[systemd-devel] Antw: [EXT] Re: Q: non-ASCII in syslog

[Ulrich Windl]

>>> Mantas Mikulenas <grawity at gmail.com> schrieb am 27.04.2022 um 12:03 in
Nachricht
<CAPWNY8XO0tu6EdpJO538qyGBJ0kOmZo5iCaoJpPc8kt4QZ+vXg at mail.gmail.com>:
> On Wed, Apr 27, 2022 at 10:09 AM Ulrich Windl <
> Ulrich.Windl at rz.uni-regensburg.de> wrote:
> 
>> Hi!
>>
>> Having written an RFC 3164 compatible syslog daemon, I noticed that
systemd
>> created syslog messages with non-ASCII characters.
>> The problem is that a remote syslogd can hardly guess the correct
character
>> set (I'm using rsyslog to forward local messages to a remote server).
>>
>> Example of such message:
>> systemd-tmpfiles[3311]: [/usr/lib/tmpfiles.d/svnserve.conf:1] Line
>> references
>> path below legacy directory /var/run/, updating /var/run/svnserve →
>> /run/svnserve; please update the tmpfiles.d/ drop-in file accordingly.
>>
>> (The arrow is encoded as three bytes (\xe2\x86\x92))
>>
>> RFC 5425 syslog messages require the use of a BOM (%xEF.BB.BF) at the
>> beginning of a message if the message used UTF-8:
>>
>>       MSG             = MSG-ANY / MSG-UTF8
>>       MSG-ANY         = *OCTET ; not starting with BOM
>>       MSG-UTF8        = BOM UTF-8-STRING
>>       BOM             = %xEF.BB.BF
>>
>> Wouldn't it make sense to add such a BOM for RFC 3164 syslog messages also
>> if
>> non-ASCII (i.e.: UTF-8) encoded characters are used?
>>
> 
> RFC 3164 over a local socket from journald to local rsyslogd? The local

Actually I wasn't quite sure about the default config in SLES12.
It seems the flow is journald -> local rsyslogd -> remote syslogd

> rsyslogd already knows if messages are UTF-8 because the system's $LANG
> (well, nl_langinfo) says so. And if rsyslog can't trust that for some
> reason (e.g. because a user might have a different locale), then
> systemd-journald won't be able to trust it either, so it won't know whether
> it could add the BOM.

How could a remote syslog server know what the locale on the sending system
is?

> 
> RFC 3164 over the network to a remote server? Outside the scope for
> systemd, since it doesn't generate the network packets; your local rsyslogd
> forwarder does. (Also, why RFC 3164 and not 5425?)

If you look outside the world of systemd, about 99% of systems create the RFC
3164 type of messages.
Some may send non-ASCII too, however.

> 
> Generally, if a message successfully decodes as UTF-8 then it's most likely
> actual UTF-8 (and if UTF-8 decode fails then you fall back to ISO8859-1).
> Various old systems get away with this without needing a UTF-8 BOM.

Yes, you can just output what you received, hoping the messages will be
presented correctly.
I't just like sending 8-bit E-Mmail without a coding system or charset in the
past.

Regards,
Ulrich