Key Features of LightDM:
- Cross-desktop - supports different desktop technologies.
- Supports different display technologies (X, Mir, ...).
- Lightweight - low memory usage and fast performance.
- Low code complexity
- Supports remote login (incoming - XDMCP, VNC, outgoing - XDMCP, pluggable).
- Easily themeable
- Support for 3D
- Guest sessions.
To know more about lightdm and about how it helps the Ubuntu login please refer to this answer.
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