Samuel FORESTIER HorlogeSkynet

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

unicorn config file

Edit file /home/gitlab/gitlab/config/unicorn.rb

Find line listen "#{app_dir}/tmp/sockets/gitlab.socket" and comment it. Uncomment line listen "127.0.0.1:8080"

required modules for apache

sudo a2enmod proxy
sudo a2enmod proxy_balancer

Each of these commands will run an ad hoc http static server in your current (or specified) directory, available at http://localhost:8000. Use this power wisely.

Discussion on reddit.

Python 2.x

$ python -m SimpleHTTPServer 8000

TLDR: I now add the following snippet to all my Dockerfiles:

# If host is running squid-deb-proxy on port 8000, populate /etc/apt/apt.conf.d/30proxy
# By default, squid-deb-proxy 403s unknown sources, so apt shouldn't proxy ppa.launchpad.net
RUN route -n | awk '/^0.0.0.0/ {print $2}' > /tmp/host_ip.txt
RUN echo "HEAD /" | nc `cat /tmp/host_ip.txt` 8000 | grep squid-deb-proxy \
  && (echo "Acquire::http::Proxy \"http://$(cat /tmp/host_ip.txt):8000\";" > /etc/apt/apt.conf.d/30proxy) \
  && (echo "Acquire::http::Proxy::ppa.launchpad.net DIRECT;" >> /etc/apt/apt.conf.d/30proxy) \
  || echo "No squid-deb-proxy detected on docker host"

This was originally posted on 2011-07-11 to http://andrewho.co.uk/weblog/clean-urls-on-jekyll-apache

I use a static site generator, specifically [jekyll][], to transform some templates into a set of static *.html files. However, I like to keep the URLs looking clean, and not display the .html extension both because I think it looks better and also so that the URLs purely reflect the content and not the underlying files or CMS used to serve that content. In short, whilst the file being served might be $DOCUMENT_ROOT/weblog/title.html, the canonical URL for that resource should be /weblog/title. Here's how I do that in .htaccess.

Linux NetFilter, IP Tables and Conntrack Diagrams

IPTABLES TABLES and CHAINS

IPTables has the following 4 built-in tables.

1) Filter Table

Filter is default table for iptables. So, if you don’t define you own table, you’ll be using filter table. Iptables’s filter table has the following built-in chains.

	//
	// Regular Expression for URL validation
	//
	// Author: Diego Perini
	// Created: 2010/12/05
	// Updated: 2018/09/12
	// License: MIT
	//
	// Copyright (c) 2010-2018 Diego Perini (http://www.iport.it)
	//

	#!/bin/bash
	# bash generate random alphanumeric string
	#

	# bash generate random 32 character alphanumeric string (upper and lowercase) and
	NEW_UUID=$(cat /dev/urandom \| tr -dc 'a-zA-Z0-9' \| fold -w 32 \| head -n 1)

	# bash generate random 32 character alphanumeric string (lowercase only)
	cat /dev/urandom \| tr -dc 'a-z0-9' \| fold -w 32 \| head -n 1

	#!/bin/sh
	#
	# Use posixregex CLI tool from: https://github.com/syzdek/dmstools/blob/master/src/posixregex.c

	RE_IPV4="((25[0-5]\|(2[0-4]\|1{0,1}[0-9]){0,1}[0-9])\.){3,3}(25[0-5]\|(2[0-4]\|1{0,1}[0-9]){0,1}[0-9])"

	posixregex -r "^(${RE_IPV4})$" \
	127.0.0.1 \
	10.0.0.1 \
	192.168.1.1 \

	// Just before switching jobs:
	// Add one of these.
	// Preferably into the same commit where you do a large merge.
	//
	// This started as a tweet with a joke of "C++ pro-tip: #define private public",
	// and then it quickly escalated into more and more evil suggestions.
	// I've tried to capture interesting suggestions here.
	//
	// Contributors: @r2d2rigo, @joeldevahl, @msinilo, @_Humus_,
	// @YuriyODonnell, @rygorous, @cmuratori, @mike_acton, @grumpygiant,