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1 | Explaining the dreaded "No init found." boot hang message |
2 | ========================================================= | |
3 | ||
4 | OK, so you've got this pretty unintuitive message (currently located | |
5 | in init/main.c) and are wondering what the H*** went wrong. | |
6 | Some high-level reasons for failure (listed roughly in order of execution) | |
7 | to load the init binary are: | |
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9 | A) Unable to mount root FS |
10 | B) init binary doesn't exist on rootfs | |
11 | C) broken console device | |
12 | D) binary exists but dependencies not available | |
13 | E) binary cannot be loaded | |
14 | ||
15 | Detailed explanations: | |
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16 | |
17 | A) Set "debug" kernel parameter (in bootloader config file or CONFIG_CMDLINE) | |
9a85b8d6 | 18 | to get more detailed kernel messages. |
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19 | B) make sure you have the correct root FS type |
20 | (and ``root=`` kernel parameter points to the correct partition), | |
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21 | required drivers such as storage hardware (such as SCSI or USB!) |
22 | and filesystem (ext3, jffs2 etc.) are builtin (alternatively as modules, | |
23 | to be pre-loaded by an initrd) | |
8887adde | 24 | C) Possibly a conflict in ``console= setup`` --> initial console unavailable. |
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25 | E.g. some serial consoles are unreliable due to serial IRQ issues (e.g. |
26 | missing interrupt-based configuration). | |
8887adde | 27 | Try using a different ``console= device`` or e.g. ``netconsole=``. |
9a85b8d6 | 28 | D) e.g. required library dependencies of the init binary such as |
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29 | ``/lib/ld-linux.so.2`` missing or broken. Use |
30 | ``readelf -d <INIT>|grep NEEDED`` to find out which libraries are required. | |
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31 | E) make sure the binary's architecture matches your hardware. |
32 | E.g. i386 vs. x86_64 mismatch, or trying to load x86 on ARM hardware. | |
33 | In case you tried loading a non-binary file here (shell script?), | |
34 | you should make sure that the script specifies an interpreter in its shebang | |
8887adde | 35 | header line (``#!/...``) that is fully working (including its library |
9a85b8d6 | 36 | dependencies). And before tackling scripts, better first test a simple |
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37 | non-script binary such as ``/bin/sh`` and confirm its successful execution. |
38 | To find out more, add code ``to init/main.c`` to display kernel_execve()s | |
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39 | return values. |
40 | ||
41 | Please extend this explanation whenever you find new failure causes | |
42 | (after all loading the init binary is a CRITICAL and hard transition step | |
43 | which needs to be made as painless as possible), then submit patch to LKML. | |
44 | Further TODOs: | |
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45 | |
46 | - Implement the various ``run_init_process()`` invocations via a struct array | |
47 | which can then store the ``kernel_execve()`` result value and on failure | |
48 | log it all by iterating over **all** results (very important usability fix). | |
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49 | - try to make the implementation itself more helpful in general, |
50 | e.g. by providing additional error messages at affected places. | |
51 | ||
52 | Andreas Mohr <andi at lisas period de> |