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rrdfetch

Name
     rrdfetch - Fetch data from an RRD.

Synopsis
     rrdtool fetch filename CF [--resolution|-r resolution]
     [--start|-s start] [--end|-e end] [--align-start|-a]
     [--daemon|-d 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).  An optional suffix may be used (e.g.
             "5m" instead of 300 seconds).  rrdfetch will try to
             match your request, but it will return data even if
             no absolute match is possible. See "RESOLUTION
             INTERVAL".

     --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.

     --align-start|-a
             Automatically adjust the start time down to be
             aligned with the resolution.  The end-time is
             adjusted by the same amount.  This avoids the need
             for external calculations described in RESOLUTION
             INTERVAL, though if a specific RRA is desired this
             will not ensure the start and end fall within its
             bounds.

     --daemon|-d 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

             Please note that due to thread-safety reasons, the
             time specified with -s and -e cannot use the complex
             forms described in "AT-STYLE TIME SPECIFICATION".
             The only accepted arguments are "simple integers".
             Positive values are interpreted as seconds since
             epoch, negative values (and zero) are interpreted as
             relative to now. So "1272535035" refers to "09:57:15
             (UCT), April 29th 2010" and "-3600" means "one hour
             ago".

  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:5m:0:U \
       RRA:AVERAGE:0.5:5m:300h \
       RRA:AVERAGE:0.5:15m:300h \
       RRA:AVERAGE:0.5:1h:50d \
       RRA:MAX:0.5:1h:50d \
       RRA:AVERAGE:0.5:1d:600d \
       RRA:MAX:0.5:1d:600d

     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 15m -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 ("15m")
     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"'

     Or using the --align-start flag:

      rrdtool fetch subdata.rrd AVERAGE -a -r 15m -s -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 one 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>
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