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.

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.

Feb 292020
 

I used to be able to remember all of the keyboard short-cuts I’d set up to insert ‘fun’ (or useful) Unicode characters … but my memory isn’t quite what it used to be, and I happened to catch a video that mentioned a menu to insert Unicode characters.

So I set out to create my own …

#!/bin/zsh
#
# Run a menu of Unicode characters to put into the clipboard

read -r -d '' menu << END
Þ       Thorn (Sym-t)
Þ	Capital thorn (Sym-T)
✓	Tick (Sym-y)
✔       Alternate tick (Sym-Y)
π	pi (Sym-p)
Π       PI (Sym-P)
★       Star
🖕      Finger
END

selectedchar=$(echo $menu |\
  rofi -dmenu -l 20 -fn misc-24 -p "Unicode inserter" |\
  awk '{print $1}')
if [ -z "$selectedchar" ]
then
  notify-send "Unicode Inserter" "Cancelled"
else
  printf "%s" $selectedchar | xclip -selection clipboard
  notify-send "Unicode Inserter" \
    "Character $selectedchar now in clipboard"
fi

This script :-

  1. Creates a variable with a whole pile of text inside it. The original script contains a lot longer list, but including it would be a) boring and b) give too much away. As it stands, the format of each line is pretty much anything you want as long as the first character is the Unicode character followed by whitespace.
  2. Runs rofi with the variable as input and selects the first field of the response.
  3. Guards against the empty selection (when the menu was cancelled) for neatness mostly.
  4. Prints the selected character (without a newline) into xclip so it can be pasted in. I did try using xdotool to type it directly into the active window, but this didn’t always work so well (i.e. xdotool couldn’t “type” some of the more esoteric characters).
  5. And uses notify-send to alert the dumb user (me!) that something has happened.

Lastly, to make this useful, I added an entry to my sxhkd configuration :-

super + F11
  /site/scripts/m-unicode-insert
Jun 052019
 

On previous occasions (yes that does mean more than once) I have messed around with the network configuration of containers to get :-

  1. A consistent behaviour.
  2. A fixed IPv4 address with no DHCP configuration (this one is easy).
  3. A fixed IPv6 address with no autoconfigured global addresses (this one has been tricky)

This turns out to be relatively easy providing that you configure the addresses within the container rather than within the container configuration. At least it looks good to go so far (I’ve been mistaken in the past).

The container configuration is quite simple :-

lxc.net.0.type = veth
lxc.net.0.flags = down
lxc.net.0.link = br0

Note that the bridge interface (br0) may be different. Also note that there is no lxc.net.0.ipv4.address, lxc.net.0.ipv4.gateway, lxc.net.0.ipv6.address, or lxc.net.0.ipv6.gateway.

The configuration within the container is dependent on what userland you are running, but for Debian (and Ubuntu if you’re not using Netplan) :-

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
    address 10.0.0.34/16
    gateway 10.0.0.1

iface eth0 inet6 static
    address 2001:0db8:cafe:dead:0000:0000:0000:3eb/64
    scope global
    gateway 2001:0db8:cafe:dead:0000:0000:0000:0001
    privext 0
    accept_ra 0
    autoconf 0

Not sure quite which options are required but having all of “privext 0”, “accept_ra 0” and “autoconf 0” does mean no additional autoconfigured IPv6 addresses.

(And no the part number of this post isn’t anything more than a joke)

Apr 102019
 

So earlier today, I had a need to mount a disk image from a virtual machine on the host, and discovered a “new” method before remembering I’d made notes on this in the past. So I’m recording the details in the probably vain hope that I’ll remember this post in the future.

The first thing to do is to add an option to include partition support in the relevant kernel module, which I’ve done by adding a line to /etc/modprobe.d/etc-modules-parameters.conf :-

options nbd max_part=63

The next step is to load the module:

# modprobe nbd

The next is to use a Qemu tool to connect a disk image to a network block device :-

# qemu-nbd -r -c /dev/nbd0 /home/mike/lib/virtual-machine-disks/W10.vdi
# ls /dev/nbd0*
/dev/nbd0  /dev/nbd0p1  /dev/nbd0p2  /dev/nbd0p3

And next mount the relevant partition :-

# mount -o ro /dev/nbd0p2 /mnt

All done! Except for un-mounting it and finally disconnecting the network block device :-

# umount /mnt
# ls /dev/nbd0*
/dev/nbd0  /dev/nbd0p1  /dev/nbd0p2  /dev/nbd0p3
# qemu-nbd -d /dev/nbd0
/dev/nbd0 disconnected
# ls /dev/nbd0*        
/dev/nbd0

The trickiest part is the qemu-nbd command (so not very tricky at all).

The “-r” option specifies that the disk image should be connected read-only, which seems to be sensible when you’re working with a disk image that “belongs” to another machine. Obviously if you need to write to the disk image then you should drop the “-r” (but consider cloning or taking a snapshot).

The “-c” option connects the disk image to a specific device and the “-d” option disconnects the specific device.

Old Metal 2
WP2Social Auto Publish Powered By : XYZScripts.com