In this tutorial as an example we create on a GNU/Linux operating system a service with systemd that runs the SimpleHTTPServer written in Python on port 8000 of the local server.
For security reasons this server should NOT be run in production environments.
Table of Contents
- Example of using systemd on GNU/Linux
- Types of drives
- Creating a service with systemd
- Create a Python script
- Starting a systemd service
- Creating a timer with systemd
- Some useful commands for systemd
- References
Example of using systemd on GNU/Linux
Systemd is an init system used in GNU/Linux distributions tobootstrap the user space and then manage all its processes. It is currently the default init system in most GNU/Linux distributions.
Systemd works withunits which are resources (network, usb, etc.) governed byunit files stored in /lib/systemd/system which contain sections and directives.
Types of drives
There are 12 unit types:
Services (.service): services
Target: drive group
Automount: filesystem auto-mount point
Device: kernel device names, which can be seen in sysfs and udev
Mount: filesystem mount point
Path: file or directory
Scope: external process not started by systemd
Slice: A unit of management processes
Snapshot: saved state of systemd
Socket: IPC (inter-process communication) socket
Swap: Swap file
Timer: systemd timers
To name a unit file you use the format<resource_name>.<unit_type>(<resource_name>.<unit_type>) for example:
reboot.service
A target looks like a SysV Init runlevel: for example graphical.target is similar to runlevel 5.
Creating a service with systemd
The steps to create a service in systemd are the following:
1) We open a terminal and create the file with the instructions for the new service:
vim /lib/systemd/system/system/example.service
[Unit]
Description=Example
After=network.target
StartLimitIntervalSec=0
Service] [Service
Type=simple
Restart=always
RestartSec=1
User=user
ExecStart=/usr/bin/env python3 /user/example.py
[Install] [Install] [Install] [Install] [Install] [Install] [Install] [Install] [Install
WantedBy=multi-user.target
Here you have to change the user name and the path to the python script with your data. Save and save the changes.
Create a Python script
2) In the directory /user/ (replace the path with your path written in the previously created file) program the following python script:
vim example.py
import http.server
import socketserver
PORT = 8000
handler = http.server.SimpleHTTPRequestHandler
with socketserver.TCPServer(("", PORT), handler) as httpd:
print("Server started at localhost:" + str(PORT))
httpd.serve_forever()
Save and save the changes.
Starting a systemd service
3) We start the service, verify that it works correctly and enable it to run automatically:
sudo systemctl start example
sudo systemctl status example
sudo systemctl enable example
Finally we open a browser and write the path to the SimpleHTTPServer replacing the IP with yours:
http://10.0.2.2:8000/
Creating a timer with systemd
In this example we will create a timer on GNU/Linux operating systems to run a bash script.
The steps to create a timer are the following:
1) We open a terminal and create the file with the instructions for the new service:
vim /lib/systemd/system/system/date.service
[Unit]
Description=A test
Service] [Service
Type=oneshot
ExecStart=/bin/bash /user/date.sh
[Install] [Install] [Install] [Install] [Install] [Install] [Install] [Install] [Install
WantedBy=multi-user.target
Here you must change the user name and the path to the bash script with your data. Save and save the changes.
2) In the directory /user/ (replace the path with yours written in the file previously created) we program the following script:
vim date.sh
#!/bin/bash
DATE=$$(date '+%Y-%m-%d %H:%M:%S'); echo -e "$DATE" >> /user/log.log
echo -e "Hello world" >> /user/log.log
Save and save the changes.
we give it execution permissions with:
chmod 755 date.sh
3) Now the timer file must be created:
vim /lib/systemd/system/system/date.timer
[Unit]
Description=Runs every 1 minutes fecha.sh
[Timer]
OnCalendar=*:0/1
[Install] [Install] [Install] [Install] [Install] [Install] [Install] [Install] [Install
WantedBy=timers.target
Save and save the changes.
4) We start the service, verify that it works correctly and enable it to run automatically:
sudo systemctl start date
sudo systemctl status date
sudo systemctl enable date
If we make any changes to the systemd files, the following command must be executed:
systemctl daemon-reload
Some useful commands for systemd
Location of drive files:
/etc/systemd/system/
/usr/lib/systemd/system/
List of running drives:
systemctl list-units -type [unit name]
systemctl list-unit-files -type=service
systemctl list-units -type service -all
Checking the status of a service:
systemctl status motd-news.service
References
Debian Wiki. https://wiki.debian.org/Debate/initsystem/systemd
Atareao.es. How to create a service with systemd. https://www.atareao.es/tutorial/trabajando-con-systemd/como-crear-un-servicio-con-systemd/
Wikipedia. systemd. https://es.wikipedia.org/wiki/Systemd
Digital Ocean Tutorial. https://www.digitalocean.com/community/tutorials/how-to-use-systemctl-to-manage-systemd-services-and-units-es
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