Chapter - Raspberry Pi User Manual

54
The Linux kernel is a single file located in the
the Pi is first switched on and begins to load the operating system, it looks for this file, and if
the file is missing, the Pi won't work . The emergency kernel is a second file, again in the
boot
The emergency kernel is, in most cases, almost identical to the standard kernel . When
changes are made to the standard kernel, to boost performance or add new features for
example, the emergency kernel is left unaltered . This way, if the changes to the standard
kernel cause stability problems, a user can simply tell the Pi to load the emergency kernel
instead .
There are two ways to boot into the emergency kernel, and both require the use of a PC and
an SD card reader if the Pi can't boot . Otherwise, the following can be carried out on the Pi
itself .
The easiest way to boot the emergency kernel is to rename the existing
kernel.img.bak
When the Pi loads, it will now load the emergency kernel by default . To go back to the stan-
dard kernel, simply reverse the process: rename
and
An alternative method to load the emergency kernel is to edit the
in the
line:
kernel=kernel_emergency.img
This tells the Pi that it should load the kernel named
the usual
and removing the entry .
You'll learn more about
in Chapter 6, "Configuring the Raspberry Pi" .
R A S P B E R R Y P I
directory, called
kernel_emergency.img
, and then rename the
to
kernel.img.bak kernel.img
directory) by adding the following entry at the end of the existing command
/boot
. Reversing the process is as simple as opening
kernel.img
cmdline.txt
U S E R G U I D E
directory called
/boot
.
kernel_emergency.img
to
kernel.img
.
kernel_emergency.img
and how it affects the operation of the Raspberry Pi
. When
kernel.img
file to
kernel.img
file to
kernel.img
kernel_emergency.img
file (located
cmdline.xt
instead of
again
cmdline.txt
/
.