I've left this enabled for now but we should consider changing this to false so that duplicate devices based on sysName aren't added.
I've also updated the addhost output so that an error is printed and not the help details as it's confusing. This could do with expanding further but it's a quick fix.
Add support for stopping devices being added with duplicate sysNames
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Seems fine, if we do set it false, then we need to have a clear explanation of why librenms thinks the device exists on the add device web page as well.
Unfortunately the addHost / createHost don't currently return anything other than true/false so nothing more than a generic failed message can be done at this time.