-# Adapt /etc/ to our needs by copying from ./etc_files. This will set
-# basic configurations affecting following steps, such as setup of APT
-# and the locale selection, so needs to be right at the beginning.
-copy_dirtree "${config_tree_prefix}/${PATH_REL_ETC}" "" ${min_modules}
-
-# Migrate to testing.
-upgrade_from_older_release
+# For upgrading only very selectively prepare /etc/ files.
+PATH_REL_APT_CONF=apt/apt.conf
+PATH_REL_SOURCES_LIST=apt/sources.list
+cp ${PATH_MANY}/${PATH_REL_ETC}/all/${PATH_REL_APT_CONF}/* /${PATH_REL_ETC}/${PATH_REL_APT_CONF}/
+apt update
+apt -y -o Dpkg::Options::='--force-confnew' upgrade
+apt -y -o Dpkg::Options::='--force-confnew' full-upgrade
+cp ../${PATH_REL_ETC}/all/${PATH_REL_SOURCES_LIST}/* /${PATH_REL_ETC}/
+apt clean
+apt update
+apt -y -o Dpkg::Options::='--force-confnew' upgrade
+apt -y -o Dpkg::Options::='--force-confnew' full-upgrade
+apt -y autoremove