Microsoft Lync 2010 Client Logging

A quick post for a commonly needed reference. Others might find it useful.

Lync 2010 Client logging is turned on/off in the Options | General settings as shown below.

Lync Logging

The Lync client needs to sign-out and sign-back-in for the settings to take effect.

The log files are stored in:


On Windows 7 or Vista this will equate to c:\users\<user name>\tracing.

The first option generates a UCC API file (e.g. Communicator-uccapi-0.uccapilog).  The second option generates *.etl files.

The UCC API is the API the Lync client uses to talk to the Lync server.  The Snooper.exe utility can be used to view traces in server and client *.uccapilog log files.  The log file can also be opened in Notepad.exe (or any text editor), but it easier to read and analyze in Snooper which is part of the Lync 2010 Server Resource Kit tool. An excellent overview of the tool and a link to download it can be found here: Microsoft Lync Server 2010 Resource Kit Tool: Snooper. Note that there are two tabs in the tools: Traces and Messages.  The Messages tab provides all the SIP interaction details.

For debugging Lync 2010 client issues with Lync Online in Office 365, you can use the MOSDAL (Microsoft Online Services Diagnostics and Logging) Support Toolkit. A good description of it is available here:

For more information on debugging Communicator 2007 R2 client issues, see: OCS Client Logging Capabilities (MOC).

Note: as a reader of this blog entry pointed out, the “Turn on logging in Lync” on the Lync client can result in large log files if left on for a long time.  It is best to use the client logging for short term debugging and troubleshooting.

Enabling Logging Via a Lync Client Policy

The Lync client event logging can be turned on and off via an Administrator Lync client side policy.  Administrators can use the Set-CsClientPolicy or the New-CsClientPolicy cmdlet’s to specify the EnableEventLogging setting.

2 comments to Microsoft Lync 2010 Client Logging

  • Ryan

    I am using Citrix XenDesktop with Profile Redirection and the Lync logs caused me a huge issue! By default, Lync was logging all conversations and in less than a year, users profiles had over 1GB (for each profile!) of logs! I forced users to disable logging and removed the log files. I was amazed at how large these would grow.

    • Ryan, yes, full Lync client logging is very verbose and is meant for short-term debugging. It is not just conversations, but all the internal workings of the Lync client! I should add that to this blog post – thanks for the feedback.

      Curious – how did logging get enabled by default?

      BTW, you need to be equally aware with server-side logging. It can grow much faster than the client…


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