Redhat Memory Question

[Neal, Jonathan W]

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?  Currently the Memory tag shows as yellow under this new Redhat server, though in my mind it should be green.

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

Thanks in advance

Wes Neal