Linux cgroups Resource Constraints

Linux cgroups (control groups) have been around for a long time providing varioius functions for resource management and the ability to segregate workloads with their own constraints. cgroups have provided the basis for container engines such as docker that has become so aggressively adopted in enterprises over the last few years.

cgroups are enabled on all contemporary linuxes with systemd being the API to manage them; the system will manage various cgroups organised in:

• slices - see systemd-cgls where we will typically see system services under the system slice users services, including the segregation for user sessions in another. Encapsulates scopes and services.
• scopes - parent for a logical grouping of units/services which can be managed (killed/stop/resource managed)
• services - logical grouping that provides a service, such as the sshd, that are usual started based on configuration in unit files

But how can cgroup and resource controls be useful for a developer?

VMware Player 12.x with 4.18.x kernels / Fedora 28

A Fedora 26 to Fedora 28 upgrade (with its 4.18.x kernel) broke VMware Player 12.5.7. However upgrading to the newer (14.x or 15.x) versions didn't work so how to fix?

Fedora 28: fixing mpv and libOpenCl.so.1: no version info and hardware acceleration

One of the great benefits of Linux is that it can run on a whole host of legacy components and still perform well. Re-purposing an old Dell E520 with a 32bit Intel Core2 Duo cpu, a PCI via vt6321a based IDE raid card, for Fedora 28 install was straight forward until we started to look at hardware accelerated mpv for watching movies files: libOpenCL.so.1: no version information available (required by /lib/libavfilter.so...

Fedora: bonding over ethernet and wifi devices finally works

Bonding network interfaces for a laptop is a useful feature allowing you to keep the same IP as you switch between a ethernet or wifi connection. However when I last tried this with Fedora26/network manager 1.8 this wasn't a s success.


With the Fedora 28 release with network manager 1.10.10, it is now possibe to create a bond over an ethernet and wifi device

Backing up an RPi SD and shrinking the disk image

There are numerous tutorials on how to resize/shrinking media but they typically advise using gparted for the task; whilst gparted is a great tool, it can fail with obscure error messages when trying to shrink partitions. This is how we can do this the old fashioned way.

RPi and iTunes <-> IOS app for music

After finally setting up Kodi to use a DAC mounted on Raspberry Pi for controlling/serving my music controlled by an IOS device, I re-discovered that IOS devices, via the Apple iTunes remote, can control remote iTunes.

But how's that help?

Kodi and DACs from a RPI to an amplifier

There are a number of options to connect a Raspberry Pi to an stereo amplier but one option is to use a DAC hat card such as an IQAudio DAC with RCA jacks. With the hardware in place it's all about the software to library/index/serve your music and to provide a pleasant user experience to select/queue/control your music - this typically means to control your music via a IOS-based smartphone/tablet.

What's preventing spindown of disks on RPI?

I have a RPi3 with an external USB hardddisk attached which appeared to be not to be spinning down although the setup (via hdparm was correct. But how to determine what was the cause of activity to the disk?

Nikkor 24mm f/2.8 AI-S Disassembly

The Nikkor 24mm f/2.8 AI-S is a lens from the late 70s but shares its optical formula with its predecesors (pre-AI and AI) and successor (AF-D). The AI-S is also quite common and as such appears on ebay frequently in various conditions.


The 24mm f/2.8 AI-S lens is reasonably simple to disassemble and teardown with the only complication being the CRC unit at the rear.

ffmpeg and Nvidia GTX hardware encoding

ffmpeg video processing on an old linux/machine, like a i7 860, running Fedora26 can be painful if you only rely on the CPU. With a recent Nvidia card supporting NVENC (GeForce 6/7/8/10.x) ffmpeg can be compiled directly to support these cards.

Another Well Regarded Legacy: Nikkor 28mm f/2.8 AI-S

The 28mm f/2.8 AI-S is a well regarded lens from the early 1980s that is still available new today. But what's the point of this compared to, say a 24-70mm f/2.8 zoom? And how does it fair for use as a walk-about or an environmental portrait lenses at/near wide open (f/2.8..f/5.6) apertures?


^{28mm f/2.8 AI-S}