upgrade-series complete fails bionic->focal

[Jake Hill]

First noticed in ntp-39 and still present in ntp-41, trying to do-release-upgrade from bionic to focal;

(osc) routergod@juju:~/openstack$ juju upgrade-series 1 complete
machine-1 complete phase started
machine-1 started unit agents after series upgrade
ceph-osd/0 post-series-upgrade hook running
ceph-osd/0 post-series-upgrade completed
nova-compute/0 post-series-upgrade hook running
nova-compute/0 post-series-upgrade completed
neutron-openvswitch/2 post-series-upgrade hook running
neutron-openvswitch/2 post-series-upgrade completed

That is all. In /var/log/juju/unit-ntp-3.log on machine 1 I find;

2020-08-11 18:41:19 DEBUG start Could not find platform independent libraries <prefix>
2020-08-11 18:41:19 DEBUG start Could not find platform dependent libraries <exec_prefix>
2020-08-11 18:41:19 DEBUG start Consider setting $PYTHONHOME to <prefix>[:<exec_prefix>]
2020-08-11 18:41:19 DEBUG start Fatal Python error: Py_Initialize: Unable to get the locale encoding
2020-08-11 18:41:19 DEBUG start ModuleNotFoundError: No module named 'encodings'
2020-08-11 18:41:19 DEBUG start
2020-08-11 18:41:19 DEBUG start Current thread 0x00007f20e72e5740 (most recent call first):
2020-08-11 18:41:20 ERROR juju.worker.uniter.operation runhook.go:136 hook "start" (via explicit, bespoke hook script) failed: signal: aborted (core dumped)
2020-08-11 18:41:20 ERROR juju.worker.dependency engine.go:671 "uniter" manifold worker returned unexpected error: executing operation "run start hook": hook failed

[Jake Hill (routergod)]

Following the procedure suggested in https://bugs.launchpad.net/charm-sysconfig/+bug/1867929/comments/3 it appears that I can resolve the situation as follows (this example a different machine than the report above);

root@ostmpv03:~# CHARM_DIR=/var/lib/juju/agents/unit-ntp-0/charm
root@ostmpv03:~# rm -rf $CHARM_DIR/wheelhouse/.bootstrapped $CHARM_DIR/../.venv
root@ostmpv03:~# JUJU_CHARM_DIR=$CHARM_DIR PYTHONPATH=$CHARM_DIR/lib python3 -c 'import charms.layer.basic; charms.layer.basic.bootstrap_charm_deps()'

Hope that helps!