Xsession: unable to launch "/usr/bin/lxsession -s Lubuntu -e LXDE"

[BionicMac]

Xsession: unable to launch "/usr/bin/lxsession -s Lubuntu -e LXDE" X session
--- "/usr/bin/lxsession -s Lubuntu -e LXDE" not found: falling back to default session.

I get this error on first boot after install and any boot thereafter.

When logging in to the graphical display manager (sddm) _after_ putting in my login credentials.

When the error message appears I click "okay" and it boots into the desktop.

[Ubuntu QA Website (ubuntuqa)]

This bug has been reported on the Ubuntu ISO testing tracker.

A list of all reports related to this bug can be found here:
http://iso.qa.ubuntu.com/qatracker/reports/bugs/1770801

[BionicMac (bionicmac)]

/usr/share/xsessions/Lubuntu.desktop is calling "/usr/bin/lxsession -s Lubuntu -e LXDE"

Contents of Lubuntu.desktop:

...
[Desktop Entry]
Name=Lubuntu
Comment=Lubuntu - Lightweight X11 desktop environment based on LXDE
Exec=/usr/bin/lxsession -s Lubuntu -e LXDE
Type=Application
...

Note: lxsession is not installed on default installation using iso from 5-11-2018.

I changed it to the following (assumming you want to use lxqt-session which is
installed by default) and rebooted:

...
[Desktop Entry]
Name=Lubuntu
Comment=Lubuntu - Lightweight X11 desktop environment based on LXDE
Exec=/usr/bin/lxqt-session
Type=Application
...

The original error is now gone, however, the screen freezes at sddm login immediately
after entering my credentials at the sddm greeter/login.

Here is a link to the log:

https://bionicmac.club/index.php/s/DtMBAr2KC5sZQNi

[BionicMac (bionicmac)]

I'll paste the log here also:

May 12 03:09:21 donald-pc sddm-greeter[709]: file:///usr/lib/x86_64-linux-gnu/qt5/qml/SddmComponents/LayoutBox.qml:51: TypeError: Cannot read property of null
May 12 03:09:21 donald-pc sddm-greeter[709]: file:///usr/lib/x86_64-linux-gnu/qt5/qml/SddmComponents/LayoutBox.qml:52: TypeError: Cannot read property of null
May 12 03:09:21 donald-pc sddm-greeter[709]: file:///usr/lib/x86_64-linux-gnu/qt5/qml/SddmComponents/LayoutBox.qml:53: TypeError: Cannot read property of null
May 12 03:09:21 donald-pc sddm-greeter[709]: file:///usr/lib/x86_64-linux-gnu/qt5/qml/SddmComponents/LayoutBox.qml:59: TypeError: Cannot read property of null
May 12 03:09:21 donald-pc sddm-greeter[709]: file:///usr/lib/x86_64-linux-gnu/qt5/qml/SddmComponents/LayoutBox.qml:60: TypeError: Cannot read property of null
May 12 03:09:22 donald-pc systemd[1]: Started Getty on tty2.
May 12 03:09:32 donald-pc login[786]: pam_unix(login:session): session opened for user donald by LOGIN(uid=0)
May 12 03:09:32 donald-pc systemd[1]: Created slice User Slice of donald.
May 12 03:09:32 donald-pc systemd[1]: Starting User Manager for UID 1000...
May 12 03:09:32 donald-pc systemd[1]: Started Session 3 of user donald.
May 12 03:09:32 donald-pc systemd-logind[575]: New session 3 of user donald.
May 12 03:09:32 donald-pc systemd[871]: pam_unix(systemd-user:session): session opened for user donald by (uid=0)
May 12 03:09:32 donald-pc systemd[871]: Listening on GnuPG network certificate management daemon.
May 12 03:09:32 donald-pc systemd[871]: Listening on GnuPG cryptographic agent and passphrase cache.
May 12 03:09:32 donald-pc systemd[871]: Reached target Paths.
May 12 03:09:32 donald-pc systemd[871]: Reached target Timers.
May 12 03:09:32 donald-pc systemd[871]: Listening on GnuPG cryptographic agent (ssh-agent emulation).
May 12 03:09:32 donald-pc systemd[871]: Listening on GnuPG cryptographic agent and passphrase cache (access for web browsers).
May 12 03:09:32 donald-pc systemd[871]: Starting D-Bus User Message Bus Socket.
May 12 03:09:32 donald-pc systemd[871]: Listening on GnuPG cryptographic agent and passphrase cache (restricted).
May 12 03:09:32 donald-pc systemd[871]: Listening on D-Bus User Message Bus Socket.
May 12 03:09:32 donald-pc systemd[871]: Reached target Sockets.
May 12 03:09:32 donald-pc systemd[871]: Reached target Basic System.
May 12 03:09:32 donald-pc systemd[871]: Reached target Default.
May 12 03:09:32 donald-pc systemd[871]: Startup finished in 155ms.
May 12 03:09:32 donald-pc systemd[1]: Started User Manager for UID 1000.
May 12 03:10:11 donald-pc sddm-greeter[709]: file:///usr/lib/x86_64-linux-gnu/qt5/qml/SddmComponents/LayoutBox.qml:51: TypeError: Cannot read property of null
May 12 03:10:11 donald-pc sddm-greeter[709]: file:///usr/lib/x86_64-linux-gnu/qt5/qml/SddmComponents/LayoutBox.qml:52: TypeError: Cannot read property of null
May 12 03:10:11 donald-pc sddm-greeter[709]: file:///usr/lib/x86_64-linux-gnu/qt5/qml/SddmComponents/LayoutBox.qml:53: TypeError: Cannot read property of null
May 12 03:10:11 donald-pc sddm-greeter[709]: file:///usr/lib/x86_64-linux-gnu/qt5/qml/SddmComponents/LayoutBox.qml:59: TypeError: Cannot read pro...

[Simon Quigley (tsimonq2)]

Right, because lubuntu-default-settings hasn't been cleaned up yet for the LXQt transition.

This can happen when you run a very early alpha of Lubuntu. ;)

[Kamilion (kamilion)]

I'm also getting this from a fresh netinstall of bionic, and picking the lubuntu desktop (qt) option from tasksel.

[Ashfaqur Rahman (ashfaqur.rahman)]

Hi

This is just a hack that I figured out when I wanted to see if it was possible to get a pure LXQt flavor in (l)ubuntu 18.04....

Everything was done in Virtualbox.

First I installed ubuntu 18.04 server (x64), as that is the only way I know of to get a minimal install without X.

Then I installed LXQt desktop pkgs with 'tasksel'

sudo tasksel install lubuntu-qt-desktop

Sure enough after that I started facing the exact same errors as mentioned by the OP.

I checked the following location..

user01@vm-ubuntu:~$ ll /usr/share/xsessions/
total 32
drwxr-xr-x 2 root root 4096 Jul 11 14:29 ./
drwxr-xr-x 289 root root 12288 Jul 11 18:04 ../
-rw-r--r-- 1 root root 157 Feb 13 01:09 Lubuntu.desktop
-rw-r--r-- 1 root root 2309 Dec 15 2017 lxqt.desktop
-rw-r--r-- 1 root root 198 Mar 12 15:41 openbox.desktop
-rw-r--r-- 1 root root 125 Feb 13 01:09 QLubuntu.desktop

I removed the 'Lubuntu.desktop' file and created a symlink with the same name pointing to the file 'lxqt.desktop' and voilà..., problem solved :)

now /usr/share/xsessions/ looks like this

user01@vm-ubuntu:~$ ll /usr/share/xsessions/
total 32
drwxr-xr-x 2 root root 4096 Jul 11 14:29 ./
drwxr-xr-x 289 root root 12288 Jul 11 18:04 ../
lrwxrwxrwx 1 root root 33 Jul 11 14:29 Lubuntu.desktop -> /usr/share/xsessions/lxqt.desktop
-rw-r--r-- 1 root root 2309 Dec 15 2017 lxqt.desktop
-rw-r--r-- 1 root root 198 Mar 12 15:41 openbox.desktop
-rw-r--r-- 1 root root 125 Feb 13 01:09 QLubuntu.desktop

Hope somebody will find this useful
Thanks
Emon