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

Introduction

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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?

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This annoying message popped up when I was Configuring firewalld.

Diagnosis

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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

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Increasing the Buffer Sizes

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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

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

Making the Changes Permanent

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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

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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.