Wednesday, November 27, 2019

Raspberry Pi NTP Time...

Some versions of the Raspberry Pi/ Raspbian have NTP disabled

# to check status
timedatectl status

# to enable NTP...
sudo timedatectl set-ntp True
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Saturday, November 02, 2019

Formatting Code on Blogs...

Finally found at how to do this using prism.js from the excellent blog post here.

This is done by adding a link to the CSS in <head>, and a link to the JS before closing the <body> tag. The theme is specified with the css name, e.g. prism.min.css or prism-tomrrow.min.css. For Blogger, this has to be done by updating the Blog Theme.

<head>
  ...
  <link
    href='https://cdnjs.cloudflare.com/ajax/libs/prism/1.17.1/themes/prism-tomorrow.min.css' 
    rel='stylesheet'/>
</head>
<body>
  ...
  <script
    src='https://cdnjs.cloudflare.com/ajax/libs/prism/1.17.1/prism.min.js'/>
  <script
    src="https://cdnjs.cloudflare.com/ajax/libs/prism/1.17.1/plugins/autoloader/prism-autoloader.min.js"/>
</body>

There is a full list of the CDN files here, and a full list of supported languages here.

Code is enclosed within the <pre> tag to preserve formatting; and within the <code> tags, also specifying the language for highlighting:

<pre><code class="language-java">   class App {
      public static void main(String[] args) {
         System.out.println("Hello World!");
      }
   }
</code></pre>

Formatting can also be done inline.

Note that to display HTML or PHP some of the symbols will need to be escaped so the browser doesn't try to parse the code. An online converter like Free Online HTML Escape Tool can do this.

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Wednesday, October 09, 2019

Installing MicroPython on the ESP8266

Check the port it is attached to in Device Manager. Download the firmware from the MicroPython downloads page.
Open a Command Prompt and do the following:
pip install esptool

# erase the flash

esptool.py --chip esp8266 erase_flash

# For the HUZZAH ESP8266 breakout buttons for GPIO0 and RESET are built in to the board
# Hold GPIO0 down, then press and release RESET (while still holding GPIO0),
# and finally release GPIO0

# install the firmware
esptool.py --chip esp8266 --port COM3 write_flash --flash_mode dio \
   --flash_size detect 0x0 esp8266-20190529-v1.11.bin
Full info on the Adafruit HUZZAH ESP8266 breakout on the Adafruit website.
Full info on MicroPython here.
Connection to the REPL over the serial prompt is at baudrate 115200 using Putty.
Note that the USB to UART serial console cable is connected as follows:
  • n/a
  • White - Tx
  • Green - Rx
  • Red - V+
  • n/a
  • Black - GND
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Sunday, January 06, 2019

VirtualBox: Creating a Centos VM...

Create the VM from the DVD ISO, including GNOME.

Make sure on Settings -> System -> Pointing Device is set to USB Tablet.

Then...

'visudo' and add the following: 'paul ALL=(ALL) NOPASSWD: ALL'

sudo yum install VBoxAdditions, gcc kernel-devel dkms perl, make
cd /run/media/****/VBOXADDITIONS*
sudo ./VBoxLiuxAdditions

sudo yum install java java-1.8-openjdk-devel git

in /etc/sysconfig/network-scripts/ifcfg-enp0s3 (or the appropriate network adaptor) set 'ONBOOT=yes'

mkdir ~/git
cd ~/git
git clone -u 'sh gup.sh' paulp@*****:d:/Users/****/Documents/git-server/miscellany.git

ln -sf ~/git/miscellany/vimrc ~/.vimrc
ln -sf ~/git/miscellany/bash_aliases ~/.bash_aliases
ln -sf ~/git/miscellany/gitconfig ~/.gitconfig

Set Terminal Custom Font to DejaVu Sans Mono Book (10 or 9)

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Wednesday, December 19, 2018

Instagram Download Links

Hmmm..... this no longer appears to work. Needs reworking, and check here.

To view a full size Instagram picture, append 

media/?size=l
, e.g.

https://www.instagram.com/p/B3hoo93BLA1UtIa4QJvMu1iyBPvX1PGbeH5XfI0/

should be updated to:

https://www.instagram.com/p/B3hoo93BLA1UtIa4QJvMu1iyBPvX1PGbeH5XfI0/media/?size=l

A simple Tampermonkey script to add a link to an Instagram page to allow the image to be downloaded.

// ==UserScript==
// @name Instagram Download Link
// @namespace http://tampermonkey.net/
// @version 0.1
// @description Add a link to download photos....
// @author Me
// @match https://www.instagram.com/*
// @grant none
// @require https://code.jquery.com/jquery-3.3.1.min.js
// ==/UserScript==

var currentPage;
var domChangeTimer = '';
var listenerInstalled = false;

$(window).bind('load', MainAction);

function MainAction() {

  // add a listener to the page so this function is run each time the page changes...
  if (!listenerInstalled) {
    document.addEventListener("DOMSubtreeModified", HandleDomChange, false);
    listenerInstalled = true;
  }

  // check the current URL. This will change as AJAX changes the page...
  if (currentPage != window.location.href) {
    currentPage = window.location.href;

    // is the link to the image available...?
    var link = $('meta[property="og:image"]').attr('content');

    // if not, and the page is just of a single image
    // e.g. https://www.instagram.com/p/BuRxiC5Hr4i/
    // then reload the page so the link is available...
    // this is clumsy, but can't find another way to get at the DOM as updated by AJAX
    if (window.location.href.match(/\/p\//) && link == undefined) {
      window.location.reload();
    } else if (!window.location.href.match(/\/p\//) && link != undefined) {

      // and if we've just mmoved off a single image page
      // reload again to get rid of the image metadata from our copy of the DOM
      // that has since been updated by AJAX
      window.location.reload();
    }

    console.log("Download link : " + link);

    // if the link is available, add it to the page...
    if (link != undefined) {
      $("article").append("Download Link");
    }
  }
}

function HandleDomChange(zEvent) {

  // why do we do this here...?
  if (typeof domChangeTimer == "number") {
    clearTimeout(domChangeTimer);
    domChangeTimer = '';
  }

  // DOM has changed, so set a timer...
  // Note that this may be updated numerous times, but the function
  // will only be called when the timer hasn't been set for x ms
  domChangeTimer = setTimeout (function() {
    MainAction();
  }, 500); // in ms
}
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Wednesday, November 28, 2018

Counting Files

A quick bash script to count the number of files in a set of directories:

DIRS=`ls -d */`
for D in $DIRS;
do
  printf "$D "
  find $D -type f|wc -l
done
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Tuesday, November 27, 2018

MySQL Scheduling

Managing Events

Switch on the event scheduler in the database

SET GLOBAL event_scheduler=on;

To set it on startup, it is necessary to update "/etc/mysql/my.cnf" to add the following:

[mysqld]
event_scheduler = on

Create event to periodically update the database

USE temperatures;
CREATE DEFINER = 'root'@'localhost' event
  IF NOT EXISTS snapshot
ON SCHEDULE EVERY 15 minute STARTS '2018-11-27 00:00:00'
DO
  INSERT INTO temperatures.minmax
    SELECT curdate(), round(min(outside_temp), 1) as min, round(max(outside_temp), 1) AS max
      FROM temperatures.readings WHERE datetime > curdate()
    ON DUPLICATE KEY UPDATE
      min = min, max = max;
Show and delete events

SHOW EVENTS;
SHOW CREATE EVENT snapshot;
DROP EVENT snapshot;
SHOW PROCESSLIST;

Note that code blocks may need the delimiter to change to allow the client to accept nested statements:

DELIMITER //

BEGIN
  SELECT * FROM mytable;
END //

To show all events:

SHOW EVENTS;

To show existing event scripts for a given event

SHOW CREATE EVENT snapshot;

And to alter event scripts

ALTER EVENT snapshot
DO
[new code];
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Wednesday, October 24, 2018

Basic MySQL

To get rid of the annoying Ctrl+c issue use mysql -u root -p --sigint-ignore

Managing Users

SELECT user, host FROM mysql.user;
CREATE USER 'user'@'server' IDENTIFIED BY 'mypassword';

SHOW GRANTS FOR 'user'@'server';
GRANT INSERT, SELECT, UPDATE ON stuff.* TO 'user'@'server';
REVOKE INSERT ON stuff.* from 'user'@'server';

DROP USER 'user'@'server';

Managing Databases

CREATE DATABASE stuff;
SHOW DATABASES;
USE stuff;
DROP DATABASE stuff;

Managing Tables

CREATE TABLE music (
  id INT unsigned NOT NULL AUTO_INCREMENT,
  artist VARCHAR(50) NOT NULL,
  title VARCHAR(50) NOT NULL,
  PRIMARY KEY (id)
);
SHOW TABLES;
DESCRIBE music;

ALTER TABLE music ADD release_date DATETIME AFTER title;
ALTER TABLE music CHANGE COLUMN release_date rel_d DATE NOT NULL;
ALTER TABLE music DROP COLUMN rel_d, RENAME TO media;

DROP TABLE music;

Managing Records

INSERT INTO music (artist, title) VALUES
  ('Prefab Sprout', 'Steve McQueen'),
  ('Elbow', 'Asleep at the Back');

SELECT COUNT(*) AS total FROM music WHERE artist LIKE 'Elb%';
SELECT * FROM music WHERE release_date IS NULL ORDER BY artist;
SELECT * FROM stuff WHERE datetime > curdate() - INTERVAL 1 DAY;
SELECT * FROM temperatures.readings
  WHERE pressure=(SELECT min(pressure) FROM temperatures.readings);

UPDATE music SET title='Cast of Thousands' WHERE title='Asleep at the Back';
DELETE FROM music WHERE artist='Elbow';
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Tuesday, July 03, 2018

systemd

Time to move on from using the init daemon to manage starting and stopping processes and services.

systemd is a system management daemon that replaces init.d and is available on most distributions.

Fedora documentation can be found here.

To create a new service, create a new configuration file /etc/systemd/system/foo.service (note that absolute path names are required, even for interpreters etc.):

[Unit]
Description=My service
Requires=network.target mysql.service

[Service]
Type=simple
ExecStart=/usr/bin/java -Dapp.properties=/home/pi/clock.properties -jar /home/pi/clock-1.1.jar

[Install]
WantedBy=multi-user.target

To start:
sudo systemctl start foo

To enable on startup:
sudo systemctl enable foo

To check if enabled
sudo systemctl is-enabled foo

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Tuesday, December 26, 2017

Installing a Fedora Guest VM


  • Download Fedora LXDE Spin
  • Create a new VM and point it at the Fedora iso
  • Run the VM and install Fedora to the hard drive
  • Remove the iso from the VM
  • 'visudo' and add the following: 'paul   ALL=(ALL)   NOPASSWD: ALL'
  • 'sudo yum update'
  • Ensure there is an optical disk attached to the VM: create if not
  • Install Guest Additions Virtual Drive: Devices-> Install Guest Additions
  • 'yum install dkms gcc kernel-devel'
  • 'cd /run/media/paul/VBOXADDITIONS*'
  • 'sudo ./VBoxLiuxAdditions'
  • 'sudo usermod -g vboxsf paul'
  • 'sudo mount -t vboxsf Temp ~/share'
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