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Re: Questions after doing update and upgrade on Stretch

On 22-05-17, Richard Owlett wrote:
> On 05/21/2017 09:31 AM, Dejan Jocic wrote:
> > On 21-05-17, Richard Owlett wrote:
> > > [snip]
> > > 
> > > My questions:
> > > 
> > > 1. In the first run, I don't understand:
> > >      Processing triggers for initramfs-tools (0.130) ...
> > >      update-initramfs: Generating /boot/initrd.img-4.9.0-2-686-pae
> > >      I: The initramfs will attempt to resume from /dev/sda5
> > >      I: (UUID=5d0c821b-26b2-4d38-b7fe-dc7db1b72576)
> > >      I: Set the RESUME variable to override this.
> > >  As /dev/sda5 is my SWAP.
> > > 
> > > 2. I don't understand any implications of:
> > >      The following packages have been kept back:
> > >        linux-image-686-pae xorg xserver-xorg
> > > 
> > > TIA
> > > 
> > > 
> > > 
> > > 
> > As for number 1 can't say much about it, I do not get it either. But 2
> > happens because you've used apt-get upgrade instead of apt-get
> > dist-upgrade. Packages that will uninstall some packages already
> > installed on your system and that will change some dependencies
> > require dist-upgrade. It happens always in case of linux-image packages.
> > It will leave your previous working linux-image on though, but will
> > uninstall one older than that, so you will always end up with chance
> > to  boot in working kernel, if new one messes up some things.
> > 
> If I had problems after doing apt-get dist-upgrade,
>   1. how would I distinguish a kernel problem from other problems?
>   2. how would I boot with the previous kernel?
>   3. is there some specific documentation I should be reading?
> I've done online upgrades before having relied on purchased DVD sets of
> point releases due to bandwidth constraints.
> Thank you.

1. That would depend on problem itself, right? As for kernel problems, I
was unusually lucky with them for years and have yet to run on problem
with upgraded kernel. Must be that new kernels really loved my hardware.

2. It is easy task, as long as there is previous kernel present in your
/boot. If everything works as expected you should have it. From debian
administrator handbook:

8.11.1. Features of a Debian Kernel Package

A Debian kernel package installs the kernel image (vmlinuz-version), its
configuration (config-version) and its symbols table
(System.map-version) in /boot/. The symbols table helps developers
understand the meaning of a kernel error message; without it, kernel
“oopses” (an “oops” is the kernel equivalent of a segmentation fault for
user-space programs, in other words messages generated following an
invalid pointer dereference) only contain numeric memory addresses,
which is useless information without the table mapping these addresses
to symbols and function names. The modules are installed in the
/lib/modules/version/ directory.

The package's configuration scripts automatically generate an initrd
image, which is a mini-system designed to be loaded in memory (hence the
name, which stands for “init ramdisk”) by the bootloader, and used by
the Linux kernel solely for loading the modules needed to access the
devices containing the complete Debian system (for example, the driver
for SATA disks). Finally, the post-installation scripts update the
symbolic links /vmlinuz, /vmlinuz.old, /initrd.img and /initrd.img.old
so that they point to the latest two kernels installed, respectively, as
well as the corresponding initrd images.

Most of those tasks are offloaded to hook scripts in the
/etc/kernel/*.d/ directories. For instance, the integration with grub
relies on /etc/kernel/postinst.d/zz-update-grub and
/etc/kernel/postrm.d/zz-update-grub to call update-grub when kernels are
installed or removed. 

As you can see there, if everything works as intended, you will still
have your old kernel installed, which you can choose from grub menu.
Think that it is under advanced options, but did not use it recently and
am not in mood to reboot now to check. Anyway, as long as you do not use
apt-get autoremove, even your older than previous kernel packages should
be around, though I did not have need for that.

3. https://debian-handbook.info/ and usual man pages for grub, kernel,
apt-get and friends, I guess.

Pleasure :)

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