¶ Create/Convert TOTP Token
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¶ Create / Convert TOTP Token
Purpose:
Generate and transform secrets for Time-based One-Time Password (TOTP) systems (e.g. RFC 6238 / Google Authenticator compatible).
TOTP secrets are typically shared in Base32 encoding, while some tools and APIs require hexadecimal format.
¶ Generate new secret
-
Base32-encoded secret (recommended for QR / authenticator apps):
openssl rand -base64 20 | base32 | tr -d '=' | head -c 32- Generates ~160-bit random secret
- Encoded in Base32 (no padding) → compatible with most TOTP apps
-
Hex-encoded secret (raw binary representation):
openssl rand -hex 20- Same entropy, different encoding
- Often used in configs, APIs, or lower-level tooling
¶ Convert between formats
-
Hex → Base32 (for use in authenticator apps):
echo "1e1e1e1e1e1e8e6fee8d7f3c1a2a4d9b0f5c6a3e" \ | xxd -r -p \ | base32 \ | tr -d '='- Converts raw hex secret into TOTP-compatible Base32
-
Base32 → Hex (for storage / debugging / APIs):
echo SPKYT4JLGTOLATSHJHIX2F74YS35GUIL \ | base32 --decode \ | xxd -p \ | tr -d '\n'- Decodes Base32 into raw bytes, then prints as hex
¶ context information
- Base32 is the canonical representation for TOTP provisioning
- Hex is a transport/debug format, not used directly by authenticator apps
- Padding (
=) is commonly removed in TOTP secrets - All transformations are lossless encoding changes, not cryptographic operations
- Ensure sufficient entropy (≥160 bits recommended)
¶ Crypt with GPG Symmetric Passphrase
gpg -c --pinentry-mode=loopback --no-symkey-cache some_file.tar.gz
gpg -d --pinentry-mode=loopback --no-symkey-cache -o some_file.tar.gz some_file.tar.gz.gpg
¶ Redirect Script Output Within the Script
#!/bin/bash
logfile=$$.log
exec > $logfile 2>&1
echo main script starts here
¶ Reduce PDF File Size
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/printer -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
¶ X11-Forwarding with sudo
In the meanwhile it's a given styandard to do your daily work rootless.
But sometimes you need to start an application as root.
This is how it works, tested with Rocky Linux 9
[chris@ws ~]$ ssh kvm.domain.tld -X -Y -C
[chris@kvm ~]$ sudo su -
[root@arjuna ~]# virt-manager
(virt-manager:13408): Gtk-WARNING **: 06:49:10.610: cannot open display:
# see, it cant find valid way to forward application window
[root@kvm ~]# export XAUTHORITY=/home/chris/.Xauthority # This does the trick
[root@kvm ~]# virt-manager
# now it works
¶ Change Keyboard Layout on the Fly
- For console:
loadkeys sg-latin1 - For X11:
setxkbmap -layout ch
¶ CLI Clipboard Handling with X11
This is for use with pipes and stdout:
alias copyc='xclip -sel clip'
alias pastec='xclip -o -sel clip'
Example:
cat /etc/hosts | copyc
pastec > myhosts
It works with mouse as well 
¶ Paste Clipboard with Keyboard
This may be super useful for console connections into VMs:
sh -c 'sleep 0.5; xdotool type "$(xclip -o -selection clipboard)"'
¶ Set Terminal Tab Label Within Console to user@host
PROMPT_COMMAND='echo -ne "\033]0;$USER@$HOSTNAME\007"'
¶ Reassign Pipe Key from AltGr-1 to AltGr-7
xmodmap -e 'keycode 10 = 1 plus brokenbar exclamdown brokenbar exclamdown'
xmodmap -e 'keycode 16 = 7 slash bar seveneighths bar seveneighths'
¶ Change Screen Resolution to Work with Beamer
xrandr -s 1024x768 -r 60
or this:
# startup 2 head (Beamer + Laptop)
xrandr --output LVDS1 --mode 1024x768 --primary
# force use 1024x768 mode of the projector
xrandr --output VGA1 --mode 1024x768 --right-of LVDS1 || (xrandr --addmode VGA1 1024x768 && xrandr --output VGA1 --mode 1024x768 --right-of LVDS1)
# shutdown
xrandr --output VGA1 --off
xrandr --output LVDS1 --auto
¶ Bash Session Recording
- Record the session:
script -t 2> demo.timing -a demo.session # Script started, file is demo.session echo do something exit # Script done, file is demo.session - Replay the session:
scriptreplay demo.timing demo.session
¶ MySQL Hints
- Repair and optimize MySQL DB:
mysqlcheck -uroot -p@secret! -A -a -o -e -c -r --auto-repair - Copy MySQL DB to other host in one ssh command:
mysqldump --add-drop-table --extended-insert --force --log-error=error.log -uUSER -pPASS OLD_DB_NAME | ssh -C user@newhost "mysql -uUSER -pPASS NEW_DB_NAME"
¶ Delay Cron Job by Random Minutes to Spread Load
1 12 * * * /bin/sleep ${RANDOM:0:2}m ; /usr/local/sbin/update.sh
¶ Generate Monthly Calendar from Command Line
pcal -E -P a4 -B -F 1 -d /8 -t /18 -n /10 -a de -o cal.ps 2012