Java Alternative Version For Ubantu

Choose Java Alternative Version :

When we have got multiple versions of Java installed, we can choose which one you want to use by running the update-alternatives command.

Running below command shows a list of installed Java JDKs and JREs allowing one to be selected as the default that is used when java needs to be executed.

$ sudo update-alternatives --config java
There are 2 choices for the alternative java (providing /usr/bin/java).
 
  Selection    Path                                            Priority   Status
------------------------------------------------------------
  0            /usr/lib/jvm/java-6-openjdk/jre/bin/java         1061      auto mode
  1            /usr/lib/jvm/java-6-openjdk/jre/bin/java         1061      manual mode
* 2            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1051      manual mode
 
Press enter to keep the current choice[*], or type selection number: 2

To choose a default javac compiler, run the following command.

$ sudo update-alternatives --config javac

If we prefer to use a gui instead of the command line, we can execute galternatives instead and define the default versions of software with the following dialog.

$ sudo galternatives

Eclipse IDE - If server option is disable due to some issue

If server option is disable due to some issue when we configure tomcat then..

1. Close Eclipse
2. In {workspace-directory}/.metadata/.plugins/org.eclipse.core.runtime/.settingsdelete the following two files:
   • org.eclipse.wst.server.core.prefs
   • org.eclipse.jst.server.tomcat.core.prefs
3. Restart Eclipse

Rotate Tomcat catalina.out (If catalina.out becomes bulky in size, tomcat crashes and fails to start without any error message)

Rotate Tomcat catalina.out

If catalina.out becomes bulky in size, tomcat crashes and fails to start without any error message. 

To avoid this scenario you should rotate catalina.out frequently. 

Step - 1)
create file [any directory] with name "tomcatrotate"

Step - 2)
add content

/opt/apache-tomcat-7.0.67/logs/catalina.out  {
compress
copytruncate
daily
dateext
dateformat %Y-%m-%d
extension .out
missingok
rotate 14
size 100k
su root root
}

Step – 3)
after move to - /etc/logrotate.d/
sudo cp -i /home/minesh/Downloads/tomcatrotate /etc/logrotate.d/

Step - 4)
change the permission 777 to 644
sudo chmod -R 644 lportal

Step – 5)
after this test with below command it will do empty catalina.out and create its catalina2016-11-11.out.gz.

sudo /usr/sbin/logrotate -vf -s /var/log/logrotate-status /etc/logrotate.d/tomcatrotate

special thanks : https://masterinwebdev.blogspot.in/2016/11/tomcat-catalina.html