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For tcp, just checking $?. If connection failed, $? won't be 0: $ >/dev/tcp/google.com/81 bash: connect: Network is unreachable bash: /dev/tcp/google.com/81: Network is unreachable $ echo $? 1 It will take time for bash to realize that the connection failed. You can use timeout to trigger bash: $ timeout 1 bash -c '>/dev/tcp/google.com/80' ...


3

In general, you can't. Unlike TCP, UDP is connectionless. You can't detect that a port is open simply by making a do-nothing connection to it like you can with TCP. Rather, you need to send data to the port and see what happens, and the details of UDP as implemented in the real world make interpreting the results difficult. Even sophisticated ...


1

In the simplest scenario, the so-called DDX (Device Dependent X) part of the X server will identify your video driver and use ioctl calls to initialize it, configure the video adapter and (usually) get the framebuffer address. The framebuffer will then be used for rendering. Here is a much more detailed description of the process. Things will get more ...



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