Linux，全称GNU/Linux，是一种免费使用和自由传播的类UNIX操作系统，其内核由林纳斯·本纳第克特·托瓦兹于1991年10月5日首次发布，它主要受到Minix和Unix思想的启发，是一个基于POSIX的多用户、多任务、支持多线程和多CPU的操作系统。
Linux下配置JDK实际上是很简单的，我按照网上的教程进行如下配置，在 /etc/profile 文件中最后添加：
export JAVA_HOME=/home/son/jdk1.8.0_144
export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
export PATH=$JAVA_HOME/bin:$PATH
通过命令启用java环境：
source /etc/profile
但是有一个问题比较恶心，那就是JDK环境变量失效的问题，关闭设置好的bash后重新打开，java环境变量就无效了
root@ubuntu:/home/son/apache-tomcat-8.5.20/bin# ./shutdown.sh
Neither the JAVA_HOME nor the JRE_HOME environment variable is defined
At least one of these environment variable is needed to run this program
root@ubuntu:/home/son/apache-tomcat-8.5.20/bin# java -version
bash: java: command not found
经大神指点， /etc/profile 文件修改一下，删除 export 就行。
JAVA_HOME=/home/son/jdk1.8.0_144
CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
PATH=$JAVA_HOME/bin:$PATH
需要再启用一下
source /etc/profile
再运行一下java
root@ubuntu:/etc# java
Usage: java [-options] class [args...]
(to execute a class)
or java [-options] -jar jarfile [args...]
(to execute a jar file)
where options include:
-d32 use a 32-bit data model if available
-d64 use a 64-bit data model if available
-server to select the"server" VM
The default VM is server, because you are running on a server-class machine.
-cp
-classpath
A : separated list of directories, JAR archives, and ZIP archives to search for class files.
-D=
set a system property
-verbose:[class gc jni]
enable verbose output
-version print product version and exit
-version:
Warning: this feature is deprecated and will be removed in a future release. require the specified version to run
-showversion print product version and continue
-jre-restrict-search -no-jre-restrict-search
Warning: this feature is deprecated and will be removed in a future release. include/exclude user private JREs in the version search
-? -help print this help message
-X print help on non-standard options
-enableassertions[:
... :]enable assertions with specified granularity
-disableassertions[:
... :]disable assertions with specified granularity
-esa -enablesystemassertions
enable system assertions
-dsa -disablesystemassertions
disable system assertions
-agentlib:[=]
load native agent library , e.g. -agentlib:hprof see also, -agentlib:jdwp=help and -agentlib:hprof=help
load native agent library by full pathname
-javaagent:[=]
load Java programming language agent, see java.lang.instrument
-splash:
show splash screen with specified image
See http://www.oracle.com/technetwork/java/javase/documentation/index.html for more details.
OK!
