After running oninit -i, IBM Informix Dynamic Server fails to come online and writes the following messages to the message log:
16:06:00 DISK INITIALIZATION ABORTED: potential instance overwrite detected.
To disable this check, set FULL_DISK_INIT to 1 in your config file and retry.
16:06:00 oninit: Fatal error in shared memory initialization
16:06:00 IBM Informix Dynamic Server Stopped.
16:06:00 mt_shm_remove: WARNING: may not have removed all/correct segments
This is expected behavior. It is a feature first put into 11.70.xC1 that prevents the accidental overwrite of an instance which can happen when using the -i (full disk initialization) option. This feature utilizes the onconfig config file parameter FULL_DISK_INIT.
By default, FULL_DISK_INIT is set to 0. This setting protects the ROOTPATH file/device from being overwritten by oninit -i. A value of 1 allows oninit -i to perform full disk initialization (destructive overwrite) of the ROOTPATH file/device.
Resolving the problem
If it is desired to overwrite the ROOTPATH file/device and perform full disk initialization (destructive overwrite), as per the error message above, set the onconfig config file parameter FULL_DISK_INIT to 1 and run oninit -i.
As the server is initializing the instance and the ROOTPATH disk/file, you will see the following messages in the message log:
16:09:48 Value of FULL_DISK_INIT has been changed to 0.
16:11:17 IBM Informix Dynamic Server Initialized -- Complete Disk Initialized.
The first message indicates that the instance is setting the value of FULL_DISK_INIT back to 0 to as a defensive mechanism to prevent a subsequent oninit -i from performing full disk initialization (destructive overwrite). The second message indicates that the instance processes, threads, shared memory segments, memory structures and full disk initialization (destructive overwrite) has completed.