Start generalized path information unit trace (GPT) from the host processor. Only one host processor at a time can start GPT. A request to start the trace from a second host processor is rejected if the trace is still active from another host processor. However, the same host processor can issue several start trace requests for different resources. Buffer and cycle utilization considerations limit the maximum number of resources that can be traced at the same time.

Stop the trace using the same procedure you used to start the trace. Specify the OFF parameter on the MODIFY command.

You can activate VTAM® traces when VTAM is started or as needed. Use the TRACE option on the START command to begin the trace when VTAM is started. Use the MODIFY TRACE command to begin the trace when VTAM is already running. The TRACE start option and the MODIFY TRACE command have additional parameters unique to the type of trace being started.

Before you start GPT for VTAM, start the generalized trace facility (GTF) with the USR option. For information about starting GTF, see z/OS MVS Diagnosis: Tools and Service Aids.

For more information about GPT, the TRACE start option, and the MODIFY TRACE command, see z/OS Communications Server: SNA Operation.

To interpret and print trace data, see ACF/TAP information in ACF/TAP and trace data.