Christian E. Lysel

LYWSD02

Thu, 23 Oct 2025 00:00:00 +0000

Sync clock

Flash ROM

USB Logic Analyzer

Tue, 06 Apr 2021 00:00:00 +0000

General

GPS lookup

Tue, 04 Aug 2020 00:00:00 +0000

General

SDR hacks

Thu, 23 Apr 2020 00:00:00 +0000

General

Sidechannel attack with tensorflow

CD Rip

Sun, 29 Mar 2020 00:00:00 +0000

Setup

Ubuntu with 3 CDROM drives: /dev/sr0, /dev/sr1 and /dev/sr2.

Install ripit

sudo apt install ripit

Script to handle one CDROM drive … it will:

Wait for CD inserted
Rip the CD to “Music/$artist/$year ‐ $album/$nr. $song” and store both flac and mp3 files.
Eject the CD
Go to 1.

If the CD is already ripped, it will just eject it. If parts of the CD is already ripped, it will just continue. If the CD is unknown, it will rip it to Unknown. The next Unkown CD will go much faster.

I genereally pile CD’s thats is ejected to fast, for later manuel handling … out of 650 CD’s I had to process 10 manually.

DEVICE=/dev/sr0
while true ; do
  while cddbget -c ${DEVICE} -I | grep "fatal error" ; do sleep 5 ; done # We need this, else ripit access the wrong CDROM driver?!
  ripit -d ${DEVICE} -c 0,2 -q 5,8 -W NTFS  --resume --loop 0 -e --nointeraction -O y --dirtemplate '"Music/$artist/$year ‐ $album"' -Z
  sleep 1
done

Run 3 instance of the program, from tmux (if you connect to the server with ssh)

Misc

Convert many files to a new format, here from mp3 to ogg

parallel --eta ffmpeg -i "{}" -map_metadata 0:s:0 -id3v2_version 3 -write_id3v1 1 "{.}.mp3" ::: */*/*.ogg

It’s better to convert from Flac as it’s lossless audio compression.

Holliday planning

Tue, 11 Feb 2020 00:00:00 +0000

Holliday

Amatør radio

Thu, 06 Feb 2020 00:00:00 +0000

General

Debug NGINX OOM

Thu, 21 Feb 2019 00:00:00 +0000

NGINX used to much memory and the Kernel OOM killed the process

[Thu Feb 21 02:23:49 2019] Out of memory: Kill process 54201 (nginx) score 900 or sacrifice child
[Thu Feb 21 02:23:49 2019] Killed process 54201 (nginx) total-vm:7430008kB, anon-rss:5617836kB, file-rss:2844kB

How do you find root cause? The process is no longer running.

We start by install the GNU debugger and symbol data for nginx

sudo apt install gdb nginx-core-dbg

Running this script every minute, will core dump the process that uses over $size_limit

#!/bin/bash

size_limit=1000000 # which total-vm size (in KB) do we create core dumps for
lock=high-mem-core.lock
cd /path/to/mountpoint/with/plenty/of/space

result=$(ps -A --sort -size --format size,pid  --no-headers|head -1)
pid=${result#* }
rss=${result% *}


if [ "$rss" -gt "$size_limit" -a ! -e "$lock" ]; then
        touch $lock
        gcore $pid
fi

Can you recognize strings?

strings core.*

Start the debugger

gdb $(which nginx) core.*

Read nginx admin debugging guide

MySQL performance

Tue, 09 Jan 2018 00:00:00 +0000

Download from www.percona.com and MAN page

Example

tcpdump -s0 -x -nn -q -tttt -i any port 3306 > mysql.tcp.txt
pt-query-digest --type tcpdump mysql.tcp.txt > mysql.report.txt

MikroTik

Sat, 14 Oct 2017 00:00:00 +0000

https://www.mikrotik.com/thedude

safemode cli ctrl-x

downloads https://mikrotik.com/download

https://wiki.mikrotik.com/wiki/Main_Page

https://wiki.mikrotik.com/wiki/Firewall https://wiki.mikrotik.com/wiki/Manual:IP/Firewall https://wiki.mikrotik.com/wiki/Manual:Packet_Flow https://wiki.mikrotik.com/wiki/Manual:IP/Fasttrack

QoS https://wiki.mikrotik.com/wiki/Manual:Queue https://wiki.mikrotik.com/wiki/Manual:Queues_-_Burst

wifi https://wiki.mikrotik.com/wiki/Manual:Spectral_scan

misc

https://github.com/codepill/script-utilities/tree/master/mikrotik

https://cumulusnetworks.com/products/cumulus-linux/