How to Reset the Machine ID on an Ubuntu Server

To reset the machine ID on Ubuntu, delete the old ID files, generate a new one with systemd-machine-id-setup, relink the D-Bus copy and reboot:

sudo rm -f /etc/machine-id /var/lib/dbus/machine-id
sudo systemd-machine-id-setup
sudo ln -sf /etc/machine-id /var/lib/dbus/machine-id
sudo reboot

This works on Ubuntu 26.04, 24.04, 22.04 and 20.04, and on Debian. The most common reason to do it is a cloned VM that gets the same DHCP IP address as the original, a problem that shows up quickly when you clone Ubuntu templates on Proxmox or VMware.

What the machine ID is

/etc/machine-id holds a unique 128-bit ID written as 32 lowercase hexadecimal characters, for example 4f1c2a9e7b3d4e6f8a0b1c2d3e4f5a6b. systemd creates it when Ubuntu is installed and services rely on it:

• systemd-networkd (used by netplan on Ubuntu Server) builds the DHCP client identifier from it.
• journald stores logs in /var/log/journal/<machine-id>/.
• D-Bus reads /var/lib/dbus/machine-id, which on Ubuntu is normally a symlink to /etc/machine-id.

See your current ID:

cat /etc/machine-id
hostnamectl | grep "Machine ID"

The systemd documentation says the ID should be treated as confidential and not exposed on untrusted networks, so do not paste it in public forums.

Step by step: reset the machine ID

1. Back up the current ID (optional)

sudo cp /etc/machine-id /root/machine-id.bak

2. Remove the old ID and the D-Bus copy

sudo rm -f /etc/machine-id /var/lib/dbus/machine-id

Removing both matters. systemd-machine-id-setup copies an existing D-Bus ID from /var/lib/dbus/machine-id if it finds a valid one, so if that file is a real file rather than a symlink, you would get the old ID straight back.

3. Generate a new machine ID

sudo systemd-machine-id-setup

The tool only writes a new ID when /etc/machine-id is missing or empty; running it with the old ID still in place does nothing. Expected output:

Initializing machine ID from random generator.

On a KVM virtual machine (Proxmox, libvirt) you may instead see Initializing machine ID from SMBIOS/DMI UUID., because systemd can use the VM's UUID. Proxmox gives a full or linked clone a new SMBIOS UUID, so the result is still unique; if you copy disk images between VMs by hand with the same UUID, set a new UUID in the VM settings as well.

4. Relink the D-Bus machine ID

sudo ln -sf /etc/machine-id /var/lib/dbus/machine-id

5. Reboot and verify

sudo reboot

After the reboot:

cat /etc/machine-id
ls -l /var/lib/dbus/machine-id

The ID should be different from your backup, and the D-Bus file should show -> /etc/machine-id. If the VM uses DHCP, check it now has its own address with ip -4 addr.

Preparing a VM template (the better way)

Fixing each clone by hand is tedious. Clean the template once so every clone generates its own ID on first boot:

sudo truncate -s 0 /etc/machine-id
sudo rm -f /var/lib/dbus/machine-id
sudo ln -s /etc/machine-id /var/lib/dbus/machine-id
sudo shutdown -h now

Keep the file empty rather than deleted. The systemd documentation recommends an empty /etc/machine-id in images used for many machines; systemd fills it with a new ID at boot. Convert the VM to a template while it is shut down and do not boot it again before cloning, or it will generate an ID that every clone inherits.

If the template uses cloud-init (common with Proxmox cloud-init images), use its clean command, which sets /etc/machine-id to uninitialized so systemd generates a new ID on the next boot, and clears cloud-init state at the same time:

sudo cloud-init clean --logs --machine-id
sudo shutdown -h now

Alternative fix for duplicate DHCP IPs: use the MAC address

If you only care about DHCP, you can tell netplan to identify the VM by its MAC address, which Proxmox and VMware make unique per clone. Edit your netplan file (often /etc/netplan/50-cloud-init.yaml or /etc/netplan/00-installer-config.yaml):

network:
  version: 2
  ethernets:
    ens18:
      dhcp4: true
      dhcp-identifier: mac

Apply it:

sudo netplan apply

Use your real interface name from ip link (ens18 is the usual name on Proxmox). This avoids the duplicate lease but leaves the duplicate machine ID in place, so it is still worth resetting the ID on clones. For a fixed address instead of DHCP, see how to set a static IP on Ubuntu 24.04.

What resetting the machine ID does not change

• SSH host keys: clones share /etc/ssh/ssh_host_*. Regenerate them:

sudo rm /etc/ssh/ssh_host_*
sudo dpkg-reconfigure openssh-server
sudo systemctl restart ssh

• Hostname: set a new one with sudo hostnamectl set-hostname new-name and update /etc/hosts.
• Old journal logs: they stay in the old /var/log/journal/<old-id>/ folder. Remove it if you do not need the history.

Troubleshooting

The ID did not change: /etc/machine-id was not empty or missing when you ran systemd-machine-id-setup, or /var/lib/dbus/machine-id was a real file with the old ID. Repeat step 2, removing both, then step 3.

Clones still get the same IP after the reset: the DHCP server still holds the old lease. Release it on the client with sudo networkctl reconfigure ens18 (or reboot), and delete the stale lease on the DHCP server (pfSense: Status > DHCP Leases).

Software licence or monitoring agent stopped working: some tools register the machine by its ID. Re-register the agent after the reset; this is expected on a cloned machine.

Related guides

• Proxmox VE guide for building and cloning Ubuntu VMs
• Import an OVA into Proxmox, another case where a reset is worth doing
• Ubuntu Server installation guide