Install libgtk2-unique-perl by entering the following commands in the terminal:
sudo apt update sudo apt install libgtk2-unique-perl
Description:
module for single instance applications
Gtk2::Unique is a Perl interface to the libunique library, which provides a way to write single instance applications. If you launch a single instance application twice, the second instance will either quit or send a message to the running instance.
Homepage: https://metacpan.org/release/Gtk2-Unique
Version: 0.05-3build1
Section: universe/perl