Time settings

In accordance with best practice, the z/OS system time is set to Coordinated Universal Time (UTC). z/OS uses several independent methods for determining the local time offset when providing local time services to programs:

• Using the offset in the CLOCKxx member of the SYS1.PARMLIB concatenation. 
  The z/OS TIME macro and many application and system programs use this method. BMC AMI Defender uses this method for the timer setting that provides statistics every midnight and for the local time timestamps found in many SMF records.

• Using a line similar to –e TZ=EST5EDT in /etc/init.options that sets the time zone for interactive UNIX shell users.

• Using the CEEPRMxx member of the SYS1.PARMLIB concatenation, that sets default Language Environment run-time options.

  The CEEDOPT statement (for instance,  CEEDOPT(... ENVAR(‘TZ=CST6CDT’), ...)) sets the non-CICS, non-AMODE 64 options. This is where Language Environment gets the time zone information that is used by BMC AMI Defender and CZASEND for most local time purposes.

• Overriding the CEEDOPT time zone specification (or lack of time zone specification) by placing an ENVAR statement in amihlq.CZAGENT.CNTL(CZALEOPT) (for instance, ENVAR(‘TZ=PST8PDT’))


The SYS1.PARMLIB members are documented in IBM documentation.

The full format of the TZ= operand is complex, but the simplest form is ssso or sssoddd, where:

• sss is a standard time zone abbreviation, such as EST.
• o is the offset in hours from UTC, such as 5 (for Eastern Standard Time) or -1 (for Central European Time).
• ddd is the daylight or summer time zone abbreviation, such as EDT. Omit ddd if your locale does not observe summer or daylight time. 

In addition, you can set the local time offset for BMC AMI Defender and CZASEND using the TIME statement. For more information, see TIME statement.

Dates before 1970

BMC AMI Defender utilizes the z/OS UNIX library for time and date formatting. The earliest date supported by UNIX is January 1, 1970 (the start of the UNIX epoch). Several date formats common on z/OS support dates as early as 1900. While it is unlikely that any valid SMF dates predate 1970, date fields containing values before 1970 are possible due to record format or processing errors. BMC AMI Defender forces all dates before 1970 to 12:00:00 UTC on January 1, 1970. If you select local time formatting, the time could be formatted as earlier or later than 12:00:00. For time zones more than 12 hours east of Greenwich, the time could be formatted as a time on January 2, 1970.

Time accuracy

If your system clock is not synchronized with an external source of accurate time and you set the clock manually, you should not rely on the absolute accuracy. However, you can rely on the relationship between two time fields (for instance, the time between two events). Certain time fields are recorded in SMF records with a granularity of hundredths of a second, but can be formatted in thousandths of a second; thus, a formatted time of 16:49:17.120 might represent any time between 16:49:17.115 and 16:49:17.124. To determine the granularity of a particular field, see General SMF record type statement.