检查java版本

[root@nailwl etc]# java -version
java version "1.7.0_181"
OpenJDK Runtime Environment (rhel-2.6.14.10.el6-x86_64 u181-b00)
OpenJDK 64-Bit Server VM (build 24.181-b00, mixed mode)
[root@nailwl etc]# echo $JAVA_HOME

 可以执行，检查$PATH

[root@nailwl etc]# echo $PATH
/usr/lib64/qt-3.3/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/home/nailwl/bin

效果不对，没有JAVA_HOME和JRE_HOME，检查java目录。

[root@nailwl etc]# whereis java
java: /usr/bin/java /etc/java /usr/lib/java /usr/share/java /usr/share/man/man1/java.1.gz

[root@nailwl etc]# which java
/usr/bin/java

[root@nailwl etc]# ls -lrt /usr/bin/java 
lrwxrwxrwx. 1 root root 22 Mar 12  2019 /usr/bin/java -> /etc/alternatives/java

[root@nailwl etc]# ls -lrt /etc/alternatives/java
lrwxrwxrwx. 1 root root 46 Mar 12  2019 /etc/alternatives/java -> /usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java

[root@nailwl etc]# cd /usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/
[root@nailwl bin]# ll
total 200
-rwxr-xr-x. 1 root root  9928 Jun 20  2018 java
-rwxr-xr-x. 1 root root 10056 Jun 20  2018 keytool
-rwxr-xr-x. 1 root root 10240 Jun 20  2018 orbd
-rwxr-xr-x. 1 root root 10088 Jun 20  2018 pack200
-rwxr-xr-x. 1 root root 11400 Jun 20  2018 policytool
-rwxr-xr-x. 1 root root 10048 Jun 20  2018 rmid
-rwxr-xr-x. 1 root root 10056 Jun 20  2018 rmiregistry
-rwxr-xr-x. 1 root root 10072 Jun 20  2018 servertool
-rwxr-xr-x. 1 root root 10280 Jun 20  2018 tnameserv
-rwxr-xr-x. 1 root root 91904 Jun 20  2018 unpack200

彻底了解里Linux系统中的java的路径情况，我们开始配置JAVA_HOME

[root@nailwl bin]# vi /etc/profile
[root@nailwl bin]# vi /etc/profile
[root@nailwl bin]# 
[root@nailwl bin]# 
[root@nailwl bin]# source /etc/profile
[root@nailwl bin]# 
[root@nailwl bin]# 
[root@nailwl bin]# echo $JAVA_HOME
/usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java
[root@nailwl bin]# echo $PATH
/usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java/bin:/usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java/jre/bin:/usr/lib64/qt-3.3/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/home/nailwl/bin
[root@nailwl bin]# 

其中vi /etc/profile之后在最底部追加以下配置信息

export JAVA_HOME=/usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java
export JRE_HOME=$JAVA_HOME/jre
export CLASSPATH=$JAVA_HOME/lib:$CLASSPATH
export PATH=$JAVA_HOME/bin:$JRE_HOME/bin:$PATH

贴个/etc/profile文件的最终效果吧，咱是讲究人。

[root@nailwl bin]# cat /etc/profile
# /etc/profile

# System wide environment and startup programs, for login setup
# Functions and aliases go in /etc/bashrc

# It's NOT a good idea to change this file unless you know what you
# are doing. It's much better to create a custom.sh shell script in
# /etc/profile.d/ to make custom changes to your environment, as this
# will prevent the need for merging in future updates.

pathmunge () {
    case ":${PATH}:" in
        *:"$1":*)
            ;;
        *)
            if [ "$2" = "after" ] ; then
                PATH=$PATH:$1
            else
                PATH=$1:$PATH
            fi
    esac
}


if [ -x /usr/bin/id ]; then
    if [ -z "$EUID" ]; then
        # ksh workaround
        EUID=`/usr/bin/id -u`
        UID=`/usr/bin/id -ru`
    fi
    USER="`/usr/bin/id -un`"
    LOGNAME=$USER
    MAIL="/var/spool/mail/$USER"
fi

# Path manipulation
if [ "$EUID" = "0" ]; then
    pathmunge /sbin
    pathmunge /usr/sbin
    pathmunge /usr/local/sbin
else
    pathmunge /usr/local/sbin after
    pathmunge /usr/sbin after
    pathmunge /sbin after
fi

HOSTNAME=`/bin/hostname 2>/dev/null`
HISTSIZE=1000
if [ "$HISTCONTROL" = "ignorespace" ] ; then
    export HISTCONTROL=ignoreboth
else
    export HISTCONTROL=ignoredups
fi

export PATH USER LOGNAME MAIL HOSTNAME HISTSIZE HISTCONTROL

# By default, we want umask to get set. This sets it for login shell
# Current threshold for system reserved uid/gids is 200
# You could check uidgid reservation validity in
# /usr/share/doc/setup-*/uidgid file
if [ $UID -gt 199 ] && [ "`/usr/bin/id -gn`" = "`/usr/bin/id -un`" ]; then
    umask 002
else
    umask 022
fi

for i in /etc/profile.d/*.sh ; do
    if [ -r "$i" ]; then
        if [ "${-#*i}" != "$-" ]; then
            . "$i"
        else
            . "$i" >/dev/null 2>&1
        fi
    fi
done

unset i
unset -f pathmunge


export JAVA_HOME=/usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java
export JRE_HOME=$JAVA_HOME/jre
export CLASSPATH=$JAVA_HOME/lib:$CLASSPATH
export PATH=$JAVA_HOME/bin:$JRE_HOME/bin:$PATH