[Bug 1619188] Re: Unattended upgrades can break persistent live media

[Nio Wiklund]

Den 2016-09-02 kl. 18:21, skrev Alberto Salvia Novella:
> Because most inexpensive modern USB drives will be able to handle that
> amount of space without problems, I believe changing the default upgrade
> method would be a drawback.
>
> For example a Kingston 32GB USB 3.0 drive costs as little as 8€, and a
> Sandisk 8GB USB 2.0 drive costs 3€. The official Ubuntu USB drive has
> 32GB and costs 6£.
>
> Upgrading automatically is a better default for at least 95% of
> situations, and the person could still easily realise that they should
> disable automatic upgrades when having a small vintage USB drive.
> Moreover the Startup Disk Creator no longer has persistence, so the
> likelihood of a novel user making that mistake is minimum.
>
> For the moment I will consider this report as an opinion, but feel free
> to bring the conversation to the Quality mailing list at
> (https://launchpad.net/~ubuntu-testing). Thanks for your always welcomed
> help and understanding.
>
> ** Changed in: casper (Ubuntu)
>        Status: Confirmed => Opinion
>
> ** Changed in: casper (Ubuntu)
>    Importance: Undecided => Wishlist
>

Hi Alberto,

I see your point, but there is definitely a problem in this case, big 
enough to report a bug.

1. Several tools for persistence are still creating a casper-rw file in 
a FAT32 file system. This will limit the size of the file and the 
loop-mounted filesystem inside it to 4 GB, which is definitely not 
enough, if you allow unattended upgrading.

2. mkusb is different, it creates a partition for persistence, but I am 
sure that many people want to use 4 GB or 8 GB pendrives, and there is 
definitely a space problem also in these cases.

3. But maybe the most severe reason to avoid excessive upgrading is that 
persistent live systems are much more sensitive than normal installed 
systems. It is well known to people who use persistent live systems, 
that you should keep the amount of upgrading to a minimum.

The kernel and certain other parts of the system cannot be upgraded, 
because the kernel from the live system is started before the overlay 
structure is created from the casper-rw file or partition. Some upgrades 
that will be used imply that the new kernel etc are used, but that is 
not possible, so the system fails to work. As it is now, the kernel is 
upgraded (but not used).

-o-

I have discussed this issue with two very knowledgeable persons with own 
experience of persistent live systems, and we agree: Changing the 
default setting of updating program packages (as what happened from 
Ubuntu 14.04 LTS to 16.04 LTS) creates problems for persistent live 
systems - problems that are severe enough to say it is a bug.

Many disappointed users will probably leave Ubuntu silently and select 
some other distro after a system crash because of this bug.

-o-

Please notice that I want to keep the general settings of the updating 
system [of installed systems], and only suggest changing the settings, 
when running live and persistent live. This is why the bug is directed 
against casper.

Best regards
Nio