The Qt4 framework has been removed from Ubuntu 20.04 main repository. It is however still required for some obsolete applications.

Though it is not recommended, you can still get Qt4 libraries (e.g., libqt4-declarative, qt4-dev-tools, qt4-qmake, libqtwebkit4, and more) as software dependencies or for building an application via this third-party PPA.

NOTE: Qt4 has reached end of life! You may run into security issues with the library. USE IT AT YOUR OWN RISK! And for Ubuntu 22.04 LTS, please scroll down for option 2.

Option 1: Install Qt4 in Ubuntu 20.04

1.) Open terminal either by pressing Ctrl+Alt+T on keyboard or by searching for ‘terminal’ from your system application launcher. When terminal opens, run command:

sudo add-apt-repository ppa:rock-core/qt4

Type user password (no asterisk feedback) when it prompts and hit enter.

2.) After adding the PPA, it should automatically refresh the system package cache. On some Ubuntu derivatives, you may run command to manually update the package cache:

sudo apt update

3.) Finally install the software .deb package, and it should automatically install the required Qt4 libraries after running sudo apt -f install.

Or you may install specified Qt4 package by running command:

sudo apt install PACKAGE_NAME

See here for a full list of available Qt4 libraries.

Option 2: Install Qt4 in Ubuntu 22.04

For the new Ubuntu 22.04 LTS, you can get the Qt4 libraries via this unofficial PPA. The packages there belongs to kelebek333.

1. Firstly, press Ctrl+Alt+T on keyboard to open terminal. When it opens, run the command below to add the PPA:

sudo add-apt-repository ppa:ubuntuhandbook1/ppa

Type user password when it asks (no asterisk feedback) and hit Enter to continue.

2. After adding the PPA, install your old app packages should automatically install Qt4 as dependencies.

To install the packages manually, either run command sudo apt install PACKNAME in terminal or use Synaptic package manager:

Uninstall Qt4:

To remove the PPA, run command:

sudo add-apt-repository --remove ppa:rock-core/qt4

Or remove the PPA for Ubuntu 22.04 using command:

sudo add-apt-repository --remove ppa:ubuntuhandbook1/ppa

To remove all Qt4 libraries, run command:

sudo apt remove --autoremove libqt4* libqtcore4 libqtgui4 libqtwebkit4 qt4*