Preboot & Early-Userspace

Introduction:

Early-Userspace is the term used to describe the intramfs capability of kernel 2.6. Kernel 2.6 has the ability to mount a ram filesystem populated by a special initrd image or an image compiled into the kernel.

IDMS Linux makes use of a default compiled in image to locate the root filesystem, mounts it and pass control over to init. By default if the root filesystem cannot be mounted, IDMS Linux will drop to an emergency console.

You can customize this image to perform emergency operations, initialize various things such as a crypto root or to even install IDMS Linux.

Preboot Options

Preboot options are specified on the boot loader commandline. Below is a list of options available.

emergency

Drop to emergency preboot environment before loading hardware controller modules or doing any scans.

raid=autodetect

Request kernel to do software RAID autodetection.

nolvm

Do not scan for LVM volumes.

noresume

Do not resume from previously hibernated state. DANGEROUS.

usb

Probe usb controllers and usb devices during preboot.

autoconfig=xyz

Auto configuration of network and system. Here is an example, not all items are required.
device:eth0 ,module:e1000, ip:192.168.1.1,netmask: 255.255.255.0 ,gw:192.168.1.254, nameserver :192.168.1.254, root:mypass

System Scripts

/init-storage-controllers

Load the modules for the various storage controllers in the order of IDE => SCSI => SATA.

/init-raid

Auto-scan for software RAID devices.

/init-lvm

Scan and activate LVM volumes.

/init-resume

If we were hibernated, resume.

Customization

The preboot image can be customized in various ways. The easiest is to append a cpio archive to the end of the preboot image.

There are a few files which are of interest that can be included in the image...

/pre-custom

Exectued after the preboot image is extracted and after udev is started, but before the disk controllers are initialized.

/post-custom

Executed after the disk controllers are initialized.

/exec-custom

Pass control from preboot over to this script after post-custom. exec is used.

/emergency-custom

Executed in emergency mode instead of /sbin/init

/passwords

Plain text file containing passwords to be set in the pre-boot environment. The format is username:password

This file is removed straight after the passwords are set.

/etc/modules.conf

1 modules name per line. These are loaded during init when entering the pre-boot image.

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