Explaining the "No working init found." boot hang message

:Authors: Andreas Mohr <andi at lisas period de> Cristian Souza <cristianmsbr at gmail period com>

This document provides some high-level reasons for failure (listed roughly in order of execution) to load the init binary.

1. Unable to mount root FS: Set "debug" kernel parameter (in bootloader config file or CONFIG_CMDLINE) to get more detailed kernel messages.

2. init binary doesn't exist on rootfs: 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).

3. Broken console device: 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=.

4. Binary exists but dependencies not available: 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.

5. Binary cannot be loaded: 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 a 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.