Not many answers on this one, only Alan replied. I don't know if it is a
bug, but considering the mess that it generates, I will not try to
reproduce it on my servers...
Meanwhile, I would advise that you never press CTRL-C or CTRL-D while dd is
doing it's work...
Original question:
Strange problem !
This afternoon, I was copying a big file to tape with the 'dd' command (dd
if=myfile.dat of=/dev/nrmt1h) and I forgot to specify a bigger block size
than the default 512 bytes. The copy was taking forever so I decided to
cancel it with CTRL-C, result: dd printed a message telling me:
xyz+a: blocks in
xyz+a: blocks out (or the usual message)
After that, the system was not giving me back the prompt, so I pressed
CTRL-D. I was logged at the graphics console at this moment. xdm stopped
responding, I tried to connet with rlogin from another host, the system was
wedged and would not let me login, I could ping it OK tough...
I waited for 5-6 minutes and the system finally came back. There were 25-30
messages on the console regarding a problem with my TLZ07 (/dev/nrmt1h) and
SCSI bus 0 reset...
Any idea what happenned ?
Attached is the output of the uerf -R -o full and the dia -R -o full commands.
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Here is a plausible answer froam Alan:
From: alan_at_nabeth.cxo.dec.com
To: Guy Dallaire <dallaire_at_total.net>
Subject: Re: Problem: CTRL-C in 'dd' results in wedged system for 5-6
minutes !
Date: Fri, 11 Apr 97 19:31:59 -0600
X-Mts: smtp
My best guess is that even though you killed the dd(1),
there were still I/O requests queue to the tape drive.
I've read that the Digital UNIX version of dd(1) does
some multi-buffered I/O. Without a process context to
handle the completed I/O requests (or to provide memory
for the returned data), the driver or tape may have
gotten confused. Whenever the driver gets too confused
or believes a device has gone insane, it resets the
bus.
Guy Dallaire
dallaire_at_total.net
"God only knows if god exists"
Received on Tue Apr 15 1997 - 17:28:34 NZST