[pkg-rrdtool.git] / doc / rrdfetch.1

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.\" ========================================================================
.\"
.IX Title "RRDFETCH 1"
.TH RRDFETCH 1 "2008-03-15" "1.3.0" "rrdtool"
.SH "NAME"
rrdfetch \- Fetch data from an RRD.
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
\&\fBrrdtool\fR \fBfetch\fR \fIfilename\fR \fI\s-1CF\s0\fR
[\fB\-\-resolution\fR|\fB\-r\fR\ \fIresolution\fR]
[\fB\-\-start\fR|\fB\-s\fR\ \fIstart\fR]
[\fB\-\-end\fR|\fB\-e\fR\ \fIend\fR]
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fBfetch\fR function is normally used internally by the graph
function to get data from \fB\s-1RRD\s0\fRs. \fBfetch\fR will analyze the \fB\s-1RRD\s0\fR
and try to retrieve the data in the resolution requested.
The data fetched is printed to stdout. \fI*UNKNOWN*\fR data is often
represented by the string \*(L"NaN\*(R" depending on your \s-1OS\s0's printf
function.
.IP "\fIfilename\fR" 8
.IX Item "filename"
the name of the \fB\s-1RRD\s0\fR you want to fetch the data from.
.IP "\fI\s-1CF\s0\fR" 8
.IX Item "CF"
the consolidation function that is applied to the data you
want to fetch (\s-1AVERAGE\s0,MIN,MAX,LAST)
.IP "\fB\-\-resolution\fR|\fB\-r\fR \fIresolution\fR (default is the highest resolution)" 8
.IX Item "--resolution|-r resolution (default is the highest resolution)"
the interval you want the values to have (seconds per
value). \fBrrdfetch\fR will try to match your request, but it will return
data even if no absolute match is possible. \fB\s-1NB\s0.\fR See note below.
.IP "\fB\-\-start\fR|\fB\-s\fR \fIstart\fR (default end\-1day)" 8
.IX Item "--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 \s-1TIME\s0 \s-1SPECIFICATION\s0
section for a detailed explanation on  ways to specify the start time.
.IP "\fB\-\-end\fR|\fB\-e\fR \fIend\fR (default now)" 8
.IX Item "--end|-e end (default now)"
the end of the time series in seconds since epoch. See also AT-STYLE
\&\s-1TIME\s0 \s-1SPECIFICATION\s0 section for a detailed explanation of how to
specify the end time.
.Sh "\s-1RESOLUTION\s0 \s-1INTERVAL\s0"
.IX Subsection "RESOLUTION INTERVAL"
In order to get RRDtool to fetch anything other than the finest resolution \s-1RRA\s0
\&\fBboth\fR the start and end time must be specified on boundaries that are
multiples of the desired resolution. Consider the following example:
.PP
.Vb 7
\& rrdtool create subdata.rrd \-s 10 DS:ds0:GAUGE:300:0:U \e
\&  RRA:AVERAGE:0.5:30:3600 \e
\&  RRA:AVERAGE:0.5:90:1200 \e
\&  RRA:AVERAGE:0.5:360:1200 \e
\&  RRA:MAX:0.5:360:1200 \e
\&  RRA:AVERAGE:0.5:8640:600 \e
\&  RRA:MAX:0.5:8640:600
.Ve
.PP
This \s-1RRD\s0 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.
.PP
Consider now that you want to fetch the 15 minute average data for the
last hour.  You might try
.PP
.Vb 1
\& rrdtool fetch subdata.rrd AVERAGE \-r 900 \-s \-1h
.Ve
.PP
However, this will almost always result in a time series that is
\&\fB\s-1NOT\s0\fR in the 15 minute \s-1RRA\s0. Therefore, the highest resolution \s-1RRA\s0,
i.e. 5 minute averages, will be chosen which in this case is not
what you want.
.PP
Hence, make sure that
.IP "1." 3
both start and end time are a multiple of 900
.IP "2." 3
both start and end time are within the desired \s-1RRA\s0
.PP
So, if time now is called \*(L"t\*(R", do
.PP
.Vb 3
\& end time == int(t/900)*900,
\& start time == end time \- 1hour,
\& resolution == 900.
.Ve
.PP
Using the bash shell, this could look be:
.PP
.Vb 4
\& TIME=$(date +%s)
\& RRDRES=900
\& rrdtool fetch subdata.rrd AVERAGE \-r $RRDRES \e
\&    \-e $(($TIME/$RRDRES*$RRDRES)) \-s e\-1h
.Ve
.PP
Or in Perl:
.PP
.Vb 3
\& perl \-e \(aq$ctime = time; $rrdres = 900; \e
\&          system "rrdtool fetch subdata.rrd AVERAGE \e
\&                  \-r $rrdres \-e @{[int($ctime/$rrdres)*$rrdres]} \-s e\-1h"\(aq
.Ve
.Sh "AT-STYLE \s-1TIME\s0 \s-1SPECIFICATION\s0"
.IX Subsection "AT-STYLE TIME SPECIFICATION"
Apart from the traditional \fISeconds since epoch\fR, RRDtool does also
understand at-style time specification. The specification is called
\&\*(L"at\-style\*(R" after the Unix command \fIat\fR\|(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 \fB\s-1TIME\s0 \s-1REFERENCE\s0\fR
specification and the \fB\s-1TIME\s0 \s-1OFFSET\s0\fR specification.
.Sh "\s-1TIME\s0 \s-1REFERENCE\s0 \s-1SPECIFICATION\s0"
.IX Subsection "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 \fBnow\fR. On its own part,
time reference consists of a \fItime-of-day\fR reference (which should come
first, if present) and a \fIday\fR reference.
.PP
The \fItime-of-day\fR can be specified as \fB\s-1HH:MM\s0\fR, \fB\s-1HH\s0.MM\fR,
or just \fB\s-1HH\s0\fR. You can suffix it with \fBam\fR or \fBpm\fR or use
24\-hours clock. Some special times of day are understood as well,
including \fBmidnight\fR (00:00), \fBnoon\fR (12:00) and British
\&\fBteatime\fR (16:00).
.PP
The \fIday\fR can be specified as \fImonth-name\fR \fIday-of-the-month\fR and
optional a 2\- or 4\-digit \fIyear\fR number (e.g. March 8 1999). Alternatively,
you can use \fIday-of-week-name\fR (e.g. Monday), or one of the words:
\&\fByesterday\fR, \fBtoday\fR, \fBtomorrow\fR. You can also specify the \fIday\fR as a
full date in several numerical formats, including \fBMM/DD/[\s-1YY\s0]YY\fR,
\&\fB\s-1DD\s0.MM.[\s-1YY\s0]YY\fR, or \fB\s-1YYYYMMDD\s0\fR.
.PP
\&\fI\s-1NOTE1\s0\fR: this is different from the original \fIat\fR\|(1) behavior, where a
single-number date is interpreted as MMDD[\s-1YY\s0]YY.
.PP
\&\fI\s-1NOTE2\s0\fR: if you specify the \fIday\fR in this way, the \fItime-of-day\fR is
\&\s-1REQUIRED\s0 as well.
.PP
Finally, you can use the words \fBnow\fR, \fBstart\fR, or \fBend\fR as your time
reference. \fBNow\fR refers to the current moment (and is also the default
time reference). \fBStart\fR (\fBend\fR) can be used to specify a time
relative to the start (end) time for those tools that use these
categories (\fBrrdfetch\fR, rrdgraph).
.PP
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 \fBnow\fR, \fBstart\fR, \fBend\fR can be abbreviated as \fBn\fR, \fBs\fR, \fBe\fR.
.Sh "\s-1TIME\s0 \s-1OFFSET\s0 \s-1SPECIFICATION\s0"
.IX Subsection "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 \fIsign\fR
(\fB+\fR\ or\ \fB\-\fR) and an \fIamount\fR. The following time units can be
used to specify the \fIamount\fR: \fByears\fR, \fBmonths\fR, \fBweeks\fR, \fBdays\fR,
\&\fBhours\fR, \fBminutes\fR, or \fBseconds\fR. 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.)
.PP
\&\fI\s-1NOTE3\s0\fR: 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 \fImktime\fR\|(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 \fImktime\fR\|(3) normalization); in the \s-1EET\s0 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 \s-1DST\s0
forward clock adjustment, see the below example).
.PP
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 \s-1EET\s0 timezone, '8:00\ Mar\ 27\ 1999\ +2\ days' = '8:00\ Mar\ 29\ 1999', but since there is 1\-hour \s-1DST\s0 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)
.PP
\&\fI\s-1NOTE4\s0\fR: The single-letter abbreviation for both \fBmonths\fR and \fBminutes\fR
is \fBm\fR. To disambiguate them, the parser tries to read your mind\ :)
by applying the following two heuristics:
.IP "1" 3
.IX Item "1"
If \fBm\fR is used in context of (i.e. right after the) years,
months, weeks, or days it is assumed to mean \fBmonths\fR, while
in the context of hours, minutes, and seconds it means minutes.
(e.g., in \-1y6m or +3w1m \fBm\fR is interpreted as \fBmonths\fR, while in
\&\-3h20m or +5s2m \fBm\fR the parser decides for \fBminutes\fR).
.IP "2" 3
.IX Item "2"
Out of context (i.e. right after the \fB+\fR or \fB\-\fR sign) the
meaning of \fBm\fR is guessed from the number it directly follows.
Currently, if the number's absolute value is below 25 it is assumed
that \fBm\fR means \fBmonths\fR, otherwise it is treated as \fBminutes\fR.
(e.g., \-25m == \-25 minutes, while +24m == +24 months)
.PP
\&\fIFinal \s-1NOTES\s0\fR: 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).
.Sh "\s-1TIME\s0 \s-1SPECIFICATION\s0 \s-1EXAMPLES\s0"
.IX Subsection "TIME SPECIFICATION EXAMPLES"
\&\fIOct 12\fR \*(-- October 12 this year
.PP
\&\fI\-1month\fR or \fI\-1m\fR \*(-- current time of day, only a month before
(may yield surprises, see \s-1NOTE3\s0 above).
.PP
\&\fInoon yesterday \-3hours\fR \*(-- yesterday morning; can also be specified
as \fI9am\-1day\fR.
.PP
\&\fI23:59 31.12.1999\fR \*(-- 1 minute to the year 2000.
.PP
\&\fI12/31/99 11:59pm\fR \*(-- 1 minute to the year 2000 for imperialists.
.PP
\&\fI12am 01/01/01\fR \*(-- start of the new millennium
.PP
\&\fIend\-3weeks\fR or \fIe\-3w\fR \*(-- 3 weeks before end time
(may be used as start time specification).
.PP
\&\fIstart+6hours\fR or \fIs+6h\fR \*(-- 6 hours after start time
(may be used as end time specification).
.PP
\&\fI931225537\fR \*(-- 18:45  July 5th, 1999
(yes, seconds since 1970 are valid as well).
.PP
\&\fI19970703 12:45\fR \*(-- 12:45  July 3th, 1997
(my favorite, and its even got an \s-1ISO\s0 number (8601)).
.SH "AUTHOR"
.IX Header "AUTHOR"
Tobias Oetiker <tobi@oetiker.ch>