issue :- 

ERROR: Failed to start security services – /usr/openv/netbackup/bin/nbatd -f
Unable to fork child process.
Configuration of auth broker failed

Error logs :- 

– [Info] Setting the hostname to “servername”.
– [Info] It may take several minutes to validate the hostname, apply the hostname to NetBackup and restart NetBackup processes.
– [Info] Hostname set successfully.
– [Info] Checking current state of the appliance
– [Info] Scanning storage system…
– [Info] The scan operation can take up to 15 minutes to complete.
– [Info] Refreshing the storage devices…
– [Info] Acquired lock on the storage.
– [Info] Looking for existing storage configurations…
– [Info] Found existing storage configuration. Attempting to import the configuration…
– [Info] Successfully imported the storage configuration.
– [Info] Upgrading storage configuration to the latest version…
– [Info] Updating disk names…
– [Info] Mounting the ‘NetBackup Catalog’ partition ‘0’…
– [Warning] Unable to mount the ‘NetBackup Catalog’ partition. The ‘NetBackup Catalog’ partition may already be mounted.
– [Info] Mounting the ‘Configuration’ partition ‘0’…
– [Warning] Unable to mount the ‘Configuration’ partition. The ‘Configuration’ partition may already be mounted.
– [Info] Moving appliance configuration database to the Configuration partition.
– [Info] Updating hostname in the NetBackup Authentication Service configuration.
– [Error] Failed to configure NetBackup Authentication Service. Stopping nbatd…
Iteration :1
Stopping nbatd…
Iteration :2
Iteration :3
set_value: Key “Mode” successfully updated
delete_value: Key “RootBrokerTag” deleted successfully
delete_value: Key “AuthBrokerTag” deleted successfully
Gathering configuration information.
ERROR: Failed to start security services – /usr/openv/netbackup/bin/nbatd -f
Unable to fork child process.
Configuration of auth broker failed

Soution :- 

Remove the DNS Server IP addresses from the configuration wizard and try to configure the roles.