[rrd-users] Graphing potentially missing files

Simon Hobson linux at thehobsons.co.uk
Fri Dec 3 13:09:08 CET 2010

Steve Shipway wrote:
>When you run rrdgraph in rrdcached mode (either via the environment 
>variable, or using the --daemon option) then it flushes the cache 
>data and also accesses the data over the rrdcached connection.  It 
>doesnt use the local file.
>RRdtool in rrdcached mode will use the local file only if (a) you're 
>asking for a function not supported by the rrdcached, AND (b) you're 
>using UNIX sockets (since if using TCP sockets, the rrd file is not 
>on this server), AND (c) it can read/write the file (since you may 
>have given permissions to allow the file to only be accessed by the 
>rrdcached).  If using the trunk 1.4 version, then this means that 
>the supported functions are update, first, last, create (with 
>limitations), fetch, graph and info.

I'm using 1.4.3 from Debian Lenny-backports.

After a little experimentation, I see I have to specify the correct 
local file path - if I link from one directory into the rrdcached db 
directory then it's not recognised.

Just to complicate matters, when I get down to modifying my scripts, 
I now remember that most of my graphs are built with rrdcgi - because 
of the difficulty of building a huge parameter list and the lack of a 
"read the rest from stdin" option to rrdgraph. Unless you now tell me 
that there is such an option and I've missed it !

>You can ask rrdcached to flush caches using 'rrdtool flushcached'

That's handy since rrdcgi doesn't seem to have been updated to 
support rrdcached.

Simon Hobson

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