Udev

If you want to match /dev/devicename to a device you own (such as a usb hard drive or usb hard disk) you can use udevinfo to find out what attributes you can map to:

udevinfo -a -p $(udevinfo -q path -n /dev/sdh1)

This will show several devices. You can only match rules from 1 parent device, not from multiple ones!

eg some of the output for above is:

looking at parent device '/devices/pci0000:00/0000:00:1a.7/usb4/4-4/4-4:1.0/ho                     st3/target3:0:0/3:0:0:0':
   KERNELS=="3:0:0:0"
   SUBSYSTEMS=="scsi"
   DRIVERS=="sd"
   ATTRS{device_blocked}=="0"
   ATTRS{type}=="0"
   ATTRS{scsi_level}=="3"
   ATTRS{vendor}=="Iomega  "
   ATTRS{model}=="External HD     "
   ATTRS{rev}=="    "
   ATTRS{state}=="running"
   ATTRS{timeout}=="30"
   ATTRS{iocounterbits}=="32"
   ATTRS{iorequest_cnt}=="0x3d"
   ATTRS{iodone_cnt}=="0x3d"
   ATTRS{ioerr_cnt}=="0x0"
   ATTRS{modalias}=="scsi:t-0x00"
   ATTRS{evt_media_change}=="0"
   ATTRS{queue_depth}=="1"
   ATTRS{queue_type}=="none"
   ATTRS{max_sectors}=="240"

looking at parent device '/devices/pci0000:00/0000:00:1a.7/usb4/4-4':
   KERNELS=="4-4"
   SUBSYSTEMS=="usb"
   DRIVERS=="usb"
   ATTRS{configuration}=="USB Mass Storage"
   ATTRS{bNumInterfaces}==" 1"
   ATTRS{bConfigurationValue}=="1"
   ATTRS{bmAttributes}=="c0"
   ATTRS{bMaxPower}=="  2mA"
   ATTRS{urbnum}=="287"
   ATTRS{idVendor}=="059b"
   ATTRS{idProduct}=="0276"
   ATTRS{bcdDevice}=="0100"
   ATTRS{bDeviceClass}=="00"
   ATTRS{bDeviceSubClass}=="00"
   ATTRS{bDeviceProtocol}=="00"
   ATTRS{bNumConfigurations}=="1"
   ATTRS{bMaxPacketSize0}=="64"
   ATTRS{speed}=="480"
   ATTRS{busnum}=="4"
   ATTRS{devnum}=="4"
   ATTRS{version}==" 2.00"
   ATTRS{maxchild}=="0"
   ATTRS{quirks}=="0x0"
   ATTRS{authorized}=="1"
   ATTRS{manufacturer}=="Iomega"
   ATTRS{product}=="Iomega External HD"
   ATTRS{serial}=="948778888888"

allows you to construct the following rules to match the device: KERNEL=="sd?1", SUBSYSTEMS=="scsi", ATTRS{model}=="External HD ", SYMLINK+="test" KERNEL=="sd?1", SUBSYSTEMS=="usb", ATTRS{serial}=="948778888888", SYMLINK+="iomega1"

Both will work. You only have to use one.

I put these in /etc/udev/rules.d/local.rules

/etc/init.d/udev restart

and then you have to unplug and replug the device for the symlink to appear in /dev (so /dev/iomega1 or /dev/test)

This can all be found here