Not connected to a cassandra instance.

Use netstat to check if Cassandra is running on port 9160.
> netstat -tulpn

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 127.0.0.1:8005          0.0.0.0:*               LISTEN      20358/java    
tcp        0      0 127.0.0.1:9160          0.0.0.0:*               LISTEN      4951/java      
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN      18848/mysqld  
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      20358/java    
tcp        0      0 0.0.0.0:42325           0.0.0.0:*               LISTEN      4951/java      
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      619/sshd      
tcp        0      0 127.0.0.1:7000          0.0.0.0:*               LISTEN      4951/java      
tcp        0      0 0.0.0.0:7199            0.0.0.0:*               LISTEN      4951/java      
tcp        0      0 0.0.0.0:53890           0.0.0.0:*               LISTEN      4951/java      
tcp6       0      0 :::22                   :::*                    LISTEN      619/sshd      
udp        0      0 0.0.0.0:68              0.0.0.0:*                           431/dhclient3

Make sure port 9160 is running.

If not, start Cassandra:
> sudo cassandra -f

Connect to Cassandra
> sudo cassandra-cli --host localhost

Keyspace: system:
  Replication Strategy: org.apache.cassandra.locator.LocalStrategy
  Durable Writes: true
    Options: [replication_factor:1]
  Column Families:
    ColumnFamily: HintsColumnFamily (Super)
    "hinted handoff data"
      Key Validation Class: org.apache.cassandra.db.marshal.BytesType
      Default column value validator: org.apache.cassandra.db.marshal.BytesType
      Columns sorted by: org.apache.cassandra.db.marshal.BytesType/org.apache.cassandra.db.marshal.BytesType
      Row cache size / save period in seconds / keys to save : 0.0/0/all
      Row Cache Provider: org.apache.cassandra.cache.ConcurrentLinkedHashCacheProvider
      Key cache size / save period in seconds: 0.01/0
      GC grace seconds: 0
      Compaction min/max thresholds: 4/32
      Read repair chance: 0.0
      Replicate on write: true
      Bloom Filter FP chance: default
      Built indexes: []
      Compaction Strategy: org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy
    ColumnFamily: IndexInfo
    "indexes that have been completed"
      Key Validation Class: org.apache.cassandra.db.marshal.BytesType
      Default column value validator: org.apache.cassandra.db.marshal.BytesType
      Columns sorted by: org.apache.cassandra.db.marshal.UTF8Type
      Row cache size / save period in seconds / keys to save : 0.0/0/all
      Row Cache Provider: org.apache.cassandra.cache.ConcurrentLinkedHashCacheProvider
      Key cache size / save period in seconds: 0.01/0
      GC grace seconds: 0
      Compaction min/max thresholds: 4/32
      Read repair chance: 0.0
      Replicate on write: true
      Bloom Filter FP chance: default
      Built indexes: []
      Compaction Strategy: org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy
    ColumnFamily: LocationInfo
    "persistent metadata for the local node"
      Key Validation Class: org.apache.cassandra.db.marshal.BytesType
      Default column value validator: org.apache.cassandra.db.marshal.BytesType
      Columns sorted by: org.apache.cassandra.db.marshal.BytesType
      Row cache size / save period in seconds / keys to save : 0.0/0/all
      Row Cache Provider: org.apache.cassandra.cache.ConcurrentLinkedHashCacheProvider
      Key cache size / save period in seconds: 0.01/0
      GC grace seconds: 0
      Compaction min/max thresholds: 4/32
      Read repair chance: 0.0
      Replicate on write: true
      Bloom Filter FP chance: default
      Built indexes: []
      Compaction Strategy: org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy
    ColumnFamily: Migrations
    "individual schema mutations"
      Key Validation Class: org.apache.cassandra.db.marshal.BytesType
      Default column value validator: org.apache.cassandra.db.marshal.BytesType
      Columns sorted by: org.apache.cassandra.db.marshal.TimeUUIDType
      Row cache size / save period in seconds / keys to save : 0.0/0/all
      Row Cache Provider: org.apache.cassandra.cache.ConcurrentLinkedHashCacheProvider
      Key cache size / save period in seconds: 0.01/0
      GC grace seconds: 0
      Compaction min/max thresholds: 4/32
      Read repair chance: 0.0
      Replicate on write: true
      Bloom Filter FP chance: default
      Built indexes: []
      Compaction Strategy: org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy
    ColumnFamily: NodeIdInfo
    "nodeId and their metadata"
      Key Validation Class: org.apache.cassandra.db.marshal.BytesType
      Default column value validator: org.apache.cassandra.db.marshal.BytesType
      Columns sorted by: org.apache.cassandra.db.marshal.TimeUUIDType
      Row cache size / save period in seconds / keys to save : 0.0/0/all
      Row Cache Provider: org.apache.cassandra.cache.ConcurrentLinkedHashCacheProvider
      Key cache size / save period in seconds: 0.01/0
      GC grace seconds: 0
      Compaction min/max thresholds: 4/32
      Read repair chance: 0.0
      Replicate on write: true
      Bloom Filter FP chance: default
      Built indexes: []
      Compaction Strategy: org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy
    ColumnFamily: Schema
    "current state of the schema"
      Key Validation Class: org.apache.cassandra.db.marshal.BytesType
      Default column value validator: org.apache.cassandra.db.marshal.BytesType
      Columns sorted by: org.apache.cassandra.db.marshal.UTF8Type
      Row cache size / save period in seconds / keys to save : 0.0/0/all
      Row Cache Provider: org.apache.cassandra.cache.ConcurrentLinkedHashCacheProvider
      Key cache size / save period in seconds: 0.01/0
      GC grace seconds: 0
      Compaction min/max thresholds: 4/32
      Read repair chance: 0.0
      Replicate on write: true
      Bloom Filter FP chance: default
      Built indexes: []
      Compaction Strategy: org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy
    ColumnFamily: Versions
    "server version information"
      Key Validation Class: org.apache.cassandra.db.marshal.UTF8Type
      Default column value validator: org.apache.cassandra.db.marshal.BytesType
      Columns sorted by: org.apache.cassandra.db.marshal.UTF8Type
      Row cache size / save period in seconds / keys to save : 0.0/0/all
      Row Cache Provider: org.apache.cassandra.cache.ConcurrentLinkedHashCacheProvider
      Key cache size / save period in seconds: 0.01/0
      GC grace seconds: 0
      Compaction min/max thresholds: 4/32
      Read repair chance: 0.0
      Replicate on write: true
      Bloom Filter FP chance: default
      Built indexes: []
      Column Metadata:
        Column Name: version
          Validation Class: org.apache.cassandra.db.marshal.UTF8Type
      Compaction Strategy: org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy