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OpenVMS VAX System Dump Analyzer Utility Manual

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This long display reflects the output of the SHOW CRASH command within the analysis of a system failure that occurred on a VAX 8800 multiprocessing system.

The first part of the display includes the following information:

  1. Identification of the system and the version of OpenVMS it was running at the time of the crash.
  2. Indication that the failed processor (CPU 00) was not the primary processor (CPU 01), but requested CPU 01 to take a CPUEXIT bugcheck. (CPU 01 was, in fact, idle at the time of the crash.)
    The next part of the display shows information particular to CPU 00:
  3. CPU 00 encountered an INVEXCEPTN bugcheck while executing the NETACP process.
  4. Although the next step in the analysis might be to examine the interrupt stack of CPU 00, the fact that the failure occurred at IPL 8 might indicate that an I/O driver is involved.

At the end of the example, SDA CPU context remains that of CPU 00; its current process context is that of the NETACP process.


Displays a list of all devices in the system and their associated data structures or displays the data structures associated with a given device or devices.


SHOW DEVICE {device-name|/ADDRESS=ucb-address}



Device or devices for which data structures are to be displayed. There are several uses of the device-name parameter.
To Display the Structures for... Action
All devices in the system Do not specify a device-name (for example, SHOW DEVICE).
A single device Specify an entire device-name (for example, SHOW DEVICE VTA20).
All devices of a certain type on a single controller Specify only the device type and controller designation (for example, SHOW DEVICE RTA or SHOW DEVICE RTB).
All devices of a certain type on any controller Specify only the device type (for example, SHOW DEVICE RT).
All devices whose names begin with a certain character or character string Specify the character or character string (for example, SHOW DEVICE D).
All devices on a single node or HSC Specify only the node name or HSC name (for example, SHOW DEVICE GREEN$).

In a VAXcluster environment, device information is displayed for each device in the cluster with the specified device-name. You can limit the display to those devices that are on a particular node or HSC by specifying the node name or HSC name as part of the device-name (for example, GREEN$D or GREEN$DB).



Indicates the device for which data structure information is to be displayed by the address of its unit control block (UCB). The /ADDRESS qualifier is thus an alternate method of supplying a device name to the SHOW DEVICE command. If both the device-name parameter and the /ADDRESS qualifier appear in a single SHOW DEVICE command, SDA responds only to the parameter or qualifier that appears first.


The SHOW DEVICE command produces several displays taken from system data structures that describe the devices in the system configuration.

If you use the SHOW DEVICE command to display information for more than one device or one or more controllers, it initially produces the DDB list display to provide a brief summary of the devices for which it renders information in subsequent screens.

Information in the DDB list appears in six columns, the contents of which are as follows:

  • Address of the device data block (DDB)
  • Controller name
  • Name of the ancillary control process (ACP) or extended QIO processor (XQP) associated with the device
  • Name of the device driver
  • Address of the driver prologue table (DPT)
  • Size of the DPT

The SHOW DEVICE command then produces a display of information pertinent to the device controller. This display includes information gathered from the following structures:

  • Device data block (DDB)
  • Primary channel request block (CRB)
  • Interrupt dispatch block (IDB)
  • Driver dispatch table (DDT)

If the controller is an HSC controller, SHOW DEVICE also displays information from its system block (SB) and each path block (PB).

Many of these structures contain pointers to other structures and driver routines. Most notably, the DDT display points to various routines located within driver code, such as the start I/O routine, unit initialization routine, and cancel I/O routine.

For each device unit subject to the SHOW DEVICE command, SDA displays information taken from its unit control block, including a list of all I/O request packets (IRPs) in its I/O request queue. For certain mass-storage devices, SHOW DEVICE also displays information from the primary class driver data block (CDDB), the volume control block (VCB), and the ACP queue block (AQB). For units that are part of a shadow set, SDA displays a summary of shadow set membership.

As it displays information for a given device unit, SHOW DEVICE defines the following symbols as appropriate.

Symbol Meaning
UCB Address of unit control block
SB Address of system block
ORB Address of object rights block
DDB Address of device data block
DDT Address of driver dispatch table
CRB Address of channel request block
AMB Associated mailbox UCB pointer
IRP Address of I/O request packet
2P_UCB Address of alternate UCB for dual-pathed device
LNM Address of logical name block for mailbox
PDT Address of port descriptor table
CDDB Address of class driver descriptor block for MSCP-served device
2P_CDDB Address of alternate CDDB for MSCP-served device
RWAITCNT Resource wait count for MSCP-served device
VCB Address of volume control block for mounted device

If you are examining a driver-related crash, you might find it helpful to issue a SHOW STACK command after the appropriate SHOW DEVICE command, examining the stack for any of these symbols. Note, however, that although SHOW DEVICE defines those symbols relevant to the last device unit it has displayed, and redefines symbols relevant to any subsequently displayed device unit, it does not undefine symbols. (For instance, SHOW DEVICE DUA0 defines the symbol PDT, but SHOW DEVICE MBA0: does not undefine it, even though the PDT structure is not associated with a mailbox device.)

To maintain the accuracy of symbols that appear in the stack listing, use the DEFINE command to modify the symbol name. For example:


See the descriptions of the READ and FORMAT commands for additional information about defining and examining the contents of device data structures.

For a detailed explanation of I/O data structures displayed by SDA, consult the OpenVMS VAX Device Support Manual.




VTA20 ==> LTA20                         VT200_Series      UCB address:  8042E4C0

Device status:   00010110 online,bsy,deleteucb
Characteristics: 0C040007 rec,ccl,trm,avl,idv,odv
                 00000200 nnm

Owner UIC [000001,000004]   Operation count       5793   ORB address    8042E590
      PID        00010064   Error count              0   DDB address    80CEF2E0
Class/Type          42/6E   Reference count          2   DDT address    807696FB
Def. buf. size         80   BOFF                  0155   CRB address    80BC8B00
DEVDEPEND        180093A0   Byte count            0100   IRP address    80BE2B00
DEVDEPND2        7962100C   SVAPTE            804801C0   I/O wait queue    empty
FLCK/DLCK        00000012   DEVSTS                0000

                                I/O request queue


 C   80BE2B00  00010064  E   FFC0  C000  00000000  29  80127458  7FFA800C  0003
     nop bufio,func

This example reproduces the SHOW DEVICE display for a single device unit, VTA20. Whereas this display lists information from the UCB for VTA20, including some addresses of key data structures and a list of pending I/O requests for the unit, it does not display information about the controller or its device driver. To display the latter sort of information, specify the device-name as VTA (for example, SHOW DEVICE VTA).


I/O data structures
                            DDB list

       Address    Controller     ACP       Driver      DPT   DPT size
       -------    ----------     ---       ------      ---   --------

      80D0B3C0    BLUES$DUA     F11XQP    DSDRIVER   807735B0  679D
      8000B2B8    RED$DUA       F11XQP    DSDRIVER   807735B0  679D
      80D0B9C0    RED$DUS       F11XQP    DSDRIVER   807735B0  679D
      80D08BA0    BIGTOP$DUA    F11XQP    DSDRIVER   807735B0  679D
      80D08AE0    TIMEIN$DUA    F11XQP    DSDRIVER   807735B0  679D
Press RETURN for more.


This excerpt from the output of the SHOW DEVICE DU command illustrates the format of the DDB list display. In this case, the DDB list concerns itself with those devices whose device type begins with DU (that is, DUA and DUS). It displays devices of these types attached to various HSCs (RED$ and BLUES$) and systems in a cluster (BIGTOP$ and TIMEIN$).

Following the DDB list, SHOW DEVICE DU produces displays for each controller and each unit on each controller, as illustrated in the next example.



I/O data structures
                            DDB list

     Address    Controller     ACP       Driver      DPT   DPT size
     -------    ----------     ---       ------      ---   --------

     80D0B9C0    RED$DUS       F11XQP    DSDRIVER   807735B0  679D

Controller: RED$DUS

                --- LOVE System Block (SB) 80D0C500 ---

System ID            00000000FFF2    Local software type          HSC
Max message size               66    Local software vers.         Y35Q
Max datagram size              62    Local software incarn.   6DF9E6E0
Local hardware type          HS50                             008FCC83
Local hardware vers. 2722722221A3    SCS poller timeout           0002
                     000000272272    SCS poller enable mask         01

                --- Path Block (PB) 80D0BEA0 ---

            Status:  0028

Remote sta. addr.    00000000000B    Remote port type              HSC
Remote state         00000000000B    Number of data paths            2
Remote hardware rev.     00000225    Cables state            A-OK B-OK
Remote func. mask        4F710200    Local state                  OPEN
Resetting port                 05    Port dev. name               PAA0
Handshake retry cnt.            1    SCS MSGBUF address       80BCD510
Msg. buf. wait queue        empty    PDT address              803B38D0

            --- Device Data Block (DDB) 80D0B9C0 ---

Driver name         DUDRIVER   Alloc. class        254   DDT address    80773640
ACP ident                F11   SB address     80D0C500
ACP class               PACK   UCB address    803B9C60

        ---  Primary Channel Request Block (CRB) 80BF7000 ---

Reference count       17    Wait queue         empty    Aux. struct.    803B4150
Due time        00012DCC    Timeout rout.   807743D1    Timeout link    8039E03C
IDB address     80D0C440                                Ctrl. init.     80773774
ADP address     80BF7F70

            --- Driver Dispatch Table (DDT) 80773640 ---

Errlog buf sz          0    Diag buf sz          104    FDT size             244
Start I/O       80773B21    Register dump     return    FDT address     80773680
Alt start I/O     return    Unit init       80775970    Mnt verify      80775BC2
Cancel I/O      807763A7    Unsol int       80774602    Cloned UCB        return

RED$DUS3                                RA81              UCB address:  803B9C60

Device status:   00021810 online,valid,unload,lcl_valid
Characteristics: 1C4D4008 dir,fod,shr,avl,mnt,elg,idv,odv,rnd
                 000002A1 clu,mscp,srv,nnm

Owner UIC [100001,000063]   Operation count      55595   ORB address    803B9D90
      PID        00000000   Error count              0   DDB address    80D0B9C0
Alloc. lock ID   00010161   Reference count          3   DDT address    80773640
Alloc. class          254   Online count             2   VCB address    8044D940
Class/Type          01/15   BOFF                  0000   CRB address    80BF7000
Def. buf. size        512   Byte count            0A00   PDT address    803B38D0
DEVDEPEND        04E00E33   SVAPTE            835C7738   CDDB address   803B4150
DEVDEPND2        00000000   DEVSTS                0004   I/O wait queue    empty
FLCK/DLCK        00000012   RWAITCNT              0000

            --- Primary Class Driver Data Block (CDDB) 803B4150 ---

Status:              1040 alcls_set,bshadow
Controller Flags:    80D6 cf_shadw,cf_mlths,cf_this,cf_misc,cf_attn,cf_replc

Allocation class     254    CDRP Queue      80BD1170    DDB address     8000B2B8
System ID       0000FFF2    Restart Queue      empty    CRB address     80BF7000
                    0000    DAP Count              1    CDDB link       803C01C0
Contrl. ID      0000FFF2    Contr. timeout        75    PDT address     803B38D0
                01010000    Reinit Count           0    Original UCB    00000000
Response ID     00000000    Wait UCB Count         0    UCB chain       803B89A0

    *** I/O request queue is empty ***

            --- Volume Control Block (VCB) 8044D940 ---

Status:  A0 extfid,system
Status2: 15 writethru,mountver,nohighwater
Shadow status: 21 shadmast,mvbegun

Mount count            1    Rel. volume            0    AQB address     80D0BAE0
Transactions           3    Max. files        111384    RVT address     803B9C60
Free blocks       205989    Rsvd. files            9    FCB queue       80BD87B0
Window size            7    Cluster size           3    Cache blk.      8044DA30
Vol. lock ID    00010167    Def. extend sz.        5    Shadow mem. FL  80CF5C40
Block. lock ID  01A50139    Record size            0    Shadow mem. BL  80CF5BE0
Shadow lock ID  00010168

        --- Shadow set $254$DUS3 member summary ---


Physical unit     Primary path      Secondary path    Member status
-------------     ------------      --------------    -------------
$254$DUA129       RED                 -- none --      Shadow set member
$254$DUA139       RED                 -- none --      Shadow set member

                --- ACP Queue Block (AQB) 80D0BAE0 ---

ACP requests are serviced by the eXtended Qio Processor (XQP)

Status: 14 defsys,xqioproc

Mount count           56    ACP type           f11v2    Request queue   00000000
                            ACP class              0

    *** ACP request queue is empty ***

RED$DUS5                               RA80              UCB address:  803B9DF0

Device status:   00021810 online,valid,unload,lcl_valid
Characteristics: 1C4D4008 dir,fod,shr,avl,mnt,elg,idv,odv,rnd
                 000002A1 clu,mscp,srv,nnm

This example illustrates the output of the command SHOW DEVICE DUS, where two shadow sets (RED$DUS3 and RED$DUS5) are associated with the HSC RED$. There is a controller display for RED$DUS and a unit display for each of the two shadow sets.


Displays the location and size of each loadable image that makes up the executive.








The executive consists of a fixed portion and a loadable portion. The fixed portion is known as SYS$SYSTEM:SYS.EXE and consists of three parts:
  • System service dispatch vectors
  • Universal executive routine vectors
  • Globally referenced data cells

The loadable portion consists of a number of independent images that perform the work of the operating system.

The SHOW EXECUTIVE command lists the location and size of each image within the loadable portion of the executive image. It can thus enable you to determine whether a given memory address falls within the range occupied by a particular loadable image. (Table SDA-13 describes the contents of each loadable image.)

By default, SDA displays each location within the loadable portion of the executive as an offset from the beginning of one of the loadable images; for instance, EXCEPTION+00282. Similarly, those symbols that represent system services point to the vector region and not to the system service's loadable code. When tracing the course of a system failure through the listings of modules contained within a given loadable executive image, you might find it useful to load into the SDA symbol table all global symbols and global entry points defined within one or all modules that make up the loadable portion of the executive image. See the description of the READ command for additional information.

The SHOW EXECUTIVE command usually shows all components of the executive image, as illustrated in the following example. In rare circumstances, you might obtain a partial listing. For instance, once it has loaded the EXCEPTION module (in the INIT phase of system initialization), the system can successfully post a bugcheck exception and save a crash dump. Later, if the system should fail sometime during initialization, it might not have been able to load some of the modules that appear above EXCEPTION in the SHOW EXECUTIVE display (see the example).


VMS Executive Layout
Image                            Base            End             Length
SYSMSG                           8015AA00        80183600        00028C00
RECOVERY_UNIT_SERVICES           80211400        80212000        00000C00
RMS                              80183600        801A7E00        00024800
CPULOA                           801B2800        801B3200        00000A00
LMF$GROUP_TABLE                  801B3800        801B3C00        00000400
SYSLICENSE                       801B4000        801B5400        00001400
SYSGETSYI                        801B5A00        801B7000        00001600
SYSDEVICE                        801B7400        801B8A00        00001600
MESSAGE_ROUTINES                 801B9000        801BB600        00002600
EXCEPTION                        801CBA00        801D3E00        00008400
LOGICAL_NAMES                    801D4600        801D6000        00001A00
SECURITY                         801D6600        801D7C00        00001600
LOCKING                          801D8200        801DA800        00002600
PAGE_MANAGEMENT                  801DAE00        801E2600        00007800
WORKING_SET_MANAGEMENT           801E2E00        801E7200        00004400
IMAGE_MANAGEMENT                 801E7C00        801EA400        00002800
EVENT_FLAGS_AND_ASTS             801EAA00        801EBE00        00001400
IO_ROUTINES                      801EC400        801F2C00        00006800
PROCESS_MANAGEMENT               801F3200        801F9400        00006200
ERRORLOG                         80204C00        80205600        00000A00
PRIMITIVE_IO                     80205C00        80206C00        00001000
SYSTEM_SYNCHRONIZATION           80207000        80208C00        00001C00
SYSTEM_PRIMITIVES                80209200        8020C400        00003200


The SHOW EXECUTIVE command displays the location and length of the loadable images included in the executive.


Displays the header of the dump file.








The SHOW HEADER command produces a 10-column display, each line of which displays both the hexadecimal and ASCII representation of the contents of the dump file header in 32-byte intervals. Thus, the first eight columns, when read right to left, represent the hexadecimal contents of 32 bytes of the header; similarly, the ninth column, when read left to right, records the ASCII equivalent of the contents. (Note that the period character [.] in this column indicates an ASCII character that cannot be displayed.)

After it displays the contents of the first header block, the SHOW HEADER command displays the hexadecimal contents of the saved error log buffers.

See the VAX/VMS Internals and Data Structures manual for a discussion of the information contained in the dump file header.

Dump file header
7FF03944 7FFED04E . . . 000000C1 00000000  ........................N...D9.. 00000000
00000000 00000000 . . . 00040000 80185200  .R.............................. 00000020
00000000 00000000 . . . 00000000 00000000  ................................ 00000040
00020000 00000000 . . . 15000011 00000000  ................................ 00000060
414E454C 45480800 . . . 0000012C 00000000  ....,.....................GARNER 00000080
FE9E007F F74D7C0A . . . 00000000 00002020  ...........%.@.o41......M....... 000000A0
Saved error log messages
00000000 00000009 . . . 801D8739 00000300  ....9.......5................... 801D8600
7B0090AC 2FCBCEC2 . . . 414E454C 45480800  ..GARNER  ...........&.zxcv.O... 801D8620
00202041 4E454C45 . . . 01080100 0000C30A  .A........d............GARNER  . 801D8640

The SHOW HEADER command displays the contents of the dump file's header from address 6B016 to address C9016. Ellipses indicate hexadecimal information omitted from the display.

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