Steam not running proton games on separate EXT4 partition

Question

I have a multi user system and if possible I'd like to prevent downloading every game 3 times. Because of that I made a separate ext4 partition for my steam games and selected the partition in steam

drwxr-xr-x 4 root root   4096 May 21 17:06 ..
drwxrwxr-x 2 root steam 16384 May  4 19:59 lost+found
drwxrwxr-x 3 root steam  4096 May 21 17:22 SteamLibrary

All proton games don't launch I used the launch option PROTON_LOG=1 and the log said this

wineserver: /mnt/steam/SteamLibrary/steamapps/compatdata/1118200/pfx is not owned by you
wine: '/mnt/steam/SteamLibrary/steamapps/compatdata/1118200/pfx' is not owned by you

I know that this is solvable with a

chown -R user:user /mnt/steam

but I don't understand why I need to own the file my group has every permission

I can't find anything online because there is a similar issue with having a ntfs partition that's filling my search results.

also my user is in the steam group.

ChatGPT mentioned something about acl and advanced permissions but this

sudo setfacl -R -d -m group:sharedgroup:rwx /mnt/steam/SteamLibrary

It seems that it would only set read/execute/write permissions, which I already have.

I wanted to ask if it is possible to fake own a mountpoint to multiple users or find some other workaround for this.

Answer 1

I don't understand why I need to own the file my group has every permission

There may not be any technical reason for this check but a program is free in which conditions it checks.

These checks are probably done during the start-up of wine so you could create

• a wrapper script
• a sudo rule

so that the wrapper script would change the owner of these files to the caller:

# start-my-game.sh

file_paths=( '/mnt/steam/SteamLibrary/steamapps/compatdata/1118200/pfx' )

sudo chown "$USER" "${file_paths[@]}"

# or for simpler sudoers rules (allow each file separately)
for file in "${file_paths[@]}"; do
    sudo chown "$USER" "$file"
done

the usual start command line