The Android update lottery is such an annoying thing. I already got a Nexus 5 specifically to get updates at all. But even when there eventually is an over-the-air (OTA) update, one ends up hitting the “check for updates” button for week without actually hitting the update lottery seed win.
So after a week or so of this silly and annoying game I finally side loaded the update over USB, sigh:
./adb reboot bootloader
./fastboot oem unlock
./fastboot flash bootloader …bootloader-hammerhead-hhz12d.img
./fastboot flash radio …radio-hammerhead-m8974a-188.8.131.52.21.img
./fastboot -w update …hammerhead-lrx21o/image-hammerhead-lrx21o.zip
./fastboot oem lock
What a cluster mess, only silicon valley companies are elite enough to innovate like this, … sigh :-/!
PS: If you get “./adb devices, … # offline” then you probably run a too old adb version, like 1.0.29 instead of the newer 1.0.31 that handles authentication or such, …
PPS: One does not need to install the whole, huge, Gigabytes of Android SDK, there are various sites that offer (ZIP) downloads with just the two CLI Kilobyte tools.