How to clear memory cache in Linux

Question

Is there any command that by using I can clean the cache in RHEL?

I used this command:

sync; echo 3 > /proc/sys/vm/drop_caches

but it didn't work.

Solution 1

Try sync; echo 1 > /proc/sys/vm/drop_caches.

Solution 2

Depending on what you want to do you can use 1,2 or 3

from https://www.kernel.org/doc/Documentation/sysctl/vm.txt

drop_caches

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.

Comments

[daisy]

define didn't work

[OmiPenguin]

Means command executed successfully but results didnt changed. Means the Cache Memory remained occupied.

[jippie]

What problem are you trying to solve?

[Joe]

There are many reasons why the cache wouldn’t be cleared. If the file is in use or if the cache size is due to tmpfs or ramfs. I have blogged about different possibilities of cache here.

[0xC0000022L]

@ott--: simple, if you want to run high level performance tests (run version X of A against version X+1 of A to measure differences), how do you eliminate the file system cache from your testing? Because if you don't you'll skew your tests. You could by rebooting, but flushing the cache is certainly another option.

[Evhz]

sudo sh -c "echo 1 > /proc/sys/vm/drop_caches"

[jiffy.of.eternity]

@Evhz Your comment should be a new answer and the accepted answer. The current accepted solution gives "Denied" even if using sudo echo 1 > ...