Free command with -o option

Question

What does free command witj -o indicate , man page says it disables buffer adjusted line. It subtracts buffer memory from free memory. What does this mean

Answer 1

Buffers and cache use up memory. The used/free values include display memory being used when it is consumed by buffers and cache. See this page for a description. http://www.linuxatemyram.com/

Here is the difference on my system. Basically my system has 2,282,608 kbytes of memory that could be used by programs if it was needed. But a significant portion of that is currently being used for buffers/cache which speed up the normal operation of the system. If a program requested RAM the memory allocated to the cache would be released and allocated to the program.

cfrancy@enterprise:$ free
             total       used       free     shared    buffers     cached
Mem:       3934188    3619656     314532          0     778412    1189664
-/+ buffers/cache:    1651580    2282608
Swap:      4882424        960    4881464

cfrancy@enterprise:$ free -o
             total       used       free     shared    buffers     cached
Mem:       3934188    3619464     314724          0     778416    1189672
Swap:      4882424        960    4881464

Answer 2

In addition to what @Zoredache said the calcs are like:

how much memory is really being used:

used - (buffers + cached)

how much memory is really free:

free + (buffers + cached)

With the above calculation, it makes more sense now (-/+ buffers/cache:)

"minus buffers and cache" for the used column and "plus buffers and cache" for the free colum