'emerge -vuND --backtrack=30 --keep-going world' fails with: ... These are the packages that would be merged, in order: Calculating dependencies... done! [ebuild U ] sys-apps/systemd-239:0/2::gentoo [238-r7:0/2::gentoo] USE="acl curl gcrypt http kmod lz4 lzma pam pcre policykit resolvconf%* seccomp split-usr ssl sysv-utils -apparmor -audit -build -cryptsetup -elfutils -gnuefi -idn -importd -libidn2 -nat -qrcode (-selinux) {-test} -vanilla -xkb" ABI_X86="32 (64) (-x32)" 0 KiB ... [ebuild rR ] media-gfx/digikam-5.9.0:5::gentoo USE="X gphoto2 handbook jpeg2k kipi lensfun mysql opengl openmp panorama -addressbook -calendar -debug -marble -mediaplayer -scanner -semantic-desktop {-test}" 0 KiB [blocks B ] net-dns/openresolv ("net-dns/openresolv" is blocking sys-apps/systemd-239) Total: 6 packages (2 upgrades, 4 reinstalls), Size of downloads: 0 KiB Conflict: 1 block (1 unsatisfied) * Error: The above package list contains packages which cannot be * installed at the same time on the same system. (net-dns/openresolv-3.9.0:0/0::gentoo, installed) pulled in by net-dns/openresolv required by (net-vpn/vpnc-0.5.3_p550:0/0::gentoo, installed) (sys-apps/systemd-239:0/2::gentoo, ebuild scheduled for merge) pulled in by sys-apps/systemd[pam] required by (sys-auth/pambase-20150213-r1:0/0::gentoo, installed) ... After deleting vpnc and openresolv 'emerge world' works again.
Disable the "resolveconf" USE flag on sys-apps/systemd if you want it to coexist with openresolv.
Removing the the resolvconf USE flag from vpnc helped as well.
