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I've made a simple python script to change my wallpaper (Ubuntu 18.04) by randomly taking an image in a specific folder. I use gsettings command. It works when I run it manually, but I want to automate it with crontab.

I had the following error because crontab hasn't all variables I had when I run my script manually:

(process:xxxxx): dconf-WARNING **: 15:07:01.547: failed to commit changes to dconf: Impossible de lancer automatiquement D-Bus sans $DISPLAY X11

So I found some solutions like :

dbus_session_bus_address = 'PID=$(pgrep gnome-session | head -n1) && export DBUS_SESSION_BUS_ADDRESS=$(grep -z DBUS_SESSION_BUS_ADDRESS /proc/$PID/environ|cut -d= -f2-) && '

command = dbus_session_bus_address + 'gsettings set org.gnome.desktop.background picture-uri ' + getRandomImage()

It seems work for most people but I have a problem, my crontab hasn't permissions :

grep: /proc/$pid/environ: Permission denied
dconf-WARNING **: 15:19:01.514: failed to commit changes to dconf: The address indicated is empty 

So I run the script with sudo crontab -e, but I have the following error :

dconf-WARNING **: 15:22:01.807: failed to commit changes to dconf: Connection is closed

Also, I prefer use my user crontab.. What is the best way to do that ?

  • Are you actually using your user crontab (crontab -e) or root's (sudo crontab -e)? I wouldn't be surprised if the latter resulted in a permission error, since /proc/$pid/environ should only be readable by $pid's owner – steeldriver Jul 7 '18 at 15:31
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Thanks to steeldriver's comment, I found the solution !

Actually, the pgrep gnome-session command gives me 2 PID.
When I ls -l /proc/, I can see the first pid directory belongs to gdm (Gnome Display Manager), and the second belongs to my user.

So in my script, I just replace PID=$(pgrep gnome-session | head -n1) by PID=$(pgrep gnome-session | tail -n1) to use the PID associate to my user.

I don't know if this solution (with tail -n1) can work for everyone. I think the best thing to do is to run the pgrep gnome-session command, look at the owner of pid folders, and choose the one that belongs to our user.

Hoping that it will be useful !

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