Tools / Commands for monitoring Memory Usage in ubuntu / Debian

Tools / Commands for monitoring  Memory Usage in ubuntu / Debian

 free - Display amount of free and used memory in the system.

 watch -n 5 free -m   -  Real time memory usge
 vmstat - Report virtual memory statistics
 top - Show top processes and memory usage
 htop - interactive process/memory usage viewer
 cat /proc/meminfo Show memory size and usage.

 gnome-system-monitor — Graphical tool for viewing process/memory/network usage