Virtual machines can write support and troubleshooting information into a virtual machine log file stored on a VMFS volume. The default settings for virtual machines are appropriate for most situations.

If your environment relies heavily on using VMotion, or if the defaults do not seem suitable for other reasons, you can modify the logging settings for virtual machine guest operating systems.

New log file creation happens as follows:

  • Each time you power on or resume a virtual machine, and each time you migrate a virtual machine with VMotion, a new log file is created.

  • Each time an entry is written to the log, the size of the log is checked. If vmx.log.rotateSize is set to a nondefault value, and the size is over the limit, the next entry is written to a new log. If the maximum number of log files exists, the oldest log file is deleted.

The default for vmx.log.rotateSize is zero (0), which means new logs are created during power on, resume, and so on. You can ensure new log file creation happens more frequently by limiting the maximum size of the log files with the vmx.log.rotateSize configuration parameter.

VMware recommends saving 10 log files, each one limited to no less than 2MB. These values are large enough to capture sufficient information to debug most problems. If you need logs for a longer time span, you can set vmx.log.keepOld to 20.