[RFE] Implement printer profiles

[zdohnal]

This issue is a placeholder for implementing printer profiles, which are needed for the case:

• CUPS temporary queues work only with LAN located devices, because the tech uses mDNS for device discovery. However, this situation isn't usually a case for enterprises, where their IT engineers tend to put printers into a separate VLAN - they do it because of security and monitoring. Without any migration plan, these use cases would be left behind if permanent queues are gone and CUPS temporary queues become the only technology in CUPS.

The idea of printer profiles was introduced by Mike Sweet during email communication within OpenPrinting group and distro maintainers and presented during PWG F2F meetups.

Set of features provided by printer profiles:

• access to queues on remote print servers, which are not in local network
• access to printers from different network
• setting default options for a printer
• setting a default printer for specific network
• every setting can be related to a specific network (f.e. show printer P1 if I'm in network A, but show printer P2 if I'm in network B, use a different default printers across the networks etc.)

Tasks:

• implement showing queues defined by printer profiles in cupsEnumDests() CUPS library function (idea: cupsEnumDests() will check /etc/cups/profiles/ and if there are some, add them to the output - this will show profile queues in print dialogs, which use cupsEnumDests())
• implement sharing profile-defined queues in cupsd/sharing cups module in modular design
• implement tests for printer profiles in CUPS test suite
• add printer profiles into CUPS documentation, man pages etc

I will try to implement this feature in meantime, but any other help is welcomed.

@michaelrsweet WDYT? Did I forget about something in tasks or do you have any recommendation what to add?

[michaelrsweet]

@zdohnal We don't want an operation for this, we want it to be in file(s) that can be installed.

[zdohnal]

Hi @michaelrsweet ,
hmm, so the expectation is the clients (lpadmin/cups web ui/control-centers/cups-browsed) will write profile files by themselves and libcups functions only pick them up?
Or should admins write profiles by hand and then save them into /etc/cups/profiles or ~/.cups/profiles/ and possibly distribute the profiles through the organization (via special packages)?

Either way, I can't help to not to see a classic PPD déjavu - in both cases above we need to count on profiles being generated and maintained correctly instead of having a full control over them. We would have to keep stable a whole profile file structure or coordinate with known profile implementations if we make some changes - it looks like a bigger challenge than keeping IPP request format stable.

Ad clients creating profiles - I guess we can add the functionality into lpadmin/cups web ui and cups-browsed, but I'm not sure how GTK or other GUI apps will be interested in writing profiles.

What do you think?

[michaelrsweet]

@zdohnal So the point of my "profiles" featurette in my CUPS slides was not to provide a way to further inject PPDs into the system but to provide a simple way for enterprises to configure/deploy IPP Everywhere queues (pointed at real printers, a central CUPS server, etc.) when mDNS/DNS-SD wasn't feasible - basically duplicating what Apple has done for iOS/iPadOS/macOS and what hundreds of users have been asking for over the years on Linux (re: supporting multiple ServerName directives in client.conf).

We can keep the format dirt simple, e.g.:

# comment
ServerName hostname-or-ip[:port]
Printer {ipp,ipps}://hostname-or-ip[:port]/path

Then libcups just contacts each of the hosts during enumeration and lists any it can contact. The auto-assigned names can use either the reported DNS-SD name (from the printer-dns-sd-name attribute) or the remote printer name (from the printer-name attribute) plus hostname, same as what we do for DNS-SD.

(the same approach would be used for LDAP support, whenever we decide to implement that again using the IETF-published schema...)

[zdohnal]

@zdohnal So the point of my "profiles" featurette in my CUPS slides was not to provide a way to further inject PPDs into the system

That wasn't what I meant by PPD dejavu remark, I'm sorry, if it sounded like that - I'll explain later.

but to provide a simple way for enterprises to configure/deploy IPP Everywhere queues (pointed at real printers, a central CUPS server, etc.) when mDNS/DNS-SD wasn't feasible - basically duplicating what Apple has done for iOS/iPadOS/macOS and what hundreds of users have been asking for over the years on Linux (re: supporting multiple ServerName directives in client.conf).

That would be great if cupsd was able to support this feature - I guess it is exactly the first point from my initial comment - can't we have libcups reading client.conf for multiple 'ServerName's and then provides queues from destinations?

However this feature will set the same default options for such queues in user's print dialog as the default options, which the queue has on the server/device - which sometimes differs from the default options user wants - it will become annoying to set the default options every time you want to print.
So IMO cupsd should have a way how to override the attributes which come from server, to give user more flexibility about such queues - and attributes (or options - I guess it will be more readable for non-IPP people) in profiles can do the trick.

Based on the info above, we still would have needed a new file and a new format (or adding it to printers.conf), f.e. like:

<Printer <name>>
URI <value>
(this one would be applied only if we put them into printers.conf) Printer-is-profile <yes/no>
<new default option1/attribute1> <value1>
.
.
.
<new default optionN/attributeN> <valueN>
</Printer>

Additionally - IIUC the permanent queues are planned to go away in the future and that's the source of other mentioned use cases (different default options, 1 device to N queues), which printer profiles can support in addition to the idea what you meant in CUPS slides (althought IIRC you proposed using printer profiles for other mentioned user cases as well when we were discussing CUPS with other maintainers at the time of forking CUPS).

And if user can change options to set new default values in print dialog, something will need to do it for him (I cannot expect an user creating a xml file by themselves), so the options are following:

1. clients will create profiles by themselves and libcups will read them - we won't need an operation for it, but we will need to count on application to create a valid profile and we will need to keep compatibility for whole profile file, otherwise users will have breakages - this is what I meant by PPD dejavu - developing profiles will be blocked/obstructed by client implementations, which aren't on track with CUPS development and compatibility scope is larger than with IPP request.
2. define IPP request/DBUS method, which clients will use to create a profile, and cupsd will create a profile as it sees fit - the pros will be an united profile generation (so not every client needs to implement it) under CUPS. The problem will be to adjust clients to use it (the same is for the former option) and to keep compatibility in IPP request, but that's smaller scope than a file structure.

IMHO it is more feasible to adjust clients to do a request than implement a profile writer, so that's why I proposed a new request type - but I wasn't that sure if we aren't restricted by RFC and PWG standards for IPP, but I didn't find IPP_OP_CREATE_LOCAL_PRINTER operation in the standard either, so I guess it's fine.

Then libcups just contacts each of the hosts during enumeration and lists any it can contact. The auto-assigned names can use either the reported DNS-SD name (from the printer-dns-sd-name attribute) or the remote printer name (from the printer-name attribute) plus hostname, same as what we do for DNS-SD.

IMO if we can decide what to use based on path in uri. If it contains /printers/, use remote printer name, otherwise use DNS-SD name if available.

(the same approach would be used for LDAP support, whenever we decide to implement that again using the IETF-published schema...)

I'm not aware about anyone who uses LDAP for printing right now, so we can leave it out for now - we can reevaluate if there is a demand.

@michaelrsweet Thoughts?

[jsmeix]

@zdohnal
thank you so much for your explanatory description of the issue.
It helps so much to better understand possible consequences
of what is planned for the upcoming new CUPS.

As far as I currently understand it it seems
an underlying fundamental change in CUPS is
that CUPS will become basically "stateless".

The cupsd itself in the upcoming new CUPS will be stateful because
while it runs it keeps some state of the IPP printers it communicates with.
But when the cupsd is stopped it does not save its state persistently into some files.
When it is started it does not load a prior saved state from some persistent files.
So in the upcoming new CUPS there will be no longer be a persistently stored state.
The cupsd configuration files specify how cupsd behaves but do not store CUPS' state.
Also files as in #2
specify an ascpect how cupsd behaves but do not specify some part of CUPS' state.

In contrast in current CUPS there is a persistently stored state
mainly /etc/cups/printers.conf and the /etc/cups/ppd/queue_name.ppd files
and when current cupsd is stopped it saves its current state to files
and when current cupsd is (re)started it (re)establishes its state
according to a prior saved state from such persistent files.
Initially such a "prior saved state" could be provided by an admin.

If my understanding is right that CUPS will become basically "stateless"
as I described above then a consequence is that the upcoming new CUPS
can no longer be used to provide traditional print server functionality
in a managed environment.

With "traditional print server functionality in a managed environment" I mean:

An admin specifies his intended print server functionality persistently in config files
and the print server service process (i.e. cupsd) obeys what the admin specified.

With "persistently (in config files)" I mean that what the admin specified persists.
I.e. what the admin specified does not "magically" change "on its own".
I.e. only the admin specifies things.

E.g. when the admin specified a print queue with certain print queue specific settings
the print server will provide that particular functionality as specified by the admin
even if it is nonsense what the admin had specified - provided his specification
is not impossibe - i.e. basically as long as his specification is syntactically correct.
For example the admin can specify print queues for printers that do not exist
or he could even specify print queue specific things that will not work
for the printer that is associated with that print queue.

Bottom line from my point of view as far as I currently understand it:
When temporary queues have become the only technology in CUPS,
CUPS will be no longer usable as a print server.

[michaelrsweet]

@zdohnal WRT default options, the existing lpoptions support (which has been in CUPS since v1.1) is intended to provide the overrides you seek. The server/printer-side defaults are the base, then any local admin-defined defaults (in /etc/cups/lpoptions), then finally any per-user defaults (in ~/.cups/lpoptions). I don't want to add yet another way to specify/override default values as we have enough trouble getting applications to support the current API.

The profile mechanism should be hooked into the client side code (so libcups, not cupsd) and should transparently show up in the output from cupsGetDests and cupsEnumDests so that applications don't need to change. Just as for printers discovered via DNS-SD, a temporary queue will be created to handle spooling and filtering the first time you print to a profile printer.

[michaelrsweet]

@jsmeix So if you look at my most recent CUPS slide deck, one of my proposed future architectural changes is to split cupsd into two services - a per-user "local server" that handles the normal printing tasks and a system-wide "sharing server" that would provide persistent queues, ACLs, accounting, etc. Most users would never install the sharing server.

[jsmeix]

@michaelrsweet
thank you for the prompt reply.
It is much appreciated.

I had read
https://ftp.pwg.org/pub/pwg/liaison/openprinting/presentations/cups-plenary-may-2021.pdf
and I had noticed the CUPS 3.0 Local Server and Sharing Server parts
but I did not see the whole idea behind - in particular I did not see that
the CUPS 3.0 Sharing Server would still provide persistent queues.
Somehow the "Configuration similar to existing cupsd" did not trigger
the right things in my brain.

So as far as I now understand things:

The CUPS 3.0 Local Server basically provides what normal end-users usually need
in particular automated setup of what is needed to "just print" on IPP (Everywhere) printers.

The CUPS 3.0 Sharing Server basically provides what admins in a managed environment need
in particular persistent queues where admins can specify print queue specific things
as they need it in their particular environment.

[michaelrsweet]

@jsmeix Right. And since the sharing server doesn't have to deal with drivers it can (hopefully) end up providing a lot better support for accounting and other enterprise-y features... :)

[zdohnal]

@jsmeix

Bottom line from my point of view as far as I currently understand it:
When temporary queues have become the only technology in CUPS,
CUPS will be no longer usable as a print server.

Before I was corrected by @michaelrsweet in the next comment, I thought there will be no permanent queues in CUPS model in the future, so I thought additional features for profiles will be needed to cover the functionality, which was provided by permanent queues.
The original idea behind this issue was to cover use cases which aren't on the same LAN or are done by permanent queues right now with new, future CUPS compatible ways, so CUPS can be used as a print server even after removals of legacy technologies - meaning we would have not removed the old until the new is implemented and tested.
With my mistake corrected, I'll update the issue description to match up with the original idea - getting devices outside of LAN.

[zdohnal]

@michaelrsweet

@zdohnal WRT default options, the existing lpoptions support (which has been in CUPS since v1.1) is intended to provide the overrides you seek.

Aha, ok - so I've tried:

• using lpoptions for setting a default option from PPD to different value by:

$ lpoptions -p <temp_queue> -o <option>=<value>

, the option was applied and a permanent queue was created (so GTK will now get two same queues again :( ...), but I can see the correct default option for both.

The questions are:

1. Will be permanent queues available in CUPS 3.0 Local Server too, since changing default options depends on it?
2. Will be CUPS Web UI available in CUPS 3.0 Local Server? To have a GUI way how to set the defaults.

• using lpadmin to set job options associated with the queue:

$ lpadmin -p <temp_queue> -o <option>-default=<value>

This way, a normal permanent queue would change the option's value listed by lpoptions -p <queue>, but if we do it on temp queue, the temp queue will become permanent, but with invalid URI and the option isn't applied.:

$ lpadmin -p HP_LaserJet_M1536dnf_MFP_42307C_ -o copies-default=2
$ lpstat -v
device for HP_LaserJet_M1536dnf_MFP_42307C_: ///dev/null
$ lpoptions -p HP_LaserJet_M1536dnf_MFP_42307C_
device-uri=ipp://HP%20LaserJet%20M1536dnf%20MFP%20(42307C)._ipp._tcp.local/ Duplex=DuplexNoTumble printer-info='HP LaserJet M1536dnf MFP (42307C)' printer-location printer-make-and-model='HP LaserJet M1536dnf MFP' printer-type=83886100

Is it expected or is it a bug?

I don't want to add yet another way to specify/override default values as we have enough trouble getting applications to support the current API.

As permanent queues will not go away, there is no need for applications to create profiles, so no need for adding new operations.

The profile mechanism should be hooked into the client side code (so libcups, not cupsd)

I mentioned cupsd because that was the place where the proposed operation was supposed to be implemented.

and should transparently show up in the output from cupsGetDests and cupsEnumDests so that applications don't need to change. Just as for printers discovered via DNS-SD, a temporary queue will be created to handle spooling and filtering the first time you print to a profile printer.

Agreed.

[michaelrsweet]

@zdohnal OK, so I think there are still some misconceptions about this.

First, using lpoptions to set default options should definitely not be creating a permanent queue (or converting a temporary queue into a permanent one) - lpoptions is all client-side and should not affect server state. Moreover, lpoptions has dealt with temporary queues since the beginning when cupsd would create an delete local queues via the old CUPS browsing mechanism, so there is NO requirement for lpoptions to work with permanent queus. So if you are seeing permanent queues getting created, that is a bug (and please file it separately...)

Second, I hope I've made it clear that the local server is supposed to be very lightweight with no permanent queues, no web interface, and very little that can be configured. It is, by design, a transient thing that comes and goes only to handle whatever print jobs the user sends to a printer or print server. Printers and servers that are setup via profiles contribute to the list of potential destinations for the user to pick but queues for them are only created as needed and destroyed when not. Think of them like you are sending an email to someone - you don't keep a persistent connection to a particular mail server on the chance you might send an email to it, you connect as needed based on the messages being sent.

Using lpadmin to change the default option value doesn't convert a temporary queue into a permanent one, although if you specify "-o printer-is-temporary=false", it will. I'm not sure why you are seeing what you are seeing unless cupsd is going away between the lpadmin and lpoptions commands - it isn't what I would expect, but then there is no place for the default values to go when it is a temporary queue so I am not surprised either...

[jsmeix]

@zdohnal
it is a long time ago since I actually used lpoptions
so perhaps this behaviour may have substantially changed.
If it still behaves basically same as in the past
you may have a look at my rather old article
https://en.opensuse.org/SDB:Print_Settings_with_CUPS
that desribes how lpoptions behaved in the past
which is basically (summary):

• lpoptions stores permanent settings in some files
• that stored settings stay in those files even when queues are deleted

So when lpoptions stores some setting for a temporary queue
that setting for a queue with that name is kept
also when the queue gets (automatically) deleted
and that setting will be used again if a queue with same name
gets (automatically) (re-)created.

Again: This is the old behaviour which might have meanwhile changed.

[jsmeix]

@michaelrsweet
my offhanded gut-feeling (I don't have a sufficient deeper understanding here) is
that the CUPS 3.0 Local Server should be as simple as possible
i.e. as small and lightweight and stateless as possible.
I think the less there is in a CUPS 3.0 Local Server the better it is.

I think a clear distinction is good (and avoids false expectations):

The CUPS 3.0 Local Server is has intentionally "plug-and-play/pray" semantics.
It does basically all fully automated in some reasonable way but nothing more.

Users who need something special (i.e. where the Local Server
does not "play" for them) must switch (because "pray" won't help them ;-)
to the CUPS 3.0 Sharing Server with all its config options and features.

[jsmeix]

Something general to find out if my understanding is right:

I think current CUPS is only for "admins in a managed environment".

To print on a printer normal (unexperienced) end-users must first
put themselves into the role of an "admin in a managed environment"
and set up a print queue - at least that is what I see on
https://openprinting.github.io/cups/
where all basically starts with "set up a print queue".

There is additional software (various kind of automated print queue setup tools)
but that is not part of CUPS itself.

With the new CUPS 3.0 Local Server normal end-users can stay normal end-users
because the Local Server does all what is needed to print on "suitable printers"
in a "sutiable environment" fully automated in some reasonable way
where "suitable printers" are in particular IPP Everywhere printers
and "sutiable environment" is the directly accessible local network.

The CUPS 3.0 Sharing Server is still for "admins in a managed environment".

[michaelrsweet]

@jsmeix Current CUPS supports temporary queues for IPP Everywhere printers (which includes printers shared from another CUPS server and certified IPP Everywhere/AirPrint/Mopria printers), and assuming that the desktop toolkits use the provided CUPS APIs they should provide access to those printers without requiring the user to setup a queue at all. I honestly don't print from Linux desktop applications enough to know whether they are using the APIs we've provided for this, but that has been the goal since CUPS 2.0 (and the APIs have been around since CUPS 1.4...)

[jsmeix]

Now it has become obvious that I know basically nothing at all about IPP Everywhere ;-)

The reason is simple: I do not have an IPP Everywhere printer.
So all I know about things like IPP Everywhere and "driverless" is from hearsay.

I have only a traditional PostScript color laser USB printer.
I hope it will continue to print reliably for some more years as it did all the time.
I also don't print from Linux desktop applications enough to know how they behave.
I use mostly the plain lp command when I print every now and then.
I assume that will continue to work for many more years.

[zdohnal]

EDIT: updated the first comment to reflect the discussion.

[mikhailnov]

I honestly don't print from Linux desktop applications enough to know whether they are using the APIs we've provided for this

@michaelrsweet Most desktop application work with libcups for printing, only very old apps call lp or other similar tools directly. Have a look at which applications from a ditro repo + proprietary repo of Google Chrome depens from libcups:

$ sudo dnf repoquery --whatrequires lib64cups2
boomaga-0:3.0.0-3.x86_64
chromium-browser-stable-0:94.0.4606.71-1.x86_64
cinnamon-settings-daemon-0:5.0.3-1.x86_64
cnrdrvcups-lipslx-0:5.40-1.x86_64
cnrdrvcups-ufr2-uk-0:5.40-1.x86_64
cnrdrvcups-ufr2-us-0:5.40-1.x86_64
cups-0:2.3.3op2-4.x86_64
cups-browsed-0:1.27.5-4.x86_64
cups-common-0:2.3.3op2-4.x86_64
cups-drivers-bjnp-0:2.0.3-3.x86_64
cups-drivers-foo2zjs-0:0.0-2.2020.2.x86_64
cups-drivers-lxx74-0:0.8.4.2-17.x86_64
cups-drivers-magicolor2430dl-0:1.6.1-22.x86_64
cups-drivers-magicolor2530dl-0:2.1.1-20.x86_64
cups-drivers-magicolor5430dl-0:1.8.1-22.x86_64
cups-drivers-magicolor5440dl-0:1.2.1-21.x86_64
cups-drivers-ptouch-0:1.6-2.x86_64
cups-drivers-splix-0:2.0.1-0.20130902svn.3.x86_64
cups-filters-0:1.27.5-4.x86_64
cups-pk-helper-0:0.2.6-0.git151fb.2.x86_64
darktable-0:3.4.1-1.x86_64
draftsight-0:2018.3.0.4215-2.x86_64
draftsight-0:2019.3.0.4107-4.x86_64
epdfview-0:0.1.8-9.x86_64
gnome-control-center-0:40.0-5.x86_64
gnome-settings-daemon-0:40.0.1-4.x86_64
gnustep-gui-0:0.29.0-2.x86_64
google-chrome-beta-0:96.0.4664.35-1.x86_64
google-chrome-stable-0:95.0.4638.69-1.x86_64
google-chrome-unstable-0:97.0.4688.2-1.x86_64
gutenprint-cups-0:5.3.3-3.x86_64
hplip-0:3.20.9-6.x86_64
hplip-0:3.21.8-1.x86_64
java-1.8.0-openjdk-headless-1:1.8.0.252.b02-0.2.ea.i686
java-1.8.0-openjdk-headless-1:1.8.0.252.b02-0.2.ea.x86_64
java-1.8.0-openjdk-headless-slowdebug-1:1.8.0.252.b02-0.2.ea.i686
java-1.8.0-openjdk-headless-slowdebug-1:1.8.0.252.b02-0.2.ea.x86_64
java-11-openjdk-headless-1:11.0.12.0.7-7.x86_64
java-11-openjdk-headless-fastdebug-1:11.0.12.0.7-7.x86_64
java-11-openjdk-headless-slowdebug-1:11.0.12.0.7-7.x86_64
kde-print-manager-0:21.08.1-1.x86_64
lib64cups-devel-0:2.3.3op2-4.x86_64
lib64cupsfilters1-0:1.27.5-4.x86_64
lib64cupsimage2-0:2.3.3op2-4.x86_64
lib64freerdp-client2-0:2.4.0-1.x86_64
lib64gnomecups-1.0_1-0:0.2.3-16.x86_64
lib64gs9-0:9.54.0-5.x86_64
lib64gtk-modules2.0-0:2.24.33-2.x86_64
lib64gtk-modules3.0-0:3.24.30-5.x86_64
lib64gtk-modules4.0-0:4.3.2-3.x86_64
lib64hpipp0-0:3.20.9-6.x86_64
lib64hpipp0-0:3.21.8-1.x86_64
lib64qt5gui5-0:5.15.2-15.x86_64
lib64samba-libs0-1:4.12.11-3.x86_64
lib64sane-hpaio1-0:3.20.9-6.x86_64
lib64sane-hpaio1-0:3.21.8-1.x86_64
libgnomeprint-0:2.18.8-12.x86_64
libreoffice-common-1:7.1.6-1.x86_64
lsb-lib64-0:5.0-0.alpha.7.x86_64
perl-Net-CUPS-0:0.610.0-9.x86_64
popcorntime-0:0.3.10-1.x86_64
python3-cups-0:1.9.74-4.x86_64
qpdfview-0:0.4.18-5.x86_64
remmina-plugins-rdp-0:1.4.9-1.x86_64
riot-0:1.4.2-1.x86_64
samsung-unified-driver-0:4.01.17-4.x86_64
samsung-unified-driver3-0:3.00.90-1.x86_64
scribus-0:1.5.7-2.x86_64
system-config-printer-udev-0:1.5.15-4.x86_64
wire-desktop-0:3.19.2928-1.x86_64
x2goclient-1:4.1.2.2-3.x86_64
xpdf-0:4.02-1.x86_64

GTK+ and Qt toolkits are also among them.

UPD. Some of applications from the list above may not really use libcups directly but can be accidently overlinked with it, I think.

[mikhailnov]

Centralizing managing printers via text configs seems to be a good idea, sssd could be taught to get and apply them from FreeIPA domain, for example.

But it seems to be a bit far from real life. Usually only a few PCs require access to one printer, trying to centralize management of it will be a big overkill in many cases.

(and most printers are some crap not ready for IPP without PPDs by the way, CUPS 3.0 will not be usable without support of PPDs either directly or indirectly, most distros simply won't package it in such case, I am pretty sure).

If I am not mistaken, currently there is no way to disable automatic discovery of printers by CUPS via mDNS/Avahi. It is possible to off advertizing them, but not discovering. CUPS can discover too many printers in even small corporate environments. CC @sibskull

split cupsd into two services - a per-user "local server" that handles the normal printing tasks and a system-wide "sharing server" that would provide persistent queues, ACLs, accounting, etc. Most users would never install the sharing server.

That sounds useful, there will be less crap being automatically advertized via mDNS, for example.

[zdohnal]

Hi @mikhailnov ,

@michaelrsweet Most desktop application work with libcups for printing, only very old apps call lp or other similar tools directly. Have a look at which applications from a ditro repo + proprietary repo of Google Chrome depens from libcups:

unfortunately working with libcups doesn't automatically mean working with modern CUPS API, which is needed for proper temp queues support and which has been the issue causing most people to install their printers.

Centralizing managing printers via text configs seems to be a good idea, sssd could be taught to get and apply them from FreeIPA domain, for example.

It seems there is a misunderstanding - the printer profiles aren't about centralizing managing printers, but about making printers, which aren't in the local network (which is the mDNS default limitation), available in a print dialog without requiring them to be installed permanently.

(and most printers are some crap not ready for IPP without PPDs by the way, CUPS 3.0 will not be usable without support of PPDs either directly or indirectly, most distros simply won't package it in such case, I am pretty sure).

Most printers made after 2010 are capable of IPP Everywhere, so they don't need a PPD for working properly.
Most probable hiccups which set an user back to a PPD usually are:

• applications don't use the modern CUPS API
• user doesn't open/does close on purpose IPP port on the printer
• user doesn't allow IPP communication in firewalls
• a state-of-art printer, which is capable of IPP Everywhere is behind an old CUPS server, which is unable of IPP Everywhere

For old devices which doesn't support IPP Everywhere, OpenPrinting's already provided a retro-fitting printer applications for several PDLs and created manual how to create a new printer application - see OpenPrinting/cups-sharing#4 .

The printer application's mechanism can be used for devices which provide more specialized settings than IPP Everywhere has to offer - Gutenprint people are working on such app.

If I am not mistaken, currently there is no way to disable automatic discovery of printers by CUPS via mDNS/Avahi. It is possible to off advertizing them, but not discovering. CUPS can discover too many printers in even small corporate environments. CC @sibskull

Hmm, you're right - I thought there is the same directive as in cups-browsed, BrowseRemoteProtocols, which sets the protocols used for discovery, and setting them to 'none' disables the discovery as whole.
However, the same can be done by a simple stopping/disabling/not installing avahi-daemon, which takes care of mDNS discovery - IMHO requiring avahi-daemon running but disabling its mDNS support for CUPS is a corner case which I won't pursue because of its scarce usage, however if there is a PR, we in OpenPrinting will review it.

[mikhailnov]

08.11.2021 10:27, zdohnal пишет:

Hi @mikhailnov <https://github.com/mikhailnov> , @michaelrsweet <https://github.com/michaelrsweet> Most desktop application work with libcups for printing, only very old apps call |lp| or other similar tools directly. Have a look at which applications from a ditro repo + proprietary repo of Google Chrome depens from libcups: unfortunately working with libcups doesn't automatically mean working with modern CUPS API, which is needed for proper temp queues support and which has been the issue causing most people to install their printers. Centralizing managing printers via text configs seems to be a good idea, sssd could be taught to get and apply them from FreeIPA domain, for example. It seems there is a misunderstanding - the printer profiles aren't about centralizing managing printers, but about making printers, which aren't in the local network (which is the mDNS default limitation), available in a print dialog without requiring them to be installed permanently.

Thanks for clarifying. It also helps to manage printers centrally.

(and most printers are some crap not ready for IPP without PPDs by the way, CUPS 3.0 will not be usable without support of PPDs either directly or indirectly, most distros simply won't package it in such case, I am pretty sure). Most printers made after 2010 are capable of IPP Everywhere, so they don't need a PPD for working properly.

I have Kyocera FS-1060DN bought in 2017. It requires a custom CUPS backend rastertokpsl and does not understand standard formats like PDF, PCL etc. I think it does not support IPP. Also there is quite a  \lot of pre-2010 printers in use. Printers of those years are usually made better then most of modern crap like printers requiring a subscription or where a new torner costs as a new printer. Many printers being sold require proprietary "drivers", sometimes those are convertors to an internal proprietary format, some times just PPDs with custom settings and calling custom scripts which do hackery with utilities like gs(1) preparing the input for the printer.

[zdohnal]

I have Kyocera FS-1060DN bought in 2017.

Unfortunately it doesn't depend on when you've bought it, but when the model was started to sell - your model (according dates on its manual) is from 2012.

It requires a custom CUPS backend rastertokpsl and does not understand standard formats like PDF, PCL etc. I think it does not support IPP.

You can check whether the device supports IPP Everywhere/AirPrint. If you have the device connected by USB, look for 7/1/4 interface in lsusb -v output. If you have the device connected via wifi/ethernet, most devices provide configuration web interface where you can see available options for your printer - look for IPP/AirPrint/Mopria/Bonjour/mDNS settings.

Brian documented nicely all driverless options here https://wiki.debian.org/CUPSDriverlessPrinting .

Also there is quite a \lot of pre-2010 printers in use.

That's what a printer application technology is for.

[michaelrsweet]

OK, proposal:

• Per-system (/etc/cups/profiles, /usr/local/etc/cups/profiles, $SNAP_COMMON/cups/profiles, /Library/Application Support/cups) and per-user (~/.cups/profiles, $XDG_CONFIG_HOME/cups/profiles, ~/Library/Application Support/cups) directories contain files pointing to servers and/or printers.
• Profiles are simple config files with "Printer" and "Server" directives; description below.
• cupsEnumDests and cupsGetDests list all printers found.

Profile format is basically as previously proposed:

# comment

# IPP System service implementation
Server {ipp,ipps}://HOSTNAME-OR-IP[:PORT]/ipp/system

# CUPS 2.x server
ServerName HOSTNAME-OR-IP[:PORT]

# IPP Everywhere printer
Printer {ipp,ipps}://HOSTNAME-OR-IP[:PORT]/PATH

[mikhailnov]

I beleive it is important to allow to block per-user profiles or specific values inside them. For secirty reasons for example.Message ID: ***@***.***>

[michaelrsweet]

@mikhailnov What security reasons?

[michaelrsweet]

WRT controlling whether profiles and/or mDNS are used on the client side, I'm not sure whether that is necessary or useful. I wouldn't mind adding filtering support (printer-type and printer-location has been available since the CUPS 1.x days in different ways, printer-geo-location could be added as well) so that enterprise networks with large numbers of printers could be whittled down a bit.

Some possibilities for filtering directives (in client.conf and the profile files):

# Don't filter by geo-location
FilterGeoLocation none

# Only show printers within a certain distance
FilterGeoLocation 20m

# Show all printers regardless of location
FilterLocation none

# Only show printers with matching location(s)
FilterLocation "Room 1"
FilterLocation "Room 1", "Room 2"
FilterLocation /^Room [1-2]$/

# Filter printers based on type(s)
FilterType any
FilterType mono
FilterType color
FilterType duplex
FilterType small
FilterType medium
FilterType large
FilterType duplex,color

[michaelrsweet]

Implementing in "profiles" branch...

[michaelrsweet]

OK, so after some prototyping and performance analysis, it seems like this should all go in the cups-local service because of the time it may take to build a list of available profile printers. Similar to how the current cups-browsed operates, cups-locald will need to monitor for network and filesystem changes so that it can update the list of available printers only when needed, and in the background so as not to disturb applications. The cups-locald service can also handle naming conflicts in a centralized way.

Moving to cups-local project.