Hardware Reference
In-Depth Information
Emergency Kernel
In the event that your Raspberry Pi does not boot up properly, an emergency kernel is
provided in
/boot
as file
kernel_emergency.img
. This kernel includes a BusyBox root
file system to provide recovery tools. Through use of
e2fsck
, you'll be able to repair your
normal Linux root file system. If necessary, you'll be able to mount that file system and
make changes with the BusyBox tools.
To activate the emergency kernel, mount your SD card in a Linux, Mac, or Windows
computer. Your computer should see the FAT32 partition, allowing you to rename files
and edit configurations. Rename your current
kernel.img
to something like
kernel.bak
(you likely want to restore this kernel image later). Then rename
kernel_emergency.img
as
kernel.img
.
If you have used special configuration options in
config.txt
and
cmdline.txt
,
you should copy these to
config.bak
and
cmdline.bak
, respectively. Then remove
any special options that might have caused trouble (especially overclocking options).
Alternatively, you can restore original copies of these two files, as provided by the
standard Raspbian image download.
■
Your Fat32 partition
(/boot
) probably has about 40 MB of free disk space (for a
standard raspbian disk image). renaming large files, rather than copying them, saves disk
space. Consequently, renaming kernel images is preferred over copying. Small files like
config.txt
or
cmdline.txt
can be copied as required.
Note
The entire procedure is summarized here:
Rename
kernel.img
to
kernel.bak
(retain the normal kernel).
1.
Rename
kernel_emergency.img
to
kernel.img
.
2.
Copy
config.txt
to
config.bak
.
3.
Copy
cmdline.txt
to
cmdline.bak
.
4.
Edit or restore
config.txt
and
cmdline.txt
to original or safe
configurations.
5.
Step 5 requires your own judgment. If you have customized hardware, there may be
some nonstandard configuration settings that you need to keep (see the previous “Avoid
Safe Mode” section). The idea is to simply give your emergency kernel as much chance
for success as possible. Disabling all overclocking options is also recommended.
