Databases, Systems & Networks

Today we are about to see how to build a DIY stopwatch just using Digital IC’s 4026 and 4017. The most highlighting feature about this project is the fact that it doesn’t use any MCU to do the job. Even though using an MCU will be a lot better option still this project will be a great DIY for those who love to play with Digital chips. 

BLOCKS OF DIY STOPWATCH:

1. Oscillator
2. Display

OSCILLATOR BLOCK:

Oscillator provides the clock source for stopwatch we are about to build. The oscillator should provide an output clock frequency of about 1Hz. There are plenty of ways to do this but each method might differ in accuracy of output wave produced. Even a simple 555 timer can be used here, but temperature drift might affect the accuracy of output. The deviation of output might not be that big but its good to have it under consideration.

Crystal powered oscillator will be the perfect solution for this problem. We are not going to discuss the oscillator section briefly in this article since this 1 Hz oscillator circuit will do a pretty good job for our DIY stopwatch project. You can always use other 1Hz clock generator circuits rather than the crystal oscillators provided your application have some tolerance on the accuracy. Lire la suite…

One of the interesting new tools in MySQL 5.1.4 is mysqlslap, a load emulator that lets you see how well a particular query set or table engine performs under high-load conditions.

A query that consumes too many database resources may be the result of designing tables incorrectly, choosing the wrong table type, or creating an inefficient query. When a query eats up a lot of database resources, it can negatively affect other application components. By using mysqlslap to stress test a server in a non-public environment, you will discover these errors sooner, allowing you to you avoid a database meltdown once your application goes live.

This tutorial shows how you can use mysqlslap to run stress tests involving multiple clients, custom queries, different table engines, and much more. Lire la suite…

Counterpoint Hackerspace, une bande de geeks localisée à Roswell dans l’état de Georgie aux États unis, a eu l’excellente idée de mettre au point un outil permettant de stocker sur Tor des fichiers, un peu à la manière d’un espace « cloud », mais avec tous les avantages que Tor peut apporter : anonymat, décentralisation et gestion par la communauté. Lire la suite…

The excitement of installing a new version of macOS, especially if it’s a High Sierra 10.13, is only tempered by the possibility of it not working properly or not being compatible with the apps you use most.

Before you begin upgrade to MacOS make a bootable backup

If you haven’t started the process of upgrading yet, check if the Mac is compatible with macOS High Sierra and make a bootable backup. 

Do it now, before you do anything else. If things go disastrously wrong at least you’ll be able to boot from macOS’ Recovery partition and migrate all your data back to your Mac. You can use any backup tool you like – Apple obviously favours Time Machine, but you don’t have to use it. You can use, for example, Get Backup Pro, which comes with your Setapp subscription. Don’t have a Setapp subscription? Click here to sign up.

Common MacOS High Sierra Problems

While most new versions of macOS are relatively problem-free, it’s not unknown for users to have issues – particularly with a beta or .0 release. Thankfully most are easy to resolve. Here’s how to fix the most common High Sierra issues.

High Sierra Installer Won’t Download

If you’re trying to download the macOS High Sierra installer, you’ll need to have signed up to App Store. If you’ve done that, and managed to start the downloading process only for it to fail, force quit the App Store app.

1. Press Cmd-Alt-Esc or go to the Apple menu and choose Force Quit.
2. Select the App Store app and confirm you want to force quit.
3. Re-launch the App Store and try downloading again.

Macos High Sierra Won’t Install

If the download completes successfully but the installation doesn’t finish, force quit the installer using the same procedure as above. 

1. Restart your Mac
2. Launch the App Store app and go to the Purchases tab. 
3. Find macOS High Sierra and click Install. 

If that doesn’t work, try deleting the downloaded installer (it’s in your Applications folder) using CleanMyMac and download it again.

If you have a copy of macOS Server in your applications folder, that may be the root of the problem. Delete it and try again.

Lire la suite…

Mon NAS Synology vient de mettre à jour son firmware DSM et je constate en lançant ma sauvegarde rsync que la connexion rsync vers le NAS ne se fait plus : après saisie du mot de passe, on obtient une erreur “permission denied”.

Voici comment remédier à ce petit désagrément en deux minutes montre en main.

Problème : connexion SSH refusée

Lors de la connexion initiale, démarrée par :

rsync --ignore-existing --progress -vr --rsh='ssh -p22222' /home/backup/* root@example.com:/volume1/video

on obtient le message d’erreur suivant, après saisie du mot de passe:

Permission denied, please try again.
rsync: connection unexpectedly closed (0 bytes received so far) [sender]
rsync error: error in rsync protocol data stream (code 12) at io.c(226) [sender=3.1.1]

Après vérification que les identifiants (user/password) sont bien corrects, il s’avère que la solution réside dans l’utilisation de l’argument --rsync-path afin d’expliciter le chemin de l’exécutable rsync présent sur le NAS.

Lire la suite…