[clug] Booting without a bootloader & alternatives to /init

Jeremy Kerr jk at ozlabs.org
Thu May 21 08:32:03 GMT 2009


> > If you're booting with an initrd, the kernel will try to run
> > /linuxrc if it can. If you're using initramfs, it will run /init.
> No, it won't.  Linux will run exactly the same set of things
> regardless of the root filesystem being a physical disk or a ramfs,
> and regardless of how it is populated.

init/main.c says otherwise. From my reading:

execute_command = "/init" (overridable with init=)
ramdisk_execute_command = "/init" (overridable with rdinit=)

  if there is no initramfs containing ramdisk_execute_command:
    ramdisk_execute_command = NULL
    -> prepare_namespace()
      -> initrd_load()
         -> handle_initrd()
              if there is an initrd present, execute its /linuxrc and
              wait for that to finish
  -> init_post()
    try to run init from ramdisk_execute_command
    try to run init from execute_command
    try to run init from /sbin/init
    try to run init from /etc/init
    try to run init from /bin/init
    try to run init from /bin/sh
    panic about not finding an init

Note that initramfs != initrd. Generally /linuxrc will set up the real 
root fs, handing control back to the kernel to then run the real init.

But the OP can probably ignore all that - just set up a script in 
/sbin/init to do the appropriate setup (eg, bring up network interfaces) 
and then exec the wanted app.



More information about the linux mailing list