Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!noao!amethyst!spock.ame.arizona.edu!chris
From: chris@spock.ame.arizona.edu (Chris Ott)
Newsgroups: comp.sys.sgi
Subject: /debug size
Message-ID: <1008@amethyst.math.arizona.edu>
Date: 16 Jul 89 05:45:32 GMT
Sender: news@amethyst.math.arizona.edu
Reply-To: chris@spock.ame.arizona.edu (Chris Ott)
Organization: Computer Aided Engineering Lab,   U of A,  Tucson, AZ
Lines: 64


lewis@castor.wustl.edu (Lewis Yuchan Geer) writes:
> Is there any way to reduce the size of /debug, as it acts like it takes
> up 50Mb on our system?  Is this a wise thing to do?  Thanks.

     No, it's not a wise thing to do. The /debug partition is actually
the swap partition for the IRIX system. Reducing its size will reduce
the amount of virtual memory available to all of the processes on the
system.

fsfacca@LERC08.LERC.NASA.GOV (Tony Facca) writes:
> As far as I can determine, this is not physical disk space, but rather some
> sort of virtual disk.

     No, it is actual, physical disk space. It is required for virtual
memory.

>                       The size allocated to /debug changes as users on the
> system do thier work.

     This is _not_ true. The amount of space _available_ in /debug
changes as users do their work, but the amount allocated is determined
when the hard disk is partitioned, just like the / and /usr filesystems.

> Even if you were to remove the files in /debug, you would not gain any
> disk space to use for permanent storage, so its probably not wise to do
> anything with it.  

     Considering that each file in the /debug partition represents the
virtual memory of a process on the system, I'd say deleting any of them
would be unwise, at best. Notice, also (in "df") that /debug's filesystem
type is "dbg", while the others are "efs" or "nfs". I wouldn't advise
writing any normal files there, even though it appears to be possible.

     Do an "ls" on /debug. Notice that all of the files' names are
numbers, rather than words. Now do a "ps". Notice that most of the PIDs
listed by "ps" match the file names in the /debug partition. Reading and
writing these files is the same as reading and writing the memory space of
the corresponding process. It is used mostly by the debugger for reading
and writing variables, hence the name /debug. Quite an ingenious idea on
Silicon Graphics' part, in my opinion (if it was they who invented it).

> So why even show it in the "df" display?

     Probably because it's a file system, just like / and /usr. The
amount of memory available (displayed by "df") represents the amount of
virtual memory left on your system. Personally, I like it.

>                                 since no one from SGI offered any advice, I
> thought I'd try to help.

     Yeah, I'm surprised at this. They're usually pretty helpful. Maybe
it's because it's the weekend...

Chris

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 Chris Ott
 Forensic Productions, Inc.               Infatuation is blind, not love. A
 Tucson, Arizona                            person in love can see the other's
                                            faults, but loves them anyway.
 Internet: chris@spock.ame.arizona.edu
 UUCP: {allegra,cmcl2,hao!noao}!arizona!amethyst!spock!chris
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