Sometimes it happens that upgrade procedure of Yosemite fails for some reason and you are left with a working system but starting App Store makes fans to go wild. Also seeing large number of log entries appended every second to/var/log/install.log in Console.app indicates that something went wrong. Bummer.
Happily support.apple.com forums sugested to download latest combo update and install it fixing the issues. Sadly the system starts to behave the same way as after starting App Store.app.
I don’t like to have my workstation unstable so I was already considering complete system reinstallation and then one idea came to my mind. Single user mode and reinstallation using CLI.
To be successful I needed mentioned Combo Upgrade package and two commands:
hdiutil mount osxupdcombo10.10.4.dmg
sudo installer -package "/Volumes/OS X 10.10.4 Update Combo/OSXUpdCombo10.10.4.pkg" -target "/Volumes/Macintosh HD"
Voilà… system is fixed and again up and running.