On Linux virtual machines, VMware supports only crash-consistent backups, however application-consistent backups are possible through the use of customer pre-freeze and post-thaw scripts.

Two methods are attempted sequentially when a quiesced snapshot is requested of a Linux virtual machine:

Procedure

  1. Using the ioctl(2) mechanisms FIFREEZE and FITHAW built into the Linux kernel.

    This option is available in only with kernel versions newer than 2.6.32 on Linux virtual machines running VMware Tools 5.x or higher (vSphere 5.0 and later).

  2. Using the sync(2) system call.

    The first method allows you define custom scripts that get called by VMware Tools before and after quiesce. Here are two commands that can be called from pre-freeze and post-freeze scripts: 

    # -f means freeze
     fsfreeze -f /

# -u means unfreeze
     fsfreeze -u /

    The mount point used in the scripts (root in the examples above) must be mounted with the noatime option, meaning do not update inode access times on the file system, for freeze and unfreeze to work.