How can i monitor umount?

[sysadm01]

Hello.
I want monitor filesystem mount status.
I want make trigger action,When umount file system.

So I made this trigger but not work.
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{Linux Server Default Template:vfs.fs.size[{#FSNAME},total].nodata(90)}<>0
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Who can make work this trigger?

[LenR]

When the umount happens, that item returns the space info for the filesystem containing the mount target.

Here is the key I use for an item to determine mount status (as a item prototype)

vfs.file.regmatch[/etc/mtab,{#FSNAME} ]