How does one check the speed and duplex on a computer running Redhat?
A simple tool (if installed) called ethtool will give such information.
You will have to use a root to get this information.
# ethtool eth0
Settings for eth0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
Advertised auto-negotiation: Yes
Port: Twisted Pair
Supports Wake-on: g
Link detected: yes
ethtool can also make changes but I have not had a need to do that yet.