Magic Spells

Published on 2 March, 2021

## Portage @world update

To upgrade a gentoo system.

```{.sh} 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](https://wiki.gentoo.org/wiki/Kernel/Upgrade). After selecting the new sources, run:

```{.sh} genkernel all -j4 ```

## Rsync backup

To backup a filesystem with rsync.

```{.sh} 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](https://audio-video.gnu.org/docs/formatguide.html). I prefer:

```{.sh} 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](https://xiph.org/theora/). * `-qscale:v 7`: Set the video quality scale (0-10). * `-codec:a libvorbis`: Use the free audio codec [Vorbis](https://xiph.org/vorbis/). * `-qscale:a 5`: Set the audio quality scale (0-10).

[Source](https://trac.ffmpeg.org/wiki/TheoraVorbisEncodingGuide), [Similar](https://dev.to/benjaminblack/use-ffmpeg-to-compress-and-convert-videos-458l).

## 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](https://www.passwordstore.org/) as password manager, with [oath-toolkit](https://www.nongnu.org/oath-toolkit/) installed and TOTP code stored as `~/.password-store/2fa/$service`.

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