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Check for valid dump in swap device

By itself, "memsize" would just tell you how much ram was installed (or technically, in use by the kernel as you could reduce that with athe "mem" boot option), but if you gave it additional arguments as described below, it could read from a kernel dump.

As it returned 0 for success, that could tell you if a dump was valid as shown here.

From: Roberto Zini <r.zini@strhold.it>
Newsgroups: comp.unix.sco.misc
Subject: Re: How to clean /dev/swap (OSR 5.06)
Date: Thu, 06 Sep 2001 18:01:55 +0200
Message-ID: <3B979DF3.BE1F79C1@strhold.it> 
References: <3B9476A3.8835CB55@club-internet.fr>
<3B95D0ED.79C438B9@strhold.it>
<3B963B62.2B6850F4@club-internet.fr> 

Fr�d�ric STOCK wrote:
> 
> Hello Roberto,
> 
> the swap device is still in /dev/ dir.
> here it is the output of the divvy command:
> 

[snip]

Good; what does "swap -l" report ?

According to /etc/dumpsave, there's a valid system dump if
"/etc/memsize /dev/swap <swaplo> <blocks>" returns an exit status 
of 2, where <swaplo> and <blocks> are the values returned
by "swap -l".

I've just did it un a running 5.0.5 system and I've got an
"memsize: Invalid checksum" message (return code = 2) which
indicates that there isn't a valid system dump; if the return
value is "0", then you have a valid dump.

Dunno about other return values; however, if you take a look
at the /etc/dumpsave script, the "remove_dump_exit" routine
shows how to remove the dump from the swap area. Take the
<swaplo> number as reported by "swap -l", add 4, and issue
the following command:

dd if=/dev/swap of=/dev/swap iseek=<number> oseek=<number> count=2 conv=swab

where <number> is the number you get from the above sum and "/dev/swap"
is your swap device.

I've just tried it on a living 5.0.5 system and it was harmless;
cannot guarantee that it'll be the same on yours though ...

Hope it helps !

Best,
Roberto
-- 
---------------------------------------------------------------------
Roberto Zini                                email : r.zini@strhold.it
Technical Support Manager -- Strhold Evolution Division  R.E. (ITALY)
---------------------------------------------------------------------
"Has anybody around here seen an aircraft carrier?"                
        (Pete "Maverick" Mitchell - Top Gun)
 

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