In Android Lollipop, I can only see the estimated time how long the device will be up. But I want to know how long my device is already running - where can I find this information? (Can't (and dont want to) believe it was removed completely from Lollipop...)
Settings > About Phone > Status and scroll to the end of the options. You'll see the up time.
Simply run the
uptime command inside a terminal (eg. via
adb or through Terminal Emulator).
You will get an output telling you how long the device is running for since the last boot.
up time: 02:57:16, idle time 10:21:25, sleep time 00:00:000
up time: as you may have expected, it's the time since boot.
idle time: I currently don't know much about where this time comes from/how it is generated; it seems to be the time it was idling in the past 12 hours.
sleep time: seems to be broken,
00:00:000is the time I get even though the phone was asleep most of the time.