====== Persistent symlinks for devices with udev ======
  - Locate the device: ''/dev/usb/hiddev0''<code>root@misaka:~# ls /dev/usb/hiddev0  -l
crw------- 1 root root 180, 0 Dec 19 13:00 /dev/usb/hiddev0</code>
  - Get device characteristics from udev. <code>root@misaka:~# udevadm info --name=/dev/usb/hiddev0 --attribute-walk

...snip...
  
  looking at device '/devices/pci0000:00/0000:00:1d.1/usb9/9-2/9-2:1.0/usbmisc/hiddev0':
    KERNEL=="hiddev0"
    SUBSYSTEM=="usbmisc"
    DRIVER==""

  looking at parent device '/devices/pci0000:00/0000:00:1d.1/usb9/9-2/9-2:1.0':
    KERNELS=="9-2:1.0"
    SUBSYSTEMS=="usb"
    DRIVERS=="usbhid"
    ...snip...

  looking at parent device '/devices/pci0000:00/0000:00:1d.1/usb9/9-2':
    KERNELS=="9-2"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ...snip...
    ATTRS{idProduct}=="0002"
    ATTRS{idVendor}=="051d"
    ATTRS{ltm_capable}=="no"
    ATTRS{manufacturer}=="APC"
    ATTRS{maxchild}=="0"
    ATTRS{product}=="Back-UPS 650 FW:822.A3.I USB FW:A3"
    ...snip...
  
  ...snip...
</code>
  - Write ''udev'' rule <code - /etc/udev/rules.d/99-apcups.rules>
ACTION=="add", SUBSYSTEM=="usbmisc", ATTRS{idProduct}=="0002", ATTRS{idVendor}=="051d", SYMLINK+="apcups"
</code>
  - Reload ''udev'' <code>root@misaka:~# udevadm control --reload-rules</code>
  - Try rules <code>root@misaka:~# udevadm test --action=add $(udevadm info -q path -n /dev/usb/hiddev0)

... snip ...

LINK 'apcups' /etc/udev/rules.d/99-apcups.rules:1
handling device node '/dev/usb/hiddev0', devnum=c180:0, mode=0600, uid=0, gid=0
preserve permissions /dev/usb/hiddev0, 020600, uid=0, gid=0
preserve already existing symlink '/dev/char/180:0' to '../usb/hiddev0'
found 'c180:0' claiming '/run/udev/links/\x2fapcups'
creating link '/dev/apcups' to '/dev/usb/hiddev0'
creating symlink '/dev/apcups' to 'usb/hiddev0'
created db file '/run/udev/data/c180:0' for '/devices/pci0000:00/0000:00:1d.1/usb9/9-2/9-2:1.0/usbmisc/hiddev0'
ACTION=add
DEVLINKS=/dev/apcups
DEVNAME=/dev/usb/hiddev0
DEVPATH=/devices/pci0000:00/0000:00:1d.1/usb9/9-2/9-2:1.0/usbmisc/hiddev0
MAJOR=180
MINOR=0
SUBSYSTEM=usbmisc
UPOWER_BATTERY_TYPE=ups
UPOWER_VENDOR=APC
USEC_INITIALIZED=23088813
Unload module index
Unloaded link configuration context.</code>
  - Apply new rules <code>root@misaka:~# udevadm trigger --sysname-match=hiddev0 --action=add --verbose
/sys/devices/pci0000:00/0000:00:1d.1/usb9/9-2/9-2:1.0/usbmisc/hiddev0

root@misaka:~# ls /dev/apcups -l
lrwxrwxrwx 1 root root 11 Dec 20 01:00 /dev/apcups -> usb/hiddev0</code>

<spoiler |Complete udev output in step 2><code>root@misaka:~# udevadm info --name=/dev/usb/hiddev0 --attribute-walk

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/usb9/9-2/9-2:1.0/usbmisc/hiddev0':
    KERNEL=="hiddev0"
    SUBSYSTEM=="usbmisc"
    DRIVER==""

  looking at parent device '/devices/pci0000:00/0000:00:1d.1/usb9/9-2/9-2:1.0':
    KERNELS=="9-2:1.0"
    SUBSYSTEMS=="usb"
    DRIVERS=="usbhid"
    ATTRS{authorized}=="1"
    ATTRS{bAlternateSetting}==" 0"
    ATTRS{bInterfaceClass}=="03"
    ATTRS{bInterfaceNumber}=="00"
    ATTRS{bInterfaceProtocol}=="00"
    ATTRS{bInterfaceSubClass}=="00"
    ATTRS{bNumEndpoints}=="01"
    ATTRS{supports_autosuspend}=="1"

  looking at parent device '/devices/pci0000:00/0000:00:1d.1/usb9/9-2':
    KERNELS=="9-2"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{authorized}=="1"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bDeviceClass}=="00"
    ATTRS{bDeviceProtocol}=="00"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bMaxPacketSize0}=="8"
    ATTRS{bMaxPower}=="0mA"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bNumInterfaces}==" 1"
    ATTRS{bcdDevice}=="0106"
    ATTRS{bmAttributes}=="e0"
    ATTRS{busnum}=="9"
    ATTRS{configuration}==""
    ATTRS{devnum}=="2"
    ATTRS{devpath}=="2"
    ATTRS{idProduct}=="0002"
    ATTRS{idVendor}=="051d"
    ATTRS{ltm_capable}=="no"
    ATTRS{manufacturer}=="APC"
    ATTRS{maxchild}=="0"
    ATTRS{product}=="Back-UPS 650 FW:822.A3.I USB FW:A3"
    ATTRS{quirks}=="0x0"
    ATTRS{removable}=="unknown"
    ATTRS{serial}=="XXXXXXXXXXXX  "
    ATTRS{speed}=="1.5"
    ATTRS{urbnum}=="48204"
    ATTRS{version}==" 1.10"

  looking at parent device '/devices/pci0000:00/0000:00:1d.1/usb9':
    KERNELS=="usb9"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{authorized}=="1"
    ATTRS{authorized_default}=="1"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bDeviceClass}=="09"
    ATTRS{bDeviceProtocol}=="00"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bMaxPacketSize0}=="64"
    ATTRS{bMaxPower}=="0mA"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bNumInterfaces}==" 1"
    ATTRS{bcdDevice}=="0409"
    ATTRS{bmAttributes}=="e0"
    ATTRS{busnum}=="9"
    ATTRS{configuration}==""
    ATTRS{devnum}=="1"
    ATTRS{devpath}=="0"
    ATTRS{idProduct}=="0001"
    ATTRS{idVendor}=="1d6b"
    ATTRS{interface_authorized_default}=="1"
    ATTRS{ltm_capable}=="no"
    ATTRS{manufacturer}=="Linux 4.9.0-4-amd64 uhci_hcd"
    ATTRS{maxchild}=="2"
    ATTRS{product}=="UHCI Host Controller"
    ATTRS{quirks}=="0x0"
    ATTRS{removable}=="unknown"
    ATTRS{serial}=="0000:00:1d.1"
    ATTRS{speed}=="12"
    ATTRS{urbnum}=="24"
    ATTRS{version}==" 1.10"

  looking at parent device '/devices/pci0000:00/0000:00:1d.1':
    KERNELS=="0000:00:1d.1"
    SUBSYSTEMS=="pci"
    DRIVERS=="uhci_hcd"
    ATTRS{broken_parity_status}=="0"
    ATTRS{class}=="0x0c0300"
    ATTRS{consistent_dma_mask_bits}=="32"
    ATTRS{d3cold_allowed}=="0"
    ATTRS{device}=="0x3a35"
    ATTRS{dma_mask_bits}=="32"
    ATTRS{driver_override}=="(null)"
    ATTRS{enable}=="1"
    ATTRS{irq}=="19"
    ATTRS{local_cpulist}=="0-3,8-11"
    ATTRS{local_cpus}=="000f0f"
    ATTRS{msi_bus}=="1"
    ATTRS{numa_node}=="0"
    ATTRS{subsystem_device}=="0x0006"
    ATTRS{subsystem_vendor}=="0x15d9"
    ATTRS{vendor}=="0x8086"

  looking at parent device '/devices/pci0000:00':
    KERNELS=="pci0000:00"
    SUBSYSTEMS==""
    DRIVERS==""
</code></spoiler>

===== See Alsos =====
  * https://unix.stackexchange.com/questions/39370/how-to-reload-udev-rules-without-reboot
  * https://unix.stackexchange.com/questions/66901/how-to-bind-usb-device-under-a-static-name
  * https://unix.stackexchange.com/questions/394411/persistent-names-for-physical-usb-ports
  * https://github.com/signal11/hidapi/blob/master/udev/99-hid.rules

{{tag>udev}}