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Under /usr/share/gnome-session/sessions are files which describe the different types of sessions available from gnome-session. In these files is a list of required components, eg for shell:


or for fallback:


This appears to be a list of executables, but it is not. If I change gnome-panel to some other type of panel, the session does not start, and I see the following errors in ~/.xsession-errors:

gnome-session[2003]: WARNING: Unable to find required component 'xfce4-panel'

So my question: What is a component, how are they defined, and where does gnome-session look for them?

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up vote 3 down vote accepted

A component is defined in a .desktop like a normal application. It must also include a key defining the name of the component it provides such as:


Here "panel" is the name of the component.

This is documented at

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the link is dead – Adam Ryczkowski Jul 4 '15 at 11:44
fixed ......... – Alistair Buxton Jul 4 '15 at 19:10

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