To set the interface speed, duplex or auto negotiation on Linux system boot up (make settings permanent), you need edit /etc/sysconfig/network-scripts/ifcfg-eth0 file for eth0 interface. This file used by Red Hat enterprise Linux, Fedora core, Cent Os etc.
Open the file:
Append following line or add the following line
Save and close the file.
Finally restart the network service
You can check the current network interface speed using the below command