китайский пазл, фиолетовый, игрушка, бегемот, lilo

Setting up a network bridge between a QEMU VM and its host on the command line

A user of ArchLinux can follow relevant parts of the wiki articles “QEMU” and “PCI passthrough via OVMF” for setting up other aspects of a QEMU VM, but these guides don't provide a short method suitable for people who are not network administrators and don't need ramified network topologies. The default network of a QEMU VM, so called “user networking”, frankly, is disconnected from its host. Below is the short method of setting up a VM such that it can communicate with other networks connected to its host like a wired channel to the internet or a home Wi-Fi network.

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китайский пазл, фиолетовый, игрушка, бегемот, lilo

cleaning kernel dumps from UEFI BIOS NVRAM

Trying to install Secure Boot certificates into UEFI BIOS NVRAM, I hit a problem that there is no free space left in the NVRAM. Most solutions recommend just to delete files starting with dump in the directory /sys/firmware/efi/efivars. A virtual filesystem exposing UEFI BIOS NVRAM variables is mounted to this directory. Indeed, these files accounted for 100 of 130 kB of used space. However, working with this file system directly is dangerous because you can accidentally delete another variable and brick your motherboard. Hence I read a little about these dump files. They are used as a backend to the so called “Linux persistent storage filesystem pstore”. It can store kernel messages when a kernel panics. pstore is exposed in the directory /sys/fs/pstore. Hence a safe way to clean UEFI BIOS NVRAM would be through this directory. Also there is a systemd-pstore.service that moves these messages to the systemd journal. When I started it, it emptied /sys/fs/pstore, but dump files were not deleted from /sys/firmware/efi/efivars for some reason. After a reboot, voilà, there is no kernel garbage in UEFI BIOS NVRAM and will never be if this service is enabled.
китайский пазл, фиолетовый, игрушка, бегемот, lilo


Diceware is a method of choosing a password (passphrase) that consists of several short words with good entropy. You can download a Diceware dictionary text file in different languages from the Diceware page. Here is the direct link to the English file.

This Python 3 program transforms a Diceware dictionary text file into 6 HTML pages. 6 pages are much more compact than 36-page printable document they offer. You can tune font size in a web browser print dialog. A program usage manual is embedded into the program. The result of applying this program to the English Diceware dictionary text file is in this Zip archive.
китайский пазл, фиолетовый, игрушка, бегемот, lilo

system-wide PulseAudio and pacmd

If the PulseAudio daemon is executed in the system-wide mode, pacmd will not work even if started by root. Instead, it will work if it is started by the user pulse with the environment variable PULSE_RUNTIME_PATH assigned to /var/run/pulse. Everything in one command for root:
sudo -u pulse -- env PULSE_RUNTIME_PATH=/var/run/pulse pacmd
китайский пазл, фиолетовый, игрушка, бегемот, lilo

On when linear maps and matrices were introduced

One striking feature of Noether's 1929 paper occurred in a footnote: “As B. L. van der Waerden has communicated to me, one can obtain an invariant connection, independent of the specific choice of basis, by separating the concepts linear transformation and matrix. A linear transformation is a homomorphism of two modules of linear forms; a matrix is an expression (the representation) of this homomorphism by a definite choice of basis” [76,670]. Here we have the essential modern connection between the notions of linear transformation, matrix, and module (or vector space). Two years later, van der Waerden's insight about the proper way of viewing that connection was presented to a much wider audience in his textbook.

Moore, Gregory H. “The Axiomatization of Linear Algebra: 1875-1940.” Historia Mathematica, volume 22, issue 3, 1995, pp. 262–303. ScienceDirect, doi:10.1006/hmat.1995.1025.
китайский пазл, фиолетовый, игрушка, бегемот, lilo


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