Hi,
On linux, the user running "esusers" commands seem to matter. When the user has the wrong access right, then the error message points to a faulty directory error like:
ERROR: The configuration directory [/etc/elasticsearch/shield] does not exist. The esusers tool expects Shield configuration files in that location.
The plugin may not have been installed with the correct configuration path. If [/usr/share/elasticsearch/config/shield] exists, please copy the shield directory to [/etc/elasticsearch]
Changing user to an admin level user like root, then the message disappears.
See Shield Authentication Error - #8 by Baboune
But yes it seems shield ignores where the rest of the CONFIG_DIR is and elects its own location, /etc/elasticsearch on linux.