Upgrade to 10.10.4 does not complete, ask to restart endlessly On a Macbook Air laptop, on 10.10.3, I'm trying to upgrade to 10.10.4.
The first time, the system downloaded the file. After the download, I had a message saying (I'm translating form french): "download of some updates did not finish; they can't be installed".
Since then, the system update shows with the "update" button, but the system does not redownload the file, I see a notification saying the system will reboot, but actually it will display the above error message.

How can I force the upgrade?
This should be easy to resolve.


Power down and boot into Recovery HD (Command R) or safe boot (shift)
Once you know the OS can boot itself - check for free space. Clean up cache or temporary files or delete large databases that you have backed up (Outlook email, Photo databases, Music Libraries) to get 20 GB of free space.
Run Disk Utility to ensure the disk structure doesn't need repair
Download the combo updater from https://support.apple.com/kb/DL1820?viewlocale=en_US&amp;locale=en_US
Run the update by hand and when the installer is running, open the log to watch for errors (Command L and then Command 3) if you desire or can see the log.