Add ledmon package

[oreo]

Problem/Justification
(What is the problem you are trying to solve with this feature/improvement or why should it be considered?)

I would like to be able to locate a physical disk bay from the Linux device (/dev/sdX)

On Debian this is possible with the ledmon package which provides the ledctl command. See user story for example usage.

Impact
(How is this feature going to impact all TrueNAS users? What are the benefits and advantages? Are there disadvantages?)

This will help users locate disk bays without having to keep an inventory of which bay holds which disk.

Because the ledmon package is part of the official Debian repository and provides an independent set of binaries that do not interfere with any other libraries or binaries, I do not see a disadvantage to including it.

User Story
(Please give a short description on how you envision some user taking advantage of this feature, what are the steps a user will follow to accomplish it)

A sysadmin needs to take out one or more disk bays knowing the device paths on the host, say /dev/sdh and /dev/sdi. They can run ledctl locate=/dev/sdh,/dev/sdi which will make the bay activity LED blink on and off at a regular interval, making the bays easy to locate.

[argumentum]

Argumentum's Note to self

Here I’ll share solutions to simple questions I had. But I’ll forget and have to research all over again hence this Note to self. How to post formatted text </> ( link to copy and paste in your post to reference to that post, to help the user with a clickable link as reference/help) How to make the HDD activity LED turn on for a while ? I needed this to find … * Device: /dev/sdu [SAT], FAILED SMART self-check. BACK UP DATA NOW!. … where in the case the drive with problems was at in the…

search for “How to make the HDD activity LED turn on for a while ?”

And yes, I’d like a button for it too

…but there are times that what you need is to light the other drives because the one you’re looking for is dead. Not even a blinking light

[oreo]

I already know about dd. It is not helpful when disks are busy, which is often the case on a NAS. ledctl will make the activity light blink on and off with a specific cadence that is recognizable even amongst drives having activity.

I also know that ledmon can be extracted from the .deb and rsync’d over. But it would be much more helpful if it could be installed by default. From the UI would be even better, but at the very least including the package as part of the distribution would greatly help and seems like a low effort.