Flush RAM memory.

We can flush RAM memory without rebooting server. First login in to server as root user and follows steps.

Check current RAM usage.

root@server [~]# free -m
total       used       free     shared    buffers     cached
Mem:        2025       1863        162          0        522        992
-/+ buffers/cache:        349       1676
Swap:         4996          0       4996

Now flush RAM memory.

root@server [~]# echo 1 > /proc/sys/vm/drop_caches

Once again check memory usage and check difference.

root@server [~]# free -m
total       used       free     shared    buffers     cached
Mem:          2025        353       1671          0          0         28
-/+ buffers/cache:        324       1700
Swap:         4996          0       4996