pythonudevpyudev

Finding only disk drives using pyudev

I'm looking to enumerate all hard disks on a computer using udev and specifically pyudev to enumerate everything:

import pyudev

context = pyudev.Context()

for device in context.list_devices(subsystem='block', DEVTYPE='disk'):
    print "{}, ({})".format(device.device_node, device.device_type)

This prints out the following:

/dev/sdb (disk)
/dev/sdc (disk)
/dev/sda (disk)
/dev/sr0 (disk)
/dev/loop0 (disk)
/dev/loop1 (disk)
/dev/loop2 (disk)
/dev/loop3 (disk)
/dev/loop4 (disk)
/dev/loop5 (disk)
/dev/loop6 (disk)
/dev/loop7 (disk)
/dev/ram0 (disk)
/dev/ram1 (disk)
/dev/ram10 (disk)
/dev/ram11 (disk)
/dev/ram12 (disk)
/dev/ram13 (disk)
/dev/ram14 (disk)
/dev/ram15 (disk)
/dev/ram2 (disk)
/dev/ram3 (disk)
/dev/ram4 (disk)
/dev/ram5 (disk)
/dev/ram6 (disk)
/dev/ram7 (disk)
/dev/ram8 (disk)
/dev/ram9 (disk)

Since I'm mainly concerned with actual drives and not optical disk drives, loopback devices, or ram devices, how can I filter my results down to only get real physical media?

Solution

  • Since udev only runs on Linux kernel (at least as of now), you could filter out by MAJOR number 8 which represents all SCSI/SATA disk driver based devices.

    for device in context.list_devices(MAJOR='8'):
    if (device.device_type == 'disk'):
        print "{}, ({})".format(device.device_node, device.device_type)

    On my system, your code outputs the following:

    /dev/sda, (disk)
/dev/sdf, (disk)
/dev/sdb, (disk)
/dev/sdc, (disk)
/dev/sdd, (disk)
/dev/sde, (disk)
/dev/sr0, (disk)
/dev/loop0, (disk)
/dev/loop1, (disk)
/dev/loop2, (disk)
/dev/loop3, (disk)
/dev/loop4, (disk)
/dev/loop5, (disk)
/dev/loop6, (disk)
/dev/loop7, (disk)

    After filtering by major number 8, I see the following output:

    /dev/sda, (disk)
/dev/sdf, (disk)
/dev/sdb, (disk)
/dev/sdc, (disk)
/dev/sdd, (disk)
/dev/sde, (disk)

    Note that you would also get USB hard drives and USB sticks in the list, since they also tend to use the same SCSI disk driver.

    I'm not really sure if IDE hard drives are mapped as sdX or hdX with the latest 2.6 or 3.x kernels. Do not have an IDE hard drive to verify and long since I have had one. :D

    UPDATE: The same device number page lists /dev/hdX to be the one used by IDE hard drives (and IDE cdroms too may be ?). If you want to filter these as well, I believe you could do something like this:

    for device in context.list_devices(DEVTYPE='disk'):
    major = device['MAJOR']
    if major == '8' or major == '3':
        print "{}, ({})".format(device.device_node, device.device_type)