mii-tool is an older Linux command used to check the link status and speed of some Ethernet interfaces. On modern systems, ethtool is usually preferred, but mii-tool may still appear on older servers.
Check an interface
sudo mii-tool eth0The output can show whether the link is up and what speed or duplex mode is detected.
Modern alternative
sudo ethtool eth0Use ip link to find current interface names such as eth0, ens33 or enp0s3.
ip link