kernel是如何执行init守护进程的

static int __ref kernel_init(void *unused)
{
	kernel_init_freeable();
	/* need to finish all async __init code before freeing the memory */
	async_synchronize_full();
	free_initmem();
	mark_rodata_ro();
	system_state = SYSTEM_RUNNING;
	numa_default_policy();

	current->signal->flags |= SIGNAL_UNKILLABLE;
	flush_delayed_fput();

	if (ramdisk_execute_command) {
		if (!run_init_process(ramdisk_execute_command))
			return 0;
		printk(KERN_WARNING "Failed to execute %s\n",
				ramdisk_execute_command);
	}

	/*
	 * We try each of these until one succeeds.
	 *
	 * The Bourne shell can be used instead of init if we are
	 * trying to recover a really broken machine.
	 */
	if (execute_command) {
		if (!run_init_process(execute_command))
			return 0;
		printk(KERN_WARNING "Failed to execute %s.  Attempting "
					"defaults...\n", execute_command);
	}
	if (!run_init_process("/sbin/init") ||
	    !run_init_process("/etc/init") ||
	    !run_init_process("/bin/init") ||
	    !run_init_process("/bin/sh"))
		return 0;

	panic("No init found.  Try passing init= option to kernel. "
	      "See Linux Documentation/init.txt for guidance.");
}

由代码可知内核启动后，先查看ramdisk_execute_command是否被设置与是否可执行，如果不可执行则执行execute_command，如果还不可执行则按前后顺序探测执行（/sbin/init,/etc/init,/bin/init,/bin/sh）