I like backupninja because of simplicity. Unfortunately it started giving me this problem:

Warning: mysqldump: Couldn't execute 'SELECT /*!40001 SQL_NO_CACHE */
dead.letter FROM GLOBAL_STATUS': The
'INFORMATION_SCHEMA.GLOBAL_STATUS' feature is disabled; see the
documentation for 'show_compatibility_56' (3167)

It looks like this can be fixed with set @@global.show_compatibility_56=ON. Unfortunately that doesn't work on my MariaDB instance:

Welcome to the MariaDB monitor. Commands end with ; or \g. Your
MariaDB connection id is 73 Server version: 10.1.26-MariaDB-0+deb9u1
Debian 9.1

Copyright (c) 2000, 2017, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input
statement.

MariaDB [(none)]> set @@global.show_compatibility_56=ON;
ERROR 1193 (HY000): Unknown system variable 'show_compatibility_56'

What else can I try to resolve this?