Tag Archives: servers

mosquitto connection refused

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Hi all, if you’ve just upgraded mosquitto server on some flavour of linux and wondered why all your mosquitto subscribers and publishers on your network have just started failing, you may have fallen foul of this:

the new mosquitto 2.0 requires a ‘listener’ be configured to the ports required, or else it will only listen to the localhost:1883.

So if all your clients start failing after, edit the configuation and add the following line to the top:

“listener 1883”

See the post here for more information: https://mosquitto.org/documentation/migrating-to-2-0/

Day 5 – Datacentre work

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Today, I was planning on scanning through NaBlogPoMo’s blogroll and pick out a couple of good ones. However, life always likes to intervene, and at about 1730 a server decided to fail. Wouldn’t boot up, nothing on the console.

As I’m on call this week, it was my turn to head into the datacentre, to have a look and try to fix it. For some reason, whilst it was showing network lights (so the network card was obviously initialized), it wouldn’t show anything, nor would it respond at all to server commands. I was planning to switch the hard-drives into a spare server, but a colleague of mine called to say that I should first reset the BIOS. (Take the battery out, short the contacts).

In the end, doing that cleared the problem, and the server came back online OK. A little confused – it thought it was 1400, rather than 2100, but apart from that it was fine.

I’ve only ever seen that trick work once before, on an old desktop machine. Still, that’s a good thing to try – if the BIOS confuses itself into oblivion, you can reset it by taking the battery out and shorting the contacts. (With a screwdriver is normally easiest – you’ll probably just have used it to open the case.)

Another hardware trick I often use, I’m not sure how relevant this will be if you’re not in the UK – Plug the computer you’re going to work on into a power socket, but make sure the socket is off at the switch. The earth pin is never disconnected – the switch will only ever interrupt the power flow, not the earth. So, if you’re not sure about static electricity in your environment, its a good way of making sure you’re clean – as the earth will be connected to the computer’s case via the PSU 🙂

A quick spelling / grammar question to those reading – is “online” a valid word, or should it be written “on-line”? I’m never certain, but my spell checker seems to think that it should be “on-line”…