AIX Basics (OS Installation, Boot up process and rootvg Filesystem structure)

Installation of AIX

Your AIX cd set normally would contain the following parts
AIX OS - The base OS and susbsystems included in OS

Expansion pack - Additional UtilitiesAIX Documentation - The documentation

AIX Toolbox for Linux - The linux utilities which can be installed on AIX as rpm (eg: unzip)

Base os cd/cds contains operating system filesets and filesets for programs included in os.
Eg: bos.nfs.client, bos.mp
Extra utilities cd contains utilities like gzip, webserver etc which may or may not be used.

Installation steps

1) Boot the server and press f1 key (or 1 key) after first beep and before second beep to bring the server
in SMS menu. Go to bootlist menu and select cdrom as first boot device.

2) Insert the cdrom and boot the server

3) Installation program comes up with a menu for installation. There are three types of installations

a) Preservation installation: Keeps files under /home directory if there is already an os exists
b) Migration installation: Keeps all files and programs as it is and this is used only to upgrade a lower version to higher (eg: AIX 5.1 to 5.3)
c) Complete overwrite: Overwrites everything.

The detailed steps are as below.

Step 1. Prepare your system
There must be adequate disk space and memory available. AIX 5L Version 5.2 and AIX 5L Version 5.3 require 128MB of memory and 2.2GB of physical disk space.
Make sure your hardware installation is complete, including all external devices.
If your system needs to communicate with other systems and access their resources, make sure you have the information in the following worksheet before proceeding with the installation:
Network Attribute
Value
Network interface
For example: en0, et0
Host name

IP address

Network mask

Nameserver

Domain name

Gateway

Step 2. Boot from the AIX product CD
Insert the AIX Volume 1 CD into the CD-ROM device.
Make sure all external devices attached to the system, such as CD-ROM drives, tape drives, DVD drives, and terminals, are turned on. Only the CD-ROM drive from which you will install AIX should contain the installation media.
Power on the system.
When the system beeps twice, press F5 on the keyboard or 5 on an ASCII terminal (To boot from CD). If you have a graphics display, you will see the keyboard icon on the screen when the beeps occur. If you have an ASCII terminal, you will see the word keyboard when the beeps occur.
Select the system console and press Enter.

Select the English language for the BOS installation menus by typing a 1 in the Choice field. Press Enter to open the Welcome to Base Operating System Installation and Maintenance screen.
Type 2 to select 2 Change/Show Installation Settings and Install in the Choice field and press Enter.

Welcome to Base Operating System Installation and Maintenance

Type the number of your choice and press Enter.

Choice is indicated by >>>.

1 Start Install Now with Default Settings

2 Change/Show Installation Settings and Install

3 Start Maintenance Mode for System Recovery

88 Help ?

99 Previous Menu>>> Choice [1]: 2

Step 3. Set and verify BOS installation settings
In the Installation and Settings screen, verify that the installation settings are correct by checking the method of installation (new and complete overwrite), the disk or disks you want to install, the primary language environment settings, and the advanced options.If the default choices are correct, type 0 and press Enter to begin the BOS installation. The system automatically reboots after installation is complete. Go to Step 4. Configure the system after installation.Otherwise, go to sub-step 2.
To change the System Settings, which includes the method of installation and disk where you want to install, type 1 in the Choice field and press Enter.
Installation and Settings Either type 0 and press Enter to install with current settings, or type the number of the setting you want to change and press Enter.

1 System Settings: Method of Installation..................New and Complete Overwrite

Disk Where You Want to Install..hdisk0 >>> Choice [0]: 1

Type 1 for New and Complete Overwrite in the Choice field and press Enter. The Change Disk(s) Where You Want to Install screen now displays.

Change Disk(s) Where You Want to Install Type one or more numbers for the disk(s) to be used for installation and press Enter. To cancel a choice, type the corresponding number and Press Enter. At least one bootable disk must be selected. The current choice is indicated by >>>.

Name Location Code Size(MB) VG Status Bootable

1 hdisk0 04-B0-00-2,0 4296 None Yes

2 hdisk1 04-B0-00-5,0 4296 None Yes

3 hdisk2 04-B0-00-6,0 12288 None Yes

>>> 0 Continue with choices indicated above

66 Disks not known to Base Operating System Installation

77 Display More Disk Information 88 Help ?

99 Previous Menu >>> Choice [0]:

In the Change Disk(s) Where You Want to Install screen:
Select hdisk0 by typing a 1 in the Choice field and press Enter. The disk will now be selected as indicated by >>>. To unselect the destination disk, type the number again and press Enter.
To finish selecting disks, type a 0 in the Choice field and press Enter. The Installation and Settings screen now displays with the selected disks listed under System Settings.
Change the Primary Language Environment Settings to English (United States). Use the following steps to change the Cultural Convention, Language, and Keyboard to English.
Type 2 in the Choice field on the Installation and Settings screen to select the Primary Language Environment Settings option.
Type the number corresponding to English (United States) as the Cultural Convention in the Choice field and press Enter.
Select the appropriate keyboard and language options.
You do not need to select the More Options selection, because you are using the default options in this scenario. For more information about the installation options available in AIX 5.2 and greater, see Installation Options in the AIX 5L Version 5.3 Installation Guide and Reference.

Verify that the selections are correct in the Overwrite Installation Summary screen, as follows:

Overwrite Installation Summary

Disks: hdisk0

Cultural Convention: en_US

Language: en_US

Keyboard: en_US64 Bit

Kernel Enabled: No

JFS2 File Systems Created: No

Desktop: CDE

Enable System Backups to install any system: Yes

Optional Software being installed:

>>> 1 Continue with Install

88 Help ? 99 Previous Menu >>> Choice [1]:
Press Enter to begin the BOS installation. The system automatically reboots after installation is complete.

Step 4. Configure the system after installation
After a new and complete overwrite installation, the Configuration Assistant opens on systems with a graphics display. On systems with an ASCII display, the Installation Assistant opens.
Select the Accept Licenses option to accept the electronic licenses for the operating system.
Set the date and time, set the password for the administrator (root user), and configure the network communications (TCP/IP). Use any other options at this time. You can return to the Configuration Assistant or the Installation Assistant by typing configassist or smitty assist at the command line.
Select Exit the Configuration Assistant and select Next. Or, press F10 or ESC+0 to exit the Installation Assistant.
If you are in the Configuration Assistant, select Finish now. Do not start the Configuration Assistant when restarting AIX and select Finish. At this point, the BOS Installation is complete, and the initial configuration of the system is complete.

Structure after installation

After installation there will be a volume group called rootvg and the following lvs on the installation disk selected.
Hd5 - Boot logical volume ( bootimage, Contains copy of kernel and a reduced odm)
Hd1 - /home
Hd2 - /usr
Hd3 - /tmp
Hd4 - /
Hd6 - Paging
Hd7 - Dump
Hd8 - jfs loglv
Hd9var - /var
Hd10opt - /opt (optional)

Hd1(home):It contains the home directories of the users.

Hd2(/usr):Its contains basic os executables and binaries.

Hd3(/tmp):It’s the temporary space used for the system/programs to temporarily keep and delete the files while processing data.

Hd4(/):It’s the root directory. It is the home directory of the root user.
/etc-it contains all configuration files.
/sbin-commands and executables super user binaries.
/bin- contains normal commands and executables.
/dev-all device files.
Hd5(boot logical volume): It keeps kernel image and reduced ODM of the aix operating system. It’s not a file system
Hd6(paging):It’s the logical volume used for the memory paging(swaping).this memory is also called virtual memory.
Hd7(dump):It’s the logical volume used for the system dump.
Hd8(log):Is used for keeping jfslog of all file systems in rootvg.
Hd9var: var file system used for varying files likes log files, spool files.
Hd10opt: It is used for to store extra software or programs.

Boot up, init process and runlevels

Boot up process

When power on happens the firmware program stored in an System board Chip (called Read only Storage [ROS] ) gets loaded into the memory

The firmware Conducts CPU and memory power on self tests, detects all controllers and hardware devices connected to the system and conducts POST for them also

The firmware reads the console path information from an NVRAM called Stable storage (NVRAM stores firmware configuration) and initializes console.

Firmware checks for first boot device in Stable storage and accesses the first 512 bytes of the first boot device (normally disk)

The first 512 bytes contains the boot strap information which locates the hd5 (blv) and kernel from BLV gets loaded to the memory

Kernel creates temporary RAM filesystem containing /, /usr, etc, dev, mnt etc.
These filesystems are virtually mounted in RAM and whatever it contains are what the kernel had read from BLV and nothing else.
Kernel starts init process from blv. Init starts rc.boot script. The rc.boot script runs in three phases to complete the boot process

Rc.boot phase 1

This phase configures base devices from reduced odm in BLV and runs cfgmgr to detect new devices. The device files for new devices will be placed under /dev in RAM.

Rc.boot phase 2

This phase activates rootvg with a special command ipl_varyon and runs fsck on /usr, / and /var filesystems.
Mounts them from disk to replace RAM filesystems.

Activates paging space hd6. Copies all device files from memory to disk. Removes RAMfs.

RC.boot phase3

Init process is replaced with the init script in the disk. This init initializes rc.boot phase3
Mounts /tmp filesystem
Configures all devices other than phase1
Console is configured by the OS and LED display is turned off
( LED display is provided with all servers which displays specific numbers indicating each stage of booting. Looking at this number and manual we can trouble shoot any boot time failures)
After rc.boot script init starts processes in the inittab one by one.
There is an entry in inittab called initdefault to indicate default run level. (Normally 2)



Init

Init (/sbin/init) is responsible for taking the system to a specific run level by starting processes listed in inittab. Init process has process id 1. init is parentprocess for all processes.

The configuration file is /etc/ inittab.

Syntax of inittab
Inittab contains four columns program id, runlevels, action, command to run separated by “:”

Eg - 7ab:1,2,3,4:respawn:/usr/bin/cron

Actions

Boot, bootwait, wait, respawn

Boot : The program is started in the boot time
Bootwait: The program is started in the boot time and to be waited to end before starting next.
Wait: To be waited to end before starting next.
Respawn: This process should never be killed. If we kill the process it will be automatically restarted by init. (eg: cron, getty).

Runlevels

AIX has run levels from 0 to 9, also a and b
0 and 1 are reserved.
2 is the default normal multiuser mode
Run levels from 3 to 9 are defined by administrator.