[OpenVMS documentation]
[Site home] [Send comments] [Help with this site] [How to order documentation] [OpenVMS site] [Compaq site]
Updated: 11 December 1998

OpenVMS System Manager's Manual


Previous Contents Index


Chapter 15
Managing Page, Swap, and Dump Files

Page, swap, and dump files are created by default. However, you should understand these files. In addition, you might want to change them to meet the needs of your site.

Information Provided in This Chapter

This chapter describes the following tasks:
Task Section
Displaying information about page and swap files Section 15.3
Calculating appropriate sizes for files Section 15.4
Minimizing dump file size when disk space is insufficient Section 15.5
Writing the dump file to a device other than the system disk Section 15.6
Using SDA to analyze the contents of a crash dump Section 15.7
++Using SDA CLUE commands to obtain and analyze summary crash dump information Section 15.8
+Using CLUE to obtain historical information about crash dumps Section 15.9
Saving the contents of the system dump file after a system failure Section 15.10
Copying dump files to tape or disk Section 15.11
Freeing dump information from the page file Section 15.12
Installing page and swap files Section 15.13
Removing page, swap, and dump files Section 15.14
Creating and modifying page, swap, and dump files Section 15.15


+VAX specific
++Alpha specific

This chapter explains the following concepts:
Concept Section
Understanding dump files Section 15.1
Understanding page and swap files Section 15.2
Understanding the order of information in a selective system dump Section 15.5.1
++Understanding SDA CLUE Section 15.8.1
+Understanding CLUE Section 15.9.1


++Alpha specific
+VAX specific

15.1 Understanding Dump Files

When the operating system detects an unrecoverable error or an inconsistency within itself that causes the system to fail, it writes the contents of the error log buffers, processor registers, and memory into the system dump file, overwriting its previous contents.

The contents of error log buffers are also written to the error log dump file. The error log dump file is provided so that the system can be updated on reboot to include error log entries that were created but not written at the time of a system crash.

System Dump File

When writing the system dump file, the system displays console messages and information about the error or inconsistency. The last message tells you that the dump file was successfully written.

Caution

Be sure to wait until you see the termination message before using the console terminal to halt the system. If you do not wait, your system might not save a complete system dump file.

Console messages and the system dump file are important sources of information in determining the cause of a system failure. Use the contents in the following ways:

The default system dump file, SYS$SPECIFIC:[SYSEXE]SYSDUMP.DMP, is furnished as an empty file in the operating system distribution kit. (You do not need a system dump file to run the operating system. However, you must have a system dump file to diagnose system crashes.) AUTOGEN automatically determines an appropriate size for the system dump file for your hardware configuration and system parameters. Refer to Section 15.5 for information about minimizing system dump file size if disk space is insufficient.

For special configurations or varying work loads, you can change the size of the system dump file. For information, see Section 15.15.1. You can place the system dump file on a disk other than the system disk. For more information, see Section 15.6.

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:

15.1.1 Using the Page File to Store System Crash Dumps

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.

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.

If you use SYS$SYSTEM:PAGEFILE.SYS 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:

For detailed instructions, see Section 15.12.

Include the appropriate commands in the SYSTARTUP_VMS.COM startup command procedure to free dump information from the page file each time the system reboots.

Caution

Be careful when using the page file for selective dumps. 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.

15.1.2 Understanding Types of System Dumps

The two types of system dumps are physical and selective. Table 15-1 defines physical and selective system dumps. Table 15-3 compares the information available in physical and selective system dump files.

Table 15-1 Definitions of Physical and Selective System Dumps
Type Description
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.
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.

Requirements for Creating a Useful System Dump

The following requirements must be met for the operating system to write a useful system dump file:

BACKUP Considerations

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.

Security Considerations

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) as explained in Section 15.10 and Section 15.12, be sure to protect the copy from world read access. For more information about file protection, refer to the OpenVMS Guide to System Security.

15.2 Understanding Page and Swap Files

As part of memory management, the operating system makes efficient use of physical memory by moving information between physical memory and files stored on disk. The system does this in two ways: paging and swapping. Table 15-2 defines these and related terms.

Table 15-2 Paging and Swapping Terminology
Term Definition
Paging A memory management operation that provides the efficient use of physical memory allotted to a process. Paging moves infrequently used portions of a process workspace out of physical memory to a file. For more information about paging, refer to the OpenVMS Performance Management.
Page file The file to which the system writes paged portions of memory. Your distribution kit includes a page file named SYS$SYSTEM:PAGEFILE.SYS. If necessary, you can use SYS$SYSTEM:PAGEFILE.SYS in place of the system crash dump file. For more information, see Section 15.1.1.
Swapping A memory management operation that provides the efficient use of physical memory available for the entire system. Swapping moves the entire workspace of a less active process out of physical memory to a file. For more information about swapping, refer to the OpenVMS Performance Management.
Swap file The file to which the system writes swapped portions of memory. Your distribution kit includes a swap file named SYS$SYSTEM:SWAPFILE.SYS.
Primary page and swap files The default page and swap files provided with your distribution kit. These files are named SYS$SYSTEM:PAGEFILE.SYS and SYS$SYSTEM:SWAPFILE.SYS.
Secondary page and swap files Additional page and swap files that you might create for performance or disk space reasons. If you kept the primary page and swap file on the system disk, the system uses the space in the secondary files for paging and swapping in addition to the space in the primary page and swap files. For information about creating secondary page and swap files, see Section 15.15.

Installing Files

Page and swap files must be installed before the system can use them. The system automatically installs the latest versions of SYS$SYSTEM:PAGEFILE.SYS and SWAPFILE.SYS during startup. If you create secondary page and swap files, you must make sure the system installs them during startup. For more information about installing page and swap files, see Section 15.13.

File Sizes and Locations

AUTOGEN automatically determines appropriate sizes for the files for your hardware configuration and system parameters. For special configurations or varying work loads, you might want to change the size of the page or swap file. For information, see Section 15.15.1.

If your system does not require the page file for storing system crash dumps, you can move it off the system disk. However, you should keep one page file on the system disk, if possible, so that you can boot the system if another disk holding the page files becomes unavailable. The swap file can also be moved off the system disk.

15.3 Displaying Information About Page and Swap Files

The DCL command SHOW MEMORY/FILES displays information about the page and swap files existing on your system, including file names, sizes, and the amount of space used. For example:


$ SHOW MEMORY/FILES
              System Memory Resources on 12-MAY-1998 11:54:20.06 
 
Paging File Usage (pages):                      Free  Reservable       Total 
  DISK$PAGE:[SYSEXE]SWAPFILE_IPL31.SYS;2       79992       79992       79992 
  DISK$PAGE:[SYSEXE]PAGEFILE_IPL31.SYS;1       23263     -370027      249992

Note that the number displayed in the column labeled "Reservable" can be a negative number. Processes can reserve more space than is available because it is unlikely that all the reserved space will be used for paging at one time.

15.4 Manually Calculating Appropriate Sizes for Dump, Page, and Swap Files

When you install or upgrade the operating system, AUTOGEN automatically calculates appropriate sizes for your system; these sizes are based on your hardware configuration and your system parameters. However, you can manually calculate the sizes for these files. The following sections describe how to determine appropriate sizes for the system page, swap, and dump files.

15.4.1 Calculating System Dump File Size

Sufficient space in the system dump file is critical to saving a complete crash dump. The AUTOGEN command procedure calculates an appropriate size for your system dump file. However, if you want to manually calculate the system dump file size, use the following formula, which calculates the file size required to hold a physical dump.

For SYSDUMP.DMP

On VAX systems, use the following formula:


size-in-blocks(SYS$SYSTEM:SYSDUMP.DMP) 
= size-in-pages(physical-memory) 
+ number-of-error-log-buffers * blocks-per-buffer 
+ 1 
 

On Alpha systems, use the following formula:


size-in-blocks(SYS$SYSTEM:SYSDUMP.DMP) 
= size-in-pages(physical-memory) * blocks-per-page 
+ number-of-error-log-buffers * blocks-per-buffer 
+ size-in-pages (physical memory)/512 
+ 2 
 
 

where:
size-in-pages Is the size of physical memory, in pages. Use the DCL command SHOW MEMORY to determine the total size of physical memory on your system.
blocks-per-page Is the number of blocks per page of memory.

On Alpha systems, calculate the number of blocks per page of memory by dividing the system's page size by 512 (the size of a block). Use the following commands:

$ PAGESIZE==F$GETSYI ("PAGE_SIZE")

$ BLOCKSPERPAGE=PAGESIZE/512
$ SHOW SYMBOL BLOCKSPERPAGE
number-of-error-log-buffers Is the value of the system parameter ERRORLOGBUFFERS. This parameter sets the number of error log buffers to permanently allocate in memory.
blocks-per-buffer Is the value of the system parameter ERLBUFFERPAGES. This parameter sets the number of pages of memory in each buffer.

A large memory system or a system with small disk capacity might not be able to supply enough disk space for a full memory dump. Under these circumstances, you should set the system parameter DUMPSTYLE to the appropriate value to indicate that the system is to dump only selective information. For more information, see Section 15.5.

For PAGEFILE.SYS

If SYS$SYSTEM:SYSDUMP.DMP does not exist, the system writes crash dumps to the primary page file SYS$SYSTEM:PAGEFILE.SYS. The AUTOGEN command procedure calculates an appropriate size for your page file. However, to manually calculate the minimum page file size required to hold crash dumps, use the following formula:

On VAX systems:


size-in-blocks(SYS$SYSTEM:PAGEFILE.SYS) 
= size-in-pages(physical-memory) 
+ number-of-error-log-buffers * blocks-per-buffer 
+ 1 
+ 1000 
 
 

On Alpha systems:


size-in-blocks(SYS$SYSTEM:PAGEFILE.SYS) 
= size-in-pages(physical-memory) * blocks-per-page 
+ number-of-error-log-buffers * blocks-per-buffer 
+ size-in-pages (physical memory)/512 
+ 2 
+ value of the system parameter RSRVPAGCNT 
 
 

where:
size-in-pages Is the size of physical memory, in pages. Use the DCL command SHOW MEMORY to determine the total size of physical memory on your system.
blocks-per-page Is the number of blocks per page of memory.

On Alpha systems, calculate the number of blocks per page of memory by dividing the system's page size by 512 (the size of a block). Use the following commands:

$ PAGESIZE==F$GETSYI ("PAGE_SIZE")

$ BLOCKSPERPAGE=PAGESIZE/512
$ SHOW SYMBOL BLOCKSPERPAGE
number-of-error-log-buffers Is the value of the system parameter ERRORLOGBUFFERS. This parameter sets the number of error log buffers to permanently allocate in memory.
blocks-per-buffer Is the value of the system parameter ERLBUFFERPAGES. This parameter sets the number of pages of memory in each buffer.
RSRVPAGCNT Is the value of the RSRVPAGCNT special system parameter.

Caution

This formula calculates only the minimum size requirement for saving a dump in the system's primary page file. For most systems, the page file must be larger than this to avoid hanging the system. For more information about calculating the page file size, see Section 15.4.3.


Previous Next Contents Index

[Site home] [Send comments] [Help with this site] [How to order documentation] [OpenVMS site] [Compaq site]
[OpenVMS documentation]

Copyright © Compaq Computer Corporation 1998. All rights reserved.

Legal
6017PRO_069.HTML