“Why do people take the path less traveled and choose an operating system based on Linux over the proprietary based ones from Microsoft Windows and also the Apple Mac OS? So welcome to the intriguing world of Linux, an operating system that’s been quietly revolutionising the tech landscape.”
DJ Ware
A virtual disk image is a block device in a file. There are a number of different disk image formats to choose from when setting up a virtual machine. QEMU Copy On Write version 2 (QCOW2) is the default virtual disk image format for the Quick Emulator (QEMU). Features such as thin provisioning, snapshots and compression make QCOW2 one of the most versatile virtual disk formats available.
In the following example, the overall objective is to shrink and optimise an existing image for random read and write operations. You can also grow disk images using the same approach.
These instructions specifically use Debian 12 with a GNOME desktop as the host, but they should also be applicable to other Linux distributions such as Ubuntu or Linux Mint. The virtual machine in this case is a Windows 10 guest using the NTFS file system.
Shut down the virtual machine and delete all existing snapshots from the image file.
Never modify images currently in use by a running virtual machine.
On the host, install the necessary tools for working with virtual disk images.
$ sudo apt-get install --yes libguestfs-tools gnome-disk-utility
Only root can access the host directory /var/lib/libvirt/images. Use the following command to obtain the necessary privileges.
$ sudo su
Continue by creating a directory in which to keep your virtual machine backups.
# mkdir /var/lib/libvirt/backups
Now create a backup of the virtual machine with the name windows by copying its QCOW2 image file to the backups directory.
# cp /var/lib/libvirt/images/windows.qcow2 /var/lib/libvirt/backups/windows-backup.qcow2
Sparsify the image file to convert any free space within the disk image to free space on the host.
# virt-sparsify --in-place /var/lib/libvirt/images/windows.qcow2
Rename the sparsified image file.
# mv /var/lib/libvirt/images/windows.qcow2 /var/lib/libvirt/images/windows-sparsified.qcow2
Check the disk size of the sparsified image file. The disk size should be smaller than the virtual size. In this particular case, the disk size is 26.7 GiB and the virtual size 64 GiB.
# qemu-img info /var/lib/libvirt/images/windows-sparsified.qcow2
image: /var/lib/libvirt/images/windows-sparsified.qcow2
file format: qcow2
virtual size: 64 GiB (68719476736 bytes)
disk size: 26.7 GiB
cluster_size: 2097152
Format specific information:
compat: 1.1
compression type: zlib
lazy refcounts: false
refcount bits: 16
corrupt: false
extended l2: false
Determine which partition to resize by obtaining more detailed information about the contents of the sparsified disk image.
# virt-filesystems --long -h --all -a /var/lib/libvirt/images/windows-sparsified.qcow2
On the virtual device /dev/sda, the size of the partition /dev/sda2 is 63G. It appears to offer the greatest scope for resizing, as the overall disk size in Step 7 is only 26.7 GiB in total.
Name Type VFS Label MBR Size Parent /dev/sda1 filesystem ntfs System Reserved - 50M - /dev/sda2 filesystem ntfs - - 63G - /dev/sda3 filesystem ntfs - - 530M - /dev/sda1 partition - - 07 50M /dev/sda /dev/sda2 partition - - 07 63G /dev/sda /dev/sda3 partition - - 27 530M /dev/sda /dev/sda device - - - 64G -
Load the network block device (NBD) kernel module.
# modprobe nbd max_part=8
Connect the sparsified image.
# qemu-nbd --connect=/dev/nbd9 /var/lib/libvirt/images/windows-sparsified.qcow2
The partition /dev/sda2 listed in Step 8 is equivalent to /dev/nbd9p2 connected as a network block device. Use GNOME Disks to shrink /dev/nbd9p2 to its Minimal Size.
Use a graphical utility to minimise the risk of introducing errors.
Disconnect the resized image.
# qemu-nbd -d /dev/nbd9
Unload the NBD kernel module.
# modprobe -r nbd
Create a target image larger than the resized source image. In this example, the size of the target image is 32G and its format QCOW2 with full preallocation and a cluster size of 2M.
# qemu-img create -f qcow2 -o preallocation=full -o cluster_size=2M /var/lib/libvirt/images/windows-target.qcow2 32G
Copy the source image to the target image and specify the partition to expand in the process.
# virt-resize --expand /dev/sda2 /var/lib/libvirt/images/windows-sparsified.qcow2 /var/lib/libvirt/images/windows-target.qcow2
Confirm the actual disk size of the target image.
# qemu-img info /var/lib/libvirt/images/windows-target.qcow2
image: /var/lib/libvirt/images/windows-target.qcow2
file format: qcow2
virtual size: 32 GiB (34359738368 bytes)
disk size: 32 GiB
cluster_size: 2097152
Format specific information:
compat: 1.1
compression type: zlib
lazy refcounts: false
refcount bits: 16
corrupt: false
extended l2: false
Obtain detailed information about the contents of the target disk image.
# virt-filesystems --long -h --all -a /var/lib/libvirt/images/windows-target.qcow2
The partition /dev/sda2 of the virtual device /dev/sda is now 31G in size. The overall disk size in Step 16 is now only 32 GiB in total.
Name Type VFS Label MBR Size Parent /dev/sda1 filesystem ntfs System Reserved - 50M - /dev/sda2 filesystem ntfs - - 31G - /dev/sda3 filesystem ntfs - - 530M - /dev/sda1 partition - - 07 50M /dev/sda /dev/sda2 partition - - 07 31G /dev/sda /dev/sda3 partition - - 27 530M /dev/sda /dev/sda device - - - 32G -
Rename the target image file.
# mv /var/lib/libvirt/images/windows-target.qcow2 /var/lib/libvirt/images/windows.qcow2
All done!
You can also modify format specific options for an existing image without having to create a target disk image. Or alternatively expand into a target image that uses a format compatible with other hypervisors, such as RAW, VMDK, VDI, VHD, VHDX or QED.
Syncthing is an open source tool that synchronises data across multiple devices. It transfers your files peer-to-peer, without the requirement to upload your information to the cloud. Packages are available for Android, Windows, macOS and Linux (including Synology DSM).
The usefulness of this project cannot be overstated.
Syncthing is included in the Debian and Ubuntu repositories, respectively. These instructions are targeting the latest release of the Syncthing stable channel. It is therefore necessary to add the Syncthing repository to your list of APT sources.
In the following example, bookworm is the local username.
Add the Syncthing release key for validation of packages downloaded from the Syncthing repository.
$ sudo curl -o /usr/share/keyrings/syncthing-archive-keyring.gpg https://syncthing.net/release-key.gpg
Add the Syncthing repository.
$ echo "deb [signed-by=/usr/share/keyrings/syncthing-archive-keyring.gpg] https://apt.syncthing.net/ syncthing stable" | sudo tee /etc/apt/sources.list.d/syncthing.list
Install Syncthing on your system.
$ sudo -- bash -c 'apt update && apt install --yes syncthing apt-transport-https'
Enable Syncthing for the local user bookworm.
$ sudo -- bash -c 'systemctl enable syncthing@bookworm.service && systemctl start syncthing@bookworm.service && systemctl status syncthing@bookworm.service'
You may need to edit your firewall settings to open ports for incoming and outgoing traffic.
Configure ufw to allow connections to Syncthing.
$ sudo ufw limit syncthing
Configure firewalld to allow connections to Syncthing.
$ sudo -- bash -c 'firewall-cmd --zone=public --add-service=syncthing --permanent && firewall-cmd --reload && firewall-cmd --info-zone=public'
Access the Syncthing configuration page by using your browser to navigate to the following address:
http://localhost:8384
Complete your setup by referring to the Syncthing documentation.
“Already 20 smartphones and laptops are ours. If he wanted to, Slotboom is now able to completely ruin the lives of the people connected.” Wouter Slotboom is one of the good guys, demonstrating to Maurits Martijn his effortless ability to retrieve people’s passwords, steal their identity, and plunder their bank accounts.
“When the N9, running MeeGo received the strongest positive reviews of any Nokia phone ever, the first handset of any brand considered better than the iPhone—what did Elop do? He said that no matter how well the N9 sold, Elop would never allow another MeeGo based device to be sold by Nokia.” Microsoft has just bought Nokia’s handset division for a knockdown price of 5.3 Billion Euros, prompting former Nokia employee Tomi Ahonen to chronicle the decline of this once mighty company since in September 2010 former Microsoft employee Steven Elop became the first non-Finnish director in Nokia’s history.
“As a lifelong Windows user, system builder, ex-gamer, and performance freak, I’m not drinking anyone’s Kool-Aid. I just want the most amount of control over my system as possible, and at this point in time, Ubuntu is the best follow-up to Windows XP.” Adam Overa walks the Windows user through the Ubuntu installation process from downloading the CD image to finding help online.
“Many people discover LaTeX after years of struggling with wordprocessors and desktop publishing systems, and are amazed to find that TeX has been around for over 25 years and they hadn’t heard of it.”
Peter Flynn
LaTeX is a free document preparation system that enables you to create beautifully typeset pages. It implements a set of commands designed to control TeX, the typesetting engine developed by Donald E Knuth. LaTeX stores the information about your documents as plain text, thus avoiding the risk of vendor lock-in and ensuring that your documents will still be editable twenty years from now. LaTeX processes the plain text data and, with pdfTeX working in the background, generates PDF output of the highest typographic quality—perfect for viewing on-screen or printing on paper. LaTeX runs on many platforms and is included as standard with most Linux distributions. Ready-to-run LaTeX systems are also available for Windows and Mac OS X.
“In a world of repressive governments and a growing reliance on insecure networks, there’s no way anyone can be sure their most sensitive messages aren’t intercepted by the forces of darkness. But you can make it mathematically improbable that all but the most well-funded snoops could ever make heads or tales of your communications.” Use Dan Goodin’s step-by-step guide to email encryption and keep your communications private.