When using MariaDB, I tried to create a backup with the following command and encountered the error mysqldump: not found:

mysqldump -uomeka -pomeka omeka > test.sql

As a workaround, I referenced the following article and found that using mariadb-dump resolved the issue:

https://mariadb.com/kb/en/mysqldump/

Specifically, the backup was successfully created using the following command:

mariadb-dump -uomeka -pomeka omeka > test.sql

I hope this serves as a useful reference for anyone experiencing the same issue.