Различные «переменные конфигурации» не определены, Apache 2.4.18

Я настраивал блог / облачный сервер на Ubuntu 16.04 с Apache 2.4.18, и после перезагрузки моей машины столкнулся с этой ошибкой.

[Wed Aug 03 01:04:41.468928 2016] [core:warn] [pid 3191] AH00111: Config variable ${APACHE_LOCK_DIR} is not defined
[Wed Aug 03 01:04:41.468964 2016] [core:warn] [pid 3191] AH00111: Config variable ${APACHE_PID_FILE} is not defined
[Wed Aug 03 01:04:41.468976 2016] [core:warn] [pid 3191] AH00111: Config variable ${APACHE_RUN_USER} is not defined
[Wed Aug 03 01:04:41.468979 2016] [core:warn] [pid 3191] AH00111: Config variable ${APACHE_RUN_GROUP} is not defined
[Wed Aug 03 01:04:41.468987 2016] [core:warn] [pid 3191] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Wed Aug 03 01:04:41.507710 2016] [core:warn] [pid 3191] AH00111: Config variable ${APACHE_RUN_DIR} is not defined
[Wed Aug 03 01:04:41.507998 2016] [core:warn] [pid 3191] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Wed Aug 03 01:04:41.508128 2016] [core:warn] [pid 3191] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Wed Aug 03 01:04:41.508138 2016] [core:warn] [pid 3191] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Wed Aug 03 01:04:41.508284 2016] [core:warn] [pid 3191] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Wed Aug 03 01:04:41.508292 2016] [core:warn] [pid 3191] AH00111: Config variable ${APACHE_LOG_DIR} is not defined

AH00526: Syntax error on line 74 of /etc/apache2/apache2.conf:
Invalid Mutex directory in argument file:${APACHE_LOCK_DIR}

Строка 74 /etc/apache2/apache.conf:

Mutex file:${APACHE_LOCK_DIR} default

Каким будет самый простой способ исправить эту проблему с переустановкой Apache?