Some Thunar Custom Action that I thought would work (namely, opening multiple folders with Sublime Text), doesn't work.
However, finding what is it that gone wrong is quite hard, since there is no output, even in terminal.
What can I do to get information on a failing Thunar Custom Action?
I know I'm late to the party but I just ran into this. To see the output of the command, you can pipe it into zenity like this:
command | zenity --text-info If you want to see errors, you can redirect stderr to stdout like this:
command 2>&1 | zenity --text-info 
| zenity --text-info at the end of your command in the Command field in the Edit Action dialog. I'm adding my answer many years late, but this is still the top google search result for the so I think it's worth pointing out an alternative for future readers. If you launch Thunar from the terminal and then execute your custom actions, you can see the command's output in the terminal. For example, the following custom action:
command1 | xargs --verbose sh -c '...' gives the following in the terminal:
sh -c '...' 