Are all of these cron jobs necessary for a production store or are some of them only for development stores? For example, the update/cron.php file doesn't exist in my installation???
* * * * * php -c /home/example/etc/php.ini /home/example/public_html/bin/magento cron:run * * * * * php -c /home/example/etc/php.ini /home/example/public_html/update/cron.php * * * * * php -c /home/example/etc/php.ini /home/example/public_html/bin/magento setup:cron:run
Of course, all the 3 cron command are significant: http://devdocs.magento.com/guides/v2.0/config-guide/cli/config-cli-subcommands-cron.html#create-the-...
"The first command (magento cron:run) reindexes indexers, send automated e-mails, generates the sitemap, and so on. Usually it’s associated with the PHP command line .ini file. The other two commands are used by the Component Manager and System Upgrade."
update/cron.php is in the magento/magento2-community-edition repository: https://github.com/magento/magento2-community-edition/blob/master/update/cron.php
I finally gave up and just reinstalled using the standard method suggested by Magento. I have no idea why this would have happened. If someone else has this issue too please post your solution, but I gave up and just did something else so will not be posting on this thread any more. You can see the list of commands I did here... about as simple as it gets.
composer create-project magento-hackathon/magento2-standard destination