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 HP OpenVMS Alpha Version 7.3-2 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.
On VAX systems, follow these steps to use the Writeboot utility:
To start the
Writeboot utility, enter the following command:
$ RUN SYS$SYSTEM:WRITEBOOT
The procedure displays the following message:
Target system device (and boot file if not VMB.EXE):?
On VAX systems, VMB.EXE is the default bootstrap image. Enter
a response in the following format:device:[VMS$COMMON.SYSEXE]VMB.EXE; Use the device name format described in the upgrade and installation
documentation for your processor. If you want to boot using a bootstrap
image other than the default, you must specify the full file specification
of the image, including device and directory.
The procedure displays the following message:
Enter VBN of boot file code (default is one):
Ordinarily, the boot code is located at virtual block number
(VBN) 1 of the bootstrap image. Press Return to accept the default
value of 1.
The procedure displays the following message:
Enter load address of primary bootstrap in HEX (default is 200):
The load address is the location in
memory (specified in hexadecimal notation) to which the system loads
the bootstrap image. Ordinarily you copy the bootstrap image to
address 200. Press Return to accept the default value of 200.
The Writeboot utility writes the information you
specified to the boot block (block 0) on the system disk.
On Alpha systems, follow these steps to use the Writeboot
utility:
To start the
Writeboot utility, enter the following command:
$ RUN SYS$SYSTEM:WRITEBOOT
The procedure asks you whether you want to write the VAX portion
of the boot block:
Update VAX portion of boot block (default is Y):
Enter NO.
The utility displays the following prompt:
Update Alpha portion of boot block (default is Y):
Press Return to accept the default value of Y.
The utility prompts you for the Alpha bootstrap
image:
Enter Alpha boot file:
On Alpha systems, APB.EXE is the default bootstrap image.
Enter a response in the following format:device:[VMS$COMMON.SYSEXE]APB.EXE; where device specifies the device name
of the system disk.
The Writeboot utility writes the information you
specified to the boot block (block 0) on the system disk.
On VAX and Alpha systems, the Writeboot utility might display
one or more of the following error messages:
"You lack LOG_IO privilege." This message means you do not have the correct privilege to
use the Writeboot utility.
"You lack READ and/or WRITE access to TARGET
DEVICE. DISMOUNT and reMOUNT it." This message means that access to the target device is limited.
Check the WRITE PROTECT button on the disk drive.
"Boot file is not contiguous." This message means that the primary bootstrap image, VMB.EXE
or APB.EXE, is not contiguous on disk. Perform one of the following
actions:
On VAX systems, the following example writes a boot block
on a system disk:
$RUN SYS$SYSTEM:WRITEBOOTTarget system device (and boot file if not VMB.EXE):? DUA0:[VMS$COMMON.SYSEXE]VMB.EXEEnter VBN of boot file code (default is one):[Return]Enter load address of primary bootstrap in HEX (default is 200): [Return]
On Alpha systems, the following example writes a boot block
on a system disk:
$ RUN SYS$SYSTEM:WRITEBOOTUpdate VAX portion of boot block (default is Y): NUpdate Alpha portion of boot block (default is Y): [Return]Enter Alpha boot file: DUA0:[VMS$COMMON.SYSEXE]APB.EXE;