rrdfetch - Online in the Cloud

PROGRAM:

NAME

rrdfetch - Fetch data from an RRD.

SYNOPSIS

rrdtool fetch filename CF [--resolution|-r resolution] [--start|-s start] [--end|-e end]
[--align-start|-a] [--daemon|-d address]

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 stdout. *UNKNOWN* data is often represented by the string
"NaN" depending on your OS's 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). An optional suffix
may be used (e.g. "5m" instead of 300 seconds). rrdfetch will try to match your
request, but it will return data even if no absolute match is possible. See
"RESOLUTION INTERVAL".

--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.

--align-start|-a
Automatically adjust the start time down to be aligned with the resolution. The
end-time is adjusted by the same amount. This avoids the need for external
calculations described in RESOLUTION INTERVAL, though if a specific RRA is desired
this will not ensure the start and end fall within its bounds.

--daemon|-d address
Address of the rrdcached daemon. If specified, a "flush" command is sent to the
server before reading the RRD files. This allows rrdtool to return fresh data even
if the daemon is configured to cache values for a long time. For a list of
accepted formats, see the -l option in the rrdcached manual.

rrdtool fetch --daemon unix:/var/run/rrdcached.sock /var/lib/rrd/foo.rrd AVERAGE

Please note that due to thread-safety reasons, the time specified with -s and -e
cannot use the complex forms described in "AT-STYLE TIME SPECIFICATION". The only
accepted arguments are "simple integers". Positive values are interpreted as
seconds since epoch, negative values (and zero) are interpreted as relative to
now. So "1272535035" refers to "09:57:15 (UCT), April 29th 2010" and "-3600" means
"one hour ago".

RESOLUTION INTERVAL
In order to get RRDtool to fetch anything other than the finest resolution 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:5m:0:U \
RRA:AVERAGE:0.5:5m:300h \
RRA:AVERAGE:0.5:15m:300h \
RRA:AVERAGE:0.5:1h:50d \
RRA:MAX:0.5:1h:50d \
RRA:AVERAGE:0.5:1d:600d \
RRA:MAX:0.5:1d:600d

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 15m -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 ("15m")

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 $(($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"'

Or using the --align-start flag:

rrdtool fetch subdata.rrd AVERAGE -a -r 15m -s -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 specification and the
TIME OFFSET specification.

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 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 single-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, end or epoch as your time reference. 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) and epoch indicates the *IX epoch (*IX timestamp 0 = 1970-01-01
00:00:00 UTC). epoch is useful to disambiguate between a timestamp value and some forms of
abbreviated date/time specifications, because it allows one to use time offset
specifications using units, eg. epoch+19711205s unambiguously denotes timestamp 19711205
and not 1971-12-05 00:00:00 UTC.

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 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 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
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 intervals, 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 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)

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 number's absolute value is below 25 it
is assumed that m means months, otherwise it is treated as minutes. (e.g., -25m == -25
minutes, 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)).

ENVIRONMENT VARIABLES

The following environment variables may be used to change the behavior of "rrdtool fetch":

RRDCACHED_ADDRESS
If this environment variable is set it will have the same effect as specifying the
"--daemon" option on the command line. If both are present, the command line argument
takes precedence.

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