I had a need to copy some specific RPM files locally to my machine, but have the general YUM database recognize them (not using yum localinstall.) I found this lovely howto that explains how to do it.
In my case, I created a folder for one RPM I wanted in the local yum repository. I then installed the createrepo package, used it on my new directory containing my RPMs, then added a repository file pointing to the new local repository.
I had a few audio files of an interview done with a late relative that I wanted to have Google transcribe for me. I wanted to supply an audio file and have it spit out the results. There are many ways to do this but I went with using the Google Cloud Platfrom speech-to-text API.
Next, I needed to create GCP storage bucket as audio more than 10 minutes long cannot reliably be transcribed via the “uploading local file” option. I did this following the documentation at https://cloud.google.com/storage/docs/creating-buckets which walks you through going to their storage browser and creating a new bucket. From that screen I uploaded my audio files (FLAC in my case.)
Then I needed to create API credentials to use. I did this by going speech API console’s credentials tab and creating a service account, then saving the key to my working directory on my local computer.
Also on said computer I installed google-cloud-sdk (on Arch Linux in my case, it was as simple as yay -S google-cloud-sdk)
With service account json file downloaded & google-cloud-sdk installed I exported the GCP service account credentials into my BASH environment like so
I created .json files following the format outlined in command line usage outlined in the quickstart documentation. I tweaked to add a line “model”: “video” to get the API to use the premium Video recognition set (as it was more accurate for this type of recording.) This is what my JSON file looked like:
I recently got a Tacx Neo 2 smart trainer for my bike and was eager to use it on my big screen TV with Zwift. Unfortunately, despite the Nvidia Shield being a more that capable Android device, Zwift does not show up in the Google play store. I didn’t want to stream Zwift from my PC because a) the Windows app is annoying and doesn’t go full screen (title bar at the top) and b) my PC is located upstairs and the bluetooth doesn’t appear to reach from the trainer to the PC.
My solution to this was to sideload the Zwift app onto my Nvidia shield. It wasn’t as straightforward as most sideloading due to how Zwift is configured: it has an APK file, and an OBB file. The APK is small and is the application itself, the OBB file is all the map data (it’s large – over 600 MB)
Fortunately, a new Android format called xapk exists, and is an archive of both in one package. This was the process I used to successfully get my Zwift on my Nvidia Shield:
Install a file explorer app on the shield via the play store (I used FX file explorer)
Use the file explorer app to open the xapk file as an archive (Archive Explorer)
Click on APK and install it by selecting to open with Android installer (grant access to when prompted)
Copy the Android/obb/com.zwift.zwiftgame folder to home / Android / obb
Access Zwift by going to settings / Apps / See all apps and scroll to the bottom
Optional: Install sideload app from the play store, launch Zwift from that app instead
The shield remote doesn’t appear to control anything within the app. Plug in a mouse so you can swipe away the first run tutorial screens (hold left click and drag to the left.) Optional: plug in a keyboard while you’re at it so you can log in faster.
Success! My trainer showed up in the pairing screen and everything works! You can even have your own music playing in the background, with a caveat: if you ever switch apps away from Zwift, it will reset back to the login screen because the Shield doesn’t appear to have enough memory to keep Zwift running when switching another app to the foreground. If you want your shield to play music, start the music first, then switch to Zwift. Once you’re in Zwift, you can’t switch away to any other app without losing your progress.
I needed to send some test packets over UDP to make sure connectivity was working. I found this site which outlined how to do it really well
nc -u <IP/hostname> <port>
Then on the next line you can send test messages, then hit CTRL+D when done. In my case I wanted to test sending syslog data, so I did nc -u <hostname> 514, then wrote test messages. the -u specifies UDP and 514 is the syslog port. I was then able to confirm on the other end the message was received. Handy.
I had a need to take a folder in one git repository and create a whole new git repository with it, preserving history for all files inside. My desire to keep git history made the process a bit more complicated than simply copying the directory into a new git repository.
First, create a new folder on the git server. I’m all command line, no GUI yet, so I need to make it a bare repository. (Thanks to geeksforgeeks on how to to do this)
#On the main git "server"
git init --bare
Now, on the desktop (not the git server) clone a copy of the repository with your desired folder into a new directory, remove the git origin server, then strip out everything except that directory (thanks to gbayer.com for the info)
In general I try to buy server-class hardware for my home lab, primarily so that I could have IPMI / Remote access console for remote OS installation & troubleshooting. I recently got a new desktop and found myself with a Threadripper 1950x that would make an excellent addition to my server cluster. The one problem being it’s a desktop-class board, so it does not have any IPMI / remote access device.
I solved my problem with pikvm. It works wonderfully! Pikvm uses a raspberry pi with some additional hardware and software to interface with a system to control power & reset capabilities, as well as KVM functions with the ability to upload OS images and do OS installations remotely. The whole project cost me about $150 since I didn’t have some of the essential items for it. It could definitely be cheaper if I didn’t buy large packs of items or already had some electronics components.
The process was straightforward as outlined on their github page. The only snag I ran into was creating the USB Y (split) cable. It did not work the first time, so I had to tear it all down and start again. One cable I used had more than 4 wires (3 red wires, 1 black, 1 green, 1 white, and 1 yellow.) When I re-assembled to include the yellow wire with the red and black, it all worked.
I scavenged the metal mounting bracket from some old networking adapter cards. With those I was able to mount the pi and the HDMI-in module to two standard PCI express card slots. I accidentally destroyed one of my SD cards while doing this so be careful if you try it! The PI is mounted at a slight angle so as to not damage the SD card. I had to mount it backwards (ethernet in the back) because I couldn’t get power to it otherwise (power port right up against the motherboard.) My workaround for this was to custom make a short length ethernet cord and use an RJ45 coupler on the outside of the chassis to provide an easy to access network port for the pi.
I wired the power & reset switch, as well as HDD and power LEDs in parallel so they would function with the chassis as well as with the KVM. To do this simply get some male-to-male jumper wires. On one end plug into the chassis wire, and on the other plug into the corresponding positive and negative slots right next to the ones going to the pi.
I upgraded to a shiny new AMD Ryzen 3rd gen processer (Threadripper 3960x.) After doing so I could not boot up my Windows 10 gaming VM (it uses VFIO / PCI Passthrough for the video card.) The message I kept getting as it tried to boot was:
in my case, it was -cpu host,migratable=on,topoext=on,kvmclock=on,hv-time,hv-relaxed,hv-vapic,hv-spinlocks=0x1fff,hv-vendor-id=1234567890ab,kvm=off \
Copy everything after -cpu and before the last backslash. Then edit your VM’s XML file (change last argument to the name of your VM)
sudo virsh edit win10
Scroll down to the bottom qemu:commandline section (if it doesn’t exist, create it right above the last line – </domain>. Paste the following information obtained from the above log (ignoring the qemu:commandline lines if they already exist.) In my case it looked like this:
Assuming you’re using network manager for your connections, create a bridge (thanks to ciberciti.biz & the arch wiki for information on how to do so.) Replace interface names with ones corresponding to your machine:
sudo nmcli connection add type bridge ifname br0 stp no
sudo nmcli connection add type bridge-slave ifname enp4s0 master br0
sudo nmcli connection show
#Make note of the active connection name
sudo nmcli connection down "Wired connection 2" #from above
sudo nmcli connection up bridge-br0
Create a second bridge bound to lo0 for host-only communication. Change IP as desired:
sudo nmcli connection add type bridge ifname br99 stp no ip4 192.168.2.1/24
sudo nmcli connection add type bridge-slave ifname lo master br99
sudo nmcli connection up bridge-br99
When creating the passthrough VM, make sure chipset is Q35.
Set the CPU model to host-passthrough (type it in, there is no dropdown for it.)
When adding disks / other devices, set the device model to virtio
Add your GPU by going to Add Hardware and finding it under PCI Host Device.
Windows 10 specific tweaks
If your passthrough VM is going to be windows based, some tweaks are required to get the GPU to work properly within the VM.
Ignore MSRs (blue screen fix)
Later versions of Windows 10 instantly bluescreen with kmode_exception_not_handled unless you pass an option to ignore MSRs. Add the kvm ignore_msrs=1 option in /etc/modprobe.d/kvm.conf to do so. Optionally add the report_ignored_msrs=0 option to squelch massive amounts of kernel messages every time an MSR was ignored.
Use the virsh edit command to make some tweaks to the VM configuration. We need to hide the fact that this is a VM otherwise the GPU drivers will not load and will throw Error 43. We need to add a vendor_id in the hyperv section, and create a kvm section enabling hidden state, which hides certain CPU flags that the drivers use to detect if they’re in a VM or not.
From the above output I see my CPU core 0 is shared by CPUs 0 & 16, meaning CPU 0 and CPU 16 (as seen by the Linux kernel) are hyperthreaded to the same physical CPU core.
Especially for gaming, you want to keep all threads on the same CPU cores (for multithreading) and the same CPU die (on my threadripper, CPUs 0-7 reside on one physical die, and CPUs 8-15 reside on the other, within the same socket.)
In my case I want to dedicate one CPU die to my VM with its accompanying hyperthreads (CPUs 0-7 & hyperthreads 16-23) You can accomplish this using the virsh edit command and creating a cputune section (make sure you have a matching vcpu count for the number of cores you’re configuring.) Also edit CPU mode with the proper topology of 1 socket, 1 die, 8 cores with 2 threads. Lastly, configure memory to only be from the proper NUMA node the CPU cores your VM is using (Read here for more info.)
Append default_hugepagesz=1G hugepagesz=1G hugepages=16 to the kernel line in /etc/default/grub and re-run sudo grub-mkconfig -o /boot/grub/grub.cfg
Configure FIFO CPU scheduling
The Arch Wiki mentions to run qemu-system-x86_64 with taskset and chrt but doesn’t mention how to do so if you’re using virt-manager. Fortunately this reddit thread outlined how to accomplish it: libvirt hooks. Create the following script and place it in /etc/libvirt/hooks/qemu , change the VM variable to match the name of your VM, mark that new file as executable (chmod +x /etc/libvirt/hooks/qemu ) and restart libvirtd
#Hook to change VM to FIFO scheduling to decrease latency
#Place this file in /etc/libvirt/hooks/qemu and mark it executable
#Change the VM variable to match the name of your VM
if [ "$1" == "$VM" ] && [ "$2" == "started" ]; then
if pid=$(pidof qemu-system-x86_64); then
chrt -f -p 1 $pid
echo $(date) changing CPU scheduling to FIFO for VM $1 pid $pid >> /var/log/libvirthook.log
echo $(date) Unable to acquire PID of $1 >> /var/log/libvirthook.log
#echo $(date) libvirt hook arg1=$1 arg2=$2 arg3=$3 arg4=$4 pid=$pid >> /var/log/libvirthook.log
Update 7/28/20: I no longer do this in favor of the qemu hook script above, which prioritizes to p1 the qemu process for the cores it needs. I’m leaving this section here for historical/additional tweaking purposes.
Update 6/28/20: Additional tuning since I was having some stuttering and framerate issues. Also read here about the emulatorpin option
Dedicate CPUs to the VM (host will not use them) – append isolcups, nohz_full & rcu_nocbs kernel parameters into /etc/default/grub