On Linux Mint 19 Tara, Umbutu, Gnome, I installed:

korganizer
plasma-workspace
Kalarm

Kalarm "Commands" work but pop-up messages do not. I create a simple message to pop up in a minute or two. When the time arrives there is no message displayed but the entry is removed from the list as I think might be expected. Also, when I click the "Try" button to test it, nothing happens and no popup occurs. There is no error message.

I tried complete removal option in the Synaptic Package Manager, then rebooted and reinstalled all three in list above. Same behavior.

This is a bug I've never heard of before. I would think that if the Try button doesn't work, it's unlikely that pop-up messages will appear. There are two display related possibilities - Gnome and Wayland - that I can think of that may conceivably be contributing to messages not appearing:

1) Which desktop are you running - Gnome or KDE Plasma? If possible, could you log on in a Plasma session and check whether KAlarm works there.

2) Are you using Wayland rather than X11 for your display? If so, perhaps KAlarm pop-up messages don't work with Wayland. You may be able to find out by entering the following commands in a terminal window:
echo $XDG_SESSION_TYPE
echo $DESKTOP_SESSION

I'm on Linux Mint 19 Tara, Umbutu, Gnome.

echo $XDG_SESSION_TYPE gives:
x11

echo $DESKTOP_SESSION gives:
xfce

I logged on as Plasma. But got "all shell packages missing" but the blank black desktop was quickly overlaid with three Kalarm test popup messages that I had created yesterday.

djarvie wrote:This is a bug I've never heard of before. I would think that if the Try button doesn't work, it's unlikely that pop-up messages will appear. There are two display related possibilities - Gnome and Wayland - that I can think of that may conceivably be contributing to messages not appearing:

1) Which desktop are you running - Gnome or KDE Plasma? If possible, could you log on in a Plasma session and check whether KAlarm works there.

2) Are you using Wayland rather than X11 for your display? If so, perhaps KAlarm pop-up messages don't work with Wayland. You may be able to find out by entering the following commands in a terminal window:
echo $XDG_SESSION_TYPE
echo $DESKTOP_SESSION

Can you please open a bug report at https://bugs.kde.org/, containing all the information which you have supplied (including running on XFCE on X11). This will make it easier to track the bug, and ensure that it doesn't get lost. Thanks.

I had another problem on the same system. I had an command set to shutdown the computer each day at a certain time. The time for the shutdown passed either because I'd not logged on in a while or because there was a gap when Kalarm was not running in the background as expected. The result was that when I clicked to start Kalarm it immediately triggered the old command and shutdown the computer. How do I prevent an old command from triggering in such cases?

Edit the alarm (or if creating a new one), and select the option "Cancel if late" (if you don't see that option, click on More Options to show it). This will prevent the alarm running if it is not triggered within the specified time delay after its scheduled time.

Thanks for the last tip!

I've created a bug report at https://bugs.kde.org/show_bug.cgi?id=409538. It would be helpful if you could check that the information there is correct, and update the bug report if necessary. If you want to be notified when the bug status is updated, please log in to KDE bugs and add yourself to the CC list for the bug.

Which edition of Mint Tara did you originally install: Cinnamon, MATE or Xfce?

Are you running the default desktop which came with your installation (i.e. Cinnamon, MATE or Xfce)? If not, which desktop are you running?