Linux change the speed and duplex settings of an Ethernet card

Task: Get speed and other information for eth0

Type following command:
# ethtool eth0Output:

Settings for eth0:
Supported ports: [ TP MII ]
Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full
Supports auto-negotiation: Yes 
Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full
Advertised auto-negotiation: Yes 
Speed: 100Mb/s 
Duplex: Full 
Port: MII 
PHYAD: 32 
Transceiver: internal 
Auto-negotiation: on 
Supports Wake-on: pumbg 
Wake-on: d 
Current message level: 0x00000007 (7) 
Link detected: yes

Task: Change the speed and duplex settings

Setup eth0 negotiated speed with ethtool# ethtool -s eth0 speed 100 duplex full
# ethtool -s eth0 speed 10 duplex halfTo make these settings permanent you need to create a shell script and call from /etc/rc.local(Red Hat) or if you are using Debian create a script into the directory /etc/init.d/ directory and run update-rc.d command to update the script.

Read man page of ethtool for more information.