How can Zabbix monitor files older than a specified time?

[sixdigit]

Hello all, I'm new to Zabbix and I have a problem that I need some help with.

I want to monitor files that are older than 30 minutes in a directory. I'm thinking of using this command:

# find /lvm_encrypted_dir/sftp/*/incoming ! -newermt '30 minutes ago' | wc -l

In the agent conf file, I've added this:

UserParameter=sftp.check.older30mins,/bin/find /lvm_encrypted_dir/sftp/*/incoming ! -newermt '30 minutes ago' | wc -l

This is for my item:

Key: sftp.check.older30mins

- This refreshes every 30s.

For the Trigger, I used this:

{<SERVERNAME>:sftp.check.older30mins.last(300)}>0

Zabbix is sending out alerts but it resolves itself after 4-5 minutes even if the files are still in the directory. I was expecting that it will only send out resolution alerts if and when it doesn't see any files in the directory anymore. What am I missing?

Appreciate any help I can get!

Thanks!