Comment 7 for bug 1531070

Regarding the comment:

"As an aside, I'm not sure what commands you ran within synaptic to get your system in this situation, but recovering from a manually-installed package's unsatisfiable dependencies should not involve installing packages from xenial onto a trusty system."

I installed the .deb for gnome-inform7 from http://sourceforge.net/projects/gnome-inform7/ - although I can't see anything that says it is for a specific Debian/Ubuntu release. Could that have been produced (a year ago) for a Xenial release?

Other than that, all I did was ask Synaptic to mark all installed packages that had updates available, and then to install them. I certainly didn't poke about in the guts and do anything weird.

Here are the exact commands I used:

# dpkg -i gnome-inform7_6L38-0ubuntu1_i386.deb
# apt-get update
# apt-get check
# apt-get install empathy
# apt-get install libqt5webkit5-qmlwebkitplugin
# apt-get -f install
# synaptic
# apt-get install synaptic
# apt-get -f install

BTW, the apt-get check resulted in this:

# apt-get check
Reading package lists... Done
Building dependency tree
Reading state information... Done
You might want to run 'apt-get -f install' to correct these.
The following packages have unmet dependencies:
 account-plugin-aim : Depends: empathy (= 3.8.6-0ubuntu9.2) but it is not installed
                      Depends: mcp-account-manager-uoa but it is not installed
 account-plugin-jabber : Depends: empathy (= 3.8.6-0ubuntu9.2) but it is not installed
                         Depends: mcp-account-manager-uoa but it is not installed
 account-plugin-salut : Depends: empathy (= 3.8.6-0ubuntu9.2) but it is not installed
                        Depends: mcp-account-manager-uoa but it is not installed
[...]

Which is why I then tried to apt-get install empathy, but it gave me warnings like this:

# apt-get install empathy
Reading package lists... Done
Building dependency tree
Reading state information... Done
You might want to run 'apt-get -f install' to correct these:
The following packages have unmet dependencies:
 account-plugin-aim : Depends: empathy (= 3.8.6-0ubuntu9.2) but 3.12.11-0ubuntu1 is to be installed
                      Depends: mcp-account-manager-uoa but it is not going to be installed
[...]
 vlc-nox : Depends: libgnutls28 (>= 3.2.10-0) but it is not installed
 zeitgeist-core : Depends: libxapian22 but it is not installed
E: Unmet dependencies. Try using -f.

I tried this, just to see what would happen if I tried t oupdate one of the missing packages:

# apt-get install libqt5webkit5-qmlwebkitplugin
Reading package lists... Done
Building dependency tree
Reading state information... Done
You might want to run 'apt-get -f install' to correct these:
The following packages have unmet dependencies:
 account-plugin-aim : Depends: empathy (= 3.8.6-0ubuntu9.2) but it is not going to be installed
[...]

Then tried:

# apt-get -f install
Reading package lists... Done
Building dependency tree
Reading state information... Done
Correcting dependencies... Done
The following packages were automatically installed and are no longer required:
  dconf-gsettings-backend:i386 gcc-4.8-base:i386 libcgmanager0:i386
  libdconf1:i386 libebook-1.2-16 libebook-contacts-1.2-2 libedata-book-1.2-25
[...]
Preparing to unpack .../libc-bin_2.21-0ubuntu5_amd64.deb ...
Unpacking libc-bin (2.21-0ubuntu5) over (2.19-0ubuntu6.6) ...
Processing triggers for man-db (2.6.7.1-1ubuntu1) ...
Errors were encountered while processing:
 /var/cache/apt/archives/plymouth_0.9.2-3ubuntu8_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

When I then tried to run synaptic, I found it was gone (from the Gnome menus, and from the system, entirely).

From what people have said here, it sounds like Xenial is a later release than Trusty, and somehow my Ubuntu 14.04 started installing packages from Xenial, is that it? Certainly, that was not my intention.

Things seems to be largely okay (though Samba has begun segfaulting). I certainly didn't force any updates, AFAIK, and saw no warnings about anything I was doing as being not recommended, so I'm still a bit confused about
a) Just what started the problem
b) How dangerous a situation I'm in now, and
c) What I should do to try to recover.