DISTDIR变量定义了 Portage 将会把下载的源码存放到哪个路径。默认值是 /var/cache/distfiles。
Source of archives
To download source code archives, Portage will download files from servers defined in the GENTOO_MIRRORS first (to alleviate load on upstream project resources and for other reasons). The SRC_URI variable in individual ebuilds, points to the package's original source files, which is originally downloaded by the ebuild maintainers during ebuild creation and development.
Part of ebuild development is the creation of Manifest files, which ensure the upstream source files are not modified from the time they are downloaded by the ebuild developer, distributed to Gentoo's mirror system, then to their destination on the endpoint system.
Bypassing Gentoo mirrors
Over time, upstream projects who host package source files will move their project's source URLs to new locations. In some instances, upstream projects will discontinue development, which eventually leads to the inability to obtain software sources from upstream locations.
Due to the Gentoo mirroring system, ebuild maintainers can still 'support' ebuilds with deprecated upstream sources. This allows software to be gracefully phased out of the gentoo:: ebuild repository, which is part of a good user experience for the Gentoo community. For these reasons and others, users who choose to bypass the Gentoo mirror system should expect unreliable downloads for source files.
To download the source archives bypassing Gentoo mirrors, set the GENTOO_MIRRORS variable to an empty value from the command-line. For example:
GENTOO_MIRRORS="" emerge --ask www-client/firefox