From Gentoo Wiki
/etc/portage/package.mask is a file, or a directory of files, controlled by the system administrator that can be used to prevent certain packages from being installed.
- One DEPEND atom per line; comment lines begin with a
- For DEPEND atom syntax, see version specifier.
# Mask beta versions greater than 1.97 of powertop since they have less features >=sys-power/powertop-1.97 # Prevent MySQL from being installed by masking the package (use MariaDB) dev-db/mysql # Want to go without Java 7; mask JDK and JRE that use Java 7. virtual/jdk:1.7 virtual/jre:1.7
- /etc/portage — the primary configuration directory for Portage, Gentoo's package manager.
- Cleaning /etc/portage/package.* from unused entries