Linux change the speed and duplex settings of an Ethernet card

Task: Get speed and other information for eth0

# ethtool eth0

Output:

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.