$ sudo service apache2 restart Job for apache2.service failed because the control process exited with error code. See "systemctl status apache2.service" and "journalctl -xe" for details.

手贱，想解决ssl 无法访问的问题，修改apache2配置，结果出问题了：

$ sudo service apache2 restart
Job for apache2.service failed because the control process exited with error code.
See "systemctl status apache2.service" and "journalctl -xe" for details.

虽然找到了许多网友的解决办法，但是没有一个全套解决办法，只好耐心一个合着试验，
最终解决了。
1、重新安装apache2

$ systemctl restart apache2
$ journal -xe 
$ sudo apt-get purge apache2
$ sudo apt autoremove apache2
$ sudo apt-get purge apache2
$ sudo apt-get purge apache2*
$ sudo apt-get install apache2
$ sudo service apache2 start

2、重点在这里：
重新安装了apache2，网站正常访问了，但是php却无法正常运行，
问题是这个
php7.3没有运行，
所以：sudo  a2enmod php7.3
但是出现如下提示：
Considering dependency mpm_prefork for php7.3:
Considering conflict mpm_event for mpm_prefork:
ERROR: Module mpm_event is enabled - cannot proceed due to conflicts. It needs to be disabled first!
Considering conflict mpm_worker for mpm_prefork:
ERROR: Could not enable dependency mpm_prefork for php7.3, aborting

所以接着：
sudo a2dismod mpm_event
Module mpm_event disabled.
To activate the new configuration, you need to run:
  systemctl restart apache2

OK，解决了

installing boost 166

issue：

 # cmake .. -DENABLE_MYSQL=OFF -DENABLE_SSL_KEYLOG=ON -DFORCE_TCP_FASTOPEN=ON -DSYSTEMD_SERVICE=AUTO

CMake Error at /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:146 (message):

  Could NOT find Boost: Found unsuitable version "1.65.1", but required is at

  least "1.66.0" (found /usr/include)

Call Stack (most recent call first):

  /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:391 (_FPHSA_FAILURE_MESSAGE)

  /usr/share/cmake-3.16/Modules/FindBoost.cmake:2179 (find_package_handle_standard_args)

  CMakeLists.txt:39 (find_package)

-- Configuring incomplete, errors occurred!

See also "/root/trojan/build/CMakeFiles/CMakeOutput.log".

See also "/root/trojan/build/CMakeFiles/CMakeError.log".

1. Download Boost from official source
2. Extract it
3. Open terminal and cd to extracted dir
4. run "./bootstrap.sh --help" command to see help
5. Then run "./bootstrap.sh" command it will take some time to build
6. Then run "sudo ./b2 install" to install boost.
7. The default installation location are "/usr/local/inlcude/boost" for header files and "/usr/local/lib" for compiled libraries

refrence:

 https://waqarrashid33.blogspot.com/2017/12/installing-boost-166-in-ubuntu-1604.html