что обозначает флаг nomerge?

emerge -pvtuDB procps

These are the packages that I would merge, in reverse order:

Calculating dependencies ...done!
[ebuild U ] sys-process/procps-3.2.5-r1 [3.2.4-r3] (-n32) 0 kB
[nomerge ] sys-apps/shadow-4.0.5-r3 +nls +pam (-selinux) -skey
[nomerge ] sys-apps/portage-2.0.51.19 -build (-selinux)
...