UML currently does not support NPTL, so using the default profile will result in failure to build glibc, see bug #120013 for details. I suggest you add a note about needing to use a non-nptl profile for 2.6 UML machines to: a) the Gentoo User Mode Linux Guide [1], b) the Gentoo Upgrading Guide [2], After NTPL support has been added to UML, users can switch to the default profile. [1] http://www.gentoo.org/doc/en/uml.xml [2] http://www.gentoo.org/doc/en/gentoo-upgrading.xml
*** Bug 137913 has been marked as a duplicate of this bug. ***
Added a note to the UML guide. Discussing UML in the gentoo upgrading guide, though, would be out of place. But the update does link to the profile switching chapter of the upgrade guide, and also includes warnings about recompiling & glibc versions (thanks to wolf31o2 for that info). Thanks for reporting.