First, to enable the inputs you need to go through the setup of the unix, in Manager > Apps and then click on the Setup link in the Unix app
Second, to get the required data sources (from /var/log) into splunk you'll need to edit the default whitelist under Manager » Data inputs » Files & Directories » /var/log - to index everything simply set this to .*
Not indexing the required data sources to populate the dashboards is a bug, and I've filed an issue SPL-33801
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