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I have a server to which I would like to have a console connection. Normally this would be done using RS232 port, or using USB to RS232 converter.

But to me it seems like it must be possible to connect the two USB ports directly, given that one of the ports can be made to act like a device. If the port is an OTG (On-the-go), this should be possible as far as I understand.

So my question is, given the above, would it be possible to directly connect two computers, using a single USB cable, for console access?

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The link-level protocol of the USB is a very different one as the RS232. It uses 2 data wires, it is packet-based, it is master-slave and it can connect many nodes on a single wire (RS232 is bidirectional). The abbreviation of "universal serial bus" is a little bit misleading: it is designed to be so universal as the RS232 was, but it is not a stream protocol.

To have a direct stream connection between two machines, some type of data stream should exist over the link-level USB protocol.

The result is that in essence you have an usb-to-serial converter, which acts as an intermediary layer between the USB and a bidirectional data stream. It shouldn't be rs232, and also it shouldn't do a physical conversion.

You can buy a simple usb link cable to interconnect two machines. As two usb slaves can't be connected directly, they also need some intermediary usb master. This works mostly by giving an usb-ethernet interface to the machines connected with them, but giving an usb-serial interface would be possible too, and these devices may exist.

Next to the RS232, the Apple has developed a hardware-extended solution named lightning for that, although I would suggest more the RS232 direction on practical reasons.

However, there is a much smaller diversity in the machines bioses of most PC architectures. If you want a console redirection with them, you have only a physical RS232 connector on the mainboard for the task. Most BIOSes/EFIs won't even use an usb-to-rs232 connector, only the physical rs232 port on the motherboard.

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  • So it is possible to directly connect a USB host with USB device/OTG and use USB serial profile for console access? If so, the tricky part would be to make sure the server has a USB device or OTG port. Also, I would probably not get support from BIOS for this, only from Linux and perhaps also GRUB. – Mats Aug 13 '17 at 11:51
  • @Mats No bios will support it (maybe you can try freebios), but with EFI you may have more luck. Linux can use rs232, probably also from an usb/serial one. – peterh Aug 15 '17 at 6:54

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