[cups] CUPS sometimes printing command codes instead of document

[Johannes Meixner]

Hello,

On Jun 6 13:33 Johannes Hass wrote (excerpt):
> Sometimes printing works fine, everything comes out as it should.
> But also sometimes you get pages full of command codes,
> always beginning with
>
> ime=10:05:20 2019/06/06?
> @PJL OKIAUXJOBINFO DATA=?DocumentName=PDF-Datei?
> ?
>
> And so on and so forth. The first line is obviously the current time
> and date. To me this looks like somewhere the beginning of the
> commands does not get recognized and thus everything following
> is interpreted as pure ASCII.

I guess it is in your CUPS mime.convs file this part
---------------------------------------------------------------
# Raw filter...
# Uncomment the following filter to allow printing
# of arbitrary files without the -oraw option.
application/octet-stream  application/vnd.cups-raw  0  -
---------------------------------------------------------------

The CUPS mime.convs file could be located in a directory
that differs from Linux distribution to Linux distribution
and/or from CUPS version to CUPS version, e.g. mine is
/usr/share/cups/mime/mime.convs
but it could also be in /etc/ or in similar directories.

When the above line is active (uncommented) any unknown
data format is sent as is directly to the printer device
and it happens that your particular printer model
interprets/prints it as if it was regular plain text.

This happens in particular on not so dumb office printers that
support several standard printer languages like PostScript and PCL
which do plain text printing as fallback mode (which makes sense
because plain text has no special header to identify the format,
cf. "There is no such thing as 'plain text'" in
https://en.opensuse.org/SDB:Plain_Text_versus_Locale

Dumb cheap (mostly inkjet) devices do usually nothing
when they get data that they cannot recognize.


Kind Regards
Johannes Meixner
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