I run Ubuntu and Fedora on a day to day basis and usually run the package manager to check for updates nearly once a day.When I get a kernel update I usually reboot, so that I'm running on the new kernel and I can see if there are any glitches (It's almost always fine).If I add apt-get update && apt-get -y upgrade or dnf check-update && dnf upgrade to my root crontab is there anything procedurally wrong?What if I set up crontab to do this at 4 a.m. and it installs a new kernel, then I don't reboot and it auto-installs a second new kernel. What if I don't reboot my Ubuntu box for a month and there have been 3 kernel updates and a couple of other patches to the same piece of software during this time?Is it OK to enable automatic updating this way? I know that there's an 'unattended upgrades' utility for Ubuntu, but I'd rather learn what other system admins do and have a more 'hands on' approach to administering my PC's.
Is there a common way of auto-updates with cron?
apt;cron;unattended upgrades
Generally, sysadmins with a mixed install base would use a cross-platform configuration management / orchestration system like Puppet, Chef, or Ansible to manage updates.You could also set up one of those tools on a smaller scale if you like. Or, on Fedora *, you can use DNF Automatic  see the Fedora page on configuring this. This is better than a simple cron script because it has better error handling and more options for output.For Ubuntu, there are instructions on the community wiki for automatic updates, but I haven't used them so I can't comment more than to just provide the pointer.* disclosure: I work on Fedora