You can use the following command to check the version of a specific package installed on a Debian or Ubuntu Linux system using the apt-get command:
apt-cache policy package_name
Alternatively, you can use the following command to achieve the same result using the aptitude command:
aptitude show package_name
In both commands, replace package_name with the name of the package you want to check the version for. The output will show the version of the package that is currently installed on the system, as well as the versions that are available for installation from the package repositories.