我一直在关注本教程：
$ sudo systemctl start nagios
Failed to start nagios.service: Unit nagios.service failed to load: No such file or directory.
问题的原因是什么？
我有：
$ sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
Nagios Core 4.0.8
Copyright (c) 2009-present Nagios Core Development Team and Community Contributors
Copyright (c) 1999-2009 Ethan Galstad
Last Modified: 08-12-2014
License: GPL
Website: http://www.nagios.org
Reading configuration data...
Read main config file okay...
Read object config files okay...
Running pre-flight check on configuration data...
Checking objects...
Checked 8 services.
Checked 1 …我怎样才能解决这个问题？
我正在使用 Amazon EC2，它是另一个 EC2 实例的映像：
ubuntu@ip:~/LabelMeAnnotationTool-master$ sudo apt-get install apache2
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
apache2-bin apache2-data
Suggested packages:
apache2-doc apache2-suexec-pristine apache2-suexec-custom apache2-utils
The following packages will be upgraded:
apache2 apache2-bin apache2-data
3 upgraded, 0 newly installed, 0 to remove and 269 not upgraded.
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