My name is Philipp C. Heckel and I write about nerdy things.
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Posts Tagged / Linux


  • Mar 18 / 2018
  • 0
Linux, Virtualization

USB disk causes blinking cursor at boot; how to “fix” the MBR bootstrap code

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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  • May 28 / 2017
  • 4
Linux

Creating a BIOS/GPT and UEFI/GPT Grub-bootable Linux system

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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  • Jan 08 / 2017
  • 18
Administration, Linux

How-To: Using ZFS Encryption at Rest in OpenZFS (ZFS on Linux, ZFS on FreeBSD, …)

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 at Datto developed it), I thought a sneak preview is absolutely necessary.

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  • Jan 01 / 2017
  • 0
Administration, Linux

zfsu: ZFS utils for offsite backup, retention and maintaining a slow mirror

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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  • Dec 31 / 2016
  • 7
Linux

How-To: Move your existing Linux install to ZFS on Root

Ever since I joined Datto 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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  • Oct 18 / 2015
  • 5
Administration

How-To: Create a Debian package and a Debian repository

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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  • May 04 / 2015
  • 1
Linux, Programming, Security

OpenSSH ‘AuthorizedKeysCommand’ with ‘fingerprint’ argument (Patch for OpenSSH 6.6p1)

Many of us developers or system administrators use OpenSSH’s public key authentication (aka password-less login) on a daily basis. The mechanism works based on public key cryptography: By adding a RSA/DSA public key to the authorized_keys file, the user with the matching private key can login without a password. The mechanism works great for a couple of hundred, thousands and even 100k thousand users (tested, login takes ~2sec).

But what if there are more keypairs, say, a million users, or a more flexible approach is desired? Maybe with an LDAP or a database backend? Think of GitHub and how they do their ssh git@github.com ... login! This blog post shows you how to do that by patching OpenSSH’s AuthorizedKeysCommand option to support an additional fingerprint argument.

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  • Mar 24 / 2015
  • 2
Code Snippets, Linux, Scripting

Snippet 0x0B: Bash completion with sub-commands and dynamic options

Every system administrator, most programmers and countless of command line surfing Linux/Mac users use it every day without thinking twice. Hitting the tab key twice, [TAB][TAB], has become the most common thing in the world. Bash completion is the magic behind the tab key. It’s easy to use, but it’s a pain to write. This tiny post demonstrates how to write scripts for bash completion, with sub-commands and dynamic parameters. A working script is embedded in my open source file sync software Syncany.

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  • May 29 / 2014
  • 3
Programming

The magic of Gradle: create Windows installers, Debian packages, manage a PPA, and optional sub-projects

Gradle is great build tool. Compared to Ant or Maven, it’s so much easier to use and write proper code for it — it’s unbelievable at times. A little while ago, I switched from an ugly Ant/Maven installation to Gradle with my open source project Syncany. Ever since then, I am simply amazed about what Gradle can do. Granted, it’s not always easy to understand and the lack of proper documentation and IDE support makes things more like a trial-and-error-based packaging experience. However, the amount of time that it saves is worth it.

Since I really like Gradle and I myself often have a hard time finding proper answers for the questions I have, I’d like to demonstrate a few solutions that I have come up with. In particular, I’ll describe how to create a Windows installer using Inno Setup under Linux, create Debian packages and manage a PPA (debuild/dput) as well as how to add an optional Gradle sub-project.

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