[ixpmanager] Grapher not working after distupgrade

[Nick Hilliard]

> This can happen if you run a dist-upgrade on ubuntu with the 
> ppa:ondrej/php repository enabled.  This PPA is necessary for ubuntu 
> 18.04 and previous versions.

... this brings up the question of general operating system upgrades. 
IXP Manager works well on ubuntu 20.04, which is the platform we'd 
generally advise people to use these days.

If you're upgrading from 16.04 or 18.04 to 20.04, ppa:ondrej/php is no 
longer required, so if you run an upgrade to 20.04, we'd suggest looking 
at the option of cleaning out the old PHP versions and fully removing 
the sury PPA. This would also be a good time to think about cleaning out 
any old PHP versions (see previous email).

After upgrading to 20.04, the dependencies will still be present on the 
system, but the packages will be non-upgradeable because the PPA is 
disabled during the upgrade.  You can remove it completely using:

# add-apt-repository ppa:ondrej/php
# apt install ppa-purge
# ppa-purge ppa:ondrej/php

I.e. it needs to be temporarily reinstalled in order to deinstall it 
properly.

This PPA is invasive in terms of low-level system libraries, and 
sometimes it leaves the sury version of libsodium23 behind after the 
rest has been removed, e.g:

> ixpmanager:/home/nick# dpkg -l | grep sury
> ii  libsodium23:amd64                      1.0.17-0.1+ubuntu18.04.1+deb.sury.org+1                  amd64        Network communication, cryptography and signaturing library
> ixpmanager:/home/nick#

If this happens, you can leave it there or attempt to remove it and use 
system libs instead.  If you want to remove it, then use:

# apt install --reinstall libsodium23

If it makes noise about removing dependencies to complete this 
transaction, then make a note of what packages were removed and manually 
reinstall them.

Obviously be careful with all of the above because there's plenty of 
scope in there to break things, i.e. make sure your backups are in good 
shape, etc.  Worse case, a manual install will resolve most problems, 
but it is important not to end up with multiple PHP versions installed 
on your system, because they will fight with each other.

There are comparable (but different) package dependency problems on all 
other platforms we use routinely (e.g. freebsd / centos / etc), so 
package dependency problems are really a question of which style you're 
most comfortable handling rather than trying to avoid them outright.

Obviously migrating ixp-m config to clean O/S installations avoids most, 
if not all of these problems.

Nick