Mac: Dock moves to other monitor

This was bugging me for ever.

Every now and then my Dock would appear at the bottom of one of my external displays. And to get it back I’d have to open up System Preferences and drag it back. Very time-consuming.

Eventually I figured it was a Mac bug.

However, it seems you can summon the Dock to a display by moving your mouse down at the bottom of that display. Which is what I must have inadvertently been doing.


Letter i was highlighting entire line on my Mac

Just solved a very weird problem on my Mac.

When I typed the letter “i” the entire line would get highlighted. Basically my Mac had become useless. I envisaged days or weeks of lost productivity whilst I sent my Mac back to get a replacement.

It turned out to be a setting I’d enabled in Accessibility > Mouse & Trackpad > Enable Mouse Keys.

Why had I done that? To solve another bug on my Mac where the cursor disappears on external monitors. There seem to be several of these ongoing bugs that have never been fixed.



Understanding Wifi signals

This was originally a post on Mac Wifi signals however I’m now adding details about Ubuntu.


wavemon is useful:

However, it outputs a load of gibberish. i.e.

Link quality:

Signal level: (same as RSSI below I think)

Noise level:

SNR: Diff between Signal and noise

According to this

Link quality = Signal to Noise Ratio (SNR)however, according to wavemon these aren’t the same.

According to this quality is stored in a variable named rssi however, I see a link quality of 57% and I see an RSSI of -70 so they seem to bear no resemblance.


wavemon documentation is more gibberish. E.g. it starts by saying it’s an ncurses-based application. How on earth is that useful to checking your Wifi signal?!

And the initial page:

says zero about link quality. All it says is look at the man page. Which says slightly less than zero – all it says is:

`Below, in the Levels section, you can see up to four bargraphs showing (1) relative signal quality` with no explanation of what this graph might represent.



If your Mac Wifi seems to be struggling here’s how to find out more about what’s actually going on.

Signal strength:

The  Mac’s menu bar has a rudimentary set of signal strength icons. E.g.

which means practically nothing.

If it’s less than 4 bars you’re probably going to struggle. However, here’s how to find out more.

  1. Alt click the icon and look for RSSI (see also Mac: WiFi Diagnostics )


This is a negative dBm number which measures from 0 to -100 with 0 being perfect (and not realistic in everyday life) to -100 being no signal. Realistic values are:

-50: good

-60: reasonable

-75: poor

-100: no signal

So, if your WiFi is between -50 to -60 then your signal is OK.

If between -75 and -100 then you’re going to have problems. This article suggests RSSI > -60 for good WiFi (greater in the standard math sense – i.e. more positive rather than larger – e.g. -55 or -50 or -45).

and I personally see WiFi problems if <-70.

The same article suggests your Quality (Signal to Noise ratio – drawn in red in the middle) should be above 25.

If those aren’t good then decrease the distance between your wifi hub and your computer. Or get a mesh or extender.


Testing an Orbi Extender

Set up a different SSID.

WiFi Analyzer proved very useful.

Gives distance to Access Point in metres and dBM.



What is DRBD

What is DRBD


DRBD is a block device which is designed to build high availability clusters. This is done by mirroring a whole block device via (a dedicated) network. You could see it as a network raid-1.


DRBD is copyright by Philipp Reisner, Lars Ellenberg and LinBit.


What is the scope of drbd, what else do I need to build a HA cluster?


DRBD takes over the data, writes it to the local disk and sends it to the other host. On the other host, it takes it to the disk there.


The other components needed are a cluster membership service, which is supposed to be heartbeat, and some kind of application that works on top of a block device.



A filesystem & fsck.

A journaling FS.

A database with recovery capabilities.