I'm thinking about buying this Meizu MX4 that comes with Android.
I was wondering if it would be possible to install Ubuntu Touch on it and keep receiving OTA updates. Being able to dual-boot it with android/ubuntu would also be nice.
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according to this article it's not such a good idea.
Not all Meizu devices are unlocked, and even if they do, they have a different partition table scheme.
This guy somehow managed to get it there: https://www.youtube.com/watch?v=qe9hKdYEMqY. I think if you are persistent about it, better to follow some tutorials on rooting the Chinese version of Meizu MX4 on XDA developers. As far as I know it is also possible to unroot it, so you would have a single boot with Ubuntu or with Android. In case if it is rewriting the architecture you would need to buy a new phone. Android phones come with a custom system partitioning, and rewriting the system multiple times even switching to CyanogenMod can result in boiling of your processor.
The bootloader on Android is usually accessible through pressing VOLUME UP and POWER button. This link seems like a good solution for building any OS into Meizu. In general it is also good to check with the Ubuntu community and ask questions there.