Common Ganeti Commands

Here’s a list of some common useful commands with Ganeti. If you want more detailed information, be sure to read the related gnt-* man pages and the online documentation.


Ganeti is a cluster virtualization environment and allows you to manage all VMs from one single master host. You should always connect to the master DNS name and never individual host. Lets use as our master host for the following commands.

All of Ganeti’s commands have a gnt- prefix. The commands you’ll use the most are tied to the gnt-instance command which interacts with your VMs. You can find simple help output by typing gnt-instance and find specific command help by typing gnt-instance <command> --help.

First, ssh to the master ganeti host for your cluster.


Instance Commands

Here’s a list of common instance, or virtual machine commands.

Starting an Instance

gnt-instance start <instance>

You can also do cool stuff like starting all the instances on a specific node:

gnt-instance start --primary <nodename>

Stopping an Instance

gnt-instance shutdown <instance>

And to stop all nodes on a specific node:

gnt-instance shutdown --primary <nodename>

If you want to quickly shutdown a VM (or otherwise known as destroy), use the following command:

gnt-instance shutdown --timeout=0 <instance>

Connecting to the Console

All of our VMs have a serial console enabled:

gnt-instance console <instance>

To escape out of the console type ctrl+].

If you want to start and connect to the console immediately after, you can run the following command. Unfortunately, there is no way currently to do this in a single command in ganeti.

gnt-instance start <hostname> && gnt-instance console <hostname>

Migrating an Instance

If you’d like to do a live migration of an instance to its secondary host, run the following command:

gnt-instance migrate <instance>

Failing over an Instance

Failing over an instance its just like migrating except its done with the instance offline so its not live:

gnt-instance failover <instance>

Adding a new Instance

Adding a new instance is generally easy however there are a lot of things to consider in your situation:

gnt-instance add -t drbd -s 10G -o image+debian \
  --net 0:link=br100 -B memory=512M \
  -H kvm:kernel_path="/boot/guest/vmlinuz-x86_64" \
  --no-start -I hail <instance>

This will do the following:


start an add action

-t drbd

use the DRBD disk template

-s 10G

set the OS disk size to 10G

-o image+debian

Use the image instance with the debian OS Variant

--net 0:link=br100

Set the network bridge to br100 (VLAN 100 in our case)

-B memory=512M

Set the VM memory to 512M

-H kvm:kernel_path="/boot/guest/vmlinuz-x86_64"

Set the kernel_path to a specific kernel we want


Don’t start the VM after it finishes building

-I hail

Use the hail iallocator for automatic allocation


FDQN of the node we’re adding

You also may have a cluster-wide default set of settings for instances. To see what those settings are, run:

gnt-cluster info

So unless you need to change from the default, you can just type the following instead:

gnt-instance add -t drbd -s 10G -o image+debian \
  --no-start -I hail <instance>

Multi-VG Support

Ganeti also supports multiple VG’s which are nice if you have a set of SSD’s and regular disks and want them on different VGs. This feature isn’t documented nearly as well so we’re doing it here. Assume doing the same instance add from above, but instead you want to put it on the ganeti-ssd VG:

gnt-instance add -t drbd --disk 0:vg=ganeti-ssd,size=10G -o image+debian \
  --no-start -I hail <instance>

Booting from a CD ISO

Sometimes you want to install an OS manually from an ISO, here’s how you do it. The first step is to create a VM using the --no-install option which creates a VM with just storage setup, no OS installed:

# disable serial console
gnt-instance modify -H serial_console=false <instance>

# disable kernel
gnt-instance modify -H kernel_path="" <instance>

# boot with iso
gnt-instance start -H \
  boot_order=cdrom,cdrom_image_path=/path/to/debian-504-amd64-netinst.iso <instance>

Now you’ll need to connect to the VNC port for the instance and do the install via that. You can find that information out by doing and “info” on the instance.

Changing Secondary disks

If you want to change where the secondary storage for a instance to a different node, the following command will do that:

gnt-instance replace-disks -n <new node> <instance>

This can be done live while the instance is still running.

Switching disk templates

If you need to change an instance from using a plain LVM disk template to DRBD, issue the following command.

# make sure the instance is down
gnt-instance shutdown <instance>

# change to drbd adding the new node as the secondary
gnt-instance modify -t drbd -n <secondary node> <instance>

# start instance
gnt-instance start <instance>

If you need to switch from the DRBD disk template to plain, replace the drbd command with the following below. Whichever node is listed as the secondary at the time will have its volumes removed.

# switch back to plain
gnt-instance modify -t plain <instance>

Moving an instance to another node

Say you have an instance that isn’t using DRBD but you want to move it to another node in the cluster:

gnt-instance move -n <primary node> <instance>

Migrate existing LVM volume

If you want to use an LVM volume that already has a guest OS installed on it, you can use Ganeti to put it into its control. This currently only works with the plain disk template and if the volume is in the same volume group that ganeti is using:

gnt-instance add -t plain -o <os-type> \
  --disk 0:adopt=<lvname> -n <node> <instance>

For example, if the device is /dev/ganeti/instance1, you would use “adopt=instance1”. This will not run any OS installation scripts.

Adding network interfaces

Say you need to add another network interface for an instance:

gnt-instance modify --net add:link=<bridge interface> <instance>
gnt-instance reboot <instance>

For example, if you want an instance to have eth1 on the backend network, you’d use add:link=br42.

Adding disks

Say you need to add another disk to an instance:

gnt-instance modify --disk add:size=<disk size> <instance>
gnt-instance reboot <instance>

For example, if you want a new 20G disk to an instance, you’d use add:size=20G.

Cluster Commands

Creating a new Cluster

Say you want to create a new cluster that:

  • uses br42 as the primary interface for Ganeti communication

  • node uses as the DRBD ip

  • enable KVM

  • set the default bridged interface for instances to br113

  • set the default KVM settings to 2 vpus & 512M RAM

  • set the default kernel path to /boot/guest/vmlinuz-x86_64

  • the master DNS name is

gnt-cluster init --master-netdev=br42 \
  --vg-name ganeti \
  -s \
  --enabled-hypervisors=kvm \
  -N link=br113 \
  -B vcpus=2,memory=512M \
  -H kvm:kernel_path=/boot/guest/vmlinuz-x86_64 \

Verifying Cluster Integrity

To verify general cluster integrity, run:

gnt-cluster verify

If you encounter any issues, check out Common Cluster Problems in their documentation.

You can also check the integrity of just disks:

gnt-cluster verify-disks

Becoming a Master Node

If you’d like to change which node is master, ssh to the node you want to become master and type the following:

gnt-cluster masterfailover

Modifying Cluster Settings

If you’d like to modify some of the cluster settings, you can do the following.

# change default vcpus, and memory settings for instances
gnt-cluster modify -B vcpus=2,memory=512M

# change default kernel
gnt-cluster modify -H kvm:kernel_path=/boot/guest/vmlinuz-x86_64

# change default instance bridge interface
gnt-cluster modify -N link=br113

Viewing Cluster Information

To see the cluster information:

gnt-cluster info

Node Commands

Adding a New Node

You’ve installed a new Ganeti server and want to add it to the cluster:

gnt-node add -s <drbd_ip> <hostname>

If this node was previously in the cluster, you should add **--readd**.

List all Nodes

gnt-node list

Mark node offline

If you need to do maintenance on node, you should mark it offline in ganeti so that it doesn’t try to communicate with it. But before you do that, you need to migrate all the instances off of it.

# migrate instances to secondary nodes
gnt-node migrate <node>

# if the node is offline, use this
gnt-node failover <node>

# now mark it offline
gnt-node modify -C no -O yes <node>

Evacuate all storage on a Node

If you need to remove all the instances from a node, you need to do this in several steps. First you need to migrate all the primary instances on the node to their secondary. Next you need to evacuate all instances that have secondary storage on the node to new nodes.

# Migrate all the primary instances
gnt-node migrate <node>

# Evacuate the node
gnt-node evacuate -I hail <node>

Remove a node from the Cluster

If you want to remove a node completely from the cluster, you can use the following command. You must remove or migrate all instances on the node before you can run this command!!

gnt-node remove <node>

Tips and Tricks

Handy Bash Aliases

There’s a few commands that we run quite often and getting annoying typing out completely, so here’s a few handy bash aliases we’ve created to help out. You can put these in your .bashrc files to use them.

Connecting to console on start

You want to start and immediately connect to the console.

# .bashrc
gnt-consolestart () { gnt-instance start $1 && gnt-instance console $1; }

# usage
gnt-consolestart <hostname>

Destroy running Instance

Say you need to stop or “destroy” a running instance immediately.

# .bashrc
gnt-destroy () { gnt-instance shutdown --timeout=0 $1 ; }

# usage
gnt-destroy <hostname>