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Thread: Fix error: Cannot autolaunch D-Bus without X11 $DISPLAY on script to change wallpaper

  1. #1
    Join Date
    Apr 2008
    Location
    Portugal
    Beans
    63
    Distro
    Lubuntu 12.04 Precise Pangolin

    Unhappy Fix error: Cannot autolaunch D-Bus without X11 $DISPLAY on script to change wallpaper

    Background

    I have created a script that changes my wallpaper periodically. The script works perfectly fine when I run it from bash, but having to manually run it on every startup is becoming annoying, so I decided I would automate the process using `systemd`.

    Scripts

    Following is the script that changes the wallpaper:

    Code:
    targetDir="/home/mypc/Pictures/Wallpapers"
    
    
    function get_next_photo() {
        # Returns a random file form targetdir
        files=( "$targetDir"/* )
        echo "${files[RANDOM % ${#files[@]}]}"
    }
    
    function set_background() {
        # Takes an absolute file path as argument. Need * for spaces in path
        bg="$*"
        echo "Setting background to $bg"
        dconf write "/org/gnome/desktop/background/picture-uri" "'file://$bg'"
    
    }
    
    
    while :
    do
    
    	background=$(get_next_photo)
    	echo "Next background is $background"
    	set_background $background
    	sleep 5m
    done
    And this is the systemd service I created for it, located in /etc/systemd/system/background-changer.service:

    Code:
    [Unit]
    Description=Periodically changes the background wallpaper, taking random images from the Pictures/wallpapers folder
    
    [Service]
    ExecStart=/bin/bash /home/mypc/background_changer.sh
    
    [Install]
    WantedBy=default.target
    Problem

    The problem is that once I start the job using systemd the wallpaper never changes.
    After checking with sudo systemd status background-changer.service, this is what I got:

    Code:
    $ sudo systemctl status background-changer.service 
    ● background-changer.service - Periodically changes the background wallpaper, taking random images from the Pictures/wallpapers folder
         Loaded: loaded (/etc/systemd/system/background-changer.service; disabled; vendor preset: enabled)
         Active: active (running) since Mon 2023-01-09 13:17:32 CET; 7min ago
       Main PID: 14196 (bash)
          Tasks: 2 (limit: 18936)
         Memory: 596.0K
            CPU: 16ms
         CGroup: /system.slice/background-changer.service
                 ├─14196 /bin/bash /home/mypc/background_changer.sh
                 └─17655 sleep 5m
    
    ene 09 13:17:32  systemd[1]: Started Periodically changes the background wallpaper, taking random images from the Pictures/wallpapers folder.
    ene 09 13:17:32 bash[14196]: Next background is /home/mypc/Pictures/Wallpapers/jonatan-pie-3l3RwQdHRHg-unsplash.jpg
    ene 09 13:17:32 bash[14196]: Setting background to /home/mypc/Pictures/Wallpapers/jonatan-pie-3l3RwQdHRHg-unsplash.jpg
    ene 09 13:17:32 bash[14198]: error: Cannot autolaunch D-Bus without X11 $DISPLAY
    ene 09 13:22:32 bash[14196]: Next background is /home/mypc/Pictures/Wallpapers/jonatan-pie-3l3RwQdHRHg-unsplash.jpg
    ene 09 13:22:32 bash[14196]: Setting background to /home/mypc/Pictures/Wallpapers/jonatan-pie-3l3RwQdHRHg-unsplash.jpg
    ene 09 13:22:32 bash[17652]: error: Cannot autolaunch D-Bus without X11 $DISPLAY
    The last line specifically caught my attention:

    Code:
    error: Cannot autolaunch D-Bus without X11 $DISPLAY
    I have searched for some time now how to fix this, but every solution I find is widely different. I went from reinstalling graphic drivers, to password managers with stuff in between, but nothing works:

    - https://anto.online/guides/cannot-au...t-x11-display/
    - https://askubuntu.com/questions/7358...ut-x11-display
    - https://github.com/zowe/zowe-cli/issues/1139
    - https://ubuntu-mate.community/t/erro...-display/11928
    - https://askubuntu.com/questions/6459.../748046#748046

    Can someone help me understand why ?

  2. #2
    Join Date
    Dec 2014
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    2,656

    Re: Fix error: Cannot autolaunch D-Bus without X11 $DISPLAY on script to change wallp

    At the point in time when your systemd service is started the desktop is not yet up and running (and even if it was, the DISPLAY variable would not be accessible to it; variables go from parent to child process, not the other way around). You basically need to start your script after you log in. Instead of using a systemd service I'd use a .desktop file in ~/.config/autostart or I'd look into a user instance of systemd with the services located in ~/.config/systemd/user/.

    Holger

  3. #3
    Join Date
    Apr 2008
    Location
    Portugal
    Beans
    63
    Distro
    Lubuntu 12.04 Precise Pangolin

    Re: Fix error: Cannot autolaunch D-Bus without X11 $DISPLAY on script to change wallp

    Quote Originally Posted by Holger_Gehrke View Post
    At the point in time when your systemd service is started the desktop is not yet up and running (and even if it was, the DISPLAY variable would not be accessible to it; variables go from parent to child process, not the other way around). You basically need to start your script after you log in. Instead of using a systemd service I'd use a .desktop file in ~/.config/autostart or I'd look into a user instance of systemd with the services located in ~/.config/systemd/user/.

    Holger
    I am manually starting the systemd job, so I know the issue has to be the DISPLAY variable not being accessible (because I am already logged in).
    I have taken you advice and I have created the following ~/.config/autostart/.desktop file:

    Code:
    [Desktop Entry]
    Version=1.0
    Name=Wallpaper Changer
    Comment=Periodically changes the background wallpaper, taking random images from the Pictures/wallpapers folder.
    Exec=/home/mypc/background_changer.sh
    Icon=/usr/share/icons/gnome-logo-text.svg
    Terminal=false
    Type=Application
    Categories=Utility;
    Other then repeatedly restarting my computer, how can I test if this works?

  4. #4
    Join Date
    Apr 2008
    Location
    Portugal
    Beans
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    Distro
    Lubuntu 12.04 Precise Pangolin

    Re: Fix error: Cannot autolaunch D-Bus without X11 $DISPLAY on script to change wallp

    After changing to a desktop file, I still found some issues, but with the help of another forum I was able to make it work. Basically the code is fine, but there were some config issues:

    - Script misses a shebang.
    - .desktop-file (not .dektop) should have a meaningful name like wallpaperchanger.desktop.
    - .desktop-file should be executable

    With these fixed, the Desktop solution worked.

    https://askubuntu.com/questions/1449...ile-is-working

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