Big disclaimer: Before this happened, I accidentally removed an important library (libreadline7), which has removed several important system libraries without me realizing (things like NetworkManager were also removed), which made Ubuntu stop booting properly. I was able to recover from this for my user by entering recovery mode from the bootloader,reinstalling ubuntu-minimal, ubuntu-standard, and ubuntu-mate-desktop. This allowed me to login to my own personal user and everything seemed to be mostly back to normal, however I'm sure some other things are broken, which is why I'm mentioning this.
I have an Ubuntu MATE 18.04 desktop installation with multiple users. For some reason, I am able to login to one user, which was the main user that was configured with the Ubuntu MATE installation. But the other user is unable to login into his MATE session.
After checking some logs in /var/log/lightdm, I could not find anything wrong with the lightdm, and I was led to the user's .xsession-errors file.
I noticed that in the .xsession-errors for that user, there are some errors that don't appear with my user
mate-session[18804]: WARNING: Unable to find provider 'mate-panel' of required component 'panel'
mate-session[18804]: WARNING: Unable to find provider 'caja' of required component 'filemanager'
mate-session[18804]: WARNING: Unable to find provider '' of required component 'dock'
mate-session[18804]: WARNING: Could not launch application 'update-notifier.desktop': Unable to start application: Failed to execute child process “update-notifier” (No such file or directory)
mate-session[18804]: WARNING: Could not launch application 'snap-userd-autostart.desktop': Unable to start application: Failed to execute child process “/usr/bin/snap” (No such file or directory)
mate-session[18804]: WARNING: Could not launch application 'print-applet.desktop': Unable to start application: Failed to execute child process “system-config-printer-applet” (No such file or directory)
mate-session[18804]: WARNING: Could not launch application 'nm-applet.desktop': Unable to start application: Failed to execute child process “nm-applet” (No such file or directory)
sh: 1: /usr/bin/nvidia-settings: not found
mate-session[18804]: WARNING: Could not launch application 'blueman.desktop': Unable to start application: Failed to execute child process “blueman-applet” (No such file or directory)
mate-session[18804]: WARNING: Could not launch application 'org.gnome.DejaDup.Monitor.desktop': Unable to start application: Failed to execute child process “/usr/lib/deja-dup/deja-dup-monitor” (No such file or directory)
mate-session[18804]: WARNING: Could not launch application 'ubuntu-mate-welcome-autostart.desktop': Unable to start application: Failed to execute child process “/snap/bin/ubuntu-mate-welcome” (No such file or directory)
mate-session[18804]: WARNING: Could not launch application 'caja-dropbox.desktop': Unable to start application: Failed to execute child process “caja-dropbox” (No such file or directory)
(process:19290): indicator-sound-WARNING **: 14:39:55.272: volume-control-pulse.vala:735: unable to get pulse unix socket: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.PulseAudio1 was not provided by any .service files
Window manager warning: Log level 128: Name com.canonical.AppMenu.Registrar does not exist on the session bus
Window manager warning: Log level 16: XPresent is not compatible with your current system configuration.
Gtk-Message: 14:41:55.124: GtkDialog mapped without a transient parent. This is discouraged.
Gtk-Message: 14:42:12.848: GtkDialog mapped without a transient parent. This is discouraged.
Xsession: X session started for root at Sun Sep 26 12:24:13 +04 2021
dbus-update-activation-environment: systemd --user not found, ignoring --systemd argument
dbus-update-activation-environment: setting DISPLAY=:0
dbus-update-activation-environment: setting XAUTHORITY=/home/santhosh/.Xauthority
localuser:root being added to access control list
localuser:boinc being added to access control list
/etc/X11/xinit/xinitrc: 2: [: x: unexpected operator
/etc/X11/xinit/xinitrc: 2: [: x: unexpected operator
dbus-update-activation-environment: systemd --user not found, ignoring --systemd argument
dbus-update-activation-environment: setting GTK_MODULES=gail:atk-bridge
/etc/X11/xinit/xinitrc: 16: /etc/X11/Xsession.d/90gpg-agent: gpgconf: not found
/etc/X11/xinit/xinitrc: 18: /etc/X11/Xsession.d/90gpg-agent: gpgconf: not found
dbus-update-activation-environment: systemd --user not found, ignoring --systemd argument
dbus-update-activation-environment: setting QT_ACCESSIBILITY=1
dbus-update-activation-environment: systemd --user not found, ignoring --systemd argument
dbus-update-activation-environment: setting SUDO_GID=1002
dbus-update-activation-environment: setting MAIL=/var/mail/root
dbus-update-activation-environment: setting LC_TIME=en_US.UTF-8
dbus-update-activation-environment: setting USER=root
I figured that there might be an issue with the user's dconf database, but I couldn't figure it out. At this point I'm not sure what to check next. Is there a way to reconfigure the user's X session settings back to defaults?