Understanding disk usage in Linux

Understanding disk usage in Linux” is a well written in-depth look into the Linux filesystem layer and how things work under the hood.  This is probably not something most people would have to deal on a day-to-day basis, but it is very useful for anyone doing system administration and looking for the better understanding of operating systems.

commandlinefu – a place to share and gather command line wisdom

commandlinefu is a place to learn and share your knowledge about command line tools and techniques.  It has thousands of tips, tricks, and handy shortcuts, covering a wide range of tools from shells and editors to version control and remote access.

Windows Notepad Finally Supports Unix, Mac OS Line Endings

This Slashdot story links to this blog post by Microsoft.  33 years later, one of the most annoying issues with the Notepad text editor is resolved:

Starting with the current Windows 10 Insider build, Notepad will support Unix/Linux line endings (LF), Macintosh line endings (CR), and Windows Line endings (CRLF) as usual. New files created within Notepad will use Windows line ending (CRLF) by default, but it will now be possible to view, edit, and print existing files, correctly maintaining the file’s current line ending format.

They shouldn’t have invented their own line ending in the first place.  But it’s great to see that they finally acknowledge the existence of the rest of the world.

htop explained

htop explained” is a very detailed guide into the htop Linux system monitoring tool.  Even if you are an experienced Linux user, and even if you are not a fan of htop (why aren’t you?), you will still find this guide useful, as it goes into a lot of detail on how htop figures out all the values and where Linux keeps bits and pieces of system information.

Linux Inside – A book-in-progress about the Linux kernel and its internals

Linux Inside” is a book-in-progress about the Linux kernel and its internals.  You can read it online or download as a PDF.  It’s also available in several languages.  Some of the things that you’ll find inside are:

  • The boot process
  • Initialization
  • Interrupts
  • System calls
  • Timers and time management
  • Synchronization primitives
  • Memory management
  • SMP
  • Data structures in the Linux kernel
  • … and more.

 

Linux utils that you might not know

Linux utils that you might not know covers a few Linux command line utilities that aren’t very famous:

  • column, for “columnating” lists, which is very useful for display of table-like data (think CSV, for example);
  • cal, for displaying calendars;
  • factor, for calculating factors;
  • numfmt, for formatting numbers and converting them to/from human-readable formats;
  • shred, for overwriting the content of a deleted file, making it much more difficult to recover.

pushd/popd vs. cd

My shell of choice and circumstance for most of my Linux life was Bash.  So, naturally, in my head, shell pretty much equals Bash, and I rarely think or get into situations when this is not true.  Recently, I was surprised by a script failure, which left me scratching my head.  The command that failed in the script was pushd.

pushd and popd, it turns out, are built into Bash, but they are not standard POSIX commands, so not all the shells have them.  My script wasn’t setting the shell explicitly, and end up executing with Dash, which I haven’t even heard of until this day.  The homepage of Dash says the following:

DASH is not Bash compatible, it’s the other way around.

Mkay… So, I’ve done two things:

  1. Set /bin/bash explicitly as my shell in the script.
  2. Switch to “cd folder && do something && cd –“, instead of pushd/popd combination, where possible.

I knew about “cd –” before, but it was interesting to learn if there are any particular differences (hint: there are) between the this approach and the pushd/popd one that I was using until now.  This StackOverflow thread (ok, ok, Unix StackExchange) was very helpful.

Things Every Hacker Once Knew

Eric Raymond goes over a few things every hacker once knew.

One fine day in January 2017 I was reminded of something I had half-noticed a few times over the previous decade. That is, younger hackers don’t know the bit structure of ASCII and the meaning of the odder control characters in it.

This is knowledge every fledgling hacker used to absorb through their pores. It’s nobody’s fault this changed; the obsolescence of hardware terminals and the near-obsolescence of the RS-232 protocol is what did it. Tools generate culture; sometimes, when a tool becomes obsolete, a bit of cultural commonality quietly evaporates. It can be difficult to notice that this has happened.

This document is a collection of facts about ASCII and related technologies, notably hardware terminals and RS-232 and modems. This is lore that was at one time near-universal and is no longer. It’s not likely to be directly useful today – until you trip over some piece of still-functioning technology where it’s relevant (like a GPS puck), or it makes sense of some old-fart war story. Even so, it’s good to know anyway, for cultural-literacy reasons.

The article goes over:

  • Hardware context
  • The strange afterlife of the outboard modem
  • 36-bit machines and the persistence of octal
  • RS232 and its discontents
  • UUCP, the forgotten pre-Internet
  • Terminal confusion
  • ASCII
  • Key dates

Found via a couple of other interesting bits –
What we still use ASCII CR for today (on Unix) and
How Unix erases things when you type a backspace while entering text.

100 Favorite Programming, Computer and Science Books

Peteris Krumins, of the Browserling fame, has a series of blog posts on his top favorite programming, computer and science books.  It’s an excellent selection of titles, from which I’ve read only a fraction.  Good timing for the Christmas shopping too.  Here are the blog posts in the series so far (5 books per post):

Even with the 30 books mentioned so far, there are new things to read and learn.  I wonder how many of the notes to self I’ll have by the time the whole 100 are listed.

Things to learn about Linux

Julia Evans has this amazing list of things to learn about Linux.  I think, it doesn’t matter how new or experienced you are with the operating system, you’ll find a few points in this list that you either know nothing about or know very little.

Personally, I’ve been using and administrating Linux systems for almost two decades now, and my own knowledge of the things on that list is either very limited or not existing.  Sure, I know about pipes and signals, but even with basic things like permissions there are some tricky questions that I’m not sure I can get right on the first go.

Some of the topics mentioned are simple and straight-forward and will only need a few minutes or a couple of hours to get up to speed with.  Others – are huge areas which might take years, if not decades (like networking, for example).

I look forward to Julia’s drawings covering some of these.