Creating a desktop shortcut

[John Hupp]

I want to create a desktop shortcut for a command that I ordinarily run in an lxterm window thus:

sudo ltsp-update-image --cleanup /

I tried a standard desktop shortcut with the relevant line:

Exec=sudo ltsp-update-image --cleanup /

but running the shortcut produces no results.

I also tried modifying that to:

Exec=gksudo ltsp-update-image --cleanup /

But likewise running that produces no results.

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I also tried creating a bash script with the contents:

#!/bin/bash
sudo ltsp-update-image --cleanup /

And alternatively with line 2:

gksudo ltsp-update-image --cleanup /

and simply also with line 2:

ltsp-update-image --cleanup /

Trying to run any of those versions, it prompts to Execute or to Execute in Terminal, but none of those choices runs the update program or even prompts
for a password.

What am I doing wrong?