Re: [gentoo-user] When to reboot after updates to the system

["Boyd Stephen Smith Jr." <bss03@volumehost.net>]

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On Friday 28 April 2006 20:04, Phil Sexton <philsexton@infoave.net> wrote 
about 'Re: [gentoo-user] When to reboot after updates to the system':
> Kevin wrote:
> > Hi All-
> >
> > I've read the portage documentation at
> > http://www.gentoo.org/doc/en/index.xml?catid=gentoo and I've searched
> > and browsed the gentoo-user mailing list archive, but I have a
> > question that I don't see answered anywhere.
> >
> > It seems to me that it must be true that sometimes, after a system
> > upgrade done with:
> >
> > emerge -uD system
> > or
> > emerge -uD world
> >
> > I must reboot the computer for the changes to take effect.
>
> I reboot if I need to install or change hardware.  As far as
> updates go, you may have to reboot after compiling a new kernel.
>
> I think that I may have read somewhere how to change kernels
> without rebooting, so you may not even need to reboot for any
> software.

Theoretically it's possible just by writing to /proc/kmem -- IIRC, that was 
one of the reasons it was writable: so you could apply (binary) patches 
against a running kernel.

I've never seen any non-malware that does so.  There is a GPL'd 
proof-of-concept rootkit that will hide its existence by 
modifying /proc/kmem.  (The rootkit doesn't actually do anything malicious 
and you have to have root access to modify /proc/kmem; the rootkit was 
just showing how to do this trickery without loading a module)

There's also the new kexec feature option in mm kernels (and it might have 
come mainline) that allows the kernel to start another kernel instead of 
rebooting your hardware.  That's basically as bad as a reboot anyway, 
because all services come down and all users are kicked out -- it is 
faster though, because you don't go down to the bootloader/BIOS level.

I found it (or my hardware) was a little bit buggy. My USB drivers would 
only work every other kexec.  Since I use a USB keyboard, this wasn't a 
workable solution.

-- 
"If there's one thing we've established over the years,
it's that the vast majority of our users don't have the slightest
clue what's best for them in terms of package stability."
-- Gentoo Developer Ciaran McCreesh

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