Execution failed: /usr/sbin/iptables-restore - exit status 4

The error message "Execution failed: /usr/sbin/iptables-restore - exit status 4" typically indicates that the iptables-restore command encountered an error related to a failure to load a required extension or match, or there is an issue with the state of the iptables command itself.

Possible Causes for Exit Status 4:

1. Missing or Unavailable Modules:

   • This error can occur if iptables-restore is trying to use a module or match that is not available or not loaded in the kernel. For example, if you are trying to use a match like conntrack or state, and the corresponding kernel module is not available, iptables-restore will fail with this error.

2. Incorrect Table or Chain Names:

   • If the rule refers to a non-existent table (like nat, filter, etc.) or chain, this can cause the restore process to fail.

3. Incompatible Rules or Options:

   • The rule set might contain options or matches that are incompatible with the installed version of iptables or with the kernel.

4. Issues with iptables-save File:

   • The file you are trying to restore may have been created with a different version of iptables or on a different system, leading to incompatibilities when trying to restore.

5. Corrupted iptables:

   • If the iptables command or its associated modules are corrupted or improperly installed, it could cause this issue.

Troubleshooting Steps:

1. Check Modules:

   • Ensure that all necessary modules are loaded. You can check which modules are available using lsmod. 

2. Verify Rules:

   • Inspect the rules file that you are trying to restore. Look for any references to modules or options that might not be available on your system. You can try simplifying the rule set to identify the problematic rule.

3. Test iptables Command:

   • Manually input one of the rules that might be causing the issue to see if iptables gives a more detailed error message. For example, try running iptables -A <rule> directly to see what happens.

4. Check Kernel Compatibility:

   • Ensure that the kernel version and iptables version are compatible. If you’ve recently upgraded the kernel, the iptables modules might not be updated.

5. Update/Reinstall iptables:

   • If you suspect that iptables itself is corrupted or outdated, try updating or reinstalling iptables.

6. Check the Exact Error Line:

   • To get more information about the specific rule causing the issue, you can use the --test option when running iptables-restore:
     bash

     iptables-restore --test < /path/to/your/rules/file
   • This will provide more detailed output on where the error occurs.

7. Consult System Logs:

   • Check system logs (e.g., /var/log/syslog or /var/log/messages) for any additional details that might give more context to the failure.

By systematically going through these steps, you should be able to identify and resolve the issue causing the iptables-restore to fail with exit status 4.