man emerge gives : package.mask The package.mask file primarily blocks the use of packages that cause problems or are known to have issues on different systems. It resides in /usr/portage/profiles. Is this right ? I expected it in /etc/portage.
No, that's correct. In the context of that section of the man page, mechanisms are listed that cause packages to be masked. portage(1) lists all the various locations where other package.mask files might be found or installed.
