Portage Profile Logic
Gentoo profile initialization has been documented in this GitHub commit, and describes how Gentoo's Portage finds and processes profiles. Basically, Gentoo's Portage looks for profiles using this algorithm:
- Does /etc/make.profile exist? If so, it defines the primary profile.
- If not, does /etc/portage/make.profile exist? If so, it defines the primary profile.
- Recursively process the parent file found in the primary profile to build a list of all cascading profiles
- if /etc/portage/profile exists, it is a user-defined profile - tack it to the end of our profile list so it can modify anything in the cascading profiles.
Here is a more detailed description of the steps:
- Look for a profile directory/symlink at /etc/make.profile, if one exists, use this as the main profile directory.
- If /etc/make.profile doesn't exist, use /etc/portage/make.profile as a back-up location if it exists.
- If neither location exists, then a main profile directory doesn't exist and is undefined (None)
Using the main profile directory/symlink found above, the LocationsManager._addProfile() recursive function will be called that will create a list of all cascading profiles. This works by looking for a parent file in the profile directory. If this file exists, then each line is treated as a relative path and used to modify the path to the current profile, pointing to a "parent" profile that this particular profile modifies. There can be more than one parent, one per line. The first line in the parent file is the highest-priority parent.
Once this list is created, the code checks to see if /etc/portage/profile directory exists. If it does, it is tacked at the end of the cascading profile list, meaning that it is evaluated last and this user-defined profile has the ability to modify any of the cascading profile settings. It provides an ideal hook point for a user-defined profile that can tweak anything the user wants to modify in the profile.