Ubuntu – Notify-send only works with sudo

Problem

sudo notify-send Test "Hello World"

Displays a notification as expected.

notify-send Test "Hello World"

Does not display a notification.

Further information

Ubuntu version 16.04.

The notifications appear to use notify-osd instead of notification-daemon. Running notify-send appears to launch a notify-osd process under the user that ran notify-send. I'm not sure what dbus is.

No error messages

There are no errors in the syslog. When I run the following code no error messages occur.

#include <libnotify/notify.h>
#include <stdio.h>
int main() {
    gboolean x = notify_init ("Hello world!");
    printf( "notify_init: %d\n", x );
    NotifyNotification * Hello = notify_notification_new ("Hello world", "This is an example notification.", "dialog-information");
    GError *err = NULL;
    x = notify_notification_show (Hello, &err);
    printf( "notify_notification_show: %d\n", x );
    if(err != NULL) {
        printf("Error detected!\n");
        printf("Error message:%s\n", err->message);
    }
    else {
        printf("No error detected.\n");
    }
    g_object_unref(G_OBJECT(Hello));
    notify_uninit();
    return 0;
}

I do not know what I'm doing. Thanks for the help.

Python Notify

In the past, I've used a python program that has working notifications. I tested a hello world notification and it works without sudo!

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import gi
gi.require_version('Notify', '0.7')
from gi.repository import Notify

Notify.init("test")
n = Notify.Notification.new('test', 'test2')
n.set_urgency(Notify.Urgency.CRITICAL)    
n.show()

Code from http://www.devdungeon.com/content/desktop-notifications-python-libnotify

I am not sure why this works. The python Notify is just wrapping the library used in the C example. I'd prefer not to use python but will if I must.

Edit

The problem occurred again. Resolved by adding urgency critical.