How to clear the buffer and pagecache

Run "sync" command first to flush pending data out to disk

# sync

To free pagecache

# echo 1 > /proc/sys/vm/drop_caches

To free dentries and inodes

# echo 2 > /proc/sys/vm/drop_caches

To free pagecache, dentries and inodes

# echo 3 > /proc/sys/vm/drop_caches