more /var/log/letsencrypt/letsencrypt.log
2018-04-04 10:48:27,872:DEBUG:certbot.main:certbot version: 0.22.2
2018-04-04 10:48:27,873:DEBUG:certbot.main:Arguments: [’–apache’]
2018-04-04 10:48:27,873:DEBUG:certbot.main:Discovered plugins: PluginsRegistry(PluginEntryPoint#manual,PluginEntryPoint#null,PluginEntryPoint#standalone,PluginEntryPoint#webroot)
2018-04-04 10:48:27,888:DEBUG:certbot.log:Root logging level set at 20
2018-04-04 10:48:27,889:INFO:certbot.log:Saving debug log to /var/log/letsencrypt/letsencrypt.log
2018-04-04 10:48:27,890:DEBUG:certbot.plugins.selection:Requested authenticator apache and installer apache
2018-04-04 10:48:27,890:DEBUG:certbot.plugins.selection:No candidate plugin
2018-04-04 10:48:27,890:DEBUG:certbot.plugins.selection:Selected authenticator None and installer None
on other systems I see plugins for:
apache, manual, nginx, null, standalone, webroot