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:

mysqldump | Server | MariaDB Documentation
Complete mysqldump guide for MariaDB. Complete reference documentation for implementation, configuration, and usage with comprehensive examples and best.
mariadb.com

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.