User`s guide

3-3
Spooler Overview
Spooler Terminology
The following terms relate to the spooler overview.
Spooler
The AIX spooler is a collection of programs, configuration files, and data files that provide
the following functions or services:
• Provides for the construction of queues, which are software entities whose function is to
process jobs in specific ways
• Allows users to submit jobs (usually but not always printer jobs) to a queue for
processing.
• Provides serial access through a queue to a device (such as a real printer), or to a
program (such as a compiler), avoiding simultaneous use of a single device or program
by multiple users
• Allows users to query the status of queues through status files
• Allows users to control the availability of queues and the status of jobs
• Performs extensive manipulation of print job data stream
• Offers a wide–range of delivery mechanisms for the processed job
Local and Remote Spooler Queues and Spooler Devices
A queue is an ordered list of requests for a specific device. A device is something that can
handle requests one at a time, such as a printer. Each queue must be serviced by at least
one device; often it can be serviced by multiple devices.
Real (physical) and Virtual Printers
A real (physical) printer is the printer hardware attached to the system via a serial or parallel
port, or through a network connection such as a network terminal server. When the real
printer is attached via a serial or parallel port local to the system, the printer device driver in
the kernel communicates with the printer hardware and provides an interface between the
printer hardware and a virtual printer.
A virtual printer is a set of attributes and their associated values that define a high–level
data stream (such as ASCII or Postscript) and the methods for processing that data stream.
This does not include information about how the real printer is attached to the host
computer or about the protocol used for transferring bytes of data to and from the real
printer. The piobe backend uses information stored in the virtual printer definition to control
print job processing. The physical storage medium of the sets of attributes and their
associated values is called a printer colon file.
Local and Remote Printers
A local printer is a real printer attached to a local host, for which there is a local queue. All
jobs submitted to this queue are processed and printed on the host on which the queue
exists. A remote printer is a real printer attached to a remote host. The queue for a remote
printer specifies a backend whose function is to send the spooled job from the local host
across the network to the remote host. All jobs submitted to this queue, on the local host,
are sent across the network to the remote host where they are processed and printed.
Spooler Backends
A spooler backend is a collection of programs (a pipeline) started by the spooler’s qdaemon
command to manage a spooler job that is queued for processing. When the backend is for a
print queue, the spooler backend typically performs the following functions:
• Receives from the qdaemon command a list of one or more jobs to be processed.