Sys-Admin

Systemd

Introduction

System and service manager for Linux acting as init system (PID 1).
Basic building block for Linux system.
First daemon serves as the root of use space’s process tree.
Bootstraps user space and manages system services. Responsible for initializing the system and launching other services and processes.

Use cases

Django webapp
Create systemd service to run /opt/project-iko/run.sh in background.
Run python app after postgres DB.
Use service account project_iko.
Auto restart on failure.
Restart interval 10 seconds.
Log service events.
Load when booting into graphical mode.

Run.sh

Create, make the script executable, start script file on /opt/project-iko/run.sh directory.

mkdir -p /opt/project-iko/
vi /opt/project-iko/run.sh
chmod +x /opt/project-iko/run.sh
ln -s /opt/project-iko/run.sh

Add:

Systemd service.

Create service file on /etc/systemd/system/ dir.

vi /etc/systemd/system/project-iko.service

Add:

[Unit]
Description=python django app for project iko
Documentation=https://doc.iko.com
After=postgres.service

[service]
ExecStart=/usr/bin/project-iko.sh
User=project-iko
Restart=on-failure
RestartSec=10

[install]
WantedBy=graphical.target

Start and enable the project-iko.service

systemctl start project-iko.service # Start the service
systemctl enable project-iko.service # Run the app on restarts

Reflector with cronjob

Reflector - is a Python script which can retrieve the latest mirror list from the Arch Linux Mirror Status page, filter the most up-to-date mirrors, sort them by speed and overwrite the file /etc/pacman.d/mirrorlist.

Systemd service

Create service file on /etc/systemd/system/reflector-daily.service to run daily cron job.
Add this:

[Unit]
Description=Update Arch Linux mirrorlist daily using Reflector
After=network-online.target
Wants=network-online.target

[Service]
Type=oneshot
ExecStart=/usr/bin/reflector --country 'Kenya,South Africa,Germany,United States' --age 12 --latest 50 --sort rate --fastest 20 --save /etc/pacman.d/mirrorlist >> /var/log/reflector.log 2>&1 # Save log to /var/log/reflector.log

Systemd timer

Create systemd timer file on /etc/systemd/system/reflector-daily.timer.

[Unit]
Description=Run reflector daily
Documentation=https://wiki.archlinux.org/title/Reflector

[Timer]
OnCalendar=daily # Daily run at midnight
Persistent=true # ensures that the task runs if the machine was off during the scheduled time

[Install]
WantedBy=timers.target

Enable and start the timer

sudo systemctl daemon-reexec
sudo systemctl daemon-reload
sudo systemctl enable --now reflector-daily.timer

Status

Check reflector-daily.service status:

systemctl status reflector-daily.service

Check reflector-daily.timer status:

systemctl status reflector-daily.timer

See next run time for systemd.timers:

systemctl list-timers | grep reflector

Debugging

Check systemd logs.

journalctl -xeu reflector-daily.service

-x - Add explanatory help text and metadata
-e - Jump to the end (most recent entries)
-u - Show logs for a specific unit (service)

Check reflector logs.

cat /var/log/reflector.log

Arduino IDE with deesktop shortcut

Download arduino-ide appimage from official site.

wget https://support.arduino.cc/hc/en-us/articles/360019833020-Download-and-install-Arduino-IDE

Make arduino executable then, move to /opt/arduino directory and create symbolic link to /usr/local/bin/arduino.

chmod +x arduino-ide*
mkdir -p /opt/arduino/
mv arduino-ide*.AppImage /opt/arduino/arduino-ide
ln -s /opt/arduino/arduino-ide /usr/local/bin/arduino

Desktop entry

Create desktop config file on /usr/share/applications/arduino-ide.desktop.

[Desktop Entry]
Version=2.3.6
Name=Arduino IDE
Comment=Open-source electronics prototyping platform
Exec=/usr/local/bin/arduino %F
Icon=/opt/arduino/resources/icons/512x512.png
Terminal=false
Type=Application
Categories=Development;Electronics;
MimeType=text/x-arduino;
StartupNotify=true

Permissions

Set proper permissions and update desktop applications.

chmod 644 /usr/share/applications/arduino-ide.desktop
update-desktop-database /usr/share/applications

Setup USB permissions.

usermod -aG dialout,lock,uucp $USER

Create udev rules for arduino devices.

vim /etc/udev/rules.d/99-arduino.rules

Add this:

# Arduino boards
SUBSYSTEMS=="usb", ATTRS{idVendor}=="2341", ATTRS{idProduct}=="0043", MODE="0666"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="2341", ATTRS{idProduct}=="0001", MODE="0666"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="2341", ATTRS{idProduct}=="0010", MODE="0666"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="2341", ATTRS{idProduct}=="0042", MODE="0666"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="2341", ATTRS{idProduct}=="0243", MODE="0666"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="2341", ATTRS{idProduct}=="0001", MODE="0666"

# CH340/CH341 (common on Arduino clones)
SUBSYSTEMS=="usb", ATTRS{idVendor}=="1a86", ATTRS{idProduct}=="7523", MODE="0666"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="1a86", ATTRS{idProduct}=="5523", MODE="0666"

# FTDI (used on some Arduino boards)
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6001", MODE="0666"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6015", MODE="0666"

Apply changes.

# Reload udev rules
sudo udevadm control --reload-rules
sudo udevadm trigger

Reboot for group changes to take effect.