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--- computing:virtmanagerhell [2022/11/13 16:15] – oemb1905
+++ computing:virtmanagerhell [2026/04/05 00:45] (current) – oemb1905
@@ Line 7: / Line 7: @@
 -------------------------------------------
-To make a VM from the command line, do the following. Note that this recipe assumes you have already created your virtual switch, br0. It also presumes you have already created your virtual disk, and if you have not, simply run ''sudo qemu-img create -f raw new.img 1000G''.
+To make a VM from the command line, do the following. Note that this recipe assumes you have already created your virtual switch, br0. It also presumes you have already created your virtual disk, and if you have not, simply run ''sudo qemu-img create -f raw new.img 1000G''. Here's a basic block:
   sudo virt-install --name=new.img \
@@ Line 18: / Line 18: @@
   --location=/mnt/vms/isos/debian-11.4.0-amd64-netinst.iso \
   --network bridge:br0
+Here's a more complex block, that enables trim on vdd, uses a preseed.cfg file to automate install, establishes a custom vnet name, enables the guest agent, and opens a terminal/console inside the shell of the host to manage the install itself:
+  virt-install --name=domain.com.qcow2 \
+    --os-variant=debian12 \
+    --vcpu=2 \
+    --memory 4096 \
+    --disk path=/mnt/machine/domain.com.qcow2,driver.discard=unmap \
+    --check path_in_use=off \
+    --graphics none \
+    --location=/mnt/isos/debian-13.1.0-amd64-netinst.iso \
+    --network bridge:br0,target=domain-com \
+    --channel unix,target_type=virtio,name=org.qemu.guest_agent.0 \
+    --initrd-inject=/mnt/configs/${hostname}/preseed.cfg \
+    --extra-args="auto=true priority=critical preseed/file=/preseed.cfg console=ttyS0,115200n8"
 To clone an existing image, do the following:
@@ Line 44: / Line 59: @@
   virsh destroy guest1
-I prefer the raw format (.img) but if I change my mind later, perhaps because I want snapshots, then I can easily shutdown the machine and convert the image as follows:
+I prefer the raw format (.img) but if I change my mind later, perhaps because I want snapshots, then I can easily shutdown the machine and convert the image as follows. If I change my mind, I can also go in reverse back to raw.
-  qemu-img convert -f raw -O qcow2 guest1.img guest1.qcow2
+  qemu-img convert -p -f raw -O qcow2 guest1.img guest1.qcow2
+  qemu-img convert -p -f qcow2 -O raw guest1.qcow2 guest1.raw
 If you do end up using this, then you will need to edit the virtual machine's xml file. To do that, open the file and edit the disk type. Change ''type'' and ''source file='' to match the new type and extension. If you also moved the location, you can edit that now as well.
@@ Line 71: / Line 87: @@
   virsh snapshot-revert guest1 --current
-If you need to delete a particular snapshot, execute this:
+If you need to delete a particular snapshot, or delete all children of a snapshot, execute:
   virsh snapshot-delete guest1 snapshot1
+  virsh snapshot-delete guest1 --current --children-only
 To list all snapshots for a particular guestOS, execute this:
@@ Line 83: / Line 101: @@
   virsh snapshot-info guest1 snapshot
   virsh snapshot-dumpxml guest1 snapshot1
+If you need to make a live backup, do the following (Note: make sure that ''sudo apt install qemu-guest-agent'' is installed on the guest OS):
+  virsh domfsfreeze guest1.qcow2
+  qemu-img create -f qcow2 -b guest1.qcow2 snapshot.qcow2
+  virsh domfsthaw guest1.qcow2
 At times you may need to resize or gather information about a particular virtual disk. If they are in the qcow2 format, gather information as follows:
@@ Line 88: / Line 114: @@
   qemu-img info disk.qcow2
-To regain space that is being used needlessly, you can sparsify the qcow2 disk as follows:
+To regain space that is being used needlessly, you can sparsify the qcow2 disk. Note that you must install virt-sparsify separately with ''sudo apt install libguestfs-tools''.
   virt-sparsify --in-place disk.qcow2
@@ Line 97: / Line 123: @@
   qemu-img resize disk.qcow2 1000G
   qemu-img resize disk.qcow2 +10G
+Okay, so another big issue with qcow2 images is them growing over time from writes/deletes and then those blocks taking up space on the hypervisor while not actually being used on the guestOS any longer. To stop this, enable unmap on the virtIO disk in virsh, and then schedule a timer within the guest OS to trim those underlying blocks.
+  sudo systemctl enable fstrim.timer
+  sudo systemctl start fstrim.timer
+You can also manually run fstrim and then power down the qcow2 image and convert it. You may optionally use compression to save more space, but it takes very long.
+  fstrim -v /
+  qemu-img convert -O qcow2 guest.qcow2 guest-trimmed.qcow2
+  qemu-img convert -O qcow2 -c guest.qcow2 guest-trimmed.qcow2
+To test trimming functionality, I use a combination of ``ncdu`` which shows actually consumed space on the host OS, along with the following dd command to easily consume and delete space:
+  dd if=/dev/urandom of=file bs=4M count=500
+To create a backup volume inside a guest you create the volume, attach it, and then shell into the guest and format, mount, and create an fstab entry. First, on the hostOS:
+  cd /mnt/vms/backups/vm1-backup-dir/
+  qemu-img create -f qcow2 vm1-backup.qcow2 32G
+  virsh attach-disk guestOS.qcow2 \
+    --source /mnt/vms/backups/vm1-backup-dir/vm1-backup \
+    --target vdb \
+    --persistent
+Then, on the guestOS:
+  mkdir /mnt/backup
+  mkfs.ext4 /dev/vdb
+  mount -t auto /dev/vdb /mnt/backup
+  nano /etc/fstab
+  /dev/vdb /mnt/backup ext4 defaults, 0 0
 The rest from here on out is my attempt at resizing an .img virtual disk using tools exclusively from virsh / virt-manager. These are highly risky moves and totally not needed for day to day operations. It was more of a mission I was on and based on a tutorial I used nearly 15 years ago when expanding a Windows VM I used for teaching software that was only on that VM. At any rate, I have only succeeded twice doing this, and often get confused looking at the l00ps. Proceed with caution!
@@ Line 177: / Line 235: @@
   kpartx -d debian10.img
+User and group perms:
+  adduser libvirt-qemu kvm
+  adduser cockpit-ws kvm
+  newgrp kvm
+Add network interface as custom name for easy tracking:
+<code>
+  virsh edit domain.com.qcow2
+  <interface type='bridge'>
+    <mac address='11:23:11:7b:99:33'/>
+    <source bridge='br0'/>
+    <target dev='domain-com'/>
+    <model type='virtio'/>
+    <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
+  </interface>
+</code>
+Make sure that Cockpit can access a terminal:
+<code>
+  virsh edit domain.com.qcow2
+  <graphics type='vnc' port='-1' autoport='yes' listen='127.0.0.1'>
+    <listen type='address' address='127.0.0.1'/>
+  </graphics>
+</code>
+If you don't have video enabled, do the following (also needed for Cockpit Terminal rendering):
+Option 1 (cirrus):
+<code>
+ <video>
+   <model type='cirrus' vram='16384' heads='1' primary='yes'/>
+   <address type='pci' domain='0x0000' bus='0x10' slot='0x01' function='0x0'/>
+ </video>
+</code>
+Option 2 (qxl)
+<code>
+ <video>
+   <model type='qxl' ram='65536' vram='65536' vgamem='16384' heads='1' primary='yes'/>
+ </video>
+</code>
+Option 3 (use commands)
+  virt-xml domain.com.qcow2 --add-device --graphics vnc,listen=127.0.0.1
+  virt-xml domain.com.qcow2 --add-device --video qxl
+  virsh reboot domain.com.qcow2
+Add virtiofs mount point. Here's two, note the staggered bus entry of ''0x07'' vs. ''0x08'':
+<code>
+  <filesystem type='mount' accessmode='passthrough'>
+    <driver type='virtiofs'/>
+    <source dir='/mnt/support1'/>
+    <target dir='support1'/>
+    <address type='pci' domain='0x0000' bus='0x07' slot='0x00' function='0x0'/>
+  </filesystem>
+  <filesystem type='mount' accessmode='passthrough'>
+    <driver type='virtiofs'/>
+    <source dir='/mnt/support2'/>
+    <target dir='support2'/>
+    <address type='pci' domain='0x0000' bus='0x08' slot='0x00' function='0x0'/>
+  </filesystem>
+</code>
+Then, inside the VM:
+  mkdir -p /mnt/support1
+  mkdir -p /mnt/support2
+  nano /etc/fstab
+  support1   /mnt/support1   virtiofs   defaults,_netdev   0 0
+  support2   /mnt/support2   virtiofs   defaults,_netdev   0 0
+If you find ''virsh console domain.com.qcow2'' does not provide a functioning terminal, then run this inside the guest:
+  sudo systemctl enable serial-getty@ttyS0.service
+  sudo systemctl start serial-getty@ttyS0.service
+Migrating an existing VDD and virsh instance ... just dump or copy paste the .xml with ''virsh dump'' or ''virsh edit'', then create a new xml file, typically in ''/var/lib/libvirtd/qemu'', then run:
+  virsh define host.com.xml
+  virsh start host.com
+You should for sure check the network interface and MAC address, the storage location directory, and obviously run through anything else that might be different on the target migration host.
- --- //[[jonathan@haacksnetworking.org|oemb1905]] 2022/11/13 08:40//
+ --- //[[alerts@haacksnetworking.org|oemb1905]] 2026/04/05 00:42//

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