release upgrade to wily freezes on dpkg's first configuration file question

[Björn Schließmann]

Started the graphical upgrade to wily; packages downloaded and apt started to install. After a while, the UI froze (no redraw). in /var/log/dist-upgrade/apt-term.log, the following is displayed:

=====
[...]
Neue Version der Konfigurationsdatei /etc/init.d/mountnfs-bootclean.sh wird installiert ...
Neue Version der Konfigurationsdatei /etc/init.d/mountdevsubfs.sh wird installiert ...
Neue Version der Konfigurationsdatei /etc/init.d/mountkernfs.sh wird installiert ...

Konfigurationsdatei »/etc/init.d/ondemand«
 ==> Geändert (von Ihnen oder von einem Skript) seit der Installation.
 ==> Paketverteiler hat eine aktualisierte Version herausgegeben.
   Wie möchten Sie vorgehen? Ihre Wahlmöglichkeiten sind:
    Y oder I : Die Version des Paket-Betreuers installieren
    N oder O : Die momentan installierte Version beibehalten
       D : Die Unterschiede zwischen den Versionen anzeigen
       Z : Eine Shell starten, um die Situation zu begutachten
 Der Standardweg ist das Beibehalten der momentanen Version.
*** ondemand (Y/I/N/O/D/Z) [Vorgabe=N] ?
=====

Normally, an interactive dialogue is supposed to open, but no such thing happened.

pstree excerpt:
         ├─wily(4352)───dpkg(17611)

strace shows dpkg hanging on reading from stdin:
# strace -p 17611
Process 17611 attached
read(0, ^CProcess 17611 detached
 <detached ...>
#

Writing "I\n" to /proc/17611/fd/0 did appear in the log, but didn't help (dpkg still stuck). Had to kill it and continue the upgrade on foot.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: ubuntu-release-upgrader-core 1:15.04.14.3
ProcVersionSignature: Ubuntu 3.19.0-49.55-generic 3.19.8-ckt12
Uname: Linux 3.19.0-49-generic x86_64
NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
ApportVersion: 2.17.2-0ubuntu1.8
Architecture: amd64
CrashDB: ubuntu
Date: Sat Feb 20 12:18:42 2016
InstallationDate: Installed on 2012-01-03 (1508 days ago)
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111012)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: dist-upgrade
UpgradeStatus: Upgraded to wily on 2016-02-20 (0 days ago)

[Björn Schließmann (b-schliessmann)]

Well, just killing dpkg continued the upgrade, I'll write again for how long. The upgrader UI was still frozen though.

[Björn Schließmann (b-schliessmann)]

After a while, dpkg and the wily process got stuck again. By manually emptying the pipe wily was writing to, dpkg continued. UI still frozen.

[Björn Schließmann (b-schliessmann)]

The Upgrader UI quit after a standstill while asking about a configuration file like above. Killing dpkg caused the upgrader to terminate. Had to complete the upgrade on foot from there (manually using dpkg).