Webserver: Nginx Unit File

Before viewing the NGINX unit file you need to know where the unit file lives.

Checking Status

Check the status of the NGINX service:

systemctl status nginx

The output contains all of the status information about the service. The location of the unit file is recorded as a part of the status command:

Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset:>

The unit file that defines the nginx.service can be viewed at: /lib/systemd/system/nginx.service.

Print the contents of the file to STDOUT with cat:

cat /lib/systemd/system/nginx.service

Output:

[Unit]
Description=nginx - high performance web server
Documentation=https://nginx.org/en/docs
After=network-online.target remote-fs.target nss-lookup.target
Wants=network-online.target

[Service]
Type=forking
PIDFile=/var/run/nginx.pid
ExecStart=/usr/sbin/nginx -c /etc/nginx/nginx.conf
ExecReload=/bin/sh -c "/bin/kill -s HUP $(/bin/cat /var/run/nginx.pid)"
ExecStop=/bin/sh -c "/bin/kill -s TERM $(/bin/cat /var/run/nginx.pid)"

[Install]
WantedBy=multi-user.target

This course will not cover systemd in great depth.

What it will cover is understanding how:

a unit is defined
to start and stop a service
to configure a service to start automatically on boot
to configure a service to restart itself when it fails.

[Unit]

The unit is defined by the [Unit] section of the unit file.

[Unit]
Description=nginx - high performance web server
Documentation=https://nginx.org/en/docs
After=network-online.target remote-fs.target nss-lookup.target
Wants=network-online.target

This section contains metadata about the unit like it’s description, and where the documentation can be found.

Bonus

The [Unit] section also defines the relationship between this and any other units. This goes beyond the scope of this class. This explains why the After= and Want= directives are found in the [Unit] section of the NGINX unit file.

[Service]

The [Service] section of the unit file provides configuration information to the service associated with this unit file.

[Service]
Type=forking
PIDFile=/var/run/nginx.pid
ExecStart=/usr/sbin/nginx -c /etc/nginx/nginx.conf
ExecReload=/bin/sh -c "/bin/kill -s HUP $(/bin/cat /var/run/nginx.pid)"
ExecStop=/bin/sh -c "/bin/kill -s TERM $(/bin/cat /var/run/nginx.pid)"

From the NGINX unit file:

Type=: the type of service to be created
PIDFile=: the file where the process id should be stored
ExecStart=: the shell command used when the start command is provided
ExecReload=: the shell command used when the reload command is provided
ExecStop=: the shell command used when the stop command is provided

In this course we are most concerned with the ExecStart= directive, and will be accepting the default values for the remaining directives as we don’t need to provide any additional configuration other than the default configuration for those directives.

For the NGINX service the ExecStart= directive is associated with the shell command: /usr/sbin/nginx -c /etc/nginx/nginx.conf.

The absolute path to the nginx package has been provided, this way their is no ambiguity on which version of nginx should be used to start this service.

You can view what this command does by viewing the help of the nginx package:

nginx -help

Output:

Bonus

You could also execute the absolute path of the nginx package as it’s defined in the unit file:

/usr/sbin/nginx -help

So the ExecStart=/usr/sbin/nginx -c /etc/nginx/nginx.conf is simply starting the NGINX webserver and telling it which configuration file to use!

[Install]

The [Install] section configures how the unit should behave when enabled or disabled.

[Install]
WantedBy=multi-user.target

From the NGINX unit file:

WantedBy=: marks this unit as a dependency for the listed argument

Before the argument multi-user.target can be completed the service defined by this unit file must be created.

Bonus

The argument provided to the WantedBy= directive can be a valid unit or a computer run level. The multi-user.target is a run level created when a user can be prompted to login to the machine. This is the only run level we will define in this course, however many other targets may be appropriate for different applications.