RRDFETCH(1)							      rrdtool							       RRDFETCH(1)

NAME

       rrdfetch - Fetch data from an RRD.

SYNOPSIS

       rrdtool fetch filename CF [--resolution|-r resolution] [--start|-s start] [--end|-e end] [--daemon address]

DESCRIPTION

       The fetch function is normally used internally by the graph function to get data from RRDs. fetch will analyze the RRD and try to retrieve
       the data in the resolution requested.  The data fetched is printed to stdout. *UNKNOWN* data is often represented by the string "NaN"
       depending on your OS's printf function.

       filename
	       the name of the RRD you want to fetch the data from.

       CF      the consolidation function that is applied to the data you want to fetch (AVERAGE,MIN,MAX,LAST)

       --resolution|-r resolution (default is the highest resolution)
	       the interval you want the values to have (seconds per value). rrdfetch will try to match your request, but it will return data even
	       if no absolute match is possible. NB. See note below.

       --start|-s start (default end-1day)
	       start of the time series. A time in seconds since epoch (1970-01-01) is required. Negative numbers are relative to the current
	       time. By default, one day worth of data will be fetched. See also AT-STYLE TIME SPECIFICATION section for a detailed explanation on
	       ways to specify the start time.

       --end|-e end (default now)
	       the end of the time series in seconds since epoch. See also AT-STYLE TIME SPECIFICATION section for a detailed explanation of how
	       to specify the end time.

       --daemon address
	       Address of the rrdcached daemon. If specified, a "flush" command is sent to the server before reading the RRD files. This allows
	       rrdtool to return fresh data even if the daemon is configured to cache values for a long time.  For a list of accepted formats, see
	       the -l option in the rrdcached manual.

		rrdtool fetch --daemon unix:/var/run/rrdcached.sock /var/lib/rrd/foo.rrd AVERAGE

   RESOLUTION INTERVAL
       In order to get RRDtool to fetch anything other than the finest resolution RRA both the start and end time must be specified on boundaries
       that are multiples of the desired resolution. Consider the following example:

	rrdtool create subdata.rrd -s 10 DS:ds0:GAUGE:300:0:U 
	 RRA:AVERAGE:0.5:30:3600 
	 RRA:AVERAGE:0.5:90:1200 
	 RRA:AVERAGE:0.5:360:1200 
	 RRA:MAX:0.5:360:1200 
	 RRA:AVERAGE:0.5:8640:600 
	 RRA:MAX:0.5:8640:600

       This RRD collects data every 10 seconds and stores its averages over 5 minutes, 15 minutes, 1 hour, and 1 day, as well as the maxima for 1
       hour and 1 day.

       Consider now that you want to fetch the 15 minute average data for the last hour.  You might try

	rrdtool fetch subdata.rrd AVERAGE -r 900 -s -1h

       However, this will almost always result in a time series that is NOT in the 15 minute RRA. Therefore, the highest resolution RRA, i.e. 5
       minute averages, will be chosen which in this case is not what you want.

       Hence, make sure that

       1. both start and end time are a multiple of 900

       2. both start and end time are within the desired RRA

       So, if time now is called "t", do

	end time == int(t/900)*900,
	start time == end time - 1hour,
	resolution == 900.

       Using the bash shell, this could look be:

	TIME=$(date +%s)
	RRDRES=900
	rrdtool fetch subdata.rrd AVERAGE -r $RRDRES 
	   -e $(($TIME/$RRDRES*$RRDRES)) -s e-1h

       Or in Perl:

	perl -e '$ctime = time; $rrdres = 900; 
		 system "rrdtool fetch subdata.rrd AVERAGE 
			 -r $rrdres -e @{[int($ctime/$rrdres)*$rrdres]} -s e-1h"'

   AT-STYLE TIME SPECIFICATION
       Apart from the traditional Seconds since epoch, RRDtool does also understand at-style time specification. The specification is called "at-
       style" after the Unix command at(1) that has moderately complex ways to specify time to run your job at a certain date and time. The at-
       style specification consists of two parts: the TIME REFERENCE specification and the TIME OFFSET specification.

   TIME REFERENCE SPECIFICATION
       The time reference specification is used, well, to establish a reference moment in time (to which the time offset is then applied to). When
       present, it should come first, when omitted, it defaults to now. On its own part, time reference consists of a time-of-day reference (which
       should come first, if present) and a day reference.

       The time-of-day can be specified as HH:MM, HH.MM, or just HH. You can suffix it with am or pm or use 24-hours clock. Some special times of
       day are understood as well, including midnight (00:00), noon (12:00) and British teatime (16:00).

       The day can be specified as month-name day-of-the-month and optional a 2- or 4-digit year number (e.g. March 8 1999). Alternatively, you
       can use day-of-week-name (e.g. Monday), or one of the words: yesterday, today, tomorrow. You can also specify the day as a full date in
       several numerical formats, including MM/DD/[YY]YY, DD.MM.[YY]YY, or YYYYMMDD.

       NOTE1: this is different from the original at(1) behavior, where a single-number date is interpreted as MMDD[YY]YY.

       NOTE2: if you specify the day in this way, the time-of-day is REQUIRED as well.

       Finally, you can use the words now, start, end or epoch as your time reference. Now refers to the current moment (and is also the default
       time reference). Start (end) can be used to specify a time relative to the start (end) time for those tools that use these categories
       (rrdfetch, rrdgraph) and epoch indicates the *IX epoch (*IX timestamp 0 = 1970-01-01 00:00:00 UTC). epoch is useful to disambiguate between
       a timestamp value and some forms of abbreviated date/time specifications, because it allows to use time offset specifications using units,
       eg. epoch+19711205s unambiguously denotes timestamp 19711205 and not 1971-12-05 00:00:00 UTC.

       Month and day of the week names can be used in their naturally abbreviated form (e.g., Dec for December, Sun for Sunday, etc.). The words
       now, start, end can be abbreviated as n, s, e.

   TIME OFFSET SPECIFICATION
       The time offset specification is used to add/subtract certain time intervals to/from the time reference moment. It consists of a sign
       (+ or -) and an amount. The following time units can be used to specify the amount: years, months, weeks, days, hours, minutes, or seconds.
       These units can be used in singular or plural form, and abbreviated naturally or to a single letter (e.g. +3days, -1wk, -3y). Several time
       units can be combined (e.g., -5mon1w2d) or concatenated (e.g., -5h45min = -5h-45min = -6h+15min = -7h+1h30m-15min, etc.)

       NOTE3: If you specify time offset in days, weeks, months, or years, you will end with the time offset that may vary depending on your time
       reference, because all those time units have no single well defined time interval value (1 year contains either 365 or 366 days, 1 month is
       28 to 31 days long, and even 1 day may be not equal to 24 hours twice a year, when DST-related clock adjustments take place).  To cope with
       this, when you use days, weeks, months, or years as your time offset units your time reference date is adjusted accordingly without too
       much further effort to ensure anything about it (in the hope that mktime(3) will take care of this later).  This may lead to some
       surprising (or even invalid!) results, e.g. 'May 31 -1month' = 'Apr 31' (meaningless) = 'May 1' (after mktime(3) normalization); in the EET
       timezone '3:30am Mar 29 1999 -1 day' yields '3:30am Mar 28 1999' (Sunday) which is an invalid time/date combination (because of 3am -> 4am
       DST forward clock adjustment, see the below example).

       In contrast, hours, minutes, and seconds are well defined time intervals, and these are guaranteed to always produce time offsets exactly
       as specified (e.g. for EET timezone, '8:00 Mar 27 1999 +2 days' = '8:00 Mar 29 1999', but since there is 1-hour DST forward clock
       adjustment that occurs around 3:00 Mar 28 1999, the actual time interval between 8:00 Mar 27 1999 and 8:00 Mar 29 1999 equals 47 hours; on
       the other hand, '8:00 Mar 27 1999 +48 hours' = '9:00 Mar 29 1999', as expected)

       NOTE4: The single-letter abbreviation for both months and minutes is m. To disambiguate them, the parser tries to read your mind :) by
       applying the following two heuristics:

       1. If m is used in context of (i.e. right after the) years, months, weeks, or days it is assumed to mean months, while in the context of
	  hours, minutes, and seconds it means minutes.  (e.g., in -1y6m or +3w1m m is interpreted as months, while in -3h20m or +5s2m m the
	  parser decides for minutes).

       2. Out of context (i.e. right after the + or - sign) the meaning of m is guessed from the number it directly follows.  Currently, if the
	  number's absolute value is below 25 it is assumed that m means months, otherwise it is treated as minutes.  (e.g., -25m == -25 minutes,
	  while +24m == +24 months)

       Final NOTES: Time specification is case-insensitive.  Whitespace can be inserted freely or omitted altogether.  There are, however, cases
       when whitespace is required (e.g., 'midnight Thu'). In this case you should either quote the whole phrase to prevent it from being taken
       apart by your shell or use '_' (underscore) or ',' (comma) which also count as whitespace (e.g., midnight_Thu or midnight,Thu).

   TIME SPECIFICATION EXAMPLES
       Oct 12 -- October 12 this year

       -1month or -1m -- current time of day, only a month before (may yield surprises, see NOTE3 above).

       noon yesterday -3hours -- yesterday morning; can also be specified as 9am-1day.

       23:59 31.12.1999 -- 1 minute to the year 2000.

       12/31/99 11:59pm -- 1 minute to the year 2000 for imperialists.

       12am 01/01/01 -- start of the new millennium

       end-3weeks or e-3w -- 3 weeks before end time (may be used as start time specification).

       start+6hours or s+6h -- 6 hours after start time (may be used as end time specification).

       931225537 -- 18:45  July 5th, 1999 (yes, seconds since 1970 are valid as well).

       19970703 12:45 -- 12:45	July 3th, 1997 (my favorite, and its even got an ISO number (8601)).

ENVIRONMENT VARIABLES

       The following environment variables may be used to change the behavior of "rrdtool fetch":

       RRDCACHED_ADDRESS
	   If this environment variable is set it will have the same effect as specifying the "--daemon" option on the command line. If both are
	   present, the command line argument takes precedence.

AUTHOR

       Tobias Oetiker <tobi@oetiker.ch>

1.4.7								    2010-11-11							       RRDFETCH(1)