I wrote a bash script that changes the wallpaper (for GNOME3).
#!/bin/bash
# Wallpaper\'s directory.
dir=\"${HOME}/images/wallpapers/\"
# Random wallpaper.
I found some solutions. When you export a variable DBUS_SESSION_BUS_ADDRESS contained in the file ~/.dbus/session-bus/*, dbus-launch does not tell more about the error. However, instead of wallpaper there are artefacts.
Added code:
sessionfile=`find "${HOME}/.dbus/session-bus/" -type f`
export `grep "DBUS_SESSION_BUS_ADDRESS" "${sessionfile}" | sed '/^#/d'`
Now the script looks like this:
#!/bin/bash
# TODO: At night only dark wallpapers.
# Wallpaper's directory.
dir="${HOME}/images/wallpapers/"
# Weird, but necessary thing to run with cron.
sessionfile=`find "${HOME}/.dbus/session-bus/" -type f`
export `grep "DBUS_SESSION_BUS_ADDRESS" "${sessionfile}" | sed '/^#/d'`
# Random wallpaper.
wallpaper=`find "${dir}" -type f | shuf -n1`
# Change wallpaper.
# https://superuser.com/questions/298050/periodically-changing-wallpaper-under-gnome-3/298182#298182
gsettings set org.gnome.desktop.background picture-options "spanned"
gsettings set org.gnome.desktop.background picture-uri "file://${wallpaper}"