how to find actual free memory (RAM) in Linux - RedHat

[ramamoorthy]

When we have Oracle 10g in RedHat, the free memory goes down soon after bootup of the system and never increases. I learnt from various forums that Linux does cache the disk files for the better performance. And when any application requires memory they get the memory and the caching does not block any memory. We want to capture the free memory available for one the harware planning activity.

1) When we use vmstat command, it gives very less free memory. since it caches large size files, the free memory is very low.
2) We tried free command, but how do we know how much actual free memory is available. i.e. excluding the cache usage

Please help if any one has a way to obtain the actual free memory

[HROAdmin26]

2) We tried free command, but how do we know how much actual free memory is available. i.e. excluding the cache usage

...the column that says "free"

[ramamoorthy]

We tried using the "free -m" command to get the free memory available in the server

[root@server~]# free -m
total used free shared buffers cached
Mem: 20066 19879 187 0 37 18938
-/+ buffers/cache: 903 19162
Swap: 20481 27 20454
[root@server~]#

Here free memory is too low 187 MB. But when we see "-/+ buffers/cache:" line, the free memory is ~19GB. We are in a fix to find out the actual memory of the server.

[Rubberman]

Free memory includes both that which is unallocated, as well as cache and buffer memory. The 'free' command shows all of that. So, when you run the "free' command, it shows "total used free shared buffers cached". Your actual available memory (before hitting the swapper) is free + buffers + cached. Because Linux uses a virtual memory model, the amount of "really" free memory is debatable...