NetworkManager attempts to keep an active network connection available at all times.
NetworkManager is composed of two parts:
A daemon running as root (network-manager).
NetworkManager will only handle interfaces not declared in /etc/network/interfaces (see README file).
The features of NetworkManager are described on its homepage.
Make sure you read the fine manual:
interfaces(5) man page
NetworkManager in Squeeze
Wired Networks are Unmanaged
Unmanaged devices means NetworkManager doesn't handle those devices. This occurs when two conditions are met:
The file /etc/network/interfaces contains anything about the interface, even:
allow-hotplug eth0 iface eth0 inet dhcp
And /etc/NetworkManager/nm-system-settings.conf contains:
[main] plugins=ifupdown,keyfile [ifupdown] managed=false
To allow NetworkManager to manage wired interfaces, either:
Comment the relevant lines in /etc/network/interfaces to restore the behavior experienced in Lenny.
Set managed=true in nm-system-settings.conf if you want network-manager to handle interfaces that are declared in /etc/network/interfaces (you need to kill nm-system-settings)
Restart network-manager or X is not enough. It seems you must reboot your computer in order to apply your changes.
(Click on the Comments to show Syslog error's error message related to this problem):
"Auto Ethernet" and "Auto eth0"
Auto Ethernet means "Select and Ethernet interface automatically"
Auto eth0 means autconfigure the eth0 interface.
- Q. How do I configure a static IP address (for a server, etc) ?
A) Configure /etc/network/interfaces.
- Q. Why can't I see NetworkManager with my new user account ?
A) Make sure human users are in the netdev group (see /usr/share/doc/network-manager-gnome/README.Debian).
http://projects.gnome.org/NetworkManager/users/ - Project homepage and GNOME front-end (with some documentation);
http://live.gnome.org/NetworkManager - Various resources (FAQ, mailing list...)
http://en.opensuse.org/Projects/KNetworkManager - KDE front-end
http://vidner.net/martin/software/cnetworkmanager/ - Command line interface