Archive | Debian

Boot your Raspberry Pi from nothing but an Ethernet cable

Zero Client: Boot kernel and root filesystem from network with a Raspberry Pi2 or Pi3

A Zero Client is a computer that has nothing on its permanent storage but a bootloader. Rather, it loads everything from the network. With the method presented in this article, you will be able to boot a Raspberry Pi into a full Debian OS with nothing more on the SD card other than the Raspberry firmware […]

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Gnome on Wayland on Raspberry Pi 2

Raspberry Pi2 and Pi3 running pure Debian 9 (“Stretch”) and the Linux Mainline/Vanilla Kernel

Update 2017 Feb 25: I have updated the step-by-step instructions based on the suggested fixes and improvements contained in the reader comments. I also have copied the step-by-step instructions from this blog post to the file hosted on From now on I will update the instructions only on github, so expect that the instructions in this […]

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How to convert images to PDF with paper and image size, without ImageMagick

ImageMagick’s convert tool is handy for converting a series of images into a PDF. Just for future reference, here is one method how you can achieve the same without convert. It is useful if you have 1-bit PBM images (e.g. scanned text) at hand:

This command concatenates all .pbm files, pipes the data to pnmtops to create an […]

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Digitizing books 
(International Dunhuang Project, CC BY-SA 3.0)

Digitize books: Searchable OCR PDF with text overlay from scanned or photographed books on Linux

Here is my method to digitize books. It is a tutorial about how to produce searchable, OCR (Optical Character Recognition) PDFs from a hardcopy book using free software tools on Linux distributions. You probably can find more convenient proprietary software, but that’s not the objective of this post. Important: I should not need to mention that depending […]

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'Hashed' brown potatoes. Hashing is important on more than just one level (picture by Jamie Davids, CC-BY-2.0)

Hashing passwords: SHA-512 can be stronger than bcrypt (by doing more rounds)

On a server, user passwords are usually stored in a cryptographically secure way, by running the plain passwords through a one-way hashing function and storing its output instead. A good hash function is irreversible. Leaving dictionary attacks aside and by using salts, the only way to find the original input/password which generated its hash, is to simply try all possible […]

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Unprivileged Unix Users vs. Untrusted Unix Users. How to harden your server security by confining shell users into a minimal jail

As a server administrator, I recently discovered a severe oversight of mine, one that was so big that I didn’t consciously see it for years. What can Unprivileged Unix Users do on your server? Any so-called “unprivileged Unix users” who have SSH access to a server (be it simply for the purpose of rsync’ing files) is not really “unprivileged” as the […]

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