Sysadmins of the North, a technical blog in English and Dutch

From time to time you need to flush MySQL’s query_cache to prevent fragmentation of free query cache memory space. Whether we need to flush the query cache is provided to us by MySQL’s Qcache_free_blocks status information. The higher the value the more fragmented free space is. Note: Flushing the query cache does not delete it. Use reset query cache for that.

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Optimizing MySQL database servers is an ever ongoing process. Every new MySQL version brings new configuration settings you can use to improve the performance. As a MySQL DBA you want your database server and databases to perform well, here is a little help.

MariaDB/MySQL 5.5.4 introduces new configuration settings for the InnoDB storage engine. This can greatly improve MySQL’s InnoDB performance, both in read and write operations. One of those settings is innodb_buffer_pool_instances.

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This project aims to provide an Open Source OpenPGP library in JavaScript so it can be used on virtually every device. Instead of other implementations that are aimed at using native code, OpenPGP.js is meant to bypass this requirement (i.e. people will not have to install gpg on their machines in order to use the library). The idea is to implement all the needed OpenPGP functionality in a JavaScript library that can be reused in other projects that provide browser extensions or server applications. It should allow you to sign, encrypt, decrypt, and verify any kind of text – in particular e-mails – as well as managing keys.

Dutch tech-news site wrote an extensive article on how to use PGP to encrypt your email. The article is somewhat comparable with my article Encrypt email with PGP/GnuPG but dives deeper into the matter.

In Dutch:

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or at least, rethink it through before buying one

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When a large scale spam run was sent through your mail servers, you need to clean up and remove those spam messages. Doing so guarantees normal, valid email messages being sent quickly and the spam messages never leave your queue. In Postfix, there are various similar commands to delete messages from the Postfix mail queue. Based on the Message-ID and/or email address.

One of those is:

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Malware Must Die! has done a great, and extensive write-up on the subject of hacked and abused FTP sites (accounts). This topic fits well within my daily routine investigating and closing down hacked websites, for which I have to use various techniques for finding those hacked sites. As you might know, website security is one of the major themes of this site.

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All you need to do to install the WebSockets feature in IIS, is executing the following PowerShell command:

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Whenever you need to test the MySQL database connectivity from a website or server, it’s handy to have various test scripts nearby. Whether it is because you are setting up a new website or you have just installed a new server and are running your tests. Nowadays, many websites depend on a MySQL or MariaDB database because CMS systems like WordPress, Joomla and Drupal are so popular, and Umbraco too. You want your webserver to connect to MySQL fast and properly :)

Throughout the examples, we always use “” as our database hostname, “example_db” as databasename and username, “password” is our password.

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How to hide file extensions, such as .php or .asp, with URL Rewrite.

Sometimes it’s important to hide the file extension of scripts you use. Security by obscurity might be one of those reasons, if you don’t want others to know what script language you are using. Or you just want to hide the file extension for no apparent reason. In this example, we hide the .php extension using the IIS URL Rewrite module, in a ready to use rule example.

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How to redirect HTTP traffic to HTTPS with IIS URL Rewrite is a question that keeps popping up, just about everywhere. Here you find a ready to use URL Rewrite rule.

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Google PageSpeed Insights recommends optimizing or compressing images such as PNGs, and to minify Javascript and CSS. Minifying resources refers to eliminating unnecessary bytes, such as extra spaces, line breaks, and indentation. Compacting HTML, CSS, and JavaScript can speed up downloading, parsing, and execution time. In addition, for CSS and JavaScript, it is possible to further reduce the file size by renaming variable names as long as the HTML is updated appropriately to ensure the selectors continue working (Source: Google PageSpeed Insights – Minify Resources).

How to accomplish this the easy, and fast way?

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While investigating SMTP authentication issues, over an Transport Layer Security (TLS) encrypted connection, it’s always handy if you are able to test the SMTP authentication and StartTLS connection from the command line. SMTP Authentication, often abbreviated SMTP AUTH, is an extension of the Simple Mail Transfer Protocol whereby an SMTP client may log in using an authentication mechanism chosen among those supported by the SMTP server.

Most problems come forth from the fact that either the username and password log in combination is wrong, or the server doesn’t support StartTLS or the authentication mechanism used. Here, we address and verify them all. Being able to verify (Start)TLS encrypted connections and SMTP AUTH options is ideal for when you’re having problems with website forms (scripts) that send emails from a website using authenticated SMTP over an TLS encrypted connection.

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On StrongLoop we find an interesting article on scaling Node.js with proxies and clusters:

Node apps essentially run single-threaded, even though file and network events could leverage multiple threads. This architecture thereby binds the performance of each application instance/process to one logical CPU core that the thread it’s attached to. To a J2EE architect like me, this highlights immaturity in Node as an enterprise ready technology. Application servers like JBoss or Weblogic already solved this 10 years back using server core multi-threading and parallelism. Little did I realize that context switching between threads ate up my memory and I still had a blocking IO problem.

In a way, discovering the lack of threading prepares the Node developer to write scalable asynchronous code and use libraries like web-sockets from the get-go rather than worry about scalability later in the application life cycle. But this code optimization is still capped to the scaling limits of a single CPU core. So, how is production scaling achieved in the Node world today?

Read on at Node.js Performance Tip of the Week: Scaling with Proxies and Clusters

Brandon Cannadya – the CTO of Modulus, a Node.js application hosting platform – wrote an absolute beginner’s guide to node.js.

There’s no shortage of Node.js tutorials out there, but most of them cover specific use cases or topics that only apply when you’ve already got Node up and running. I see comments every once and awhile that sound something like, “I’ve downloaded Node, now what?” This tutorial answers that question and explains how to get started from the very beginning.

What is Node.js?
A lot of the confusion for newcomers to Node is misunderstanding exactly what it is. The description on definitely doesn’t help.

An important thing to realize is that Node is not a webserver. By itself it doesn’t do anything. It doesn’t work like Apache. There is no config file where you point it to you HTML files. If you want it to be a HTTP server, you have to write an HTTP server (with the help of its built-in libraries). Node.js is just another way to execute code on your computer. It is simply a JavaScript runtime.

Read on at An Absolute Beginner’s Guide To Node.js

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About Sysadmins of the North

Hi and welcome to Sysadmins of the North!
Sysadmins of the North is just another technical blog. Just like so many others out there. Most posts are written in English, some in Dutch. On you can find all kinds of computer, server, web, sysadmin, database and security related stuff.

About me: My name is Jan Reilink. I am not a hacker, coder, developer, programmer or guru. I am merely a system administrator, doing his daily thing at Vevida Services in the Netherlands. Living in the north of the Netherlands, so hence the name Sysadmins of the North :-)
Drop me a comment somewhere or send an email to say hi, or discuss about security, website or WordPress, performance, Windows or IIS topics.


If you feel that Sysadmins of the North has helped solve your problem, saved you time, or you just simply like, then please consider making a donation with Paypal. Thanks! :)

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