invitation to the Singularity slack + Question about relative soft link using $SINGULARITY_ROOTFS in the setup part of the Singularity recipe file

[Robert Po]

I added the following question on Github but it seems here is a better way to ask it. Also I don't have permissions to add the Slack group so I would ask here. But first of all, is it possible to share an invitation to the Singularity slack group?

The question: 

### Version of Singularity:

What version of Singularity are you using? Run:

```

$ singularity version

3.7.1-1

```

### Question

I'm trying to create soft link in the `%setup` section of the Singularity recipe file. If the link is relative, it does not work. For example:

```

ln -s ${SINGULARITY_ROOTFS}../python2/2.7.5a ${SINGULARITY_ROOTFS}/usr/pkgs/python/2.7.5

```

It creates:

```

lrwxrwxrwx 1 root root 49 Apr 24 06:33 /tmp/build-temp-976030219/rootfs/usr/pkgs/python/2.7.5 -> /tmp/build-temp-976030219/rootfs../python2/2.7.5a

```

The `/tmp/build-temp-976030219/rootfs../python2/2.7.5a` is of course invalid path. I don't want to start getting the realpath because I could get other links on the way. How to make it work with **relative paths**? Am I not using the `${SINGULARITY_ROOTFS}` properly?