Linux CentOS how to force 1000megabits ifconfig eth0
ethtool -s eth0 speed 1000 duplex full autoneg off
In my case it's peth0.
Other commands:
lspci |grep Ethernet
dmesg |grep eth0
ethtool eth0
ethtool -k eth0
ethtool -S eth0
To make the changes permanent, edit
/etc/sysconfig/network-scripts/ifcfg-eth0
add
ETHTOOL_OPTS="speed 1000 duplex full autoneg off"
Ref:
http://www.cyberciti.biz/tips/howto-linux-add-ethtool-duplex-settings-permanent.html
http://www.centos.org/modules/newbb/viewtopic.php?topic_id=19544&forum=40
http://www.dslreports.com/forum/r22221731-Gigabit-NIC-only-working-as-100meg-in-CentOS
Adrenalin's Experience 
Online video telephones operate fantastic primarily cable television along with T1 connections. The digital subscriber line relationship could be more difficult, because the distribute speed in the dsl service can often be sluggish …dsl
hi, is that valid for red hat 4.8?
This doesn’t work for me, I know for a fact I have 1000bit cards on both my pc and router (Cisco). Running Kali Linux if it makes a difference.
“””
edge-case@HIVE-PC-01:~$ sudo ethtool -s eth0 speed 1000 duplex full autoneg off
Cannot set new settings: Invalid argument
not setting speed
not setting duplex
not setting autoneg
“””