sysctl -p /etc/sysctl.conf returns error

In a fresh installation of CenotOS 6 in a VPS after running sysctl -p /etc/sysctl.conf I got this errors:

error: "net.bridge.bridge-nf-call-ip6tables" is an unknown key
error: "net.bridge.bridge-nf-call-iptables" is an unknown key
error: "net.bridge.bridge-nf-call-arptables" is an unknown key

What is the starting point to solving this errors?

You mention in your question that you are using a VPS. What kind of VPS? It sounds like you are in a OpenVZ VPS. If it is OpenVZ, it is sharing the kernel among many containers like yours and you cannot change the kernel configuration per container but directly on the host. I actually build a litlle OpenVZ centos container and I tried to apply the kernel config net.bridge.bridge-nf-call-ip6tables = 0 followed by sysctl -p and I got the same error as you do. If you really need it, that means you may have to think about changing the type of virtualization you are using or you may try to contact your VPS provider and ask him to enable this setting.

Best.

Try:

modprobe bridge
lsmod | grep bridge

You don't the those modules loaded into the kernel.

There are several bugreports about this on Red Hat Bugzilla, for example here, here and here.

Just remove the lines or run sysctl -e -p instead of sysctl -p.

You get the errors because you do not have the bridge kernel module loaded. Three choices:

1. Load the module if you need it
2. Comment those lines out from /etc/sysctl.conf
3. Let sysctl ignore the errors by giving it the -e flag.