NetworkManager is a set of co-operative tools that make networking simple and
straightforward. Whether WiFi, wired, 3G, or Bluetooth, NetworkManager allows
you to quickly move from one network to another.

It has two components:

1. a system level service which manages connections and reports network changes
2. a graphical desktop applet which allows the user to manipulate network
   connections. The nmcli tool provides similar functionality on the command
   line.


system connections and security
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In NetworkManager version 0.9, network connections are stored as keyfiles in
the /etc/NetworkManager/system-connections/ directory.
When creating new wireless or wired connections, they are by default
system-owned (i.e. available to everyone) and the secrets (e.g WPA-PSK or WEP
key) are stored as plain text in the corresponding connection configuration
file. The advantage of system connections is, that they can be active before a
user has logged in and they are active across user sessions.
Modifying or creating such system-owned connections requires admin privileges.
To avoid prompts for the root/admin password, NetworkManager ships a PolicyKit
configuration file which grants everyone in group "netdev" or "sudo" the
privilege to modify a system connection without prior authentication. Adding a
user to group sudo grants him root-like privileges though. If that is not
wanted, you can choose to add him to group netdev instead.
If the user should not have the privilege to add and modify system connections
don't add him to either groups.
In that case, the user clients (like nm-applet) will default to creating
user-owned connections where the secrets are stored in the user keyring.
VPN and 3G type connections are by default also user-owned.

For more information see NetworkManager.conf(5) or
http://live.gnome.org/NetworkManager/SystemSettings

The keyfile specification is available at
https://developer.gnome.org/NetworkManager/0.9/ref-settings.html

unmanaged devices and /etc/network/interfaces
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Network devices which are configured in /etc/network/interfaces will typically
be managed by ifupdown. Such devices will by default be marked as "unmanaged"
in NetworkManager.

You can tell NetworkManager to read and use the network configuration from
/etc/network/interfaces by editing /etc/NetworkManager/NetworkManager.conf
and changing the configuration as follows:

  [ifupdown]
  managed=true

After modifying /etc/NetworkManager/NetworkManager.conf or
/etc/network/interfaces you need to restart the NetworkManager service via
"service network-manager restart".

It needs to be considered though that the network interface will also still be
managed by ifupdown. This can lead to unexpected behaviour if two network
configuration systems manage the same device.

If you want to have a network interface managed by NetworkManager it is thus
recommended to manually remove any configuration for that interface from
/etc/network/interfaces.