mysql-server fails to install if it cannot start due to not enough memory

[Simos Xenitellis ]

The default installation of mysql-server is completed successfully if it manages to start at the same time. If for some reason mysql-server cannot start, then the installation fails without giving a comprehensive error message. The user has no clue as to why the installation failed. The only file with information is /var/log/mysql/error.log.

Users run Ubuntu on affordable servers with little memory (Amazon EC2 600MB RAM, or DigitalOcean 512MB RAM). In addition, users may use containers like LXD which means that mysql-server may not get as much memory as required. Therefore, the installation may or may not fail. In addition, mysql-server may crash latter if not enough memory is available.
The default requirement for memory for mysql-server is 128MB (InnoDB).

There should be a way to inform the user that mysql-server does not install if there is not enough memory.

[Simos Xenitellis  (simosx)]

Attempt for installation of mysql-server, which fails due to not enough memory.
The messages do not give a clue that the problem is memory-related.

The commands (systemctl, journalctl) that are mentioned, do not provide a hint.

[Christian Ehrhardt  (paelzer)]

FYI - We discussed if that would be a dup to bug 1571865.
While a fix to the former one will help the situation a bit (by hopefully providing a better error message right away) it is intentionally not flagged as duplicate.

[Simos Xenitellis  (simosx)]

I had a look at the other bug report.

I think the significance in this report is that the mysql-server package can fail to install altogether (if the installation misjudges how much memory to assign to mysql), requiring the administrator to use package management commands in order to fix.

I got this problem when trying out Juju on the LXD provider.
The server had 2GB RAM, shared among the containers.
The installed mysql-server package got (auto?)configured to allocate 1.6GB of memory, thus failing to start, and failing to complete the installation. This is my recollection of what happened.
I had a look at the packaging of "mysql-server" and did not see any "autoconfiguration" for the memory. Therefore, it might just be Juju that configured the 1.6GB.
I'll try again to install Juju and get a better picture of what is happening.

[Robie Basak (racb)]

Perhaps we could have mysql-server.postinst follow some heuristic to determine if the system has lower-than-will-work-by-default memory, and if so, then enable a (/etc/mysql/mysql.conf.d/lowmem.cnf -> /usr/share/mysql/lowmem.cnf) symlink or something. We could have a low priority debconf option to permit (no heuristic/always lowmem/never lowmem/use heuristic) overrides.