To list all packages on a Debian-based Linux system, such as Ubuntu, that could be updated and applied to the system, you can use the apt-get or apt command with the upgrade option.
To list all upgradeable packages using apt-get, run the following command:
apt-get upgrade -u
To list all upgradeable packages using apt, run the following command:
apt upgrade -u
This will list all packages that have updates available, along with the current version and the version that would be installed by the upgrade. It will also show the size of the package and the amount of disk space that would be required to install the update.
You can then choose to upgrade the packages individually or upgrade all packages at once by running the apt-get upgrade or apt upgrade command without the -u option.
Keep in mind that upgrading packages may cause some configuration files to be modified or replaced, so it is a good idea to make a backup of important files before upgrading.