CPUs are computers

So I wanted to get a Shuttle DX30 working under LTSP. First step, it uses a pxe-client-id that's 9 bytes long. CentOS's dhcpd throws away anything that doesn't have a 17 byte pxe-client-id. I have no idea why. I tried poking around the RFCs but didn't find much of interest.

Once I patched dhcped, PXE booting worked and I managed to load a kernel. Except it was slow.

Very.

Very.

Very.

Slow.

Just how slow? It took over 30 minutes to get to a XDM prompt slow.

I saw Machine check events going past. To track those down, I put my laptop's 2.5 inch HDD into it. This was also slow. While not as bad, it was clearly not working properly. But I got mcelog to grab the following:

mcelog: failed to prefill DIMM database from DMI data
mcelog: mcelog read: No such device
Hardware event. This is not a software error.
MCE 0
CPU 0 BANK 4 
ADDR fef5d200 
TIME 1531800239 Tue Jul 17 00:03:59 2018
MCG status:
MCi status:
Error overflow
Uncorrected error
MCi_ADDR register valid
Processor context corrupt
MCA: Internal unclassified error: 408
Running trigger `unknown-error-trigger'
STATUS e600000000020408 MCGSTATUS 0
MCGCAP c07 APICID 0 SOCKETID 0 
CPUID Vendor Intel Family 6 Model 92

After some messing around, cursing the Gods, discussing Intel NUCs on #ltsp, general lack of sleep, I found the solution : kernel-ml

yum -y  --enablerepo=elrepo-kernel install kernel-ml
joe /etc/grub.conf # set default=0

It should be noted it took over 10 minutes for dracut to create the initrd for kernel-ml. But once I then booted into the new kernel, everything was fine. I installed kernel-lt as a test, because it needs the CPU and the disk to run smoothly and it took 2 minutes, which is annoying but expected. For reference, installing kernel-ml on my desktop takes 1.5 minutes but it has an SSD.

kernel-lt was a failure, 9m54 to install kernel-ml-4.17.5-1.el6.elrepo.x86_64. I booted back into kernel-ml, removed and reinstalled kernel-ml-4.17.5-1.el6.elrepo.x86_64 and it took 1m52. So kernel-ml is the clear winner.

Now to find out how to install kernel-ml into LTSP.

LTSP and x11vnc

A few years back, I wrote a system that ended up replacing about 200 terminals in 5 different offices with LTSP running on VMs. 2 and bit years latter, the last bunch of users were moved from terminals to LTSP. This time, they got FIT-PC2s as opposed to diskless PCs. Lucky them; less noise. But they are complaining that they find the mouse to unwieldy. And because they have locked down desktops, they don't have a config app to tweak the mouse acceleration and threshold. So I poked around and found that the settings are in :

/home/$USER/.config/xfce4/mcs_settings/mouse.xml

Now, that is hardly exciting.

What is exciting: I then wanted to set up x11vnc so that I could see what the users were experiencing. I've used x11vnc often on the same desktop, but my first attempt at doing it with LTSP failed. So I go on #LTSP to complainlook for a solution, which turned out to be -noshm.

They first complained that LTSP-4 (which I'm using) is far to archaic (which it is). They then got me on track for the next little bit of bash:

#!/bin/bash



USER=$1



error () { echo "$*" >&2; exit 5 }



if [[ ! $USER ]] ; then

    error "Usage: $0 user"

fi



userpid="$(pgrep -u $USER xfwm4)"

if [[ ! $userpid ]] ; then

    error "User $USER isn't logged in"

elif [[ $userpid =~ ' ' ]] ; then

    error "User $USER is probably logged on several times: $userpid"

fi



userenv="$(tr '\0' '\n' < /proc/$userpid/environ | egrep '^DISPLAY=|^XAUTHORITY=')"



eval "$userenv"

if [[ ! $XAUTHORITY ]] ; then

    XAUTHORITY=/home/$USER/.Xauthority

fi

export DISPLAY XAUTHORITY



echo DISPLAY=$DISPLAY

echo XAUTHORITY=$XAUTHORITY



exec x11vnc -noshm -nopw

All the error checking might be hiding the really interesting bit: I'm pulling DISPLAY and XAUTHORITY from the user's environment, via /proc. Something I'd never thought of doing before.

SSDs are not ready

The drive on Corey is/was in the process of dieing. It is going on 7 years old, has been spinning at 7200rpm every hour of most days for those 7 years. I don't begrudge it failing. It did mean I had to spend 2-3 days reconfiguring my daily use computer. Annoying. More details later.

I bought a Western Digital Green 1.5TB drive. 100 CAD! Cheap! It's only 5400rpm in the hopes it will make less noise. But it's still to noisy. Not so much rotation whine but an annoying click every 4-5 seconds. Something I had back in the day with SCSI drives, but I don't think the old IDE drive had this problem. So either I get an SSD or a fit-pc2 to put it in. Or boot LTSP from the basement.

Also, Jean-Phillipp brought up that maybe we should look into moving our clients' MySQL DBs to SSD. Even at the high prices of SSD, it would cost less then what we are currently doing, which is throwing RAM at the problem. Also, there's only so much RAM that a server can hold. And with datasets getting larger then 33 GB, that approach has reached its limit. However, it turns out that SSD, along with being expensive aren't quite ready for prime-time.