Ubuntu has finally introduced the Phased Updates Process. Actually, it was ready on every Ubuntu 13.04 Raring Ringtail, but the server side wasn’t implemented until last week.
Everybody that updates his system via the update-manager is automatically taking part to the Phased Update process. Basicly, what the phased update process does is release updates for 10% of the users, and if nothing bad happens (no errors, no bugs and no issues occur), another 10% of users receive updates and the process repeats until it brings updates to 100% of the users.
So, to be short, the phased update works like this: 10% of the users get updates and if only no errors occur, other 10% of the users get updates and the process repeats.
If you don’t want to use Phased Updates, this is how you disable it:
Open the /etc/apt/apt.conf with sudo / root privileges:
$ gksudo gedit /etc/apt/apt.conf
Paste this line in the /etc/apt/apt.conf file and save the changes: