Device without Internet

[FredZwarts]

Hello,
I started using Cacti a few weeks ago, so I am rather new. I succeeded to create graphs for more or less standard devices, such as my NAS, my Router and the Linux system that hosts the Cacti server, using SNMP and local templates.
Now I want to add a new device, my Solar Panel system. I tried to create a new template for this device, but I have a few problems. Maybe I missed it in the documentation, so, I would be happy with pointers to the documentation, or with other suggestions.
The first problem is that each device seems to require a FQDN or IP address, but my device is not on the Network. It communicates with my Linux system using a serial port connection. I want to write some scripts to interface this system with Cacti. I do not think that I am the first one in such a situation. So my question is how does one configure a Cacti device for a device without IP?
The second question is a related one. I would like to use an offline detection method, because my solar panels are only online (via the serial line) during day time (and 'day time' means when there is enough light, which varies from day to day). For offline detection I see only methods that use IP (ping or SNMP). Is it possible to create my own offline detection method, using a script and how is it done?

[TheWitness]

If you use localhost, you don't need internet, an use service check none. for data input method just use a script to gather the data. Easy peasy.

[FredZwarts]

If you use localhost, you don't need internet, an use service check none. for data input method just use a script to gather the data. Easy peasy.

Thanks, localhost will work, but it is more a work-around than a solution.
Further, do you mean that it not possible to make my own offline detection method? That would be a pity, because I would like to provide uptime information for the device.

[TheWitness]

That is offline, are you meaning, you would like to store the data elsewhere and siphone it into the RRDfiles as opposed to polling?

[FredZwarts]

That is offline, are you meaning, you would like to store the data elsewhere and siphone it into the RRDfiles as opposed to polling?

No, I mean that during the night the device is down, so it does not gather data and cannot be contacted. I can poll it normally only during day time. I thought that that is where offline detection is for. To tell cacti when it makes no sense to poll because a device is offline.

[TheWitness]

How do you know it's up or down in the script?

[TheWitness]

What I would likely do for this, as a beginner is write a cron that simply writes the last good known data to a file, and cactus data input method would just read from the file every polling cycle. File is always there, so no timeouts.

[TheWitness]

Second option is to auto-disable and enable the device through a cron script.

[FredZwarts]

How do you know it's up or down in the script?

When the script sees a time-out when contacting the device over the serial line.

[FredZwarts]

What I would likely do for this, as a beginner is write a cron that simply writes the last good known data to a file, and cactus data input method would just read from the file every polling cycle. File is always there, so no timeouts.

Is it also possible for a script to report invalid data? E.g., what happens when a script returns null, or nan, instead of a valid number? I ask this, because the last good known data are not very useful, I would prefer to see a hole in the graph instead of values that look as if they mean something.

[TheWitness]

If the script return 'U'. That means a bad response. We recently added a function in cacti where you can set a timeout for you PHP script like 3-4 seconds so it does not block you poller too.

[TheWitness]

It's in lib/poller.php

[FredZwarts]

If the script return 'U'. That means a bad response. We recently added a function in cacti where you can set a timeout for you PHP script like 3-4 seconds so it does not block you poller too.

That is good to hear. The problem remains that the solar panel system has many parameters and therefore it will need many scripts. Even if each of them times out in a few seconds, the added time-outs will still be significant. That is the reason why I would like to be able to add an offline detection method, so that the time-out would happen only once (because I hope that if cacti knows about the offline status, it will not poll the other parameters).
Wouldn't it be a nice feature if we could create our own offline detection methods?