In all Linux distributions, programs that can be installed on the system are distributed as software packages. Software packages are typically a set of data packaged in a file that contains the software itself, as well as a number of additional information (metadata) about the software, such as package descriptions, installation scripts, dependency data, and so on. Linux distributions maintain their own repositories, into which software packages can only be accessed after strict checks. Packages consist of a package database containing package information and an organized structure of downloadable binary package files.