FIFOLOG(1) BSD General Commands Manual FIFOLOG(1)NAME
fifolog_create, fifolog_writer, fifolog_reader — initialize, write, seek
and extract data from a fifolog
fifolog_create [-l record-size] [-r record-count] [-s size] file
fifolog_reader [-t] [-b tstart] [-B Tstart] [-e tend] [-E Tend]
[-o ofile] [-R regexp] [-T timefmt] file
fifolog_writer [-w write-rate] [-s sync-rate] [-z compression] file
Fifologs provide a compact round-robin circular storage for recording
text and binary information to permanent storage in a bounded and pre‐
dictable fashion, time and space wise.
A fifolog can be stored either directly on a disk partition or in a regu‐
The input data stream is encoded, compressed and marked up with time‐
stamps before it is written to storage, such that it is possible to seek
out a particular time interval in the stored data, without having to
decompress the entire logfile.
The fifolog_create utility is used to initialize the first sector of a
disk device or file system file to make it a fifolog and should be called
Running fifolog_create on an existing fifolog will reset it so that
fifolog_reader and fifolog_writer will not see the previous contents.
(The previous contents are not physically erased, and with a bit of hand-
work all but the first record can be easily recovered.)
If the file does not already exist, fifolog_create will attempt to create
and ftruncate(2) it to the specified size, defaulting to 86400 records of
512 bytes if the -r, -l or -s options do not specify otherwise.
The fifolog_writer utility will read standard input and write it to the
end of the fifolog according to the parameters given.
Writes happen whenever the output buffer is filled with compressed data
or when either of two timers expire, forcing a partially filled buffer to
The first and faster timer, -w write-rate, forces available data to be
written but does not flush and reset the compression dictionary. This
timer is intended to minimize the amount of logdata lost in RAM in case
of a crash and by default it fires 10 seconds after the previous write.
The second and slower timer, -s sync-rate, forces a full flush and reset
of the compression engine and causes the next record written to be a syn‐
chronization point with an uncompressed timestamp, making it possible to
start reading the logfile from that record. By default this timer fires
a minute after the previous sync.
The -z compression option controls the zlib(3) compression level; legal
values are zero to nine which is the default.
The fifolog_reader utility will retrieve records from the fifolog accord‐
ing to the specified parameters and write them either to standard output
or the file specified with -o.
It is possible to specify a start and end time to limit the amount of
data fifolog_reader will report. The lower-case variants -b and -e take
a time_t value, whereas the upper-case variants -B and -E take human-
readable specifications such as “1 hour ago”.
The -t option forces timestamps to be formatted as “YYYYMMDDhhmmss”
instead of as time_t, and -T allows the specification of an strftime(3)
Finally, records can be filtered such that only records matching the
(REG_BASIC) regular expression specified with -R are output.
The data stored in the fifolog consists of three layers, an outer layer
that allows searches to synchronization points based on timestamps with‐
out having to decompress and decode the actual contents, a compression
layer implemented with zlib(3), and an inner serialization and timestamp‐
The exact encoding is described in the fifolog.h file.
Fifolog is particularly well suited for use on Flash based media, where
it results in much lower write-wear, than a file system with regular log
files rotated with newsyslog(8) etc.
Create a fifolog with 1024*1024 records of 512 bytes:
fifolog_create -r 10m /tmp/fifolog
Write a single record to this file:
date | fifolog_writer /tmp/fifolog
Read it back with human readable timestamps:
One particular useful use of fifolog_writer is with syslogd(8) using a
line such as this in /etc/syslog.conf(5):
*.* |fifolog_writer /var/log/syslog_fifolog
The fifolog tools have been liberated from an open source SCADA applica‐
tions called “measured”, which monitors and controls remote radio naviga‐
tion transmitters for the Danish Air Traffic Control system.
The fifolog tools were written by Poul-Henning Kamp.
BSD February 9, 2008 BSD