Running Headless - checking Boot screen messages

Question

Its fairly easy now to run headless from scratch with an RPi,

One area it might be an issue though is debugging issues with devices that have been added to the RPi. Often you get indication of these problems in the messages that scroll through during boot.

Are these messages echoed anywhere - to a log - or are they only available if you connect a monitor during boot?

Answer 1

Yes, there are logs for everything.

If you connect a new device to the Pi then the module being loaded will show in dmesg. Eg;

$ dmesg | tail 
[16037.102139] Initializing USB Mass Storage driver...
[16037.102299] scsi4 : usb-storage 2-2:1.0
[16037.102422] usbcore: registered new interface driver usb-storage
[16037.102425] USB Mass Storage support registered.

All other logs will have their place in /var/log/. Some important ones include:

• /var/log/boot - For all boot messages, such as daemons starting.

• /var/log/Xorg.0.log - All Xorg logs. Including any errors.

• /var/log/errors.log - Any system error will also be logged here.

Answer 2

You can see bootup messages by connecting to the UART on pin 14/15 of the GPIO port

Here is how to connect it to one of the PL2303 UARTs that can be found on ebay for a few dollars.

I didn't need to connect GND because I am powering the RPi from a USB port on the same computer.

If you just want to see the boot messages, you'd only need the orange wire. If you want to log in once it boots, you'll need the purple wire too.

If you need to connect GND, it should go to the pin to the left of the orange wire.

Set the serial port to 115200 baud and you are all set