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linux_course_doc/modules/qualifying/learning_udev.md

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adds udev doc and some placeholders
2021-08-20 12:03:36 +02:00
# udev
## What is udev?
Udev (userspace /dev) is a Linux sub-system for dynamic device detection and management, since kernel version 2.6. It’s a replacement of [devfs](https://wiki.debian.org/DevFS) and hotplug.
It dynamically creates or removes device nodes (an interface to a device driver that appears in a file system as if it were an ordinary file, stored under the /dev directory) at boot time or if you add a device to or remove a device from the system.
It then propagates information about a device or changes to its state to user space.
The goal of udev, as stated by the [project](https://www.linux.com/news/udev-introduction-device-management-modern-linux-system/) is:
* Run in user space.
* Create persistent device names, take the device naming out of kernel space and implement rule based device naming.
* Create a dynamic /dev with device nodes for devices present in the system and allocate major/minor numbers dynamically.
* Provide a user space API to access the device information in the system.
One of the pros of udev is that it can use persistent device names to guarantee consistent naming of devices across reboots, despite their order of discovery.
This feature is useful because the kernel simply assigns unpredictable device names based on the order of discovery.
## How does it work?
As udev runs in [userland](https://unix.stackexchange.com/questions/137820/whats-the-difference-of-the-userland-vs-the-kernel), it runs a service which on most modern distributions is controlled by [systemd](./learning_systemd.md).
If we have a look at our running processes and search for `udev` we find the following.
```
➜ ~ git:(master) ✗ ps aux | grep udev
root 430 0.0 0.0 23252 4164 ? Ss Aug06 0:01 /lib/systemd/systemd-udevd
waldek 11628 0.0 0.0 6208 896 pts/4 S+ 10:11 0:00 grep --color=auto --exclude-dir=.bzr --exclude-dir=CVS --exclude-dir=.git --exclude-dir=.hg --exclude-dir=.svn udev
➜ ~ git:(master) ✗
```
The first line hints us to a process run by root with a pretty low `PID`.
It seems to be part of the `systemd` *suite* of programs.
As always, let's have a look at the `man systemd-udevd` to learn what it is and how we can interact with it.
```
DESCRIPTION
systemd-udevd listens to kernel uevents. For every event, systemd-udevd executes matching instructions
specified in udev rules. See udev(7).
The behavior of the daemon can be configured using udev.conf(5), its command line options, environment
variables, and on the kernel command line, or changed dynamically with udevadm control.
```
The description is pretty solid and points us to a specific program we can use to *talk* to the daemon.
This is very similar to how we have been talking to `systemd` via `systemctl` but here, to talk to `systemd-udevd`, we'll use `udevadm`.
## Interacting with udev
### Monitoring events
To analyse what udev is receiving we can monitor it with `sudo udevadm monitor`.
You'll see see the following output with a *blinking* cursor on the last line to show we're monitoring *live*.
```
➜ ~ git:(master) ✗ sudo udevadm monitor
monitor will print the received events for:
UDEV - the event which udev sends out after rule processing
KERNEL - the kernel uevent
```
If we now **plug in** a device we'll see a bunch of messages arriving.
He I **added** a device by plugging it into the **USB** port.
You can see a lot of *sound* and *midi* messages so it's safe to say I plugged in a MIDI keyboard.
Do notice that once the keyboard is fully recognized and initialized by the system the messages stop.
Udev has done it's work and will remain silent until some changes happen to the system.
```
KERNEL[212709.657308] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2 (usb)
KERNEL[212709.657495] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0 (usb)
KERNEL[212709.657545] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1 (sound)
KERNEL[212709.657658] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/midiC1D0 (sound)
KERNEL[212709.657725] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/midi1 (sound)
KERNEL[212709.657774] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/dmmidi1 (sound)
KERNEL[212709.657801] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/seq-midi-1-0 (snd_seq)
KERNEL[212709.657829] bind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/seq-midi-1-0 (snd_seq)
KERNEL[212709.657910] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/controlC1 (sound)
KERNEL[212709.657967] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/mixer1 (sound)
KERNEL[212709.658046] bind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0 (usb)
KERNEL[212709.658086] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.1 (usb)
KERNEL[212709.658121] bind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.1 (usb)
KERNEL[212709.658166] bind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2 (usb)
UDEV [212709.673568] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2 (usb)
UDEV [212709.675863] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0 (usb)
UDEV [212709.676560] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.1 (usb)
UDEV [212709.677850] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1 (sound)
UDEV [212709.678004] bind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.1 (usb)
UDEV [212709.690171] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/midiC1D0 (sound)
UDEV [212709.690273] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/midi1 (sound)
KERNEL[212709.692086] change /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1 (sound)
UDEV [212709.692888] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/seq-midi-1-0 (snd_seq)
UDEV [212709.693659] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/mixer1 (sound)
UDEV [212709.694897] bind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/seq-midi-1-0 (snd_seq)
UDEV [212709.696017] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/dmmidi1 (sound)
UDEV [212709.705167] add /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/controlC1 (sound)
UDEV [212709.706615] bind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0 (usb)
UDEV [212709.710665] bind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2 (usb)
UDEV [212709.712669] change /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1 (sound)
```
When I **unplug** the MIDI keyboard we get the following output.
Notice the sequence of events here.
The kernel reports changes which udev uses to **trigger** events and actions.
```
KERNEL[213014.417312] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/mixer1 (sound)
KERNEL[213014.417546] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/controlC1 (sound)
KERNEL[213014.417574] unbind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/seq-midi-1-0 (snd_seq)
KERNEL[213014.417593] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/seq-midi-1-0 (snd_seq)
KERNEL[213014.417655] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/midi1 (sound)
KERNEL[213014.417711] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/dmmidi1 (sound)
KERNEL[213014.417782] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/midiC1D0 (sound)
KERNEL[213014.417808] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1 (sound)
KERNEL[213014.417837] unbind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0 (usb)
KERNEL[213014.417870] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0 (usb)
KERNEL[213014.417904] unbind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.1 (usb)
KERNEL[213014.417939] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.1 (usb)
KERNEL[213014.418036] unbind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2 (usb)
KERNEL[213014.418080] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2 (usb)
UDEV [213014.419887] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/controlC1 (sound)
UDEV [213014.420067] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/mixer1 (sound)
UDEV [213014.420472] unbind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/seq-midi-1-0 (snd_seq)
UDEV [213014.421955] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/seq-midi-1-0 (snd_seq)
UDEV [213014.422602] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/midiC1D0 (sound)
UDEV [213014.422717] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/midi1 (sound)
UDEV [213014.424188] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1/dmmidi1 (sound)
UDEV [213014.424383] unbind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.1 (usb)
UDEV [213014.425445] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.1 (usb)
UDEV [213014.425718] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/sound/card1 (sound)
UDEV [213014.427640] unbind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0 (usb)
UDEV [213014.430208] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0 (usb)
UDEV [213014.432609] unbind /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2 (usb)
UDEV [213014.438393] remove /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2 (usb)
```
**In virtualbox you can add or remove USB devices via the menu bar of you virtual machine.**
We can use `udevadm` for more than just monitoring.
Tab complete to the rescue!
```
➜ ~ git:(master) ✗ sudo udevadm
control -- control the udev daemon
info -- query sysfs or the udev database
monitor -- listen to kernel and udev events
settle -- wait for the event queue to finish
test -- test an event run
test-builtin -- test a built-in command
trigger -- request events from the kernel
```
You can query the help information of a specific sub command by adding the `--help` argument.
A full manual can be read via `man udevadm`.
```
➜ ~ git:(master) ✗ sudo udevadm monitor --help
udevadm monitor [OPTIONS]
Listen to kernel and udev events.
-h --help Show this help
-V --version Show package version
-p --property Print the event properties
-k --kernel Print kernel uevents
-u --udev Print udev events
-s --subsystem-match=SUBSYSTEM[/DEVTYPE] Filter events by subsystem
-t --tag-match=TAG Filter events by tag
➜ ~ git:(master) ✗
```
### Listing information
#### Via external programs
Udev can be used to query device information via the `info` subcommand but there are a few other programs that are very handy to know.
We'll focus on USB devices for now, but keep in mind that udev manages everything connected to our system.
My MIDI keyboad is **not** plugged in for now and below is the output of `lsusb`.
```
➜ ~ git:(master) ✗ lsusb
Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 003: ID 04f2:b217 Chicony Electronics Co., Ltd Lenovo Integrated Camera (0.3MP)
Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
➜ ~ git:(master) ✗
```
Next I plug it **in** and review the output of `lsusb`.
A device is added but it's not saying much!
This is vedor dependant and this company did not fully document it's device.
Most of the time however, you'll see a short description of the device.
```
➜ ~ git:(master) ✗ lsusb
Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 003: ID 04f2:b217 Chicony Electronics Co., Ltd Lenovo Integrated Camera (0.3MP)
Bus 001 Device 006: ID 2702:1110
Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
➜ ~ git:(master) ✗
```
The **hexadecimal** numbers you see listed are `VENDOR_ID:PROCUCT_ID` and can be used to digg deeper into a specific device.
For this we use the `-d VENDOR_ID:PROCUCT_ID` argument, together with `-v` for verbosity.
```
➜ ~ git:(master) ✗ lsusb -d 2702:1110 -v
Bus 001 Device 006: ID 2702:1110
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 1.10
bDeviceClass 0
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 64
idVendor 0x2702
idProduct 0x1110
bcdDevice 0.01
iManufacturer 0
iProduct 0
iSerial 0
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 0x0065
bNumInterfaces 2
bConfigurationValue 1
iConfiguration 0
bmAttributes 0x00
(Missing must-be-set bit!)
(Bus Powered)
MaxPower 100mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 1 Control Device
bInterfaceProtocol 0
iInterface 0
AudioControl Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 1 (HEADER)
bcdADC 1.00
wTotalLength 0x0009
bInCollection 1
baInterfaceNr(0) 1
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 0
bNumEndpoints 2
bInterfaceClass 1 Audio
bInterfaceSubClass 3 MIDI Streaming
bInterfaceProtocol 0
iInterface 0
MIDIStreaming Interface Descriptor:
bLength 7
bDescriptorType 36
bDescriptorSubtype 1 (HEADER)
bcdADC 1.00
wTotalLength 0x0041
MIDIStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (MIDI_IN_JACK)
bJackType 1 Embedded
bJackID 1
iJack 0
MIDIStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (MIDI_IN_JACK)
bJackType 2 External
bJackID 2
iJack 0
MIDIStreaming Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 3 (MIDI_OUT_JACK)
bJackType 1 Embedded
bJackID 3
bNrInputPins 1
baSourceID( 0) 2
BaSourcePin( 0) 1
iJack 0
MIDIStreaming Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 3 (MIDI_OUT_JACK)
bJackType 2 External
bJackID 4
bNrInputPins 1
baSourceID( 0) 1
BaSourcePin( 0) 1
iJack 0
Endpoint Descriptor:
bLength 9
bDescriptorType 5
bEndpointAddress 0x02 EP 2 OUT
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 0
bRefresh 0
bSynchAddress 0
MIDIStreaming Endpoint Descriptor:
bLength 5
bDescriptorType 37
bDescriptorSubtype 1 (GENERAL)
bNumEmbMIDIJack 1
baAssocJackID( 0) 1
Endpoint Descriptor:
bLength 9
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 0
bRefresh 0
bSynchAddress 0
MIDIStreaming Endpoint Descriptor:
bLength 5
bDescriptorType 37
bDescriptorSubtype 1 (GENERAL)
bNumEmbMIDIJack 1
baAssocJackID( 0) 3
can't get debug descriptor: Resource temporarily unavailable
Device Status: 0x0000
(Bus Powered)
➜ ~ git:(master) ✗
```
A USB stick presents itself as follows and offers quite a bit more information than our generic MIDI keyboard.
We get a unique serial number, speeds, power usage and more.
```
➜ ~ git:(master) ✗ lsusb -d 0781:5591 -v
Bus 001 Device 007: ID 0781:5591 SanDisk Corp. Ultra Flair
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.10
bDeviceClass 0
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 64
idVendor 0x0781 SanDisk Corp.
idProduct 0x5591 Ultra Flair
bcdDevice 1.00
iManufacturer 1 USB
iProduct 2 SanDisk 3.2Gen1
iSerial 3 0101afb5176b84241e77e68fb386ea23b31fe4cf9eafe43b465def85b4531ad93da300000000000000000000014b07c6ff8d260091558107b52921c2
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 0x0020
bNumInterfaces 1
bConfigurationValue 1
iConfiguration 0
bmAttributes 0x80
(Bus Powered)
MaxPower 224mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 2
bInterfaceClass 8 Mass Storage
bInterfaceSubClass 6 SCSI
bInterfaceProtocol 80 Bulk-Only
iInterface 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0200 1x 512 bytes
bInterval 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x02 EP 2 OUT
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0200 1x 512 bytes
bInterval 0
Binary Object Store Descriptor:
bLength 5
bDescriptorType 15
wTotalLength 0x0016
bNumDeviceCaps 2
USB 2.0 Extension Device Capability:
bLength 7
bDescriptorType 16
bDevCapabilityType 2
bmAttributes 0x00000002
HIRD Link Power Management (LPM) Supported
SuperSpeed USB Device Capability:
bLength 10
bDescriptorType 16
bDevCapabilityType 3
bmAttributes 0x00
wSpeedsSupported 0x000e
Device can operate at Full Speed (12Mbps)
Device can operate at High Speed (480Mbps)
Device can operate at SuperSpeed (5Gbps)
bFunctionalitySupport 1
Lowest fully-functional device speed is Full Speed (12Mbps)
bU1DevExitLat 10 micro seconds
bU2DevExitLat 256 micro seconds
can't get debug descriptor: Resource temporarily unavailable
Device Status: 0x0000
(Bus Powered)
➜ ~ git:(master) ✗
```
#### Via udevadm
We can get the same information via `udevadm` with the `info` subcommand.
We'll have to specify *which* device we want to query and this can be done via different identifiers.
The USB stick I inserted is still plugged in and represented in my filesystem via `/dev/sdc`.
Remember TAB complete!
```
➜ ~ git:(master) ✗ sudo udevadm info --path /sys/block/sdc
[sudo] password for waldek:
P: /devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/host6/target6:0:0/6:0:0:0/block/sdc
N: sdc
L: 0
S: disk/by-id/usb-USB_SanDisk_3.2Gen1_0101afb5176b84241e77e68fb386ea23b31fe4cf9eafe43b465def85b4531ad93da300000000000000000000014b07c6ff8d260091558107b52921c2-0:0
S: disk/by-path/pci-0000:00:1a.0-usb-0:1.2:1.0-scsi-0:0:0:0
E: DEVPATH=/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.2/1-1.2:1.0/host6/target6:0:0/6:0:0:0/block/sdc
E: DEVNAME=/dev/sdc
E: DEVTYPE=disk
E: MAJOR=8
E: MINOR=32
E: SUBSYSTEM=block
E: USEC_INITIALIZED=216426658045
E: ID_VENDOR=USB
E: ID_VENDOR_ENC=\x20USB\x20\x20\x20\x20
E: ID_VENDOR_ID=0781
E: ID_MODEL=SanDisk_3.2Gen1
E: ID_MODEL_ENC=\x20SanDisk\x203.2Gen1
E: ID_MODEL_ID=5591
E: ID_REVISION=1.00
E: ID_SERIAL=USB_SanDisk_3.2Gen1_0101afb5176b84241e77e68fb386ea23b31fe4cf9eafe43b465def85b4531ad93da300000000000000000000014b07c6ff8d260091558107b52921c2-0:0
E: ID_SERIAL_SHORT=0101afb5176b84241e77e68fb386ea23b31fe4cf9eafe43b465def85b4531ad93da300000000000000000000014b07c6ff8d260091558107b52921c2
E: ID_TYPE=disk
E: ID_INSTANCE=0:0
E: ID_BUS=usb
E: ID_USB_INTERFACES=:080650:
E: ID_USB_INTERFACE_NUM=00
E: ID_USB_DRIVER=usb-storage
E: ID_PATH=pci-0000:00:1a.0-usb-0:1.2:1.0-scsi-0:0:0:0
E: ID_PATH_TAG=pci-0000_00_1a_0-usb-0_1_2_1_0-scsi-0_0_0_0
E: ID_PART_TABLE_UUID=2ab572a6-8db9-4324-9d21-1a3640f4fb19
E: ID_PART_TABLE_TYPE=gpt
E: DEVLINKS=/dev/disk/by-id/usb-USB_SanDisk_3.2Gen1_0101afb5176b84241e77e68fb386ea23b31fe4cf9eafe43b465def85b4531ad93da300000000000000000000014b07c6ff8d260091558107b52921c2-0:0 /dev/disk/by-path/pci-0000:00:1a.0-usb-0:1.2:1.0-scsi-0:0:0:0
E: TAGS=:systemd:
➜ ~ git:(master) ✗
```
We can also inspect information about the **partions** on the disk, even without **mounting** them.
I'll spare you the output of the command but you would do `sudo udevadm info --name=/dev/sdc1` wich gives us the label, type of format, etc.
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