hellerbarde

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

shamil

How to mount a qcow2 disk image

This is a quick guide to mounting a qcow2 disk images on your host server. This is useful to reset passwords, edit files, or recover something without the virtual machine running.

Step 1 - Enable NBD on the Host

modprobe nbd max_part=8

Manu343726

# Install quemu, docker, etc
yaourt -S qemu qemu-user-static binfmt-support

# The quemu-user-static AUR package is outdated and broken. The .deb package they pull is no longer in the ubuntu repository.
# Edit the PKGBUILD and use qemu-user-static_2.4+dfsg-3_amd64.deb (With SHA1 sum "84d83a16c60c82b6c579f2f750b04a3ac26c249b")

# Enable ARM emulation
update-binfmts --enable qemu-arm

spalladino

# Backup
docker exec CONTAINER /usr/bin/mysqldump -u root --password=root DATABASE > backup.sql

# Restore
cat backup.sql | docker exec -i CONTAINER /usr/bin/mysql -u root --password=root DATABASE

mosquito

Docker compose as a systemd unit

Create file /etc/systemd/system/docker-compose@.service. SystemD calling binaries using an absolute path. In my case is prefixed by /usr/local/bin, you should use paths specific for your environment.

[Unit]
Description=%i service with docker compose
PartOf=docker.service
After=docker.service

ForgottenUmbrella

How to publish Python apps for human beings

So, you've created a Python app (be it a graphical user interface with Qt or the like, or a simple command line interface). Great! But how are others going to use it? Python applications often have dependencies (e.g. from third-party modules), and they also need a Python interpreter to run them. For a developer, installing all the necessary bits and bobs to make things work is okay, but that's unacceptable for a normal user - they just want to download the thing and run it.

Below are simple instructions to publish your app on the three main operating systems: Windows, macOS and Linux.

jaytaylor

One liner for deleting images from a v2 docker registry

Just plug in your own values for registry and repo/image name.

registry='localhost:5000'
name='my-image'
curl -v -sSL -X DELETE "http://${registry}/v2/${name}/manifests/$(
    curl -sSL -I \
        -H "Accept: application/vnd.docker.distribution.manifest.v2+json" \

yangxuan8282

FROM arm32v6/alpine

RUN apk add --no-cache dnsmasq

EXPOSE 53/tcp \
       53/udp \
       67/udp

ENTRYPOINT ["dnsmasq", "--no-daemon", "--user=dnsmasq", "--group=dnsmasq"]

ScriptingSquirrel

(Assuming a Debian 8-like system)

• Install prometheus-node-exporter

  $ sudo apt update && sudo apt install prometheus-node-exporter

• Configure prometheus-node-exporter to expose metrics only to localhost, not on to all networks. Modify file /etc/default/prometheus-node-exporter:

  # Set the command-line arguments to pass to the server.

grugnog

# Install these packages (use your favorite AUR tool here)
yay -S minikube kubectl docker-machine-driver-kvm2 libvirt qemu-headless ebtables

# Get libvirt going
sudo systemctl enable libvirtd.service
sudo usermod -a -G libvirt $(whoami)

# This fix thanks to http://blog.programmableproduction.com/2018/03/08/Archlinux-Setup-Minikube-using-KVM/
sudo virsh net-autostart default