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When to Run an LPD Server
Conceptually, network printing is similar to file sharing. In
network printing, the client sends a file to the server, much as a file-sharing
client may send a file to a file-sharing server. The main difference is what happens
to the file. In the case of file sharing, the server stores the file on its
disk, presumably to be accessed at a later date by the same or some other user.
In network printing, the server sends the file on to a printer, and usually
deletes the spool file once this is done. These two tasks are so similar at a
network level that some protocolsmost importantly, the Server Message Block
(SMB)/Common Internet Filesystem (CIFS) protocolsuse a single server (Samba in
the case of Linux) to handle both tasks. Native UNIX tools, though, separate
these two functions into two servers: the Network Filesystem (NFS) server for
file sharing, and LPD for printer sharing.As noted earlier, Linux's standard LPD tools integrate local
and network printing operations, so if your Linux system is configured to print
using these standard tools, it takes very little additional effort to configure
the system to either accept remote print jobs or send print jobs to a networked
printer. In some sense, therefore, the question of when to run an LPD server is
one of when you want to do network printing. As a general rule, network
printing is useful in many small- and mid-size offices as a method of
stretching available resources. Rather than buy inexpensive (say, $300) laser
printers for a dozen computers (for a total cost of $3600), you can buy one
much more capable $1500 laser printer. For that price difference, you could
even throw in an inexpensive color inkjet or further upgrade the laser printer
to one that can handle color, and still come out ahead. LPD is one of the
critical components that allows you to do this.LPD isn't the only network printing protocol, though. As noted
earlier, SMB/CIFS includes printing capabilities. So do competing protocols and
packages like AppleTalk (via Linux's Netatalk). On another level, then, the
question becomes: When should you use LPD as opposed to some other
printer-sharing tools? This question is more subtle than the earlier question.
There are two major points to consider in answering it: What is best supported by the client? Linux
supports a wide variety of network printing protocols, so a Linux computer can
function as a print server for many different types of clients. Because clients
usually outnumber servers on any given network, you'll save yourself
considerable effort by using whatever protocol is best supported by the
clients. When your clients are UNIX or Linux systems, this means LPD. When
they're DOS, Windows, or OS/2 systems, this means SMB/CIFS. When they're
Macintoshes, AppleTalk is a good bet, although MacOS X also works well with
LPD. Do the competing protocols provide differing
levels of support for features you need? Network printing is simpler in many
ways than is file sharingfor instance, filename and permission issues are less
troublesome in network printing than in file sharing. Nonetheless, each
protocol supports its own set of options, such as authentication procedures. You
might want to use a protocol that's not the default for your clients in order
to obtain one of these features.This second point deserves some elaboration. LPD,
like NFS, uses a trusted hosts security model,
in which the server relies on the client to control access to the shared
resource. The server restricts access based primarily on the IP address of the
client. This method is convenient when working with multi-user client OSs, but
it's not as secure as a method that requires usernames and passwords to access
the server. SMB/CIFS, in particular, works in this way, so you might want to
favor it if you prefer to require a password for printer access. (If your
clients are Linux or UNIX computers, though, you'll end up storing printer
passwords in some globally readable configuration file unless you write new
printing scripts from scratch. The result may not be an improvement over
trusted hosts security.) The newer Internet Printing Protocol (IPP) favored by
CUPS also supports the use of usernames and passwords, but this feature is
optional in CUPS.If your clients are Windows computers,
chances are you'll want to use SMB/CIFS for printer sharing, although there are
LPD clients available for these systems. You might consider foregoing SMB/CIFS,
and the complications of Samba configuration, if you have just a few Windows
clients on a network dominated by UNIX, Linux, MacOS, or some other system that
doesn't normally use SMB/CIFS.A related question is when to use Linux as a print server. You can run most Linux print
servers on other UNIX-like OSs, so when you have a choice of Linux versus
another UNIX-like OS for using BSD protocols, the issue is one of convenience. Linux
makes an excellent unifying platform if you need to share printers with Linux,
UNIX, Windows, MacOS, and other OSs because you can run so many different
printer-sharing protocols simultaneously.Another option in many situations is to use a dedicated
printer-sharing box. These devices are dedicated network appliances with an
Ethernet interface, server protocols built into firmware, and parallel, RS-232
serial, or USB ports for connecting one or more printers. They can be very good
choices if you don't want to configure printer sharing on a regular
computersay because the computer won't be powered up at all times or because
you're concerned about the security aspects of running a server on whatever
computer might be convenient. Some high-end printers come with network
connectors that function much like dedicated print servers.TIP
align=left border=0> You can convert an old computer into a dedicated print
server by using Linux. Install Linux, strip it of unnecessary tools and
servers, and even an old 386 makes an adequate print server. With a fast
enough CPU, the print server can use Ghostscript to process PostScript files,
turning the combination of the dedicated computer and an inexpensive
non-PostScript printer into a networked PostScript printer. Particularly if
you add extra parallel ports or use USB devices, a single Linux computer can
serve several printers. Of course, a more powerful computer can function as a
print server and perform other server or
nonserver tasks.
