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Title
An error "Enter valid hosts file entries for persistent hostnames" appears when defining hostnames using a combination of lowercase and uppercase letters in the Persistent hostname list. -
Description
When defining hostnames using a combination of lowercase and uppercase letters in Log | Options | Name resolving | Persistent hostname list, an error below appears.
=> dns_hosts
Enter valid hosts file entries for persistent hostnames.
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Resolution
The persistent hostname list used in syslog-ng is written into the /opt/syslog-ng/etc/hosts file, which functions similarly to the /etc/hosts file. This file is for syslog-ng's use.
The DNS is case insensitive, therefore from a technical perspective, uppercase hostnames have minimal added value.
It's recommended to use lowercase hostnames in the persistent hostname list to avoid validation errors.