=head1 NAME rrdtool fetch - fetch data from an rrd. =for html <div align="right"><a href="rrdfetch.pdf">PDF</a> version.</div> =head1 SYNOPSIS B<rrdtool> B<fetch> I<filename> I<CF> S<[B<--resolution>|B<-r> I<resolution>]> S<[B<--start>|B<-s> I<start>]> S<[B<--end>|B<-e> I<end>]> =head1 DESCRIPTION The B<fetch> function is normally used internally by the graph function, to get data from B<RRD>s. B<fetch> will analyze the B<RRD> and will try to retrieve the data in the resolution requested. The data fetched is printed to stdout. I<*UNKNOWN*> data is often represented by the string "NaN" depending on your OSs printf function. =over 8 =item I<filename> the name of the B<RRD> you want to fetch the data from. =item I<CF> which consolidation function should have been applied to the data you want to fetch? (AVERAGE,MIN,MAX,LAST) =item B<--resolution>|B<-r> I<resolution> (default is the highest resolution) what interval should the values have (seconds per value). B<rrdfetch> will try to match your request, but it will return data even if no absolute match is possible. =item B<--start>|B<-s> I<start> (default end-1day) when should the data begin. 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 start time. =item B<--end>|B<-e> I<end> (default now) when should the data end. Time in seconds since epoch. See also AT-STYLE TIME SPECIFICATION section for a detailed explanation of how to specify end time. =back =head2 AT-STYLE TIME SPECIFICATION Apart from the traditional I<Seconds since epoch>, rrdtool does also understand at-style time specification. The specification is called "at-style" after Unix command at(1) that has moderately complex ways to specify time to run your job at. The at-style specification consists of two parts: B<TIME REFERENCE> specification and B<TIME OFFSET> specification. =head2 TIME REFERENCE SPECIFICATION Time reference specification is used, well,... to establish a reference moment in time (for time offset to be applied to). When present, it should come first, when omitted, it defaults to B<now>. On its own part, time reference consists of I<time-of-day> reference (which should come first, if present) and I<day> reference. I<Time-of-day> can be specified as B<HH:MM>, B<HH.MM>, or just B<HH>, you can suffix it with B<am> or B<pm> or use 24-hours clock. The few special times of day are understood as well, these include B<midnight> (00:00), B<noon> (12:00) and British B<teatime> (16:00). The I<day> can be specified as I<month-name> I<day-of-the-month> and optional 2- or 4-digit I<year> number (e.g. March 8 1999). Alternatively, you can use I<day-of-week-name> (e.g. Monday), or one of the words: B<yesterday>, B<today>, B<tomorrow>. You can also specify I<day> as a full date in several numerical formats; these include: B<MM/DD/[YY]YY>, B<DD.MM.[YY]YY>, B<YYYYMMDD>. I<NOTE1>: this is different from the original at(1) behavior, which interprets a single-number date as MMDD[YY]YY. I<NOTE2>: if you specify I<day> this way, the I<time-of-day> is REQUIRED to be present. Finally, you can use words B<now>, B<start>, or B<end> as your time reference. B<Now> refers to the current moment (and is also a default time reference). B<Start> (B<end>) can be used to specify time relative to the start (end) time for those tools that use these categories (rrdfetch, rrdgraph). Month and weekday names can be used in their naturally abbreviated form (e.g., Dec for December, Sun for Sunday, etc.). The words B<now>, B<start>, B<end> can be abbreviated to B<n>, B<s>, B<e>. =head2 TIME OFFSET SPECIFICATION Time offset specification is used to add (or subtract) certain time interval to (from) the time reference moment. It consists of I<sign> (S<B<+> or B<->>) and I<amount>. The following time units can be used to specify the I<amount>: B<years>, B<months>, B<weeks>, B<days>, B<hours>, B<minutes>, B<seconds>, these 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 together (e.g., -5mon1w2d), as well as several time offsets can be concatenated (e.g., -5h45min = -5h-45min = -6h+15min = -7h+1h30m-15min, etc.) I<NOTE3>: If you specify time offset in days, weeks, months, or years, you will end with the time offset that may vary depending on you time reference, because all those time units have no single well defined time interval value (S<1 year> contains either 365 or 366 days, S<1 month> is 28 to 31 days long, and even S<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 taking 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. S<'May 31 -1month'> = S<'Apr 31'> (meaningless) = S<'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 invalid time/date combination (because of 3am -> 4am DST forward clock adjustment, see the below example). On the other hand, 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, S<'8:00 Mar 27 1999 +2 days'> = S<'8:00 Mar 29 1999'>, but since there is 1-hour DST forward clock adjustment takes place around S<3:00 Mar 28 1999>, the actual time interval between S<8:00 Mar 27 1999> and S<8:00 Mar 29 1999> equals 47 hours; on the other hand, S<'8:00 Mar 27 1999 +48 hours'> = S<'9:00 Mar 29 1999'>, as expected) I<NOTE4>: The single-letter abbreviation for both B<months> and B<minutes> is B<m>. To disambiguate, the parser tries to read your S<mind :)> by applying the following two heuristics: =over 3 =item 1 If B<m> is used in context of (i.e. right after the) years, months, weeks, or days it is assumed to mean B<months>, while in the context of hours, minutes, and seconds it means minutes. (e.g., in -1y6m or +3w1m B<m> means B<months>, while in -3h20m or +5s2m B<m> means B<minutes>) =item 2 Out of context (i.e. right after the B<+> or B<-> sign) the meaning of B<m> is guessed from the number it directly follows. Currently, if the number absolute value is below 25 it is assumed that B<m> means B<months>, otherwise it is treated as B<minutes>. (e.g., -25m == -25 minutes, while +24m == +24 months) =back I<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., S<'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) =head2 TIME SPECIFICATION EXAMPLES I<Oct 12> -- October 12 this year I<-1month> or I<-1m> -- current time of day, only a month before (may yield surprises, see the NOTE3 above) I<noon yesterday -3hours> -- yesterday morning; can be put also as I<9am-1day> I<23:59 31.12.1999> -- 1 minute to the year 2000 I<12/31/99 11:59pm> -- 1 minute to the year 2000 for imperialists I<12am 01/01/01> -- start of the new millennium I<end-3weeks> or I<e-3w> -- 3 weeks before end time (may be used as start time specification) I<start+6hours> or I<s+6h> -- 6 hours after start time (may be used as end time specification) I<931225537> -- 18:45 July 5th, 1999 (yes, seconds since 1970 are valid as well) I<19970703 12:45> -- 12:45 July 3th, 1997 (not quote standard, but I love this ...) =head1 AUTHOR Tobias Oetiker <oetiker@ee.ethz.ch>
