At shut down, Suricata reports the packet loss statistics it gets from
pcap, pfring or afpacket

::

  [18088] 30/5/2012 -- 07:39:18 - (RxPcapem21) Packets 451595939, bytes 410869083410
  [18088] 30/5/2012 -- 07:39:18 - (RxPcapem21) Pcap Total:451674222 Recv:451596129 Drop:78093 (0.0%).

Usually, this is not the complete story though. These are kernel drop
stats, but the NIC may also have dropped packets. Use ethtool to get
to those:

::

  # ethtool -S em2
  NIC statistics:
       rx_packets: 35430208463
       tx_packets: 216072
       rx_bytes: 32454370137414
       tx_bytes: 53624450
       rx_broadcast: 17424355
       tx_broadcast: 133508
       rx_multicast: 5332175
       tx_multicast: 82564
       rx_errors: 47
       tx_errors: 0
       tx_dropped: 0
       multicast: 5332175
       collisions: 0
       rx_length_errors: 0
       rx_over_errors: 0
       rx_crc_errors: 51
       rx_frame_errors: 0
       rx_no_buffer_count: 0
       rx_missed_errors: 0
       tx_aborted_errors: 0
       tx_carrier_errors: 0
       tx_fifo_errors: 0
       tx_heartbeat_errors: 0
       tx_window_errors: 0
       tx_abort_late_coll: 0
       tx_deferred_ok: 0
       tx_single_coll_ok: 0
       tx_multi_coll_ok: 0
       tx_timeout_count: 0
       tx_restart_queue: 0
       rx_long_length_errors: 0
       rx_short_length_errors: 0
       rx_align_errors: 0
       tx_tcp_seg_good: 0
       tx_tcp_seg_failed: 0
       rx_flow_control_xon: 0
       rx_flow_control_xoff: 0
       tx_flow_control_xon: 0
       tx_flow_control_xoff: 0
       rx_long_byte_count: 32454370137414
       rx_csum_offload_good: 35270755306
       rx_csum_offload_errors: 65076
       alloc_rx_buff_failed: 0
       tx_smbus: 0
       rx_smbus: 0
       dropped_smbus: 0

Kernel drops
------------

stats.log contains interesting information in the
capture.kernel_packets and capture.kernel_drops. The meaning of them
is different following the capture mode.

In AF_PACKET mode:

* kernel_packets is the number of packets correctly sent to userspace
* kernel_drops is the number of packets that have been discarded instead of being sent to userspace

In PF_RING mode:

* kernel_packets is the total number of packets seen by pf_ring
* kernel_drops is the number of packets that have been discarded instead of being sent to userspace

In the Suricata stats.log the TCP data gap counter is also an
indicator, as it accounts missing data packets in TCP streams:

::

  tcp.reassembly_gap        | Detect                    | 789

Ideally, this number is 0. Not only pkt loss affects it though, also
bad checksums and stream engine running out of memory.

Tools to plot graphs
--------------------

Some people made nice tools to plot graphs of the statistics file.

* `ipython and matplotlib script <https://github.com/regit/suri-stats>`_
* `Monitoring with Zabbix or other <http://christophe.vandeplas.com/2013/11/suricata-monitoring-with-zabbix-or-other.html>`_ and `Code on GitHub <https://github.com/cvandeplas/suricata_stats>`_