You can soft or hard reboot a running instance. A soft reboot attempts a graceful shut down and restart of the instance. A hard reboot power cycles the instance.
By default, when you reboot an instance, it is a soft reboot.
$ openstack server reboot SERVER
To perform a hard reboot, pass the –hard parameter, as follows:
$ openstack server reboot --hard SERVER
It is also possible to reboot a running instance into rescue mode. For example, this operation may be required, if a filesystem of an instance becomes corrupted with prolonged use.
Rescue mode provides a mechanism for access, even if an image renders the instance inaccessible. By default, it starts an instance from the initial image attaching the current boot disk as a secondary one.
To perform an instance reboot into rescue mode, run the following command:
$ openstack server rescue SERVER
The timeout value can be overridden on a per image basis by means of os_shutdown_timeout that is an image metadata setting allowing different types of operating systems to specify how much time they need to shut down cleanly.
To restart the instance from the normal boot disk, run the following command:
$ openstack server unrescue SERVER
If you want to rescue an instance with a specific image, rather than the default one, use the –rescue_image_ref parameter:
$ openstack server rescue --rescue_image_ref IMAGE_ID SERVER