Boot process in solaris

Followin steps describes the solaris 10 sparc boot process.

1 . Boot PROM Phase:

This  phase starts at the time of switching on the machine and is boot prom phase, it displays a identification banner mentioning machine host id , serial number , memory type and MAC address. Then power on self test (POST) is run.

2. Boot Programs phase:

The bootblock program is loaded by PROM. This process ultimately looks for the default boot device and reads the boot program from the boot block which is located on the 1-15 blocks of boot device. The boot block contains the ufs file system reader which is required by the next boot processes.

The ufs file system reader opens the boot device and loads the secondary boot program from /usr/platform/`uname –i`/ufsboot ( uname –i expands to system architecture type)

The boot program above loads a platform specific kernel along with a generic solaris kernel.

3. Kernel Initilization Phase:

The ufs boot program loads the kernel into memory. The  kernel initialize itself and uses the ufsboot program to locate and load OS modules to control the system. A module is a piece of software with a specific functionality, such as interfacing with a particular hardware device. After loading enough modules to mount the root (/) file system. At the end of kernel initilization phase , the kernel starts the /sbin/init process.

4. The init phase.

The kernal start the /sbin/init process. Then the following process is run.

*   init phase

*   inittab file

*  rc scripts & Run Level

 init phase
Init phase is started by the execution of /sbin/init program and starts other processes after reading the /etc/inittab file as per the directives in the /etc/inittab file .

Two most important functions of init are
a) It runs the processes to bring the system to the default run level state ( Run level 3 in Solaris , defined by initdefault parameter in /etc/inittab )
b) It controls the transition between different run levels by executing appropriate rc scripts to start and the stop the processes for that run level.

/etc/inittab file
This file states the default run level and some actions to be performed while the system reaches up to that level. The fields and their explanation are as follows :

S3:3:wait:/sbin/rc3 > /dev/console 2>&1 < /dev/console

S3 denotes a identification if the line

3 is run level
wait is action to be performed

/sbin/rc3 is the command to be run.

So the fields in the inittab are

Identification : run level : action : process

The complete line thus means run the command /sbin/rc3 at run level 3 and wait until the rc3 process is complete.

The action field can have any of the following keywords :

Initdefault : default run level of the system

Respawn : start and restart the process if it stops.
Powerfail : stop on powerfail
Sysinit : start and wait till console in accessible .
Wait : wait till the process ends before going on to the next line.

 RC scripts & Run Levels
Rc scripts performs the following functions :

a) They check and mount the file systems
b) Start and stop the various processes like network , nfs etc.
c) Perform some of the house keeping jobs.

System goes in to one of the following run level after booting depending on default run level and the commands issued for changing the run level to some other one.

0 Boot prom level ok
1 Administrative run level . Single user mode
2 Multiuser mode with no resource sharing .
3 Multiuser level with nfs resource sharing
4 Not used
5 Shutdown & power off (Sun 4m and 4u architecture )
6 Reboot to default run level
S s Single user mode user logins are disabled.

System can be either of the following two states.

Single user – Minimum processes running , user logins disabled and root password is required to gain access to the shell .
Multiuser – All system processes are running and user logins are permitted