A wrap-around line trace exists for each channel. This trace is kept in a 4 KB buffer for
each channel in the channel initiator address space. Trace is produced for each channel, so it is
ideal for problems where a channel appears to be hung, because information can be collected about
the activity of this channel long after the normal trace has wrapped.
About this task
The line trace is always active; you cannot turn it off. It is available for both LU 6.2 and TCP
channels and should reduce the number of times a communications trace is required.
You can view the trace as unformatted trace that is written to CSQSNAP.
You can display the trace by following these steps:
Procedure
- Ensure that the CHIN procedure has a SNAP DD statement.
- Start a CHIN trace, specifying IFCID 202 as follows:
START TRACE(CHINIT) CLASS(4) IFCID(202)
- Display the channel status for those channels for which the line trace is required:
DISPLAY CHSTATUS(channel) SAVED
This dumps the current line for the selected channels to CSQSNAP. For more information,
see
Snap dumps on z/OS.
The line trace buffer is unformatted. Each entry
starts with a clock, followed by a time stamp, and an indication of whether this is an OUTBOUND or
INBOUND flow. Use the time stamp information to find the earliest entry.
Notes:
- The addresses of the storage dump are incorrect because the CSQXFFST mechanism takes a copy of the storage before writing it
to CSQSNAP.
- The dump to CSQSNAP is only produced the first time you run the DISPLAY CHSTATUS
SAVED command. This is to prevent getting dumps each time you run the command.
- To obtain another dump of line trace data, stop and restart the current trace.
- You can use a selective STOP TRACE command to stop just the trace that was
started to gather the line trace data. To do this, note the TRACE NUMBER assigned to the trace as
shown in this example:
+ssid START TRACE(CHINIT) CLASS(4) IFCID(202)
CSQW130I +ssid 'CHINIT' TRACE STARTED, ASSIGNED TRACE NUMBER 01
- To stop the trace, issue the following command:
+ssid STOP TRACE(CHINIT) TNO(01)
- You can then enter another START TRACE command with a DISPLAY
CHSTATUS SAVED command to gather more line trace data to CSQSNAP.