How to find the driver (module) associated with a device on Linux?
To get this information from sysfs for a device file, first determine the major/minor number by looking at the output of ls -l, eg
$ ls -l /dev/sda
brw-rw---- 1 root disk 8, 0 Apr 17 12:26 /dev/sda
The 8, 0 tells us that major number is 8 and the minor is 0. The b at the start of the listing also tells us that it is a block device. Other devices may have a c for character device at the start.
If you then look under /sys/dev, you will see there are two directories. One called block and one called char. The no-brainer here is that these are for block and character devices respectively. Each device is then accessible by its major/minor number is this directory. If there is a driver available for the device, it can be found by reading the target of the driver link in this or the device sub-directory. Eg, for my /dev/sda I can simply do:
$ readlink /sys/dev/block/8\:0/device/driver
../../../../../../../bus/scsi/drivers/sd
This shows that the sd driver is used for the device. If you are unsure if the device is a block or character device, in the shell you could simply replace this part with a *. This works just as well:
$ readlink /sys/dev/*/8\:0/device/driver
../../../../../../../bus/scsi/drivers/sd
Block devices can also be accessed directly through their name via either /sys/block or /sys/class/block. Eg:
$ readlink /sys/block/sda/device/driver
../../../../../../../bus/scsi/drivers/sd
Note that the existence of various directories in /sys may change depending on the kernel configuration. Also not all devices have a device subfolder. For example, this is the case for partition device files like /dev/sda1. Here you have to access the device for the whole disk (unfortunately there are no sys links for this).
A final thing which can be useful to do is to list the drivers for all devices for which they are available. For this you can use globs to select all the directories in which the driver links are present. Eg:
$ ls -l /sys/dev/*/*/device/driver && ls -l /sys/dev/*/*/driver
lrwxrwxrwx 1 root root 0 Apr 17 12:27 /sys/dev/block/11:0/device/driver -> ../../../../../../../bus/scsi/drivers/sr
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/block/8:0/device/driver -> ../../../../../../../bus/scsi/drivers/sd
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/block/8:16/device/driver -> ../../../../../../../bus/scsi/drivers/sd
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/block/8:32/device/driver -> ../../../../../../../../../bus/scsi/drivers/sd
lrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:0/driver -> ../../../../bus/usb/drivers/usb
lrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:1024/driver -> ../../../../bus/usb/drivers/usb
lrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:128/driver -> ../../../../bus/usb/drivers/usb
lrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:256/driver -> ../../../../bus/usb/drivers/usb
lrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:384/driver -> ../../../../bus/usb/drivers/usb
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/189:512/driver -> ../../../../bus/usb/drivers/usb
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/189:513/driver -> ../../../../../bus/usb/drivers/usb
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/189:514/driver -> ../../../../../bus/usb/drivers/usb
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/189:640/driver -> ../../../../bus/usb/drivers/usb
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/189:643/driver -> ../../../../../bus/usb/drivers/usb
lrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:768/driver -> ../../../../bus/usb/drivers/usb
lrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:896/driver -> ../../../../bus/usb/drivers/usb
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/21:0/device/driver -> ../../../../../../../bus/scsi/drivers/sd
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/21:1/device/driver -> ../../../../../../../bus/scsi/drivers/sd
lrwxrwxrwx 1 root root 0 Apr 17 12:27 /sys/dev/char/21:2/device/driver -> ../../../../../../../bus/scsi/drivers/sr
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/21:3/device/driver -> ../../../../../../../../../bus/scsi/drivers/sd
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/250:0/device/driver -> ../../../../../../../bus/hid/drivers/hid-generic
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/250:1/device/driver -> ../../../../../../../bus/hid/drivers/hid-generic
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/250:2/device/driver -> ../../../../../../../bus/hid/drivers/hid-generic
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/252:0/device/driver -> ../../../../../../../bus/scsi/drivers/sd
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/252:1/device/driver -> ../../../../../../../bus/scsi/drivers/sd
lrwxrwxrwx 1 root root 0 Apr 17 12:27 /sys/dev/char/252:2/device/driver -> ../../../../../../../bus/scsi/drivers/sr
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/252:3/device/driver -> ../../../../../../../../../bus/scsi/drivers/sd
lrwxrwxrwx 1 root root 0 Apr 17 19:53 /sys/dev/char/254:0/device/driver -> ../../../bus/pnp/drivers/rtc_cmos
lrwxrwxrwx 1 root root 0 Apr 17 19:53 /sys/dev/char/29:0/device/driver -> ../../../bus/platform/drivers/simple-framebuffer
lrwxrwxrwx 1 root root 0 Apr 17 19:53 /sys/dev/char/4:64/device/driver -> ../../../bus/pnp/drivers/serial
lrwxrwxrwx 1 root root 0 Apr 17 19:53 /sys/dev/char/4:65/device/driver -> ../../../bus/platform/drivers/serial8250
lrwxrwxrwx 1 root root 0 Apr 17 19:53 /sys/dev/char/4:66/device/driver -> ../../../bus/platform/drivers/serial8250
lrwxrwxrwx 1 root root 0 Apr 17 19:53 /sys/dev/char/4:67/device/driver -> ../../../bus/platform/drivers/serial8250
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/6:0/device/driver -> ../../../bus/pnp/drivers/parport_pc
lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/99:0/device/driver -> ../../../bus/pnp/drivers/parport_pc
Finally, to diverge from the question a bit, I will add another /sys glob trick to get a much broader perspective on which drivers are being used by which devices (though not necessarily those with a device file):
find /sys/bus/*/drivers/* -maxdepth 1 -lname '*devices*' -ls
Update
Looking more closely at the output of udevadm, it appears to work by finding the canonical /sys directory (as you would get if you dereferenced the major/minor directories above), then working its way up the directory tree, printing out any information that it finds. This way you get information about parent devices and any drivers they use as well.
To experiment with this I wrote the script below to walk up the directory tree and display information at each relevant level. udev seems to look for readable files at each level, with their names and contents being incorporated in ATTRS. Instead of doing this I display the contents of the uevent files at each level (seemingly the presence of this defines a distinct level rather than just a subdirectory). I also show the basename of any subsystem links I find and this showing how the device fits in this hierarchy. udevadm does not display the same information, so this is a nice complementary tool. The parent device information (eg PCI information) is also useful if you want to match the output of other tools like lshw to higher level devices.
#!/bin/bash
dev=$(readlink -m $1)
# test for block/character device
if [ -b "$dev" ]; then
mode=block
elif [ -c "$dev" ]; then
mode=char
else
echo "$dev is not a device file" >&2
exit 1
fi
# stat outputs major/minor in hex, convert to decimal
data=( $(stat -c '%t %T' $dev) ) || exit 2
major=$(( 0x${data[0]} ))
minor=$(( 0x${data[1]} ))
echo -e "Given device: $1"
echo -e "Canonical device: $dev"
echo -e "Major: $major"
echo -e "Minor: $minor\n"
# sometimes nodes have been created for devices that are not present
dir=$(readlink -f /sys/dev/$mode/$major\:$minor)
if ! [ -e "$dir" ]; then
echo "No /sys entry for $dev" >&2
exit 3
fi
# walk up the /sys hierarchy one directory at a time
# stop when there are three levels left
while [[ $dir == /*/*/* ]]; do
# it seems the directory is only of interest if there is a 'uevent' file
if [ -e "$dir/uevent" ]; then
echo "$dir:"
echo " Uevent:"
sed 's/^/ /' "$dir/uevent"
# check for subsystem link
if [ -d "$dir/subsystem" ]; then
subsystem=$(readlink -f "$dir/subsystem")
echo -e "\n Subsystem:\n ${subsystem##*/}"
fi
echo
fi
# strip a subdirectory
dir=${dir%/*}
done
You can use the udevadm tool to discover this.
The command would be udevadm info -a -n /dev/sda, and then look at the DRIVER== parameters.
# udevadm info -a -n /dev/sda | grep -oP 'DRIVERS?=="\K[^"]+'
sd
ahci
This shows that there are actually 2 drivers involved in providing this device, sd and ahci. The first one, sd is directly responsible for the /dev/sda device, but it uses the ahci driver underneith.
The output of the udevadm command looks like this, and includes a description of how it works.
# udevadm info -a -n /dev/sda
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/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0/block/sda':
KERNEL=="sda"
SUBSYSTEM=="block"
DRIVER==""
ATTR{ro}=="0"
ATTR{size}=="500118192"
ATTR{stat}==" 84786 1420 3091333 40215 966488 12528 14804028 2357668 0 1146934 2396653"
ATTR{range}=="16"
ATTR{discard_alignment}=="0"
ATTR{events}==""
ATTR{ext_range}=="256"
ATTR{events_poll_msecs}=="-1"
ATTR{alignment_offset}=="0"
ATTR{inflight}==" 0 0"
ATTR{removable}=="0"
ATTR{capability}=="50"
ATTR{events_async}==""
looking at parent device '/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0/0:0:0:0':
KERNELS=="0:0:0:0"
SUBSYSTEMS=="scsi"
DRIVERS=="sd"
ATTRS{rev}=="VZJ4"
ATTRS{type}=="0"
ATTRS{scsi_level}=="6"
ATTRS{model}=="LITEONIT LMT-256"
ATTRS{state}=="running"
ATTRS{queue_type}=="simple"
ATTRS{iodone_cnt}=="0x10daad"
ATTRS{iorequest_cnt}=="0x10ead1"
ATTRS{queue_ramp_up_period}=="120000"
ATTRS{device_busy}=="0"
ATTRS{evt_capacity_change_reported}=="0"
ATTRS{timeout}=="30"
ATTRS{evt_media_change}=="0"
ATTRS{ioerr_cnt}=="0x2"
ATTRS{queue_depth}=="31"
ATTRS{vendor}=="ATA "
ATTRS{evt_soft_threshold_reached}=="0"
ATTRS{device_blocked}=="0"
ATTRS{evt_mode_parameter_change_reported}=="0"
ATTRS{evt_lun_change_reported}=="0"
ATTRS{evt_inquiry_change_reported}=="0"
ATTRS{iocounterbits}=="32"
ATTRS{eh_timeout}=="10"
looking at parent device '/devices/pci0000:00/0000:00:1f.2/ata1/host0/target0:0:0':
KERNELS=="target0:0:0"
SUBSYSTEMS=="scsi"
DRIVERS==""
looking at parent device '/devices/pci0000:00/0000:00:1f.2/ata1/host0':
KERNELS=="host0"
SUBSYSTEMS=="scsi"
DRIVERS==""
looking at parent device '/devices/pci0000:00/0000:00:1f.2/ata1':
KERNELS=="ata1"
SUBSYSTEMS==""
DRIVERS==""
looking at parent device '/devices/pci0000:00/0000:00:1f.2':
KERNELS=="0000:00:1f.2"
SUBSYSTEMS=="pci"
DRIVERS=="ahci"
ATTRS{irq}=="41"
ATTRS{subsystem_vendor}=="0x144d"
ATTRS{broken_parity_status}=="0"
ATTRS{class}=="0x010601"
ATTRS{enabled}=="1"
ATTRS{consistent_dma_mask_bits}=="64"
ATTRS{dma_mask_bits}=="64"
ATTRS{local_cpus}=="0f"
ATTRS{device}=="0x1e03"
ATTRS{msi_bus}==""
ATTRS{local_cpulist}=="0-3"
ATTRS{vendor}=="0x8086"
ATTRS{subsystem_device}=="0xc0d3"
ATTRS{numa_node}=="-1"
ATTRS{d3cold_allowed}=="1"
looking at parent device '/devices/pci0000:00':
KERNELS=="pci0000:00"
SUBSYSTEMS==""
DRIVERS==""
Use the command hwinfo and output model and driver. If there is no driver it will not be shown. For example for disks:
# hwinfo --block | grep -Ei "driver\:|model\:" Model: "Floppy Disk" Model: "FUJITSU MHZ2080B" Driver: "ahci", "sd" Model: "Partition" Model: "Partition" Model: "Partition" Model: "Generic Multi-Card" Driver: "ums-realtek", "sd" Model: "Realtek USB2.0-CRW" Driver: "ums-realtek"
For network cards:
# hwinfo --netcard | grep -Ei "driver\:|model\:" Model: "Broadcom NetXtreme BCM5764M Gigabit Ethernet PCIe" Driver: "tg3" Model: "Intel Wireless WiFi Link 5100" Driver: "iwlwifi"
For USB devices:
# hwinfo --usb | grep -Ei "driver\:|model\:" Model: "Linux 3.11.10-7-desktop uhci_hcd UHCI Host Controller" Driver: "hub" Model: "Linux 3.11.10-7-desktop uhci_hcd UHCI Host Controller" Driver: "hub" Model: "IDEACOM IDC 6680" Driver: "usbhid" [...]
Use hwinfo --help to find out what other device types you can query. hwinfo is installed by default e.g. on SUSE Linux.