Linux – What driver is behind a certain device file

block-devicedevicesdriverslinux

Given a device file, say /dev/sdb, is it possible to determine what driver is behind it?

Specifically, I want to determine what driver my storage devices are using. fdisk -l lists 2 devices: /dev/sda and /dev/sdb. One is a SATA hard drive and the other is a USB Mass Storage device – actually an SD card.

How do I determine, programmatically, which is which?

I am writing a piece of software, and I want to protect the beginner from obliterating their hard drives, whilst allowing them to obliterate their SD cards.

Best Answer

Run udevadm info -a -n /dev/sda and parse the output. You'll see lines like

DRIVERS=="ahci"

for a SATA disk using the ahci driver, or

DRIVERS=="usb-storage"

for an USB-connected device. You'll also be able to display vendor and model names for confirmation. Also,

ATTR{removable}=="1"

is present on removable devices.

All of this information can also be obtained through /sys (in fact, that's where udevadm goes to look), but the /sys interface changes from time to time, so parsing udevadm is more robust in the long term.

Related Solutions

How to prevent /sda /sdb changes between boots

Most filesystems have unique UUIDs and have labels which you can set to a distinctive values. These allow you to refer to the volume containing the filesystem through /dev/disk/by-uuid or /dev/disk/by-label. Other types of volumes (RAID, LVM, etc.) generally have a name as well. RAID and LVM volumes are assembled based on unique identifiers in the physical volumes, regardless of how the volume is connected. So it's unusual to need to refer to a disk as such.

If you really need to access a disk based on the way it's connected, you can use /dev/disk/by-id. Entries there are of the form BUS-SERIAL or BUS-NAME-SERIAL. All the /dev/disk/ subdirectories are maintained by udev, by the way, specifically the persistent storage rules.

Another solution is to create your own symbolic links under /dev. You can write udev rules to do this. Add a file /etc/udev/rules.d/50-local-persistent-disks.rules containing rules like

SUBSYSTEM=="block", ATTRS{model}=="Yoyodine HD9001", \
  ATTRS{serial}=="123-456-789", \
  SYMLINK+="myfancyname"

Run udevadm info -a /dev/sda to see what …==… patterns you can use. If you use multiple patterns, they have to be from the same output block, you can't mix patterns from different parent devices.

Linux Terminology – Correct Term for ‘sda’ in ‘/dev/sda’

sda is the device name. /dev/sda is the device path.

Think of /sbin/fdisk, fdisk is the file name, while /sbin/fdisk is the file path.

Best Answer

Related Solutions

How to prevent /sda /sdb changes between boots

Linux Terminology – Correct Term for ‘sda’ in ‘/dev/sda’

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