System crashing when swap hits 25%

[Todd Denniston]

Simon Slater wrote, On 03/10/2008 06:37 PM:
> 	G'day all,
> 		This is an inconvenience that I would like to get to the bottom of.  I
> have a PII 233MHz 512 MbRAM running FC6. All is fine until swap reaches
> about 25% used then the system hangs.  It will run for days with the
> swap at 10-15%.  My first thought was to run badblocks to see if that
> was the problem, since it is an old drive, but couldn't find the swap
> device with mount.
> 

Been there, done that.

WARNING: before using badblocks in full rw mode on swap space, remember two 
things:
1) some how you would have to convince mkswap to retake what ever label is 
being used in /etc/fstab, or you would need to use a new label/device name in 
/etc/fstab.
2) don't be using it for swap while checking it. :)

/sbin/swapon -s
will display which partitions/files are being used in the system for swap.
/sbin/swapoff -a
will turn swap off. probably should shut down any programs down that you don't 
need so that you can get under 512MB, then badblocks (with full read/write 
test and re-`mkswap -c` on it, or Use non-destructive read-write mode) sounds 
like a reasonable thing.

If you find a single bad block, you should really be looking for new hardware.
I have done the thing where you partition around the bad blocks, but it only 
buys you a little time.
If I understand the man-page for mkswap the -c will print the bad block 
locations, it says nothing of setting up swap to avoid them.

> 	My questions are: what would cause this system to hang when the swap
> file is used?; 

[from experience I know] Bad blocks in swap cause errors that look _just_ like 
failing ram.  That is, programs just die, system locks up in weird ways.

> where is the swap file?; 

Most times it is a swap partition, `/sbin/swapon -s` or `cat /proc/swaps` will 
help here.

> if in the VG, how do I umount it
> to run badblocks?  

/sbin/swapoff

> Here is some output that may be useful.
> 
> 	Thanks.

Good luck.

-- 
Todd Denniston
Crane Division, Naval Surface Warfare Center (NSWC Crane)
Harnessing the Power of Technology for the Warfighter