[rrd-users] rrd graph not flushing cached data (symlink problem)

Eduardo Bragatto eduardo at bragatto.com
Tue May 25 17:53:27 CEST 2010


I have continued researching this problem and after running strace on  
the rrd graphs calls, I found the issue is being caused by a symlink  
in the path.

Here's what I see in the telnet,  when testing:
with symlink:
FLUSH /usr/local/rrd/myproject/repository/local/switches/myswitch/ 
0 Nothing to flush: /usr/local/rrd/myproject/repository/local/switches/ 

without it (same file):

Flush /usr/local/rrd/myproject/rrd/switches/myswitch/10146.rrd
0 Successfully flushed /usr/local/rrd/myproject/rrd/switches/myswitch/ 

According to the documentation, symlinks are not allowed in the base  

"WARNING: The paths up to and including the base directory MUST NOT BE  
symbolic links. In other words, if the base directory is specified as:

     -b /base/dir/somewhere
... then NONE of the following should be symbolic links:


Since I'm not using -b, it's configured to default /tmp. My rrd files  
are stored in a long path, like this:
However, I'm referencing the files via a symlink:
/usr/local/rrd/myproject/reporsitory/local is a symlink to /usr/local/ 

Considering that there's no symlink in the base directory (where the  
documentation says it's forbidden) and also that I'm using an absolute  
path, outside the base directory, shouldn't the symlink work in my case?
According to the documentation I'm not doing anything wrong, but the  
software does not work as expected. Do we have a bug in rrdcached, or  
is it the documentation that's not complete on how it deals with  

Eduardo Bragatto.
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