Updating Packages Using Apt On Old Debian Installs
Sep 20th, 2016 by pixel

When attempting to install a new package or update an existing package if you are presented with the error

E: Release file expired, ignoring (invalid since 189d 0h 42min 32s)

You will need to execute the following command as root:

$ echo 'Acquire::Check-Valid-Until "false";' > /etc/apt/apt.conf.d/90ignore-release-date

And then perform…

$ apt update

or if you are using aptitude…

$ aptitude update

You may need to execute the above command twice to make sure everything is up to date.

Profiling PHP with XHProf & XHGui
Dec 18th, 2015 by pixel

For a well described tutorial on basic PHP profiling and optimization I would recommend the 3 part article written by Davey Shafik:

Profiling PHP Part 1: Intro to Xhprof & Xhgui

Profiling PHP Part 2: Xhgui In-Depth

Profiling PHP Part 3: Practical Performance Tuning

OpenSSH Public Key Authentication
Nov 17th, 2009 by pixel

Key Generation

ssh-keygen -q -f ~/.ssh/id_rsa -t rsa
Enter passphrase (empty for no passphrase): …
Enter same passphrase again: …

Key Distribution

# first, upload public key from client to server

scp ~/.ssh/

# next, setup the public key on server

cat ~/ >> ~/.ssh/authorized_keys
chmod 600 ~/.ssh/authorized_keys
rm ~/

Principles of Electricity Video (1945)
Mar 19th, 2009 by pixel

Breaks down structure of matter into atoms and, by use of conventional symbols, shows the action of electrons within an atom. The principles involved in the flow of current are explained and a volt, ampere and Ohm are defined.

full details…

Basic Ocilliscope Tutorial
Oct 4th, 2008 by pixel

Basic Ocilliscope Tutorial

Definately the best tutorial on the basic control and use of a dual channel ocilliscope.