Linux - How to monitor memory usage

Question : How to monitor memory [%MEM] in Linux?
Answer : ps command can be used to report a snapshot of the current processes in Linux. Use option aux and sort based on the column to get the top usage based on the parameter you need. If you need to get %MEM then you will need to sort column 4.
Example :

[root@server ~]# watch -n 2 'echo `ps aux |head -1`;ps aux |sort -nrk 4| head -10'

Note : Above command will output top 10 processes with highest %MEM in an interval of 2 seconds.


Question : How to monitor memory [%MEM] in Linux?
Answer : Besides using method above, top command can be used to monitor %MEM in Linux. Issue command top. It will display a list of processes sorted based on CPU usage. Then issue "M" to sort based on %MEM. Alternative issue top with option "m".
Example :

[root@server ~]# top -m

Question : How to monitor free and used memory in Linux?
Answer : free command can be used to monitor free and used memory in Linux. To include a line containing total memory and swap option "t" can be used. Option "m" can be used display value in megabytes [MB]. Option "s" along with a interger value can be used to specific interval of monitoring needed.
Example :

[root@server ~]# free -mt -s 3 total used free shared buffers cached Mem: 7979 7665 313 0 191 5777 -/+ buffers/cache: 1696 6282 Swap: 32767 0 32767 Total: 40747 7665 33081

Question : How to monitor memory [%MEM] of a specific process in Linux?
Answer : top command with option "p" followed by PID can be used to specific which process to monitor.
Example :

[root@server ~]# top -p <PID>