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

  • May 28 / 2017
  • 0

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
  • 6
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
  • 2

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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  • Dec 04 / 2015
  • 4
Administration, Code Snippets, Linux, Scripting, Security

Snippet 0x0D: Let’s Encrypt – 5 min guide to set up cronjob based certificate renewal

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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  • 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 ... 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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  • Mar 22 / 2015
  • 2
Linux, Scripting, Security

Circumvent Internet blockages/filters/censorship with socksproxy and netcat

These days, ISPs are often forced to block the access to certain sites, because their government considers these sites dangerous and/or illegal. While one could certainly discuss the usefulness of such measures in great detail, this tiny post focuses on the more interesting subject of how to circumvent these blockages. It’s not a lenghty post, and it doesn’t show all the ways there are, but I’ll show two simple ways to circumvent Internet non-DNS-based filters.

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  • Jul 18 / 2013
  • 11
Administration, Linux, Security

How To: DNS spoofing with a simple DNS server using Dnsmasq

The Domain Name System (DNS) is one of the fundamental services of the Internet. By resolving domain names to IP addresses, it makes routing of IP packets possible and thereby lets browsers and other clients connect to remote servers using all kinds of protocols. By blindly connecting to the IP address returned by the DNS server, however, users put a lot of trust into DNS, because by default, DNS responses are not validated or verified.

In this blog post, I’d like to demonstrate how to easily set up a DNS server that allows you to easily forge certain entries manually — thereby allowing you to either block certain domains from your network or to pretend that you are a certain website. This scenario is commonly referred to as DNS forgery or DNS spoofing.

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