You have plugged in a USB device and want to make sure Linux recognizes it.
Use the lsusb command. This will list all the devices attached to the USB ports on your Raspberry Pi:
$ lsusb Bus 001 Device 002: ID 0424:9512 Standard Microsystems Corp. Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. Bus 001 Device 004: ID 15d9:0a41 Trust International B.V. MI-2540D [Optical mouse] |
Discussion
This command will tell you whether a device is connected or not, but it will not guarantee that it is working correctly. There may be drivers to install or configuration changes to make for the hardware.
See Also
For an example of using lsusb when attaching an external webcam, see Recipe 4.5.