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System Management Concepts: Operating System and Devices
Most users perform a hard disk
boot when starting the system for general operations. The system finds
all information necessary to the boot process on its disk drive.
When the system is started by
turning on the power switch (a cold boot) or restarted with the
reboot or shutdown commands (a warm boot), a number of
events must occur before the system is ready for use. These events can
be divided into the following phases:
- Read Only Storage (ROS)
Kernel Init Phase
- Base Device Configuration
- System Boot Phase.
The ROS kernel initialization
phase involves the following steps:
- The On-Chip Sequencer (OCS) bring-up microprocessor (BUMP)
checks to see if there are any problems with the system motherboard.
Control is passed to ROS, which performs a power-on self-test (POST).
- The ROS initial program load (IPL) checks the user boot
list, a list of available boot devices. This boot list can be altered
to suit your requirements using the bootlist
command. If the user boot list in Non-Volatile Random Access Memory
(NVRAM) is not valid or if a valid boot device is not found, the default boot
list is then checked. In either case, the first valid boot device found
in the boot list is used for system startup. If a valid user boot list
exists in NVRAM, the devices in the list are checked in order. If no
user boot list exists, all adapters and devices on the bus are checked.
In either case, devices are checked in a continuous loop until a valid boot
device is found for system startup.
system maintains a default boot list located in ROS and a user boot list
stored in NVRAM, for a normal boot. Separate default and user boot
lists are also maintained for booting from the Service key position.
- When a valid boot device is found, the first record or
program sector number (PSN) is checked. If it is a valid boot record,
it is read into memory and is added to the IPL control block in memory.
Included in the key boot record data are the starting location of the boot
image on the boot device, the length of the boot image, and instructions on
where to load the boot image in memory.
- The boot image is read sequentially from the boot device
into memory starting at the location specified in the boot record. The
disk boot image consists of the kernel, a random access memory (RAM) file
system, and base customized device information.
- Control is passed to the kernel, which begins system
- ROS runs init, which runs phase 1 of the
When the kernel initialization
phase is completed, base device configuration begins.
The init process starts
the rc.boot script. Phase 1 of the
rc.boot script performs the base device configuration, and
it includes the following steps:
- The boot script calls the restbase program
to build the customized Object Database Manager (ODM) database in the RAM file
system from the compressed customized data.
- The boot script starts the configuration manager,
which accesses phase 1 ODM configuration rules to configure the base
- The configuration manager starts the sys,
bus, disk, SCSI, and the Logical Volume Manager (LVM)
and rootvg volume group (RVG) configuration methods.
- The configuration methods load the device drivers,
create special files, and update the customized data in the ODM
The System Boot Phase involved the
- The init process starts phase 2 running of
the rc.boot script. Phase 2 of
rc.boot includes the following steps:
- Call the ipl_varyon program to vary on the
rootvg volume group (RVG).
- Mount the hard disk file systems onto their normal
- Run the swapon program to start
- Copy the customized data from the ODM database in the
RAM file system to the ODM database in the hard disk file system.
- Exit the rc.boot script.
- After phase 2 of rc.boot, the boot
process switches from the RAM file system to the hard disk root file
- Then the init process runs the processes
defined by records in the /etc/inittab file. One of the instructions in
the /etc/inittab file runs phase 3 of the rc.boot
script, which includes the following steps:
- Mount the /tmp hard disk file
- Start the configuration manager phase 2 to configure
all remaining devices.
- Use the savebase command to save the
customized data to the boot logical volume
- Exit the rc.boot script.
At the end of this process, the
system is up and ready for use.
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