Cannot login to MATE for one user but not the other

Solution 1:

You have to fully reinstall Ubuntu MATE desktop task-package by

sudo apt-get install ubuntu-mate-desktop^ --reinstall

Note: the ^ in the end of ubuntu-mate-desktop^ means task, so ubuntu-mate-desktop package will be reinstalled with all its dependencies forcibly.

Then carefully reinstall things which are mentioned in the xsession-errors log:

sudo apt-get install --reinstall mate-panel caja update-notifier snapd \
mate-dock-applet system-config-printer network-manager-gnome blueman deja-dup \
caja-dropbox gpgconf

and

sudo snap install software-boutique --classic
sudo snap install ubuntu-mate-welcome --classic

then reboot and try to login using ordinary (not root) user.

After successful login you have to run debsums to reinstall corrupted/removed files which came from deb-packages by using commands below

sudo apt-get install debsums

followed by

xargs -rd '\n' -a <(sudo debsums -c 2>&1 | cut -d " " -f 4 | sort -u | xargs -rd '\n' -- dpkg -S | cut -d : -f 1 | sort -u) -- sudo apt-get install -f --reinstall --

(formatted as inline code for readabilty, please do not edit)

Problems with login of otheruser may be caused by permissions issue. Restore them to defaults using sudo chown -R otheruser:otheruser /home/otheruser (replace otheruser with correct username) and then reboot.