how-to fix the XS version of Scalar::Util error in CentOS / RHEL / Fedora

It’s being some month now that at work we have encountered a nasty problem with Perl’s module Compress::Zib usage in a tool developed by a colleague. At the moment to start the graphical rendering of a web page the system gave error to our users.

Searching in Apache2’s log I’ve encoutered many error of this kind:

dualvar is only available with the XS version of Scalar::Util at /var/www/html/$MY-APP-PATH/perl/Compress/ line 8

This is because the Scalar-List-Utils module precompiled in RHEL/Fedora/CentOS and similar does NOT have the support of XS weaken function.

You will see a lot of bugs issued on this topic in this part of Linux distro’s.

My solution was to install perl-Task-Weaken package:

In fact as we can read in the package’s description:

rpm -qi perl-Task-Weaken
URL         :
Summary     : Ensure that a platform has weaken support
Description : One recurring problem in modules that use Scalar::Util's weaken function is that it is not present in the pure-perl variant.

This restores the functionality testing to a dependency you do once in your Makefile.PL, rather than something you have to write extra tests for each time you write a module.

Happy coding!


What files are provided by $package.rpm?

Today I needed to install the openMPI package on a development machine, and occurred to me to know if by installing it the system’s GCC (and similar). So asked my friend Gianluca an hand and he pointed me to the repoquery command.

So I did the following:

yum whatprovides "*/repoquery"

which gived to me:

yum-utils-1.1.16-14.el5.centos.1.noarch : Utilities based around the yum package manager
Repo : base
Matched from:
Filename : /usr/bin/repoquery

so I did a simple:

yum install yum-utils

followed by a:

repoquery -ql openmpi-devel.x86_64

… and I obtained the needed infos. Thanks Gianluca!

migration from RHEL to CentOS, done!

Last year at work we brought a little server … you know, fiberchannel hard disks, 32GB of RAM, four quad core XEON … usual stuff 😉
We also got a 1 year of Red Hat Enterprise Linux subscription. Obviuosly this year the money for a renewal of it’s licence aren’t available so, to keep safe and up-2-date, what do we do?

features rhel

We’ve decided to migrate to CentOS, given their famous binary compatibility with the Prominent North American Enterprise Linux Vendor 😉 Thanks to the Lord the process was simple and straightfoward as shown on the page of the official CentOS’ wiki.

Even with the subscription to RHN out-of-date, I did manage to upgrade r5.4 to 5.5 … the process cleaned ALL the official RedHat’s repo files from /etc/yum.repos.d … so beware, make a backup copy of them.

Then I’ve disabled the (few) 3rd party repo sources from my system (they are currently just adobe, epel and remi).

At this point I’ve followed the advice to disable first, and remove later, the yum’s rhnplugin since some CentOS’s forum user issued some warning or error if that was not done. Hence the following commands sequence was given (as root):

cp /etc/redhat-release /etc/redhat-release-saved
rpm -e --nodeps redhat-release-notes redhat-release yum-rhn-plugin redhat-logos

We’ve nearly there … I’ve manually downloaded on the system the three packages: centos-release, centos-release-notes and redhat-logos-X.X.XX-XX.el5.centos.noarch.rpm from the nearest (and fastest) distribution mirror available (they are placed in the ../5/os/$YOUR-ARCH/CentOS/ directory, by the way) and then manually installed with plain old rpm.

yum update

completed the process and here we are:


[root@localhost ~]# cat /etc/issue
CentOS release 5.5 (Final)
[root@localhost ~]# uname -a
Linux localhost 2.6.18-194.3.1.el5 #1 SMP Sun May 2 04:17:42 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux


enable Java plugin on Firefox with CentOS or RHEL (64bit)

centos logo During last weeks I’ve installed and configuread a 64bit RHEL server, paying attention to include the open source java-openJDK and the official Sun’s JRE.

This morning a colleague called me via skype telling me that his Firefox didn’t have a proper Java plugin installed. At first glance I didn’t knew what to do and the first results of a Google’ session were useless refferring to old incompatibility between a 64bit Firefox and 32bit java vitual machine, old releases of both softwares, wrong *.so files to include.

Google and google I found this post, pointing the focus on the file which, on my machine, is placed under the /usr/java/jre1.6.0_16/lib/amd64/ path.

So I went to /usr/lib64/firefox-3.0.14/ folder {ignoring the old ones visible on the directory}, created a sub-directory called plugins (as root) and gave the command:

ln -s /usr/java/jre1.6.0_16/lib/amd64/

The I restarted Firefox and once loaded went to the Java Test Page to check my virtual machine installation and witnessed the correct, and aspected, result:

Your Java configuration is as follows:
Vendor: Sun Microsystems Inc.
Version: Java 6 Update 16
Operating System: Linux 2.6.18-164.2.1.el5
Architecture: amd64

Hope this will be useful to you too!

RedHat 5, preliminary review

redhat logo A quick note to submit to your attention the nice article by U.K. online magazine Linux Format on the “new, more open Red Hat” covering the latest features of the distro alongside a little “gallery” of interviews to Max Spevack from Fedora, Karanbir Singh from CentOS and Nick Carr from RedHat itself.

Read it here: LINK

RedHat / CentOS release 5, interest gets higher

For the second time I have the impression of having been a little ahead of times when reporting some news.

This time I’m referring to my post “CentOS 5, first rumors” which is seeing a growing trend of access in these days:

CentOS post statistics

Well, the wait is near the end and today we the 13th March we had the announce:

This release corresponds to the upstream vendor EL5 beta2 release.

NOTE: This software is BETA and should be treated as such. It is for
testing purposes only. Please ensure it meets your needs completely
before using in a production environment.


Please see the CentOS specific release notes here:

which a bunch of hours ago was followed up by the official announcement of the release of Red Hat Enterprise Linux 5 I’ve been illustrating in the last week, so the CentOS 5 clone should be released very soon ….

Can’t wait to update my workstation (and possibly a server, we’ll see …)