Container (non-root) user can't write to /dev/stdout or /dev/stderr

[ignoramous]

@tom93

cmd='whoami; ls -l /dev/stdout /proc/self/fd/1; echo "test" >>/dev/stdout'
# su -s /bin/sh -c "$cmd" www-data >/tmp/out

Will you pls explain what these two lines test? I can see that the string test wouldn’t append to /tmp/out (which is a regular file?), but have trouble understanding how /tmp/out became a stdout sink and why /bin/sh -c ... >/tmp/out didn’t (or isn’t expected to) truncate /tmp/out…?

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@Alex21

But if there’s a way to launch an app/machine as the root user regardless of the user instruction that’s in the image, then doing that

Yes, via the experimental section of an app’s fly.toml (docs, ref), or the processes section (where app is the default name for an entrypoint / main process on Fly):

Change a containers CMD via the fly.toml file

Thinking about it, I think the new preferred way to do this would be using the new Preview: multi process apps (get your workers here!). Something like: app = "your-app" [processes] app = "path/to/command arg1 arg2" By default, an app process will be infered if you don’t have one.

(unsure if flyctl commands for Machines / Apps v2 support experimental section, but it does support processes ref).