Chromium – Open downloaded files

If you wonder, how chromium decides, with which program it opens a downloaded file, take a look at xdg-open

To change the behavior you have to edit ~/.local/share/applications/mimeapps.list

You can also do that, by using a nice tool. For example, if you want to let chromium open pdf files with evince try this
xdg-mime default evince.desktop application/pdf

SSH X forwarding – MIT-MAGIC-COOKIE

If you get the following error

Invalid MIT-MAGIC-COOKIE-1 keyError: Can't open display:

try the following things.

Required software on client site:

xhost
xauth

Required client config (/etc/ssh/ssh_config):

Host *
ForwardX11 yes
ForwardX11Trusted yes