Command free via ssh only shows how many memory used, but people always seem to forget about that. Cached memory is still techincaly *free* memory that can be used. The Linux OS just doesn't free it, it keeps it there to help speed up other applications that may need the data there. If you still want force release those cached memory/ram, and it bothers you that its not really *freeing* the memory, you can force to free the cached/buffered memory to clear out by ssh command: echo 1 > /proc/sys/vm/drop_caches
Example:
[root @ www.ComfortVPS.com ]# free
total used free shared buffers cached
Mem: 248488 183244 65244 0 29136 112964
-/+ buffers/cache: 41144 207344
Swap: 262136 17940 244196
[root @ www.ComfortVPS.com ]# echo 1 > /proc/sys/vm/drop_caches
[root @ www.ComfortVPS.com ]# free
total used free shared buffers cached
Mem: 248488 46896 201592 0 112 7384
-/+ buffers/cache: 39400 209088
Swap: 262136 17940 244196
Something More:
Flush file system buffers by executing,
# sync
Kernels 2.6.16.x and newer versions of kernel provide a mechanism to have the kernel drop the page cache and/or inode and dentry caches on command, which can be helpful to free up a lot of memory.
To free page cache:
# echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
# echo 2 > /proc/sys/vm/drop_caches
To free page cache, dentries and inodes:
echo 3 > /proc/sys/vm/drop_caches
Above commands are non-destructive and will only release unused memory. As we have used sync, so it will flush all Dirty Objects which are not free able and make it as unused memory.
