How do you change tcp_congestion_control on OpenVZ?

Tyler Scott asked:

I have a network of OpenVZ machines that I am testing various congestion control methods on. I need to know how to change the congestion control. Currently I get nothing but permission denied. Is it even possible to change this on this sort of configuration?

[tylersc@center ~]$ sudo sysctl -w net.ipv4.tcp_congestion_control=reno
error: permission denied on key 'net.ipv4.tcp_congestion_control'
[tylersc@center ~]$ sudo sysctl net.ipv4.tcp_congestion_control
net.ipv4.tcp_congestion_control = cubic

Correction: OpenVZ not OpenVM

My answer:

OpenVZ is container-based, and as such, uses a shared kernel. Containers can only change a very small, restricted set of sysctls (which ones, unfortunately, aren’t even documented). If you need to do this, you need to be using something other than OpenVZ.

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