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Andrey Mikhalchuk’s Blog

Technoblog about life

Resume and bio of the author Couple of articles related to my hobby - robotics My impressions about immigration to Australia. In Russian only. Recipes for everyday problems solving
Linux-related posts Windows-related posts Software-related posts A lot of info about hardware
Different tools you might find useful Posts about various web technologies Everything that doesn't fit the rest of the menu RSS feed for this blog

Recent Posts

Jul 18, 2014 How to migrate ownCloud 6 from sqlite to MySQL

Those who do not know what ownCloud is probably should read about it here: http://owncloud.com. This is an awesome tool that provides functionality similar to dropbox, but uses your own server to host the files. We all know about dropbox’s bad behavior like storing passwords on the server side, accessing your content when you don’t want it. Actually recently I was monitoring disk activity on a computer with dropbox installed on it and found that for some reason dropbox keeps reading files where it has not business to do. It was clearly configured to replicate files in its own folder, yet was reading all files on the disk. One way or another there are a lot of reasons to get rid of dropbox and switch to ownCloud. It’s cheaper, secure and can be used to store business or confidential information where dropbox fails to provide both security and confidentiality.

By default ownCloud uses sqlite3 to keep records of the files it stores and people like myself that decided to go forth with the default configuration get trapped with this configuration. Once you load more than couple gigs of data you will notice that it gets slower and sloooower and slo… Sometimes you might even experience complete freeze on the client side.

The solution to the problem is moving the data from sqlite to something mroe serious like MySQL. Both databases have SQL in their name so the migration should be easy. Unfortunately ownCloud doesn’t provide any means to automate this migrate. To make matters worse the dialects sqlite3 and MySQL use are a little bit different so you can’t feed sqlite3 database dump directly into MySQL. I saw multiple solutions to the problem migrating ownCloud 5, but nothing for OC6 so far. Here is how I migrated it in just a few simple commands:

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Apr 11, 2014 Attaching >2Tb disks to Linux

Here is the sequence of commands to make disk space usable in Linux for disks >2Tb (so your regular fdisk won’t help you here).

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Apr 4, 2014 Tips and tricks for your Riviera Maya trip (Cancun, Playa del Carmen, Akumal, Tumlum etc)

Hola!

There are plenty of great posts about what to expect when you’re traveling to Mexico in general and Riviera Maya in particular. So instead of writing another one let me just list couple lessons learned that hopefully will make your trip to Mexico even more enjoyable.

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Mar 20, 2014 How to silence a piezo buzzer in your microwave, alarm clock etc

Almost every time I buy a piece of electronics with some sort of alarm it always includes a super loud and mega annoying buzzer notifying about the end of cycle. Though tuning it off completely is an easy operation (just open the case and cut the wire) making it just not as loud is a more complicated task involving knowledge of electronics and some soldering skills. Fortunately there is a much simpler way to accomplish the task, sometimes not even requiring the device disassembly …

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Dec 22, 2013 Fixing Sony Pulse Elite Edition Wireless Headset Blue Light of Death

Sony Pulse Elite Edition Wireless Headset is the finest you can find for PS3 and it totally worth its sticker price between $100 to $150. This is one of only a few options providing Surround sound for PS3, thanks to Sony proprietary protocols used for sound delivery to your ears.

Unfortunately the product was not tested well and just like many other complex solutions it glitches more than a user expect for such an expensive piece of electronics. One of the most famous problems typically occurs when you shelf the headset for a few days. After you blow the dust off you will find a tiny blue LED on the headset blinking twice every second. What’s interesting it will keep blinking even after you turn the headset off! The problem is very widespread and a lot of people experience it. Unfortunately Sony support is not very helpful in solving the problem. Replacing the headset does not solve the problem, eventually BLOD will happen to the new headset just like it happened to the old one.

Here is how to fix the problem:

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Nov 15, 2013 How to make browser offline cache retrieve new version of the page when browser is online, but keep using cache when it is offline

Offline cache is awesome! For certain things. For most regular web pages it is unfortunately not. Here is web developer’s most frequent use for the offline cache: make browser use cached version of the page when browser is offline but refresh it when it gets online. What could be simpler and more natural purpose for the OC? Well, unfortunately it wasn’t designed to work like this out of the box. Even when your browser goes online it will keep using the cached version “indefinitely” until the cache manifest is updated. So what do we do in this situation?

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Nov 12, 2013 AWS EC2 ssh not responding in RHEL 6.4 AMI

I was fighting with an AWS bug today seeming just ridiculous for a system that makes ssh the only way to access the server. With no console login EC2 users are completely dependent on flawless sshd operation and Amazon team just did a really bad job preparing the RHEL 6.4 image.
So here are the symptoms: you create an image from a perfectly working system with the purpose to clone it. Then you create new instance from the AMI and it seems working fine too, you can ssh to it no problem. After a reboot or too it suddenly stops responding to ssh thought the rest of the system seems working fine (HTTP server for instance). Server logs do not show any errors. Reboots do not help and EC2 doesn’t provide console access to the server.
Here is the solution:

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Nov 8, 2013 How to use large / multiline text as a field in mongodb

I’m working on a project that requires storing large multiline chunks of text in MongoDB. The chunks should be inserted in the database during initial database population, so I need to enter them somewhere in db population script. Unfortunately you can’t just put something like this:

db.tests.insert( {
name: 'test',
text: 'this is
my superawesome
multiline content'
} )

Javascript/JSON do not support multiline text like this. Fortunately there are several options that made my life easier. Here they are:

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Sep 27, 2013 rPlay rocks!

I’m currently beta-testing rPlay and this software totally rocks! What’s rPlay? Well, imagine yourself willing to share content of your iPhone or iPad screen with you family. There are couple ways to do this: you can get an Apple TV ($99) or … well, that’s actually it. AirPlay is a proprietary protocol so the number of options is actually extremely limited.

Last year a small revolution happened: Raspberry Pi got released to the markets. Raspi (short for Raspberry Pi) is awesome. For just $35 you can get a computer powerful enough to output 1080p video to your TV yet small enough to fit your pocket. There are currently dozen mostly Linux-based operating systems running on this computer and the platform is totally open (unlike Apple). Obviously it didn’t take long for hackers to implement AirPlay on Raspi so now for just $35 (well, plus SD card, cables, power supply, case, shipping = about $70) you can play music from any i-device to speakers attached to Raspi. Effectively you can turn Raspi into an Apple equivalent of AirPort Express, but not Apple TV.

For streaming video Apple uses slightly different functionality called AirPlay Mirroring and this protocol was not implemented on Raspi yet. Until now. Smart guys from VMLite finally figured out a way to mirror video from iPhone/iPad via Raspi to the TV. Not sure how long it took them to do this incredible work, but it actually works. Well, it is still in beta, but totally usable and shows great performance.

rPlay is a great tool for presentations, sharing Youtube videos with your friends and family or playing iPhone games on a large screen. Here are a few great features of this software:
- It supports both landscape and portrait mode (rotate your iPhone and the image on the TV will rotate as well)
- Has great video and sound synchronization – something a lot of streaming software lacks. Well, there is a half-second delay when you output sound via HDMI, but if you plug speakers via USB port all is in sync. I guess that’s why they call it beta.
- It is quite stable. I kept switching streaming from one iDevice to another and once it froze. But, again, this is beta and I kept beating it hard, so given the circumstances it is very solid even in beta-version
- One extra cool feature is a limited support for Google Chromecast. Personally I do not use it much as AirPlay covers it all but for Android users that’s some great news.

I already mentioned multiple times that the current version is in beta stage, so there are a fe quirks which hopefully will get resolved in the final version:
- the video and sound being not in sync when sound is played over HDMI (use USB sound output to fix this problem)
- Netflix 1080p streaming is not smooth enough. If you overclock Raspi it gets better, yet still not as smooth as being played without mirroring
And that’s basically it. I saw a lot of “final versions” being released with such minor defects. Microsoft would totally release it :) Still I’m really glad VMLite decided to keep polishing the software until perfect and can’t wait for the final product.

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Sep 24, 2013 Fixing Verizon FiOS DNS Problems

Your superfancy FiOS internet link is getting flaky for no reason every now and then? The reason could be not the fiber-optic cable (which is awesome), but a problem with part of infrastructure called DNS servers. The DNS (Domain Name Resolution) servers are responsible for translating domain names such as google.com or yahoo.com into internet addresses computers use for sending traffic across the internet. When DNS is not working properly your web surfing becomes either slow or impossible.

I was debugging corporate email problems recently and besides many other interesting things was fixing the CEO’s complain about email not working from his home most of the time. Surprisingly the root cause of the problem was absolutely horrible reliability of FiOS DNS servers. For some reasons every other DNS lookup was ending up not knowing anything at all about our company’s domain. The solution to the problem is getting rid of FiOS DNS servers in you router configuration and replacing them with OpenDNS servers. That’s much easier to do than it sounds, I recommend doing that even if you don’t have DNS troubles in your home network yet. Some Internet research shown that many people are having sporadic problems with DNS while using FiOS and this recipe will solve some of them.

Let’s fix this …

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