Updated: June 11th, 2015

The Problem

I am throwing up a quick post about a relatively cryptic error that Solr started throwing the other day here at Plaxo. After happily running for a few days, I suddenly started getting pages about failed Solr indexing.

Upon closer examination, I saw the following repeatedly in the log file:

catalina.2009-09-18.log:SEVERE: java.io.IOException: directory 'DATADIR/index'
exists and is a directory, but cannot be listed: list() returned null

I tried to see if sending an OPTIMIZE command would help but the server returned the same response.

Digging Deeper

The reason was these errors was quite simple – Solr was running into the system level limit on allowed number of open files (ulimit). This limit can be seen by running


Updated: September 27th, 2009


Welcome to part 2 of the Essential Firefox Extensions And Tips – A Comprehensive Guide series. In this article I’m going to describe a number of time saving pragmatic extensions that make me a better, faster, more efficient browser user (browserer?).

Pragmatic Extensions

All-in-One Gestures

All-in-One Gestures introduces customizable gestures for all kinds of actions. To perform a gesture, hold the right (by default) button and move the mouse in the specified direction, drawing the needed shape.

Btw, I believe Opera has gestures without any extensions, so Opera users should feel right at home using All-in-One Gestures.


I use it mostly for 3 things: history back/forward and close tab (see below). Once you start using gestures, there is no …


How To List Files Within tgz (tar.gz) Archives

Posted by Artem Russakovskii on April 26th, 2008 in Linux

This may not be very obvious but this is the command line to list files within a tar.gz archive on the fly:

tar -tzf file.tar.gz

-t: lists files
-f: instructs tar to deal with the following filename (file.tar.gz)
-z: informs tar that the it's dealing with a gzip file (-j if it's bzip2)…