SYSTEM DISK MONITOR - SYSDSK_MON

OVERVIEW
SYSDSK_MONITOR is designed to run as a detached process, submitted at system
startup, that monitors the free space on the system disk.  Through this
monitoring, it will give a warning when the percentage of free space falls
below a pre-determined level.  The warning is sent to the console device, and
pre-determined user(s) (usually the systems manager(s)) if desired.
                                                                       
Two things are assumed, that the console device is OPA0:, and that     
the logical name SYS$SYSDEVICE points to the system disk.              
                                                                       
If the symbol SYSDSK_THRESHOLD (i.e. SYSDSK_THRESHOLD == 10)           
is present, it's value is used as the percentage threshold.            
If not specified, the value of the variable TH_DEFAULT is used.        


PROCESSING
SYSDSK_MON first determines the system disk device by using the translate
logical name system routine (SYS$TRNLNM).  This logical must point to the
system disk. 

The next step searches for the symbol SYSDSK_THRESHOLD. If the symbol is
present, it is converted to an integer and used as the low limit of free space
for alarms.  If it is not present, then the pre-set limit is used (currently
25%). 

The nodename for the current node is determined (LIB$GETSYI) for use in
the log file.

If the logical name SYSDSK_MON_LOG is defined, the nodename is concatenated
to the end, and it is used as the log file specification.  This log file
is written once per hour (presently, this can be altered), and can be used
for historical purposes.  If not specified, no log file is kept.  The log
file is created when the program is initially run, and appended to at the
determined interval (see above).  The file is closed between writes, and
opened for append when needed.

At this point, an infinite loop is initiated.  This loop determines the total
blocks and total free-blocks for the system disk. The percentage of free-blocks
is determined and a message string is created containing the necessary
information (using LIB$SYS_FAO).  If it is time to write the log file, if there
is one, the file is opened (for append) written to, and closed.  The free-block
percentage is then checked and if it is below the current threshold, the
formated string is sent to the console device (OPA0:) using the system
breakthrough routine (SYS$BRKTHRU).  Specific users (usually system managers)
may also be notified at this time via the breakthrough routine.  If the
free-block percentage is above the threshold value, no action is taken.  A
delta time is determined (SYS$BINTIM), a wakeup scheduled (SYS$SCHDWK), and the
process hibernates (SYS$HIBER).  Upon waking up from the hibernate, the loop
repeats. 


ASSOCIATED FILES
SYSDSK_MON.TXT			This file.
SYSDSK_MON.FOR			Source file for SYSDSK_MON.EXE.
SYSDSK_MON.EXE			Executable image.
SYSDSK_MON.COM			Command procedure to run SYSDSK_MON.EXE.
SYSDSK_MON_START.COM		Command procedure submitting SYSDSK_MON.COM
				as a detached process.

Note that SYSDSK_MON.COM may contain the symbol and logical name definitions
required. 

						Jay Jenkins