By default, VNC Server and VNC Viewer record basic information about connection activity. You can increase the amount of information recorded, change the type of activity, or alter the destination. In addition, you can start recording information about other VNC Connect programs and sub-processes.
The following table lists the default destinations for output from VNC Server (as determined by its Log parameter) and VNC Viewer (as determined by its Log parameter):
|VNC Server||Service Mode||
syslog, to the USER facility (see note 5)
(see note 4)
|Virtual Mode||Standard Error (see note 6)|
|Virtual Mode daemon||syslog, to the DAEMON facility (see also note 7)|
|VNC Viewer||Standard Error||Standard Error||Standard Error|
The following notes apply to the table above:
- If the destination is to file, the location is determined by the LogDir and LogFile parameters. Containing directories must be writable.
- If the destination is to file, the contents of that file are overwritten each time a program is restarted. To preserve information, choose a different destination, for example Standard Error. (You could still redirect this to file, for example by using a command such as
vncserver-x11 -Log=*:stderr:100 2>>myfile.)
- Under Windows, you must ensure the Windows Event Log service is running and that Event Viewer > Windows Logs > Application > Properties is set to overwrite as needed. If the service is not running or the event log is full, connections cannot be established.
- This location is for Windows 7, though note
AppDatamay be hidden by default. The location is slightly different under some other versions of Windows.
- Under Linux, VNC Server in Service Mode can be configured to log to different facilities using the SyslogFacility parameter.
- Under Linux, the default destination for VNC Server in Virtual Mode is Standard Error, but
vncserversymlink) automatically redirects this to file at
~/.vnc/<computer>:<display-number>.log. Note the output of the X server session is included.
- Under Linux, each time a user connects to the VNC Server in Virtual Mode daemon, a new instance of VNC Server in Virtual Mode is immediately started, and its log output automatically redirected to file as above.
- As of version 6.7.0 of VNC Server, default logging to event logs (windows) and syslog (Mac and Linux) defaults to level 10. Logging to file across all operating systems in the table above also defaults to level 30 from version 6.7.0 of VNC Server.
*Under Linux or Mac, VNC Server also automatically logs connections authenticated using the system authentication or single sign-on schemes to the syslog AUTHPRIV facility, typically located at
Quickly generating debug logs
You may be eligible to contact Support if you encounter a problem or require assistance.
The Support team rely on comprehensive debug log files to troubleshoot problems, equivalent to setting the VNC Server and VNC Viewer
Log parameters to
In order to quickly generate a debug log file for either VNC Server or VNC Viewer:
- On the Troubleshooting page of the Options or Properties dialog respectively, choose Create a debug log file, and then OK.
- Restart the program.
- Recreate the problem, and send the file in the specified location to the Support team.
Recording information about other programs and sub-processes
You can apply the
LogDir parameters to VNC Connect programs other than VNC Server and VNC Viewer, and also to VNC Server sub-processes. This may be useful if the Support team requests that you dig deeper into any problems you may encounter.
You can apply parameters to the following programs and sub-processes by creating special keys in the Windows Registry. Alternatively, for some programs you can apply parameters at the command line.
|Program or sub-process||Registry key||Parameters can be applied...||Registry hive|
|VNC Server||Service Mode user interface||
|User Mode user interface||
|Licensing||At the command line||
||Registry or command line|
|Using the Licensing Wizard||
For example, to create a log file for the VNC Server in Service Mode user interface:
- Using Registry Editor, navigate to
- Select New > Key from the shortcut menu, and create
- Select New > String Value from the shortcut menu, and create
- Select Modify from the shortcut menu, and specify appropriate Value data, for example
Repeat steps 3 and 4 for the
LogDir parameters, if necessary. Restart the program to create the new log file.
To create a log file for a program at the command line, apply parameters before any command, for example:
vnclicense.exe -Log=*:file:100 -LogFile=license.log -add <key>
You can apply parameters to the following programs when run from the command line:
Do so before any command, for example:
vnclicense -Log=*:file:100 -LogDir=/home/dev/logs -add <key>
You can apply the logging parameters to the following programs when run from the command line:
Do so before any command, for example:
/Library/vnc/VNC\ Server\ Licensing.app/Contents/MacOS/vnclicensewiz -Log=*:file:100
*Two files are created for the VNC Server Licensing Wizard:
Mac OS Catalina requires you change the shell to bash before running this command.