{} ok boot -ar

1- # boot cdrom -s (inserting the Solaris OS CD in the cdrom).
2- #fsck –y /dev/rdsk/c0t0d0s0 
3- #mkdir /a
4- #mount /dev/dsk/c0t0d0s0 /a
5- #grep rootdev /a/etc/system

The result will be something like this :
*       rootdev:        Set the root device.  This should be a fully
*               rootdev:/sbus@1,f8000000/esp@0,800000/sd@3,0:a
rootdev:/pseudo/md@0:0,0,blk       (for example)
The line that needs to be noted is the line beginning with rootdev. In the above example, the line "rootdev:/pseudo/md@0:0,0,blk" should 
be the line noted.

6- #mv /a/etc/path_to_inst /a/etc/orig.path_to_inst
7- #init 0
8- ok>boot –ar
Resetting... 
Software Power ON
Clock board TOD does not match TOD on any IO board.
Clock board TOD does not match TOD on any IO board.

slot Sun Enterprise 4000/5000, No Keyboard
OpenBoot 3.2.27, 320 MB memory installed, Serial #7923805.
Copyright 2000 Sun Microsystems, Inc.  All rights reserved
Ethernet address 8:0:20:78:e8:5d, Host ID: 8078e85d.

Rebooting with command: boot -ar
Boot device: /sbus@3,0/QLGC,isp@0,10000/sd@8,0:a  File and args: -ar
|
NOTICE: 64-bit OS installed, but the 32-bit OS is the default
 for the processor(s) on this system.
 See boot(1M) for more information.

Booting the 32-bit OS ...

9- Enter filename [kernel/unix]: (press enter)
Enter default directory for modules [/platform/SUNW,Ultra-Enterprise/kernel /platform/sun4u/kernel /kernel /usr/kernel]: 

10- Name of system file [etc/system]: (press enter)  
SunOS Release 5.8 Version Generic_117350-02 32-bit
Copyright 1983-2003 Sun Microsystems, Inc.  All rights reserved.
/
11- The /etc/path_to_inst on your system does not exist or is empty.
 Do you want to rebuild this file [n]? y
root filesystem type [ufs]: 

12- Enter physical name of root device
[/sbus@3,0/QLGC,isp@0,10000/sd@8,0:a]: <ENTER ROOTDEV noted  ABOVE in BOLD HERE >

13- After the system boots check for the presence of the file
cd /etc/
ls –l