[cups] [UNKN] STR #4320: Strange problem with CUPS on a Linux (CentOS 5.10) LAN

[Robert Heller]

At Wed, 22 Jan 2014 08:43:55 -0500 Michael Sweet <msweet at apple.com> wrote:

> 
> Robert,
> 
> On Jan 22, 2014, at 8:34 AM, Robert Heller <heller at deepsoft.com> wrote:
> >> ...
> >> Just set up queues with no PPDs; if you have already created a queue you can revert it to a raw queue with:
> >> 
> >>    lpadmin -p printer -m raw
> > 
> > I expect that lpadmin will fail, since the /etc/ directory is on a read-only 
> > file system -- I *cannot* use the 'normal' admin utilities it all *has* to be 
> > done using a text editor...  CUPS pretty much sucks for this sort of 
> > situation, esp. since the documentation does not really document how to admin 
> > things that way.
> 
> With all due respect, you are not following the file system standards that
> all system services rely on. In particular, /usr can be read-only and shared
> but /etc is supposed to be read-write. The usual way of propagating writable
> configuration files like this is through tools like "puppet". Putting
> /etc/cups on a read-only filesystem is NOT supported.

This is a 'special case' of a *shared* NFS mounted root file system.  Having 
root *writable* AND *shared* for several machines leads to all sorts of odd 
problems (changing the configuration on one machine changes things on another 
machine).  (Actually the actual root file system is writable, but is a 
ramdisk, with symlinks for /etc, /sbin, /bin, /lib, etc and with /var 
initially copied from the readonly root to the ramdisk.)  There is not any 
requirement that /etc, /sbin, /bin, and /lib be writable.  /var *does* need to 
be writable for lock files (/var/lock), logs (/var/log), etc. 

The *original* UNIX standard allowed for the root file system being read-only.
It is only in this 'modern' time of 'cheap' disks and GUI / web-based that
needs places like /etc to be generally writable. This is really one of the
*bad* things about CUPS vs. the (old) LPD system: the LPD system had no
'tools' for mucking with its config files -- one did that with a text editor
(vi, emacs, sed, ed, whatever). CUPS follows *Apple's* notion that the GUI is
the be-all-end-all. MacOSX installs the graphics subsystem, even for 'server'
installs (just like MS-Windows). The idea of MacOSX without *any* web browser
installed is not considered possible. (It is not as bad as MS-Windows with IE
'embedded' in the OS -- Safari can be completed deleted from a MacOSX install,
but presumably, one would have installed Firefox or Chrome or Opera.) UNIX
*traditionally* had no GUI at all, much less a web browser. It is possible to
install Linux *without* any GUI or web browser.


> 
> Anyways, if you have to do things by hand, delete the PPD file in the
> /etc/cups/ppd directory. You might also have to remove Filter lines from
> /etc/cups/printers.conf (I don't remember how much information is in the
> older versions of CUPS off hand, we've been adding a lot of caching of data
> in recent releases to speed startup...)


> 
> > Next question:
> > 
> > With a local printers.conf, I am now seeing two copies of the queues (the 
> > 'local' printers.conf version and the version picked up via network).  How do 
> > I prevent this duplication.
> 
> If you are using an old version of CUPS and have static queues defined, you
> need to disable browsing.

OK, I'll keep that in mind.  What I have done is removed the static local 
queues and swapped boxes -- we shall have to wait and see if the problem 
re-appears (and whether it follows the machine swap or not will be telling).

> 
> > Also, we have been getting errors relating to probably with file format 
> > strangeness (nonsense about bad stream type, application/octect).  I'm 
> > *guessing* because of the fact that I have queues to the server's ipp address, 
> > but with PPD file at the same time.
> 
> I'd need to see the error messages to provide any useful answers.


OK, if/when they show up I'll pass them on.

> 
> _________________________________________________________
> Michael Sweet, Senior Printing System Engineer, PWG Chair
> 
>                                      

-- 
Robert Heller             -- 978-544-6933 / heller at deepsoft.com
Deepwoods Software        -- http://www.deepsoft.com/
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