On Windows, once in a while there is a Patch Tuesday when the only update is Internet Explorer, a program that I neither wanted, nor installed, nor opened since I got tired of it years ago. Clearly, I need to reboot my computer for this.

On Ubuntu, certain packages are labeled as needing a reboot, and when you update them the control menu thing with a gear in the upper-right corner turns red, and the Update utility says you should reboot. Then you know you should, but it doesn’t force you to.

EDIT: There’s also Ksplice, which was going be a standard until Oracle bought it, and Red Hat kpatch. Those allow you to update a kernel without rebooting. Most other programs still require restarting, but Linux benefits from a saner architecture, where the web browser isn’t an “integral part of the operating system,” and the font renderer for the GUI and for printing is not part of the kernel. You need to reboot less.

>How do they solve the problem without requiring, at minimum, closing all of the user's applications and restarting them, then closing all system services and restarting them? (At which point, you've basically done a de-facto OS restart.)

But this is not what you suggested, is it?