Engineering and technology notes

Ubuntu — ZoneMinder Socket_sendto or no live streaming

Jovan Stosic August 1, 2018

After you have setup your camera make sure you can view Monitor streams, if not check some of the common causes:

  • Check Apache cgi module is enabled.

  • Check Apache /etc/apache2/conf-enabled/zoneminder.conf ScriptAlias matches PATH_ZMS.

    ScriptAlias /zm/cgi-bin /usr/lib/zoneminder/cgi-bin

    From console go to Options->Path and make sure PATH_ZMS is set to /zm/cgi-bin/nph-zms.

Source: Ubuntu — ZoneMinder documentation

Democritus

Jovan Stosic August 1, 2018

Democritus (/dɪˈmɒkrɪtəs/; Greek: Δημόκριτος, Dēmókritos, meaning “chosen of the people”; c.460 — c.370 BC) was an Ancient Greek pre-Socratic philosopher primarily remembered today for his formulation of an atomic theory of the universe.

Democritus was born in Abdera, Thrace, around 460 BC, although there are disagreements about the exact year. His exact contributions are difficult to disentangle from those of his mentor Leucippus, as they are often mentioned together in texts. Their speculation on atoms, taken from Leucippus, bears a passing and partial resemblance to the 19th-century understanding of atomic structure that has led some to regard Democritus as more of a scientist than other Greek philosophers; however, their ideas rested on very different bases. Largely ignored in ancient Athens, Democritus is said to have been disliked so much by Plato that the latter wished all of his books burned. He was nevertheless well known to his fellow northern-born philosopher Aristotle. Many consider Democritus to be the “father of modern science”. None of his writings have survived; only fragments are known from his vast body of work.
href=”https://en.wikipedia.org/wiki/Democritus”>Democritus – Wikipedia

Owncloud is slow when a federation server is down

Jovan Stosic July 31, 2018

I had two ownclouds 9.1.8. I shutdown the one owncloud  server, resulting in terible reduction in speed of the other owncloud server. Deleting from the web interface was not possible, too.

Deleting the rows in the database of oc_share_external worked, external shares are now gone and the performance of the active owncloud normalized.

apt – Can’t install xdebug – Depends: phpapi-20121212 – ubuntu 14.04 – Ask Ubuntu

Jovan Stosic July 28, 2018

You’re using manually installed PHP packages that don’t stem from the official repositories. Anything could happen in that case and I suggest that you report the issue to their maintainer.

Solution 1: Switch/downgrade to in-repository packages

The immediate solution is to revert to the in-repository packages with:

sudo apt install php5=5.5.9+dfsg-1ubuntu4.20 php5-xdebug=2.2.3-2build1

If you have other packages depending on that php5version you’ll need to install their respective in-repository versions in the same fashion.

Solution 2: Install PHP 5.6 and xdebug from an actual PPA and not manually with dpkg -i

How do I install different (upgrade or downgrade) PHP version in still supported Ubuntu release? has an excellent answer that lists such a PPA.

  1. You probably want to remove the current PHP 5 installation since the PPA packages have different names to allow different independent PHP installations:

    sudo apt remove php5 php5-xdebug

  2. Add the PPA, upgrade your packages and install the new PHP and xdebug packages:

    sudo add-apt-repository ppa:ondrej/php
sudo apt update
sudo apt upgrade
sudo apt install php5.6 php-xdebug

As in the previous solution you’ll need to remove packages that depend on php5 (happens automatically with apt remove php5) and later re-add their php5.6counterparts

The error is as a result of the fact you are loading an xdebug which was compiled with a php versiondifferent from the one installed on your system

And you should look for one that was compiled with the same php version on your system.

Look at this article here for further help.

https://askubuntu.com/questions/856996/cant-install-xdebug-depends-phpapi-20121212-ubuntu-14-04

Lagrangian mechanics

Jovan Stosic July 27, 2018

Overall, the Lagrangian has units of energy, but no single expression for all physical systems. Any function which generates the correct equations of motion, in agreement with physical laws, can be taken as a Lagrangian. It is nevertheless possible to construct general expressions for large classes of applications. The non-relativistic Lagrangian for a system of particles can be defined by[9]

where

is the total kinetic energy of the system, equalling the sum Σ of the kinetic energies of the particles,[10] and V is the potential energy of the system.

Kinetic energy is the energy of the system’s motion, and vk2 = vk · vk is the magnitude squared of velocity, equivalent to the dot product of the velocity with itself. The kinetic energy is a function only of the velocities vk, not the positions rk nor time t, so T = T(v1, v2, …).

The potential energy of the system reflects the energy of interaction between the particles, i.e. how much energy any one particle will have due to all the others and other external influences. For conservative forces (e.g. Newtonian gravity), it is a function of the position vectors of the particles only, so V = V(r1, r2, …). For those non-conservative forces which can be derived from an appropriate potential (e.g. electromagnetic potential), the velocities will appear also, V = V(r1, r2, …, v1, v2, …). If there is some external field or external driving force changing with time, the potential will change with time, so most generally V = V(r1, r2, …, v1, v2, …, t).

 

https://en.wikipedia.org/wiki/Lagrangian_mechanics