I recently had to upgrade from Debian Sid to Buster and this seemed to break Zoneminder.
The first problem was both PHP 7.0 and 7.3 were now installed and Apache was using 7.0 still. This made going to the Zoneminder URL give a one line error:
Unable to connect to ZM db.could not find driver
Removing PHP 7.0 and pointing Apache to PHP 7.3 fixed this first problem.
Next problem was seeing odd variables on the Zoneminder login page and the Apache log giving warnings such as:
PHP Warning: Use of undefined constant ZM_WEB_TITLE – assumed ‘ZM_WEB_TITLE’
This was tricky to track down, but it turns out the Debian installer script did not, nor tell you to, run ‘zmupdate.pl‘. Running this manually gave the error:
‘ERROR 1142 (42000) at line 98: INDEX command denied to user ‘zmuser’@’localhost’ for table ‘Monitors’.
This was fixed by running ‘MariaDB [mysql]> grant all on zm.* to ‘zmuser’@localhost identified by ‘zmpass’;‘.