How to identify persistently an external hard drive on Linux ?

The following command will help us to identify our hardware and will help us to write the udev conditions (adjust /sys/block/sdb/sdb1/ for your case): 

udevadm info --query all --path /sys/block/sdb/sdb1/ --attribute-walk

When my external hard drive is connected I get this : 

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 '/block/sdb/sdb1':
    KERNEL=="sdb1"
    SUBSYSTEM=="block"
    DRIVER==""
    ATTR{partition}=="1"
    ATTR{start}=="2048"
    ATTR{size}=="1250260992"
    ATTR{alignment_offset}=="0"
    ATTR{stat}=="      73       30      818      380        1        0        8        0        0      376      380"
    ATTR{inflight}=="       0        0"

  looking at parent device '/devices/pci0000:00/0000:00:1a.7/usb1/1-5/1-5:1.0/host6/target6:0:0/6:0:0:0/block/sdb':
    KERNELS=="sdb"
    SUBSYSTEMS=="block"
    DRIVERS==""
    ATTRS{range}=="16"
    ATTRS{ext_range}=="256"
    ATTRS{removable}=="0"
    ATTRS{ro}=="0"
    ATTRS{size}=="1250263728"
    ATTRS{alignment_offset}=="0"
    ATTRS{capability}=="52"
    ATTRS{stat}=="     100       33     1058      756        1        0        8        0        0      752      756"
    ATTRS{inflight}=="       0        0"

  looking at parent device '/devices/pci0000:00/0000:00:1a.7/usb1/1-5/1-5:1.0/host6/target6:0:0/6:0:0:0':
    KERNELS=="6:0:0:0"
    SUBSYSTEMS=="scsi"
    DRIVERS=="sd"
    ATTRS{device_blocked}=="0"
    ATTRS{type}=="0"
    ATTRS{scsi_level}=="3"
    ATTRS{vendor}=="SAMSUNG "
    ATTRS{model}=="HM641JI         "
    ATTRS{rev}=="    "
    ATTRS{state}=="running"
    ATTRS{timeout}=="30"
    ATTRS{iocounterbits}=="32"
    ATTRS{iorequest_cnt}=="0x76"
    ATTRS{iodone_cnt}=="0x76"
    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/usb1/1-5/1-5:1.0/host6/target6:0:0':
    KERNELS=="target6:0:0"
    SUBSYSTEMS=="scsi"
    DRIVERS==""

  looking at parent device '/devices/pci0000:00/0000:00:1a.7/usb1/1-5/1-5:1.0/host6':
    KERNELS=="host6"
    SUBSYSTEMS=="scsi"
    DRIVERS==""

  looking at parent device '/devices/pci0000:00/0000:00:1a.7/usb1/1-5/1-5:1.0':
    KERNELS=="1-5:1.0"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb-storage"
    ATTRS{bInterfaceNumber}=="00"
    ATTRS{bAlternateSetting}==" 0"
    ATTRS{bNumEndpoints}=="02"
    ATTRS{bInterfaceClass}=="08"
    ATTRS{bInterfaceSubClass}=="06"
    ATTRS{bInterfaceProtocol}=="50"
    ATTRS{modalias}=="usb:v152Dp2329d0100dc00dsc00dp00ic08isc06ip50"
    ATTRS{supports_autosuspend}=="0"
    ATTRS{interface}=="MSC Bulk-Only Transfer"

  looking at parent device '/devices/pci0000:00/0000:00:1a.7/usb1/1-5':
    KERNELS=="1-5"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{configuration}=="USB Mass Storage"
    ATTRS{bNumInterfaces}==" 1"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bmAttributes}=="c0"
    ATTRS{bMaxPower}=="  2mA"
    ATTRS{urbnum}=="374"
    ATTRS{idVendor}=="152d"
    ATTRS{idProduct}=="2329"
    ATTRS{bcdDevice}=="0100"
    ATTRS{bDeviceClass}=="00"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bDeviceProtocol}=="00"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bMaxPacketSize0}=="64"
    ATTRS{speed}=="480"
    ATTRS{busnum}=="1"
    ATTRS{devnum}=="4"
    ATTRS{version}==" 2.00"
    ATTRS{maxchild}=="0"
    ATTRS{quirks}=="0x0"
    ATTRS{authorized}=="1"
    ATTRS{manufacturer}=="JMicron"
    ATTRS{product}=="USB to ATA/ATAPI Bridge"
    ATTRS{serial}=="2390A02056FF"

  looking at parent device '/devices/pci0000:00/0000:00:1a.7/usb1':
    KERNELS=="usb1"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{configuration}==""
    ATTRS{bNumInterfaces}==" 1"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bmAttributes}=="e0"
    ATTRS{bMaxPower}=="  0mA"
    ATTRS{urbnum}=="49"
    ATTRS{idVendor}=="1d6b"
    ATTRS{idProduct}=="0002"
    ATTRS{bcdDevice}=="0206"
    ATTRS{bDeviceClass}=="09"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bDeviceProtocol}=="00"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bMaxPacketSize0}=="64"
    ATTRS{speed}=="480"
    ATTRS{busnum}=="1"
    ATTRS{devnum}=="1"
    ATTRS{version}==" 2.00"
    ATTRS{maxchild}=="6"
    ATTRS{quirks}=="0x0"
    ATTRS{authorized}=="1"
    ATTRS{manufacturer}=="Linux 2.6.32-5-686 ehci_hcd"
    ATTRS{product}=="EHCI Host Controller"
    ATTRS{serial}=="0000:00:1a.7"
    ATTRS{authorized_default}=="1"

  looking at parent device '/devices/pci0000:00/0000:00:1a.7':
    KERNELS=="0000:00:1a.7"
    SUBSYSTEMS=="pci"
    DRIVERS=="ehci_hcd"
    ATTRS{vendor}=="0x8086"
    ATTRS{device}=="0x3b3c"
    ATTRS{subsystem_vendor}=="0x1458"
    ATTRS{subsystem_device}=="0x5006"
    ATTRS{class}=="0x0c0320"
    ATTRS{irq}=="18"
    ATTRS{local_cpus}=="ffffffff"
    ATTRS{local_cpulist}=="0-31"
    ATTRS{modalias}=="pci:v00008086d00003B3Csv00001458sd00005006bc0Csc03i20"
    ATTRS{enable}=="1"
    ATTRS{broken_parity_status}=="0"
    ATTRS{msi_bus}==""
    ATTRS{companion}==""

  looking at parent device '/devices/pci0000:00':
    KERNELS=="pci0000:00"
    SUBSYSTEMS==""
    DRIVERS==""

Then I create a udev rules in this file /etc/udev/rules.d/backup.rules : 

ATTRS{vendor}=="SAMSUNG ", ATTRS{model}=="HM641JI         ", SYMLINK+="mygreathdd"

Notice that ATTRS{vendor} and ATTRS{model} are a copy/paste from the hdd description above.

SYMLINK+="mygreathdd" means that a persistent /dev/mygreathdd file will be created when I insert my external hard drive.

Let's try this rule :

Then it's easy to automount this disk and for example to use it for automatic backup.

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