debian set eth0 autoneg off speed 1000 duplex full: Invalid argument
Solution 1:
Did you try,
sudo ethtool -s eth0 speed 1000 duplex full autoneg off
but I support Zoredache's comment, you should probably not be forcing the link speed, and unless it doesn't work without it, you should leave the machine set to autoneg, and ensure the network port is set to the right speed.
Solution 2:
Autonegotiation is a requirement for using 1000BASE-T according to Section 28D.5 of IEEE 802.3-2002 specification, so you cannot disable autonegotiation with 1000BASE-T.
Try -
sudo ethtool -s eth0 speed 1000 duplex full autoneg on