Enable and access the configuration drive

To enable the configuration drive, pass the --config-drive=true parameter to the nova boot command.

The following example enables the configuration drive and passes user data, two files, and two key/value metadata pairs, all of which are accessible from the configuration drive:

$ nova boot --config-drive=true --image my-image-name --key-name mykey --flavor 1 --user-data ./my-user-data.txt myinstance --file /etc/network/interfaces=/home/myuser/instance-interfaces --file known_hosts=/home/myuser/.ssh/known_hosts --meta role=webservers --meta essential=false

You can also configure the Compute service to always create a configuration drive by setting the following option in the /etc/nova/nova.conf file:

force_config_drive=true

	Note
	If a user passes the `--config-drive=true` flag to the nova boot command, an administrator cannot disable the configuration drive.

If your guest operating system supports accessing disk by label, you can mount the configuration drive as the /dev/disk/by-label/configurationDriveVolumeLabel device. In the following example, the configuration drive has the config-2 volume label.
```
# mkdir -p /mnt/config
# mount /dev/disk/by-label/config-2 /mnt/config
```
Note
Ensure that you use at least version 0.3.1 of CirrOS for configuration drive support.
If your guest operating system does not use udev, the /dev/disk/by-label directory is not present.
You can use the blkid command to identify the block device that corresponds to the configuration drive. For example, when you boot the CirrOS image with the m1.tiny flavor, the device is /dev/vdb:
```
# blkid -t LABEL="config-2" -odevice
```
```
/dev/vdb
```
Once identified, you can mount the device:
```
# mkdir -p /mnt/config
# mount /dev/vdb /mnt/config
```

Configuration drive contents

In this example, the contents of the configuration drive are as follows:

ec2/2009-04-04/meta-data.json
ec2/2009-04-04/user-data
ec2/latest/meta-data.json
ec2/latest/user-data
openstack/2012-08-10/meta_data.json
openstack/2012-08-10/user_data
openstack/content
openstack/content/0000
openstack/content/0001
openstack/latest/meta_data.json
openstack/latest/user_data

The files that appear on the configuration drive depend on the arguments that you pass to the nova boot command.

OpenStack metadata format

The following example shows the contents of the openstack/2012-08-10/meta_data.json and openstack/latest/meta_data.json files. These files are identical. The file contents are formatted for readability.

{
   "availability_zone":"nova",
   "files":[
      {
         "content_path":"/content/0000",
         "path":"/etc/network/interfaces"
      },
      {
         "content_path":"/content/0001",
         "path":"known_hosts"
      }
   ],
   "hostname":"test.novalocal",
   "launch_index":0,
   "name":"test",
   "meta":{
      "role":"webservers",
      "essential":"false"
   },
   "public_keys":{
      "mykey":"ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAAAgQDBqUfVvCSez0/Wfpd8dLLgZXV9GtXQ7hnMN+Z0OWQUyebVEHey1CXuin0uY1cAJMhUq8j98SiW+cU0sU4J3x5l2+xi1bodDm1BtFWVeLIOQINpfV1n8fKjHB+ynPpe1F6tMDvrFGUlJs44t30BrujMXBe8Rq44cCk6wqyjATA3rQ== Generated by Nova\n"
   },
   "uuid":"83679162-1378-4288-a2d4-70e13ec132aa"
}

Note the effect of the --file /etc/network/interfaces=/home/myuser/instance-interfaces argument that was passed to the nova boot command. The contents of this file are contained in the openstack/content/0000 file on the configuration drive, and the path is specified as /etc/network/interfaces in the meta_data.json file.

EC2 metadata format

The following example shows the contents of the ec2/2009-04-04/meta-data.json and the ec2/latest/meta-data.json files. These files are identical. The file contents are formatted to improve readability.

{
   "ami-id":"ami-00000001",
   "ami-launch-index":0,
   "ami-manifest-path":"FIXME",
   "block-device-mapping":{
      "ami":"sda1",
      "ephemeral0":"sda2",
      "root":"/dev/sda1",
      "swap":"sda3"
   },
   "hostname":"test.novalocal",
   "instance-action":"none",
   "instance-id":"i-00000001",
   "instance-type":"m1.tiny",
   "kernel-id":"aki-00000002",
   "local-hostname":"test.novalocal",
   "local-ipv4":null,
   "placement":{
      "availability-zone":"nova"
   },
   "public-hostname":"test.novalocal",
   "public-ipv4":"",
   "public-keys":{
      "0":{
         "openssh-key":"ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAAAgQDBqUfVvCSez0/Wfpd8dLLgZXV9GtXQ7hnMN+Z0OWQUyebVEHey1CXuin0uY1cAJMhUq8j98SiW+cU0sU4J3x5l2+xi1bodDm1BtFWVeLIOQINpfV1n8fKjHB+ynPpe1F6tMDvrFGUlJs44t30BrujMXBe8Rq44cCk6wqyjATA3rQ== Generated by Nova\n"
      }
   },
   "ramdisk-id":"ari-00000003",
   "reservation-id":"r-7lfps8wj",
   "security-groups":[
      "default"
   ]
}

User data

The openstack/2012-08-10/user_data, openstack/latest/user_data, ec2/2009-04-04/user-data, and ec2/latest/user-data file are present only if the --user-data flag and the contents of the user data file are passed to the nova boot command.

Configuration drive format

The default format of the configuration drive as an ISO 9660 file system. To explicitly specify the ISO 9660 format, add the following line to the /etc/nova/nova.conf file:

config_drive_format=iso9660

By default, you cannot attach the configuration drive image as a CD drive instead of as a disk drive. To attach a CD drive, add the following line to the /etc/nova/nova.conf file:

config_drive_cdrom=true

For legacy reasons, you can configure the configuration drive to use VFAT format instead of ISO 9660. It is unlikely that you would require VFAT format because ISO 9660 is widely supported across operating systems. However, to use the VFAT format, add the following line to the /etc/nova/nova.conf file:

config_drive_format=vfat

If you choose VFAT, the configuration drive is 64 MB.

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	Note
	Ensure that you use at least version 0.3.1 of CirrOS for configuration drive support.