Disables auto-upping due to `[ifupdown] managed=true` even if network-manager is not installed

Are you sure that this is the case? This does not appear to be documented in the NetworkManager.conf manpage. By what mechanism does ifupdown refrain from touching these interfaces?

By this mechanism:

=== ifupdown.nw ===

<<main functions>>=
static int auto_disabled() {
       static int initialized = 0;
       static int auto_up_disabled = 0;

       if (!initialized) {
               dictionary *ini_dict;
               initialized = 1;

               ini_dict = iniparser_load (nm_system_settings);
               if (ini_dict) {
                       int managed = iniparser_getboolean (ini_dict, "ifupdown:managed", 0);
                       auto_up_disabled = managed ? 1 : 0;
                       iniparser_freedict (ini_dict);
                       ini_dict = 0;
               } else {
                       auto_up_disabled = 0;
               }
       }

       return auto_up_disabled;
}
@

Thanks! Am I missing some documentation of this behaviour somewhere, or is it really only documented in the code and in a printed warning on execution? It seems to me that it is essential that this should be documented, because it's an interaction that one wouldn't expect. Is this a separate bug?

It was mentioned in the changelog.

ifupdown (0.6.8ubuntu10) intrepid; urgency=low
  https://lists.ubuntu.com/archives/ubuntu-devel/2008-October/026656.html:
  * stop ifupdown to auto-up/down interfaces if network-manager's
    ifupdown plugin is in managed=true mode
    [...]
 -- Alexander Sack <email address hidden> Thu, 09 Oct 2008 16:46:47 +0200

The feature should certainly be documented in interfaces(5) and/or ifup(8) too.

Thanks Thomas. I've filed bug 1188169.