Red Hat

If you really want to free up some memory space, by clearing out free page caches, directory entries and inode caches, try the below:

Code:

for i in 1 2 3; do sync; sleep 1; done; sysctl -w vm.drop_caches=3

Do not expect to see huge free memory instantly though.

Reboot should not be the first troubleshooting step, especially for Un*x.

If your server's memory is being consumed almost 100% constantly, check free -m and concentrate on used column for -/+ buffers/cache:. This tells you how much memory is used by the applications apart from the cache and file system buffers.

If that amount is too high, run sar -B and concentrate on majflt/s field. This tells you how many major page faults (when kernel does not find a page in RAM and incurs reading pages from disk swap area) are occurring per second.

Compare that data with the data gathered when your system had reasonable free memory. If you see differences are high, check which processes are eating up memory, which can be found by issuing top and sorting the RES column.