Have you ever rebooted your computer only to see a black screen with a blinking cursor? If you have a USB drive attached, chances are the blinking cursor is caused by invalid bootstrap code in the Master Boot Record (MBR) on that drive which has caused the normal boot execution to stop without returning control to the BIOS. If you have physical access to the machine, simply remove the USB drive and/or change the boot order to pick the OS disk first.

If you have no physical access, things are a bit more tricky: This exact thing happened to me at work the other day. Unfortunately, it didn’t happen to my computer, but to a few dozen of our customer backup appliances during their scheduled upgrade/reboot. Now, while dozens out of over 60k isn’t that much, our customers rely on these devices, so it’s not acceptable to have them not boot properly.

In this short post, I’ll demonstrate how to reproduce the blinking cursor problem, and how to “fix” the MBR to ensure the computer still boots, regardless of the boot order.

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Good old Master Boot Record (MBR) unfortunately cannot address anything beyond 2TB, so partitioning large disks and making them bootable is impossible using MBR. The GUID Partition Table (GPT) solves this problem: It supports disks up to 16EB. However, installing grub does not work without a special BIOS boot partition. If you also want to support booting the same system via UEFI, another partition, the EFI System Partition (ESP), is necessary.

This should post shows you how to partition a disk with GPT and make a bootable Linux system via BIOS/Legacy and UEFI.

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An upcoming feature of OpenZFS (and ZFS on Linux, ZFS on FreeBSD, …) is At-Rest Encryption, a feature that allows you to securely encrypt your ZFS file systems and volumes without having to provide an extra layer of devmappers and such. To give you a brief overview of what the feature can do, I thought I’d write a short post about it.

The current ZFS encryption implementation is not (yet) merged into the upstream repository (as of January 2017). There is a pretty big pull request which is still being reviewed, but because the feature is so incredibly cool (and because my colleague Tom Caputi developed it), I thought a sneak preview is absolutely necessary.

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My laptop runs ZFS as its root file system (see this blog post) — meaning that I can snapshot my root file system and I can send it to another machine as a backup very easily. Unfortunately, while ZFS provides the raw functionality, there is no great tool to manage offsite backups and retention. To ease this pain, I wrote/forked and packaged a few helper scripts which I called zfsu, a collection of ZFS utilities.

It consists of the following tools: zfsu tx (aka zfstx) maintains a mirror of a ZFS pool over the network. zfsu ret (aka zfsret) is a simple script to apply local retention (destroy snapshots) of a file system and its snapshots. zfsu res (aka zfsres) is a script to resilver a slow mirror, e.g. a HDD disk if mirrored with a SSD.

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Ever since I joined my new company two years ago, ZFS has been part of my work every day. And every day, I am amazed how great it is. So naturally, I wanted to move my existing Linux Mint 18 installation to boot off of ZFS. Why, you may wonder? Well that’s easy. Because now I can snapshot my root file system, I can roll back if I need to, and I can restore individual files in a heartbeat.

It took a bit of fiddling in the beginning, but once you know how it works, it’s a piece of cake. This short post shows you how to move your existing Linux installation to ZFS on root (preferably Ubuntu 16.04+ based, may work for others).

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I was using dyndns.org and no-ip.com for a long time, and because I’m too cheap to buy the premium version for a simple service like this, I finally decided to set up my own dynamic DNS server for my various systems.

This is a short tutorial describing how I did it. It’s really not rocket science, so don’t expect too much.

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At my work, we use JSON-RPC based APIs very heavily, in particular with our PHP JSON-RPC library php-json-rpc. While JSON-RPC is not as wide spread as REST, it fits our needs quite nicely. In particular, it is protocol independent and can be used over HTTP, SSH or as local CLI. With our library and its numerous extensions (HTTP, SSH, authentication, validation, request-to-class mapping and logging), development is super fast and incredibly easy.

In this post, I’d like to demonstrate how to set up a PHP based JSON-RPC API, with authentication, validation and logging.

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Let’s Encrypt was officially released to the open public today. That means the Internet can finally get free, trusted SSL/TLS certificates. This quick guide shows how to set up Let’s Encrypt with auto-renewal through a cronjob — using the simp_le client, an alternative client developed by one of the same authors who develop the official client.

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Debian packages and repositories are everywhere, yet many people don’t understand that creating them is actually pretty easy. While there are dozens of tutorials out there, none of them seemed to really show a good step-by-step. This is a quick tutorial on how to create a Debian package from scratch, and how to create a simple Debian repository.

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Remember the times when we copied PHP “libraries” into our project folder, or we copy and pasted code from some random site into our project? Those times are over. Composer and Packagist are the modern way to manage PHP dependencies. They are great. Almost as good as The Maven repos and their build tools in the Java world. However, while Composer is really good at managing the dependencies of a single project, i.e. one composer.json file, it does not play well if you want to plug different projects together at runtime. And by “does not play well” I mean it simply doesn’t work if you have two or more composer.json files. This quick post demonstrates a way around this limitation. Quick and dirty. Just like the foundations of PHP :-)

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