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