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CentOS 7.0 - man page for rrdfetch (centos section 1)

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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>

1.4.8					    2013-05-23				      RRDFETCH(1)
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