AIX boot proccess
AIX Boot Process
POWER ON
POST (Power on Self Test) / BIST (Built-in Self Test for AIX)
ROS Initialization (Checks Mother Board using OCS BUMP)
Hardware ROS Software ROS
3 types:
- Primary Devices: processor, mother board, RAM
- Secondary Devices: HD, CD, Floppy, Tape, magnetic tape etc.
- Base Devices: Keyboard, Mouse
- Checks User Bootlist
- Locates boot strap code to find bootable devices in User boot list
- Bootlist is of 2 types:
- Bootlist in Normal Boot
- Bootlist in Service Mode
- Bootlist in Normal Boot & Service mode each is of 2 types:
- Default Bootlist in ROS
- User Bootlist in NVRAM
User BootList: 3 Scenarios
- Available in NVRAM and is valid: loads Boot device from the user Bootlist found
- Available in NVRAM AND IS INVALID: Checks in Default Bootlist in ROS and loads the boot device
- Unavailable: keep checking the adapters and devices on BUS till valid bootlist is found to load the boot devices.
Once a Valid boot device is found
PSN (Program Sector Number) is checked
PSN gets loaded in IPL (Initial Program Load)
IPL contains information about the boot image
Boot Image is made up of:
- Kernel
- RAM FS
- Device Information (ODM)
- RC Boot (it’s a directory)
Control goes over to the Kernel
AIX Kernel gets initiated and RAM FS is created
Kernel will start the INIT process with Process ID = 1
INIT starts RC.Boot1 (Boot Phase 1)
- Copies ODM information from BLV into RAM FS (Command: # restbase)
- Starts sys, bus, SCSI, LVM, RVG configuration methods and updates data present in ODM in RAM FS (Command: # cfgmgr -f). cfgmgr command will check for all plug and play devices.
- Determines the last boot device (Command: # bootinfo -b)
Now the system is ready for installation, maintenance or diagnostic
INIT starts RC.Boot2 (Boot Phase 2)
- Activates the Root VG information available in ODM in RAM FS (Command: # ipl_varyon)
- Mounts HD FS (Hard disk FS) in RAM FS. All 10 partitions gets loaded
- Copies ODM from RAM FS into HD FS and scans the file system (Command: # fsck -f)
- Delete RAM FS
Up to this no console is available; boot progress is checked through LED display. All boot information is written in log file, can be checked by running the following command:
# alog –t boot -o
INIT will execute the processes defined in /etc/inittab
One of the processes is RC.Boot3 (Boot Phase 3)
- Checks stale partitions in VG and mounts temp in HD FS (Command: # syncvg)
- Synchronize VG information available in ODM (Command: # savebase)
- Initialize the console (Command: # cfgcon)
Kernel will start all the Background daemon services present in /etc/inittab
LED display is OFF
Login Display will appear
End of Boot process, Root FS is mounted
Init reads /etc/inittab
If default entry does not exists, init will ask user to enter the Run level from system console
If /etc/inittab does not exists, system will go into maintenance mode
Init re-reads /etc/inittab every 60 seconds
Points To Remember:
- ODM: Object Database Manager: is a database that has complete device configuration and informational data of the entire OS.
Information stored in ODM is:
Network Configuration
LVM Configuration
PV VG LV Configuration
Device Information
Smit menus, screens and commands
Hardware information
- OCS BUMP stands doe On Chip Sequencer and Built in Micro processor
- S: All information available here is gained and compiled from various RED HAT IBM Books & PDFs.
This is an effort to make understanding of AIX Booting Process simpler and user friendly.
All thoughts and reflections are welcomed.