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]
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 std
out. *UNKNOWN* data is often represented by the string "NaN" depending
on your OSs 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.
RESOLUTION INTERVAL
In order to get RRDtool to fetch anything other than the finest resolu
tion 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 $(echo $(($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 speci
fication and the TIME OFFSET specification.
TIME REFERENCE SPECIFICATION
The time reference specification is used, well, to establish a refer
ence 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 sin
gle-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, or end as your time refer
ence. 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).
Month and day of the week names can be used in their naturally abbrevi
ated 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 ref
erence, 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 inter
vals, 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 adjust
ment 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
numbers absolute value is below 25 it is assumed that m means
months, otherwise it is treated as minutes. (e.g., -25m == -25 min
utes, 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)).
AUTHOR
Tobias Oetiker
1.2.15 2006-07-14 RRDFETCH(1)
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