[SOLVED] How to see Linux Booting over Serial Port

[LeanMan82]

I just bought a small form factor computer (Dell Optiplex 9020) that has a serial port and mint installed but when I boot up the machine I can't monitor its serial information through this serial port. On another machine (a laptop) I have a Serial to USB converter cable directly connected to the Dell Optiplex 9020's serial port. I can't seem to get any type of response from the Optiplex's serial port. Any ideas? Thanks for any responses.

 

[Grobe]

Try to check if the serial port adapter is in fact recognised.

In Terminal, type lsusb -t, and then post back the result (use code tag for better to read).

 

[LeanMan82]

Try to check if the serial port adapter is in fact recognised.

In Terminal, type lsusb -t, and then post back the result (use code tag for better to read).

Here is the results of lsusb -t although I don't know if that makes sense since I said that I am trying to monitor the serial port attached to the motherboard. For that reason I've also attached dmesg | grep tty output. Let me know if there are any other debugging steps I can take on. Thanks!

adminuser@OptiPlex-9020:~$ lsusb -t
/:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/6p, 5000M
/:  Bus 03.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/15p, 480M
    |__ Port 6: Dev 2, If 0, Class=Mass Storage, Driver=usb-storage, 480M
    |__ Port 6: Dev 2, If 1, Class=Human Interface Device, Driver=usbhid, 480M
    |__ Port 6: Dev 2, If 2, Class=Human Interface Device, Driver=usbhid, 480M
    |__ Port 12: Dev 3, If 1, Class=Human Interface Device, Driver=usbhid, 12M
    |__ Port 12: Dev 3, If 2, Class=Human Interface Device, Driver=usbhid, 12M
    |__ Port 12: Dev 3, If 0, Class=Human Interface Device, Driver=usbhid, 12M
/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/3p, 480M
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/8p, 480M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/3p, 480M
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/6p, 480M

adminuser@OptiPlex-9020:~$ dmesg | grep tty
[    0.000000] console [tty0] enabled
[    0.760257] 00:06: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A
[    0.782035] 0000:00:16.3: ttyS4 at I/O 0xf0e0 (irq = 19, base_baud = 115200) is a 16550A

 

[Grobe]

Ok, but you're talking about "Serial to USB converter cable", so then it suggested usb to serial converter.

I suggest you rephrase the first post so it makes it clear what you have actually done, and if it worked or not.

 

[LeanMan82]

Ok, but you're talking about "Serial to USB converter cable", so then it suggested usb to serial converter.

I suggest you rephrase the first post so it makes it clear what you have actually done, and if it worked or not.

Hi Grobe, I've updated my original post. Hopefully its a bit clearer.

 

[LeanMan82]

So I performed a simple loopback test using the directions here both on the Optiplex 9020 and on my USB/Serial cable connected to my laptop and I confirmed that the loopback works. So I know the serial ports work but no data from the BIOS/dmesg/etc are being logged to the serial port on the linux machine. Maybe thats the problem? Do I need to configure the linux machine to output bios and other data out to the serial port perhaps?

 

[LeanMan82]

So I have done a little bit more work on this now. I was able to transmit characters from the DELL serial port to the Laptop's Serial/USB converter cable by connecting pin 3 (TX) of the DELL and pin 2 (RX) of the Laptop and then when I sent characters from the DELL to the Laptop, I was able to see the characters show up on the Laptop.

Does this mean I have the wrong hardware maybe? Am supposed to get some kind of adapter cable for my serial port or USB/Serial converter cable? If anyone knows, I would really appreciate it! Thank you!

 

[LeanMan82]

Figured it out. I was missing a Null Modem cable otherwise known as a crossover cable. Also followed the following directions for the linux grub configuration to see serial output: https://www.hiroom2.com/2018/04/30/ubuntu-1804-serial-console-en/