_prepare_basetgz() {
    TS_FILE="$UBUILD_WORK_DIR/$CONFIGURATION.tgz.timestamp"
    if ! [ -e "$BASE_TGZ" ]; then
        if sudo pbuilder --create $(_pbuilder_options) \
            "$USE_OTHERMIRRORS" "$OTHER_MIRRORS"; then
            date +%s > $TS_FILE
        else
            RET=$?
            rm -f "$BASE_TGZ"
            return $?
        fi
    else
        if [ -f $TS_FILE ] || [ -n $FORCE_BASETGZ_UPDATE ]; then
            TS=$(cat $TS_FILE)
            CURTIME=$(date +%s)

            VAL=$(expr '(' "$TS" '+' '(' "$BASETGZ_UPDATE_TIMEOUT" '*' 86400 ')' ')' '<' "$CURTIME" ||:)
            if [ $VAL -eq 0 ]; then
                # Okay, the tgz is fresh enough
                return 0
            fi
        fi
            
        if sudo pbuilder --update \
            $(_pbuilder_options) \
            --override-config \
            "$USE_OTHERMIRRORS" "$OTHER_MIRRORS"; then
            date +%s > $TS_FILE
        else
            return $?
        fi
    fi
}