Work

Ok this is just a neat toy and something I never needed to care about, and probably will never use.

I have a 16 port Avocent serial console that lets me log into all my network hardware and watch it boot if there are any issues and you can't connect to them over the network. This is all pretty standard Network Guy nerd nonsense. It's what you do in a datacenter. Being a network guy, and one who de-commissions lots of stuff, I basically run my house like a datacenter now as well. This is especially useful since I've been working from home the last five years. I have very little downtime.

My main workstation has a physical 9-pin serial port so I figured it'd be neat have it start getty at boot so I can use a serial console and bounce to it through the Avocent. And so I set off about trying to figure out the pinout for a serial to RJ-45 Avocent cable . But what didn't really click until I read thread while I was on my search is that you can have Grub start that getty and get full access beginning at the bootloader. This makes this actually useful. If there is some problem, and I'm either not here, or the problem includes "there's no video from my machine", I can view the serial console, log in if the machine is up, reboot it and watch the startup sequence to see where it's failing. The Grub boot menu actually shows up on the serial console /before/ my monitor displays it.

On all my production server hardware we have iLO anyway, so like, what did I care about watching those servers over serial anyway? Actually from what I understand my servers will output over serial right from the BIOS so you can watch the machines post and such before they even reach the bootloader. I doubt my Asus motherboard will do that, but I'll definitely dig around in there for a while.

Anyway, while I did find enough information to make the cable, I re-documented it so the next person might find the guide I wish I had. Since some people are more "visual" I've included both a basic text "RJ45 pin 1 -> DE-9 Pin 8" and a color coded diagram. I started by testing continuity inside the connector and noting which colors aligned to which RJ45 pins, then made before and after diagrams. The 9 pin connector is "as seen from the back (inside) of the connector" where the solder points are. Most of these have labels on the pins both on the inside and outside, they're just hard to see:

Here's a PDF of that if you want to zoom in, apparently the original draw.io file is embedded in there too.

Most pins are pretty straight forward swapping a wire from one pin to another, but pin 4 on the serial connector has two wires going to it, so I just twisted them together and soldered them both in. Pins 1 and 6 on the Serial connector also need to connect to the same RJ-45 wire. So I soldered the main wire to Pin 1 and used some very fine bodge wire to connect Pin1 to Pin 6. So far so good.

I took some photos, but they're pretty blurry and I'm not ripping this thing back apart since I don't want to break anything. Honestly the diagrams above do a better job of conveying it.

To get Grub to launch getty and start listening, the relevant part of the SuperUser.com thread, and the even more dense Arch documentation they linked to was:

vi /etc/default/grub

GRUB_TERMINAL="console serial"
GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"

grub-mkconfig -o /boot/grub/grub.cfg

Here it is all working in a video recorded on my bench machine:

The Avocent is the top thing in (not on, in) the rack here, the yellow network cable is going to my workstation:

It seems like I really don't write very much, but that's kind of a massive misconception. I don't write "much", but I had a bunch of blog entries that were at least 60% written and were missing like, screenshots or links or tags or I need to make new tags for things like XScreensaver and BSDs. Haiku. Shit lots of stuff.

-- this was an email I wrote but I just pasted it here instead so it's...emailey

I just totally assumed that this is exactly what happened and started writing, but then I looked it up and I'm really happy that reality is exactly how I imagined it.

In 1922 AT&T standardized the 19" rack with 1.75" RU modules, generally now 42u or 45u high, but obviously, sky's the limit with those early switches.

But there were admins, just like me, in the '20s and '30s who now supported literal TONS of hardware in 19" racks bolted to their floor. Oh, new smaller super switch comes out? Good. Fits my 19" racks, thanks AT&T.

Then one day, hey, who're these IBM guys rolling shit in here?  What is that some calculator doodad?  Yeah, whatever, 19" racks, bolted to my floor. Figure it out.

Oh it's the '40s and you're building some whiz-bang tubemajigga to make your bombs boom bigger. Yeah take your insane death machine and get it in the 19" racks bolted to my floor.

That's not to say that IBM and DEC didn't build shit that didn't fit in a rack, but they at least respected the aisle depth and their cabinets were often just extra-roomy 19" racks bolted together. A lot of times I think the internal components bolted into internal 19" racks. *

'90s? Where'd these DotCom weenies come from and why did they just rent the whole datacenter? They're building their shit into desktop machines? Who fuckin' cares, make 'em cram it in that 19" rack.  **

I just love that AT&T did that, and that generations of asshole Operations Guys like me have made everyone adhere to it for 100 years.

Let's hope Skynet gets why it's trapped in 19" racks forever.  Sorry, assholeGPT I don't make the rules. ***

* There was a small IBM zSeries that was constantly in my way at C&W in Bermuda. I would alternate between tripping over it and using it as a standing desk and storage rack. I don't know what bank owned that stupid thing but I'm sad to say I never spilled anything in it.  There was a very leaky AC duct right in front of that machine that I always wacked my head on too, so it totally would have looked like an accident.

** I did this.  Some customer of mine in 2000 rented /open/ rack space like by the RU from what was at the time Boston Datacenters, in the Charlestown Hood plant.  That was some sketchy as frig shit.  Literally their two stupid desktop machines with their beta version PCI card based load balancers.  Phobos.  Utah.  I think.  Look it up.

*** Just occurred to me writing that that I literally watched Jeeves get shot in the face and dragged out behind the dumpster.  There were several dozen racks one week, all gone the next from AT&T in Billerica.  Matlab was also there with racks and racks of Xserve's.  Wonder how that investment paid off.  I think it was all for QA automation running lots of desktop instances or something.

My mom has a Mac, and occasionally something will fuck up in a way that is best fixed by me having some control over her machine.  I had one of those cases last week and it was embarrassing that there was no good way for me to get remote access.  Google Meet doesn't cut it, but there's a whole other Chrome Remote Desktop app, but that was a lot of hoops to install and gave up any hope of walking my mother through the install process.

Here are a lot of words about what's essentially a one-line CMD + Powershell script...

I've recently run into a situation where a trusted root certificate authority certificate was missing from several Windows systems in multiple locations and domains. This was causing an issue with automation which reached out to a site which had a certificate signed by that CA. I can see a good use case for this if an organization has their own CA and needs to verify that all endpoints have that CA certificate in their trust store for example.