Issue Error on Server Wide Backup

[BNO]

I got the folling errors when server-wide backup runs:

WARNING:      (Service plan object 'Unlimited')      DB query failed: SQLSTATE[HY000]: General error: 23 Out of resources when opening file '/var/tmp/#sql_48c_0.MAD' (Errcode: 24 "Too many open files"), query was: DESCRIBE `TmplData`


WARNING:      (Service plan object 'Default Simple')      DB query failed: SQLSTATE[HY000]: General error: 23 Out of resources when opening file '/var/tmp/#sql_48c_0.MAD' (Errcode: 24 "Too many open files"), query was: DESCRIBE `TmplData`


WARNING:      (Service plan object 'comPlus')      DB query failed: SQLSTATE[HY000]: General error: 23 Out of resources when opening file '/var/tmp/#sql_48c_0.MAD' (Errcode: 24 "Too many open files"), query was: DESCRIBE `TmplData`


WARNING:      (Service plan object 'comStart')      DB query failed: SQLSTATE[HY000]: General error: 23 Out of resources when opening file '/var/tmp/#sql_48c_0.MAD' (Errcode: 24 "Too many open files"), query was: DESCRIBE `TmplData`


WARNING:      (Service plan object 'Default Reseller')      DB query failed: SQLSTATE[HY000]: General error: 23 Out of resources when opening file '/var/tmp/#sql_48c_0.MAD' (Errcode: 24 "Too many open files"), query was: DESCRIBE `TmplData`


WARNING:      (Service plan additional service object 'magicspam')      DB query failed: SQLSTATE[HY000]: General error: 23 Out of resources when opening file '/var/tmp/#sql_48c_0.MAD' (Errcode: 24 "Too many open files"), query was: DESCRIBE `PlanItemProperties`


WARNING:      (Server object 'hostname')      Unable to back up mail server settings. Error: DB query failed: SQLSTATE[HY000]: General error: 23 Out of resources when opening file '/var/tmp/#sql_48c_0.MAD' (Errcode: 24 "Too many open files"), query was: DESCRIBE `smtp_poplocks`


WARNING:      (Server object 'hostname')      Unable to back up DNS server settings. Error: DB query failed: SQLSTATE[HY000]: General error: 23 Out of resources when opening file '/var/tmp/#sql_48c_0.MAD' (Errcode: 24 "Too many open files"), query was: DESCRIBE `dns_recs_t`


WARNING:      (Server object 'hostname')      Unable to back up notifications. Error: DB query failed: SQLSTATE[HY000]: General error: 23 Out of resources when opening file '/var/tmp/#sql_48c_0.MAD' (Errcode: 24 "Too many open files"), query was: DESCRIBE `Notifications`


WARNING:      (Server object 'hostname')      Unable to back up event handlers. Error: DB query failed: SQLSTATE[HY000]: General error: 23 Out of resources when opening file '/var/tmp/#sql_48c_0.MAD' (Errcode: 24 "Too many open files"), query was: DESCRIBE `event_handlers`


WARNING:      (Server object 'hostname')      Unable to back up misc parameters. Error: DB query failed: SQLSTATE[HY000]: General error: 23 Out of resources when opening file '/var/tmp/#sql_48c_0.MAD' (Errcode: 24 "Too many open files"), query was: DESCRIBE `misc`


WARNING:      (Server object 'hostname')      Unable to back up restricted domains. Error: DB query failed: SQLSTATE[HY000]: General error: 23 Out of resources when opening file '/var/tmp/#sql_48c_0.MAD' (Errcode: 24 "Too many open files"), query was: DESCRIBE `RestrictedDomains`

what can i do ?