man > rrdfetch(1)

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]
       [--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" 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" 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 (UTC), 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 6 it is
          assumed that m means months, otherwise it is  treated  as  minutes.   (e.g.,  -6m  ==  -6m
          minutes, while +5m == +5 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).

       931200300 -- 18:45 (UTC), July 5th, 1999 (yes, seconds since 1970 are valid as well).

       19970703 12:45 -- 12:45  July 3th, 1997 (my favorite, and it  has  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 AT oetiker.ch>

1.7.2                                        2024-03-31                                  RRDFETCH(1)