Just a guess here as I'm a Fedora guy. Maybe use update instead of upgrade.
In Fedora, yum update will check all installed apps for their latest stable version.
yum upgrade, will upgrade your system to the next version like Core 4 to Core 5
or Core 5 to Core 6. Probably not what you intended.

Because NOBODY is supposed to gain root permissions. Period. You need to use one a variety of hacks or exploits or R&D modes to do this, and it's simply assumed you know what you're doing at that point.

The primary problem is that attempting to upgrade a running application framework will fail, destroying the existing one, preventing any sort of bootup. In order to avoid this, it's necessary to use a serial console or apt-get over a non-running framework, such as updating one stored on an mmc chroot-ed in from one running on flash.

It's not NOT showing destructive packages, it's ONLY showing packages explicitly vetted for end-user use.

One of the packages with an upgrade in the repo (which is really designed for the SDK) is maemo-af-launcher. The lifeguard process on the device forces a reboot if this is killed.

It certainly needs a bit more sanity checking in its actions.

Still, the problem is that even if you upgrade maemo-launcher via ssh with the lifeguard reboot turned off, once you disable developer mode and re-enable the lifeguard reset, the tablet is in a reboot loop again.

I googled to find the list of applications that were watchdogged by dsme, but I could not figure out what is prompting dsme to do the reboot.

I think I'll just give up on this and switch back to the OS2006 and install applications only via the appmanager.

SSH and RD-mode required to solve problem
 

I got my 770 rebooting always when I tried to install new programs. It's because dpkg tried to reconfigure maemo-launcher -program. If you try to install anything, package-management software will restart maemo-launcher service. And it will always reboot your 770 unless you are on R&D and no-lifeguard-reset -mode.

I had sshd running on my 770 (can't install it if your 770 is already on bad phase) beforehand. Then I changed mode:
And when 770 was up and running, I connected to WLAN. Then I was able to ssh in and change to root. Run commands:
When apt-get was running, it told that it's stopping maemo-launcher. That caused 770 to reboot but not now because of no-lifeguard-reset -mode. But this stage I noticed that graphical UI disappeared on 770 screen. But it didn't matter because I had working ssh connection.
Finally apt-get started maemo-launcher again but graphical UI didn't show up. So I run reboot -command.
Finally it's time to disable RD mode:
So 770 goes up normally. And all updates and installations are working perfectly again.

BR, HenriP

Re: Reboot loop / apr-get upgrade / 20 Jun 2006 firmware
 

@Tobler: your post was precious - I was kept in a similar reboot loop with a borked apt - after updating a number of packages with apt-get. Entering R&D mode and disabling lifeguard allowed me to recover apt.