Uli (and all), hello.
On 24 Oct 2017, at 21:54, Ulrich Sibiller wrote:
Iirc systemd refused usernames starting with a number. There was a
huge
discussion in the systemd bugtracker but I don't remeber the outcome
anymore.
Thanks for the pointer.
There seem to have been two intermixed discussions there, first about
whether '0day' was a valid username, and secondly about systemd's
behaviour when it encountered such a username.
Early in the discussion, 'poettering' asserts that '"0day" is not a
valid username' and 'the username is clearly not valid', without
pointing to any justification for either assertion. Neither assertion
is supported by the POSIX/SingleUnix or Debian sources I mentioned
earlier. In other words, I think poettering is simply wrong to assert
that such a username is generally invalid.
Other participants in that discussion pointed to the Single Unix spec
(which permits all-digit usernames), and to a passage in the GNU
Coreutils manual
<https://www.gnu.org/software/coreutils/manual/coreutils.html#Disambiguating-names-and-IDs>
which explicitly acknowledges that an all-digits username is legitimate,
and describes how the coreutils resolve the ambiguity.
It may be that _some_ unixes deem a username which starts with a digit
to be invalid, but it's clearly not universal. I'm not aware of any
current unix where this is the case.
Note that (if I recall correctly) some unixes will work fine with an
all-digits username, but the standard tool will not allow you to create
such usernames (this might be true of Debian?).
Part of the problem is that commands accept both usernames and userid
AS
parameters and there just be some clear way to distinguish those two.
The coreutils manual attempts to match a string as a username (even if
all digits) and as a numeric uid only if that fails. It says that
'POSIX requires [this]', but doesn't point to where (I couldn't find
that requirement myself).
Now, in the case of the example there, a user_name_ of '42' really is
asking/begging for trouble, but that library goes out of its way to
process that as a valid username.
Best wishes,
Norman
--
Norman Gray : https://nxg.me.uk
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