1RRDFETCH(1) rrdtool RRDFETCH(1)
2
6 rrdfetch - Fetch data from an RRD.
7
9 rrdtool fetch filename CF [--resolution|-r resolution]
10 [--start|-s start] [--end|-e end]
11
13 The fetch function is normally used internally by the graph function to
14 get data from RRDs. fetch will analyze the RRD and try to retrieve the
15 data in the resolution requested. The data fetched is printed to std‐
16 out. *UNKNOWN* data is often represented by the string "NaN" depending
17 on your OS's printf function.
18 filename
20 the name of the RRD you want to fetch the data from.
21 CF the consolidation function that is applied to the data you want
23 to fetch (AVERAGE,MIN,MAX,LAST)
24 --resolution|-r resolution (default is the highest resolution)
26 the interval you want the values to have (seconds per value).
27 rrdfetch will try to match your request, but it will return
28 data even if no absolute match is possible. NB. See note below.
29 --start|-s start (default end-1day)
31 start of the time series. A time in seconds since epoch
32 (1970-01-01) is required. Negative numbers are relative to the
33 current time. By default, one day worth of data will be
34 fetched. See also AT-STYLE TIME SPECIFICATION section for a
35 detailed explanation on ways to specify the start time.
36 --end|-e end (default now)
38 the end of the time series in seconds since epoch. See also AT-
39 STYLE TIME SPECIFICATION section for a detailed explanation of
40 how to specify the end time.
41 RESOLUTION INTERVAL
43 In order to get RRDtool to fetch anything other than the finest resolu‐
45 tion RRA both the start and end time must be specified on boundaries
46 that are multiples of the desired resolution. Consider the following
47 example:
48 rrdtool create subdata.rrd -s 10 DS:ds0:GAUGE:300:0:U \
50 RRA:AVERAGE:0.5:30:3600 \
51 RRA:AVERAGE:0.5:90:1200 \
52 RRA:AVERAGE:0.5:360:1200 \
53 RRA:MAX:0.5:360:1200 \
54 RRA:AVERAGE:0.5:8640:600 \
55 RRA:MAX:0.5:8640:600
56 This RRD collects data every 10 seconds and stores its averages over 5
58 minutes, 15 minutes, 1 hour, and 1 day, as well as the maxima for 1
59 hour and 1 day.
60 Consider now that you want to fetch the 15 minute average data for the
62 last hour. You might try
63 rrdtool fetch subdata.rrd AVERAGE -r 900 -s -1h
65 However, this will almost always result in a time series that is NOT in
67 the 15 minute RRA. Therefore, the highest resolution RRA, i.e. 5 minute
68 averages, will be chosen which in this case is not what you want.
69 Hence, make sure that
71 1. both start and end time are a multiple of 900
73 2. both start and end time are within the desired RRA
75 So, if time now is called "t", do
77 end time == int(t/900)*900,
79 start time == end time - 1hour,
80 resolution == 900.
81 Using the bash shell, this could look be:
83 TIME=$(date +%s)
85 RRDRES=900
86 rrdtool fetch subdata.rrd AVERAGE -r $RRDRES \
87 -e $(($TIME/$RRDRES*$RRDRES)) -s e-1h
88 Or in Perl:
90 perl -e '$ctime = time; $rrdres = 900; \
92 system "rrdtool fetch subdata.rrd AVERAGE \
93 -r $rrdres -e @{[int($ctime/$rrdres)*$rrdres]} -s e-1h"'
94 AT-STYLE TIME SPECIFICATION
96 Apart from the traditional Seconds since epoch, RRDtool does also
98 understand at-style time specification. The specification is called
99 "at-style" after the Unix command at(1) that has moderately complex
100 ways to specify time to run your job at a certain date and time. The
101 at-style specification consists of two parts: the TIME REFERENCE speci‐
102 fication and the TIME OFFSET specification.
103 TIME REFERENCE SPECIFICATION
105 The time reference specification is used, well, to establish a refer‐
107 ence moment in time (to which the time offset is then applied to). When
108 present, it should come first, when omitted, it defaults to now. On its
109 own part, time reference consists of a time-of-day reference (which
110 should come first, if present) and a day reference.
111 The time-of-day can be specified as HH:MM, HH.MM, or just HH. You can
113 suffix it with am or pm or use 24-hours clock. Some special times of
114 day are understood as well, including midnight (00:00), noon (12:00)
115 and British teatime (16:00).
116 The day can be specified as month-name day-of-the-month and optional a
118 2- or 4-digit year number (e.g. March 8 1999). Alternatively, you can
119 use day-of-week-name (e.g. Monday), or one of the words: yesterday,
120 today, tomorrow. You can also specify the day as a full date in several
121 numerical formats, including MM/DD/[YY]YY, DD.MM.[YY]YY, or YYYYMMDD.
122 NOTE1: this is different from the original at(1) behavior, where a sin‐
124 gle-number date is interpreted as MMDD[YY]YY.
125 NOTE2: if you specify the day in this way, the time-of-day is REQUIRED
127 as well.
128 Finally, you can use the words now, start, or end as your time refer‐
130 ence. Now refers to the current moment (and is also the default time
131 reference). Start (end) can be used to specify a time relative to the
132 start (end) time for those tools that use these categories (rrdfetch,
133 rrdgraph).
134 Month and day of the week names can be used in their naturally abbrevi‐
136 ated form (e.g., Dec for December, Sun for Sunday, etc.). The words
137 now, start, end can be abbreviated as n, s, e.
138 TIME OFFSET SPECIFICATION
140 The time offset specification is used to add/subtract certain time
142 intervals to/from the time reference moment. It consists of a sign
143 (+ or -) and an amount. The following time units can be used to specify
144 the amount: years, months, weeks, days, hours, minutes, or seconds.
145 These units can be used in singular or plural form, and abbreviated
146 naturally or to a single letter (e.g. +3days, -1wk, -3y). Several time
147 units can be combined (e.g., -5mon1w2d) or concatenated (e.g., -5h45min
148 = -5h-45min = -6h+15min = -7h+1h30m-15min, etc.)
149 NOTE3: If you specify time offset in days, weeks, months, or years, you
151 will end with the time offset that may vary depending on your time ref‐
152 erence, because all those time units have no single well defined time
153 interval value (1 year contains either 365 or 366 days, 1 month is 28
154 to 31 days long, and even 1 day may be not equal to 24 hours twice a
155 year, when DST-related clock adjustments take place). To cope with
156 this, when you use days, weeks, months, or years as your time offset
157 units your time reference date is adjusted accordingly without too much
158 further effort to ensure anything about it (in the hope that mktime(3)
159 will take care of this later). This may lead to some surprising (or
160 even invalid!) results, e.g. 'May 31 -1month' = 'Apr 31' (meaningless)
161 = 'May 1' (after mktime(3) normalization); in the EET timezone '3:30am
162 Mar 29 1999 -1 day' yields '3:30am Mar 28 1999' (Sunday) which is an
163 invalid time/date combination (because of 3am -> 4am DST forward clock
164 adjustment, see the below example).
165 In contrast, hours, minutes, and seconds are well defined time inter‐
167 vals, and these are guaranteed to always produce time offsets exactly
168 as specified (e.g. for EET timezone, '8:00 Mar 27 1999 +2 days' =
169 '8:00 Mar 29 1999', but since there is 1-hour DST forward clock adjust‐
170 ment that occurs around 3:00 Mar 28 1999, the actual time interval
171 between 8:00 Mar 27 1999 and 8:00 Mar 29 1999 equals 47 hours; on the
172 other hand, '8:00 Mar 27 1999 +48 hours' = '9:00 Mar 29 1999', as
173 expected)
174 NOTE4: The single-letter abbreviation for both months and minutes is m.
176 To disambiguate them, the parser tries to read your mind :) by applying
177 the following two heuristics:
178 1 If m is used in context of (i.e. right after the) years, months,
180 weeks, or days it is assumed to mean months, while in the context of
181 hours, minutes, and seconds it means minutes. (e.g., in -1y6m or
182 +3w1m m is interpreted as months, while in -3h20m or +5s2m m the
183 parser decides for minutes).
184 2 Out of context (i.e. right after the + or - sign) the meaning of m
186 is guessed from the number it directly follows. Currently, if the
187 number's absolute value is below 25 it is assumed that m means
188 months, otherwise it is treated as minutes. (e.g., -25m == -25 min‐
189 utes, while +24m == +24 months)
190 Final NOTES: Time specification is case-insensitive. Whitespace can be
192 inserted freely or omitted altogether. There are, however, cases when
193 whitespace is required (e.g., 'midnight Thu'). In this case you should
194 either quote the whole phrase to prevent it from being taken apart by
195 your shell or use '_' (underscore) or ',' (comma) which also count as
196 whitespace (e.g., midnight_Thu or midnight,Thu).
197 TIME SPECIFICATION EXAMPLES
199 Oct 12 -- October 12 this year
201 -1month or -1m -- current time of day, only a month before (may yield
203 surprises, see NOTE3 above).
204 noon yesterday -3hours -- yesterday morning; can also be specified as
206 9am-1day.
207 23:59 31.12.1999 -- 1 minute to the year 2000.
209 12/31/99 11:59pm -- 1 minute to the year 2000 for imperialists.
211 12am 01/01/01 -- start of the new millennium
213 end-3weeks or e-3w -- 3 weeks before end time (may be used as start
215 time specification).
216 start+6hours or s+6h -- 6 hours after start time (may be used as end
218 time specification).
219 931225537 -- 18:45 July 5th, 1999 (yes, seconds since 1970 are valid
221 as well).
222 19970703 12:45 -- 12:45 July 3th, 1997 (my favorite, and its even got
224 an ISO number (8601)).
225
227 Tobias Oetiker <tobi@oetiker.ch>
2281.2.27 2008-02-17 RRDFETCH(1)