[cups] Printing via SMB-Kerberos not working in Ubuntu 18.04

[Johannes Meixner]

Hello,

On Sep 27 14:36 Alex Persson wrote (excerpt):
> In Ubuntu 18.04 I've now tried to print via SMB-Kerberos
> through smbspool on the command line and it works!
...
> Any idea why CUPS don't try printing through SMB-Kerberos?

Regardless that I know basically nothing about Kerberos
there is a generic major difference when you do Kerberos stuff
under your normal user account e.g. by running whatever program
that does Kerberos stuff under your normal user account
compared to when "CUPS" does that.

When "CUPS" does Kerberos stuff, the cupsd runs whatever
program that does Kerberos stuff not under your normal
user account but usually as user 'lp' (or perhaps
as user 'root').

But usually the needed Kerberos tickets are only available
for the program that does Kerberos stuff when it runs
under your normal user account while you are logged in.

In general doing Kerberos stuff cannot be easily delegated
to another user.

Certain more or less ugly and fragile workarounds are needed
to let another user like 'lp' or 'root' do Kerberos stuff
for you as if it was you under your normal user account
(i.e. "trampoline" into the user account to send
the print job as the user) which fall apart if you are
no longer logged in when your print job should be sent
or when your print job should be sent from a remote CUPS
server where you are never logged in and things like that.

For some details and background info you may have a look at
https://bugzilla.opensuse.org/show_bug.cgi?id=899118


Kind Regards
Johannes Meixner
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