Greenwich Mean Time (GMT)

The HTTP protocol (like most international networking protocols) requires that dates and times, where used, be quoted in GMT. The personal computers on which OS/2 runs, however, do not require that a GMT clock be available--instead, the clock is usually set to local time.

Various mechanisms are used in OS/2 to indicate and calculate the current offset from GMT. The most common is to use an OS/2 environment variable named 'TZ', and for many people running GoServe this will already be set (for example to 'EST5EDT' for the USA East Coast). See the separate section on setting the value of the TZ variable.

If TZ is not set, GoServe will only use local time (and HTTP protocols and header fields that require GMT will not be used or generated).

If the TZ variable is set, GoServe will convert from local time to GMT as appropriate. It will also detect a clock dislocation (that is, when the time-of-day clock is changed by more than 10 seconds) automatically, and record and re-calculate the GMT offset when this occurs--such as when you change your clock for daylight-savings time.

Notes:

  1. You can see the offset that GoServe has computed by using the CONTROL STATISTICS command or the GMTOFFSET() function.
  2. For a few seconds between when you change the time and when GoServe detects that it has been changed, incoming transactions may be processed with anomalous time data; to avoid this, stop GoServe before making large time adjustments and restart it afterwards.
  3. Files in the PC-DOS and OS/2 FAT and HPFS file systems are timestamped with the local time of creation or last modification. The time-zone and daylight savings regime of that zone (and hence the GMT offset) are not available. GoServe therefore calculates the GMT timestamp of a file by using the current GMT offset.
  4. If you are running a machine as a dedicated Web server, you may wish to set its clock to GMT and leave it set that way all year; in this case, set TZ to 'GMT0'.

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From 'goserve.doc', version 2.32.
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