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āœļø Evert Mouw
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Shared qBittorrent data on a dual-boot PC

One of my computers has both Linux and Windows installed. I often switch between operating systems, but I want to use the same torrents. Normally I would use a server or NAS in such a scenario, but this time I didnā€™t have such a solution. This blogpost is meant for advanced computer users who want to accomplish the same.

Note that you have to change directory pathnames to suit your own configuration.

You can also download the scripts: qBittorrent_dualboot.zip

Set a shared filesystem

First, you need storage that is accessible by both Linux and Windows. I choose a spare SSD, formatted with the exfat filesystem. In Windows, itā€™s mounted asĀ S:, and in Linux, asĀ /mnt/scratch.

Default Save Path

Second, you need to set the right download ā€œDefault Save Pathā€ in qBittorrent, both in Linux and in Windows.

Set the path to a location accessible by both Linux and Windows.

Fastresume and Torrent file location

The torrent files and their state, fastresume files, are stored in theseĀ locations:

You also need to store the files inĀ BT_backupĀ in the same location, accessible by both Linux and Windows. Iā€™ve symlinked theĀ BT_backupĀ folders to a new folder on my ā€œscratchā€ disk:

mkdir -p /mnt/scratch/qBittorrent/_activetorrents/BT_backup

cd ~/.local/share/data/qBittorrent
rmdir BT_backup
ln -s /mnt/scratch/qBittorrent/_activetorrents/BT_backup BT_backup

And then in Windows:

cd %LOCALAPPDATA%\qBittorrent
rmdir BT_backup
mklink /d BT_backup S:\qBittorrent\_activetorrents\BT_backup

Convert savepaths between Linux and Windows

The savepaths are stored in fastresume files. Alas, the savepaths are incompatible between Linux and Windows. The same base location for downloaded files is written differently:

The torrent and fastresume files are encoded asĀ bencodedĀ files. This means you cannot just useĀ sed because strings are precedes with a number indicating their length.

To convert bencoded files to something you can edit from a shellscript easily, you can useĀ bencode-pretty. Download, runĀ make, and copy the binaries toĀ /usr/local/bin/.

Iā€™ve make a quick-and-dirty shellscript to convert the Windows savepaths to POSIX savepaths and back again. Note that if you use different paths, then you need to edit the script.

/usr/local/bin/qbittorrent_fastresume_savepaths_convert.sh

#!/bin/sh

# Converts qBittorrent shared storage between POSIX and Windows savepaths

# Evert Mouw, 2021-03

# change savepaths for .fastresume files used by qBittorrent
# handy when switching between Windows and Linux (posix paths)
# while using the same qBittorrent download folder and BT_backup folder
# dependency: https://github.com/tool-maker/bencode-pretty
# also see the systemd unit below

# argument 1: { windows || posix }

# These constants should be set in a configuration file or set
# as an argument, but currenty this is just for personal use.
BT_backup="/home/evert/qBittorrent/_activetorrents/BT_backup"
sed_toPos='s/S:\\qBittorrent\\/\/home\/evert\/qBittorrent\//g'
sed_toWin='s/\/home\/evert\/qBittorrent\//S:\\qBittorrent\\/g'

case $1 in
  windows) SED_STRING="$sed_toWin" ;;
  posix)   SED_STRING="$sed_toPos" ;;
  *)
    echo "No valid first argument."
    exit 1
    ;;
esac

cd "$BT_backup"
for FILE in *.fastresume
do
    cat $FILE | bencode_pretty | sed "$SED_STRING" | bencode_unpretty > $1.tmp
    cp $1.tmp $FILE
    rm $1.tmp
done

Make it happen automatically

Now I donā€™t want to have to run this manually. I want this:

Then you can boot into Windows and the fastresume files are ready, or you can boot back in Linux and the savepaths will be converted to POSIX style.

Just use this systemd unit file:

[Unit]
Description=Converts qBittorrent shared storage between POSIX and Windows savepaths
After=multi-user.target

[Service]
Type=oneshot
RemainAfterExit=true
ExecStart=/usr/local/bin/qbittorrent_fastresume_savepaths_convert.sh posix
ExecStop=/usr/local/bin/qbittorrent_fastresume_savepaths_convert.sh windows

[Install]
WantedBy=multi-user.target

Iā€™ve saved it as:Ā /etc/systemd/system/qbittorrent_fastresume_savepaths_convert.service

Enable and start using:

systemctl enable qbittorrent_fastresume_savepaths_convert
systemctl start qbittorrent_fastresume_savepaths_convert
systemctl status qbittorrent_fastresume_savepaths_convert

Youā€™re set!

If all goes well, you will see downloads resuming after booting into another operating system.

Note, however, that I didnā€™t include support to categorize torrents or use subfolders or download locations other than the default.

Happy leeching šŸ™‚


Deze blogpost werd in december 2022 overgezet van WordPress naar een methode gebaseerd op Markdown; het is mogelijk dat hierbij fouten of wijzigingen zijn ontstaan t.o.v. de originele blogpost.