Though my track record with in-place upgrades of Linux/Unix systems is far from positive, I decided to do just that with my long-running (since late 2010) Debian Squeeze laptop today.
It went surprisingly well -- and by that I mean I'm using a fully upgraded Debian Wheezy laptop to create this post in Nautilus via sftp.
My preparation started this morning with something I do regularly: a full backup of my user files via rsync. I did the backup knowing that if things went awry, I could do a full reinstall and then roll my user files onto the new system.
I poked around for "how to upgrade Debian from Squeeze to Wheezy" posts, and I figure I'd be in for some serious preparation, as the upgrade from Lenny to Squeeze required quite a lot of tweaking before getting started with apt and the actual act of upgrading.
The guide I used from DoDebian was refreshingly simple (and nearly intuitive for anybody who's been using Debian for a few cycles):
Basically it worked. I redid all my Debian repos, turned off Debian Multimedia, the Mozillla Debian APT archive and Debian Backports, kept the repos for Google Chrome and Dropbox unchanged and did my aptitude upgrade as root.
Then I did aptitude full-upgrade (again as root). Aptitude brought down 1,800+ packages, which took about 45 minutes to download on my very fast connection. I didn't time how long it took those packages to be configured and installed, but suffice to say it was quite a while.
The biggest "glitch" I had was that the system logged me out before the aptitude full-upgrade process was finished. I rebooted successfully (which was unnecessary; I could've just logged back in), tried to resume the process and followed the terminal's instructions for resuming a "locked" Aptitude session. If you've been using Debian or Ubuntu for any length of time, you've run into this before, and it didn't catch me off guard at all.
Eventually Aptitude finished all the way. I logged out, rebooted (again, there was probably no reason to do this, but I wanted to be in the newer kernel instead of the Debian Backports kernel I had been using, so I did it) and was in GNOME 3/Shell.
Mousing over into the "hot corner" (upper left; I have a bit of experience in GNOME Shell, so I'm not totally lost), I soon found that many of my applications appeared twice in the Applications list, generally once with a clear icon and again with a blurry, bitmapped one.
A bit of Googling led me to this successful solution from the Debian Forums:
I cleaned out all .desktop files in ~/.local/share/applications and ~/.local/share/applications/menu-xdg. That got rid of all of the cruft in the other menu which got rid of the duplicates. I never intentionally put any of these .desktop files in these directories. The .desktop files would have gotten there with the normal install process of packages.
I did just that: I deleted everything that ended in .desktop in these two directories (they were in my user account, so I didn't even need to use rootly privileges), logged out, logged back in (again, I'm unsure whether logging out was necessary), and the duplicates were gone.
The first thing I did was install two apps I couldn't install in Squeeze without Debian Multimedia -- the OpenShot and KDENlive video editors. They both installed fine.
Then I added gnome-tweak-tool. About the only thing I've been able to do with this tool thus far is get the month and date to show up along with the day and time at the top of the screen.
I removed a few "defaults" from the application dock on the left side of the screen in "Activities" mode, and I added a bunch of the ones I do use. My upper GNOME panel in GNOME 2 was pretty packed. I'm trying for the same thing here. The icons are a bit smallish, and I'd like to figure out how to make them bigger.
I tried to hook up my Google account with the GNOME desktop. It keeps saying that there's a "network error." I'm not sure what to make of this just yet. Clicking "edit account" in the dialog that opens up has the effect of logging me out of the desktop. Not helpful.
On the other hand, Dropbox is working fine. So is Icedove (aka Thunderbird) with all the extensions (Iceowl, gContactSync).
In both OpenOffice.org and then LibreOffice in Squeeze and from squeeze-backports, respectively, the PDF Importer extension in the repository didn't work. My workaround then was to manually download the extension from OpenOffice.org and load it in through OpenOffice or LibreOffice. once I had the updated LibreOffice in Wheezy, that extension no longer worked. So I used Synaptic to install the PDF Importer package. It works! Editing PDFs in OpenOffice/LibreOffice Draw is something I do often -- I consider it OO/LO's "killer feature," and I'm glad I still have it in Wheezy.
I'll withhold judgment for now on how I like GNOME 3 compared to GNOME 2, as I'm very early into the process of using this new desktop environment. The more you use this "new" desktop paradigm, the easier it is to navigate. Whether it's better, I don't know.
But the fact that I was able to do this in-place upgrade from Squeeze and have it work is both significant and encouraging. The Wheezy "freeze" is supposed to happen any day now (I think the end of June), and I wanted to be on board. Now I am.
Note: This laptop (Lenovo G555) started on Debian Squeeze in November 2010, and at the time I opted for the default ext3 filesystem with LVM. I have two encrypted volumes -- one each for /swap and /home. And yes, I need to enter the passphrase twice -- once for each volume.
I don't know about now, but back then in the Debian installer you couldn't easily create a fully encrypted LVM with a Windows partition (or partitions) on the same hard drive. (That's easy to do in Fedora/Red Hat's Anaconda installer, by the way). So encrypting volumes individually appeared (to me at the time) to be the only way you can easily get something similar in Debian.
I hope things are different in the Wheezy installer, but I haven't heard anything one way or the other.
I'm sure I'll have more to say on Debian Wheezy in the days ahead, but for now it's back to work ...