https://0xacab.org/leap/bitmask_help/commit/d23b1e6af36e0d22990da87b2a84d67fd5abd074
'I think those instructions are too complicated - `sh -c` will be
difficult to parse for new (or even experienced) users and is error
prone. Nevertheless, the instructions as is will not work because the
redirection does not run as root, as is the case for the other
instructions. This was probably forgotten when adding the backports
entry (which goes to show this is error-prone). (I would instead
recommend "piping to tee", like `echo ... | sudo tee -a sources.list`,
for example.)'