Re: what partitions to mount during upgrade ?
On Mon, 19 Jun 2017 10:44:23 +0000
"Blair, Charles E III" <c-blair@illinois.edu> wrote:
> I am an unsophisticated user who has finally gotten
> around to upgrading a desktop from wheezy to jessie. I am
> trying to follow the instructions in the "release notes,"
> but don't really know what I'm doing.
>
> My current question is to clarify the instructions about
> mounting partitions at the beginning of section 4.4. I
> think I am supposed to issue as superuser the commands
>
> mount -o remount,rw /
> mount -o remount,rw /usr
>
> Are there any other mount commands to issue before
> apt-get upgrade ? How do I find out? I don't think
> it matters, but this is a dual-boot using grub with
> windows as the other system.
>
As an aside, do you have a separate partition for /usr? Most previous
Debian installers suggested doing so as an option, but jessie after
upgrade will be based on systemd and really isn't happy about a
separate /usr.
/usr is really required for boot nowadays, certainly with systemd. If
your /usr is a separate partition, you can rebuild the initrd file to
include /usr mounting instructions. Alternatively, you can merge /usr
into /, which may be difficult if you previously went with the
suggested few hundred MB size for / where /usr, /var and /home are on
separate partitions. The voice of experience...
As to mounting, the original purpose of /usr was to hold application
code, which was never written to except for upgrade, and was shared by
all users. Under those circumstances, it could be mounted read-only
during normal use, to prevent accidental damage to it, or one user
modifying something without realising that other users would be
affected. If you're an 'unsophisticated user', you are unlikely to have
set up the system in that way. Also, / may be mounted read-only after a
serious boot error, so this is a warning to anyone who has a dodgy or
exotic system to make absolutely sure that both / and /usr are mounted
with writing enabled. You do also need /var and /home mounted, if they
are separate to /, but if they were not mounted properly you would know
about it already. I would guess also that it is possible to try an
upgrade of a dead system using chroot, and again, you should check to
make sure you know what's going on. A chroot is a meld of two systems,
and it is relatively easy to make changes to the wrong one.
Any package upgrade will require read-write mounting, and any problem
here will be obvious very quickly. If you're upgrading a working,
running system, than you can safely assume that the right things are
mounted already. It's not a big risk, because one of the upgrade
preliminaries is to make sure that your existing system is fully
upgraded before the version upgrade is attempted, and any mounting
problems would show up at that stage, long before anything irrevocable
has happened.
I suspect this warning exists because someone once had a mounting
problem, and the upgrade did not follow the expected path, and they
complained that the release notes did not take account of this
possibility. Now they do.
--
Joe
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