From collectd Wiki

The DF plugin collects file system usage information, i. e. basically how much space on a mounted partition is used and how much is available. It's named after and very similar to the df(1) UNIX command that's been around forever.

However, not all "partitions" are of interest. For example /proc and /dev usually don't get filled and their "size" doesn't make a lot of sense. That's why the DF plugin offers to select only specific devices, mount points or filesystem types.

[edit] Synopsis

<Plugin "df">
  Device "/dev/hda1"
  MountPoint "/home"
  FSType "ext3"
  IgnoreSelected false
  ReportReserved false
  ReportInodes false
</Plugin>

[edit] Example graph

[edit] Dependencies

• Most UNIXes
  • statfs(2) or statvfs(2)
  • getmntent(3)
• 4.4BSD or Mac OS X
  • statfs(2) or statvfs(2)
  • getfsstat(2)

[edit] Caveats

[edit] Reserved disk space

If the ReportReserved configuration option is set to false (the version 4 default), the disk space reserved for the root user is reported as "free". It may therefore happen that user processes can't write to a partition despite the graph showing remaining "free" disk space.

Setting ReportReserved to true is recommended and the (only) behavior of version 5.