Monitoring Memory

free command

The free command when used by itself will display memory usage in kilobytes. It displays total memory available, used, and swap memory in addition to cache and buffers.

# displays output in bytes
free -b 
# displays output in megabytes
free -m
# displays output in gigabytes
free -g
# displays output in human-readable format
free -h
# continuously polls free every {number of seconds}
free -s {number of seconds}
# free will output every 3 seconds
free -s 3

free example

[root@he fast]# free -h
             total       used       free     shared    buffers     cached
Mem:          126G       125G       532M       176K       510M        94G
-/+ buffers/cache:        30G        95G
Swap:         8.0G       995M       7.0G
[root@he fast]# free -g
             total       used       free     shared    buffers     cached
Mem:           126        125          0          0          0         94
-/+ buffers/cache:         30         95
Swap:            7          0          7