If this is AGX Xavier dev kit, then if you look to the left of the 40-pin header there will be a micro-OTG USB socket. That socket accepts the provided micro-B USB cable, which causes the AGX to become a “device” when plugged in through that to a host PC. If you monitor “dmesg --follow” on the host PC, and then plug in the USB cable, you will see in dmesg the various “devices” the AGX emulates. Each device creates a file in “/dev”, and so for example, you might see the dmesg log indicating “/dev/ttyTCU0” or “/dev/ttyACM0” (the name depends on the driver). The first tty device should be the serial console.
If you run a serial console program on your Linux host PC, then this can talk to that device just like it is a local login on text/command line.
I prefer “gtkterm”, but “minicom” is popular, and some people use “PuTTY” (which also runs on Windows, but getting the name of the “COM” port in Windows might be more difficult). You can add “gtkterm” with “sudo apt-get install gtkterm”. Then, to talk to the serial console (I’m assuming it is “/dev/ttyACM0”, but adjust for your case), you would do this (but read the next paragraph):
gtkterm -b 8 -t 1 -s 115200 -p /dev/ttyACM0
(this runs with setting 115200 8N1 on port ttyACM0)
The port device special file itself will be owned by root, and group dialout. A regular user can’t perform the above command without using “sudo”, but this is unnecessary. You can simply add your user to group “dialout” instead of sudo every time. If your user name on the PC is “ubuntu”, then this would add your user to group “dialout” (a secondary group):
sudo usermod -aG dialout ubuntu
(after this user “ubuntu” can use any of the regular serial ports without sudo)
Note that serial console programs have the ability to log to file (or clear screen followed by log to file). It is quite easy to tell the program to start logging right before you plug in the Jetson, and whatever you see will be logged from the moment the Jetson starts. You can attach this log to the forum and it says a lot since it include content from before Linux ever loads (dmesg only works if you can log in and then only for logs once Linux starts…it is better if even the boot stages get logged).
Incidentally, when using the capitalized “Image” I speak of the kernel file in “/boot”. When speaking of lower case “image” I am referring to the partition content of the root filesystem (“Image” is installed on the “image” prior to flash).