OCI: OSMS Error "failed to start plugin:[osms] err: Unrecognized remote plugin message:

APPLIES TO:

Oracle Cloud Infrastructure - Version N/A and later

Linux x86-64 on Oracle Public Cloud

SYMPTOMS:

The /var/log/oracle-cloud-agent/agent.log shows

failed to start plugin:[osms] err: Unrecognized remote plugin message: This usually means that the plugin is either 
invalid or simply needs to be recompiled to support the latest protocol.

CAUSE:

/etc/sudoers was heavily customized, and while customizing, the line was missing:

#includedir /etc/sudoers.d

Due to that, the following files were not loaded when using sudo

/etc/sudoers.d/090-oca-vss-plugin-commands

/etc/sudoers.d/091-oca-alx-plugin-commands

/etc/sudoers.d/100-oracle-cloud-agent-users

And hence the OSMS agent cannot use sudo anymore and fails to run any commands.