systemctl Use systemd to Start a Linux Service at Boot

What is systemd?

systemd is a Linux system tool initially developed by the Red Hat Linux team. It includes many features, including a bootstrapping system used to start and manage system processes. It is currently the default initialization system on most Linux distributions. Many commonly used software tools, such as SSH and Apache, ship with a systemd service.

It is simple to create a custom systemd service that will run any script or process you choose. Although there are several ways to run a script or start a process when your Linode boots, a custom systemd service makes it easy to start, stop, or restart your script, as well as configure it to start automatically on boot. systemd offers the advantage of using a standardized interface that is consistent across all Linux distributions that support it.

Create a Custom systemd Service

  1. Create a script or executable that the service will manage. This guide uses a simple Bash script as an example:

    File: test_service.sh
    1
    2
    3
    4
    5
    6
    7
    8
    
    DATE=`date '+%Y-%m-%d %H:%M:%S'`
    echo "Example service started at ${DATE}" | systemd-cat -p info
    
    while :
    do
    echo "Looping...";
    sleep 30;
    done

    This script will log the time at which it is initialized, then loop infinitely to keep the service running.

  2. Copy the script to /usr/bin and make it executable:

    sudo cp test_service.sh /usr/bin/test_service.sh
    sudo chmod +x /usr/bin/test_service.sh
    
  3. Create a Unit file to define a systemd service:

    File: /lib/systemd/system/myservice.service
    [Unit]
    Description=Example systemd service.
    
    [Service]
    Type=simple
    ExecStart=/bin/bash /usr/bin/test_service.sh
    
    [Install]
    WantedBy=multi-user.target

    This defines a simple service. The critical part is the ExecStart directive, which specifies the command that will be run to start the service.

  4. Copy the unit file to /etc/systemd/system and give it permissions:

    sudo cp myservice.service /etc/systemd/system/myservice.service
    sudo chmod 644 /etc/systemd/system/myservice.service
    

    For more information about the unit file and its available configuration options, see the systemd documentation.

Start and Enable the Service

  1. Once you have a unit file, you are ready to test the service:

    sudo systemctl start myservice
    
  2. Check the status of the service:

    sudo systemctl status myservice
    

    If the service is running correctly, the output should resemble the following:

      ● myservice.service - Example systemd service.
       Loaded: loaded (/lib/systemd/system/myservice.service; enabled; vendor preset: enabled)
       Active: active (running) since Tue 2018-05-01 18:17:14 UTC; 4s ago
     Main PID: 16266 (bash)
        Tasks: 2
       Memory: 748.0K
          CPU: 4ms
       CGroup: /system.slice/myservice.service
               ├─16266 /bin/bash /usr/bin/test_service.sh
               └─16270 sleep 30
    
    May 01 18:17:14 localhost systemd[1]: Started Example systemd service..
    May 01 18:17:14 localhost cat[16269]: Example service started at 2018-05-01 18:17:14
    May 01 18:17:14 localhost bash[16266]: Looping...
    
  3. The service can be stopped or restarted using standard systemd commands:

    sudo systemctl stop myservice
    sudo systemctl restart myservice
    
  4. Finally, use the enable command to ensure that the service starts whenever the system boots:

    sudo systemctl enable myservice
    
      Created symlink from /etc/systemd/system/multi-user.target.wants/myservice.service to /lib/systemd/system/myservice.service.
    
  5. Reboot your Linode from the Linode Manager and check the status of the service:

    sudo systemctl status myservice
    

    You should see that the service logged its start time immediately after booting:

      ● myservice.service - Example systemd service.
       Loaded: loaded (/usr/lib/systemd/system/myservice.service; enabled; vendor preset: disabled)
       Active: active (running) since Wed 2018-05-02 15:03:07 UTC; 48s ago
     Main PID: 2973 (bash)
       CGroup: /system.slice/myservice.service
               ├─2973 /bin/bash /usr/bin/test_service.sh
               └─3371 sleep 30
    
    May 02 15:03:07 localhost systemd[1]: Started Example systemd service..
    May 02 15:03:07 localhost systemd[1]: Starting Example systemd service....
    May 02 15:03:07 localhost bash[2973]: Looping...
    May 02 15:03:37 localhost bash[2973]: Looping...
    

Troubleshooting

  • “Example service started at …” line does not appear in the output of the status command. The systemd-cat output is not reliable because of a race condition. As a workaround update the test_service.sh file as follows:
    File: test_service.sh
     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    
    info=/tmp/myservice-systemd-cat-pipe-info
    mkfifo "$info"
    trap "exec 3>&-; rm $info" EXIT
    systemd-cat -p info < "$info" &
    exec 3>"$info"
    
    DATE=`date '+%Y-%m-%d %H:%M:%S'`
    echo "Example service started at ${DATE}" | systemd-cat -p info
    
    while :
    do
    echo "Looping...";
    sleep 30;
    done
0 (0)
Article Rating (No Votes)
Rate this article
Attachments
There are no attachments for this article.
Comments
There are no comments for this article. Be the first to post a comment.
Full Name
Email Address
Security Code Security Code
Related Articles RSS Feed
ZPOOL: Verify/change properties of a zpool
Viewed 858 times since Sun, Jun 3, 2018
How to automate SSH login with password? ssh autologin
Viewed 817 times since Fri, Jun 8, 2018
Script to Offline and Remove A Disk In Linux
Viewed 657 times since Mon, Jan 28, 2019
Linux An introduction to swap space on Linux systems
Viewed 1208 times since Thu, Jan 23, 2020
Expand or grow a file system on a Linux VMWare VM without downtime
Viewed 835 times since Fri, Jul 27, 2018
RHEL: Rebuilding the initial ramdisk image
Viewed 2717 times since Sat, Jun 2, 2018
Easily Find Bugs In Shell Scripts With ShellCheck
Viewed 1029 times since Thu, Apr 18, 2019
12 Tcpdump Commands – A Network Sniffer Tool
Viewed 963 times since Fri, Jul 27, 2018
RHEL: Create a local RPM repository
Viewed 1637 times since Sun, May 27, 2018
Fedora 32: Simple Local File-Sharing with Samba CIFS Linux
Viewed 619 times since Sun, Dec 6, 2020