fifolog_reader man page on FreeBSD

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FIFOLOG(1)		  BSD General Commands Manual		    FIFOLOG(1)

NAME
     fifolog_create, fifolog_writer, fifolog_reader — initialize, write, seek
     and extract data from a fifolog

SYNOPSIS
     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

DESCRIPTION
     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‐
     lar file.

     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
     only once.

     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
     be written.

     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)
     formatting string.

     Finally, records can be filtered such that only records matching the
     (REG_BASIC) regular expression specified with -R are output.

IMPLEMENTATION NOTES
     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‐
     ing layer.

     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.

EXAMPLES
     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:

	   fifolog_reader -t /tmp/fifolog

     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

HISTORY
     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.

AUTHORS
     The fifolog tools were written by Poul-Henning Kamp.

BSD			       February 9, 2008				   BSD
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