: Getting error while starting the server

Unhandled exception in thread started by <function check_errors.<locals>.wrapper at 0xb2da8074>
Traceback (most recent call last):
  File "/usr/local/lib/python3.4/dist-packages/django/db/backends/__init__.py", line 133, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.4/dist-packages/django/db/backends/__init__.py", line 122, in connect
    self.connection = self.get_new_connection(conn_params)
  File "/usr/local/lib/python3.4/dist-packages/django/db/backends/postgresql_psycopg2/base.py", line 134, in get_new_connection
    return Database.connect(**conn_params)
  File "/usr/local/lib/python3.4/dist-packages/psycopg2/__init__.py", line 164, in connect
    conn = _connect(dsn, connection_factory=connection_factory, async=async)
psycopg2.OperationalError: could not translate host name "localhost" to address: Name or service not known


The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/local/lib/python3.4/dist-packages/django/utils/autoreload.py", line 222, in wrapper
    fn(*args, **kwargs)
  File "/usr/local/lib/python3.4/dist-packages/django/core/management/commands/runserver.py", line 107, in inner_run
    self.check_migrations()
  File "/usr/local/lib/python3.4/dist-packages/django/core/management/commands/runserver.py", line 159, in check_migrations
    executor = MigrationExecutor(connections[DEFAULT_DB_ALIAS])
  File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/executor.py", line 17, in __init__
    self.loader = MigrationLoader(self.connection)
  File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/loader.py", line 48, in __init__
    self.build_graph()
  File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/loader.py", line 183, in build_graph
    self.applied_migrations = recorder.applied_migrations()
  File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/recorder.py", line 59, in applied_migrations
    self.ensure_schema()
  File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/recorder.py", line 49, in ensure_schema
    if self.Migration._meta.db_table in self.connection.introspection.get_table_list(self.connection.cursor()):
  File "/usr/local/lib/python3.4/dist-packages/django/db/backends/__init__.py", line 165, in cursor
    cursor = self.make_debug_cursor(self._cursor())
  File "/usr/local/lib/python3.4/dist-packages/django/db/backends/__init__.py", line 138, in _cursor
    self.ensure_connection()
  File "/usr/local/lib/python3.4/dist-packages/django/db/backends/__init__.py", line 133, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.4/dist-packages/django/db/utils.py", line 94, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/local/lib/python3.4/dist-packages/django/utils/six.py", line 658, in reraise
    raise value.with_traceback(tb)
  File "/usr/local/lib/python3.4/dist-packages/django/db/backends/__init__.py", line 133, in ensure_connection
    self.connect()
  File "/usr/local/lib/python3.4/dist-packages/django/db/backends/__init__.py", line 122, in connect
    self.connection = self.get_new_connection(conn_params)
  File "/usr/local/lib/python3.4/dist-packages/django/db/backends/postgresql_psycopg2/base.py", line 134, in get_new_connection
    return Database.connect(**conn_params)
  File "/usr/local/lib/python3.4/dist-packages/psycopg2/__init__.py", line 164, in connect
    conn = _connect(dsn, connection_factory=connection_factory, async=async)
django.db.utils.OperationalError: could not translate host name "localhost" to address: Name or service not known

can anyone tell me what is the reason for this error.?

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