. It won't recognize ^C either.