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                       .                     |      :
                       : .                   :      |
                       | .     Logswan       .      |
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                         |                       :


Logswan is a fast Web log analyzer using probabilistic data structures. It is targeted at very large log files, typically APIs logs. It has constant memory usage regardless of the log file size, and takes approximatively 4MB of RAM.

Unique visitors counting is performed using two HyperLogLog counters (one for IPv4, and another one for IPv6), providing a relative accuracy of 0.10%. String representations of IP addresses are used and preferred as they offer better precision.

Project design goals include: speed, memory-usage efficiency, and keeping the code as simple as possible.

Logswan is opinionated software:

  • It only supports the Common Log Format, in order to keep the parsing code simple. It can of course process the Combined Log Format as well (referer and user agent fields will be discarded)
  • It does not split results per day, but log files can be split prior to being processed
  • Input file size and bandwidth usage are reported in bytes, there are no plans to format or round them

Logswan is written with security in mind and is running sandboxed on OpenBSD (using pledge). Experimental seccomp support is available for selected architectures and can be enabled by setting the ENABLE_SECCOMP variable to 1 when invoking CMake. It has also been extensively fuzzed using AFL and Honggfuzz.


Currently implemented features:

  • Counting used bandwidth
  • Counting number of processed lines / invalid lines
  • Counting number of hits (IPv4 and IPv6 hits)
  • Counting visits (unique IP addresses for both IPv4 and IPv6)
  • GeoIP lookups (for both IPv4 and IPv6)
  • Hourly hits distribution
  • HTTP method distribution
  • HTTP protocol distribution
  • HTTP status codes distribution


Logswan uses the CMake build system and requires Jansson and libmaxminddb libraries and header files.

Installing dependencies

  • OpenBSD: pkg_add -r cmake jansson libmaxminddb
  • NetBSD: pkgin in cmake jansson libmaxminddb
  • FreeBSD: pkg install cmake jansson libmaxminddb
  • macOS: brew install cmake jansson libmaxminddb
  • Alpine Linux: apk add cmake gcc make musl-dev jansson-dev libmaxminddb-dev
  • Debian / Ubuntu: apt-get install build-essential cmake libjansson-dev libmaxminddb-dev
  • Fedora: dnf install cmake gcc make jansson-devel libmaxminddb-devel


mkdir build
cd build
cmake ..

Logswan has been successfully built and tested on OpenBSD, NetBSD, FreeBSD, macOS, and Linux with both Clang and GCC.


Logswan packages are available for:

GeoIP2 databases

Logswan looks for GeoIP2 databases in ${CMAKE_INSTALL_PREFIX}/share/dbip by default, which points to /usr/local/share/dbip.

A custom directory can be set using the GEOIP2DIR variable when invoking CMake:

cmake -DGEOIP2DIR=/var/db/dbip .

The free Creative Commons licensed DB-IP IP to Country Lite database can be downloaded here.

Alternatively, GeoLite2 Country database from MaxMind can be downloaded free of charge here, but require accepting an EULA and is not freely licensed.


logswan [-ghv] [-d db] logfile

If file is a single dash (`-'), logswan reads from the standard input.

The options are as follows:

-d db	Specify path to a GeoIP database.
-g	Enable GeoIP lookups.
-h	Display usage.
-v	Display version.

Logswan outputs JSON data to stdout.


Logswan is released under the BSD 2-Clause license. See LICENSE file for details.


Logswan is developed by Frederic Cambus.


Project homepage: