##Boot Process on Sparc Platforms.##
The boot process can be divided in 4 parts in Sparc Platforms. However the last three steps are common on the SPARC and x86 hardwares.
1. OpenBoot PROM phase
-The OpenBoot Program starts looking for a filesystem reader, it reads the partition map on the boot disk, called a VTOC , at sector 0 . The utility will find and load a file reader from sectors 0-15 , an area called the boot block.
-Now it can find and read the boot archive , a collection of configuration files and driver code that prepares the system to load and execute the kernel program.
Imp1 : We can override the values that are passed as defaults to the kernel by running "
boot -a "
Imp2:
We can also change the running state or the logging level of Solaris 11 system using "
boot -m "
boot -m milestone=<milestone> ( none | all | single-user |multi-user|multi-user-server ] -For setting run state.
boot -m [quiet|verbose|debug] --For Logging
##Boot Process on x86 Platforms.##
In x86 boot process the BIOS call the Master Boot Record (MBR) , 512-byte construct that includes support for a partition table and bootstrap code. The MBR provides support for multibooting, a practice of putting multiple operating systems on a single disk.
The x86 counterpart to the OBP boot utility is the GRUB(Grand Unified Boot Loader)
2. Booter phase
At this point the boot archive file gets read. it comes in a sequence before a file system is available, which is why system needs a special file reader, identified by bootfs variable , to begin with.
Imp: There are three important variables which are being passed.
-bootfs - Locates the file system reader. (variable value eg: rpool/ROOT/solaris)
-kernel -This variable locates the kernel program (variable value eg: /platform/i86pc/kernel/amd64/unix
-module - This variable locates the boot archive file (variable value eg: /platform/i86pc/amd64/boot_archive )
3. Ramdisk phase
The Ramdisk component is a file in ISO format that is mounted and used as a stand-alone, read-only filesystem. It contains drivers and configuration files which setup the earliest stanges of initalizing the kernel program.
Imp: Boot archive is the ramdisk image.
4. Kernel phase
Once those drivers supports the root file system and can attach it to the root device specified in system setup.
The kernel then extracts the remaining primary modules from the boot archive, initializes itself, mounts the real root file system, then discards the boot archive. Once initialized, the kernel program can call other programs that build the system to a user-accessible state.
In details:
Once the kernel is loaded, it starts the UNIX system, mounts the necessary file systems from vfstab and runs /usr/sbin/init to bring the system to the “initdefault” state specified in /etc/inittab.
When the system is booted, init is invoked and the following occurs. First, it reads the properties for the svc:/system/environment:init service. Among these properties are values for locale-related environments, such as LANG or LC_CTYPE. init then looks in /etc/inittab for the initdefault entry
Inittab Important Entires
ap::sysinit:/usr/sbin/autopush -f /etc/iu.ap
smf::sysinit:/lib/svc/bin/svc.startd >/dev/msglog 2<>/dev/msglog </dev/console
p3:s1234:powerfail:/usr/sbin/shutdown -y -i5 -g0 >/dev/msglog 2<>/dev/msglog
Lets understand each of the top two important entries.
ONE ap::sysinit:/usr/sbin/autopush -f /etc/iu.ap
The autopush command configures the list of modules to be automatically pushed onto the stream when a device is opened. It can also be used to remove a previous setting or get information on a setting.
cat iu.ap -This file contains
# major minor lastminor modules
wc -1 0 ldterm ttcompat
qcn 0 255 ldterm ttcompat
The mentioned modules in the file are present in /kernel/drv directory. For example wc.conf is mentioned in the /kernel/drv and the modules will be loaded accordingly.
SECOND
smf::sysinit:/lib/svc/bin/svc.startd >/dev/msglog 2<>/dev/msglog </dev/console
svc.startd is the master restarter daemon for Service Management Facility (SMF) and the default restarter for all services. svc.startd starts, stops, and restarts services based on administrative requests, system failures, or application failures
So, Now lets understand what is boot-archive.
When we install Solaris 11, the system creates the archive by copying key files from the root filesystem . And when ever we make any configuration change which might affect one of these files, so it's important to keep boot archive in sync with the root filesystem copy before shutting down.(sync using update-archive command )
Imp: In solaris 11 the bootadm utility is used to perform the below task.
SPARC: bootadm list-archive and update-archive
x86 : bootadm list-archive | update-archive | list-menu |set-menu
Imp:
