Mukundan314/README.md

## README.md

      
    Raw
  

              README.md
            
          
    Creating a systemd service

Format of systemd service files

service files for systemd are writtern in a format similar to toml and ini
Sections in the service file


[Unit] and [Install] - carries generic information about the unit that is not dependent on the type of unit
[Service] - carries information about the process the service files executes

Creating the systemd service file

The service files need to be stored inside /etc/systemd/system for systemd to recognize.

So we will create a file name systemd-example.service inside /etc/systemd/system
We can specify how to start the process with the ExecStart option under the service section:
[Service]
ExecStart=/usr/local/bin/systemd-example
We also need to specify the Type option under the service section to tell systemd about the type of the program (i.e. is it a daemon?, will it notify systemd after it started, etc).
In our case out go program is not a daemon and is considered unactive if the process exits so we will be using the Simple as the option for Type:
[Service]
Type=Simple
ExecStart=/usr/local/bin/systemd-example
Since we want to restart the process the it crashes we will need set the Restart option to always:
[Service]
Type=Simple
Restart=always
ExecStart=/usr/local/bin/systemd-example
Next we need to specify the services that needs to be running before the process starts. which we can specify with the WantedBy or RequiredBy options in the install section
For the program we wrote if sockets are started it should work but to be safe we will tell systemd it requries everything required by multi-user.target which requires everything need to setup a multi-user shell:
[Service]
Type=Simple
Restart=always
ExecStart=/usr/local/bin/systemd-example

[Install]
WantedBy=multi-user.target
We can add a description for our service under the unit section:
[Unit]
Description=Example systemd service.

[Service]
Type=Simple
Restart=always
ExecStart=/usr/local/bin/systemd-example

[Install]
WantedBy=multi-user.target
Using the service file

First we need to make systemd load the service file we just created this can be done by either restarting the system or running systemctl daemon-reload
Starting the service

systemctl start systemd-example.service

Running service at startup

systemctl enalbe systemd-example.service


## server.go
package main

import (
	"log"
	"io"
	"net/http"
)

func indexHandler(w http.ResponseWriter, _ *http.Request) {
	io.WriteString(w, "<a href='/crash'>Crash</a>")
}

func crashHandler(w http.ResponseWriter, _ *http.Request) {
	log.Fatal("crashHandler called")
}

func main() {
	http.HandleFunc("/", indexHandler)
	http.HandleFunc("/crash", crashHandler)

	log.Fatal(http.ListenAndServe(":8080", nil))
}

## systemd-example.service
[Unit]
Description=Example systemd service.

[Service]
Type=simple
Restart=always
ExecStart=/usr/local/bin/systemd-example

[Install]
WantedBy=multi-user.target
	package main

	import (
	"log"
	"io"
	"net/http"
	)

	func indexHandler(w http.ResponseWriter, _ *http.Request) {
	io.WriteString(w, "<a href='/crash'>Crash</a>")
	}

	func crashHandler(w http.ResponseWriter, _ *http.Request) {
	log.Fatal("crashHandler called")
	}

	func main() {
	http.HandleFunc("/", indexHandler)
	http.HandleFunc("/crash", crashHandler)

	log.Fatal(http.ListenAndServe(":8080", nil))
	}
	[Unit]
	Description=Example systemd service.

	[Service]
	Type=simple
	Restart=always
	ExecStart=/usr/local/bin/systemd-example

	[Install]
	WantedBy=multi-user.target