and other storage media (USB keydrive, hard disks...) can be used as well, using apt-cdrom or adding file:/ URI to the source list file. apt-cdrom can specify a folder other than a CD-ROM, using the -d option (i.e. a hard disk or a USB keydrive). The Debian CDs available for download contain Debian repositories. This allows non-networked machines to be upgraded. One can also use apt-zip.

Problems may appear when several sources offer the same package(s). Systems that have