Essential boot information in AIX

Here's some practical tips on boot information in AIX.


h4. uptime and when was it last rebooted.

In RHEL and Solaris, we can only find the uptime and when was it last rebooted.

# uptime
  10:06AM   up  19:09,  1 user,  load average: 0.35, 0.64, 0.65

# who -b
   .        system boot Aug 16 14:58


In AIX, we have this additional command to find history of reboot records. Power of ODM.

# last reboot
reboot    ~                                   Aug 16 14:58
reboot    ~                                   Aug 16 14:42
reboot    ~                                   Aug 15 13:59
reboot    ~                                   Aug 15 10:44
reboot    ~                                   Aug 14 15:14
reboot    ~                                   Jul 10 16:25
reboot    ~                                   May 25 12:14
reboot    ~                                   May 10 16:22
reboot    ~                                   May 07 17:02
reboot    ~                                   May 02 16:24
reboot    ~                                   May 02 15:58
reboot    ~                                   Apr 30 16:41
reboot    ~                                   Apr 25 15:19
reboot    ~                                   Apr 24 16:15
reboot    ~                                   Apr 24 15:35

wtmp begins     Apr 24 15:35


h4. State of the boot record

Here, we can spool and find out which disk has boot records for you to boot from.

# ipl_varyon -i
[S 8257680 9306164 08/17/12-10:07:37:395 ipl_varyon.c 1270] ipl_varyon -i


PVNAME          BOOT DEVICE     PVID                    VOLUME GROUP ID
hdisk0          YES             00f72ff5025fdaf30000000000000000        00f72ff500004c00
hdisk1          YES             00f72ff5025fdb3c0000000000000000        00f72ff500004c00
hdisk2          NO              00f72ff32bcd79f10000000000000000        00f72ff500004c00
hdisk3          NO              00f72ff32b5332f20000000000000000        00f72ff300004c00
hdisk4          NO              00f72ff32b5334930000000000000000        00f72ff300004c00
hdisk5          NO              00f72ff32b5336370000000000000000        00f72ff300004c00
[E 8257680 0:274 ipl_varyon.c 1410] ipl_varyon: exited with rc=0


h4. Creation of boot record

In the firmware (SMS), we can set the boot devices, e.g. disk, cd-rom, network. For disk, we would also need to create the boot record so that the server know HOW to load up AIX.

we create the boot record like this.

# bosboot -ad /dev/hdisk1

If you want to remove the boot record, you can try the following.

# chpv -c hdisk1

h4. Creation of boot list

Here, we create the boot list so that the server know WHERE to load up AIX.

Below, we see that there are 2 devices that we can boot up from. And it corresponds to the above ipl_varyon command. You can compare with what is set in SMS, they should match.

# bootlist -m normal -ov
'ibm,max-boot-devices' = 0x5
NVRAM variable: (boot-device=/pci@800000020000101/pci1014,0339@0/sas/disk@40600:2 /pci@800000020000101/pci1014,0339@0/sas/disk@40700:2)
Path name: (/pci@800000020000101/pci1014,0339@0/sas/disk@40600:2)
match_specific_info: ut=disk/sas/scsd
hdisk0 blv=hd5 pathid=0
Path name: (/pci@800000020000101/pci1014,0339@0/sas/disk@40700:2)
match_specific_info: ut=disk/sas/scsd
hdisk1 blv=hd5 pathid=0

If you need just the list of what we can boot up from, just drop the 'v' to reduce verbosity.

# bootlist -m normal -o
hdisk0 blv=hd5 pathid=0
hdisk1 blv=hd5 pathid=0

How to create or add the boot list, you may ask. Here's the command and example to create for the above.

# bootlist -m normal hdisk0 hdisk1

If you need to do a network boot all the time, you can set like the following.

bootlist -m normal en0 bserver=10.106.101.1 gateway=10.106.101.250 client=10.106.101.5

where
'bs' means boot server
'client' means the machine what we reboot


h4. Where is the boot image?

The boot image is usually found in hd5 (Boot PV). Below example shows that the server is booted from hd5 in hdisk0.

# bootinfo -v
hd5

# bootinfo -b
hdisk0

Attention: Never reboot the system when you suspect the boot image is corrupted.

h4. Recreation of boot image (Boot LV).

In the event you suspect the boot image is corrupted, you can recreate it using the following.

# bosboot -a -d /dev/hdisk0

** If the command fails and you receive the following message:

    0301-165 bosboot: WARNING! bosboot failed - do not attempt to boot device.

    Try to resolve the problem using one of the following options, and then run the bosboot command again until you have successfully created a boot image:

        Delete the default boot logical volume (hd5) and then create a new hd5.

    Or
        Run diagnostics on the hard disk. Repair or replace, as necessary.{info}

* If the bosboot command continues to fail, contact your customer support representative.
* Attention: If the bosboot command fails while creating a boot image, do not reboot your machine.
* When the bosboot command is successful, reboot your system to confirm.

Once done, update 'mini-ODM' in boot LV.

# savebase -v

Quote from Reference:
The bootrec (also known as bootstrap) is read by a special part of the firmware called System ROS (- the Read Only Storage is responsibe for the initial preparation of the machine -), and it (bootrec)  tells the ROS that it needs to jump X bytes into the disk platter, to read the boot logical volume, hd5.

During reading the blv, there is a mini-ODM read into the RAM. (Later, when the real rootvg fs comes online, AIX merges the data in mini-ODM with the real ODM held in /etc/objrepos.)

When an LVM commands changes the mini-ODM, the command 'savebase' needed to run as well. Savebase takes a snapshot of the ODM and compresses it

h4. How all these gel together. (My understanding and value adding just in case, people complain i copy too much) :P

After powering on, the server will POST.

Then it will use the boot list to find which disk, cdrom, network to load the Boot LV (inside hd5) from. Boot LV contains the AIX kernel, rc.boot file and commands required during the boot process and the mini-ODM.

next, kernel will take over the boot process. 

The kernel will then loads up the file system before executing the init process (from Boot LV) which will execute the rc.boot. The rootvg will be activated and then init process from the disk will be executed to replace the init process from Boot LV and become PID 1.

The kernel will move through the rc states and get the system ready.


Thanks to the reference that i understand more. <http://aix4admins.blogspot.sg/2011/08/mkitab-adds-record-to-etcinittab-file.html>