Tales From The Sysadmin: Dumped Into The Grub Command Line

November 25, 2019 by 53 Comments

Today I have a tale of mystery, of horror, and of hope. The allure of a newer kernel and packages was too much to resist, so I found myself upgrading to Fedora 30. All the packages had downloaded, all that was left was to let DNF reboot the machine and install all the new packages. I started the process and meandered off to find a cup of coffee: black, and darker than the stain this line of work leaves on the soul. After enough time had elapsed, I returned, expecting the warming light of a newly upgraded desktop. Instead, all that greeted me was the harsh darkness of a grub command line. Something was amiss, and it was bad.

(An aside to the reader, I had this experience on two different machines, stemming from two different root problems. One was a wayward setting, and the other an unusual permissions problem.)

How does the fledgling Linux sysadmin recover from such a problem? The grub command line is an inscrutable mystery to the uninitiated, but once you understand the basics, it’s not terribly difficult to boot your system and try to restore the normal boot process. This depends on what has broken, of course. If the disk containing your root partition has crashed, then sorry, this article won’t help.

In order to get a system booting, what exactly needs to happen? How does booting Linux work, even? Two components need to be loaded into memory: the kernel, and the initramfs. Once these two elements are loaded into memory, grub performs a jump into the kernel code, which takes over and finishes the machine’s boot. There is one more important detail that we care about — the kernel needs to know where to find the root partition. This is typically part of the kernel parameters, specified on the kernel boot line.

When working with an unfamiliar shell, the help command is a good starting point. grub runs in a very limited environment, and running the help command scrolls most of the text off the screen. There is an environment variable that helps out here, enabling output paging:set pager=1.
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Wipe Your Nozzle To Avoid Stringing

November 25, 2019 by 21 Comments

[Design Prototype Test] likes his Ender 3 printer. There was only one problem. When printing PETG — which is notorious for stringing — the hot end would pick up material and eventually ruin the print. The answer was to mount a cheap Harbor Freight brush somewhere and make the head pass over it after each layer. You can see the video of the design, below.

It sounds as though it worked well and after explaining the concept, he dives into the details of how he designed the fixture and how he mounted it. There’s a lot of good information in there about his particular toolchain and workflow.

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Incredibly Tiny RF Antennas For Practical Nanotech Radios

November 25, 2019 by 18 Comments

Researchers may have created the smallest-ever radio-frequency antennas, a development that should be of interest to any nanotechnology enthusiasts. A group of scientists from Korea published a paper in ACS Nano that details the fabrication of a two-dimensional radio-frequency antenna for wearable applications. Most antennas made from metallic materials like aluminum, cooper, or steel which are too thick to use for nanotechnology applications, even in the wearables space. The newly created antenna instead uses metallic niobium diselenide (NbSe2) to create a monopole patch RF antenna. Even with its sub-micrometer thickness (less than 1/100 the width of a strand of human hair), it functions effectively.

The metallic niobium atoms are sandwiched between two layers of selenium atoms to create the incredibly thin 2D composition. This was accomplished by spray-coating layers of the NbSe2 nanosheets onto a plastic substrate. A 10 mm x 10 mm patch of the material was able to perform with a 70.6% radiation efficiency, propagating RF signals in all directions. Changing the length of the antenna allowed its frequency to be tuned from 2.01-2.80 GHz, which includes the range required for Bluetooth and WiFi connectivity.

Within the ever-shrinking realm of sensors for wearable technologies, there is sure to be a place for tiny antennas as well.

[Thanks Qes for the tip!]

AI Phone App Learns Baseball Signals

November 24, 2019 by 1 Comment

Watching a sport can be a bit odd if you aren’t familiar with it. Most Americans, for example, would think a cricket match looked funny because they don’t know the rules. If you were not familiar with baseball, you might wonder why one of the coaches was waving his hands around, touching his nose, his ears, and his hat seemingly at random. Those in the know however understand that this is a secret signal to the player. The coach might be telling the player to steal a base or bunt. The other team tries to decode the signals, but if you don’t know the code that is notoriously difficult. Unless you have the machine learning phone app you can see in the video below.

If you are not a baseball fan, it works like this. The coach will do a number of things. Perhaps touch his cap, then his nose, brush his left forearm, and touch his lips. However, the code is often as simple as knowing one attention signal and one action signal. For example, the coach might tell you that if they touch their nose and then their lips, you should steal. Touching their nose and then their ear is a bunt. Touching their nose and then the bill of their cap is something else. Anything they do that doesn’t start with touching their nose means nothing at all. If the signal is this easy, you really don’t even need machine learning to decode it. But if it were more complicated — say, the gesture that occurs third after they touch their nose unless they also kick dirt at which point it means nothing — it would be much harder for a human to figure out.

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Secret C64 Program Found On A Christian Rock Band’s Vinyl Record

November 24, 2019 by 29 Comments

How often do you find Easter eggs in old vinyl records?

It sure was a surprise for [Robin Harbron] when he learned about a Commodore 64 program hidden on one of the sides of a record from the 1985 album of Christian rock band Prodigal. The host of the YouTube channel 8-Bit Show and Tell shows the “C-64” etching on one side of the vinyl, which he picked up after finding out online that the record contained the hidden program.

The run-out groove on records is typically an endless groove that keeps the record player from running off the record (unless there is an auto-return feature, which just replays the record). On side one of the vinyl, the run-out groove looks normal, but on side two, it’s a little thicker and contains some hidden audio. Recording the audio onto a cassette and loading it onto a dataset reveals a short C64 program.

The process is a little more troublesome that that, but after a few tries [Harbron] reveals a secret message, courtesy of Albert Einstein and Jesus Christ. It’s not the most impressive program ever written, but it’s pretty cool that programmers 35 years ago were able to fit it into only a few seconds of audio.

Unfortunately, we won’t be hearing much actual music from the album – [Harbron] chose not to play the songs to avoid copyright issues on YouTube.

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Hackaday Links: November 24, 2019

November 24, 2019 by 2 Comments

It barely seems like it, but it’s been a week since the 2019 Hackaday Superconference wrapped up in sunny Pasadena. It was an amazing weekend, filled with fun, food, camaraderie, and hacks galore. For all who were there, it’ll likely take quite some time before spinning down to Earth again from the post-con high. For those who couldn’t make it, or for those who did but couldn’t squeeze in time for all those talks with everything else going on, luckily we’ve got a ton of content for you to review. Start on the Hackaday YouTube channel, where we’ve got videos already posted from most of the main stage talks. Can’t-miss talks include Chris Gammell’s RF deep-dive, Kelly Heaton’s natural electronic art, and Mohit Bhoite’s circuit sculpture overview. You’ll also want to watch The State of the Hackaday address by Editor-in-Chief Mike Szczys. More talks will be added as they’re edited, so watch that space for developments.

One of the talks we missed – and video of which appears not to be posted yet – was Adam Zeloof’s talk on thermodynamic design for your circuits. While we wait for that, here’s an interesting part that might prove useful for your next high-power design. It’s a Thermal Jumper Chip, which is essentially a ceramic SMD component that can conduct heat but not electricity. It’s intended to be used where a TO-220 case needs to be electrically isolated but thermally connected to a heatsink. Manufacturer TT Electronics has a whole line of the chips in various sizes and specs, plus a lot of other cool components like percussive igniters.

We got an interesting tip this week about a new development in the world of 3D-printing. A group from Harvard demonstrated a multinozzle extruder that can print multimaterial objects in a single pass. The work is written up in a Nature article entitled “Voxelated soft matter via multimaterial multinozzle 3D printing”, which is unfortunately paywalled, but the abstract and supplementary videos are really interesting. This appears not to be a standard hot plastic extrusion process; rather, the extruder uses elastomeric inks that cure after they’re extruded. They manage some clever tricks, including a millipede-like, vacuum-powered soft robot extruded in one pass from both soft and rigid silicone elastomers. It’s genuinely interesting stuff, and watching the multimaterial extruder head switch materials at up to 50 times per second is mesmerizing.

People really seemed to get worked up over the transit of Mercury across the face of the Sun last week, and for good reason – astronomical alignments such as these which can be seen from Earth are rare indeed, and worth taking time to see. Not everyone was in the right place at the right time with the right gear to view the transit directly, though, which is why we were glad that Justin over at The Thought Emporium did a video on leveraging online assets for space-based observations. We’ve featured a ton of hacks using SDRs and the like to intercept data from weather satellites, and while those hacks are fun and you should totally try them, Justin points out that most of these streams are readily available for free over the Internet. Clouds, lightning, forest fires and Earth changes, and yes, even the state of the Sun can all be monitored from the web.

Speaking of changes, do you know what has changed in Unix over the last 50 years? For that matter, did you know that Unix turned 50 recently? Sean Haas did after reading this article in Advent of Computing, which he shared on the tipline. The article compares a modern Debian distro to documentation from 1971 that pre-dates Unix version 1; we assume the “Dennis_v1” folder in the doc’s URL refers to none other than Dennis Ritchie himself. It turns out that Unix is remarkably well-conserved over 50 years, at least in the userspace. File system navigation and shell commands are much the same, while programming was much different. C didn’t yet exist – Dennis was busy – but there were assemblers and linkers, plus a FORTRAN compiler and an interpreter for BASIC. It’s comforting to know that if you drop into a wormhole and end up sitting in front of a PDP-11 with Three Dog Night singing “Joy to the World” on the radio in the background, you’ll at least be able to look like you belong there.

And finally, it’s nearly Sparklecon time again. Sparklecon VII will be held on January 25 and 26, 2020, at the 23b Shop hackspace in Fullerton, California. We’ve covered previous Sparkelcons and we’ve even sponsored the meetup in the past, and it looks like a blast. The organizers have put out a Call for Proposals for talks and workshops, so if you’re in the mood for some mischief, get your application going. And be quick about it – the CFP closes on December 8.

InstaBeat Started Out Of Spite

November 24, 2019 by 27 Comments

[Tom] teaches electronics with this small programmable MP3 player, but it didn’t get its start as a teaching tool.

As all parents are sometimes required to do, [Tom] was acting as chauffeur for his daughter and his friends. When he played the Beatles one of his passengers informed him that she was completely devoid of taste and didn’t like them at all. So he decided what the world needed was a Beatles appliance. This way all the ignorant plebs could educate themselves at the push of a button.

The machine is based around some SEED studio parts and a simple PCB. It was able to hold all 12 original albums and even announced their titles in a generated voice. Since the kit is easy to put together it was quickly re-purposed as a teaching aid. They get to learn the laser cutter and do some through-hole soldering.

He has plans to turn it into a more formal how-to workshop that anyone can duplicate.He’d also like to make a small software suite for playing with text-to-speech and hacking the speaker into other roles such as a multi meter.

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