Nagios Support Forum

Hello
how do I Nagios check one service 1 in 1 second?

Can I get a little clarification here? Do you want to check the same service every single second..?

exactly friend, I would like Nagios check if a service every second

Active checks by default are a minimum of every minute. You can hack something together, but it not supported nor recommended by us. Setting up passive checks may be more be more beneficial to your use case. Have a read of this document.