hacdc-wiki/Old Pages/3D Printing/Dynamic_symlinks_for_3D_printers.md

### Executive Summary

From the 3d printing server (reachable from the network via
pronterhost.local and pronterhost.hacdc.org) 3d printers can be
referenced by /dev/TAZ, /dev/MINI, and /dev/ROSTOCK. (added by Tom
9/9/2019)

### The problem

When powering cycling computers and various USB devices attached to said
computer, one does not necessarily get the same `/dev/ttyACM...`
associated with the same physical device every time. This makes it a
royal pain in the ass to use `pronsole` or other applications that need
to be explicitly told what to connect to, because each time you want to
connect to a specific printer you have to do somersaults to determine
the ACM number du jour for the printer (or other device) you want.

### The solution

So, on the artist currently known as `pronterhost.local`, as of
2019.01.21... Julia had previously created
`/etc/udev/rules.d/80-printer-names.rules`, the contents of which were:

    # This file was automatically generated by the /lib/udev/write_net_rules
    # program, run by the persistent-net-generator.rules rules file.
    #
    # You can modify it, as long as you keep each rule on a single
    # line, and change only the value of the NAME= key.

    SUBSYSTEM=="tty", KERNEL=="ttyACM?", ATTRS{serial}=="7403431393835160C070", SYMLINK+="MINI"
    # old
    #SUBSYSTEM=="tty", KERNEL=="ttyACM?", ATTRS{serial}=="6403636363835110D101", SYMLINK+="TAZ"
    SUBSYSTEM=="tty", KERNEL=="ttyACM?", ATTRS{serial}=="640363534303516070A1", SYMLINK+="TAZ"
    SUBSYSTEM=="tty", KERNEL=="ttyACM?", ATTRS{serial}=="64032373833351906091", SYMLINK+="ROSTOCK"

Following directions at [How to write udev Rules for USB
Devices](https://weininger.net/how-to-write-udev-rules-for-usb-devices.html),

`$ `<span style="font-weight:bold; background:#ffffd0;">`lsusb`</span>
`Bus 005 Device 006: ID 0bda:0158 Realtek Semiconductor Corp. USB 2.0 multicard reader`
`Bus 005 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub`
`Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub`
`Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub`
`Bus 002 Device 003: ID 413c:2003 Dell Computer Corp. Keyboard`
`Bus 002 Device 002: ID 27b1:0001`
`Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub`
`Bus 001 Device 003: ID 27b1:0001`
`Bus 001 Device 002: ID 27b1:0001`
`Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub`

I'm going to take a guess at the new TAZ being one of the three lines
above which contain no human-readable vendor information (while the
other two lines will correspond to the known 3D printers in the space --
the ROSTOCK and MINI):

- Bus 002 Device 002: ID 27b1:0001
- Bus 001 Device 003: ID 27b1:0001
- Bus 001 Device 002: ID 27b1:0001

Testing two of them (Bus 001 Devices 003 and 002) yielded:

`$ `<span style="font-weight:bold; background:#ffffd0;">`udevadm info -a -p $(udevadm info -q path -n /dev/bus/usb/001/003) | \`
`   egrep "(7403431393835160C070|6403636363835110D101|640363534303516070A1|64032373833351906091)"`</span>
`   ATTR{ID_SERIAL}=="UltiMachine__ultimachine.com__RAMBo_64032373833351906091"`
`   ATTR{ID_SERIAL_SHORT}=="64032373833351906091"`

`$ `<span style="font-weight:bold; background:#ffffd0;">`udevadm info -a -p $(udevadm info -q path -n /dev/bus/usb/001/002) | \`
`   egrep "(7403431393835160C070|6403636363835110D101|640363534303516070A1|64032373833351906091)"`</span>
`   ATTR{ID_SERIAL}=="UltiMachine__ultimachine.com__RAMBo_7403431393835160C070"`
`   ATTR{ID_SERIAL_SHORT}=="7403431393835160C070"`

Note that the first `udevadm ...` yields a serial number that matches
Julia's serial number for the ROSTOCK and the second `udevadm ...`
matches that of the MINI.

Testing Bus 002 Device 002 did not match any of the existing numbers but
did provide a serial number with RAMBo in the name. Looking a the entire
output of the command,

`$ `<span style="font-weight:bold; background:#ffffd0;">`udevadm info -a -p $(udevadm info -q path -n /dev/bus/usb/002/002)`</span>

`Udevadm info starts with the device specified by the devpath and then`
`walks up the chain of parent devices. It prints for every device`
`found, all possible attributes in the udev rules key format.`
`A rule to match, can be composed by the attributes of the device`
`and the attributes from one single parent device.`

`  looking at device '//devices/pci0000:00/0000:00:1d.1/usb2/2-1':`
`    KERNEL=="2-1"`
`    SUBSYSTEM=="usb"`
`    DRIVER=="usb"`
`    ATTR{SUBSYSTEM}=="usb"`
`    ATTR{DRIVER}=="usb"`
`    ATTR{DEVTYPE}=="usb_device"`
`    ATTR{PRODUCT}=="27b1/1/1"`
`    ATTR{TYPE}=="2/0/0"`
`    ATTR{BUSNUM}=="002"`
`    ATTR{DEVNUM}=="002"`
`    ATTR{MAJOR}=="189"`
`    ATTR{MINOR}=="129"`
`    ATTR{USEC_INITIALIZED}=="3639901"`
`    ATTR{ID_VENDOR}=="UltiMachine__ultimachine.com_"`
`    ATTR{ID_VENDOR_ENC}=="UltiMachine\x20\x28ultimachine.com\x29"`
`    ATTR{ID_VENDOR_ID}=="27b1"`
`    ATTR{ID_MODEL}=="RAMBo"`
`    ATTR{ID_MODEL_ENC}=="RAMBo"`
`    ATTR{ID_MODEL_ID}=="0001"`
`    ATTR{ID_REVISION}=="0001"`
`    ATTR{ID_SERIAL}=="UltiMachine__ultimachine.com__RAMBo_6403335373035101E171"`
`    ATTR{ID_SERIAL_SHORT}=="6403335373035101E171"`
`    ATTR{ID_BUS}=="usb"`
`    ATTR{ID_USB_INTERFACES}==":020201:0a0000:"`

And so, the second `TAZ` line in
`/etc/udev/rules.d/80-printer-names.rules` gets commented out and

    SUBSYSTEM=="tty",  KERNEL=="ttyACM?", ATTRS{serial}=="6403335373035101E171", SYMLINK+="TAZ"      # Current

gets appended to the file (and the lines, rearranged). The end result:

`# You can modify it, as long as you keep each rule on a single`
`# line, and change only the value of the NAME= key.`
`#`
`# Last modified by Ubuntourist <ubuntourist@hacdc.org> 2019.01.21 (kjc) `
`#`
`# 2019.01.21 KJC - Updated the serial number of the TAZ to our current beastie`
`#`

`#SUBSYSTEM=="tty", KERNEL=="ttyACM?", ATTRS{serial}=="6403636363835110D101", SYMLINK+="TAZ"      # Oldest`
<span style="color:#7f0000; background:#d0d0d0;">`#SUBSYSTEM=="tty", KERNEL=="ttyACM?", ATTRS{serial}=="640363534303516070A1", SYMLINK+="TAZ"      # Older (Julia's)`</span>
<span style="color:#007f00; background:#ffffd0; font-weight:bold;">`SUBSYSTEM=="tty",  KERNEL=="ttyACM?", ATTRS{serial}=="6403335373035101E171", SYMLINK+="TAZ"      # Current`</span>
`SUBSYSTEM=="tty",  KERNEL=="ttyACM?", ATTRS{serial}=="64032373833351906091", SYMLINK+="ROSTOCK"`
`SUBSYSTEM=="tty",  KERNEL=="ttyACM?", ATTRS{serial}=="7403431393835160C070", SYMLINK+="MINI"`

Reboot (because I'm too lazy to figure out which service(s) I need to
restart) and done! I hope.

[Category: 3D Printers](Category:_3D_Printers "wikilink")