The monitor can get stuck in 640*480 mode if the system is booted with no monitor connected.
To get the monitor size back for Linux systems, complete the following steps after opening Terminal:
- Type cd /etc/X11
- Type sudo mv xorg.conf xorg.bak.conf
- Restart the system with a monitor attached.
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Get-the-Monitor-Size-resolution-Back-for-Linux-Systems.pdf