Sometimes an error like the following occurs by invoking singularity build with qrsh.

INFO:   Starting build...
FATAL:   While performing build: conveyor failed to get: error getting username and password: error reading JSON file"/run/user/0/containers/auth.json": open /run/user/0/containers/auth.json:permission denied

As a workaround, do the following after qrsh:

unset XDG_RUNTIME_DIR

and then do singularity build

2020/12/03 update:

Unsetting XDG_RUNTIME_DIR is now done by the job scheduler, therefore the above is no longer required.