Update singularity.md

[e-kotov]

without --server-user=$(whoami) latest RStudio Server will not start in Singularity/Apptainer container with error [rserver] ERROR Attempt to run server as user 'rstudio-server' (uid 999) from account 'user_account' (uid 1001) without privilege, which is required to run as a different uid

[eitsupi]

Thanks for your contribution!

@nathanweeks @frederikziebell Could you take a look at this? Thanks.

[e-kotov]

Ok, this seems to be NOT about the latest RStudio server, it seems this persists over many versions and seems to have more to do with how Rocker containers are packaged. In any case, I have done a lot of testing and on a clean Ubuntu VPS with either Singularity installed from source or with Apptainer installed from package manager, the line I suggested is critical to launch the rserver in container. If this option is not passed, Apptainer/Singularity tries to run the rsever process with rstudio-server user, which does not exist on parent system.

I stumbled upon this problem while testing for the rang R package. Details on my launch procedure are in this pull request. These are results of extensive testing on a VPS with both root and user privileges:
gesistsa/rang#134 (comment)

[e-kotov]

The solution with setting the --server-user was originally mentioned here rocker-org/rocker-versioned2#105 (comment) and I believe since then the discussion participants simply did not follow up to update the documentation, even though someone suggested to do that.

[nathanweeks]

That's right; rserver --server-user=... has been required to run Rocker RStudio Server in a Singularity/Apptainer container since RStudio Server 2021.09.* per the referenced issue. A doc update is certainly in order.

FWIW, id -un is more "standard" (POSIX) than whoami (and on macOS the manual for whoami states 'The whoami utility has been obsoleted by the id(1) utility, and is equivalent to "id -un"...'), but in practice, it realistically shouldn't matter.

[eitsupi]

Sorry I forgot to take care of this!
And, thank you @nathanweeks for checking this!

I will merge this, so please let me know if it needs to be modified again.