A system dump file is a file to which the system writes the contents of the error log buffers, processor registers, and memory when a system failure occurs, overwriting its previous contents.
The operating system uses the latest version of SYS$SYSTEM:SYSDUMP.DMP to store system crash dumps. If SYSDUMP.DMP does not exist in SYS$SYSTEM, the operating system uses the system page file, SYS$SYSTEM:PAGEFILE.SYS, overwriting the contents of that file. Note that SYSDUMP.DMP should not be deleted. The reason for this is that if you DELETE a dump file, it will be marked for delete but not deleted - the deletion will occur at shutdown, but if the system crashes before the shutdown, the dump file will still be mapped and the dump will get written there and not to the page file - and you will not be able to access it. If you need to delete the dump file, rename it, reboot the system, and then delete the renamed file.
If the SAVEDUMP system parameter is set, the crash dump is retained in PAGEFILE.SYS when the system is booted. If SAVEDUMP is clear, the system uses the page file for paging; any dump written to the page file is lost. Selective dumps use up all available space. If your page file is small, selective dump information might fill the entire page file, leaving no space for paging during system boot. This can cause the system to hang during reboot. If SYS$SYSTEM:PAGEFILE.SYS is used to capture system crash dumps, you should later free the space occupied by the dump for use in system paging, with either of the following methods:
- Use the SDA COPY command to copy the dump from the page file to a different file.
- Use the SDA RELEASE command to delete the information from the page file.
Dump File on an Alternate Disk
Dump file can be located on an alternate ODS-2 or ODS-5 disk that cannot be a part of a volume set and should preferably not be part of a shadow set. If the dump file is located on an alternate disk, the following should be performed:
- the dump file should be created in:
(make sure the specification mirrors the directory structure of your system disk)
- set the DUMP_DEV console variable to the disk name in the SRM console or the EFI Shell
- set bit 2 in the DUMPSTYLE system parameter
- set DUMPFILE_DEVICE to disk name using AUTOGEN
- define CLUE$DOSD_DEVICE to the disk name.
The following requirements must be met for the operating system to write a useful system dump file:
- The system parameter DUMPBUG must be set to 1 (the default value).
- If the system parameter SAVEDUMP is set to 0 (the default) the file SYS$SPECIFIC:[SYSEXE]SYSDUMP.DMP must exist on the system disk.
- If the file SYS$SPECIFIC:[SYSEXE]SYSDUMP.DMP does not exist on the system disk, the page file must be used to store the dump. The system parameter SAVEDUMP must be set to 1 and the file SYS$SPECIFIC:[SYSEXE]PAGEFILE.SYS must exist on the system disk.
- If the file SYS$SPECIFIC:[SYSEXE]SYSDUMP.DMP does not exist and SYS$SPECIFIC:[SYSEXE]PAGEFILE.SYS is not available for system dumps, you must create the dump file on an alternate disk (see Section 16.7).
- If sufficient disk space is not available to allow a system dump file that can hold all of memory, the system parameter DUMPSTYLE must be set to the appropriate value to store a selective system dump. For more information, refer to OpenVMS System Management Utilities Reference Manual Vol. II (N-Z).
The system dump file (or page file if the SAVEDUMP system parameter is set) must be large enough to hold all information that is to be written if the system fails. If the system parameter DUMPBUG is set, AUTOGEN automatically sizes SYSDUMP.DMP if enough disk space is available. If the system parameter SAVEDUMP is set, AUTOGEN performs no operations on the system dump file. AUTOGEN sizes the page file only for paging use, regardless of whether the SAVEDUMP system parameter is set.
A system dump file has the NOBACKUP attribute; therefore, the Backup utility (BACKUP) does not copy the file unless you use the qualifier /IGNORE=NOBACKUP when invoking BACKUP. When you use the SDA COPY command to copy the system dump file to another file, the operating system does not automatically set the new file to NOBACKUP. If you want to set the NOBACKUP attribute on the copy, use the SET FILE command with the /NOBACKUP qualifier as described in the OpenVMS DCL Dictionary.
By default, SYS$SYSTEM:SYSDUMP.DMP is protected against world access. Because a system dump file can contain privileged information, you should keep this level of protection on system dump files. Similarly, when you copy system dump files using the System Dump Analyzer utility (SDA), be sure to protect the copy from world read access.
Types of System Dumps
The two types of system dumps are physical and selective. A physical dump writes the entire contents of physical memory to the system dump file. To ensure a useful physical dump, the system dump file must be large enough to contain all of physical memory. A selective dump stores those portions of memory most likely to be useful in crash dump analysis. A selective system dump is useful when disk space is not available to hold all of physical memory.
Error Log Dump File
AUTOGEN creates the error log dump file during installation; its size depends on your configuration and system parameters. Error log dump files on VAX and Alpha systems have the following differences:
On Alpha systems, the error log dump file is called SYS$ERRLOG.DMP; it is located on the system disk. When an operator initiates a shutdown, the system writes the contents of error log buffers to the error log dump file and not to the system dump file. Thus, the last system crash dump is not overwritten. On VAX systems, the error log dump file is called SYSDUMP.DMP. How the system handles this file depends on whether you are using dump off system disk (DOSD): With DOSD, error logs are written to a stub error log dump file, SYSDUMP.DMP, on the system disk. Also, both the error logs and system memory are written to the SYSDUMP.DMP file on the DOSD disk. Without DOSD, both the error log and system memory are written to the SYSDUMP.DMP file on the system disk.
On VAX systems with or without DOSD, the last system crash dump is always overwritten when an operator initiates a shutdown.