Linux Fu: The SSD Super Cache

NVMe solid state disk drives have become inexpensive unless you want the very largest sizes. But how do you get the most out of one? There are two basic strategies: you can use the drive as a fast drive for things you use a lot, or you can use it to cache a slower drive.

Each method has advantages and disadvantages. If you have an existing system, moving high-traffic directories over to SSD requires a bind mount or, at least, a symbolic link. If your main filesystem uses RAID, for example, then those files are no longer protected.

Caching sounds good, in theory, but there are at least two issues. You generally have to choose whether your cache “writes through”, which means that writes will be slow because you have to write to the cache and the underlying disk each time, or whether you will “write back”, allowing the cache to flush to disk occasionally. The problem is, if the system crashes or the cache fails between writes, you will lose data.

Compromise

For some time, I’ve adopted a hybrid approach. I have an LVM cache for most of my SSD that hides the terrible performance of my root drive’s RAID array. However, I have some selected high-traffic, low-importance files in specific SSD directories that I either bind-mount or symlink into the main directory tree. In addition, I have as much as I can in tmpfs, a RAM drive, so things like /tmp don’t hit the disks at all.

There are plenty of ways to get SSD caching on Linux, and I won’t explain any particular one. I’ve used several, but I’ve wound up on the LVM caching because it requires the least odd stuff and seems to work well enough.

This arrangement worked just fine and gives you the best of both worlds. Things like /var/log and /var/spool are super fast and don’t bog down the main disk. Yet the main disk is secure and much faster thanks to the cache setup. That’s been going on for a number of years until recently.

The Upgrade Issue

I recently decided to give up using KDE Neon on my main desktop computer and switch to OpenSUSE Tumbleweed, which is a story in itself. The hybrid caching scheme seemed to work, but in reality, it was subtly broken. The reason? SELinux.

Tumbleweed uses SELinux as a second level of access protection. On vanilla Linux, you have a user and a group. Files have permissions for a specific user, a specific group, and everyone else. Permission, in general, means if a given user or group member can read, write, or execute the file.

SELinux adds much more granularity to protection. You can create rules that, for example, allow certain processes to write to a directory but not read from it. This post, though, isn’t about SELinux fundamentals. If you want a detailed deep dive from Red Hat, check out the video below.

youtube.com/embed/_WOKRaM-HI4?…

The Problem

The problem is that when you put files in SSD and then overlay them, they live in two different places. If you tell SELinux to “relabel” files — that is, put them back to their system-defined permissions, there is a chance it will see something like /SSD/var/log/syslog and not realize that this is really the same file as /var/log. Once you get the wrong label on a system file like that, bad, unpredictable things happen.

There is a way to set up an “equivalence rule” in SELinux, but there’s a catch. At first, I had the SSD mounted at /usr/local/FAST. So, for example, I would have /usr/local/FAST/var/log. When you try to equate /usr/local/FAST/var to /usr/var, you run into a problem. There is already a rule that /usr and /usr/local are the same. So you have difficulties getting it to understand that throws a wrench in the works.

There are probably several ways to solve this, but I took the easy way out: I remounted to /FAST. Then it was easy enough to create rules for /var/log to /FAST/var/log, and so on. To create an equivalence, you enter:

semanage fcontext -a -e /var/log /FAST/var/log

The Final Answer

So what did I wind up with? Here’s my current /etc/fstab:

UUID=6baad408-2979-2222-1010-9e65151e07be / ext4 defaults,lazytime,commit=300 0 1
tmpfs /tmp tmpfs mode=1777,nosuid,nodev 0 0
UUID=cec30235-3a3a-4705-885e-a699e9ed3064 /boot ext4 defaults,lazytime,commit=300,inode_readahead_blks=64 0 2
UUID=ABE5-BDA4 /boot/efi vfat defaults,lazytime 0 2
tmpfs /var/tmp tmpfs rw,nosuid,nodev,noexec,mode=1777 0 0

<h1>NVMe fast tiers</h1>

UUID=c71ad166-c251-47dd-804a-05feb57e37f1 /FAST ext4 defaults,noatime,lazytime 0 2
/FAST/var/log /var/log none bind,x-systemd.requires-mounts-for=/FAST 0 0
/FAST/usr/lib/sysimage/rpm /usr/lib/sysimage/rpm none bind,x-systemd.requires-mounts-for=/FAST 0 0
/FAST/var/spool /var/spool none bind,x-systemd.requires-mounts-for=/FAST 0 0

As for the SELinux rules:

/FAST/var/log = /var/log
/FAST/var/spool = /var/spool
/FAST/alw/.cache = /home/alw/.cache
/FAST/usr/lib/sysimage/rpm = /usr/lib/sysimage/rpm
/FAST/alw/.config = /home/alw/.config
/FAST/alw/.zen = /home/alw/.zen

Note that some of these don’t appear in /etc/fstab because they are symlinks.

A good rule of thumb is that if you ask SELinux to relabel the tree in the “real” location, it shouldn’t change anything (once everything is set up). If you see many changes, you probably have a problem:

restorecon -Rv /FAST/var/log

Worth It?

Was it worth it? I can certainly feel the difference in the system when I don’t have this setup, especially without the cache. The noisy drives quiet down nicely when most of the normal working set is wholly enclosed in the cache.

This setup has worked well for many years, and the only really big issue was the introduction of SELinux. Of course, for my purposes, I could probably just disable SELinux. But it does make sense to keep it on if you can manage it.

If you have recently switched on SELinux, it is useful to keep an eye on:

ausearch -m AVC -ts recent

That shows you if SELinux denied any access recently. Another useful command:

systemctl status setroubleshootd.service

Another good systemd “stupid trick.” Often, any mysterious issues will show up in one of those two places. If you are on a single-user desktop, it isn’t a bad idea to retry any strange anomalies with SELinux turned off as a test: setenforce 0. If the problem goes away, it is a sure bet that something is wrong with the SELinux system.

Of course, every situation is different. If you don’t need RAID or a huge amount of storage, maybe just use an SSD as your root system and be done with it. That would certainly be easier. But, in typical Linux fashion, you can make of it whatever you want. We like that.

hackaday.com/2025/12/08/linux-…

Cheap And Aggressive DRAM Chip Tester

People enjoy retrocomputing for a wide variety of reasons – sometimes it’s about having a computer you could fully learn, or nostalgia for chips that played a part in your childhood. There’s definitely some credit to give for the fuzzy feeling you get booting up a computer you built out of chips. Old technology does deteriorate fast, however, and RAM chip failures are especially frustrating. What if you got a few hundred DRAM chips to go through? Here’s a DRAM chip tester by [Andreas]/[tops4u] – optimized for scanning speed, useful for computers like the ZX Spectrum or Oric, and built around an ATMega328P, which you surely still have in one of your drawers.

The tester is aimed at DIP16/18/20 and ZIP style DRAM chips – [Andreas] claims support for 4164, 41256, 6416, 6464, 514256, and 44100 series RAM chips. The tester is extremely easy to operate, cheap to build, ruthlessly optimized for testing speed, sports a low footprint, and is fully open-source. If you’re ever stuck with a heap of RAM chips you want to quickly test one by one, putting together one of these testers is definitely the path to take, instead of trying to boot up your well-aged machine with a bunch of chips that’d take a while to test or, at worst, could even fry it.

[Andreas] includes KiCad PCB and Arduino source files, all under GPL. They also provide adapter PCBs for chips like the 4116. What’s more, there are PCB files to build this tester in full DIP, in case that’s more your style! It’s far from the first chip tester in the scene, of course, there are quite a few to go around, including some seriously featureful units that even work in-circuit. Not only will they save you from chips that failed, but they’ll also alert you to fake chips that are oh so easy to accidentally buy online!

youtube.com/embed/vsYpcPfiFhY?…

hackaday.com/2025/12/08/cheap-…

Agenzie USA colpite da impiegati infedeli muniti di AI. 96 database governativi cancellati

Il Dipartimento di Giustizia degli Stati Uniti ha accusato i fratelli gemelli Muneeb e Sohaib Akhter di aver cancellato 96 database contenenti informazioni sensibili, tra cui verbali di indagini e documenti richiesti ai sensi del Freedom of Information Act (FOIA), dopo aver lasciato il loro lavoro presso un appaltatore del governo federale e di aver utilizzato strumenti basati sull’intelligenza artificiale per coprire le loro tracce .

Secondo gli inquirenti, gli Akhter avrebbero deliberatamente attaccato l’infrastruttura IT del loro ex datore di lavoro, che forniva servizi a diverse agenzie governative statunitensi. I fratelli avrebbero continuato ad accedere ai sistemi anche dopo aver lasciato il lavoro , bloccato l’accesso ad altri utenti, distrutto dati e tentato di coprire le proprie tracce. L’atto d’accusa è stato emesso il 13 novembre.

L’episodio più grave, secondo i pubblici ministeri, si è verificato il 18 febbraio.

Quel giorno, avrebbero cancellato circa 96 database, inclusi file FOIA e materiali relativi a indagini sensibili. Appena un minuto dopo aver cancellato uno dei database, appartenente al Dipartimento per la Sicurezza Interna (DHS), secondo gli investigatori, avrebbe avuto accesso a uno strumento basato sull’intelligenza artificiale chiedendo come cancellare i log di sistema. Gli investigatori ritengono che questo sia un chiaro segno di un tentativo di occultamento delle prove.

Nella corrispondenza inclusa nel fascicolo, i fratelli hanno anche discusso di come “ripulire” la loro casa in caso di una visita delle forze dell’ordine. I computer portatili aziendali, che erano ancora in loro possesso dopo il licenziamento, sono stati completamente cancellati prima di essere restituiti al datore di lavoro.

Un’altra accusa contro i Muneeb è quella di aver avuto accesso illegalmente ai dati dell’Internal Revenue Service (IRS). Secondo il Dipartimento di Giustizia, avrebbero avuto accesso ai registri fiscali federali di almeno 450 persone. Sohaib, a sua volta, è accusato di aver condiviso una password per un sistema governativo, il che costituisce di per sé un reato federale.

Sono quindi accusati di cospirazione per commettere frode informatica, distruzione di documenti, furto di dati governativi e furto d’identità aggravato. Complessivamente, rischiano fino a 45 anni di carcere. Sohaib è accusato di cospirazione, distruzione di documenti e trasmissione di una password che potrebbe essere utilizzata per hackerare un computer governativo; le sue accuse prevedono una pena massima fino a sei anni.

Il Ministero della Giustizia ha dichiarato che i fratelli hanno abusato della loro fiducia trovandosi dalla parte sbagliata della barricata, da appaltatori incaricati della gestione di dati governativi sensibili a persone accusate di aver minato processi governativi critici. Tuttavia, gli Akhter rimangono tecnicamente innocenti fino a prova contraria in tribunale.

L'articolo Agenzie USA colpite da impiegati infedeli muniti di AI. 96 database governativi cancellati proviene da Red Hot Cyber.

Belting out the Audio

Today, it is hard to imagine a world without recorded audio, and for the most part that started with Edison’s invention of the phonograph. However, for most of its history, the phonograph was a one-way medium. Although early phonographs could record with a separate needle cutting into foil or wax, most record players play only records made somewhere else. The problem is, this cuts down on what you can do with them. When offices were full of typists and secretaries, there was the constant problem of telling the typist what to type. Whole industries developed around that problem, including the Dictaphone company.

The issue is that most people can talk faster than others can write or type. As a result, taking dictation is frustrating as you have to stop, slow down, repeat yourself, or clarify dubious words. Shorthand was one way to equip a secretary to write as fast as the boss can talk. Steno machines were another way. But the dream was always a way to just speak naturally, at your convenience, and somehow have it show up on a typewritten page. That’s where the Dictaphone company started.

History of the Dictaphone

Unsurprisingly, Dictaphone’s founder was the famous Alexander Graham Bell. Although Edison invented the phonograph, Bell made many early improvements to the machine, including the use of wax instead of foil as a recording medium. He actually started the Volta Graphophone Company, which merged with the American Graphophone Company that would eventually become Columbia Records.

In 1907, the Columbia Phonograph Company trademarked the term Dictaphone. While drum-based machines were out of style in other realms, having been replaced by platters, the company wanted to sell drum-based machines that let executives record audio that would be played back by typists. By 1923, the company spun off on its own.

Edison, of course, also created dictation machines. There were many other companies that made some kind of dictation machine, but Dictaphone became the standard term for any such device, sort of like Xerox became a familiar term for any copier.

Dictaphones were an everyday item in early twentieth-century offices for dictation, phone recording, and other audio applications. Not to mention a few other novel uses. In 1932, a vigilante organization used a Dictaphone to bug a lawyer’s office suspected of being part of a kidnapping.

Some machines could record and playback. Others, usually reserved for typists, were playback-only. In addition, some machines could “shave” wax cylinders to erase a cylinder for future use. Of course, eventually you’d shave it down to the core, and then it was done.

The Computer History Archives has some period commercials and films from Dictaphone, and you can see them in the videos below.

youtube.com/embed/76r81PEEjFY?…

As mentioned, Dictaphone wasn’t the only game in town. Edison was an obvious early competitor. We were amused that the Edison devices had a switch that allowed them to operate on AC or DC current.

Later, other companies like IBM would join in. Some, like the Gray Audograph and the SoundScriber used record-like disks instead of belts or drums. Of course, eventually, magnetic tape cassettes were feasible, too, and many people made recorders that could be used for dictation and many other recording duties.

youtube.com/embed/jQqyLIxfWZo?…

The Dictabelt

For the first half of the twentieth century, Dictaphones used wax cylinders. However, in 1947, they began making machines that pressed a groove into a Lexan belt — a “Dictabelt,” at first called a “Memobelt.” These were semi-permanent and, since you couldn’t easily melt over some of the wax, difficult to tamper with, which helped make them admissible in court. Apparently, you could play a Dictabelt back about 20 times before it would be too beat up to play.

These belts found many uses. For one, Dictaphone was a major provider to police departments and other similar services, recording radio traffic and telephone calls. In the late 1970s, the House Select Committee on Assassinations used Dictaphone belts from the Dallas police department recording in 1963 to do audio analysis on the Kennedy assassination. Many Dictaphones found homes in courtrooms, too.

As you can see in the commercials in the video, Dictabelts would fit in an envelope: they are about 3.5 in x 12 in or 89 mm x 300 mm. The “portable” machine promised to let you dictate from anywhere, keep meeting minutes, and more. A single belt held 15 minutes of audio, and the color gives you an idea of when the belt was made.

youtube.com/embed/M-edbrhcrWY?…

Magnetic Personality

Of course, Dictaphone wasn’t the only game in town for machines like this. IBM released one that used a magnetic belt called a “Magnabelt’ that you could edit. Dictaphone followed suit. These, of course, were erasable.

Even as late as 1977, you could find Dictaphones in “word processing operations” like the one in the video with the catchy tune, below. Of course, computers butted into both word processing and dictation with products like Via Voice or DragonDictate. Oddly, DragonDictate is from Nuance, which bought what was left of Dictaphone.

Insides

Since this is Hackaday, of course, you want to see the insides of some of these machines. A video from [databits] gives us a peek below.

youtube.com/embed/wb0yENdMQeI?…

Offices have certainly changed. Most people do their own typing now. Your phone can record many hours of crystal-clear audio. Computers can even take your dictation now, if you insist.

Should you ever find a Dictabelt and want to digitize it for posterity, you might find the video below from [archeophone] useful. They make a modern playback unit for old cylinders and belts.

youtube.com/embed/_nRREq3v6vY?…

We’d love to see a homebrew Dictabelt recorder player using more modern tech. If you make one, be sure to let us know. People recorded on the darndest things. Tape caught on primarily because of World War II Germany and Bing Crosby.

hackaday.com/2025/12/08/beltin…

В Японии ожидают цунами высотой около 3 метров после мощного землетрясения

жителей прибрежной зоны призывают немедленно эвакуироваться, сообщили сейсмологи.

Зеленський і Стармер перейшли до двосторонніх переговорів, тоді як Макрон і Мерц залишили зустріч.

Вони відмовилися відповідати на будь-які запитання журналістів.

Це можуть бути вирішальні дні для всіх нас щодо України. У нас багато карт у руках, – Мерц і Макрон

▪️Кір Стармер заявив, що сьогодні лідери мають ухвалити "важливі рішення".

▪️Фрідріх Мерц заявив, що він скептично ставиться до деяких деталей у документах, що надходять із США, але тому вони зібрались сьогодні і будуть працювати.

Зеленський прибув на Даунінг-стріт до резиденції прем'єра Великої Британії Стармера.

Раніше туди також прибули канцлер Німеччини Мерц і президент Франції Макрон.