MySQL Bugs: #91405: Can't update/remove mysql on host system if you have running mysql in docker

Bug #91405	Can't update/remove mysql on host system if you have running mysql in docker
Submitted:	25 Jun 2018 10:20	Modified:	7 May 2019 17:58
Reporter:	Evgeniy Patlan (OCA)	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Packaging	Severity:	S2 (Serious)
Version:	8.0.1, 5.7.22	OS:	Any
Assigned to:	Lars Tangvald	CPU Architecture:	Any

Description:
If you have running mysql in docker and on host system it is not possible to update/remove mysql on host system

===================
dpkg: error processing package mysql-community-server (--purge):
 subprocess installed post-removal script returned error exit status 1
===================

===================
ubuntu@ubuntu-xenial:~$ ps -ef | grep "/usr/sbin/mysqld"
999      15261 15207  0 09:28 ?        00:00:00 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib64/mysql/plugin --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/lib/mysql/mysql.sock
ubuntu   15991  1747  0 09:53 pts/0    00:00:00 grep --color=auto /usr/sbin/mysqld
===================

So one of these processes is running in docker and another one on host machine.

Command `ps -ef | grep "/usr/sbin/mysqld"` is a part of postrm and preinst script 

It is in procedure: get_pcount

How to repeat:
Install mysql, install docker, create container with running mysql in it, try to update/remove mysql on host system

Suggested fix:
There are several ways to fix:
- use Debian's start-stop-daemon infrastructure
- detect if it is docker: for example
  * user 999
  * detect if it is docker from mount info of the preocess
===============
/proc/15261/task/15261/mounts:overlay / overlay rw,relatime,lowerdir=/var/lib/docker/overlay2/l/523HPF6XTNGXSEIVPXNHRDFEWQ:/var/lib/docker/overlay2/l/F2FQL65M4G7IBRHOYH36T2IZXX:/var/lib/docker/overlay2/l/OUWX435LOMCHECGN6SSFDTKQ2P,upperdir=/var/lib/docker/overlay2/30b56fbfbfabba73f03df67c83d4497f86015baeebbe53c72bce42db332fe08a/diff,workdir=/var/lib/docker/overlay2/30b56fbfbfabba73f03df67c83d4497f86015baeebbe53c72bce42db332fe08a/work 0 0
===============

Hi!

Thanks for your report!

Can you explain why you what to upgrade MySQL server inside a running docker
image?

To switch to new release you should start a new a image with wanted MySQL server
version inside.

I'm trying to update/remove mysql on the HOST machine.
Let me explain it in another words:
I have machine which is running mysql locally and on the same machine I have docker which is also running mysql.

So while updating/removing locally installed mysql the issue appeared

Sorry, now I understand what you.

MySQL deb packaging scripts in host get confused by other mysqld running inside
docker on the same machine, this is due too simple logic to count mysqlds:

 ps -ef | grep "/usr/sbin/mysqld"  | wc -l

Yes I understand this situation.
That's why I've submitted bug report.
There are several ways to proceed:
- use Debian's start-stop-daemon infrastructure
- detect if it is docker: for example
   The most reliable way is to check /proc/${pid}/cgroup. It will tell you the control groups of the init process, and when you are not in a container, that will be / for all hierarchies.

On the first glance the easiest way is to check cgroup and exclude process if it is running in docker or in lxc.

At first clance it seems like using start-stop-daemon infrastructure is the best way forward.

Thanks again for you report and suggestions!

Might be using cgroup is better, as least using old school ps and wc is not the way forward :-)

I don't think we actually need these checks at all for an upgrade.

It is entirely valid for a debian|ubuntu user to have disabled the service
(so all starting|stopping of the service needs to be manual), in which case
an upgrade should be able to complete without stopping the old server process
or starting a new one.

We'll go through these scripts and update them for this scenario (we'll
probably still want some check on this for a package purge, at least).

Posted by developer:
 
Fixed in 8.0.15.

If MySQL was running on the host system and within Docker, it was not
possible to update or remove MySQL on the host system.