how printing works

[Antoine Martin]

Hi,

I am trying to figure out how NX does the printer forwarding.
How does it tell the client sessions to connect to a different printer
on the fly when the client connects from a different location?
Can it be done/is it done without samba?

Can anyone point me to some documentation?
I would like to understand the mechanism, and emulate it using simple
scripts. (I am not interested in using it via NX, rather I want to
understand it/test it by hand).

Thanks
Antoine
________________________________________________________________
     Were you helped on this list with your FreeNX problem?
    Then please write up the solution in the FreeNX Wiki/FAQ:

http://openfacts2.berlios.de/wikien/index.php/BerliosProject:FreeNX_-_FAQ
 
         Don't forget to check the NX Knowledge Base:
                 http://www.nomachine.com/kb/ 

________________________________________________________________
       FreeNX-kNX mailing list --- FreeNX-kNX@...
      https://mail.kde.org/mailman/listinfo/freenx-knx
________________________________________________________________

[ChrisB-6]

Antoine Martin <antoine@...> wrote on 29/09/2009 09:39:21:

> Hi,
>
> I am trying to figure out how NX does the printer forwarding.

Well . . .

It uses an ssh tunnel which redirects a port on the FreeNX server back to the workstation, so you can then connect to a port on the WS :631 or :445, via the redirected port.


> How does it tell the client sessions to connect to a different printer
> on the fly when the client connects from a different location?


FreeNX runs a separate cups printer daemon for each user, which it configures with the printer/queue identified by  . . .

1/ the printer name on the workstation, as configured on the workstation cups daemon if the workstation is NIX or the printer share if the WS is windows
2/ the port on the server which is redirected to the workstation, via which the user cupsd spools
3/ the printer/share name and the login details ( for connecting back to the workstation ) which are set up in the NX client, and passed over during connection
4/ a .ppd driver file to correspond to the printer's MODEL, which FreeNX asks the user to select because it can't (well, doesn't anyway) tell just from the printer name.


> Can it be done/is it done without samba?
>


Samba (smb:// smbspool)is used if the WS is windows or NIX configured with smbspool printing to a samba share.

ipp:// is used if the WS is running cupsd ie a NIX WS.


Basic printing stuff which you should know already . . .

For a Postscript printer, the user cupsd, using the normal .ppd driver, passes Postscript on to the remote printer, which does a raw dump to the printer, ie it doesn't process again.

For a non Postscript (ie. windows) printer, the user cupsd .ppd driver causes cupsd to pass the postscript print job through a postscript to windows printing converter ( automagically ) then on to the remote printer, again you need a raw dump to the printer, which windows does automatically but smbd needs to have configured.


> Can anyone point me to some documentation?


No ! Did you not try Google.


> I would like to understand the mechanism, and emulate it using simple
> scripts. (I am not interested in using it via NX, rather I want to


You need a print share on the windows workstation or a cups printer set up on the NIX workstation.

You need to set up a reverse tunnel from the workstation to a port on the NIX server. Use Openssd on a NIX WS or cygwin's Openssh on windows WS.

For a NIX workstation, you need to set up an ipp printer (typically) in cups on the server, pointing via the re-directed port to the workstation.

For a windows WS you need an smb printer set up in cups on the server, which uses smbspool to connect via the redirected port to the print share on the workstation after the .ppd file has kicked off PS to Windows conversion.


> understand it/test it by hand).
>


Good luck !!


Note, there is quite a bit more to FreeNX printing, ( the bit you are not interested in ), and some of the windows printing is a bit creacky.

The FreeNX authors did a sizable amount of work though overall !!! and I dread to think how much time they have spent . . .
 

> Thanks
> Antoine
> ________________________________________________________________
>      Were you helped on this list with your FreeNX problem?
>     Then please write up the solution in the FreeNX Wiki/FAQ:
>
> http://openfacts2.berlios.de/wikien/index.php/BerliosProject:FreeNX_-_FAQ
>  
>          Don't forget to check the NX Knowledge Base:
>                  http://www.nomachine.com/kb/
>
> ________________________________________________________________
>        FreeNX-kNX mailing list --- FreeNX-kNX@...
>       https://mail.kde.org/mailman/listinfo/freenx-knx
> ________________________________________________________________

________________________________________________________________
     Were you helped on this list with your FreeNX problem?
    Then please write up the solution in the FreeNX Wiki/FAQ:

http://openfacts2.berlios.de/wikien/index.php/BerliosProject:FreeNX_-_FAQ
 
         Don't forget to check the NX Knowledge Base:
                 http://www.nomachine.com/kb/ 

________________________________________________________________
       FreeNX-kNX mailing list --- FreeNX-kNX@...
      https://mail.kde.org/mailman/listinfo/freenx-knx
________________________________________________________________

[Antoine Martin]

ChrisB wrote:

> Antoine Martin <antoine@...> wrote on 29/09/2009 09:39:21:
>
>> Hi,
>>
>> I am trying to figure out how NX does the printer forwarding.
>
> Well . . .
>
> It uses an ssh tunnel which redirects a port on the FreeNX server back to
> the workstation, so you can then connect to a port on the WS :631 or :445,
> via the redirected port.

That's the easy part... with ssh -R
But how do you tell the client applications running on the server to
talk to this particular cups server?
In a hosted environment there may be dozens of these cups servers
running (one for each session)
That's the bit I am missing...

>> How does it tell the client sessions to connect to a different printer
>> on the fly when the client connects from a different location?
>
>
> FreeNX runs a separate cups printer daemon for each user, which it
> configures with the printer/queue identified by  . . .
>
> 1/ the printer name on the workstation, as configured on the workstation
> cups daemon if the workstation is NIX or the printer share if the WS is
> windows
> 2/ the port on the server which is redirected to the workstation, via
> which the user cupsd spools
> 3/ the printer/share name and the login details ( for connecting back to
> the workstation ) which are set up in the NX client, and passed over
> during connection
> 4/ a .ppd driver file to correspond to the printer's MODEL, which FreeNX
> asks the user to select because it can't (well, doesn't anyway) tell just
> from the printer name.
>

If I only deal with the somewhat easier case of nix workstations with
cupsd running on the client, why can't I just get the server to point
the apps to talk directly to that remote cups server? (via ssh -R or
plain tcp if on a secure LAN)
And if so... how?
(same question as above really)

>> Can it be done/is it done without samba?
>>
>
>
> Samba (smb:// smbspool)is used if the WS is windows or NIX configured with
> smbspool printing to a samba share.
>
> ipp:// is used if the WS is running cupsd ie a NIX WS.
>
>
> Basic printing stuff which you should know already . . .

[snip]
>
>> Can anyone point me to some documentation?
>
>
> No ! Did you not try Google.
Yes.
I never bother dozens of people on mailing lists without spending a fair
amount of time doing my homework.
Thanks for your very detailed response though!

>> I would like to understand the mechanism, and emulate it using simple
>> scripts. (I am not interested in using it via NX, rather I want to
>
>
> You need a print share on the windows workstation or a cups printer set up
> on the NIX workstation.
Check.

> You need to set up a reverse tunnel from the workstation to a port on the
> NIX server. Use Openssd on a NIX WS or cygwin's Openssh on windows WS.
Check. (or plink on windows)

> For a NIX workstation, you need to set up an ipp printer (typically) in
> cups on the server, pointing via the re-directed port to the workstation.
I would like to avoid this part (as mentioned above).
If not, can this be done easily/reliably from a script? (and without
generating a whole new cupsd.conf if possible)

> For a windows WS you need an smb printer set up in cups on the server,
> which uses smbspool to connect via the redirected port to the print share
> on the workstation after the .ppd file has kicked off PS to Windows
> conversion.
Sigh.

>> understand it/test it by hand).
>>
>
>
> Good luck !!
>
>
> Note, there is quite a bit more to FreeNX printing, ( the bit you are not
> interested in ), and some of the windows printing is a bit creacky.
>
> The FreeNX authors did a sizable amount of work though overall !!! and I
> dread to think how much time they have spent . . .

Thanks for the hint... I think I'll try to keep it simple for now!

Antoine

>  
>
>> Thanks
>> Antoine
>> ________________________________________________________________
>>      Were you helped on this list with your FreeNX problem?
>>     Then please write up the solution in the FreeNX Wiki/FAQ:
>>
>>
> http://openfacts2.berlios.de/wikien/index.php/BerliosProject:FreeNX_-_FAQ
>>          Don't forget to check the NX Knowledge Base:
>>                  http://www.nomachine.com/kb/ 
>>
>> ________________________________________________________________
>>        FreeNX-kNX mailing list --- FreeNX-kNX@...
>>       https://mail.kde.org/mailman/listinfo/freenx-knx
>> ________________________________________________________________
>
>
> ------------------------------------------------------------------------
>
> ________________________________________________________________
>      Were you helped on this list with your FreeNX problem?
>     Then please write up the solution in the FreeNX Wiki/FAQ:
>
> http://openfacts2.berlios.de/wikien/index.php/BerliosProject:FreeNX_-_FAQ
>  
>          Don't forget to check the NX Knowledge Base:
>                  http://www.nomachine.com/kb/ 
>
> ________________________________________________________________
>        FreeNX-kNX mailing list --- FreeNX-kNX@...
>       https://mail.kde.org/mailman/listinfo/freenx-knx
> ________________________________________________________________

________________________________________________________________
     Were you helped on this list with your FreeNX problem?
    Then please write up the solution in the FreeNX Wiki/FAQ:

http://openfacts2.berlios.de/wikien/index.php/BerliosProject:FreeNX_-_FAQ
 
         Don't forget to check the NX Knowledge Base:
                 http://www.nomachine.com/kb/ 

________________________________________________________________
       FreeNX-kNX mailing list --- FreeNX-kNX@...
      https://mail.kde.org/mailman/listinfo/freenx-knx
________________________________________________________________

[ChrisB-6]

Antoine Martin <antoine@...> wrote on 30/09/2009 10:23:06:

> ChrisB wrote:
> > Antoine Martin <antoine@...> wrote on 29/09/2009 09:39:21:

> > It uses an ssh tunnel which redirects a port on the FreeNX server back to
> > the workstation, so you can then connect to a port on the WS :631 or :445,
> > via the redirected port.
> That's the easy part... with ssh -R

Hmmmm

> But how do you tell the client applications running on the server to
> talk to this particular cups server?

????

You tell KDE etc. which cupsd to talk to not the client applications . . .


> In a hosted environment there may be dozens of these cups servers
> running (one for each session)

Yup, one for each user printing through the tunnel.

> That's the bit I am missing...
>
> If I only deal with the somewhat easier case of nix workstations with
> cupsd running on the client, why can't I just get the server to point
> the apps to talk directly to that remote cups server? (via ssh -R or
> plain tcp if on a secure LAN)


It's not an easier case if you have windows workstations not running cupsd, it's impossible. Given the large windows user base, it would be a fatal reduction in user base to not support them.

Most people want to spool to a queue on a local disk, then background the network transfer.

Cups deals with printer drivers, access rights etc locally.
In the olden days it was all lp to a remote IP, but then you had to manually set up printer options, trays paper size etc.


> And if so... how?
> (same question as above really)
>

Try it !!

> >
> >> Can anyone point me to some documentation?
> >
> >
> > No ! Did you not try Google.
> Yes.
> I never bother dozens of people on mailing lists without spending a fair
> amount of time doing my homework.
> Thanks for your very detailed response though!

That was not a detailed response !!!

You are now asking cups questions, for which there is slightly too much documentation !!

 
> > For a NIX workstation, you need to set up an ipp printer (typically) in
> > cups on the server, pointing via the re-directed port to the workstation.
> I would like to avoid this part (as mentioned above).

Why, do you know anything easier ??

> If not, can this be done easily/reliably from a script? (and without

Yup.

> generating a whole new cupsd.conf if possible)

Nope.

One of the reasons for a userland cupsd is that the printing is only set up after the user has successfully logged in and their session has started.

If you didn't mind having all your users being printer administrators then you could just use the system cupds ( which of course you also use if you are NOT setting up remote printing ), because users could then set up and delete their own printers ( and everyone else's, and redirect everyone elses printing ) which in the real world, would not of course be considered rational behavior.

>
> > For a windows WS you need an smb printer set up in cups on the server,
> > which uses smbspool to connect via the redirected port to the print share
> > on the workstation after the .ppd file has kicked off PS to Windows
> > conversion.
> Sigh.

It ( nearly ) works. What's the problem ??







________________________________________________________________
     Were you helped on this list with your FreeNX problem?
    Then please write up the solution in the FreeNX Wiki/FAQ:

http://openfacts2.berlios.de/wikien/index.php/BerliosProject:FreeNX_-_FAQ
 
         Don't forget to check the NX Knowledge Base:
                 http://www.nomachine.com/kb/ 

________________________________________________________________
       FreeNX-kNX mailing list --- FreeNX-kNX@...
      https://mail.kde.org/mailman/listinfo/freenx-knx
________________________________________________________________

[Antoine Martin]

ChrisB wrote:

>>> It uses an ssh tunnel which redirects a port on the FreeNX server back
> to
>>> the workstation, so you can then connect to a port on the WS :631 or
> :445,
>>> via the redirected port.
>> That's the easy part... with ssh -R
>
> Hmmmm
>
>> But how do you tell the client applications running on the server to
>> talk to this particular cups server?
>
> ????
>
> You tell KDE etc. which cupsd to talk to not the client applications . . .

Sure, that's what I meant, Gnome/KDE/other.
I still don't know *how* to do that!
Is there a freedesktop.org specification on this that I have missed?
Is it via an environment variable before you launch the app? (I've tried
CUPS_SERVER - no effect).

Let's use a simple example: say I just launch "gedit" and nothing else
in an Xvnc session (no nx, no desktop, no dbus,..), how do I tell it to
use my newly started cups server?? (say: 127.0.0.1:10631)

^ This is the crucial bit that I am missing.

(I realize that it is not a freeNX question, rather a "desktop"
environment question, apologies to the list... It's just that you guys
seem to know about this stuff.)

>> In a hosted environment there may be dozens of these cups servers
>> running (one for each session)
>
> Yup, one for each user printing through the tunnel.
>
>> That's the bit I am missing...
>>
>> If I only deal with the somewhat easier case of nix workstations with
>> cupsd running on the client, why can't I just get the server to point
>> the apps to talk directly to that remote cups server? (via ssh -R or
>> plain tcp if on a secure LAN)
>
>
> It's not an easier case if you have windows workstations not running
> cupsd, it's impossible. Given the large windows user base, it would be a
> fatal reduction in user base to not support them.

That's not my intention! Just an example.
I would just like to avoid the complication of having an extra cups
server if it is not strictly necessary. At the very least for testing.

If the client has cups: point the server (the bit above I still don't
know how to do) directly to the tunnelled cups port. (or even direct to
a cups port if on a LAN - ignoring access rights issues for now).
If it does not (ie: Windows) then use a local cups server and point to
that. (and let it forward via smbspool/ppd)

^^ It's the "point to" part that I want to know how to do.

> Most people want to spool to a queue on a local disk, then background the
> network transfer.
If the benefits of using a local cups server outweigh the costs, then I
would add that extra step. In a local LAN use case (even just 100Mbit)
most jobs would be sent to the cupsd on the client within seconds (and
it can deal with spooling/queueing)

> Cups deals with printer drivers, access rights etc locally.
> In the olden days it was all lp to a remote IP, but then you had to
> manually set up printer options, trays paper size etc.
>
>
>> And if so... how?
>> (same question as above really)
>>
>
> Try it !!

Duh! (I wouldn't be asking if I hadn't!)

The bit that I am missing is how you tell the applications which cups
server to talk to. (host:port or preferably a local socket)
Sorry if I didn't make it clear in my original question.

The rest of the discussion is very interesting (and will be very useful
to me), but not a show-stopper for what I am trying to achieve at the
moment.

>>>> Can anyone point me to some documentation?
>>>
>>> No ! Did you not try Google.
>> Yes.
>> I never bother dozens of people on mailing lists without spending a fair
>> amount of time doing my homework.
>> Thanks for your very detailed response though!
>
> That was not a detailed response !!!
>
> You are now asking cups questions, for which there is slightly too much
> documentation !!

Yup. IMO too much is a hell of a lot better than too little!

>>> For a NIX workstation, you need to set up an ipp printer (typically)
> in
>>> cups on the server, pointing via the re-directed port to the
> workstation.
>> I would like to avoid this part (as mentioned above).
>
> Why, do you know anything easier ??
As explained above. (point to the cupsd server on the client directly,
or via a tunnel without having a cupsd running on the server)

>> If not, can this be done easily/reliably from a script? (and without
>
> Yup.
>
>> generating a whole new cupsd.conf if possible)
>
> Nope.
Hah.
Not too bad I guess, the config would be minimal with just:
Listen /home/user/applications_please_use_this.socket
And printers.conf would just point to the client's ipp/smbspool.

> One of the reasons for a userland cupsd is that the printing is only set
> up after the user has successfully logged in and their session has
> started.
>
> If you didn't mind having all your users being printer administrators then
> you could just use the system cupds ( which of course you also use if you
> are NOT setting up remote printing ), because users could then set up and
> delete their own printers ( and everyone else's, and redirect everyone
> elses printing ) which in the real world, would not of course be
> considered rational behavior.

Haha, that could be amusing... except for the local sysadmin.
But not very productive!

>>> For a windows WS you need an smb printer set up in cups on the server,
>
>>> which uses smbspool to connect via the redirected port to the print
> share
>>> on the workstation after the .ppd file has kicked off PS to Windows
>>> conversion.
>> Sigh.
>
> It ( nearly ) works. What's the problem ??
In this case you need the .ppd file, which will have to be a manual step
(as you pointed out). It's just a shame that's all.
I wished Windows could just talk ipp... (or ps or whatever)

Thanks for your time!
Antoine

>
>
>
>
>
>
>
>
>
> ------------------------------------------------------------------------
>
> ________________________________________________________________
>      Were you helped on this list with your FreeNX problem?
>     Then please write up the solution in the FreeNX Wiki/FAQ:
>
> http://openfacts2.berlios.de/wikien/index.php/BerliosProject:FreeNX_-_FAQ
>  
>          Don't forget to check the NX Knowledge Base:
>                  http://www.nomachine.com/kb/ 
>
> ________________________________________________________________
>        FreeNX-kNX mailing list --- FreeNX-kNX@...
>       https://mail.kde.org/mailman/listinfo/freenx-knx
> ________________________________________________________________

________________________________________________________________
     Were you helped on this list with your FreeNX problem?
    Then please write up the solution in the FreeNX Wiki/FAQ:

http://openfacts2.berlios.de/wikien/index.php/BerliosProject:FreeNX_-_FAQ
 
         Don't forget to check the NX Knowledge Base:
                 http://www.nomachine.com/kb/ 

________________________________________________________________
       FreeNX-kNX mailing list --- FreeNX-kNX@...
      https://mail.kde.org/mailman/listinfo/freenx-knx
________________________________________________________________