darkstat - network statistics gatherer
darkstat [ -i interface ] [ -r file ] [ --snaplen bytes ] [ --pppoe ] [
--syslog ] [ --verbose ] [ --no-daemon ] [ --no-promisc ] [ --no-dns ]
[ --no-macs ] [ --no-lastseen ] [ -p port ] [ -b bindaddr ] [ -f filter
] [ -l network/netmask ] [ --chroot dir ] [ --user username ] [
--daylog filename ] [ --import filename ] [ --export filename ] [
--pidfile filename ] [ --hosts-max count ] [ --hosts-keep count ] [
--ports-max count ] [ --ports-keep count ] [ --highest-port port ] [
--wait secs ] [ --hexdump ]
darkstat is a packet sniffer that runs as a background process, gathers
all sorts of statistics about network usage, and serves them over HTTP.
All settings are passed on the commandline.
Capture traffic on the specified network interface. This is the
only mandatory commandline argument.
Instead of capturing live traffic, read it from a pcap(3)
capture file. This is only useful for development and
benchmarking. The -r and -i arguments are mutually exclusive.
How many bytes to capture from the start of each packet. You
should not need to specify this; darkstat will calculate it
Don’t use this.
Instead, capture on the tunnel interface that your PPPoE
software provides, for example tun0 on FreeBSD, pppoe0 on
OpenBSD or NetBSD.
If you really must, you can capture on an Ethernet interface and
pass this argument to have darkstat decode PPPoE frames and
ignore everything else. Make sure you also specify your local
address with the -l argument!
Errors, warnings, and verbose messages will go to syslog
(facility daemon, priority debug) instead of stderr.
On some systems, these messages end up in /var/log/debug by
Produce more verbose debugging messages.
Do not detach from the controlling terminal; stay in the
Do not use promiscuous mode to capture. Note that an interface
may already be in promiscuous mode, or may later enter
promiscuous mode, due to circumstances beyond darkstat’s
control. If this is a problem, use -f to specify an appropriate
Do not resolve IPs to host names. This can significantly reduce
memory footprint on small systems as an extra process is created
for DNS resolution.
Do not display MAC addresses in the hosts table.
Do not display the last seen time in the hosts table.
Bind the web interface to the specified port. The default is
Bind the web interface to the specified address. The default is
to listen on all interfaces.
Use the specified filter expression when capturing traffic. The
filter syntax is beyond the scope of this manual page; please
refer to the tcpdump(1) documentation.
Define a "local network" according to the network and netmask
addresses. All traffic entering or leaving this network will be
graphed, as opposed to the default behaviour of only graphing
traffic to and from the local host.
The rule is that if ip_addr & netmask == network, then that
address is considered local. See the usage example below.
Force darkstat to chroot() into the specified directory.
Without this argument, a default directory will be used, which
is determined at build time. Usually /var/empty or
For security reasons, this directory should be empty, and the
user that darkstat is running as should not have write access to
However, if you wish to use --daylog or --export, darkstat will
need write access to the chroot. If you are uncomfortable with
the security implications, don’t use any functionality that
requires write access.
Force darkstat to drop privileges to the uid and gid of the
specified user. Without this argument, a default value will be
used, which is set at build time. Usually nobody.
For security reasons, this should not be root.
Log daily traffic statistics into the named file, relative to
the chroot directory. If you wish to use --daylog, you must
first specify a --chroot directory, and it must be writeable by
the darkstat user. A writeable chroot has security
implications; if you are uncomfortable with this, do not use the
If the daylog argument is not specified, no logging is
The daylog format is:
Lines starting with a # are comments stating when logging
started and stopped.
Upon starting, import a darkstat database from the named file,
relative to the chroot directory. If you wish to use --import,
you must first specify a --chroot directory. If the import is
unsuccessful, darkstat will start with an empty database.
On shutdown, and upon receiving SIGUSR1, export the in-memory
database to the named file, relative to the chroot directory.
If you wish to use --export, you must first specify a --chroot
directory, and it must be writeable by the darkstat user. A
writeable chroot has security implications - if you are
uncomfortable with this, do not use the --export functionality.
Creates a file containing the process ID of darkstat. This file
will be unlinked upon clean shutdown. As with all pidfiles, if
darkstat dies uncleanly, a stale pidfile can be left over.
For example, start darkstat with:
darkstat -i fxp0 --chroot /var/run/darkstat --pidfile
And stop with:
kill ‘cat /var/run/darkstat/darkstat.pid‘
By default, kill(1) will send SIGTERM, which will cause darkstat
to shut down cleanly.
The maximum number of hosts that will be kept in the hosts
table. This is used to limit how much accounting data will be
kept in memory. The number of --hosts-max must be greater than
When the hosts table hits --hosts-max and traffic is seen from a
new host, we clean out the hosts table, keeping only the top
--hosts-keep number of hosts, sorted by total traffic.
The maximum number of ports that will be tracked for each host.
This is used to limit how much accounting data will be kept in
memory. The number of --ports-max must be greater than
When a ports table fills up, this many ports are kept and the
rest are discarded.
Ports that are numerically higher than this will not appear in
the per-host ports tables, although their traffic will still be
accounted for. This can be used to hide ephemeral ports. By
default, all ports are tracked.
Don’t use this. It’s a hack to help victims of NetworkManager
and similar systems.
You should start darkstat after the capture interface has come
up. If you can’t, specifying the --wait option will make
darkstat sleep up to the specified number of seconds for the
interface to become ready. Zero means wait indefinitely.
Show hex dumps of received traffic. This is only for debugging,
and implies --verbose and --no-daemon.
To gather statistics on the fxp0 interface:
darkstat -i fxp0
We want to account for traffic on the Internet-facing interface, but
only serve web pages to our private local network where we have the IP
darkstat -i fxp0 -b 192.168.0.1
We want to serve web pages on the standard HTTP port:
darkstat -i fxp0 -p 80
We are on Optus (cable) and don’t want to account for the constant ARP
traffic we are receiving:
darkstat -i fxp0 -f "not arp"
We only want to account for SSH traffic:
darkstat -i fxp0 -f "port 22"
We don’t want to account for traffic between internal IPs:
darkstat -i fxp0 -f "not (src net 192.168.0 and dst net
(For a full reference on filter syntax, refer to the tcpdump(1)
We have a network consisting of a gateway server (192.168.1.1) and a
few workstations (192.168.1.2, 192.168.1.3, etc.) and we want to graph
all traffic entering and leaving the local network, not just the
gateway server (which is running darkstat):
darkstat -i fxp0 -l 192.168.1.0/255.255.255.0
On some systems, we can’t capture on a "decoded" interface but only on
nas0 which returns PPPoE encapsulated packets. Do PPPoE decoding, and
override the local IP manually since it cannot be automatically
detected. Note the /32 netmask:
darkstat -i nas0 --pppoe -l 192.168.1.1/255.255.255.255
To shut darkstat down cleanly, send a SIGTERM or SIGINT signal to the
darkstat parent process.
Sending the SIGUSR1 signal will cause darkstat to empty out its in-
memory database. If an --export file was set, it will first save the
database to file.
FREQUENTLY ASKED QUESTIONS
How many bytes does each bar on the graph represent?
Hover your mouse cursor over a bar and you should get a tooltip saying
exactly how many bytes in and out the bar represents.
Why aren’t there labels / tics / a scale on the graphs?
Because implementing them is hard. And doing so correctly, and in a
way that works across all browsers, looks pretty much impossible.
I might attempt it some day. In the meantime, patches would be gladly
Why are the graphs blank? All the bars are zero.
The graphs only show traffic in/out of the local host, which is
determined by getting the IP address of the interface you’re sniffing
You can use the -l argument to override the local address for
accounting purposes. You can also use it to do accounting for a whole
subnet by specifying an appropriate netmask.
darkstat was written in 2001, largely as a result of a certain
Australian cable Internet provider introducing a 3GB monthly traffic
Emil Mikulic and others. (see the AUTHORS file)