Determine Linux ethernet interface speed and duplex

Determine the auto-negotiated Ethernet connection speed and duplex using the mii-tool command.

Running the following command as superuser with no options will generate basic information about all of the Ethernet interfaces on the computer:

mii-tool

The resulting output will look something like:

eth0: negotiated 100baseTx-FD, link ok

This output shows one interface (eth0) which was auto-negotiated to 100 Mbps (100baseTx) and full duplex (FD).

Adding the -v option to the command generates verbose output and will tell you more about the interface including the manufacturer and model (if available) and the interface’s capabilities.