`landrun --ro /usr/bin --ro /lib --ro /lib64 --rw /path/to/dir touch /path/to/dir/newfile`
vs
`landrun --ro /usr/bin --ro /lib --ro /lib64 --exec /usr/bin/bash`
seems to indicate that `--exec` is only required if the command you're executing then uses an `exec`-call internally, which `bash` would need to be able to fork.
So `touch` should not need `--exec`, while `bash` should be able to run anything it can read (including that whitelisted `/tmp`).