14.2.2 USB Device and Device File
14.2.2.1 USB Device and “/dev” File
A USB device is a bus type device. In Raspberry Pi system, USB device is managed by “/dev/bus/usb” folder. If you look inside the 001 folder, you will see the following files. File names are in the form of 001 ~ 016, which means the device number of USB device. You can see that you have a one-to-one correspondence with the USB device that you inquired before with the “lsusb” command.
14.2 USB Device
14.2.1 “lsusb” Command – Confirm USB Device
You can use the “lsusb” command to see what USB devices are installed in Raspberry Pi system.
14.1.4 Network Device
14.1.4.1 Characteristics of Network Device
In Linux, a network device is thought of as an entity that sends and receives data packets. A network device is usually a physical device, such as an Ethernet card. However, there are some network devices defined with only software, such as loopback device that is used to send data to itself.
14.1.3 Block Device
14.1.3.1 Block Device Characteristics
The block device inputs and outputs data in unit of block when processing data in the device, and increases the processing performance by placing a intermediate buffer.
14.1.2 Character Device
14.1.2.1 Charateristics
The character device is the simplest of all Linux devices, and it inputs and outputs data in character unit when processing data in the device, and there is no intermediate buffer.
14.1 Device Overview
14.1.1 Device Type and “/dev” Directory
In the devices used in Linux, there are character device such as keyboards, block device such as disk, and network device such as Ethernet.
Chapter 14 Understanding Device
Chapter’s Main Topics
This charpter describes the various device available on Linux systems and the “/dev” file that contains information about these devices, and describes the characteristics of USB device.
It includes descriptions on the following topics:
■ Device type and “/dev” directory
■ Character device
■ Block device
■ Network device
■ Usb device
13.2.2 Changing Permissions on File
13.2.2.1 Changing Permission with “chmod” Command
To change processing permissions on a file, use the “chmod” command. This command specifies user scope, operation type, and permission type.
13.2 Changing Permission on File
13.2.1 Changing Owner User and Owner Group of File
13.2.1.1 “chown” Command – Change Owner User of File
To change the owner user of a file, use the “chown” command. You can change the owner user information, and if necessary, change the owner group for the file at the same time.
13.1.4 Permission System on File
The following is a subdivision of the permission information among the above information.
r
w
x
r
–
x
r
–
x
read
write
execute
read
write
execute
read
write
execute
owner user permission
owner group permission
other permission
The meaning of the permission granted to each user is as follows: