Debian packages of the form <variant>-server-core-<version> provide
binaries for MySQL and variant server daemons only. These are intended
for users who wish to manage database data directories and daemon and
service configurations themselves.

Debian packages of the form <variant>-server-<version> depend on the
corresponding <variant>-server-core-<version> packages and add automatic
management of database data directories and daemon and service
configuration via maintainer scripts.

It is possible for a <variant>-server-<version> maintainer script to
detect a local customisation that means that it cannot continue. Each
known case is documented in a separate file in this directory.

When such a situation arises, the <variant>-server-<version> maintainer
scripts will enter "frozen mode". We consider this preferable to the
maintainer script failing with a non-zero return code, which was the
previous behaviour. The previous behaviour would cause dpkg to fail,
causing apt to fail, leaving system packaging in a broken state and
causing a release upgrade to fail for example. This seemed excessive for
what could be an intended configuration change by the user.

Instead, "frozen mode" stops the <variant>-server-<version> maintainer
scripts from making changes until the user intervenes. The maintainer
scripts will not start the daemon, perform database upgrades or make
similar changes.

When "/etc/mysql/FROZEN" exists (even if it is a broken symlink), then
frozen mode is defined to be turned on. Usually a maintainer script
turning frozen mode on will create a symlink at /etc/mysql/FROZEN
pointing to further documentation on the specific case encountered in
this directory with an explanation and suggestions for resolution.

To resolve frozen mode, resolve the situation documented by
/etc/mysql/FROZEN and only then remove the /etc/mysql/FROZEN symlink,
and run "dpkg-reconfigure <package>" where <package> should usually be
in the form <variant>-server-<version>.