Bug#730177: I can't really understand whats happening.

[John Hughes]

The only difference I can see between the sessions that work (with 
/usr/local unmounted) and those that fail (with /usr/local nfs mounted, 
so all accesses get EACCES) is that when things go well I see the message:

gnome-session[2575]: DEBUG(+): Detected that screensaver has appeared on the bus


But when things fail that message is never printed.

The "Detected" message seems to be printed in response to 
["/usr/bin/dbus-launch", "--exit-with-session", 
"/usr/bin/gnome-session", "--autostart", 
"/usr/share/gdm/greeter/autostart", "--debug"] receiving this message:

recvmsg(8, {msg_name(0)=NULL, msg_iov(1)=[{"l\4\1\1-\0\0\0f\0\0\0\211\0\0\0\1\1o\0\25\0\0\0/org/freedesktop/DBus\0\0\0\2\1s\0\24\0\0\0org.freedesktop.DBus\0\0\0\0\3\1s\0\20\0\0\0NameOwnerChanged\0\0\0\0\0\0\0\0\7\1s\0\24\0\0\0org.freedesktop.DBus\0\0\0\0\10\1g\0\3sss\0\0\0\0\0\0\0\0\25\0\0\0org.gnome.ScreenSaver\0\0\0\0\0\0\0\0\0\0\0\4\0\0\0:1.7\0"..., 2048}], msg_controllen=0, msg_flags=MSG_CMSG_CLOEXEC}, MSG_CMSG_CLOEXEC) = 205


This message was sent by a child of gdm3:

sendmsg(12, {msg_name(0)=NULL, msg_iov(2)=[{"l\4\1\1-\0\0\0f\0\0\0\211\0\0\0\1\1o\0\25\0\0\0/org/freedesktop/DBus\0\0\0\2\1s\0\24\0\0\0org.freedesktop.DBus\0\0\0\0\3\1s\0\20\0\0\0NameOwnerChanged\0\0\0\0\0\0\0\0\7\1s\0\24\0\0\0org.freedesktop.DBus\0\0\0\0\10\1g\0\3sss\0\0\0\0\0\0\0\0", 160}, {"\25\0\0\0org.gnome.ScreenSaver\0\0\0\0\0\0\0\0\0\0\0\4\0\0\0:1.7\0", 45}], msg_controllen=0, msg_flags=0}, MSG_NOSIGNAL)           = 205


But basically I get lost in a twisty little maze of sendmsgs all alike.

I've tried debugging the problem using fuse, and can replicate it by 
simply making /usr/local a fuse filesystem that returns EACCES for all 
operations.

Any ideas about how to go forwards?