I have been setting up a blog/cloud server on Ubuntu 16.04 with Apache 2.4.18 and after rebooting my machine, came across this error.
[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}
Line 74 of /etc/apache2/apache.conf:
Mutex file:${APACHE_LOCK_DIR} default
What would be the easiest way to fix this short of reinstalling Apache?