This question already has an answer here:
So once again apt-get bothered me with the infamous message that package installation failed because a dependency “is not going to be installed”:
~ $ sudo apt-get install php-apcu Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: php-apcu : Depends: phpapi-20151012 Recommends: php-apcu-bc but it is not going to be installed E: Unable to correct problems, you have held broken packages.
As I understand, default is to install all missing dependencies along with the requested packages. What would cause apt-get to refuse to install certain dependencies? (And if there is more than one thing leading to this, how can I find out which it is?)