Chap8 Devices and UDEV

Question 1

udev

Answer 1

device manager for discovering hardware and peripheral devices both during system boot, and later when they are connected to the system.
- It is the successor of devfs and hotplug.

Question 2

device nodes

Answer 2

created automatically and then used by apps and o/s subsystems to communicate with and transfer data to and from devices

Question 3

Character (‘c’) Device

Answer 3

Driver communicates by sending and receiving single characters (bytes, octes) IE. serial ports, sound cards

Question 4

Block (‘b’) Device

Answer 4

Driver communicates by sending entire blocks of data IE. hard disks, USB cameras

Question 5

Character and Block devices have filesystem entries associated with them; which devices do not?

Answer 5

Network devices.
These devices work by transmitting and receiving packets, which must be constructed by breaking up streams of data and reassembled

Question 6

device driver

Answer 6

may manage multiple device nodes, which are normally placed in the /dev directory.

Question 7

Major and Minor

Answer 7

numbers identify the driver associated with the device. 179 = major 0,1,2=minor
ryan@s6261-pi3:/lib/modules$ ls -l /dev/mmcblk0*
brw-rw—- 1 root disk 179, 0 Feb 11 2016 /dev/mmcblk0
brw-rw—- 1 root disk 179, 1 Feb 11 2016 /dev/mmcblk0p1
brw-rw—- 1 root disk 179, 2 Feb 11 2016 /dev/mmcblk0p2
The minor number is used only by the device driver to differentiate between the different devices it my control. IE. 1 and 2 HDD partition

Question 8

The u in udev stands for?

Answer 8

user, and indicates that most of the work of creating, removing, and modifying device nodes is done in user-space

Question 9

Persistent Device Naming?

Answer 9

names need not depend on the order of device connection or plugging in. Controlled by udev rules

Question 10

library which allows access to information about the devices?

Answer 10

libudev

Question 11

2 daemons that manages the /dev directory?

Answer 11

udevd

systemd-udevd

Question 12

utility for control and diagnostics?

Answer 12

udevadm

Question 13

/etc/udev/udev.conf

Answer 13

the main config file contains information such as where to place device nodes, default permissions and ownership. (Mostly empty file on new systems)

Question 14

/etc/udev/rules.d

Answer 14

rules directory for device naming. IE. 30-usb.rules

Question 15

udevadm info command to check HDD

Answer 15

$ sudo udevadm info /dev/sda