Ubuntu uses systemd to configure the startup of services.

title: "Configuring Startup Service with systemd in Ubuntu"
date: 2021-12-01T22:44:28+08:00
slug: ubuntu_systemd_service
type: posts
draft: false
categories: ["Linux","Using Software"]
tags: ["ubuntu"]#

systemd#

Systemd is a Linux system tool used to start and manage daemons, and it has become the standard configuration for most distributions.

Background#

Historically, Linux startup used the init process.

The following commands are used to start services.

    $ sudo /etc/init.d/apache2 start
    # or
    $ service apache2 start

This method has two drawbacks.

First, it has a long startup time. The init process starts processes in a serial manner, where the next process can only start after the previous one has started.

Second, the startup scripts are complex. The init process only executes the startup scripts and does not handle other tasks. The scripts need to handle various situations on their own, which often makes the scripts lengthy.

Overview of systemd#

Systemd was created to address these issues. Its design goal is to provide a complete solution for system startup and management.

According to Linux conventions, the letter "d" stands for daemon. The name "systemd" means that it is responsible for managing the entire system.

With systemd, there is no need to use init anymore. Systemd replaces initd and becomes the first process of the system (PID equals 1), with all other processes being its child processes.

    $ systemctl --version

The above command is used to check the version of systemd.

Using systemd to Execute Shell Scripts at Startup#

General Steps#

Create a script that you want to execute immediately at startup. In this example, the script is stored in the location /home/navxin/Example/startup.sh, and its content is as follows:

#!/bin/bash
# Create a file named StartupTouch.txt in the same directory as the script during startup
touch /home/navxin/Example/startup.sh.txt

The script to be executed at startup needs to have executable permissions in order to be run by systemd. Use the following commands:#

chmod u+x /home/navxin/Example/startup.sh
chmod g+x /home/navxin/Example/startup.sh

Go to the directory where systemd places services. In this directory, you can see a large number of service configuration files. Use the following command:#

# Go to the systemd service directory
cd /usr/lib/systemd/system
# View the file list
ls -al

Create a new .service file in this directory to configure the startup script. In this example, the file is named StartupExample.service, and the executed command and the configuration content in the file are as follows:

Create a service configuration file#

sudo touch /usr/lib/systemd/system/StartupExample.service

The following is the content of the StartupExample.service configuration file:

[Unit]
Description=Startup Example

[Service]
ExecStart=/home/navxin/Example/startup.sh

[Install]
WantedBy=multi-user.target

Try manually running the newly created service using the following command:#

# Manually run StartupExample.service
sudo systemctl start StartupExample.service
# View the running log
systemctl status StartupExample.service

    # Delete the file created during the service test
    rm -f /home/navxin/Example/startup.sh.txt
    # Set the service to enable state to run at startup
    sudo systemctl enable StartupExample.service
    # Reboot the machine
    systemctl reboot

Note: Unit#

Systemd can manage all system resources. Different resources are collectively referred to as Units.

There are a total of 12 types of Units.

    Service unit: system services
    Target unit: a group of multiple Units
    Device Unit: hardware devices
    Mount Unit: mount points of file systems
    Automount Unit: automatic mount points
    Path Unit: files or paths
    Scope Unit: external processes not started by systemd
    Slice Unit: process groups
    Snapshot Unit: systemd snapshots, can revert to a specific snapshot
    Socket Unit: inter-process communication sockets
    Swap Unit: swap files
    Timer Unit: timers

The systemctl list-units command can be used to view all Units in the current system.

    # List running Units
    $ systemctl list-units

    # List all Units, including those without configuration files or failed to start
    $ systemctl list-units --all

    # List all inactive Units
    $ systemctl list-units --all --state=inactive

    # List all failed Units
    $ systemctl list-units --failed

    # List all running Units of type service
    $ systemctl list-units --type=service

    # List all running Units of type mount
    $systemctl list-units --type=mount

    # The command is used to list all configuration files.
    $systemctl list-unit-files

    $systemctl list-unit-files --type=mount

Modify the myadmin.service file and add the statement

    After=network-online.target remote-fs.target nss-lookup.target navxin-kn1.mount
    Wants=network-online.target

The complete file content is as follows (part of the content is referenced from nginx.service):

    # /lib/systemd/system/myadmin.service
    [Unit]
    Description=Start myAdmin web server
    Documentation=https://www.lyhuilin.com/
    After=network-online.target remote-fs.target nss-lookup.target navxin-kn1.mount
    Wants=network-online.target

    [Service]
    Environment="WELCOME=Baicai myAdmin Base Environment."
    ExecStartPre=/bin/echo ${WELCOME}
    ExecStart=/baicai/systemdStart/my_admin/my_admin -c /baicai/systemdStart/my_admin/conf/config.yaml
    ExecStop=/bin/kill -s TERM ${MAINPID}

    [Install]
    WantedBy=multi-user.target