My sites are giving this error, I don't know how to solve this... so if you could help I would appreciate it 
thanks in advance
Error:
Warning: Unknown: write failed: No space left on device (28) in Unknown on line 0
Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/tmp) in Unknown on line 0
thanks in advance
Error:
Warning: Unknown: write failed: No space left on device (28) in Unknown on line 0
Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/tmp) in Unknown on line 0