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Switching Java versions on a Debian/Ubuntu system

I recently found some issues with the openjdk Ubuntu/Debian default Java implementation. Specifically I had issues with their web start support (javaws). I found that the Sun implementation of Java did not have such a deficiency and the Sun implementation is available through the regular Ubuntu/Debian package sources. I installed the Sun implementation and wanted to switch the default Java to that version.

So what have I found out ?

When you want to switch to the Sun implementation:

sudo update-java-alternatives --set java-6-sun

When you want to go back to the openjdk implementation:

sudo update-java-alternatives --set java-6-openjdk

Notice that once you do any of the above you leave “auto” mode which means that new installation of Java implementation will not switch your default one. If that is what you want then ok. If not you can return to “auto” mode with:

sudo update-java-alternatives --auto

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WordPress and UNIX security (part 2)

In an effort to secure my blog I once again did battle with the mighty Word press. It seems that you can run a perfectly healthy blog with no write permissions by the HTTP server (usually www-data) to your service directory.

What do I suggest? Change owner ship to root on your blog area. When you know that you need to upload stuff to Word press then open the permissions on the relevant folders. This happens when you want to add or remove plug-ins, upload media, themes etc. After the relevant operation clamp down on security again. There are plugins (like xLanguage) that write all kinds of junk log files into the upload folder as part of their operation. Obviously you cannot use these if you want better security.

Advantages: better security.
Disadvantages: A little discomfort and the need to write very simple short script to do the chmod for you. The Inability to use certain brain dead plug-ins.

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Finding thread info on Solaris

As part of a crusade to find bugs in a C++ program running on a Solaris system I needed to find out information about all the threads belonging to a certain process.

The program is written the way it is because you rarely need thread info about all threads running in a system but rather threads limited to a certain process. A different way to get this info is through the /proc file system but unfortunately (or fortunately ?!?) files in this Solaris file system usually have binary content as opposed to the textual content that one usually finds on a Linux system.

#!/usr/bin/perl -w
 
# Give this script the name of a process and it will show you thread
# infomation about your process...
 
 
use strict;
use diagnostics;
 
 
if(@ARGV<1) {
    die("usage myps.pl [process names...]");
}
 
 
for(my($p)=0;$p<@ARGV;$p++) {
    my($pname)=$ARGV[$p];
    print "showing diagnostics information for process $pname\n";
 
 
    # first lets find out the pid of the process
    my($pid)=`pgrep $pname`;
    chop($pid);
    print "The process id of the process is $pid\n";
 
 
    # now lets print all the thread info for that process...
    my(@lines)=`ps -eL`;
    for(my($i)=0;$i<@lines;$i++) {
        my($line)=$lines[$i];
        my(@fields)=split(" ",$line);
        if($fields[0] eq $pid) {
            print $line;
            #print(join('-',@fields));
        }
    }
}