PHP extension seg-faulting

29th March 2021

Task at hand: Call Cobol (=GnuCOBOL) from PHP. I used FFI for this: <?php $cbl = FFI::cdef("int phpsqrt(void); void cob_init_nomain(int,char**); int cob_tidy(void);", "/srv/http/phpsqrt.so"); $ffj0 = FFI::cdef("double j0(double);",…

Add Disjoint IP Addresses To SSHGuard Blacklist

15th March 2021

Problem at hand: There are multiple machines running SSHGuard. Each of these machines accumulates different sets of blacklists. Task: Add disjoint IP addresses from one machine to another machine's blacklist. 1. Copy from "master" machine: scp -p master:/var/db/sshguard/blacklist.db…

Lesser Known Static Site Generators

7th March 2021

Well known static site generators are Hugo (written in Go), Pelican (written in Python), Grav (written in PHP), or Eleventy (written in JavaScript). For a list of static site generators see Jamstack (322 generators listed) or Static Site Generators (460 generators listed). The following three…

Testing J-Pilot feature-gtk3 branch

2nd March 2021

J-Pilot 1.8 still relies on GTK+ 2, which is heading towards planned deprecation. The entire work to migrate to GTK+ 3 is done by volunteers, Judd Montgomery and David Malia. This post is about testing this new experimental branch feature-gtk3 from GitHub. Installing this branch is…

Analysis And Usage of SSHGuard

28th February 2021

To ban annoying ssh access to your Linux box you can use fail2ban. Or, alternatively, you can use SSHGuard. SSHGuard's installed size is 1.3 MB on Arch Linux. Its source code, including all C-files, headers, manuals, configuration, and makefiles is 8 KLines. In contrast, for fail2ban just the…

ssh as SOCKS server

21st February 2021

Assume three computers A, B, and C. A can connect to B via ssh, but A cannot connect to C, but B can connect to C. A -> B -> C On A open ssh as SOCKS-server with ssh -N -D 9020 user@B Now on A one can use brave --proxy-server="socks5://localhost:9020" The browser will then show…

Poisson Log-Normal Distributed Random Numbers

9th February 2021

Task at hand: Generate random numbers which follow a lognormal distribution, but this drawing is governed by a Poisson distribution. I.e., the Poisson distribution governs how many lognormal random values are drawn. Input to the program are \(\lambda\) of the Poisson distribution, modal value and…

Performance comparison Ryzen vs. Intel vs. Bulldozer vs. ARM

1st February 2021

For comparing different machines I invert the Hilbert matrix $$ H = \left(\begin{array}{ccccc} 1 & {1\over2} & {1\over3} & \cdots & {1\over n} \\ {1\over2} & {1\over3} & {1\over4} & \cdots & {1\over n+1} \\ {1\over3} &…

dumpe2fs: When was my hard-drive first formatted?

23rd January 2021

I repeatedly forget to remember when my hard-drive or SSD was first formatted. Command for this is dumpe2fs. This command is part of package e2fsprogs. Example: # dumpe2fs -h /dev/sda1 dumpe2fs 1.45.6 (20-Mar-2020) Filesystem volume name: <none> Last mounted on: /boot Filesystem…

Unitymedia und SIP VoIP

16th January 2021

Folgendes schrieb ich an die Firma Unitymedia, jetzt Vodafone: Ich möchte gerne meine Rufnummer XXX über meine YYY Telefonanlage via VoIP betreiben. Ich verwende den von Ihnen bereitgestellten Router "Vodafone Station". Meine Kundennummer lautet ZZZ. Ich benötige nun folgende sieben…

Compiling Java source to binary (native)

19th December 2020

With GraalVM you can now fully compile a Java file to a native binary. This is also called AOT, ahead-of-time compilation. Compilation is very slow, and resulting binary is huge as it must contain all code which might be referenced. In contrast the class file usually is quite small. Though, it is…

Windows 10 very slow after reboot

13th November 2020

I repeatedly noticed that my Microsoft Windows 10 laptop is noticeably slow when restarted. This time I rebooted the laptop and just watched what happened in task manager. Below are the results. Waiting for more than 10 minutes doing nothing: one third of the machine is loaded with managing its…

Statistics of this Blog: Crossed 110.000 Views

7th October 2020

This blog was viewed more than 110.000 times since its inception and had more than 84.500 visitors. The averages per month are: The most popular posts this year are: The most popular posts over all years are: Distribution of countries accessing this blog over last 365 days, USA is number one,…

Configure boot settings in UEFI

29th August 2020

Main source for trouble-shooting is Arch-Wiki UEFI. It describes the commands: bcfg within UEFI shell Linux command efibootmgr 1. It is ighly recommended to install the UEFI-shell, which is in package edk2-shell. On Asrock copy cp -p /usr/share/edk2-shell/x64/Shell_Full.efi /boot/shellx64.efi So…

SSD Speed on Dell XPS 13 9350 with Samsung EVO 970 Plus

9th August 2020

In continuation of blog-post SSD Speed on Dell XPS 13 9350, here are performance measurements for a Samsung EVO 970 Plus in Dell XPS 13. Caveat from Dell xps 13 9350 and Samsung 970 evo M.2 nvme Compatability?: However, be aware that although the XPS 13 9350 uses a PCIe x4 configuration for its…

Blocking IP addresses with ipset

14th July 2020

In Chinese Hackers I mentioned that I block ssh attackers with the help of fail2ban. Unfortunately, fail2ban uses iptables to create firewall rules in "Chain f2b-SSH" for each individual IP address. For a modern processor this is no problem, even if you have thousands of these rules.…

ASRock DeskMini A300M with AMD Ryzen 3400G

7th July 2020

Below are some photographs during assembly of the Asrock A300M with an AMD Ryzen 5 Pro 3400G processor. The Asrock web-site detailing the specs of the A300M: DeskMini A300 Series. Three noticable reviews on the A300M: Anandtech has a very readable review of the A300M: Home> Systems …

Reply to: Neural Network Back-Propagation Revisited with Ordinary Differential Equations

30th June 2020

This article is worth reading: Neural Network Back-Propagation Revisited with Ordinary Differential Equations I replied: Thank you very much for this very informative article providing many links, the Python code, and the results. According the mentioned paper from Owens + Filkin the speedup…

Calling C from Julia

23rd June 2020

Two ways to compute the error function or Bessel function in Julia. 1. Calling C. On UNIX libm provides erf() and j0(). So calling them goes like this: ccall(("erf","libm.so.6"),Float64,(Float64,),0.1) ccall(("j0"),Float64,(Float64,),3) In this case one can omit the…

Gunnar Uldall's Tax Tariff

16th June 2020

Gunnar Uldall wrote a a book with title "Die Steuerwende" in 1996. 1. Proposal. In this book he proposed the following tariff, \(x\) is in DEM. $$ t_u(x) = \begin{cases} 0 & \mbox{if } x\le12000 \\ 0.08\left(x-12000\right) & \mbox{if } 12001\le x\le20000 \\ …

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