What is the debian-sys-maint MySQL user (and more)?

I have been bitten several times by the 'debian-sys-maint' user that is installed by default on the mysql-server packages installed from the Ubuntu repositories.

Generally what happens is I pull a fresh copy of our production database (which is not running on Debian/Ubuntu) for troubleshooting or new development and forget to exclude the mysql.user table hence losing the debian-sys-maint user.

If we add new mysql users for whatever reason, I have to 'merge' these into my development environment as opposed to just overlaying the table.

Without the user my system still seems functional, but plagued with errors such as:

sudo /etc/init.d/mysql restart
Stopping MySQL database server: mysqld...failed.
error: 'Access denied for user 'debian-sys-maint'@'localhost' (using password: YES)'

• What is debian-sys-maint used for?
  • Is there a better way for the package maintainers to do what they're trying to do?
• What is the easiest way to restore it after I've lost it?
• What is the correct/minimal set of privileges for this user?
  • Seems like poor idea to 'grant all privileges on *.* ...'

Edit

Additional question - Is the password in /etc/mysql/debian.cnf already hashed or is this the plaintext password? It matters when you go to recreate the user and I never seem to get it right on the first try.

Thanks

What is debian-sys-maint used for?

One major thing it is used for is telling the server to roll the logs. It needs at least the reload and shutdown privilege.

See the file /etc/logrotate.d/mysql-server

It is used by the /etc/init.d/mysql script to get the status of the server. It is used to gracefully shutdown/reload the server.

Here is the quote from the README.Debian

* MYSQL WON'T START OR STOP?:
=============================
You may never ever delete the special mysql user "debian-sys-maint". This user
together with the credentials in /etc/mysql/debian.cnf are used by the init
scripts to stop the server as they would require knowledge of the mysql root
users password else.

What is the easiest way to restore it after I've lost it?

The best plan is to simply not lose it. If you really lose the password, reset it, using another account. If you have lost all admin privileges on the mysql server follow the guides to reset the root password, then repair the debian-sys-maint.

You could use a command like this to build a SQL file that you can use later to recreate the account.

mysqldump --complete-insert --extended-insert=0 -u root -p mysql | grep 'debian-sys-maint' > debian_user.sql

Is the password in /etc/mysql/debian.cnf already hashed

The password is not hashed/encrypted when installed, but new versions of mysql now have a way to encrypt the credentials (see: https://serverfault.com/a/750363).

The debian-sys-maint user is by default a root equivalent. It is used by certain maintenance scripts on Debian systems, and as a side-effect, allows users with root access on the box to view the plaintext password in /etc/mysql/debian.cnf (good or bad?)

You can re-create the user by:

GRANT ALL PRIVILEGES on *.* TO `debian-sys-maint`@`localhost` IDENTIFIED BY 'your password' WITH GRANT OPTION;

Just make sure the password matches that in /etc/mysql/debian.cnf

You could also:

sudo dpkg-reconfigure mysql-server-5.0

Which will give you the option to recreate the debian-sys-maint user. Existing users and databases are safe.

I wanted to just comment, but I think correct syntax deserves it's own entry. This will create the debian-sys-maint user:

mysql> GRANT ALL PRIVILEGES on *.* TO 'debian-sys-maint'@'localhost' IDENTIFIED BY 'plaintextpassword' WITH GRANT OPTION; FLUSH PRIVILEGES;

If you still have the /etc/mysql/debian.cnf file, just use the password in there.

Feel free to come up with a more paranoid secure solution.