Backup not running after adding clint (ubuntu client os )

i am getting a error while doing file backup on ubuntu client which has just added.

29.04.16 22:02 ERROR Constructing of filelist of “ubuntu” failed: no backup dirs. Please add paths to backup on the client (via tray icon) or configure default paths to backup.
29.04.16 22:02 ERROR Backup had errors. Deleting partial backup.
29.04.16 22:02 WARNING Exponential backoff: Waiting at least 2h 40m before next file backup
29.04.16 22:16 INFO Starting full file backup…
29.04.16 22:16 DEBUG ubuntu: Connecting for filelist…
29.04.16 22:16 DEBUG ubuntu: Waiting for filelist
29.04.16 22:16 ERROR Constructing of filelist of “ubuntu” failed: no backup dirs. Please add paths to backup on the client (via tray icon) or configure default paths to backup.
29.04.16 22:16 ERROR Backup had errors. Deleting partial backup.
29.04.16 22:16 WARNING Exponential backoff: Waiting at least 5h 20m before next file backup
29.04.16 22:18 DEBUG Getting client settings…
29.04.16 22:19 DEBUG Getting client settings…

what might be the reason , how to add correct path i need just root / to backup

It looks like you are receiving a permissions error. You will need to give the UrBackup service permissions to the directories it needs to backup, otherwise it cannot read them.