Hardware Reference
In-Depth Information
his will print out the entire kernel ring bufer, which will contain all messages output by the
kernel since the Pi was switched on. If the Pi has been running a while, that can be a lot of
text. To locate error message particular to the wireless adapter, it can help to send the output
of
dmesg
through a tool called
grep
. Using
grep
, you can search through the bufer for text
relating to missing irmware. By
piping
the output of
dmesg
through
grep
with a search
term, things become signiicantly clearer. Type the following at the terminal:
dmesg | grep ^usb
he
|
symbol is known as a
pipe
, and tells Linux to send the output of one program—which
would normally go to a ile or the screen—to the input of another. Multiple programs can be
chained this way. In this example,
grep
is being told to search through the output of
dmesg
—the screens full of text from the earlier command—for any use of the term
usb
at
the start of the line (denoted by the
^
character).
he exact output of that search will depend on the manufacturer of your USB wireless
adapter. In Figure 4-3, the output is shown with a Zyxel NWD2015 Wireless USB Adapter
connected to the Pi.
Figure 4-3:
Searching the
kernel ring
bufer for
usb
with a Zyxel
wireless adapter
connected
