[all variants] Automatic Check for Updates

I may have a problem with automatic update checks. I haven't seen any update notifications on this 16.04 system that I can recall. I have done some updating myself, but not more recent than Jun 17 from history.log.

From what I read here:

http://serverfault.com/questions/207...d-with-apt-get

update-success-stamp shows the last time apt-get update was run.

Output from my Xubuntu 16.04 (done Jul 11):

dmn@Sydney:/var/lib/apt/periodic$ ls -l
total 0
-rw-r--r-- 1 root root 0 Apr 26 11:36 unattended-upgrades-stamp
-rw-r--r-- 1 root root 0 Jul 11 08:03 update-stamp
-rw-r--r-- 1 root root 0 Jun 17 08:26 update-success-stamp
-rw-r--r-- 1 root root 0 Apr 26 11:36 upgrade-stamp

Also, what is the significance of the "update-stamp" and "upgrade-stamp"? I don't find information on those. On this system, Apr 26 is the date the OS was installed.

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