If one package blocks another package, the two packages conflict such that they cannot be installed simultaneously. These conflicts are often due to file collisions. In some cases, packages that block each other can be temporarily installed simultaneously. In order to resolve file collisions that occur between two blocking packages that are installed simultaneously, the overlapping files must be removed from the contents list of the package which was installed first.
Some cases may exist such that temporary simultaneous installation of blocking packages will cause some sort of problem. However, this type of solution will only be chosen for blockers that can not be satisfied in any other way, such as by simple adjustment of merge order. In addition, this type of solution will not be chosen if a blocking package will overwrite files belonging to packages from the system set, or packages that are runtime dependencies of Portage itself. These constraints serve to limit the probability that a chosen solution will cause an unforeseen problem.
gtk-doc-am vs. gtk-doc-1.8-r2
These are the packages that would be merged, in reverse order: Calculating dependencies... done! [blocks b ] dev-util/gtk-doc-am (is blocking dev-util/gtk-doc-1.8-r2) [uninstall ] dev-util/gtk-doc-1.8-r2 USE="emacs -debug -doc" [nomerge ] x11-libs/gtk+-2.12.9-r2 USE="X cups jpeg tiff xinerama -debug -doc -vim-syntax" [ebuild N ] dev-util/gtk-doc-am-1.10-r1 0 kB Total: 1 package (1 new, 1 uninstall), Size of downloads: 0 kB Conflict: 1 block
coreutils vs. mktemp
These are the packages that would be merged, in reverse order: Calculating dependencies... done! [nomerge ] sys-apps/coreutils-6.11 [6.9-r1] USE="acl nls xattr (-selinux) -static -vanilla%" [blocks b ] sys-apps/mktemp (is blocking sys-apps/coreutils-6.11) [blocks b ] >=sys-apps/coreutils-6.10 (is blocking sys-apps/mktemp-1.5) [uninstall ] sys-apps/mktemp-1.5 [ebuild U ] sys-apps/coreutils-6.11 [6.9-r1] USE="acl nls xattr (-selinux) -static -vanilla%" 0 kB Total: 1 package (1 upgrade, 1 uninstall), Size of downloads: 0 kB Conflict: 2 blocks