From http://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt:
Further on you can check the actual RAM+swap use of a tmpfs instance with df(1) and du(1).
So simply use df or du (you can also use them for ramfs):
$ df | grep tmpfs tmpfs 205032 1136 203896 1% /run so 1136 KB is in use.
$ sudo du -s /run [sudo] password for jaume: 1416 /run so 1416 KB is in use.
Thats's interesting... df and du report different sizes. What is happening here and which one is right?
/run has a subfolder called /run/shm, which is itself a separate tmpfs filesytem (although shown as none):
$ df | grep run tmpfs 205032 1136 203896 1% /run none 5120 0 5120 0% /run/lock none 512572 280 512292 1% /run/shm Adding both amounts you get the size reported by du:
$ expr 1136 + 280 1416 So the whole story is that 2 tmpfs filesystems use 1416 KB.
(Here's another reason why du and df outputs may differ.)