# Merging Traces

Two or more trace files from simultaneous sessions that were captured on the same machine can be merged into a single trace file. The following command merges two files named Kernel.etl and User.etl into one file, System.etl:

```
xperf -merge kernel.etl user.etl system.etl

```

For information on starting and stopping traces please see the Starting a Trace and Stopping a Trace sections of this document.

The resulting trace file, System.etl, contains the trace information from both Kernel.etl and User.etl, as well as additional system information that is critical for symbol decoding.

Important   An unmerged kernel trace cannot be symbol decoded correctly. For more information, see the Symbol Supportsection of this document.