Fixing "COMMAND_FAILED: 'python-nftables' failed: netlink: Error: Could not process rule: No buffer space available" Error

September 5, 2023(September 5, 2023)

firewalld, troubleshooting, error, networking, linux

Introduction #

I recently ran into a baffling error while configuring firewalld on my system: COMMAND_FAILED: 'python-nftables' failed: netlink: Error: Could not process rule: No buffer space available. Here’s how I diagnosed and resolved the issue.

When Did I Encounter This Error? #

This annoying message popped up when I was Configuring firewalld.

Diagnosis #

After some digging, I found that the issue was likely related to the net.core.rmem_max and possibly net.core.rmem_default system parameters.

I checked the current settings with these commands(Since I was using LXC, I also had to check these settings on the host system):

sysctl -n net.core.rmem_max
sysctl -n net.core.rmem_default

How I Solved It #

Increasing the Buffer Sizes #

I temporarily increased the buffer sizes this way:

sysctl -w net.core.rmem_max=new_value_max
sysctl -w net.core.rmem_default=new_value_default

Testing #

After making these changes, I tried configuring firewalld again and this time, it worked.

Making the Changes Permanent #

Because this solved my problem, I made the changes permanent by adding them to a sysctl config file.

I added the settings to /etc/sysctl.d/network_buffer.conf like so:

echo "net.core.rmem_max = new_value_max" >> /etc/sysctl.d/network_buffer.conf
echo "net.core.rmem_default = new_value_default" >> /etc/sysctl.d/network_buffer.conf

Conclusion #

For me, tweaking the net.core.rmem_max and net.core.rmem_default parameters cleared up the “No buffer space available” error. If you’re facing a similar issue, especially while configuring firewalld, you might want to try this out. But as always, make sure to test extensively after making any changes like this.