Magic Spells

2 March 2021

Portage @world update

To upgrade a gentoo system.

emerge -aqvuDU --keep-going=y @world

• -a: Ask before running.
• -q: Quiet (don’t show build output).
• -v: Verbose (show USE flag changes).
• -u: Upgrade all packages to the most recent version.
• -D: Look deep in the dependency tree to find updated libraries.
• -U: Include packages with changed USE flags.
• --keep-going=y: If a package fails to install, continue trying to install the rest.

Kernel upgrade

Upgrading the Linux kernel guide. After selecting the new sources, run:

genkernel all -j4

Rsync backup

To backup a filesystem with rsync.

rsync -aAXvP SRC DEST

• -a: Copy in archive mode, preserving modification times, permissions, etc.
• -A: Preserve ACLs (i.e. file permissions).
• -X: Copy all extended attributes.
• -v: Verbose (show all file changes).
• -P: Progress (show copying progress).

ffmpeg quick compression/conversion

Raw recorded video is too big, and most compression snippets you find convert to patented formats with proprietary standards. I prefer:

ffmpeg -i input.mkv -codec:v libtheora -qscale:v 7 -codec:a libvorbis -qscale:a 5 output.ogv

• -codec:v libtheora: Use the free video codec Theora.
• -qscale:v 7: Set the video quality scale (0-10).
• -codec:a libvorbis: Use the free audio codec Vorbis.
• -qscale:a 5: Set the audio quality scale (0-10).

Source, Similar.

White noise

Turn down your volume before trying these.

Interesting but not very pleasant:

pacat /dev/urandom &
# or
aplay /dev/urandom &

Nicer “pink” noise but not as interesting:

speaker-test -l 0

Generate one-time passcodes using a TOTP code

Using pass as password manager, with oath-toolkit installed and TOTP code stored as ~/.password-store/2fa/$service.

oathtool --totp --base32 $(pass 2fa/$service)