Download an installation medium directly to your flash drive

For a longer time I was looking for a more direct and faster method to setup my Linux installation medium on an USB flash drive. Usally one would download an ISO image and wait for it to finish before copying to the drive. Both tasks could take some time, depending on your internet connection and USB speed.
Considering you’ll doing both at the same time, downloading and writing the image, you could save half the time. It took a while for me to figure out, that one of my favorite downloading tools for the command line, Aria2, could do exactly this job. It will download your file, supporting different protocols (sftp, https, bittorrent), and write it directly to any block device.
Of course not every installation image could be written directly without any modifications and thus will be bootable, but my favorite Linux distributions support this feature (e.g. ArchLinux, Ubuntu).
In this example, we’re going to download the most recent Archlinux iso using a Bittorrent magnet link (get the newest magnet link from here). Further we select only the iso-file in the torrent and write it to our flash drive at /dev/sdc:

aria2c "magnet:?xt=urn:btih:2d3b3d65b369ba519292dd8ce420afe95120df1e&dn=archlinux-2018.01.01-x86_64.iso&tr=udp://tracker.archlinux.org:6969&tr=http://tracker.archlinux.org:6969/announce" --select-file=1 --index-out=1=sdc --dir /dev --allow-overwrite=true --file-allocation=none --save-session=/tmp/tmp.aria2

We can also download a “*.torrent”-file to memory and start downloading it’s contents:

aria2c "http://torrent.ubuntu.com/xubuntu/releases/bionic/release/desktop/xubuntu-18.04-desktop-amd64.iso.torrent" --select-file=1 --index-out=1=sdc --dir /dev --allow-overwrite=true --file-allocation=none --save-session=/tmp/tmp.aria2 --follow-torrent=mem

Caution: Running this code with root is dangerous when you’re unsure about the destination path of your block device. You could easly overwrite, for example, your system partition, brick your system or lose important data!

Aria2 will start downloading the installation medium and write it directly to your installation medium :) The cool thing is, as long as you keep Aria2 open and your flash drive inserted, the iso will still be seeded from your device.