1Explaining the "No working init found." boot hang message
2=========================================================
3:Authors: Andreas Mohr <andi at lisas period de>
4          Cristian Souza <cristianmsbr at gmail period com>
5
6This document provides some high-level reasons for failure
7(listed roughly in order of execution) to load the init binary.
8
91) **Unable to mount root FS**: Set "debug" kernel parameter (in bootloader
10   config file or CONFIG_CMDLINE) to get more detailed kernel messages.
11
122) **init binary doesn't exist on rootfs**: Make sure you have the correct
13   root FS type (and ``root=`` kernel parameter points to the correct
14   partition), required drivers such as storage hardware (such as SCSI or
15   USB!) and filesystem (ext3, jffs2, etc.) are builtin (alternatively as
16   modules, to be pre-loaded by an initrd).
17
183) **Broken console device**: Possibly a conflict in ``console= setup``
19   --> initial console unavailable. E.g. some serial consoles are unreliable
20   due to serial IRQ issues (e.g. missing interrupt-based configuration).
21   Try using a different ``console= device`` or e.g. ``netconsole=``.
22
234) **Binary exists but dependencies not available**: E.g. required library
24   dependencies of the init binary such as ``/lib/ld-linux.so.2`` missing or
25   broken. Use ``readelf -d <INIT>|grep NEEDED`` to find out which libraries
26   are required.
27
285) **Binary cannot be loaded**: Make sure the binary's architecture matches
29   your hardware. E.g. i386 vs. x86_64 mismatch, or trying to load x86 on ARM
30   hardware. In case you tried loading a non-binary file here (shell script?),
31   you should make sure that the script specifies an interpreter in its
32   shebang header line (``#!/...``) that is fully working (including its
33   library dependencies). And before tackling scripts, better first test a
34   simple non-script binary such as ``/bin/sh`` and confirm its successful
35   execution. To find out more, add code ``to init/main.c`` to display
36   kernel_execve()s return values.
37
38Please extend this explanation whenever you find new failure causes
39(after all loading the init binary is a CRITICAL and hard transition step
40which needs to be made as painless as possible), then submit a patch to LKML.
41Further TODOs:
42
43- Implement the various ``run_init_process()`` invocations via a struct array
44  which can then store the ``kernel_execve()`` result value and on failure
45  log it all by iterating over **all** results (very important usability fix).
46- Try to make the implementation itself more helpful in general, e.g. by
47  providing additional error messages at affected places.
48
49