Recent Grml ISOs, including our Grml-Sipwise ISO (v2023-06-01), include
grml-autoconfig v0.20.3 which execute the grml-autoconfig service under
`StandardInput=null`. This is necessary to not conflict with tty usage,
like used with serial console. See
1e268ffe4f
Now that we run with /dev/null for stdin, we can't interact with the
user, so let's try to detect when running from within grml-autoconfig's
systemd unit, and if so assume that we're executing on /dev/tty1 and
use/reopen that for stdin.
Change-Id: Id55283c7f862487a6ef8acb8ab01f67a05bd8dd7
(cherry picked from commit 561303359e)
Michael Prokop
c476cca52d