Gnome Shell refuses to load on 12.04

Question

Gnome Shell isn't loading and I can't figure out why. According to this snapshot of .xsession-errors, it seems to(?) have something to do with magnifier:

(gnome-shell:2886): GLib-GIO-ERROR **: Settings schema 'org.gnome.desktop.a11y.magnifier' does not contain a key named 'invert-lightness'
gnome-session[2262]: WARNING: Application 'gnome-shell.desktop' killed by signal 5
gnome-session[2262]: WARNING: App 'gnome-shell.desktop' respawning too quickly
gnome-session[2262]: CRITICAL: We failed, but the fail whale is dead. Sorry....

Now, org.gnome.desktop.a11y.magnifier most definitely does contain invert-lightness because I just added it in both dconf-editor and gconf-editor as false, as suggested here. After a reboot, the message still appears.

So, what does this error mean? Is adding invert-lightness not what it's asking for?

Answer 1

So it turns out it wasn't the settings in dconf-editor it was looking for specifically, but somehow the schema had gotten out of sync.

First try reinstalling the package gsettings-desktop-schemas; it didn't work in my case:

If that doesn't work, and this is a bit of a hack, but using the information from the Gnome Shell docs, I recreated the schema entries and compiled them. Gnome Shell lives!

Add missing values

Using (after backing up the file)

gksudo gedit /usr/share/glib-2.0/schemas/org.gnome.desktop.a11y.magnifier.gschema.xml

add the following somewhere in the middle:

<key type="b" name="invert-lightness">
  <default>false</default>
  <summary>Invert lightness</summary>
  <description>(none)</description>
</key>
<key type="d" name="brightness-red">
  <default>0</default>
  <range min="-1.0" max="1.0"/>
  <summary>Brightness (red)</summary>
  <description>Values range between -1.0 to 1.0, where zero indicates no change in brightness, negative values indicate a decrease in brightness and positive values, an increase.</description>
</key>
<key type="d" name="brightness-green">
  <default>0</default>
  <range min="-1.0" max="1.0"/>
  <summary>Brightness (green)</summary>
  <description>Values range between -1.0 to 1.0, where zero indicates no change in brightness, negative values indicate a decrease in brightness and positive values, an increase.</description>
</key>
<key type="d" name="brightness-blue">
  <default>0</default>
  <range min="-1.0" max="1.0"/>
  <summary>Brightness (blue)</summary>
  <description>Values range between -1.0 to 1.0, where zero indicates no change in brightness, negative values indicate a decrease in brightness and positive values, an increase.</description>
</key>
<key type="d" name="contrast-red">
  <default>0</default>
  <range min="-1.0" max="1.0"/>
  <summary>Contrast (red)</summary>
  <description>(none)</description>
</key>
<key type="d" name="contrast-green">
  <default>0</default>
  <range min="-1.0" max="1.0"/>
  <summary>Contrast (green)</summary>
  <description>(none)</description>
</key>
<key type="d" name="contrast-blue">
  <default>0</default>
  <range min="-1.0" max="1.0"/>
  <summary>Contrast (blue)</summary>
  <description>(none)</description>
</key>

Recompile the Schema

sudo glib-compile-schemas /usr/share/glib-2.0/schemas

Once you next logout, select "GNOME" at log in and it should be fixed.

(Note: If the above xml data I recreated could be updated at some point from a working installation, I think that would be even better.)