There are three methods which are attempted sequentially if a quiescing snapshot is requested of a Linux Virtual Machine:
1. Using FIFREEZE/FITHAW ioctls build into the kernel
* this option is only available in kernels newer than 2.6.32 on Linux VMs running vmtools 5.x or higher (vSphere 5).
2. Using a VMware kernel module (vmsync)
* this option is available in kernels 2.6.6 -> 2.6.29 on Linux VMs running vmtools 4.x or higher (vSphere 4) and is experimental
**Message seen when installing tools in Linux***
[EXPERIMENTAL] The VMware FileSystem Sync Driver (vmsync) is a new feature that
creates backups of virtual machines. Please refer to the VMware Knowledge Base
for more details on this capability. Do you wish to enable this feature?
3. Using the Linux sync command
Each of the above methods also allows you define custom scripts which are called by vmtools before and after the quiesce.
An example of creating your own freeze/thaw scripts is below:
/usr/sbin/pre-freeze-script
----------------------------------
fsfreeze -f /
/usr/sbin/post-thaw-script
---------------------------------
fsfreeze -u /
**Note: mount point being used in above scripts needs to be mounted with the "noatime" option for the above to work