(It wasn't due to an update since I haven't switched wifi on in a while. I have stock KOT49H Android, rooted.)
Then it was stuck loop-rebooting at the big Google logo.
Trying to clear cache gave this kind of error:
E:failed to mount /cache (Invalid argument) E:can't mount /cache/recovery/log E:Can't open /cache/recovery/log E:failed to mount /cache (Invalid argument) failed closing /dev/block/platform/msm_sdcc ...
So, thanks to some guides, I downloaded the factory image for hammerheadkot49h from google developers.
Extracted cache.img from it and
fastboot flash cache cache.img
Tried to reboot : red warning sign again
Tried to clear cache : same error
Tried to reboot... New Screen - Success! A picture of standing android with a web in its panel and some traits below with :
-- Wiping cache... Formatting /cache...
Start worrying and search the forums : the long formatting cache is normal, and DO NOT switch off the phone meanwhile if you don't want BAD THINGS to happen.
Waiting 30 minutes.
Giving up and going to go something else...
Now my Nexus 5 is stuck there for about TEN HOURS.
What should I do? I'd like to keep my personal data if possible... (would "e2fsck /dev/block/platform/msm_sdcc.1/by-name/userdata" help?)
Thank you in advance for your answer.