Elastic Agent fails to start on a sysvinit system when following the instructions for systems not based on systemd that can be found in the getting started docs:

# service elastic-agent start
Error: unknown command "test" for "elastic-agent"
Run 'elastic-agent --help' for usage.
unknown command "test" for "elastic-agent"
   ...fail!

Same happens when init.d script is called directly:

# /etc/init.d/elastic-agent start
Error: unknown command "test" for "elastic-agent"
Run 'elastic-agent --help' for usage.
unknown command "test" for "elastic-agent"
   ...fail!

The problem seems to be that this script calls the subcommand test config, that is not available in Agent:

If this script is supposed to work, the test subcommand should be supported by Agent, or it shouldn't be called there. If only systemd is supported, the init script should be removed, and docs updated.

In principle all the Linux distributions supported by Agent, support systemd (see support matrix). Though SysV init can be used at least in Debian 9 and 10 (by installing the sysvinit-core package).

Reported in discuss: https://discuss.elastic.co/t/elastic-agent-init-script-calls-unavailable-test-command/253811