Hardware Reference
In-Depth Information
This will print out the entire kernel ring buffer, 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 messages particular to the wireless adapter, it can help to send the out-
put of
dmesg
through a tool called
grep
. Using
grep
, you can search through the buffer for
text relating to missing firmware. By
piping
the output of
dmesg
through
grep
with a search
term, things become significantly clearer. Type the following at the terminal:
dmesg -t | grep ^usb
he
|
symbol is known as a
pipe
, and it tells Linux to send the output of one program—which
would normally go to a file 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
)
.
The exact output of that search will depend on the manufacturer of your USB wireless
adapter. In Figure 5-3, the output is shown with a Zyxel NWD2015 Wireless USB Adapter
connected to the Pi.
Figure 5-3:
Searching the
kernel ring
buffer for usb
with a Zyxel
wireless adapter
connected
