Systemd, by default, limits pipes to stdout and stderr only, which is
why `tee /proc/self/fd/3' fails.
that claim makes no sense. the new fd is created by the previous
command, and systemd doesn't prevent it (otherwise there would be an
error).
what might be happening is that stdout is a journald socket, which
cannot be opened via the .../fd/x mechanism. chatgpt claims this, so
there is a slight chance that it might be true ...
the proper solution is to include a systemd timer unit with debsums. the
current script's complexity is ~100% stuff that systemd has built-ins
for.
