[Xymon] Redhat Memory Question

[J.C. Cleaver]

On Thu, March 19, 2015 5:19 pm, Jeremy Laidman wrote:
> On Fri, Mar 20, 2015 at 2:25 AM Neal, Jonathan W via Xymon
> <xymon at xymon.com>
> wrote:
>
>> I have never monitored any Redhat systems before, all Solaris in the
>> past
>> for the most part.  Since top and free always show all the physical
>> memory
>> in use on Redhat, how do people monitor memory usage accurately with
>> Xymon?
>
>
> Xymon tracks swap usage, physical memory usage, and "actual" memory usage.
> The last of these is what most people care about.  In analysis.cfg you can
> set thresholds on any of these.  On my system the thresholds for physical
> memory usage are 100% for yellow and 101% for red.
>
> Under Linux, "actual memory" is obtained from the output of "free" which
> is
> recorded in the [free] section of the client data, specifically from the
> "buffers/cache" line.  The value for "actual used" comes from the first
> number.  The "actual total" is the total physical memory and is the first
> number in the "Mem:" line.
>
>   Currently the Memory tag shows as yellow under this new Redhat server,
>> though in my mind it should be green.
>>
>
> For actual memory usage, yes.
>
> Mem:  16435916k total, 16311612k used,   124304k free,  6255112k buffers
>> Swap: 18481144k total,        0k used, 18481144k free,  6391000k cached
>>
>>              total       used       free     shared    buffers
>> cached
>> Mem:      16435916   16311588     124328          0    6255116
>> 6391040
>> -/+ buffers/cache:    3665432   12770484
>> Swap:     18481144          0   18481144
>>
>
> In your case, on your "memory" status page you would see "Actual 3579M
> 16050M 22%" meaning 3.5GB non-cache/buffer RAM usage used out of 16GB
> total
> physical RAM, which is 22%.
>
> So actual usage is 22%.  If your yellow threshold for MEMACT is the
> default
> of 90, then this 22% is well short of triggering a yellow condition.  And
> it must be something else.
>
> On your memory status page each line should have its own coloured dot.
> Which of the lines has a yellow dot?  I'm guessing it's the "Physical",
> and
> someone has modified the MEMPHYS threshold in analysis.cfg to go yellow at
> 99% instead of 100%.
>
> J


The whole concept of 'free memory' is really a bit tricky. Linux 3.14+ has
provided a solution in /proc/meminfo
(https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=34e431b0ae398fc54ea69ff85ec700722c9da773),
but it's not available everywhere. Furthermore, the 'free -a' output
depends on your specific version of procps(-ng) and possibly your sysctl
setting of meminfo_legacy_layout
(https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html-single/6.6_Technical_Notes/index.html#ch-Important-Changes-to-External-Kernel-Parameters).


Regards,

-jc