QHST history log

The history log (QHST) consists of a message queue and a physical file known as a log version.

Messages sent to the history log message queue (QHST) are written by the system to the current log version physical file. The history log contains a high-level trace of system activities such as system, subsystem, and job information, device status, and system operator messages.

When a log version is full, a new version of the log is automatically created. Each version is a physical file that is named in the following way:

Qxxxyydddn

where the following is true:

xxx: Is a 3-character description of the log type (HST)
yyddd: Is the Julian date of the first message in the log version
n: Is a sequence number within the Julian date (A through Z and 0 through 9)

Note: The number of records in each version of the history log is specified in the system value QHSTLOGSIZ. There is also a value of *DAILY to allow a new log version to be created each day instead of creating a new file based only on size.

The text of the log version file contains the date and time of the first message and last message in the log version. The date and time of the first message are in positions 1-13 of the text; the date and time of the last message are in positions 14-26. The date and time are in the format cyymmddhhmmss, where:

c: Is the century guard digit
yymmdd: Is the date the message was sent
hhmmss: Is the time the message was sent

You can create a maximum of 36 log versions with the same Julian date. If more than 36 log versions are created on the same day, the next available Julian day is used for subsequent log versions. If some of the older log versions are then deleted, it is possible to use the names again. Log versions are out of order when sequenced by name if log versions are deleted and names used again.

You can write a program to process the history log files or use IBM-supplied functions to process the files. IBM provides the Display Log (DSPLOG) CL command and the Open List of History Log Messages (QMHOLHST) API. Because several versions of each log might be available, you must select the log version to be processed. To determine the available log versions, use the Display Object Description (DSPOBJD) command. For example, the following DSPOBJD command displays what versions of the history log are available:

DSPOBJD   OBJ(QSYS/QHST*)   OBJTYPE(*FILE)

You can delete logs on your system by using the delete option from the display that is presented on the Work with Objects (WRKOBJ) command.

You can display or print the information in a log using the Display Log (DSPLOG) command. You can select the information you want displayed or printed by specifying any combination of the following:

Period of time
Name of job that sent the log entry
Message identifiers of entries

The following Display Log (DSPLOG) command displays all the available entries for the job OEDAILY in the current day:

DSPLOG JOB(OEDAILY)

The resulting display is:

                       Display History Log Contents
 
 Job OEDAILY started
 Database file OEMSTR in library OELIB expired
 Job OEDAILY abnormally ended
 Job OEDAILY started
 Job OEDAILY ended
 
 
 
 
 
 
 
 
 
 
 
 
                                                                 
        Bottom
 Press Enter to continue.
 
 F3=Exit   F10=Display all   F12=Cancel

If you reset the system date or time to an earlier setting, or if you advanced the system date and time by more than 48 hours, a new log version is started. This ensures that all messages in a single log version are in chronological order.

Log versions created on a release before V3R6M0 may contain entries that are not in chronological order if the system date and time was reset to an earlier setting. Therefore, when you try to display the log version, some entries may be missed. For example, if the log version contains entries dated 1988 followed by entries dated 1987, and you want to display those 1987 entries, you specify the 1987 dates on the PERIOD parameter on the Display Log (DSPLOG) command but the expected entries are not displayed. You should always use the system date (QDATE) and the system time (QTIME), or you should specify the PERIOD parameter as follows:

PERIOD((start-time start-date) (*AVAIL *END))

The system writes the messages sent to a log message queue to the current log version physical file when the message queue reaches a certain size or when the Display Log (DSPLOG) command was used. If you want to ensure the current log version is up-to-date, specify a fictitious message identifier, such as ###0000, on the DSPLOG command. No messages are displayed, but the messages in the message queue are copied to the log version physical file to make it current.

Note: If a message is sent to QHST and the Display Log (DSPLOG) command is done immediately, the DSPLOG command will show messages from the log version physical file. Depending on the number of messages being copied to the log version, your message may not be shown until a second Display Log (DSPLOG) command is run later.

If you print the information in a log using the Display Log (DSPLOG) command and output parameter *PRINT, (DSPLOG OUTPUT(*PRINT)), only one line from each message is printed, using the first 105 characters of each message.

If you print the information in a log using the Display Log (DSPLOG) command and output parameter *PRTWRAP, (DSPLOG OUTPUT(*PRTWRAP)), messages longer than 105 characters are wrapped to include additional lines to a limit of 2000 characters.

If you print the information in a log using the Display Log (DSPLOG) command and output parameter *PRTSECLVL, messages longer than 105 characters are wrapped to include additional lines to a limit of 2000 characters. The second-level message text is also printed if available, up to a maximum of 6000 characters.

If you display the information in a log using the Display Log (DSPLOG) command, only 105 characters of message text are shown. Any characters after 105 characters are truncated at the right.