free

Implemented by the procps package on Ubuntu 14.04.

Print RAM and swap memory in Megabytes:

free

Sample output:

             total       used       free     shared    buffers     cached
Mem:       3767368    3629844     137524     457068      30312    1098720
-/+ buffers/cache:    2500812    1266556
Swap:      3910652     445044    3465608

-h: human readable output:

             total       used       free     shared    buffers     cached
Mem:          3.6G       3.4G       172M       451M        29M       1.0G
-/+ buffers/cache:       2.4G       1.2G
Swap:         3.7G       434M       3.3G

Other flags:

-s1, -s0.01: repeat every N seconds. ms resolution.