How to clear Linux RAM memory cache

Writing to this will cause the kernel to drop clean caches, dentries and inodes from memory, causing that memory to become free.

• 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

As this is a non-destructive operation, and dirty objects are not freeable, the user should run "sync" first in order to make sure all cached objects are freed.

Memory before:

[root@server1 ~]# free -m
                   total       used        free     shared    buffers     cached
Mem:          7860       7040        820        0        343          5076
-/+ buffers/cache:       1620       6240
Swap:         3999          0          3999

[root@server ~]# sync
[root@server ~]# echo 3 > /proc/sys/vm/drop_caches

Memory after:

[root@server1 ~]# free -m
                   total       used         free     shared    buffers     cached
Mem:          7860       1279        6581          0          0         33
-/+ buffers/cache:       1245       6615
Swap:         3999          0          3999