28.8. Memory Usage: free

The utility free examines RAM usage. Details of both free and used memory (and swap areas) are shown:

$ free
             total       used       free     shared    buffers     cached
Mem:        514736     273964     240772          0      35920      42328
-/+ buffers/cache:     195716     319020
Swap:      1794736     104096    1690640

With -m, have all sizes expressed in megabytes:

$ free -m
             total       used       free     shared    buffers     cached
Mem:           502        267        235          0         35         41
-/+ buffers/cache:        191        311
Swap:         1752        101       1651

The really interesting information is contained in this line:

-/+ buffers/cache:        191        311

It calculates the amount of memory taken up with buffers and caches.

The parameter -d delay ensures that the display is refreshed every delay seconds. For example, free -d 1.5 produces an update every 1.5 seconds.