Created attachment 910889 [details]
screenshot illustrating the issue (in a VM)

comparing a 2014-05-12 boot.iso (which is my current 'known good' one) and one that shows this issue, I note that right after "Starting window manager, pid XXXX" in anaconda.log, there is:

Problems running the window manager: [Errno 0] SIGCHLD caught when trying to start the X server.

in the bugged case. That's not there in the working case.

In the bugged case, the pid listed in the "Starting window manager, pid XXXX" message does not show up in 'ps aux' output. In the working case, the pid listed in that message is the pid of the anaconda process itself (the actual window manager, metacity, has a higher pid). In the bugged case, there is an anaconda process running, but with a different pid - in the test I just ran, the message referred to 'pid 1085', while the anaconda process has pid 1001.

Yeah, metacity's not starting because there's no libcanberra-gtk3.so.0, which I think is because this needs to be applied:

diff --git a/share/runtime-cleanup.tmpl b/share/runtime-cleanup.tmpl
index c7d345e..5150172 100644
--- a/share/runtime-cleanup.tmpl
+++ b/share/runtime-cleanup.tmpl
@@ -224,7 +224,7 @@ removefrom libbonobo /usr/${libdir}/bonobo/monikers/*
 removefrom libbonobo /usr/${libdir}/orbit-2.0/Bonobo_module.so
 removefrom libcanberra /usr/${libdir}/libcanberra-*
 removefrom libcanberra-gtk2 /usr/${libdir}/gtk-2.0/*
-removefrom libcanberra-gtk3 /usr/bin/* /usr/${libdir}/*
+removefrom libcanberra-gtk3 /usr/bin/*
 removefrom libcap /usr/sbin/*
 removefrom libconfig /usr/${libdir}/libconfig++*
 removefrom libcroco /usr/bin/*

At least, running scripts/makeupdates -a ~/libcanberra-gtk3-0.30-6.fc21.x86_64.rpm results in an updates.img that makes my boot.iso work.

I believe http://koji.fedoraproject.org/koji/buildinfo?buildID=539896 fixes this: closing (can re-open if it's not resolved in the nightlies, once that util-linux bug is fixed too).