Jul 182021
 

This is a procedure to replace one working drive in a fully functional mirror vdev; if you are replacing a failed disk there is no advantages in following this procedure. Although if you have a somewhat functional disk it may be worth trying.

So why not simply yank out the working disk you want to replace? Well, you can of course and that would work but there is nothing Murphy likes more than a mirrored vdev temporarily down to a single disk – resilvering onto a new disk guarantees a higher chance of failure of the previously working disk (I have actually seen this happening).

So I’m going to describe how to make a three-way mirror with three disks and then detach the disk you wanted to replace.

To do this there are some prerequisites :-

  1. You will need space to install an additional disk into your system; perhaps temporarily in an “unsuitable” location.
  2. You will need a spare SATA controller port to plug the new disk into. If necessary with an additional PCIe SATA controller (which sounds expensive but safety is worth the cost).
  3. You will need a SATA data cable and a SATA power cable.

The first step is to make very careful note of what devices you are going to “swap over” – ideally using their WWNs. If you don’t use WWNs, sorting out which disk is which is going to be a bit trickier.

The second step is to practice the steps involved using a ‘fake’ storage pool backed up by tiny disk files :-

# cd /pool1/temp
# for w in one two three
do
  dd if=/dev/zero of=test-disk-${w}.img bs=1M count=1000
done
# zpool create test mirror /pool1/temp/test-disk-one.img /pool1/temp/test-disk-two.img
# zpool attach test /pool1/temp/test-disk-one.img /pool/temp/test-disk-three.img
# zpool detach test /pool1/temp/test-disk-one.img

That’s pretty much it in a nutshell.

The real process is a bit more disturbing of course and most of the work is physical. The first difference from practice is that when you attach the new disk to one or other of the existing devices within the mirror, you will have to wait until the resilvering process is complete.

Whilst you will receive an estimate for that if you run zpool status, the estimate that you get :-

  scan: resilver in progress since Sun Jul 18 08:20:54 2021
	8.25T scanned at 1.09G/s, 7.28T issued at 981M/s, 8.25T total
	995G resilvered, 88.23% done, 0 days 00:17:16 to go

(Only showing the relevant part as the full output from my system is confusing and deceptive)

Is wildly inaccurate – partially because the resilvering process takes second place to any ordinary file system activity. My own estimate (1 hour per Tbyte) is probably also wildly inaccurate; basically it is done when it is done.

Detaching the old device is fast – you won’t need to sit down to wait for it.

Oct 102020
 

One of the big names in the opensource world – Eric Raymond – has declared that Windows will soon be effectively a Linux distribution. Which seems like a ridiculous notion; except technically it might make a lot of sense.

How?

It seems impossible for Microsoft to replace Windows with Linux, but actually it could be done. Windows itself consists of a bunch of software applications which call Windows “APIs” which in turn make calls to the legacy NT kernel. If all that software is written cleanly (it won’t be, but bear with me), it should be possible to make modifications to both (or either) the Linux kernel and the Windows APIs to allow Windows software to run natively.

Impossible? Nope – it has already been done to a certain extent – Wine and Proton allow a considerable amount of Windows software (and games!) to run under Linux.

Why?

So it’s not impossible, but surely it is a lot of work. So why?

Microsoft has a bit of a problem – they don’t make a huge amount of money selling the Windows operating system, and maintaining it is hugely expensive. All those security fixes, all those bug fixes, and all those new features they want to introduce.

Now most of this is done to the “userland” rather than the kernel itself, but the kernel does still need to be maintained. But what if you could use the Linux kernel and get some level of maintenance supplied by those not employed by Microsoft?

Would that save Microsoft money? It seems quite possible, and you can bet someone in Microsoft has estimated whether it would or not.

Will It Happen?

There are those who point to certain actions by Microsoft – the Linux subsystem for Windows, the Edge browser for Linux, the rumour of an Office build under Linux, etc. as indicators that Microsoft is planning this.

I think they’re wrong to the extent that those actions don’t say whether Microsoft is planning to make Windows a Linux distribution or not. There are plenty of reasons why Microsoft is releasing Linux software not least because they will almost certainly have developers that believe that porting software is a good way of finding bugs.

The real answer is that the only people who know are inside Microsoft.

The Join
Jul 112020
 

So I am currently messing around with a tiling window manager on my laptop – I prefer tiling window managers in general (I use Awesome on my main desktops). These are (in general) not “desktop environments” but just manage windows (and sometimes a “status bar”).

As it happens the window manager I’m messing with doesn’t come as part of a distribution package with a pre-prepared file for GDM3 to use. So I created a ~/.xsession file – something that has worked since display managers first arrived.

Didn’t work.

Turns out that I need to “hack” GDM3 to make a long standard bit of functionality functional again. As an aside (and especially to the GNOME people), all you had to do to keep this functional was detect if someone had a ~/.xsession file and then offer that up as a menu option. Not that difficult to do and even if it isn’t your preferred way of doing things, it’s a nice thing to do for us old-timers.

Anyway, to restore this functionality all it took was to create a file in //usr/share/xsessions/ called xsession.desktop with the following contents :-

[Desktop Entry]
Name=XSession
Comment=This session uses the custom xsession file
Exec=/etc/X11/Xsession
Type=Application
DesktopNames=GNOME-Flashback;GNOME;
X-Ubuntu-Gettext-Domain=gnome-flashback

Dead simple.

And yes I stole this and adapted it myself – I’m putting this up here so that I know where to look when I need it again.

Jun 222020
 

I have a problem with serial ports (usually “virtual ones” or USB←→serial port dongles) – I have too many of them, and I usually end up with the wrong one. And selecting a TrueRNG serial port and connecting a terminal emulator to it gets very messy very quickly.

So I was searching around, semi-idly wondering if I could somehow build a device name to USB name mapping that I could stuff into rofi (or dmenu) and I discovered the /dev/serial/by-id/ which did 99% of the work for me.

So yes, I can invoke kermit and up will pop a menu allowing me to select which serial port to connect to :-

ls /dev/serial/by-id |\
  rofi -dmenu -l 20 -p "Pick a serial device" -font "mono 20"

That is the core of it, but to make it functional I need to embed it into a command line argument to kermit :-

alias kermit='kermit -C "set line /dev/serial/by-id/$(ls /dev/serial/by-id | rofi -dmenu -l 20 -p "Pick a serial device" -font "mono 20"),set carrier-watch off"'

Which is admittedly a bit of a mouthful!

But so useful if you have two or three USB to serial adopters plugged in plus a switch’s console port and a Linux widget that provides a serial console.

Jun 222020
 

Unfortunately, the serial communication program I tend to use (kermit) appears to have not been updated in quite a while. Which in some ways is reasonable (it’s a very old program and probably does not need much work), understandable (the main developer is no longer employed to make it work), but is somewhat frustrating when it no longer compiles.

To get it to work on my latest system :-

  1. Download the cku302.tar.gz source code and unpack.
  2. Try the first compile with make linux KFLAGS=-DNOARROWKEYS (losing the arrow keys is unfortunate but not fatal unless you’re in command mode far too long).
  3. If that doesn’t compile with zillions of undefined references to curses sounding functions (printw, stdscr, wmove, etc.) then scroll up to the top of the errors where the final command to “compile” all the objects into a final binary is available. Paste that command and add a “-lncurses” :-
$ gcc  -o wermit \
      ckcmai.o ckclib.o ckutio.o ckufio.o \
      ckcfns.o ckcfn2.o ckcfn3.o ckuxla.o \
      ckcpro.o ckucmd.o ckuus2.o ckuus3.o \
      ckuus4.o ckuus5.o ckuus6.o ckuus7.o \
      ckuusx.o ckuusy.o ckuusr.o ckucns.o \
      ckudia.o ckuscr.o ckcnet.o ckusig.o \
      ckctel.o ckcuni.o ckupty.o ckcftp.o \
      ckuath.o ck_crp.o ck_ssl.o -lutil -lresolv -lcrypt -lncurses -lm

The final output of “wermit” just needs to be stripped, moved to a proper location, and renamed :-

$ strip wermit
$ sudo mv wermit /opt/bin/kermit

And there it seems to work fine.

Of course this is not a proper fix, and we are missing a lot of features but it is at least working. And saves me from having to struggle with minicom, screen, or cu.

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