readme.md

knowledge

references for linux admin and development

---

• ai misc
  • angular
  • typescript / javascript
  • css
  • csharp
  • cpp
  • networking
  • linux
• csharp
• shell
• development tools
• c++
• database
• webdevel
• electronics
• general development
• gis
• math
• sysadm
• networking
• python
• linux
• security
• mobile native
• tools
• media

---

ai misc

angular

• angular wait rxjs var until a value matches
• angular copy to clipboard
• angular rxjs best practice change field of an object directly on the behaviorsubject then call next or work on a clone then next
• angular set multiple behaviorsubject at once
• angular pipe recompute on rxjs event
• angular prevent dialog from close clock outside
• angular directive to track size and position of an element included begin values and margins
• angular combineLatest skip when next equals previous
• angular htmldivelement create a canvas at runtime
• angular two way binding property
• angular get only innertext from a string containing html tags
• angular ngx-leaflet map add custom control
• angular gsap circle that follow mouse and drop circle where click happens
• angular directive elementRef become undefined under mouse click event handler
• angular gsap animate from a color to another and then back to original one
• angular lib-ng-swiper generate items at runtime when next slide occurs
• angular dialog intercept click outside to execute action before close
• angular mat-toggle-button set initial value from a variable without using mat-button-toggle-group
• angular input matInput on value change
• angular rxjs interval with emission of first
• build android app using angular and capacitor
• angular capacitor with ios output ipa
• angular component that accept other components as children and render these with a separator charater between
• angular require a service programmatically from code out of constructor
• angular rxjs subscribe get current and previous value
• angular @let with async inside @for makes infinite loop
• angular what does it do ngModel underneath
• angular difference between #name of a element and id
• angular add layer to leaflet map without using external libraries but leaflet one
• angular semaphore slim
• angular production include sourcode map
• angular define local component scss variables at runtime
• angular set a scss variable of a class applied to an element using ViewChild

typescript / javascript

• typescript full qualify Map type name
• typescript print difference between two json
• typescript Date to locale string with dayname abbrev day number and month abbrev with custom timezone
• typescript invoke static method using this
• typescript parse json date only string YYYY-MM-DD to date object assuming italy timezone with time 00:00
• typescript create ICAL event with location latitude and longitude
• typescript convert day month year to full iso date and time given a timezone
• javascript mousemove get coordinates relative to a div
• javascript intercept all console error

css

• css div shadow blur
• css get color with alpha from a color given a var()

csharp

• csharp add to a cancellable async call a cancellation token with timeout to existing cancellation token using linked token but catch only if operation timeout cames from the addictional cancellation token
• csharp ef core when create an entity that refer another entity how to pass the referred entity by id if the object model doesn't refer the id but only the related object because the id field in database implicitly created as relationship
• csharp difference between CreateScope and CreateScopeAsync
• csharp language features from 9 to 14 with code example
• c# parse month name with italian locale
• dotnet build pass a variabile to use in csproj Condition
• csharp openapi-generator-cli use api generated passing baseurl considering the constructor parameters are logger, loggerFactory, httpclient, jsonserializeroptions, apievents
• csharp postgres linq to sql given a queryable with (x, y) points compute integral area
• csharp ef core disable cascade delete
• csharp struct vs record
• c# ensure an async Task started and reached a region before to proceeed with other instructions
• csharp difference between != and is not null
• csharp efcore bulk delete
• csharp efcore sweep records one at time without loading into memory
• csharp efcore add record to database without retain into memory
• csharp compute md5sum from given stream
• csharp asp net core specify different cors for controller
• asp net core controller return File from memoryStream
• csharp DllImport with function that returns an array of struct objects counted with a returned number by pointer
• csharp struct of 6 bytes size where each bit is named for some status purpose
• csharp system.text.json parse json with an array of objects as a property but allowing also an empty string to be equivalent as an empty array

cpp

• cplusplus simple linux Makefile to build main.cpp using existing so library

networking

• make curl with cors
• curl check if a url request cors
• linux send email from commandline using smtp 587

linux

• linux btrfs report size progressive of each snapshot

---

csharp

• language notes
• send email 465
• dotnet scripts
• member not null
• math
  • csharp angouri math expr eval
• task programming
• dotnet core
  • publish self contained dotnet publish -c Release --runtime linux-x64 --sc
  • dotnet3 and 5 on ubuntu20.04
  • dotnet6 and 7 on ubuntu24.04
  • netcore csproj ( generate doc, copy to output, define macro, exclude files from compile, disable warnings )
  • test coverage
  • view unit test output logger : open Output and select C# Dev Kit - Test Explorer
  • netcore platform environment ( os type, debug macro )
  • asp net core
  • dotnet sdks - installers
  • dotnet cmdline
  • dotnet core unix interop
  • dotnet gui
    • uno
    • avalonia
      • notes
      • app icon
      • vscode xaml intellisense
  • dotnet netcorestandard testunit
  • troubleshoot
  • view version of dll exiftool file.dll | grep 'Product Version'
• regex
• csharp to typescript
• xlsx finalize worksheet freeze columns
• wpf
• tuple value read write
• read from special serial ttyACM cdc type
• trap ctrl+c
• c# coding standards
• ef core
  • disable validation for some prop [ValidateNever] attribute
  • psql ef codefirst
  • transaction
• opengl
  • silk net under virtualbox opengl3.3
• user secrets

shell

• bash
  • bash scripting
  • bash locale
  • prompt colors
  • ls colors
• executing dir in bash script exdir=$(dirname "$(readlink -f "$BASH_SOURCE")")
• text screencast
  • ttyrec ttygif
  • asciinema
• find files sorted by size find -type f -name "*.pdf" -printf '%s\t%p\n' | sort -nr | less
• linux scripts
• trap control+c
• function arguments expansion
• formatted print
• diff huge files
• find xargs and exec
• get file size
• file age sec
• elapsed seconds date
• terminal color
• escape html
• uri encode
• jq json tool
• ensure kill process
• ls in mb ls -la --block-size=MB
• monitor progress of pipe cat /dev/random | pv > /dev/null
• sed
  • replace newline
  • skip first line cat file | sed -n '1d;p'
  • skip line range sed A,Bd file ( skip lines with index range [A,B] )
  • delete empty lines cat file | sed -r '/^\s*$/d'
• time
  • GMT TZ=GMT date +@GMT-%Y.%m.%d-%H.%M.%S
  • time from unixtime date -d @VALUE
• show dialog notification notify-send title msg
• short uuid

development tools

• opensource dev
• git
  • git
  • git animate
  • github git ssh
• run github action workflows locally
• fast gui diff fldiff file1 file2
• api docfx
• mono
• perf
  • dotnet trace
  • trace x11 (xtrace -n cmd args)
• vscode
  • tips
  • keybinding
  • fold functions
  • settings
  • useful extensions
  • troubleshoot
  • react debug chrome
  • debug firefox
  • show external code
  • remote host through docker
• gnome development
• nuget
  • linux-install
  • local packages
  • troubleshoot
  • msbuild: dotnet msbuild
  • search pkgs command line
• docx documentation generator
• librecalc
• dump c++ symbols from .so lib nm -gDC LIB.so
• graphics
  • gnuplot
  • debug opengl programs apt install renderdoc
• get PID from window xprop | awk '/PID/ {print $3}'
• limit cpu apt install cpulimit ; cpulimit -p PID -l 5 ( limit process PID to 5% )

c++

• clang format
• linux vscode debug
• dump-file-to-c

database

• System.Linq.Dynamic.Core
• create db server using docker
• postgres
  • create psql container
  • backup restore
  • password in file
  • select datetime timezone
  • pgadmin install docker run --restart=unless-stopped --name=pgadmin -p 8080:80 -e 'PGADMIN_DEFAULT_EMAIL=email' -e 'PGADMIN_DEFAULT_PASSWORD=pass' -d dpage/pgadmin4
  • index array
  • sequence schema
  • create db and assign user
• mssql
  • docker local mssql server
• diagramming schema
  • schema crawler
  • automatic generate psql db diagram
• entity framework
  • load related entities

webdevel

• odata
• ts hello world
• javascript/jquery
  • momentjs date
• bootstrap css
• sandbox repro
• chrome
• imagemap ( just use gimp Filters/Web/Imagemap )
• grunt troubleshoot
• css
  • padding 1-4 values
    • 1 value ( all sides equal )
    • 2 value ( top/bottom left/right )
    • 3 value ( top left/right bottom )
    • 4 value ( top, right, bottom, left )
• npm
  • tips
  • proxy cache
• typescript
  • create console app
  • support for optional chaining conditional ? operator (upgrade react-scripts to 3.3.0)
  • troubleshoot
• react / material.ui ( typescript )
  • examples
  • snippets
  • create react typescript npm create vite@latest test-app -- --template react-ts
  • app skeleton and global states
  • create react library useHook error
  • resposive drawer with styles and theme
  • common styles combined

electronics

• arduino
  • vscode arduino
  • vscode arduino platformio
    • atmega328
    • atmega8
    • platformio troubleshoot
  • vscode arduino nano platformio
  • arduino on atmega8
  • atmega power save
  • arduino examine elf
  • esp8266 board plugin ( use http://arduino.esp8266.com/staging/package_esp8266com_index.json for development )
  • esp8266 twi arduino nano problems
  • esp8266 tips
  • serial baud rate
• stm32
  • vscode debugging
  • string stream
  • tips
  • multiple devices
• schematics and pcb editor
• circuit simulator
  • circuitjs
  • qucs
  • everycircuit
• pcb etching
• transistor biasing
• measure usb cable resistance
• UM34C linux log
• 3d print tips

general development

• references

gis

• geojson

math

• c# AngouriMath symbolic
• octave symbolic

sysadm

• backup imap

networking

• netplan
• wired hotspot
• get current public ip address curl -s ifconfig.me
• ubuntu desktop disable network manager
• ssh
  • ssh misc
  • ssh ctrl channel
  • ssh mount dir
• send a tcp packet echo sample | nc 10.10.2.10 1000
• test tcp port echo "test" | netcat -w 5 -W 1 host port ; if [ "$?" == "0" ]; then echo "OK"; else echo "UNREACHABLE"; fi
• test webapi
• send simple message over udp
• send email
• nginx
  • tune nginx for webapi
  • exec shell script with fastcgi
• wireshark
  • run wireshark as nonroot
  • wireshark chrome decrypt ssl
• https proxy sniffer
• xrdp remmina
• zimbra
  • force smtp auth
  • backup/restore mailbox
• mobile server
• samba
  • get ip from netbios name nmblookup <name>
  • scan netbios name in net nbtscan <netaddr>
• monitor interfaces bandwidth bmon -p eth0,eth1 or nload -m
• quick list interface addresses ip -br a
• ethernet cabling T568A T568B
• scan hostnames nmap -sn addr/mask
• bluetooth
• tcpdump
  • cheat sheet
  • examples
• cert fingerprint
• retrieve bandwidth utilization continously for given interface with ifstat -i devname
• download remote http folder wget -r --no-parent URL
• x11vnc headless

python

• plotting
  • plot 2d 2var function
• calc
  • solve eq

linux

• cpu bench
• server
  • quick and dirty virtualized vlan os install notes
  • quick and dirty os install notes
  • prevent unattended upgrades
  • resize lvm cache in favor of swap partition
  • ubuntu server post install
  • custom boot script
  • disable sleep
  • systemd services
  • zfs
  • how much is wear ssd
  • netfilter
  • self signed cert
  • journalctl
  • crontab
  • wake-on-lan
  • test cpu speed apt install sysbench ; sysbench cpu run then see events per seconds ( higher better )
  • detached screen
  • nfs4 acl
  • chroot env
  • rescue notes
  • free up buff/cache echo 3 > /proc/sys/vm/drop_caches
  • purge old kernels
  • disable kde graphical ask pass
• desktop
  • kubuntu 26.04 post install
• kde
  • disable input method completion
• gnome
  • shell extension with bash
  • fix sort icon direction
  • custom open with
  • desktop icons
  • gnome bookmarks
  • reload shell with top panel killall gnome-shell
  • always on top apt install compiz-plugins
  • chrome freeze when attach files ( could try apt install xdg-desktop-portal-gnome to change file dialog )
• devices
  • cpu bench sysbench --threads="$(nproc)" cpu run
  • kubuntu enable touchpad tapping
  • udev rules
  • nautilus file manager folder right click -> open in terminal apt install nautilus-open-terminal
  • hardware inventory inxi
  • minisforum UM773 LITE - F7BFD graphics drivers
• log
  • tail generic color
  • colourized log grc --colour=on tail -f /var/log/syslog
  • grep only in file pattern grep -r --include="*.EXT" <search-string> <beginpath>
  • tail grep continous
  • force log rotate
• remotely assist linux can't boot
• ubuntu pendrive custom kernel arg
• flash win bootable pendrive
• monitor disk temperature
• tune inotify watches
• disable oom killer
• fix dual boot
• su with sudo colorful prompt
• i18n decimal separator dot
• draftsight open dxf
• packages
  • packages build dep
  • dpkg and package source
  • upgrade single package apt-get install --only-upgrade package
  • retrieve list of upgradable packages apt list --upgradable
  • retrieve version current and older apt-cache policy package
  • install old version apt-get install package=version
• processes
  • show process memory graph smem --pie=name
  • process management ( process swap memory usage )
  • autorespawn process using supervisor
  • show memoy usage smem --pie name -s rss
• ubuntu tune
  • locale and timezone
  • kubuntu 22.04
  • ubuntu 22.04 tune
  • ubuntu 20.04 tuf gx505
  • ubuntu 20.04 asus P2550
  • disable tracker miner
  • ubuntu 19.04
  • ubuntu 18.04
  • directory color on dark theme, set /etc/bash.bashrc with export LS_COLORS='di=0;34:ow=1;34'
• virtualization
  • virsh storage
  • virsh tips and backup
  • virtualbox
  • virsh qemu connect physical disk
  • boot win phydisk
  • set virtualbox guest motherboard-cpu-id
  • copy qcow2 over network rsync --sparse --inplace -zv --progress src.qcow2 dst:folder
• remove desktop
  • fix Authentication Required to Create Managed Color Device ref
• strip log
• devices
  • card reader
  • bit4id minilector evo driver 64bit
  • wacom inkscape pressure
  • epson scanner gt-s50
  • usb and udev
• disks
  • raid
    • autotune raid reconstruction speed
    • raid management
    • replace raid md damaged disk
  • loopback devices
  • monitor disks activity iostat -dx 5 or for device (mb/s) iostat -sm -p /dev/DEVICE 1
  • create bootable iso
  • force reread partition : partprobe <device>
  • create uefi usb from iso
  • encrypt disk
  • selfcheck disk health
  • disk space analyzer apt install baobab
  • compare two directories diff -rq DIR1 DIR2
• files
  • search duplicate files find . ! -empty -type f -exec md5sum {} + | sort | uniq -w32 -dD > dupfiles.txt
• docker containers
  • docker xwindows
  • modify created docker env
  • docker buildx
  • docker registry
  • docker without iptables
  • docker backup
  • show layer commands
  • doc not included ( see /etc/dpkg/dpkg.cfg.d/excludes )
  • test swap memory
  • scripts ( dk-id, dk-purge-log, dk-net, ... )
  • add xrdp to docker container
  • btrfs tools
  • tail log continously docker logs -f CONTAINER | grep --line-buffered -ia WORD
  • run gitlab ci from terminal
• battery nfo
• nextcloud
  • tips
  • rclone
• fonts
• general
  • firefox

security

• gpg
• iptables firewall
• generate htpasswd
• cert management
• id_rsa
• letsencrypt acme dns
• fail2ban
• passbolt

mobile native

• intellij android studio
• android push notify

tools

• development
  • convert json to csharp
• cygwin install
• win10 quick assist
• drawings
  • dwg viewer
  • dxf editor qcad
  • draftsight troubleshoot
• document
  • translator
  • xlsx
  • nano editor
  • github latex math
  • hex editor : bless
  • markdown refs
  • markdown toc
  • markdown to pdf
  • markdown server
  • useful unicode
  • google drive direct link https://drive.google.com/uc?export=download&id=DRIVE_FILE_ID

media

• editing
  • pdf edit inking apt install xournal
  • pdf join into single page
  • convert jpg to pdf convert *.jpg -auto-orient out.pdf
• sound
  • console player apt install mocp
• tv
  • kaffeine apt install kaffine w-scan
• graphics
  • test 3d working
  • qrcode
  • screen cast gif
  • freecad
    • troubleshoot svg import
    • tips
  • image info identify image.jpg
  • crop image convert input.jpg -crop wxh+x+y out.jpg
  • resize image
  • video transcoding
  • remove image exif
  • grab screen to image
  • ubuntu cast to chromecst apt install mkchromecast
  • show opengl limits glxinfo -l
  • compare two images compare -metric AE image1.png image2.png diffout.png
  • create favicon
• misc
  • stream dvbt to chromecast