Overview of the SPARC Boot Architecture

The boot processes on the SPARC platform have been redesigned and improved to increase commonality with the x86 boot experience. The SPARC boot design enables the addition of new features, for example new file system types, without necessitating any changes to multiple portions of the boot chain. Changes also include the implementation of boot phase independence.

Highlights of these improvements include:

• Commonality in boot processes on the SPARC and x86 platforms

• Commonality in the network boot experience

• Boot architecture flexibility that enables booting a system from different file system types more easily

The following four boot phases are now independent of each other:

1. Open Boot PROM (OBP) phase

   The OBP phase of the boot process on the SPARC platform is unchanged.

   For disk devices, the firmware driver usually uses the OBP label package's load method, which parses the VTOC label at the beginning of the disk to locate the specified partition. Sectors 1-15 of the partition are then read into the system's memory. This area is commonly called the boot block and usually contains a file system reader.

2. Booter phase

   During this phase the boot archive is read and executed. Note that this is the only phase of the boot process that requires knowledge of the boot file system format. Protocols that are used for the transfer of the boot loader and the boot archive include local disk access, NFS, and HTTP.

3. Ramdisk phase

   The ramdisk is a boot archive that is comprised of kernel modules any other components that are required to boot an instance of Oracle Solaris..

   The SPARC boot archive is identical to an x86 boot archive. The boot archive file system format is private. Therefore, knowledge of the file system type that is used during a system boot, for example an HSFS file system, is not required by the booter or the kernel. The ramdisk extracts the kernel image from the boot archive and then executes it.

4. Kernel phase

   The kernel phase is the final stage of the boot process. During this phase, Oracle Solaris is initialized and a minimal root file system is mounted on the ramdisk that was constructed from the boot archive. In some environments, such as an installation, the ramdisk is used as the root (/) file system and remains mounted.The ramdisk contains a set of kernel files and drivers that is sufficient to mount the root file system on the specified root device.

   The kernel then extracts the remainder of the primary modules from the boot archive, initializes itself, mounts the real root file system, then discards the boot archive.

Support for Booting Multiple Kernels

On SPARC based systems, when you boot the system from the ok prompt, the default boot device is automatically selected. An alternate boot device can be specified by changing the NVRAM variable for the boot-device. You can also specify an alternate boot device or an alternate kernel (boot file) from the command line at boot time. See SPARC: How to Boot a Kernel Other Than the Default Kernel.

Implementation of the Boot Archives on SPARC

The boot archives, previously only available on the x86 platform, are now an integral part of the SPARC boot architecture.

The bootadm command has been modified for use on the SPARC platform. This command functions the same as it does on the x86 platform. The bootadm command handles the details of archive update and verification. On the x86 platform the bootadm command updates the GRUB menu during an installation or system upgrade. You can also use the bootadm command to manually manage the boot archives.

The boot archive service is managed by the Service Management Facility (SMF). The service instance for the boot archive is svc:/system/boot-archive:default. To enable, disable, or refresh this service use the svcadm command. For information about managing services by using SMF, see Chapter 11, Managing Services (Overview).

The files that are included in the SPARC boot archives are located in the /platform directory.

The contents of the /platform directory is divided into two groups of files:

• Files that are required for a sun4u boot archive

• Files that are required for sun4v boot archive

For information about managing the boot archives, see Managing the Oracle Solaris Boot Archives (Task Map).