Scroll to navigation

HORST(8) System Manager's Manual HORST(8)


horst - Highly Optimized Radio Scanning Tool


horst [-v] [-h] [-q] [-D] [-a] [-c file] [-C channel] [-i interface] [-t sec] [-V view] [-d ms] [-b bytes] [-M file] [-s] [-u] [-N] [-n IP] [-p port] [-o file] [-X name] [-x command] [-e mac] [-f pkt_name] [-m mode] [-B BSSID]


horst is a small, lightweight IEEE802.11 wireless LAN analyzer with a text interface. Its basic function is similar to tcpdump, Wireshark or Kismet, but it's much smaller and shows different, aggregated information which is not easily available from other tools. It is mainly targeted at debugging wireless LANs with a focus on ad-hoc (IBSS) mode in larger mesh networks. It can be useful to get a quick overview of what's going on on all wireless LAN channels and to identify problems.

Shows signal values per station.
Calculates channel utilization ("usage") by adding up the amount of time the packets actually occupy the medium.
"Spectrum Analyzer" shows signal levels and usage per channel.
Text-based "graphical" packet history, with signal, packet type and physical rate
Shows all stations per ESSID and the live TSF per node as it is counting.
Detects IBSS "splits" (same ESSID but different BSSID - this is a common driver problem).
Statistics of packets/bytes per physical rate and per packet type.
Has some support for mesh protocols (OLSR and batman).
Can filter specific packet types, source MAC addresses or BSSIDs.
Client/server support for monitoring on remote nodes.
Can be controlled via a named pipe.


Show version.
Show summary of options.
Quiet mode. Don't show user interface. This is only useful in conjunction when running in server mode (-C) or writing to a file (-o).
Show lot's of debugging output, including a full package dump. Only available when compiled with DEBUG=1.
Always add virtual monitor interface. Don't try to set existing interface to monitor mode.
Use configfile instead of the default "/etc/horst.conf".
Set inital channel (number not frequency).
Operate on the given network interface instead of the default "wlan0".
Timeout (remove) nodes after not receiving packets from them for this time in seconds (default: 60 sec).
Display 'view'. Valid view names are "history", "hist", "essid", "statistics", "stats", "spectrum", "spec".
Display update interval. The default value of 100ms can be increased to reduce CPU load caused by redrawing the screen.
Receive buffer size. The receive buffer size can be set to tune memory consumption and reduce lost packets under load.
MAC address to host name mapping file. The file can either be a dhcp.leases file from dnsmasq or contain mappings in the form "MAC<space>name" (e.g.: "00:01:02:03:04:05 test") line by line (default filename: /tmp/dhcp.leases).
Show a poor mans "spectrum analyzer". The same can be achieved by running horst as normal and pressing the button 's' (Spec); then 'c' (Chan) and 'a' (Automatically change channel).
Upper channel limit for the automatic channel change.
Allow client connections. Server mode. Only one client connection is supported at the moment (default: off).
Connect to a horst instance running in server-mode at the specified IP address.
Use the specified port (default: 4444) for client/server connections.
Write a information about each received packet into file. Note that you can send to STDOUT by using -o /dev/stdout. See OUTPUT FILE FORMAT below.
Accept control commands on a named pipe (default /tmp/horst).
-X name
Accept control commands on a named pipe with given name or set pipe name used with -x.
Send control command to another horst process who was started with -X and then exit. Multiple commands can be concatenated with ';'. Currently implemented commands are:

Pause horst processing

Resume horst processing

Reset all history, statistics and views
Set channel channel number
Automatically change channels (1 or 0)
Set channel dwell time when automatically changing channel (ms)
Set max channel when automatically changing channel
Write to outfile named X. If the file is already open, it is cleared and re-openend. If filename is not specified ("outfile=") any existing file is closed and no file is written.

Filter all MAC addresses except these, to show only packets originating from the specified MAC addresses. This option can be specified multiple times.
Filter all packets except these. This option can be specified multiple times. For valid packet names see NAMES AND ABBREVIATIONS below.
Only show/include packets and nodes of this mode. Note that the mode is infered by the information of packets we received and it may take some time until a node is properly classified. This option can be specified multiple times.
Only show/include packets which belong to the given BSSID.


The ncurses-based text interface tries to display a lot of information, so it may look confusing at first. Below we describe the different screens and options.

The initial (main) screen is split into three parts. The upper area shows a list of aggregated "node" information, the most useful information about each sender which was discovered, one per line:


"Spinner" to show activity

Percentage of this node's packets in relation to all received packets

Percentage of retried frames of all frames this node sent

Channel number

Signal value (RSSI) in dBm

Physical data rate
MAC address of sender


Encryption (WPA1, WPA2, WEP)


Additional info like "BATMAN", IP address...

The lower area shows a scrolling list of packets as they come in:

Channel number

Signal value (RSSI) in dBm

Physical data rate
MAC address of sender



Additional info like ESSID, TFS, IP address...

The lower right box shows bar graphs for:

of last received packet in green
Bits per second of all received packets
Percentage of channel use

The lower edge is the menu and status bar, it shows which keys to press for other screens. The status shows ">" when horst is running or "=" when it is paused, then "F" when any kind of filter is active, the Channel, the monitor interface in use and the time.

Can be used to pause/resume horst. When horst is paused it will loose packets received in the mean time.

Clears all history and aggregated statistical data.

The history screen scrolls from right to left and shows a bar for each packet indicating the signal level. In the line below that, the packet type is indicated by one character (See NAMES AND ABBREVIATIONS below) and the rough physical data rate is indicated below that in blue.

ESSID ('e')

The ESSID screen groups information by ESSID and shows the mode (AP, IBSS), the MAC address of the sender, the BSSID, the TSF, the beacon interval, the channel, the signal, a "W" when encrytoion is used and the IP address if known.

The statistics screen groups packets by physical rate and by packet type and shows other kinds of aggregated and statistical information based on packets.

The "poor mans spectrum analyzer" screen is only really useful when horst is started with the -s option or the "Automatically change channel" option is selected in the "Chan" settings, or the config option channel_scan is set.

It shows the available channels horizontally and vertical bars for each channel:

Signal in green
Physical rate in blue
Channel usage in orange/brown

By pressing the 'n' key, the display can be changed to show only the average signal level on each channel and the last 4 digits of the MAC address of the individual nodes at the level (height) they were received. This can give a quick graphical overview of the distance of nodes.

This configuration dialog can be used to define the active filters.

This configuration dialog can be used to change the channel changing behaviour of horst or to change to a different channel manually.

Only active in the main screen, can be used to sort the node list in the upper area by Signal, Time, BSSID or Channel.


802.11 standard frames

Management frames
a ASOCRQ Association request
A ASOCRP Associaion response
a REASRQ Reassociation request
A REASRP Reassociation response
p PROBRQ Probe request
P PROBRP Probe response
T TIMING Timing Advertisement
D DISASC Disassociation
u AUTH Authentication
U DEAUTH Deauthentication
c ACTNOA Action No Ack

Control frames
w CTWRAP Control Wrapper
b BACKRQ Block Ack Request
B BACK Block Ack
f CFENDK CF-End + CF-Ack

Data frames
F DCFACK Data + CF-Ack
F DCFPLL Data + CF-Poll
F DCFKPL Data + CF-Ack + CF-Poll
n NULL Null (no data)
f CFACK CF-Ack (no data)
f CFPOLL CF-Poll (no data)
f CFCKPL CF-Ack + CF-Poll (no data)
F QDCFCK QoS Data + CF-Ack
F QDCFPL QoS Data + CF-Poll
F QDCFKP QoS Data + CF-Ack + CF-Poll
N QDNULL QoS Null (no data)
f QCFPLL QoS CF-Poll (no data)
f QCFKPL QoS CF-Ack + CF-Poll (no data)
* BADFCS Bad frame checksum

Similar to 802.11 frames above but higher level and as a bit field (types can overlap, e.g. DATA + IP) and including more information, like IP, ARP, BATMAN, OLSR...

Packet types
CTRL 0x000001 WLAN Control frame
MGMT 0x000002 WLAN Management frame
DATA 0x000004 WLAN Data frame
BADFCS 0x000008 WLAN frame checksum (FCS) bad
BEACON 0x000010 WLAN beacon frame
PROBE 0x000020 WLAN probe request or response
ASSOC 0x000040 WLAN associaction request/response frame
AUTH 0x000080 WLAN authentication frame
ACK 0x000200 WLAN ACK or BlockACK
NULL 0x000400 WLAN NULL Data frame
QDATA 0x000800 WLAN QoS Data frame (WME/WMM)
ARP 0x001000 ARP packet
IP 0x002000 IP packet
ICMP 0x004000 IP ICMP packet
UDP 0x008000 IP UDP
TCP 0x010000 IP TCP
OLSR 0x020000 OLSR protocol
BATMAN 0x040000 BATMAND Layer3 or BATMAN-ADV Layer 2 frame
MESHZ 0x080000 MeshCruzer protocol

Bit field of operating mode type which is infered from received packets. Modes may overlap, i.e. it is common to see STA and PRB at the same time.

Operating modes
AP 0x01 Access Point (AP)
ADH 0x02 Ad-hoc node
STA 0x04 Station (AP client)
PRB 0x08 Sent PROBE requests
WDS 0x10 WDS or 4 Address frames
UNKNOWN 0x20 Unknown e.g. RTS/CTS or ACK


To capture and analyze 802.11 traffic, the interface needs to be in monitor mode. You can either setup the interface manually beforehand or let horst setup it automatically at startup. Usually, root privileges are required to modify an interface setup.

horst should work with any wireleass LAN card and driver which supports monitor mode, with either "prism2" or "radiotap" headers. This includes most modern mac80211-based drivers.

If the interface is not in monitor mode at startup, horst first tries to put the interface in monitor mode. If it fails (for example when the interface is already in use), a new virtual monitor interface (horst0) is added and used instead. The virtual monitor interface is removed when horst exits. Note that changing the channel via a virtual monitor interface is not allowed by the wireless driver, so options -C and -s do not work when virtual monitor interface is used.

Examples of how to setup an interface manually:

iw wlan0 interface add mon0 type monitor
sudo iw wlan1 set type monitor
sudo iw wlan1 set channel 6

iwconfig wlan0 mode monitor
iwconfig wlan0 channel 1
ifconfig wlan0 up

wlanconfig wlan0 create wlandev wifi0 wlanmode monitor

iwconfig wlan0 mode monitor
iwpriv wlan0 monitor_type 1


Signal values and ranges may differ between wireless drivers and versions.


The format of the output file (-o flag) is a comma separated list of the following fields in the following order, one packet each line.

Local time, including microseconds (e.g. 2015-05-16 15:05:44.338806 +0300)
802.11 MAC packet type name as defined in the section "NAMES AND ABBREVIATIONS".
Source MAC address
Destination MAC address
Higher level packet name as defined in section "NAMES AND ABBREVIATIONS".
Signal strength in dBm
Packet length (MAC)
Physical data rate
Received while tuned to this frequency.
TFS timer value
ESSID, network name
Operating modes as defined in "NAMES AND ABBREVIATIONS".
Channel number
Encryption in use
WPA1 Encryption in use
RSN (WPA2) Encryption in use
IP source address (if available)
IP destionation address (if available)


horst.conf(5), tcpdump(1), wireshark(1), kismet(1), README,


horst was written by Bruno Randolf <>.

This manual page was written by Antoine Beaupré <>, for the Debian project (and may be used by others).

July 22, 2015