Linux password retrieval, graphical interface and command line switching and common commands, installation (JDK)

Today, a simple pseudo-distributed cluster of Hadoop was built, with three CentOS systems on a virtual machine, but the password was forgotten. I would like to install a set of Oraclelinux, because of the time, or decided to check the method of retrieving the CentOS password. Make a record for easy access.

1. All passwords have been forgotten.

Press and hold ESC, enter an interface, select the second item by E, enter a space of +1, and then select the second item by B to enter the root screen.

passwd Root Reset root password

passwd centos Reset CentOS user password

Vi/etc/inittab 3,5 graphical and command line switching

Vi/etc/shadow file saved by user password

Shutdown-r now reboot

Who view current logged in user

Last View user login record

Tips : You can not skip the problem, you need to actively consult the data to solve the problem, so as to progress.

Service iptables Status View firewall state

Service iptables Stop shutting down the firewall

Installation of the JDK

Tar zxvf./jdk-8u91-linux-x64.tar.gz-c/usr/java

Gedit ~/.BASHRC

Export java_home=/usr/java/jdk1.8.0_91

Export JRE_HOME=${JAVA_HOME}/JRE

Export Classpath=.:${java_home}/lib:${jre_home}/lib

Export Path=${java_home}/bin: $PATH

SOURCE ~/.BASHRC

Java-version

which installation path for Java programs:/usr/local/apps/jdk1.7.0_79/bin/java

Linux password retrieval, graphical interface and command line switching and common commands, installation (JDK)