NetBeans always shows warning: “The authenticity of host x can’t be established” after upload, download or synchronize

You can create an empty file and set it as the Known Hosts File in the Manage Remote Connections window. The next time you tell NetBeans to connect anyway, it will save the fingerprint in that file and stop bothering you. I think it’s safe to assume that if the key changes, you will be prompted again.

1. Open an Explorer window and navigate to Documents/NetBeansProjects
2. Create a text file called KnownHosts.txt
3. In Netbeans right-click on a project
4. Click Properties
5. Click Run Configuration
6. Click Manage
7. Next to the input field Known Host Files click Browse
8. Navigate to the directory where you created the KnownHosts text file
9. Select that file
10. Click OK
11. Click OK
12. In the project upload something. The prompt will appear this one time but not again.