[Techtalk] memory used on ubuntu server

Gayathri Swaminathan gayathri.swa at gmail.com
Tue Feb 7 02:56:20 UTC 2012


Hiya Anne,

On Mon, Feb 6, 2012 at 2:20 PM, Anne Wainwright <anotheranne at fables.co.za>
wrote:

> Daily inspection of this message caused me to think that all was well.
> On the contrary. The percentage in question is of the RAM plus swap plus
> buffer as investigation with 'free' revealed. It was not the percentage
> of the installed RAM as I imagined.
>

When it comes to verifying actual memory usage, I often trust vmstat
command more than free. The man page is vivid but here are the highlights:

<snip>
[wombat at athena vms]$ vmstat 5 5
procs -----------memory---------- ---swap-- -----io---- --system--
-----cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id
wa st
 1  3      0 171108  17164 2330504    0    0  6528  6321  886 1259  7  5 44
44  0
 1  3      0 168444  17160 2329144    0    0 20892 26430 1155 1933  1  4 13
82  0
 0  3      0 197052  17156 2301160    0    0 24147 25630 1288 2122  2  5  9
83  0
 0  3      0 194664  17136 2303020    0    0 27137 20673 2043 2803  3  5 12
80  0
 0  4      0 203036  17140 2293928    0    0 24962 22437 1645 2099  2  5 16
78  0
</snip>

Under,
procs: you see "r"  for running processes, "b" for background or sleeping
processes
Memory: has swpd - Virtual memory usage, free - actual Idle memory, buff -
memory used as buffers, cache - total used in cache
swap: has si - memory swapped in from the disk and so - memory swapped to
the disk
io: has bi - blocks read from disk and bo - blocks written to the disk
system: has in - number of interrupts and cs - number of context switches
cpu: has us - time spent on user activities, sy - time spent by kernel, id
- idle time, wa - io waits

It takes a few tries to read those numbers and interpret them. Also it's
advisable you run this during "peak" windows of system usage ( possibly
cron a job to append output to a file).

Lately I have gotten lazy to just run "sar" on my hosts and review sar data
using kSar to catch something out of the ordinary...

-- 
Gayathri Swaminathan
gpgkey: 3EFB3D39
Volunteer, FDP


More information about the Techtalk mailing list