the /debug partition

[Larry Grose]

In article <8807260558.AA07135 at uunet.UU.NET> bernie at cidam.rmit.OZ.AU (Bernard Kirby) writes:
>
>We recently had one of our machines upgraded to a 4D-70GT running
>version 3 of the operating system (4sight 1.0 etc). After all the
>software was installed we noticed that a  "df" showed an "extra"
>partition /dev/debug of type dbg mounted on /debug. It was about
>50Mb in size! There appeared to be files in the /debug directory,
>but whenever you tried to look at them, nothing happened, like they
>were zero length files, except that "ls -l" showed that some of them
>were quite large in size. The number and size of files varied as the
>machine was used. This partition was not in /etc/fstab but was in 
>/etc/mtab. So, one day in a fit of experimentality we simply "umount"ed
>it, and it hasn't reappeared since, even after a reboot. 

(Specific questions deleted.)

Basically, this is your standard swap partition which has been there all
along.  There has been no change in your disk partitioning.  Each file in
the partition corresponds to a running task (I believe the file "name" is
the process id), and the size of the file corresponds to the size of the
process's virtual memory.  Our in-house users had the same questions about
whether or not that partition could be used for storing files, and the
answer from SGI was "no".  This window into the swap partition was made
available so that you could debug programs that were already running (I
didn't ask how).  One other convenient use is that you can quickly see how
full virtual memory is by doing a 'df'.  I haven't tried dismounting it,
but I don't imagine there should be any problem with it if it bothers you
to see it in the 'df' listing.  I agree with the complaint about the lack
of documentation concerning it.  It was a rather disconcerting thing for
us to discover, too.
-- 
Larry Grose
CAMAX Systems, Minneapolis MN