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docs: admin-guide: Clarify sentences
Changes to make the text more formal and organized. The reasons are now cited and described at the same time.
Minor grammatical problems have also been fixed.
Signed-off-by: Cristian Souza <cristianmsbr@gmail.com>
Link: https://lore.kernel.org/r/20200411010201.GA22706@darkstar
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
authored by
Cristian Souza
and committed by
Jonathan Corbet
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Documentation/admin-guide/init.rst
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Documentation/admin-guide/init.rst
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Explaining the dreaded "No init found." boot hang message
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Explaining the "No working init found." boot hang message
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=========================================================
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:Authors: Andreas Mohr <andi at lisas period de>
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Cristian Souza <cristianmsbr at gmail period com>
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OK, so you've got this pretty unintuitive message (currently located
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in init/main.c) and are wondering what the H*** went wrong.
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Some high-level reasons for failure (listed roughly in order of execution)
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to load the init binary are:
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This document provides some high-level reasons for failure
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(listed roughly in order of execution) to load the init binary.
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A) Unable to mount root FS
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B) init binary doesn't exist on rootfs
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C) broken console device
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D) binary exists but dependencies not available
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E) binary cannot be loaded
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1) **Unable to mount root FS**: Set "debug" kernel parameter (in bootloader
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config file or CONFIG_CMDLINE) to get more detailed kernel messages.
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Detailed explanations:
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2) **init binary doesn't exist on rootfs**: Make sure you have the correct
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root FS type (and ``root=`` kernel parameter points to the correct
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partition), required drivers such as storage hardware (such as SCSI or
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USB!) and filesystem (ext3, jffs2, etc.) are builtin (alternatively as
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modules, to be pre-loaded by an initrd).
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A) Set "debug" kernel parameter (in bootloader config file or CONFIG_CMDLINE)
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to get more detailed kernel messages.
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B) make sure you have the correct root FS type
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(and ``root=`` kernel parameter points to the correct partition),
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required drivers such as storage hardware (such as SCSI or USB!)
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and filesystem (ext3, jffs2 etc.) are builtin (alternatively as modules,
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to be pre-loaded by an initrd)
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C) Possibly a conflict in ``console= setup`` --> initial console unavailable.
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E.g. some serial consoles are unreliable due to serial IRQ issues (e.g.
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missing interrupt-based configuration).
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3) **Broken console device**: Possibly a conflict in ``console= setup``
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--> initial console unavailable. E.g. some serial consoles are unreliable
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due to serial IRQ issues (e.g. missing interrupt-based configuration).
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Try using a different ``console= device`` or e.g. ``netconsole=``.
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D) e.g. required library dependencies of the init binary such as
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``/lib/ld-linux.so.2`` missing or broken. Use
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``readelf -d <INIT>|grep NEEDED`` to find out which libraries are required.
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E) make sure the binary's architecture matches your hardware.
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E.g. i386 vs. x86_64 mismatch, or trying to load x86 on ARM hardware.
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In case you tried loading a non-binary file here (shell script?),
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you should make sure that the script specifies an interpreter in its shebang
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header line (``#!/...``) that is fully working (including its library
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dependencies). And before tackling scripts, better first test a simple
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non-script binary such as ``/bin/sh`` and confirm its successful execution.
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To find out more, add code ``to init/main.c`` to display kernel_execve()s
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return values.
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4) **Binary exists but dependencies not available**: E.g. required library
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dependencies of the init binary such as ``/lib/ld-linux.so.2`` missing or
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broken. Use ``readelf -d <INIT>|grep NEEDED`` to find out which libraries
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are required.
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5) **Binary cannot be loaded**: Make sure the binary's architecture matches
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your hardware. E.g. i386 vs. x86_64 mismatch, or trying to load x86 on ARM
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hardware. In case you tried loading a non-binary file here (shell script?),
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you should make sure that the script specifies an interpreter in its
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shebang header line (``#!/...``) that is fully working (including its
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library dependencies). And before tackling scripts, better first test a
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simple non-script binary such as ``/bin/sh`` and confirm its successful
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execution. To find out more, add code ``to init/main.c`` to display
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kernel_execve()s return values.
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Please extend this explanation whenever you find new failure causes
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(after all loading the init binary is a CRITICAL and hard transition step
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which needs to be made as painless as possible), then submit patch to LKML.
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which needs to be made as painless as possible), then submit a patch to LKML.
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Further TODOs:
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- Implement the various ``run_init_process()`` invocations via a struct array
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which can then store the ``kernel_execve()`` result value and on failure
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log it all by iterating over **all** results (very important usability fix).
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- try to make the implementation itself more helpful in general,
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e.g. by providing additional error messages at affected places.
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- Try to make the implementation itself more helpful in general, e.g. by
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providing additional error messages at affected places.
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Andreas Mohr <andi at lisas period de>