How to start netmgr and xhost on linux Fedora Core 5

Question

Hi
I have couple of questions.
1. I am having problem in starting netmgr on my linux. I am getting following error.
Exiting
java.lang.NullPointerException
at oracle.ewt.lwAWT.BufferedApplet.<init>(Unknown Source)
at oracle.sysman.emSDK.client.appContainer.WebApplication.<init>(WebApplication.java:752)
at oracle.net.mgr.container.NetApplication.<init>(Unknown Source)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
2. How to start xhost . The error I am getting is ..
xhost: unable to open display "xxx.xxx.xxx.xxx:0.0"
Please help me.
Thanks,

Answer 1

Some tips, based on my experience:
1) Avoid logging in a root, unless you want to allow your Linux machine to be insecure (at least as insecure as any Windows machine);
2) Never run X11 as root, as X11 has some known insecurities. (X11 means gnome, KDE, and the other window managers.) It is failrly easy for bad gus to take over the machine when running X11 as root.;
3) Normally log in as a regular user and su to root, not log in to root and su to a user.
4) The xhost command needs to be run as the user that is running 'X11' because it tells the X program to allow requests from any user on the host specified. Running 'xhost +' means 'any host. Running xhost by rhe owner of the X11 process should be done before issuing the "export DISPLAY=:0.0" and running the request to use the X11 display (invoking the program);
5) A quick way of checking whether the permissions are set up properly is to run 'xeyes' at the command line. It seems to be almost always installed and sets up faster than most Oracle programs. (Ctrl-C to exit xeyes.)