To make it work with steam-run, we also need to put the unshareXXX code into the buildFhsUserEnv created in the passthru.run = buildFHSUserEnv. Also, does it make sense to copy all the unshare stuff, like unshare{User,Ipc,Pid,Net,Uts,CGroup}?

To make it work with steam-run, we also need to put the unshareXXX code into the buildFhsUserEnv

done

Thanks a lot, I can confirm it works. By the way, if you have any idea on how to make bubblewrap run packages that require fuse internally, I would be very happy to hear about it. This is used for example by some AppImages like LittleWeeb (and since appimage-run segfault on that image, I would have love to see if steam-run could get anything better). But anyway, I guess it's a different topic, this PR can be merged independently. Thanks again.

My assumption is that using a new user space is breaking file IO, but would need to run an strace to know for sure

$ ./result/bin/bwrap --help
...
    --unshare-user               Create new user namespace (may be automatically implied if not setuid)
    --unshare-user-try           Create new user namespace if possible else continue by skipping it
    --unshare-ipc                Create new ipc namespace
    --unshare-pid                Create new pid namespace
    --unshare-net                Create new network namespace
    --unshare-uts                Create new uts namespace
    --unshare-cgroup             Create new cgroup namespace

anyway, was able to launch steam and csgo with changes