The command "service <name> start" is obsolete and deprecated in Ubuntu 16.04 and above.  That command is for upstart, and upstart is gone and replaced by systemd in 16.04.  They did do some mapping of the "service" command to the systemd equivalent, so it mostly still works, but you really now should be using the systemd commands directly:

systemctl <command> <name>

where <command> is start, stop, restart, reload and a whole pile of other less used things.  See "man systemctl".  I have found that systemd is very good for creating a service out of a program, now that I understand it well enough.  But most programs used as services get installed as a service anyway - the package has the necessary config files.  To see if there is a service installed, try a command like:

systemctl list-unit-files | grep cron

which will show you all the systemd "units" that have "cron" in their name.  Anything that has ".service" at the end is a service.