First, AtoM 2.6 is intended to be installed using Ubuntu 18.04 and PHP 7.2. There are a few known incompatibilities in PHP 7.4, which we have addressed in the upcoming 2.7 release. These fixes required code changes in AtoM to resolve - so as we finalize the 2.7 release, trying to use PHP 7.4 with AtoM 2.6.x may be causing issues for you. Consider downgrading to PHP 7.2.
In most cases, the issue you describe is caused by not setting the correct SQL modes during installation. See the MySQL section in the installation documentation
- the only SQL modes we recommend setting in a /etc/mysql/conf.d/mysqld.cnf
configuration file are as follows:
If this step is skipped then the NO_ZERO_IN_DATES sql mode may be set by default, which can cause problems. You can check and change your SQL mode setting with the following instructions:
Hopefully, making those two changes will resolve the issue. If not, let us know!