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I have tried

sudo sh -c 'echo 3 > /proc/sys/vm/drop_caches'

sudo echo 3 > /proc/sys/vm/drop_caches

echo 3 > /proc/sys/vm/drop_caches

echo 3 | sudo tee /proc/sys/vm/drop_caches

and a bunch of other variations but with every try I get

bash: /proc/sys/vm/drop_caches: Permission denied

How do I clear the ram used for buffers/cache in my centos6 openvz container?

It seems like the only way to do what I need is to reboot the container.

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Why would you want to? – David Schwartz Dec 3 '12 at 2:45
up vote 3 down vote accepted

Get a real non-OpenVZ machine (KVM, Xen, etc) and this will work just fine. With OpenVZ, you don't get your own kernel instance and as such, are restricted from performing commands like this.

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echo 3 | sudo tee /proc/sys/vm/drop_caches
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That was one of the things I also tried and it doesn't work – Omar Jackman Dec 3 '12 at 0:14

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