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ethtool(8) - Display or change ethernet card settings

This command is found on newer versions of linux. It lets you query and set various network interface (NIC) parameters like speed, duplex and autonegotiation.

Here is an example of querying the eth0 parameters.

jetson:~> sudo ethtool eth0
Settings for eth0:
       Supported ports: [ MII ]
       Supported link modes:   10baseT/Half 10baseT/Full 
                               100baseT/Half 100baseT/Full 
                               1000baseT/Half 1000baseT/Full 
       Supports auto-negotiation: Yes
       Advertised link modes:  Not reported
       Advertised auto-negotiation: No
       Speed: 100Mb/s
       Duplex: Full
       Port: Twisted Pair
       PHYAD: 1
       Transceiver: internal
       Auto-negotiation: off
       Supports Wake-on: g
       Wake-on: d
       Current message level: 0x000000ff (255)
       Link detected: yes

Here is an example showing how to set a NIC to 100baseT/Full - turning autonegotiate off also.

jetson:~> sudo ethtool -s eth0 speed 100 duplex full autoneg off

The examples shown above were used on an Ubuntu box. Red Hat and it's variants can take ethtool arguments passed in via the ifcfg files. For instance, the following line could appear in /etc/sysconfig/network-scripts/ifcfg-eth0. This would ensure the values are set persistently.

ETHTOOL_OPTS="speed 100 duplex full autoneg off"

ethtool can be used to query the NIC for version and driver info!

mdf@sushi ~ $ sudo ethtool -i eth0
driver: e1000e
version: 1.0.2-k4
firmware-version: 0.5-1
bus-info: 0000:02:00.0