Ubuntu Vm Images 〈No Survey〉

<memoryBacking> <locked/> </memoryBacking> The serial console is your only lifeline. Common failures:

virt-customize -a ubuntu.qcow2 --install prometheus-node-exporter virt-customize -a ubuntu.qcow2 --ssh-inject ubuntu:file:/home/me/key.pub This tool mounts the filesystem offline – significantly faster than booting. Even a perfect image can perform badly if the hypervisor configuration mismatches. 6.1 Disk I/O: Writeback vs. None Libvirt’s default cache mode for QCOW2 is writeback . This is dangerous: host crash = data loss in guest. Change to writethrough or none (if using persistent memory). To check: ubuntu vm images

| Component | Desktop Default | Cloud Image Default | |-----------|----------------|----------------------| | Root password | Set by user | Locked ( * in shadow) | | SSH | Not installed | Installed and enabled | | Password auth | Allowed | Disabled (key-only) | | Firewall | None (ufw inactive) | None (cloud security groups handle isolation) | | Automatic updates | Unattended-upgrades off | Unattended-upgrades on (security updates only) | | Kernel livepatch | Off | Available via UA subscription | Change to writethrough or none (if using persistent memory)

Packer launches a VM, runs an autoinstall (Ubuntu's new declarative installer), provisions with shell/Ansible, and outputs QCOW2, VMDK, or raw. Generate a fake metadata disk: For databases or real-time apps

virsh dumpxml vm-name | grep "driver name" # Look for cache='none' or cache='writethrough' Ubuntu’s kernel sees vCPUs as separate cores. For NUMA-aware workloads (databases), pin vCPUs to physical cores:

<vcpu placement='static'>4</vcpu> <cputune> <vcpupin vcpu='0' cpuset='2'/> <vcpupin vcpu='1' cpuset='3'/> </cputune> Without pinning, vCPUs float across cores, thrashing L2/L3 caches. Balloon driver ( virtio_balloon ) allows host to reclaim unused guest memory. However, it adds latency. For databases or real-time apps, disable ballooning and set memoryBacking to locked :