localhost ~ #  mkdir -p /var/db/pkg/sys-devel/linux-headers-2.6.19.2-r2
localhost ~ # echo sys-kernel> /var/db/pkg/sys-kernel/linux-headers-2.6.19.2-r2/CATEGORY
bash: /var/db/pkg/sys-kernel/linux-headers-2.6.19.2-r2/CATEGORY: Not a directory
localhost ~ # emerge -C =linux-headers-2.6.19.2-r2


!!! The short ebuild name "=linux-headers-2.6.19.2-r2" is ambiguous.  Please specify
!!! one of the following fully-qualified ebuild names instead:

    sys-devel/linux-headers
    sys-kernel/linux-headers

localhost ~ # emerge -C =linux-headers-2.6.19.2-r2