My Xubuntu freezes

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You can monitor the perfomance of your linux with top.

Here you can see which processes how much system resources consume.

htop is a program based on top with color highlighting and fancier design.

You could also run the command line utility dmesg in a terminal to read the kernel log after you regained control of the system. It will display system critical events such as losing the network connection, which may help to debug the issue. Usually only the last view lines are important therefore try dmesg --color=always | tail -n 20 to limit the command's output.

If you loose the network connection for any reason, this could indeed cause a freeze of your session since in the 'Rechnerhalle', your home folder is located on a network share.