QEMUTips

QEMUTips

Running Debian on macOS 12 (Monterey)

Install qemu from MacPorts

Create a disk image:

$ qemu-img create -f qcow2 debian.qcow2 15G

Install from an ISO image:
```
$ sudo qemu-system-x86_64 -name MyTest \
-M accel=hvf \
-cpu host -smp cpus=2 -m 2G \
-drive file=debian.qcow2,if=none,id=hd \
-vga virtio -display cocoa,show-cursor=on \
-device virtio-blk-pci,drive=hd \
-usb -device usb-audio -device usb-tablet \
-nic vmnet-bridged,ifname=en1 \
-cdrom debian-12.0.0-amd64-netinst.iso
```
The -nic option creates a bridged network with the VM. Replace en1 with whichever device is appropriate for your network connection. Run ifconfig on the Mac to list the network interfaces. You can skip that element if you don't want a bridged network. You also won't need to use sudo in that situation.
Run using the newly created image using the above command but omitting the -cdrom option.

References

Running FreeBSD

Download qcow2 images from the Get FreeBSD site. It may be best to choose one of the STABLE images.

Create a copy of the image, e.g.

$ xz -dk FreeBSD-13.2-RELEASE-amd64.qcow2.xz

Resize the image with sufficient space for your initial needs:
```
$ qemu-img resize FreeBSD-13.2-RELEASE-amd64.qcow2 +10G
```
On first boot, the image should call growfs / to expand the root partition to fill the available space. If you expand the image thereafter, boot into single-user mode and manually issue the command as root.

Start the virtual machine, e.g.

$ qemu-system-x86_64 \
    -name FreeBsd -M accel=hvf -cpu host -smp cpus=2 -m 2G \
    -drive file=FreeBSD-13.2-RELEASE-amd64.qcow2,if=none,id=hd \
    -vga virtio \
    -device virtio-blk-pci,drive=hd \
    -usb -device usb-tablet -device usb-audio
    -nic vmnet-bridged,ifname=en1 \
    -display cocoa,show-cursor=on

You may need to modify the command to suit your environment, most likely the last two lines for the network and display.

Login as root without a password
Enable SSH for subsequent restarts:
```
# sysrc sshd_enable="YES"
```
Manually start the SSH server:
```
# service sshd start
```
Set a password for the root user:
```
# passwd
```
Create a new user using the adduser command interactively:
```
# adduser
```
You can use the defaults for all questions other than Username. Add the wheel group when prompted with Invite $USERNAME into other groups? if you want the new user to be able to use the su command.

Optionally install the sudo package:

# pkg install sudo

or as the new user:

$ su -l root -c 'pkg install sudo'

Optionally, enable sudo for the wheel group:

$ su -l root -i
# chmod u+w /usr/local/etc/sudoers
# sed -i '~' -r 's/# %wheel ALL=\(ALL:ALL\) ALL/%wheel ALL=(ALL:ALL) ALL/' \
/usr/local/etc/sudoers
# exit
$ sudo whoami

Snapshots

Managing these snapshots must be done when the VM is offline.

Create a snapshot:

$ qemu-img snapshot -c snap01 debian.qcow2

List snapshots:

$ qemu-img snapshot -l debian.qcow2

Revert to a previous snapshot:

$ qemu-img snapshot -a snap01 debian.qcow2

Delete snapshot:

$ qemu-img snapshot -d snap01 debian.qcow2

Shrinking a qcow2 image

$ qemu-img convert -O qcow2 source.qcow2 shrunk.qcow2

Fully test the shrunk image before deleting the original source image.

See https://serverfault.com/questions/432119/is-there-any-way-to-shrink-qcow2-image-without-converting-it-raw

Automating a Debian Install

Some of a Debian install can be automated using a preseed file.

Create a preseed.cfg file as described in the Debian Wiki.

You can create a preseed file from an existing installation with:

$ sudo apt-get install debconf-utils
$ echo "#_preseed_V1" | tee preseed.cfg
$ sudo debconf-get-selections --installer | tee -a preseed.cfg
$ sudo debconf-get-selections | tee -a preseed.cfg

Optionally, run debconf-set-selections -c preseed.cfg in a Debian system to check the file for errors.
Run a web-server for the directory containing the preseed.cfg file.
```
$ python3 -m http.server --directory .
```
Perform an install of Debian as described above, choose Advanced options, then choose the Automated install option.
After the installer has installed support for networking, enter the url to the file on the host web server started in the earlier step. e.g. http://192.168.1.100:8000/preseed.cfg.

All being well, the installation should complete and reboot into the newly installed system.

Examine /var/log/installer/syslog to debug any installation failures.

Increasing an LVM Volume Size

Resizing is a risky operation. Make sure you have backups before proceeding.

Increase the size of the QEMU disk image, e.g. on the host:
```
$ qemu-img resize debian.qcow2 +20G
```

Boot from a live ISO image, e.g. https://www.debian.org/CD/live/ or if your QEMU image doesn't have Internet access (needed to install GParted, which is missing from the Debian live CD) use the GParted Live ISO image, which is also a considerably smaller image size.

Use the bootindex property to boot by default from the live ISO image. The -boot menu=on option can also be used to choose the boot device by pressing the Esc key on the first boot screen. E.g.:

$ sudo qemu-system-x86_64 \
    -name Bookworm -M accel=hvf -cpu host -smp cpus=2 -m 2G \
    -drive format=qcow2,file=debian.qcow2,if=none,id=hd \
    -device virtio-blk-pci,drive=hd \
    -nic "vmnet-bridged,ifname=en1" \
    -drive file=debian-live-12.2.0-amd64-lxde.iso,if=none,index=2,media=cdrom,id=cd \
    -device virtio-blk-pci,drive=cd,bootindex=1 \
    -vga virtio \
    -usb -device usb-tablet -device usb-audio \
    -display cocoa,show-cursor=on \
    -boot menu=on

You may want to resize the monitor. In LXDE this can be done by running lxrandr. Press Alt-F2 to open the command window or use the menu. If using the GParted Live ISO image, you can minimise the GParted window by clicking on its icon in the bottom toolbar. The Screen resolution application icon is then visible on the desktop. There is full documentation on the GParted Live CD website.
Run lxterminal to get an interactive terminal window.
Make sure the volume group is not active:
```
$ sudo vgchange -a n
```
Resize the partions using gparted.
```
$ sudo apt-get install gparted
$ sudo gparted
```
If the partition is within an extended partition, you will need to grow that one first. Then grown the partition containing the volume group.
Use sudo pvdisplay to view the PV Name and check it using the whole of the resized partition. If not run pvresize, e.g. for a PV Name of /dev/vda5:
```
$ sudo pvresize /dev/vda5
```
Use sudo vgdisplay to see how much space is now free and extend any logical volumes as required. After extending the logical volume, activate the volume group and resize the underlying partition. E.g. for an ext3 or ext4 volume:
```
$ sudo vgchange -a y
$ sudo lvresize -L+20G /dev/mapper/debian--vg-root
$ sudo e2fsck -f /dev/mapper/debian--vg-root
$ sudo resize2fs /dev/mapper/debian--vg-root
```

Reboot into the QEMU image as normal and the additional space will be available.

Trouble Shooting

Incorrect keyboard mappings with host on macOS See also Keyboard layouts in lightweight virtualisation

References

https://wiki.debian.org/QEMU

-- Frank Dean - 5 Oct 2023

Related Topics: DebianTips, InstallingMacPorts, LogicalVolumeManagement