How To Set Java Path In Linux?

How to set java path in Linux?

Ans : Check where java is installed by using below command

#update-alternatives --config java
This command will show installed java packages in your machine.

Example output :
# update-alternatives --config java

There are 2 programs which provide 'java'.

Selection ----------------------------------------------- 1 /usr/lib/jvm/jre-1.4.2-gcj/bin/java *+ 2
From above you can see java version in use it. 1.6.

Setting java path(In Temporary way)

#JAVA_HOME=/usr/lib/jvm/jre-1.6.0-openjdk #export $JAVA_HOME

Setting java path (In Permanent way)
Edit ~/.bashrc and place below two lines in that file and save the file.

Vi ~/.bashrc
JAVA_HOME=/usr/lib/jvm/jre-1.6.0-openjdk export $JAVA_HOME

Now save the file and exit, then logout and login to make those changes to reflect.

Command

/usr/lib/jvm/jre-1.6.0-openjdk/bin/java

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How to Set Priority for a service at booting of Linux

This is possible with renaming of the scripts located in running configuration(rc) folders. As you people know that
all the startup scripts are stored in rc1.d, rc2.d etc... each of these folders corresponding to scripts to be started in that run-level 
for example.. if you want to start some script in runlevel 1 they are kept in /etc/rc1.d folder so that when Linux is booting up these scripts are executed at runlevel 1.


So how can i set priority to my scripts/services?
Just go in to one of the rc folders, you can see all the scripts which are started in that runlevel.. 
if you observe those scripts, these scripts will start with different numbers. here are some for your reference.

K09apache2
K15pulseaudio
K20acpi-support
K20kerneloops
K20saned
K20speech-dispatcher
K20virtualbox-ose
K20virtualbox-ose-guest-utils
K74bluetooth
README
S30killprocs
S70dns-clean
S70pppd-dns
S90single

so the script(services) start sequence will be like K09apache2 then K15pulseaudio so on.. so if you want to give priority to your service just name with less number.. as shown below..


K09apache2
K01pulseaudio
K20acpi-support
K20kerneloops
K20saned
K20speech-dispatcher
K20virtualbox-ose
K20virtualbox-ose-guest-utils
K74bluetooth
README
S30killprocs
S70dns-clean
S70pppd-dns
S90single


So now the first script/service which start in this list is K01pulseaudio


Please comment your thoughts on this..

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How To Change The Java Version In Linux?

This post is regarding how to change java version if multiple java versions are installed?


Check what are the java versions are installed on your system


#java -version


Example output

OpenJDK Runtime Environment (build 1.6.0-b09)

OpenJDK Client VM (build 1.6.0-b09, mixed mode)


So now I want to change the one version to another version.

If more than one java is installed. Execute below command to see how many java versions are installed? And what is the default version (Default version will be indicated by *)


#update-alternatives --config java


This command will display which is default java version used by your machine..

Example output.

# update-alternatives --config java


There are 2 programs which provided 'java'.


Selection Command


-----------------------------------------------


1. /usr/lib/jvm/jre-1.4.2-gcj/bin/java


*+ 2 /usr/lib/jvm/jre-1.6.0-openjdk/bin/java


Enter to keep the current selection[+], or type selection number:


So if you want to change the java version from 1.6 (now 2 is default version as shown) to 1.4 just press “1” with out quotes.

Please let us know if you know other way of changing java version.

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