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Re: comment and new question--when do upgrades take effect (was: Re: Kernel for Spectre and Meltdown)

Does checkrestart (apt-get install checkrestart) prompt for application restarts on library updates, or only for daemons?

On Jan 29, 2018 08:43, "Joe" <joe@xxxxxxxxxxxxxx> wrote:
On Mon, 29 Jan 2018 08:18:35 -0500
rhkramer@xxxxxxxxx wrote:

> I regularly download "security" upgrades for Wheezy.  I assume that
> most of those don't take effect until I restart the application.  For
> instance, a Firefox upgrade does not take effect until I shutdown
> Firefox and restart it.
> Correspondingly, I assume that a Linux kernel upgrade does not take
> effect until I reboot the machine.

Yes, but it's a little more complicated. The modules used by the kernel
(and the kernel file itself) *are* replaced during the process of
upgrading the kernel, but the running code is not. There is a tiny
chance of some kind of mismatch if new modules are loaded, so rebooting
is recommended soon, and in the past I used to see a message to that
effect, displayed during the upgrade.

Generally, user applications (e.g. Firefox) will not be restarted
automatically, but most daemons will be e.g. mysql, exim4. Some
important daemons may request your input as to whether to restart or
not e.g. during a major upheaval such as a libc upgrade. Pretty much
all software on a server is in the form of daemons, and generally
rebooting a server is only necessary after a change of kernel.