Technical data

Starting Up and Shutting Down the System
4.7 Writing a New Boot Block on the System Disk
4.7 Writing a New Boot Block on the System Disk
Block 0 on a system disk is the boot block. It contains the size and location of
the primary bootstrap image, which is used to boot the system.
On VAX systems, the primary bootstrap image is VMB.EXE.
On Alpha systems, the primary bootstrap image is APB.EXE.
Certain processors must read the boot block to obtain the location of the primary
bootstrap image. Processors that read a boot block include the following ones:
• VAX–11/750
• VAX 8200, 8250, 8300, and 8350
• VAX 6000–200, 6000–300, 6000–400, 6000–500, and 6000–600
• VAX 7000 and VAX 10000
• All Alpha systems (subject to change for future systems)
To determine if your system reads the boot block, check one of the following
manuals:
• On VAX systems, refer to the most recent versions of the OpenVMS
VAX Upgrade and Installation Manual and the upgrade and installation
supplement for your VAX computer.
• On Alpha systems, refer to the most recent version of the OpenVMS Alpha
Upgrade and Installation Manual.
If you suspect that the boot block on the system disk is invalid, you can write a
new boot block using the Writeboot utility (WRITEBOOT). The following actions
might cause a boot block to become invalid:
• Modifying the primary bootstrap image with the SET FILE/MOVE command
or the $MOVEFILE system service.
• Restoring a backup of the system disk created without the /IMAGE qualifier.
• Adding a new version of the primary bootstrap image, for example, during an
operating system upgrade. (When the upgrade procedure adds a new version
of the primary bootstrap image, it automatically uses WRITEBOOT to write a
new boot block.)
• Adding a new version of the primary bootstrap image that is not contiguous
on disk. (Use the DIRECTORY/FULL command to determine this.)
You must have LOG_IO privilege to use the Writeboot utility.
How to Perform This Task
On VAX systems, follow these steps to use the Writeboot utility:
1. To start the Writeboot utility, enter the following command:
$ RUN SYS$SYSTEM:WRITEBOOT
2. The procedure displays the following message:
Target system device (and boot file if not VMB.EXE):?
On VAX systems, VMB.EXE is the default bootstrap image. Enter a response
in the following format:
device:[VMS$COMMON.SYSEXE]VMB.EXE;
Starting Up and Shutting Down the System 4–19