[Xymon] external script problem - question

[Jeremy Laidman]

On Thu, Oct 6, 2011 at 7:37 AM, Henrik Størner <henrik at hswn.dk> wrote:

> * Have you looked at the vmstat1 graphs for these systems ? How is the "I/O
> wait" on them ? Some types of I/O on Linux systems can cause quite a
> slow-down; deleting large files on ext2 or ext3 systems could be quite
> time-consuming and cause the whole system to really stall. Also doing things
> that touch a lot of files - a large find, or grep'ing through a large number
> of files, especially if you don't mount filesystems with the "noatime"
> option - can cause a lot of I/O that slows down filesystem operations.
>

I've seen this happen during log rotation and compression, shown by "sar -d"
(I recommend installing sar if you haven't already).  The I/O contention
during removal of a big file after compression is sufficient to cause any
filesystem operation to block for a loooong time.  For me, this causes
sufficient back-pressure that syslog-ng starts dropping UDP packets while it
waits for the logfile to become writeable.

To prove that it's not a Xymon problem, why not create a cron task that does
the same thing, but logs how long it takes.  If the log shows delays, then
it's got nothing to do with Xymon.  Perhaps create /etc/cron.d/touchtest
with the following:

 * * * * * root time touch /path/to/file >> /tmp/touchlog 2>&1
 50 23 * * * root cp /dev/null /tmp/touchlog

Cheers
Jeremy
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