今天升級kali 導致apache 無法啓動，問題如下：
root@kali:~# apache2 -k start
[Sat Jan 21 21:01:16.273933 2017] [core:warn] [pid 3248] AH00111: Config variable ${APACHE_RUN_DIR} is not defined
apache2: Syntax error on line 80 of /etc/apache2/apache2.conf: DefaultRuntimeDir must be a valid directory, absolute or relative to ServerRoot或：
root@kali:/etc/apache2# apache2 -k start
[Sat Jan 21 22:05:56.705639 2017] [core:warn] [pid 10577] AH00111: Config variable ${APACHE_PID_FILE} is not defined
[Sat Jan 21 22:05:56.705819 2017] [core:warn] [pid 10577] AH00111: Config variable ${APACHE_RUN_USER} is not defined
[Sat Jan 21 22:05:56.705866 2017] [core:warn] [pid 10577] AH00111: Config variable ${APACHE_RUN_GROUP} is not defined
[Sat Jan 21 22:05:56.705919 2017] [core:warn] [pid 10577] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Sat Jan 21 22:05:56.713958 2017] [core:warn] [pid 10577:tid 3073427200] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Sat Jan 21 22:05:56.714454 2017] [core:warn] [pid 10577:tid 3073427200] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Sat Jan 21 22:05:56.715159 2017] [core:warn] [pid 10577:tid 3073427200] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
AH00543: apache2: bad user name ${APACHE_RUN_USER}這是由於升級後apache 配置文件變化，沒有導入新的apache 環境變量。
解決辦法 :
source /etc/apache2/envvars
或
. /etc/apache2/envvars