MySQL Bugs: #82709: setting datadir in my.cnf is not used in mysql-systems-start sanity check

Bug #82709	setting datadir in my.cnf is not used in mysql-systems-start sanity check
Submitted:	24 Aug 2016 12:36	Modified:	6 Mar 2017 19:19
Reporter:	Lars Van Casteren	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Packaging	Severity:	S3 (Non-critical)
Version:	5.6.30-1	OS:	Debian (stretch/sid)
Assigned to:	Lars Tangvald	CPU Architecture:	Any
Tags:	mysql-systemd-start, pre sanity, service

Description:
When setting a datadir in /etc/mysql/my.cnf and restarting the service journalctl shows: 

Aug 24 13:56:28 nuc mysql-systemd-start[1764]: MySQL data dir not found at /var/lib/mysql. Please create one.
Aug 24 13:56:28 nuc systemd[1]: mysql.service: Control process exited, code=exited status=1
Aug 24 13:56:28 nuc systemd[1]: Failed to start MySQL Community Server.
Aug 24 13:56:28 nuc systemd[1]: mysql.service: Unit entered failed state.
Aug 24 13:56:28 nuc systemd[1]: mysql.service: Failed with result 'exit-code'.

However, manual cmdline startup of mysql with the same my.cnf worked. 
Is seems that /usr/share/mysql/mysql-systemd-start is called from the unit and executes the pre sanity check. 

  if [ ! -d /var/lib/mysql ] && [ ! -L /var/lib/mysql ]; then
    echo "MySQL data dir not found at /var/lib/mysql. Please create one."
    exit 1
  fi

But if that directory does not exist which is possible due to using another datadir mysql cannot be started.
At this point it is not clear what the problem is. Did the cnf file load correctly? Are the permissions on the new datadir correct? 

How to repeat:
Change datadir in my.cnf
remove default datadir /var/lib/mysql or rename it
execute service mysql restart --> fail
check journalctl -xe for error message

Suggested fix:
don't hardcode the datadir location in a script. Maybe just throw a non-blocking warning as it could be the user changed the default location and removed / renamed the default location

It's possible to get the value from the config, so it doesn't need to be hardcoded at all.

This bug also affects MySQL 5.7.17 running under systemd (tested on Debian Jessie). The /etc/init.d/mysql script finds the datadir using my_print_defaults.

This Bug is security relavant and missleading.
I was reinitializing an already configured mysqld under debian jessie.
The datadir differs to default, mysqld was started and initialized the datadir correctly at first boot. At second boot this code dropped my root password and set auth_socket as authentication plugin which is not allowed by policy inside the environment infrastructure here:
 /usr/share/mysql/mysql-systemd-start:
        if [ ! "$(ls -A ${MYSQLDATA}/mysql)" ];
        then
                SQL=$(mktemp -u ${MYSQLFILES}/XXXXXXXXXX)
                install /dev/null -m0600 -omysql -gmysql "${SQL}"
                cat << EOF > ${SQL}
USE mysql;
INSTALL PLUGIN auth_socket SONAME 'auth_socket.so';
ALTER USER 'root'@'localhost' IDENTIFIED WITH 'auth_socket';
SHUTDOWN;
EOF

While another systemd service script written and delivered inside the same debian package fulfills the same approach without hardcoding:
-- /etc/init.d/mysql --
MYSQLDATA=$(get_mysql_option mysqld datadir "/var/lib/mysql")

Why this Bug is assigned to the initial Submitter and why this is classified as Non-critical?
Before I found out, what happened my first suggestion was to use another package for mysql5.7. 
This is a painful bug which breaks backward compatibility, security concerns and reboot safety !
How to get a reclassification without recreating a duplicate?

Posted by developer:
 
Hi,

You can report a new bug without it being a duplicate, since it's not the exact same issue (and not one we've fully considered).
Having all the scripts properly honor custom configs is a bigger task that requires some more other changes to be in place first, while the script overriding root auth on a preexisting database is both far more serious and simpler to fix.

Posted by developer:
 
Noted in 5.6.36, 5.7.18, 8.0.1 changelogs.

On Debian/Ubuntu platforms, the systemd startup script for MySQL
ignored datadir settings in /etc/mysql/my.cnf.