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
16 stdout. *UNKNOWN* data is often represented by the string "NaN"
17 depending 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
44 resolution RRA both the start and end time must be specified on
45 boundaries that are multiples of the desired resolution. Consider the
46 following example:
47 rrdtool create subdata.rrd -s 10 DS:ds0:GAUGE:300:0:U \
49 RRA:AVERAGE:0.5:30:3600 \
50 RRA:AVERAGE:0.5:90:1200 \
51 RRA:AVERAGE:0.5:360:1200 \
52 RRA:MAX:0.5:360:1200 \
53 RRA:AVERAGE:0.5:8640:600 \
54 RRA:MAX:0.5:8640:600
55 This RRD collects data every 10 seconds and stores its averages over 5
57 minutes, 15 minutes, 1 hour, and 1 day, as well as the maxima for 1
58 hour and 1 day.
59 Consider now that you want to fetch the 15 minute average data for the
61 last hour. You might try
62 rrdtool fetch subdata.rrd AVERAGE -r 900 -s -1h
64 However, this will almost always result in a time series that is NOT in
66 the 15 minute RRA. Therefore, the highest resolution RRA, i.e. 5 minute
67 averages, will be chosen which in this case is not what you want.
68 Hence, make sure that
70 1. both start and end time are a multiple of 900
72 2. both start and end time are within the desired RRA
74 So, if time now is called "t", do
76 end time == int(t/900)*900,
78 start time == end time - 1hour,
79 resolution == 900.
80 Using the bash shell, this could look be:
82 TIME=$(date +%s)
84 RRDRES=900
85 rrdtool fetch subdata.rrd AVERAGE -r $RRDRES \
86 -e $(($TIME/$RRDRES*$RRDRES)) -s e-1h
87 Or in Perl:
89 perl -e '$ctime = time; $rrdres = 900; \
91 system "rrdtool fetch subdata.rrd AVERAGE \
92 -r $rrdres -e @{[int($ctime/$rrdres)*$rrdres]} -s e-1h"'
93 AT-STYLE TIME SPECIFICATION
95 Apart from the traditional Seconds since epoch, RRDtool does also
96 understand at-style time specification. The specification is called
97 "at-style" after the Unix command at(1) that has moderately complex
98 ways to specify time to run your job at a certain date and time. The
99 at-style specification consists of two parts: the TIME REFERENCE
100 specification and the TIME OFFSET specification.
101 TIME REFERENCE SPECIFICATION
103 The time reference specification is used, well, to establish a
104 reference moment in time (to which the time offset is then applied to).
105 When present, it should come first, when omitted, it defaults to now.
106 On its own part, time reference consists of a time-of-day reference
107 (which should come first, if present) and a day reference.
108 The time-of-day can be specified as HH:MM, HH.MM, or just HH. You can
110 suffix it with am or pm or use 24-hours clock. Some special times of
111 day are understood as well, including midnight (00:00), noon (12:00)
112 and British teatime (16:00).
113 The day can be specified as month-name day-of-the-month and optional a
115 2- or 4-digit year number (e.g. March 8 1999). Alternatively, you can
116 use day-of-week-name (e.g. Monday), or one of the words: yesterday,
117 today, tomorrow. You can also specify the day as a full date in several
118 numerical formats, including MM/DD/[YY]YY, DD.MM.[YY]YY, or YYYYMMDD.
119 NOTE1: this is different from the original at(1) behavior, where a
121 single-number date is interpreted as MMDD[YY]YY.
122 NOTE2: if you specify the day in this way, the time-of-day is REQUIRED
124 as well.
125 Finally, you can use the words now, start, or end as your time
127 reference. Now refers to the current moment (and is also the default
128 time reference). Start (end) can be used to specify a time relative to
129 the start (end) time for those tools that use these categories
130 (rrdfetch, rrdgraph).
131 Month and day of the week names can be used in their naturally
133 abbreviated form (e.g., Dec for December, Sun for Sunday, etc.). The
134 words now, start, end can be abbreviated as n, s, e.
135 TIME OFFSET SPECIFICATION
137 The time offset specification is used to add/subtract certain time
138 intervals to/from the time reference moment. It consists of a sign
139 (+ or -) and an amount. The following time units can be used to specify
140 the amount: years, months, weeks, days, hours, minutes, or seconds.
141 These units can be used in singular or plural form, and abbreviated
142 naturally or to a single letter (e.g. +3days, -1wk, -3y). Several time
143 units can be combined (e.g., -5mon1w2d) or concatenated (e.g., -5h45min
144 = -5h-45min = -6h+15min = -7h+1h30m-15min, etc.)
145 NOTE3: If you specify time offset in days, weeks, months, or years, you
147 will end with the time offset that may vary depending on your time
148 reference, because all those time units have no single well defined
149 time interval value (1 year contains either 365 or 366 days, 1 month is
150 28 to 31 days long, and even 1 day may be not equal to 24 hours twice a
151 year, when DST-related clock adjustments take place). To cope with
152 this, when you use days, weeks, months, or years as your time offset
153 units your time reference date is adjusted accordingly without too much
154 further effort to ensure anything about it (in the hope that mktime(3)
155 will take care of this later). This may lead to some surprising (or
156 even invalid!) results, e.g. 'May 31 -1month' = 'Apr 31' (meaningless)
157 = 'May 1' (after mktime(3) normalization); in the EET timezone '3:30am
158 Mar 29 1999 -1 day' yields '3:30am Mar 28 1999' (Sunday) which is an
159 invalid time/date combination (because of 3am -> 4am DST forward clock
160 adjustment, see the below example).
161 In contrast, hours, minutes, and seconds are well defined time
163 intervals, and these are guaranteed to always produce time offsets
164 exactly as specified (e.g. for EET timezone, '8:00 Mar 27 1999 +2 days'
165 = '8:00 Mar 29 1999', but since there is 1-hour DST forward clock
166 adjustment that occurs around 3:00 Mar 28 1999, the actual time
167 interval between 8:00 Mar 27 1999 and 8:00 Mar 29 1999 equals 47 hours;
168 on the other hand, '8:00 Mar 27 1999 +48 hours' = '9:00 Mar 29 1999',
169 as expected)
170 NOTE4: The single-letter abbreviation for both months and minutes is m.
172 To disambiguate them, the parser tries to read your mind :) by applying
173 the following two heuristics:
174 1. If m is used in context of (i.e. right after the) years, months,
176 weeks, or days it is assumed to mean months, while in the context of
177 hours, minutes, and seconds it means minutes. (e.g., in -1y6m or
178 +3w1m m is interpreted as months, while in -3h20m or +5s2m m the
179 parser decides for minutes).
180 2. Out of context (i.e. right after the + or - sign) the meaning of m
182 is guessed from the number it directly follows. Currently, if the
183 number's absolute value is below 25 it is assumed that m means
184 months, otherwise it is treated as minutes. (e.g., -25m == -25
185 minutes, while +24m == +24 months)
186 Final NOTES: Time specification is case-insensitive. Whitespace can be
188 inserted freely or omitted altogether. There are, however, cases when
189 whitespace is required (e.g., 'midnight Thu'). In this case you should
190 either quote the whole phrase to prevent it from being taken apart by
191 your shell or use '_' (underscore) or ',' (comma) which also count as
192 whitespace (e.g., midnight_Thu or midnight,Thu).
193 TIME SPECIFICATION EXAMPLES
195 Oct 12 -- October 12 this year
196 -1month or -1m -- current time of day, only a month before (may yield
198 surprises, see NOTE3 above).
199 noon yesterday -3hours -- yesterday morning; can also be specified as
201 9am-1day.
202 23:59 31.12.1999 -- 1 minute to the year 2000.
204 12/31/99 11:59pm -- 1 minute to the year 2000 for imperialists.
206 12am 01/01/01 -- start of the new millennium
208 end-3weeks or e-3w -- 3 weeks before end time (may be used as start
210 time specification).
211 start+6hours or s+6h -- 6 hours after start time (may be used as end
213 time specification).
214 931225537 -- 18:45 July 5th, 1999 (yes, seconds since 1970 are valid
216 as well).
217 19970703 12:45 -- 12:45 July 3th, 1997 (my favorite, and its even got
219 an ISO number (8601)).
220
222 Tobias Oetiker <tobi@oetiker.ch>
2231.3.8 2008-03-15 RRDFETCH(1)