Linux change the speed and duplex settings of an Ethernet card

Task: Get speed and other information for eth0

Type following command as root user:
# 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
Or use mii-tool command as follows:
# mii-tool eth0
Output:

eth0: negotiated 100baseTx-FD flow-control, link ok

Task: Change the speed and duplex settings

Setup eth0 negotiated speed with mii-tool
Disable autonegotiation, and force the MII to either 100baseTx-FD, 100baseTx-HD, 10baseT-FD, or 10baseT-HD:
# mii-tool -F 100baseTx-HD
# mii-tool -F 10baseT-HD
Setup eth0 negotiated speed with ethtool
# ethtool -s eth0 speed 100 duplex full
# ethtool -s eth0 speed 10 duplex half

To 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.