Ubuntu system usage records

Ubuntu uses the 64-bit ubuntu. Real-world permission problems: to enable the root account # sudo passwd-u root # sudo passwd root. Then you can use su root to install jdk. First, the openjdk uninstall command is installed in ubuntu by default. # apt-get purge openjdk * Environment variable configuration in/etc/profile (I used to configure it in/etc/environment) # vim/etc/profile add export JAVA_HOME =/usr/app/jdk1.7 export CLASSPATH =.: export PATH = $ JAVA_HOME/bin: $ PATH # source/etc/profile there are several points to note: the first problem is: export PATH = $ JAVA_HOME/bin: $ PATH cannot be written as export PATH = $ PATH: $ JAVA_HOME/ Bin's second problem is:/usr/app/jdk1.7. This is the PATH where you decompress jdk. The third problem is that $ PATH must be added, otherwise, the previous path will disappear (very serious, there should be a recovery method) # java-version later, it seems useless to uninstall openjdk. By default, after jdk1.6 is uninstalled, it becomes jdk1.5, that is to say, it is unclear what jdk1.5 still exists. Disable bluetooth: # vim/etc/rc. local. Then, add the following rfkill block bluetooth to guess that it is a solution to kill the bluetooth process after the system is started.