path_to_inst is a device instance number file and mappings of physical device names to instance numbers. The instance number of a device is encoded in its minor number, and is the way that a device driver determines which of the possible devices that it may drive is referred to by a given special file. In order to keep instance numbers persistent across reboots, the system records them in /etc/path_to_inst. This file is read only at boot time. The system administrator can change the assignment of instance numbers by editing this file and doing a reconfiguration reboot. However, any changes made in this file will be lost if add_drv or devfsadm is run before the system is rebooted. If the file is removed the system may not be bootable (as it may rely on information found in this file to find the root, usr or swap device).
Additional note:
It is generally not necessary for the system administrator to change this file, as the system will maintain it.
But, if you encountered this error. You still can rebuild the file in order to boot again. Following are the steps that need to done.
Cannot open "/etc/path_to_inst"
1. Get the system to the ok prompt and with boot with option -ar
# boot -ar Rebooting with ....... Boot device: ........
2. You will be prompted with some system verification, just hit enter to continue.
Enter filename ..... Enter default directory for modules ............ Name of system file ..... SunOS Release ..... Copyright .....
3. Next, the system will ask you to rebuild the /etc/path_to_inst file. Type ‘yes‘ otherwise it won’t rebuild it.
The /etc/path_to_inst on your system does not exist or is empty. Do you want to rebuild this file [n]? root filesystem ..... Enter physical name
4. The system will continue booting after rebuild the file. Now, wait for the system to up!
