Submitted by sudo in LiGNUx

In this post, I’ll step through how to get a thermal receipt printer with USB interface appearing on Linux. The aim of this is to be able to point a driver such as escpos-php at the device. The printer used here is an Epson TM-T20, which is very common in point-of-sale environments.

I have previously written quite a bit about how to use thermal receipt printer protocols, but the previous printer I covered had only a network interface, not USB like this one:

(Image) (Image)

The directions below are for Debian, but could be adapted for any other Linux.

Find the device file

Plug in your printer, and check that usblp sees it:

dmesg
[12724.994550] usb 8-4: new full-speed USB device number 5 using ohci-pci
[12725.168956] usb 8-4: New USB device found, idVendor=04b8, idProduct=0e03
[12725.168963] usb 8-4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[12725.168968] usb 8-4: Product: TM-T20
[12725.168971] usb 8-4: Manufacturer: EPSON
[12725.168975] usb 8-4: SerialNumber: ....
[12725.175114] usblp 8-4:1.0: usblp1: USB Bidirectional printer dev 5 if 0 alt 0 proto 2 vid 0x04B8 pid 0x0E03

This kernel module makes your printer visible as a device file, so that it can be accessed in the old-fashioned way. Find the new device file under /dev/usb:

ls /dev/usb

In my case, this was /dev/usb/lp1. The next step is to see if you can write to it:

echo "Hello" >> /dev/usb/lp1

Chances are, you will get a permission denied error at this point, so find out what group the printer is in:

stat /dev/usb/lp1

Which will show output something like:

File: ‘/dev/usb/lp1’
  Size: 0         	Blocks: 0          IO Block: 4096   character special file
Device: 5h/5d	Inode: 220997      Links: 1     Device type: b4,1
Access: (0660/crw-rw----)  Uid: (    0/    root)   Gid: (    7/      lp)

This file is owned by group lp (“line printer”). If your username was bob, you would add yourself to this group using:

sudo usermod -a -G lp bob

If you plan to build a web-based point-of-sale system with this, then also add the www-data user to that group.

Now log out and back in, and the previous test should now be working:

echo "Hello" >> /dev/usb/lp1

Troubleshooting: Check usblp

If these steps don’t work, then your computer ether doesn’t have, or isn’t using usblp. You’ll need to check a few things:

  • Install a different linux-image if the driver is not on your computer at all.
  • modprobe or insmod usblp
  • blacklist a vendor driver which has claimed the interface.
  • run lsusb -v and usb-devices (look for driver=)

Printing something useful

As a duplicated section from my earlier post, the printer uses ESC/POS, which means it accepts plaintext with some special commands for formatting.

A simple receipt-generator, foo.php, might look like this:

<?php
/* ASCII constants */
const ESC = "\x1b";
const GS="\x1d";
const NUL="\x00";

/* Output an example receipt */
echo ESC."@"; // Reset to defaults
echo ESC."E".chr(1); // Bold
echo "FOO CORP Ltd.\n"; // Company
echo ESC."E".chr(0); // Not Bold
echo ESC."d".chr(1); // Blank line
echo "Receipt for whatever\n"; // Print text
echo ESC."d".chr(4); // 4 Blank lines

/* Bar-code at the end */
echo ESC."a".chr(1); // Centered printing
echo GS."k".chr(4)."987654321".NUL; // Print barcode
echo ESC."d".chr(1); // Blank line
echo "987654321\n"; // Print number
echo GS."V\x41".chr(3); // Cut
exit(0);

And you would send it to the printer like this:

php foo.php > /dev/usb/lp1

Scaling this up

The codes are quite tricky to work with manually, which is why I put together the escpos-php driver. You can find it at:

The above example would be written using escpos-php as:

<?php
require __DIR__ . '/autoload.php';
use Mike42\Escpos\Printer;
use Mike42\Escpos\PrintConnectors\FilePrintConnector;
$connector = new FilePrintConnector("/dev/usb/lp1");
$printer = new Printer($connector);

/* Print some bold text */
$printer -> setEmphasis(true);
$printer -> text("FOO CORP Ltd.\n");
$printer -> setEmphasis(false);
$printer -> feed();
$printer -> text("Receipt for whatever\n");
$printer -> feed(4);

/* Bar-code at the end */
$printer -> setJustification(Printer::JUSTIFY_CENTER);
$printer -> barcode("987654321");
$printer -> cut();
?>

This would be sent to the printer by loading it from the web, or running the script on the command-line:

php foo2.php
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Comments

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MHC wrote

This is about USB connection, as opposed to Ethernet network. The user has to work at the command line. And they need to understand concepts such as a workgroup. This article therefore is not for the technically clueless!

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