In the URL above there is the code line # umount /mnt/gentoo/boot /mnt/gentoo/proc /mnt/gentoo which suggests that something was previously mounted to /mnt/gentoo/proc. However, there is no such mount command in lower-numbered pages of the manual. For comparison, the old on-line guide (http://www.gentoo.org/doc/en/gentoo-x86-install.xml) had a mount command in code listing 8.6 # mount -t proc proc /mnt/gentoo/proc and a corresponding umount in listing 26.1 # umount /mnt/gentoo/proc
Spend a look at chapter 4.k "Mounting", the proc mounting stuff is explained there. http://www.gentoo.org/doc/en/handbook/handbook.xml?part=1&chap=4#doc_chap11
Stupid of me ... I did search the pages, just must have missed this one somehow. OK, all in order then.
*** Bug 51358 has been marked as a duplicate of this bug. ***