RAM plays an important role in the performance of a system. So we should monitor this memory usage to troubleshoot system. free is the basic command to get details of RAM and swap usage.

#free

Example :

# free
total used free shared buffers cached
Mem: 3059872 2842016 217856 0 33936 2012684
-/+ buffers/cache: 795396 2264476
Swap: 2000052 67672 1932380

When you see it’s giving total size, used and free size in bytes. If you want to see in MB specify
-m option in free

#free -m

Example :

# free -m
total used free shared buffers cached
Mem: 2988 2784 203 0 33 1974
-/+ buffers/cache: 776 2211
Swap: 1953 66 1887

Any other commands to check RAM?
The answer for this is yes.
1. Use proc file system to get detailed RAM usage of the system.

#cat /proc/meminfo

2. Use top command to see RAM usage

So with top too you can see RAM usage live.