The "got duplicate tcp line" error message in the netstat command is usually seen when there are multiple entries for the same TCP connection in the output of the netstat command. This can be caused by a number of factors, such as a problem with the TCP stack or a bug in the netstat command.
To fix this error, you can try the following steps:
systemctl restart network
Check for kernel updates: Another possible cause of the error is a bug in the kernel. You can check for updates to the kernel and install any available updates to see if this resolves the issue.
Check for errors in the TCP stack: If the problem persists after trying the above steps, it could be due to a problem with the TCP stack. You can use the tcpdump command to capture packets on the network and see if there are any errors or issues with the TCP stack.
Check for malware: If the problem persists after trying the above steps, it could be due to malware on the system. You can use a malware scanning tool to scan your system for malware and remove any infections.
You can find more information about troubleshooting the "got duplicate tcp line" error and other issues with the netstat command in the netstat man page by running man netstat in a terminal.