我已将 Ubuntu 更新至 14.04，并且 apache 停止工作。
我已经重新安装了 apache 和所有依赖项，但没有成功。
当我输入 localhost 时，我看到 apache 正在索引 www/ 文件夹，但该文件夹是空的（尽管我有几个文件和文件夹）。当我输入一个文件夹时，我知道它存在，但我得到了 404。
这是 error.log 输出：
juan@juan-TE5:/var$ tail /var/log/apache2/error.log
[Mon Apr 21 14:46:48.899984 2014] [mpm_prefork:notice] [pid 21861] AH00163: Apache/2.4.7 (Ubuntu) configured -- resuming normal operations
[Mon Apr 21 14:46:48.900108 2014] [core:notice] [pid 21861] AH00094: Command line: '/usr/sbin/apache2'
[Mon Apr 21 14:46:50.326343 2014] [mpm_prefork:notice] [pid 21861] AH00169: caught SIGTERM, shutting down
[Mon Apr 21 14:46:51.650818 2014] [mpm_prefork:notice] [pid 21937] AH00163: Apache/2.4.7 (Ubuntu) PHP/5.5.9-1ubuntu4 configured -- resuming normal operations
[Mon Apr 21 14:46:51.650896 2014] [core:notice] [pid 21937] AH00094: Command line: '/usr/sbin/apache2'
当我输入 apache2 时会发生这种情况
juan@juan-TE5:/var$ apache2
[Mon Apr 21 14:50:24.933493 2014] [core:warn] [pid 22112] AH00111: Config variable ${APACHE_LOCK_DIR} is not defined
[Mon Apr 21 14:50:24.933700 2014] [core:warn] [pid 22112] AH00111: Config variable ${APACHE_PID_FILE} is not defined
[Mon Apr 21 14:50:24.933734 2014] [core:warn] [pid 22112] AH00111: Config variable ${APACHE_RUN_USER} is not defined
[Mon Apr 21 14:50:24.933749 2014] [core:warn] [pid 22112] AH00111: Config variable ${APACHE_RUN_GROUP} is not defined
[Mon Apr 21 14:50:24.933788 2014] [core:warn] [pid 22112] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Mon Apr 21 14:50:24.941240 2014] [core:warn] [pid 22112] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Mon Apr 21 14:50:24.941401 2014] [core:warn] [pid 22112] AH00111: Config variable ${APACHE_LOG_DIR} is not defined
[Mon Apr 21 14:50:24.941419 2014] [core:warn] [pid 22112] 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}