lpstat -v shows device as /dev/null

[biizz]

Hello,

I am new to HP-UX servers, can someone explain to me what does the /dev/null in the result of "lpstat -v" means? Been trying to search the answer but could not find any. Most of the printer queue on the server is pointing to /dev/null

Here is the sample result:

# lpstat -v <printqueue>
device for <printqueue>: /dev/null

Also, what is the difference from this lpstat result?

# lpstat -v <printqueue>
device for <printqueue>: /dev/null
remote to IP

Thanks!

[Bill Hassell · Accepted solution]

HP-UX has been around for a long time and back in the old days, printers used a parallel interface known as a Centronix interace. Another interface was called HP-IB. Both are actual devices, like a tape drive. Then printers adopted RS-232 (serial) as an interface, but still a device.

But none of these printers could be very far away from the computer, typically in the computer room. Cable lengths were very short (10 to 50 ft). So the concept of sharing a printer over the network became a reality. It was called remote line printer (rlp) and now there is no device. Instead, the spooler must negotiate over the network with another computer and send the job over a network connection. lpr was mostly Unix in implementation until Windows adopted a compatible lpr (aka, printer sharing).

As the 1980s rolled along, printers became much cheaper and smaller and the demand to send print jobs directly to the printer became a possibility. The printer actually had a LAN port and IP address. And inside was a tiny computer that knew how to negotiate the lpr protoco over port 515.

But lpr is extremely primitive with virtually no status and feedback to the computer sending the job. So HP designed a new network protocol called JetDirect which used port 9100. This is a full wrtie/read connection which then allowed for printer status and control. It was designed in the HP Boise location, primarily for PCs and Macs but they also created HP-UX tools and the rest is history. Every printer manufacturer eventually adopted the JetDirect protocol.

Back to HP-UX. So a device file is only meaningful if there is a direct connection from an I/O card to the printer. Once the print path uses the network, the device becomes /dev/null.

[biizz]

Thank you so much for explanation! I understand now. This is really helpful. ☺️

[Bill Hassell]

One thing that I left out was how to identify the 3 printer connections:

1. serial or Centronics or HP-IB

These are real devices and you'll see the device file in the lpstat listing.

2. lpr (port 515 networking)

These can seen with the word remote in lpstat along with /dev/null

3. JetDirect (port 9100)

Just the /dev/null identifier.

For JetDirect printers, there are a lot of utilities to add, modify, delete, query and setup. Take a look at the man pages for:

hpnpadmin (query)
hpnpf (direct print, also can trace the print data and handshake)
hppi (the menu program, used by SAM or SMH)
addqueue (add a printer
removequeue (delete printer)
modifyqueue (make changes to printer setup)