Purge of maas-common packages sometimes fails due to process using maas user

Hey Jason,

I'm unable to reproduce. Any chance you can gather the output of:

ps faux | grep rackd
ps faux | grep regiond

Also, sudo service maas-rackd status & sudo service maas-regiond status if possible.

I was able to reproduce this. It seems its because MAAS leaves linguering processes that still run under the 'maas' user causing this:

Purging configuration files for libipmiconsole2 (1.4.11-1.1ubuntu4.1) ...
Purging configuration files for maas-common (2.5.0~beta2-7253-gbf4047776-0ubuntu1~18.04.1) ...
Removing user `maas' ...
Warning: group `maas' has no more members.
userdel: user maas is currently used by process 7083
/usr/sbin/deluser: `/usr/sbin/userdel maas' returned error code 8. Exiting.
/usr/sbin/delgroup: `maas' still has `maas' as their primary group!
userdel: user maas is currently used by process 7083
/usr/sbin/deluser: `/usr/sbin/userdel maas' returned error code 8. Exiting.
/usr/sbin/delgroup: `maas' still has `maas' as their primary group!
dpkg: error processing package maas-common (--purge):
 installed maas-common package post-removal script subprocess returned error exit status 128
Errors were encountered while processing:
 maas-common
E: Sub-process /usr/bin/dpkg returned an error code (1)
ubuntu@maas00:~$ ps faux | grep maas
ubuntu 28095 0.0 0.0 13136 1040 pts/1 S+ 18:46 0:00 | \_ grep --color=auto maas
ubuntu 16674 0.0 0.0 6212 836 pts/3 S+ Sep19 0:04 | \_ tail -f /var/log/maas/rackd.log
maas 7083 0.0 0.0 581136 10156 ? Ssl 14:41 0:07 /usr/sbin/rsyslogd -n -f /var/lib/maas/rsyslog.conf -i /var/lib/maas/rsyslog.pid
maas 7246 0.0 0.0 4628 740 ? Ss 14:41 0:00 /bin/sh -c exec /usr/sbin/rackd 2>&1 | tee -a $LOGFILE
maas 7248 1.4 0.5 719460 88916 ? Sl 14:41 3:26 \_ /usr/bin/python3 /usr/sbin/rackd
maas 7537 0.1 0.3 139880 51448 ? S 14:41 0:27 | \_ /usr/bin/python3 /usr/lib/maas/maas-common observe-beacons eno1
root 7791 0.0 0.0 64104 3564 ? S 14:41 0:00 | | \_ sudo -n /usr/lib/maas/beacon-monitor eno1
maas 7540 0.1 0.3 139880 51412 ? S 14:41 0:23 | \_ /usr/bin/python3 /usr/lib/maas/maas-common observe-beacons usb0
root 7793 0.0 0.0 64104 3628 ? S 14:41 0:00 | | \_ sudo -n /usr/lib/maas/beacon-monitor usb0
maas 7890 0.0 0.3 139624 51440 ? S 14:41 0:03 | \_ /usr/bin/python3 /usr/lib/maas/maas-common observe-arp eno1
root 7917 0.0 0.0 64104 3632 ? S 14:41 0:00 | | \_ sudo -n /usr/lib/maas/network-monitor eno1
maas 7891 0.0 0.3 139624 51324 ? S 14:41 0:01 | \_ /usr/bin/python3 /usr/lib/maas/maas-common observe-arp usb0
root 7921 0.0 0.0 64104 3568 ? S 14:41 0:00 | | \_ sudo -n /usr/lib/maas/network-monitor usb0
maas 7892 0.0 0.3 139624 51296 ? S 14:41 0:01 | \_ /usr/bin/python3 /usr/lib/maas/maas-common observe-mdns
maas 7916 0.0 0.0 35180 2952 ? S 14:41 0:00 | | \_ /usr/bin/avahi-browse --all --resolve --no-db-lookup --parsable --no-fail
maas 7249 0.0 0.0 6180 604 ? S 14:41 0:00 \_ tee -a /var/log/maas/rackd.log

ubuntu@maas00:~$ dpkg -l | grep maas-rack-controller
ubuntu@maas00:~$ sudo service maas-regiond stop
Failed to stop maas-regiond.service: Unit maas-regiond.service not loaded.

to provide more context, seems that maas-rack-controller is being purged first:

Please, remove /var/spool/squid yourself.
Purging configuration files for bind9 (1:9.11.3+dfsg-1ubuntu1.2) ...
dpkg: warning: while removing bind9, directory '/var/cache/bind' not empty so not removed
dpkg: warning: while removing bind9, directory '/etc/bind' not empty so not removed
Purging configuration files for maas-region-controller (2.5.0~beta2-7253-gbf4047776-0ubuntu1~18.04.1) ...
Purging configuration files for maas-rack-controller (2.5.0~beta2-7253-gbf4047776-0ubuntu1~18.04.1) ...
nginx.service is a disabled or a static unit, not starting it.
dpkg: warning: while removing maas-rack-controller, directory '/var/log/maas/http' not empty so not removed
dpkg: warning: while removing maas-rack-controller, directory '/var/lib/maas/http' not empty so not removed
Purging configuration files for avahi-daemon (0.7-3.1ubuntu1.1) ...
rmdir: failed to remove '/var/run/avahi-daemon': Directory not empty
Purging configuration files for python3-twisted (17.9.0-2) ...
Purging configuration files for freeipmi-common (1.4.11-1.1ubuntu4.1) ...
Purging configuration files for isc-dhcp-server (4.3.5-3ubuntu7) ...
Purging configuration files for libvirt-clients (4.0.0-1ubuntu8.5) ...
dpkg: warning: while removing libvirt-clients, directory '/etc/libvirt' not empty so not removed
Purging configuration files for dbconfig-common (2.0.9) ...
dpkg: warning: while removing dbconfig-common, directory '/var/log/dbconfig-common' not empty so not removed
dpkg: warning: while removing dbconfig-common, directory '/etc/dbconfig-common' not empty so not removed
Purging configuration files for libipmiconsole2 (1.4.11-1.1ubuntu4.1) ...
Purging configuration files for maas-common (2.5.0~beta2-7253-gbf4047776-0ubuntu1~18.04.1) ...

This should stop all services

Ok, from the looks of it, systemd may not be killing the processes or something in MAAS is preventing from that being the case:

https://pastebin.ubuntu.com/p/svfgrQDCSf/