Cronjobs are usually CLI scripts. But JoliNotif's Unix/Linux drivers are GUI applications. This means you need to specify the display where the notification will be sent.
You can achieve this by setting the XDG_RUNTIME_DIR environment variable in your
cronjob:
* * * * * XDG_RUNTIME_DIR=/run/user/$(id -u) php /path/to/your/script
Note On some system, you may also/instead need to set DISPLAY env var and/or to run
xhost +local:. For more information, please have a look at https://help.ubuntu.com/community/CronHowto#GUI_Applications
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