This occurred when I've tried to rebuild an instance:
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters [req-c424068b-996a-40d0-8897-42d7ffec986c - - - - -] DBAPIError exception wrapped from (pymysql.err.InternalError) (23, u'Out of resources when opening file \'/tmp/#sql_e56_0.MAD\' (Errcode: 24 "Too many open files")') [SQL: u'SELECT anon_1.instances_created_at AS anon_1_instances_created_at, anon_1.instances_updated_at AS anon_1_instances_updated_at, anon_1.instances_deleted_at AS anon_1_instances_deleted_at, anon_1.instances_deleted AS anon_1_instances_deleted, anon_1.instances_id AS anon_1_instances_id, anon_1.instances_user_id AS anon_1_instances_user_id, anon_1.instances_project_id AS anon_1_instances_project_id, anon_1.instances_image_ref AS anon_1_instances_image_ref, anon_1.instances_kernel_id AS anon_1_instances_kernel_id, anon_1.instances_ramdisk_id AS anon_1_instances_ramdisk_id, anon_1.instances_hostname AS anon_1_instances_hostname, anon_1.instances_launch_index AS anon_1_instances_launch_index, anon_1.instances_key_name AS anon_1_instances_key_name, anon_1.instances_key_data AS anon_1_instances_key_data, anon_1.instances_power_state AS anon_1_instances_power_state, anon_1.instances_vm_state AS anon_1_instances_vm_state, anon_1.instances_task_state AS anon_1_instances_task_state, anon_1.instances_memory_mb AS anon_1_instances_memory_mb, anon_1.instances_vcpus AS anon_1_instances_vcpus, anon_1.instances_root_gb AS anon_1_instances_root_gb, anon_1.instances_ephemeral_gb AS anon_1_instances_ephemeral_gb, anon_1.instances_ephemeral_key_uuid AS anon_1_instances_ephemeral_key_uuid, anon_1.instances_host AS anon_1_instances_host, anon_1.instances_node AS anon_1_instances_node, anon_1.instances_instance_type_id AS anon_1_instances_instance_type_id, anon_1.instances_user_data AS anon_1_instances_user_data, anon_1.instances_reservation_id AS anon_1_instances_reservation_id, anon_1.instances_launched_at AS anon_1_instances_launched_at, anon_1.instances_terminated_at AS anon_1_instances_terminated_at, anon_1.instances_availability_zone AS anon_1_instances_availability_zone, anon_1.instances_display_name AS anon_1_instances_display_name, anon_1.instances_display_description AS anon_1_instances_display_description, anon_1.instances_launched_on AS anon_1_instances_launched_on, anon_1.instances_locked AS anon_1_instances_locked, anon_1.instances_locked_by AS anon_1_instances_locked_by, anon_1.instances_os_type AS anon_1_instances_os_type, anon_1.instances_architecture AS anon_1_instances_architecture, anon_1.instances_vm_mode AS anon_1_instances_vm_mode, anon_1.instances_uuid AS anon_1_instances_uuid, anon_1.instances_root_device_name AS anon_1_instances_root_device_name, anon_1.instances_default_ephemeral_device AS anon_1_instances_default_ephemeral_device, anon_1.instances_default_swap_device AS anon_1_instances_default_swap_device, anon_1.instances_config_drive AS anon_1_instances_config_drive, anon_1.instances_access_ip_v4 AS anon_1_instances_access_ip_v4, anon_1.instances_access_ip_v6 AS anon_1_instances_access_ip_v6, anon_1.instances_auto_disk_config AS anon_1_instances_auto_disk_config, anon_1.instances_progress AS anon_1_instances_progress, anon_1.instances_shutdown_terminate AS anon_1_instances_shutdown_terminate, anon_1.instances_disable_terminate AS anon_1_instances_disable_terminate, anon_1.instances_cell_name AS anon_1_instances_cell_name, anon_1.instances_cleaned AS anon_1_instances_cleaned, instance_extra_1.flavor AS instance_extra_1_flavor, instance_extra_1.created_at AS instance_extra_1_created_at, instance_extra_1.updated_at AS instance_extra_1_updated_at, instance_extra_1.deleted_at AS instance_extra_1_deleted_at, instance_extra_1.deleted AS instance_extra_1_deleted, instance_extra_1.id AS instance_extra_1_id, instance_extra_1.instance_uuid AS instance_extra_1_instance_uuid, security_groups_1.created_at AS security_groups_1_created_at, security_groups_1.updated_at AS security_groups_1_updated_at, security_groups_1.deleted_at AS security_groups_1_deleted_at, security_groups_1.deleted AS security_groups_1_deleted, security_groups_1.id AS security_groups_1_id, security_groups_1.name AS security_groups_1_name, security_groups_1.description AS security_groups_1_description, security_groups_1.user_id AS security_groups_1_user_id, security_groups_1.project_id AS security_groups_1_project_id, security_group_rules_1.created_at AS security_group_rules_1_created_at, security_group_rules_1.updated_at AS security_group_rules_1_updated_at, security_group_rules_1.deleted_at AS security_group_rules_1_deleted_at, security_group_rules_1.deleted AS security_group_rules_1_deleted, security_group_rules_1.id AS security_group_rules_1_id, security_group_rules_1.parent_group_id AS security_group_rules_1_parent_group_id, security_group_rules_1.protocol AS security_group_rules_1_protocol, security_group_rules_1.from_port AS security_group_rules_1_from_port, security_group_rules_1.to_port AS security_group_rules_1_to_port, security_group_rules_1.cidr AS security_group_rules_1_cidr, security_group_rules_1.group_id AS security_group_rules_1_group_id, instance_system_metadata_1.created_at AS instance_system_metadata_1_created_at, instance_system_metadata_1.updated_at AS instance_system_metadata_1_updated_at, instance_system_metadata_1.deleted_at AS instance_system_metadata_1_deleted_at, instance_system_metadata_1.deleted AS instance_system_metadata_1_deleted, instance_system_metadata_1.id AS instance_system_metadata_1_id, instance_system_metadata_1.`key` AS instance_system_metadata_1_key, instance_system_metadata_1.value AS instance_system_metadata_1_value, instance_system_metadata_1.instance_uuid AS instance_system_metadata_1_instance_uuid, instance_info_caches_1.created_at AS instance_info_caches_1_created_at, instance_info_caches_1.updated_at AS instance_info_caches_1_updated_at, instance_info_caches_1.deleted_at AS instance_info_caches_1_deleted_at, instance_info_caches_1.deleted AS instance_info_caches_1_deleted, instance_info_caches_1.id AS instance_info_caches_1_id, instance_info_caches_1.network_info AS instance_info_caches_1_network_info, instance_info_caches_1.instance_uuid AS instance_info_caches_1_instance_uuid \nFROM (SELECT instances.created_at AS instances_created_at, instances.updated_at AS instances_updated_at, instances.deleted_at AS instances_deleted_at, instances.deleted AS instances_deleted, instances.id AS instances_id, instances.user_id AS instances_user_id, instances.project_id AS instances_project_id, instances.image_ref AS instances_image_ref, instances.kernel_id AS instances_kernel_id, instances.ramdisk_id AS instances_ramdisk_id, instances.hostname AS instances_hostname, instances.launch_index AS instances_launch_index, instances.key_name AS instances_key_name, instances.key_data AS instances_key_data, instances.power_state AS instances_power_state, instances.vm_state AS instances_vm_state, instances.task_state AS instances_task_state, instances.memory_mb AS instances_memory_mb, instances.vcpus AS instances_vcpus, instances.root_gb AS instances_root_gb, instances.ephemeral_gb AS instances_ephemeral_gb, instances.ephemeral_key_uuid AS instances_ephemeral_key_uuid, instances.host AS instances_host, instances.node AS instances_node, instances.instance_type_id AS instances_instance_type_id, instances.user_data AS instances_user_data, instances.reservation_id AS instances_reservation_id, instances.launched_at AS instances_launched_at, instances.terminated_at AS instances_terminated_at, instances.availability_zone AS instances_availability_zone, instances.display_name AS instances_display_name, instances.display_description AS instances_display_description, instances.launched_on AS instances_launched_on, instances.locked AS instances_locked, instances.locked_by AS instances_locked_by, instances.os_type AS instances_os_type, instances.architecture AS instances_architecture, instances.vm_mode AS instances_vm_mode, instances.uuid AS instances_uuid, instances.root_device_name AS instances_root_device_name, instances.default_ephemeral_device AS instances_default_ephemeral_device, instances.default_swap_device AS instances_default_swap_device, instances.config_drive AS instances_config_drive, instances.access_ip_v4 AS instances_access_ip_v4, instances.access_ip_v6 AS instances_access_ip_v6, instances.auto_disk_config AS instances_auto_disk_config, instances.progress AS instances_progress, instances.shutdown_terminate AS instances_shutdown_terminate, instances.disable_terminate AS instances_disable_terminate, instances.cell_name AS instances_cell_name, instances.cleaned AS instances_cleaned \nFROM instances \nWHERE instances.deleted = %(deleted_1)s AND instances.uuid = %(uuid_1)s \n LIMIT %(param_1)s) AS anon_1 LEFT OUTER JOIN instance_extra AS instance_extra_1 ON instance_extra_1.instance_uuid = anon_1.instances_uuid LEFT OUTER JOIN (security_group_instance_association AS security_group_instance_association_1 INNER JOIN security_groups AS security_groups_1 ON security_groups_1.id = security_group_instance_association_1.security_group_id AND security_group_instance_association_1.deleted = %(deleted_2)s AND security_groups_1.deleted = %(deleted_3)s) ON security_group_instance_association_1.instance_uuid = anon_1.instances_uuid AND anon_1.instances_deleted = %(deleted_4)s LEFT OUTER JOIN security_group_rules AS security_group_rules_1 ON security_group_rules_1.parent_group_id = security_groups_1.id AND security_group_rules_1.deleted = %(deleted_5)s LEFT OUTER JOIN instance_system_metadata AS instance_system_metadata_1 ON anon_1.instances_uuid = instance_system_metadata_1.instance_uuid LEFT OUTER JOIN instance_info_caches AS instance_info_caches_1 ON instance_info_caches_1.instance_uuid = anon_1.instances_uuid'] [parameters: {u'uuid_1': u'5dacdca6-65e8-4771-9110-828283176a06', u'param_1': 1, u'deleted_5': 0, u'deleted_4': 0, u'deleted_3': 0, u'deleted_2': 0, u'deleted_1': 0}] (Background on this error at: http://sqlalche.me/e/2j85): InternalError: (23, u'Out of resources when opening file \'/tmp/#sql_e56_0.MAD\' (Errcode: 24 "Too many open files")')
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters Traceback (most recent call last):
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line 1193, in _execute_context
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters context)
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/default.py", line 507, in do_execute
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters cursor.execute(statement, parameters)
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/lib/python2.7/site-packages/pymysql/cursors.py", line 166, in execute
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters result = self._query(query)
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/lib/python2.7/site-packages/pymysql/cursors.py", line 322, in _query
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters conn.query(q)
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/lib/python2.7/site-packages/pymysql/connections.py", line 856, in query
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters self._affected_rows = self._read_query_result(unbuffered=unbuffered)
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/lib/python2.7/site-packages/pymysql/connections.py", line 1057, in _read_query_result
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters result.read()
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/lib/python2.7/site-packages/pymysql/connections.py", line 1340, in read
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters first_packet = self.connection._read_packet()
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/lib/python2.7/site-packages/pymysql/connections.py", line 1014, in _read_packet
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters packet.check_error()
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/lib/python2.7/site-packages/pymysql/connections.py", line 393, in check_error
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters err.raise_mysql_exception(self._data)
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters File "/usr/lib/python2.7/site-packages/pymysql/err.py", line 107, in raise_mysql_exception
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters raise errorclass(errno, errval)
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters InternalError: (23, u'Out of resources when opening file \'/tmp/#sql_e56_0.MAD\' (Errcode: 24 "Too many open files")')
2018-08-29 17:11:02.438 5151 ERROR oslo_db.sqlalchemy.exc_filters
The strange thing is that sometimes have happened with another operations on Dashboard project instances such as allocate floating IP, delete instance, attach interface, etc.
This isn't a nova problem, you're system is out of resources:
InternalError: (23, u'Out of resources when opening file \'/tmp/ #sql_e56_ 0.MAD\' (Errcode: 24 "Too many open files")')