the /debug partition

[Archer Sully]

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. 
> Now for the questions.
> 
> a) Is this a "hidden" partition that is secretly present on all SGI
>    machine's disks, only manifesting itself when explicitly mounted?

yes, it is present, because it is really the swap partition.

> 
> b) Is it really about 50Mb in size, or is that simply a function of "df"
>    misinterpreting a file system of type dbg.
> 
> 	OR
> 
> c) Did the Version 3 system repartition our disk without telling us?
>    If it did, then it must have zapped some files. 
> 
It really is 50MB.

> d) Can we use it for something else, like an NFS partition?
> 

no

> e) If we can't use it for anything else, can we reclaim the disk space?
>    (If in fact is really is using disk space)
> 
Since it doesn't use any space that wasn't already allocated, this 
isn't a problem.

> f) What the F**k's it for? Why did it just show up unannounced, with no
>    documentation about what it's doing.
> 
/debug is used by debuggers and other programs that like to control
processes other than themselves.  The idea is that when you access a 
file in the /debug partition, the kernel actually performs an operation
on another process.  This is what allows dbx to attach to a running 
process.

If /debug won't remount, check your /etc/fstab.  it should have this 
line in it:

/debug /debug dbg rw 0 0

If it doesn't, put it back.  If it does, make sure that the /debug
mount point is still there.  If both conditions are true, then I
have no idea what you've done to your system.  Try re-installing
3.0, or waiting for the maintenance release to get there.

There will be a man page for /debug in the next general software release.

> Thanks, 
> 	Bernie Kirby.


You're Welcome,
	Archer Sully