Tales From The Sysadmin: Dumped Into The Grub Command Line

November 25, 2019 by Jonathan Bennett 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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East Coast RepRap Festival Comes Alive In Second Year

November 22, 2019 by Tom Nardi 2 Comments

By pretty much any metric you care to use, the inaugural East Coast RepRap Festival (ERRF) in 2018 was an incredible success. There was plenty to see, the venue was accommodating, and the ticket prices were exceptionally reasonable. But being a first-time event, there was an understandable amount of trepidation from both exhibitors and the attendees. Convincing people to travel hundreds of miles to an event with no track record can be a difficult thing, and if there was a phrase that would best describe the feel of that first ERRF, it would probably have been “cautious optimism”.

But this year, now that they had some idea of what to expect, the 3D printing community descended on Bel Air, Maryland with a vengeance. In 2019, everything at ERRF was bigger and better. There were more people, more printers, and of course, more incredible prints. Activities like the 3D Printed Derby returned, and were joined by new attractions including full-body 3D scanning and a shooting gallery where attendees could try out the latest in printable NERF weaponry.

The official tally shows that attendance nearly doubled over last year, and with growth like that, we wouldn’t be surprised if the ERRF organizers consider relocating to a larger venue for 2020 or 2021. As far as problems go, growth so explosive that it requires you to rethink where you hold the event isn’t a bad one to have. The Midwest RepRap Festival, which served as the inspiration for ERRF, found they too needed to move into more spacious digs after a few years. Something to keep in mind the next time somebody tells you the bubble has burst on desktop 3D printing.

Trying to distill an event as large and vibrant as ERRF 2019 into a few articles is always difficult. Even after spending hours walking around the show floor, you would still stumble upon something you hadn’t seen previously. As such, this article is merely a taste of what was on hand. The East Coast RepRap Festival 2020 should absolutely be marked on your calendar for next year, but until then let’s take a look at just some of what made this year’s event such a smash.

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This Week In Security: More WhatsApp, Nextcry, Hover To Crash, And Android Permissions Bypass

November 22, 2019 by Jonathan Bennett 7 Comments

There is another WhatsApp flaw, but instead of malicious GIFs, this time it’s malicious mp4 files. Facebook announced the vulnerability late last week. An update has been released, so first go make sure WhatsApp is updated. Facebook’s advisory is a bit light on the details, simply saying that a “stack-based buffer overflow” was possible as a result of “parsing the elementary stream metadata of an mp4 file”.

Shortly after the bug was announced, a GitHub repository popped up, with a claimed proof-of-concept mp4 file for CVE-2019-11931. (Thanks to [justtransit] on Reddit for the link.) I can’t easily test the PoC file, but we can take a look at it to see what the vulnerability is. What tools do we need to take a look? A hex editor is a good start. I’m using GHex, simply because it was available and easily installed on Fedora. Continue reading “This Week In Security: More WhatsApp, Nextcry, Hover To Crash, And Android Permissions Bypass” →

Retrotechtacular: 934 MHz CB Radio

November 21, 2019 by Jenny List 49 Comments

The radio spectrum is carefully regulated and divided up by Governments worldwide. Some of it is shared across jurisdictions under the terms of international treaties, while other allocations exist only in individual countries. Often these can contain some surprising oddities, and one of these is our subject today. Did you know that the UK’s first legal CB radio channels included a set in the UHF range, at 934 MHz? Don’t worry, neither did most Brits. Behind it lies a tale of bureaucracy, and of a bungled attempt to create an industry around a barely usable product.

Hey, 2019, Got Your Ears On?

Did this car make you want a CB radio? Stuurm [CC BY-SA 3.0]

Mention CB radio in 2019 it’s likely that the image conjured in the mind of the listener will be one from a previous decade. Burt Reynolds and Jerry Reed in Smokey and the Bandit perhaps, or C. W. McCall’s Convoy. It may not be very cool in the age of WhatsApp, but in the 1970s a CB rig was the last word in fashionable auto accessories and a serious object of desire into which otherwise sane adults yearned to speak the slang of the long-haul trucker.

If you weren’t American though, CB could be a risky business. Much of the rest of the world didn’t have a legal CB allocation, and correspondingly didn’t have access to legal CB rigs. The bombardment of CB references in exported American culture created a huge demand for CB though, and for British would-be CBers that was satisfied by illegally imported American equipment. A vibrant community erupted around UK illegal 27 MHz AM CB in the late 1970s, and Government anger was met with campaigning for a legal allocation. Brits eventually got a legal 27 MHz allocation in November 1981, but the years leading up to that produced a few surprises.

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Training Bats In The Random Forest With The Confusion Matrix

November 21, 2019 by Pat Whetman 4 Comments

When exploring the realm of Machine Learning, it’s always nice to have some real and interesting data to work with. That’s where the bats come in – they’re fascinating animals that emit very particular ultrasonic calls that can be recorded and analysed with computer software to get a fairly good idea of what species they are. When analysed with an FFT spectogram, we can see the individual call shapes very clearly.

Nyctalus noctula (noctule bat)

Myotis nattereri (natterera’s bat)

Plecotus auritus (brown long eared)

Pipistrellus pipistrellus (common pipistrelle)

Creating an open source classifier for bats is also potentially useful for the world outside of Machine Learning as it could not only enable us to more easily monitor bats themselves, but also the knock on effects of modern farming methods on the natural environment. Bats feed on moths and other night flying insects which themselves have been decimated in numbers. Even in the depths of the countryside here in the UK these insects are a fraction of the population that they used to be 30 years ago, but nobody seems to have monitored this decline.

So getting back to our spectograms, it would be perfectly reasonable to throw these images at a convolutional neural network (CNN) and use an image feature-recognition strategy. But I wanted to explore the depths of the mysterious Random Forest. Continue reading “Training Bats In The Random Forest With The Confusion Matrix” →

Texas Tesla Tower Titillates

November 20, 2019 by Al Williams 109 Comments

One of the nice things about a road trip is you often get to see something that really surprises you. A recent trip through Texas may have resulted in my second most surprising sighting. There’s a strange tower that looks oddly like a Tesla tower in the middle of rural Texas, right off the main interstate. What is it? Although Google did answer the question — sort of — I’m still not sure how legitimate its stated purpose is.

First Sighting

I was driving between Wimberly and Frisco — two towns that aren’t exactly household names outside of Texas. Near Milford, there’s a very tall structure that looks like a giant mechanical mushroom on top of a grain silo. If the mushroom were inverted or pointing towards the horizon, it would be easy to imagine it was some very odd antenna. This dish, however, is pointed right down its own odd-shaped mast. The top of the thing sure looks like the top of a Van de Graf generator.

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Brussels Looks Towards Banning Fossil Fuel Transportation As Soon As 2035

November 20, 2019 by Zoe Skyforest 168 Comments

Many cities around the world routinely struggle with smog. Apart from being unsightly, heavy air pollution has serious negative health effects, both in the short term and with regards to long-term life expectancy. Over the years, governments have tried to tackle the problem with varied tactics around the world.

When talking about smog, Brussels is not one of the cities that comes first to mind. Regardless, the local government has developed its new climate plan that seeks to abolish fossil fuel vehicles from its streets by 2035. The scheme has a variety of measures that will be staggered over the coming years. It’s part of a broadening trend in transportation, and something we’ll likely see more of around the world in coming years.

What’s The Go?

Brussels is in the process of reducing congestion by converting former roads into pedestrian-only spaces. REUTERS/Eric Vidal

Under the new plan, diesel vehicles will be banned from the city’s Low Emission Zone, or LEZ, by 2030. This will further extend to gasoline vehicles in 2035. Furthermore, special categories of higher polluting vehicles will have bans enforced even earlier. Motorcycles had previously been exempt from the LEZ, but moving forward, the most polluting models will be locked out of the city centre as soon as 2022. The aim is to reduce emissions, with a goal of cutting CO2 output by 40 percent by 2030, and becoming carbon neutral by 2050. The city is also exploring the concept of a Zero Emission Zone, or ZEZ, expanding upon earlier efforts which transformed the Boulevard Anspach from a heavily-trafficked road into a pedestrian-only plaza. Continue reading “Brussels Looks Towards Banning Fossil Fuel Transportation As Soon As 2035” →