So I've had my N900 a couple of days and I'm looking through the applications in extras-testing. I'm thinking of enabling this repo, but I want to know, what are the real dangers of it? I've read the usual "here be dragons" warnings etc, but what is the real danger, and are there any procedures to get back to a good state without having to re-flash? Is it as easy as using dpkg to fix things, or do things get worse?

Thanks in advance everyone!

you should now that a reflash is the solution for 99,9 percent of your n900 issues.
but it takes a little bit time and you will lost all your data.
the repositorys can make your phone laggy,weird,crash,reboot,data corruption,lose some other phone function and make your phone totally unstable.
but not all devel/extras apps are evil.
i would read the updating your firmware wiki and after you are good with flashing give it a try.

Thanks for the info. I'd be interested in hearing specific issues people have had that have enabled the testing repo.. I understand that all the issues are possible but what is the real-world likely hood?

I think I'll practice a re flash whilst the phone is still fairly new (i.e not full of important stuff yet!) and then I'll see how I feel

i just install things i really need and i never had problems(after the pr.1.2 i had to reflash but thats all)
and i have many apps installed like emulators second media players and all kind of stuff.
you have to test a little bit around and you will see whats good and whats bad.
but if you install something from the repos try to install one app at the time so if something goes wrong you know what you have to deinstall.
but i wish you many fun with the repos then if you know how to,they are really great

I would say the same. I've installed a couple of apps from both testing and devel, and so far I'm all good. But you should really be ready for serious issues. Make backups and don't install fishy stuff if you have an important call waiting . Also make backups, and be prepared to mess with the device if it would come to that.

Most important probably is to read up on the specific apps, on maemo.org/packages you can find any package and see the versions and changelogs. Usually there is also a forum thread, generally there will be posts if there is any serous risk, but take nothing for granted. As mentioned on the wiki testing and devel are for packages not ready for the end-user. I recomend that you should feel familiar with your phone and whit the filesystem, you know, just in case

@scottuss - you'll be fine.
The benefits far outweigh the risks.

The dangers in extras-testing and extra-devel are wildly exaggerated.

But so is the inconvenience of flashing. Flashing is an essential tool. You need to back up your data and be ready to flash as necessary to use your N900 properly, meaning to be able to use apps that are in extras-devel and testing without fear.

I have not been paying attention to whether apps are from extras-devel or testing from day one, with no bad consequences.

Even newbies who got here yesterday should learn how to flash their devices, because they might need that ability. It might be a pain to a certain extent, because Nokia apparently never understood how to deal with 64-bit Windows 7 -- I have seen dozens of threads about it, and even seasoned veterans instantly give up when they see it and insist that people install some version of Linux to flash. That is ridiculous -- it should not be necessary, and it seems that Nokia has not fixed that problem, though they have had a long, long time to work on it.

But you need to be able to flash. And in my opinion, to use your N900 properly, you need to use extras-devel and testing from time to time.

Depends. How is your LinuxFu and DebianFu? Are they strong, or are you in training? If not, or you're not adventurous, maybe you should stop reading. But if so, as root or with sudo, the following commands can sometimes help you fix things without a reflash:

Obviously, always watch your disk space and the disk space needed, before and after an install.

But don't be too frightened by the following three paragraphs. They represent rare occurrences, and most problems can be solved or avoided if you're paranoid and diligently use the commands above. Most importantly, make sure if there are DEBIAN/postinst and/or DEBIAN/preinst files (wget <package URL>; dpkg -e <package deb file>) that they don't do anything too interesting that you can't fix.

Developers don't touch shared resources that often, but things can get sucky when a developer either overwrites or writes to a system configuration file without making a backup first. And even if they do make a backup, if their uninstall (DEBIAN/prerm and/or DEBIAN/postrm) doesn't put things back correctly, bad stuff can remain.

Along the same lines as the above paragraph, some packages start daemons that could be running. If the uninstall doesn't handle these correctly, you need to kill the daemon as simply as possible. Regardless, some files could still be lingering around.

These are just some of the nasties. A developer could also write to a shared database. If they corrupt or bloat the db, its tables or its indicies, fixing this is very non-trivial, and even with sophisticated backups with tools such as rsync, you could still be in a bad state, a state that makes your device consistently perform poorly, or not at all.

Proceed with caution, but don't be afraid of your own shadow. A backup and a reflash aren't the worst things that could happen to you.

Good luck!

ive had all the repositories enabled since i got the phone. never had any problems at all. i was scared at first because of users in this forum telling everyone devel is dangerous when it isnt!

Same here, extras-devel etc enabled since day one and no problems at all. Get comfortable with the reflashing wiki (including eMMC if things really go bad) and like mentioned above, 99% of your problems will be resolved. Use the phone's backup utility and store it on an SDMicro card if possible and/or laptop HDD.

Don't know why, but somehow my N900 reflashing frequency seems to coincide with reconfiguring the OS in my dual/triple boot netbook (currently Ubuntu 10.04 NBE with MeeGo). I guess it's the constant need to start with something "fresh"...