Singularity documentation: please specify defaults for environment variables

[GodloveD]

@mgjf commented on Wed May 15 2019

Version of Singularity:

3.1, 3.2 documentation on https://www.sylabs.io/guides/3.2/user-guide/

Expected behavior

It would be nice to have the defaults of environment variables (in particular SINGULARITY_CACHEDIR and SINGULARITY_TMPDIR) documented in places such as
https://www.sylabs.io/guides/3.2/user-guide/appendix.html
or
https://www.sylabs.io/guides/3.2/user-guide/build_env.html

Actual behavior

Defaults for some variables are not documented, so users need to guess / experiment to find out a) what are the defaults, and b) which directory components Singularity appends to the values of these variables if they are set.

Steps to reproduce behavior

Take for example the description in buid_env.html: if I set SINGULARITY_CACHEDIR to /my/dir, it is not evident if Singularity will put cache contents into /my/dir/.singularity/cache/{library,oci,oci-tmp} or into /my/dir/{library,oci,oci-tmp}. Similarly for SINGULARITY_TMPDIR. Also, will Singularity try to mkdir -p a missing prefix? Will Singularity use TMPDIR if this is set, but SINGULARITY_TMPDIR is not set?

In appendix.html the defaults for these (and some other) variables are also not documented.