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The Monitor utility (MONITOR) is a system management tool used to record and display information about operating system performance such as system I/O statistics, page management statistics, and time spent in each of the processor modes. It is invoked with the MONITOR command.


MONITOR [/qualifier[,...]] classname[,...] [/qualifier[,...]]


MONITOR collects system performance data by class. The following classes are available:

Monitors processes much like SHOW SYSTEM, but in real time.

Initiates monitoring of the PROCESS STATES class, which shows the number of processes in each of the 14 scheduler states.

Initiates monitoring of the File Control Primitive statistics class, which includes information about all Files-11 ancillary control processes (ACPs) and extended QIO processors (XQPs) on the local node.

  • LOCK
  • DISK

Initiates monitoring of the DISK statistics class. The maximum number of disks that can be monitored for record output is 909, and for display and summary output is 1817.


Initiates monitoring of the Distributed Lock Manager.

  • SCS
  • CLUSTER - incompatible with other classes; DECnet must be installed
  • RMS
  • VBS (VAX Only)

Several classes can be specified with commas or plus signs as delimiters. All classes can be specified with the ALL_CLASSES parameter.

Monitoring Duration

Generally, each MONITOR request runs from the time specified with the /BEGINNING qualifier until the time specified or implied by the /ENDING qualifier. To exit from MONITOR, enter the EXIT command at the MONITOR> prompt or press Ctrl/Z. To terminate a MONITOR request without exiting from the utility, press Ctrl/C.


Default settings for commands and qualifiers can be reestablished with the INITIALIZE command.

Flush Interval

By default, the interval at which MONITOR buffers are written to disk, is 300 seconds. It can be modified with the /FLUSH_INTERVAL qualifier that takes a value in seconds from 1 to 9999. If the data is written to a shared recording file currently in use, the interval should be short to ensure that the data in the file is as current as possible and as little data as possible is lost as a result of a system failure.


MONITOR produces the following types of output:

  • A disk recording file in binary format (run with /RECORD)
  • Statistical terminal displays (run without /RECORD or /OUTPUT)
  • A disk file containing statistical summary information in ASCII format

Pre-version 5.0 MONITOR recording files can be converted to the current format with the CONVERT command. The files can be converted to CSV by T4, another layered product for performance analysis.


MONITOR can execute scripts (files containing MONITOR commands) with the EXECUTE command (or preceded with an @ sign).

Batch mode

MONITOR can be run in batch mode; specify /NODISPLAY.


SYS$EXAMPLES contains three MONITOR-related command procedures:

  • SUBMON.COM starts MONITOR.COM as a detached process.
  • MONITOR.COM creates a summary file from the binary recording file of the previous boot, then begins recording for this boot. The recording interval is 10 minutes.
  • MONSUM.COM (VAX only) generates two OpenVMS Cluster multifile summary reports: one for the previous 24 hours and one for the previous day’s prime-time period (9 a.m. to 6 p.m.). These reports are mailed to the system manager, and then the procedure resubmits itself to run each day at midnight.

See also