After doing a fresh install of Ubuntu 18.04 (using gnome), I installed virtualbox both through sudo apt-get install virtualbox

However, when I run it from the command line I get:

VirtualBox: supR3HardenedMainGetTrustedMain: dlopen("/usr/lib/virtualbox/VirtualBox.so",) failed: libQt5Core.so.5: cannot open shared object file: No such file or directory

I tried providing further info, as already suggested here: Virtualbox not starting

When I checked for Qt libs, I can see that they are properly installed since they have ii status.

dpkg -l | grep libqt5

ii libqt5concurrent5:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 concurrent module
ii libqt5core5a:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 core module
ii libqt5dbus5:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 D-Bus module
ii libqt5gui5:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 GUI module
ii libqt5network5:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 network module
ii libqt5opengl5:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 OpenGL module
ii libqt5opengl5-dev:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 OpenGL library development files
ii libqt5printsupport5:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 print support module
ii libqt5sql5:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 SQL module
ii libqt5sql5-sqlite:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 SQLite 3 database driver
ii libqt5svg5:amd64 5.9.5-0ubuntu1 amd64 Qt 5 SVG module
ii libqt5test5:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 test module
ii libqt5widgets5:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 widgets module
ii libqt5x11extras5:amd64 5.9.5-0ubuntu1 amd64 Qt 5 X11 extras
ii libqt5x11extras5-dev:amd64 5.9.5-0ubuntu1 amd64 Qt 5 X11 extras development files
ii libqt5xml5:amd64 5.9.5+dfsg-0ubuntu1 amd64 Qt 5 XML module

However, the following libraries are not found:

ldd /usr/lib/virtualbox/VirtualBox.so | grep not

libQt5Core.so.5 => not found
libQt5Gui.so.5 => not found
libQt5Widgets.so.5 => not found
libQt5Gui.so.5 => not found
libQt5Core.so.5 => not found
libQt5Widgets.so.5 => not found
libQt5Gui.so.5 => not found
libQt5Core.so.5 => not found
libQt5Widgets.so.5 => not found
libQt5Gui.so.5 => not found
libQt5Core.so.5 => not found

Same here:

ldd /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 | grep not
ldd: /usr/lib/x86_64-linux-gnu/libQt5Core.so.5: No such file or directory

Also:

dpkg -S /usr/bin/virtualbox
virtualbox-qt: /usr/bin/virtualbox

I then did a further search regarding Qt and reached this thread, but the solution doesn't work either:Ubuntu 18.4 libQt5Core.so.5: cannot open shared object file: No such file or directory

You can also see where the library files are pointing to:

ls -alht /usr/lib/x86_64-linux-gnu/libQt5*
lrwxrwxrwx 1 root root 24 Apr 14 21:31 /usr/lib/x86_64-linux-gnu/libQt5X11Extras.so.5 -> libQt5X11Extras.so.5.9.5
lrwxrwxrwx 1 root root 24 Apr 14 21:31 /usr/lib/x86_64-linux-gnu/libQt5X11Extras.so.5.9 -> libQt5X11Extras.so.5.9.5
-rw-r--r-- 1 root root 15K Apr 14 21:31 /usr/lib/x86_64-linux-gnu/libQt5X11Extras.so.5.9.5
lrwxrwxrwx 1 root root 18 Apr 14 21:23 /usr/lib/x86_64-linux-gnu/libQt5Svg.so.5 -> libQt5Svg.so.5.9.5
lrwxrwxrwx 1 root root 18 Apr 14 21:23 /usr/lib/x86_64-linux-gnu/libQt5Svg.so.5.9 -> libQt5Svg.so.5.9.5
-rw-r--r-- 1 root root 342K Apr 14 21:23 /usr/lib/x86_64-linux-gnu/libQt5Svg.so.5.9.5
lrwxrwxrwx 1 root root 25 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Concurrent.so.5 -> libQt5Concurrent.so.5.9.5
lrwxrwxrwx 1 root root 25 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Concurrent.so.5.9 -> libQt5Concurrent.so.5.9.5
-rw-r--r-- 1 root root 27K Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Concurrent.so.5.9.5
lrwxrwxrwx 1 root root 37 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5EglFSDeviceIntegration.so.5 -> libQt5EglFSDeviceIntegration.so.5.9.5
lrwxrwxrwx 1 root root 37 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5EglFSDeviceIntegration.so.5.9 -> libQt5EglFSDeviceIntegration.so.5.9.5
-rw-r--r-- 1 root root 714K Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5EglFSDeviceIntegration.so.5.9.5
lrwxrwxrwx 1 root root 30 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5EglFsKmsSupport.so.5 -> libQt5EglFsKmsSupport.so.5.9.5
lrwxrwxrwx 1 root root 30 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5EglFsKmsSupport.so.5.9 -> libQt5EglFsKmsSupport.so.5.9.5
-rw-r--r-- 1 root root 96K Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5EglFsKmsSupport.so.5.9.5
lrwxrwxrwx 1 root root 18 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5 -> libQt5Gui.so.5.9.5
lrwxrwxrwx 1 root root 18 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9 -> libQt5Gui.so.5.9.5
-rw-r--r-- 1 root root 5.4M Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.9.5
lrwxrwxrwx 1 root root 21 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5OpenGL.so.5 -> libQt5OpenGL.so.5.9.5
lrwxrwxrwx 1 root root 21 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5OpenGL.so.5.9 -> libQt5OpenGL.so.5.9.5
-rw-r--r-- 1 root root 346K Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5OpenGL.so.5.9.5
lrwxrwxrwx 1 root root 27 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5PrintSupport.so.5 -> libQt5PrintSupport.so.5.9.5
lrwxrwxrwx 1 root root 27 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5PrintSupport.so.5.9 -> libQt5PrintSupport.so.5.9.5
-rw-r--r-- 1 root root 443K Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5PrintSupport.so.5.9.5
lrwxrwxrwx 1 root root 18 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Sql.so.5 -> libQt5Sql.so.5.9.5
lrwxrwxrwx 1 root root 18 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Sql.so.5.9 -> libQt5Sql.so.5.9.5
-rw-r--r-- 1 root root 292K Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Sql.so.5.9.5
lrwxrwxrwx 1 root root 19 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Test.so.5 -> libQt5Test.so.5.9.5
lrwxrwxrwx 1 root root 19 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Test.so.5.9 -> libQt5Test.so.5.9.5
-rw-r--r-- 1 root root 217K Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Test.so.5.9.5
lrwxrwxrwx 1 root root 22 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5 -> libQt5Widgets.so.5.9.5
lrwxrwxrwx 1 root root 22 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5.9 -> libQt5Widgets.so.5.9.5
-rw-r--r-- 1 root root 6.3M Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5.9.5
lrwxrwxrwx 1 root root 21 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5 -> libQt5XcbQpa.so.5.9.5
lrwxrwxrwx 1 root root 21 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.9 -> libQt5XcbQpa.so.5.9.5
-rw-r--r-- 1 root root 1.1M Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5XcbQpa.so.5.9.5
lrwxrwxrwx 1 root root 18 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Xml.so.5 -> libQt5Xml.so.5.9.5
lrwxrwxrwx 1 root root 18 Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Xml.so.5.9 -> libQt5Xml.so.5.9.5
-rw-r--r-- 1 root root 240K Apr 13 00:24 /usr/lib/x86_64-linux-gnu/libQt5Xml.so.5.9.5

Any help?

Thanks cmak.fr for pointing me towards the solution. I had to reinstall the the libqt5core5a and libdouble-conversion1 packages. Note that this also removed virtualbox-qt, which had to be reinstalled:

sudo apt-get remove libqt5core5a
sudo apt-get install libqt5core5a

sudo apt-get remove libdouble-conversion1
sudo apt-get install libdouble-conversion1

sudo apt-get install virtualbox-qt

At the end, one can check with ldd /usr/lib/x86_64-linux-gnu/libQt5Core.so.5 to see if there are other missing dependencies. If there are, try finding the corresponding package names and reinstall them.

Just to add information, these are the steps I have followed:

# Attempt to run virtualbox from terminal 
$> virtualbox

Qt FATAL: This application failed to start because it could not find or load the Qt platform plugin "xcb" in "".

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.

Reinstalling the application may fix this problem.
Aborted (core dumped)

Finding the path to the executable

$> which virtualbox

/usr/bin/virtualbox

Find a Program's Shared Libraries

$> ldd /usr/bin/virtualbox
not a dynamic executable

Use strace

$> strace /usr/bin/virtualbox
This application failed to start because it could not find or load the Qt platform plugin "xcb"
in "**/usr/lib/x86_64-linux-gnu/qt5/plugins/platforms**".

Available platform plugins are:.... many plugins here 

The Next thing I did (as suggested from another site) was:

#>vim /etc/ld.so.conf.d/libc.conf
# libc default configuration
#/usr/local/lib # comment it out this line

Then issue the following to update the library cache.

#> sudo ldconfig

Then try to run VirtualBox again from the terminal

$> virtualbox
{Finally Works!!!

Hope this helps to fix your Virtualbox. Not sure if I have to uncomment the line /usr/local/lib from above.

Yes, I did uncomment the line

/usr/local/lib # comment it out this line

and everything continues to work fine. I did a reboot to do clean check all is well.

Cheers