How to Clean Cache in Linux

Open a command shell and type 

echo 1 > /proc/sys/vm/drop_caches 

followed by "Enter" to free the pagecache.

Type

echo 2 > /proc/sys/vm/drop_caches

to free up the dentries and inodes. 

Type

echo 3 > /proc/sys/vm/drop_caches

to clear pagecache, dentries and inodes at the same time. It is necessary to clear them in this order so the cache doesn't fill back up.

Type 

sync; echo 3 > /proc/sys/vm/drop_caches

and press "Enter." This clears the entire cache, freeing up a significant amount of memory. 

In Ubuntu Linux, this command is 

sudo sh -c "sync; echo 3 > /proc/sys/vm/drop_caches"