請教大家
參考網址https://tecadmin.net/install-java-8-on-centos-rhel-and-fedora/# 使用下列的指令
alternatives --install /usr/bin/java java /opt/jdk1.8.0_131/bin/java 2
但會出現alternatives command not found的訊息，而我有執行過sudo apt-get update,但問題仍然一樣，煩請大家指點
謝謝
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alternatives用來替換系統預設的元件. 但CentOS並未預設安裝alternatives命令.
# yum install alternatives
感謝，但我這是在ubuntu下，而我試著執行下列語法，並沒辦法更新
如有其他方向指點，再請幫忙協助
您上個問題是在CentOS.
Ubuntu, 可以直接使用OpenJDK, 這是Oracle所用的 Hotspot JVM, 兩者的差異極小且不涉及JAVA功能, 所以是一樣的. 以下是我的安裝過程, 其中我裝了openjdk-8-jre和openjdk-9-jre, 並在兩者間用update-alternatives切換. 您也可以裝openjdk-8-jdk. 當然, 您也可以自己下載Oracle Hotspot JVM安裝.
$ sudo apt-get install openjdk-8-jre
$ java -version
openjdk version "1.8.0_131"
OpenJDK Runtime Environment (build 1.8.0_131-8u131-b11-0ubuntu1.16.04.2-b11)
OpenJDK 64-Bit Server VM (build 25.131-b11, mixed mode)
$ sudo apt-get install openjdk-9-jre
$ java -version
openjdk version "9-internal"
OpenJDK Runtime Environment (build 9-internal+0-2016-04-14-195246.buildd.src)
OpenJDK 64-Bit Server VM (build 9-internal+0-2016-04-14-195246.buildd.src, mixed mode)
$ sudo update-alternatives --config java
There are 2 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-9-openjdk-amd64/bin/java 1091 auto mode
1 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1081 manual mode
2 /usr/lib/jvm/java-9-openjdk-amd64/bin/java 1091 manual mode
Press <enter> to keep the current choice[*], or type selection number: 1
update-alternatives: using /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java to provide /usr/bin/java (java) in manual mode
$ java -version
openjdk version "1.8.0_131"
OpenJDK Runtime Environment (build 1.8.0_131-8u131-b11-0ubuntu1.16.04.2-b11)
OpenJDK 64-Bit Server VM (build 25.131-b11, mixed mode)
您上個問題是在CentOS.
Ubuntu, 可以直接使用OpenJDK, 這是Oracle所用的 Hotspot JVM, 兩者的差異極小且不涉及JAVA功能, 所以是一樣的. 以下是我的安裝過程, 其中我裝了openjdk-8-jre和openjdk-9-jre, 並在兩者間用update-alternatives切換. 您也可以裝openjdk-8-jdk. 當然, 您也可以自己下載Oracle Hotspot JVM安裝.
$ sudo apt-get install openjdk-8-jre
$ java -version
openjdk version "1.8.0_131"
OpenJDK Runtime Environment (build 1.8.0_131-8u131-b11-0ubuntu1.16.04.2-b11)
OpenJDK 64-Bit Server VM (build 25.131-b11, mixed mode)
$ sudo apt-get install openjdk-9-jre
$ java -version
openjdk version "9-internal"
OpenJDK Runtime Environment (build 9-internal+0-2016-04-14-195246.buildd.src)
OpenJDK 64-Bit Server VM (build 9-internal+0-2016-04-14-195246.buildd.src, mixed mode)
$ sudo update-alternatives --config java
There are 2 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-9-openjdk-amd64/bin/java 1091 auto mode
1 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1081 manual mode
2 /usr/lib/jvm/java-9-openjdk-amd64/bin/java 1091 manual mode
Press <enter> to keep the current choice[*], or type selection number: 1
update-alternatives: using /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java to provide /usr/bin/java (java) in manual mode
$ java -version
openjdk version "1.8.0_131"
OpenJDK Runtime Environment (build 1.8.0_131-8u131-b11-0ubuntu1.16.04.2-b11)
OpenJDK 64-Bit Server VM (build 25.131-b11, mixed mode)
而update-alternatives所做的事只是在/etc/alternatives/中建立連結:
$ ls -ls /etc/alternatives/java
0 lrwxrwxrwx 1 root root 46 6月 16 09:26 /etc/alternatives/java -> /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java
因此, 可以手動自行更改:
$ sudo unlink /etc/alternatives/java
$ sudo ln -s /usr/lib/jvm/java-9-openjdk-amd64/bin/java /etc/alternatives/
$ ls -ls /etc/alternatives/java
0 lrwxrwxrwx 1 root root 42 6月 16 09:40 /etc/alternatives/java -> /usr/lib/jvm/java-9-openjdk-amd64/bin/java
既然是 Ubuntu
請參考 How To Install Java with Apt-Get on Ubuntu 16.04
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