降级在ubuntu 14.04中打开jdk 8到7 [英] Downgrade open jdk 8 to 7 in ubuntu 14.04
问题描述
我在ubuntu 14.04中意外升级了整个系统。
我正在尝试部署一个需要JDK7的war文件。
我试图安装JDK7并将其用作默认值
root：floyd~＃update-alternatives --config java
链接组java中只有一个替代方法（提供/ usr / bin / java）：/ usr / lib / jvm / java-8-openjdk-amd64 / jre / bin / java
没什么配置。
但它也没有安装。尝试安装JDK 7时出现以下错误。
root @ floyd：〜＃apt-get install openjdk-7-jdk
阅读包列表...完成
构建依赖树
读取状态信息...完成
包openjdk-7-jdk不可用，但由另一个包引用。
这可能意味着包丢失，已经过时，或者
只能从其他来源获得
N：忽略文件'50unattended-upgrades.ucf-dist'in目录'/etc/apt/apt.conf.d/'，因为它的文件扩展名无效
E：包'openjdk-7-jdk'没有安装候选者
我想我有两个选择。
- 安装JDK7并将其用作默认值。
- 将JDK8降级为JDK7。
我认为降级可能是一个不错的选择，但我无法做任何选择。
在默认配置中安装JRE / JDK
OpenJDK 7默认安装在Ubuntu 12.10及更高版本中。
安装Java，其中apt-get很简单：
sudo apt-get update
java -version
如果执行后我们有类似的东西：程序java可以在下面找到包，这意味着没有安装Java。所以，我们需要：
sudo apt-get install default-jre
结果，将安装 Java运行时环境（JRE）。当我们想要安装 Java Development Kit（JDK）时，我们需要安装Java-app（例如，Apache Ant，Apache Maven，Eclipse和IntelliJ IDEA）要做的事情：
sudo apt-get install default-jdk
现在，安装了Java。
安装 OpenJDK 7 （可选）
sudo apt-get install openjdk-7-jre
执行后将安装Java运行时环境（JRE）。对于 Java Development Kit（JDK），我们执行：
sudo apt -get install openjdk-7-jdk
安装Oracle JDK（可选）
Oracle JDK是一个正式的JDK，但现在，Oracle不支持默认安装在Ubuntu中。
我们可以通过apt-get安装它，但在我们需要执行下一个命令之前：
sudo apt-get install python -software-properties
sudo add-apt-repository ppa：webupd8team / java
sudo apt-get update
稍后，我们必须选择所需的版本并执行：
对于Oracle JDK 6
sudo apt-get install oracle-java6-installer
对于Oracle JDK 7
sudo apt-get install oracle-java7-installer
对于Oracle JDK 8
sudo apt-get install甲骨文JA va8-installer
对于Oracle JDK 9
sudo apt-get install oracle-java9-installer
管理Java（可选）
当我们安装了某个版本的Java时，我们可以选择其中一个作为默认值：
sudo update-alternatives --config java
结果我们会看到像这个：
备用java有两种选择（提供/ usr / bin / java）。
选择路径优先级状态
---------------------------------- --------------------------
* 0 / usr / lib / jvm / java-7-oracle / jre / bin / java 1062自动模式
1 / usr / lib / jvm / java-6-openjdk-amd64 / jre / bin / java 1061手动模式
2 / usr / lib / jvm / java-7-oracle / jre / bin / java 1062手动模式
按Enter键保留当前选项[*]或类型选择号：
我们可以在屏幕上看到它：
现在，我们需要重新启动此文件：
source / etc / environment
要检查它我们可以：
echo $ JAVA_HOME
在屏幕上：
我们现在有了输入方式（在我们的示例中为/ usr / lib / jvm / java-7-oracle）它将意味着我们成功地完成它。换句话说，我们需要更加专心，并检查所有这些步骤。
I accidentally upgraded the whole system in ubuntu 14.04.
I am trying to deploy a war file which requires JDK7.
I tried to install JDK7 and use it as default
root:floyd~# update-alternatives --config java
There is only one alternative in link group java (providing /usr/bin/java): /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java
Nothing to configure.
but it is not installing as well. It gives following error while trying to install JDK 7.
root@floyd:~# apt-get install openjdk-7-jdk
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package openjdk-7-jdk is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
N: Ignoring file '50unattended-upgrades.ucf-dist' in directory '/etc/apt/apt.conf.d/' as it has an invalid filename extension
E: Package 'openjdk-7-jdk' has no installation candidate
I guess I have two options.
- Install JDK7 and use it as default.
- Downgrade JDK8 to JDK7.
I think downgrading can be a good option but I am not able to do any of them.
Installing JRE/JDK in default configuration OpenJDK 7 is installed as default in Ubuntu 12.10 and later. Installing Java whereby apt-get is easy:
sudo apt-get update
java -version
If after execution we have something like: "The program java can be found in the following packages", it means that Java isn't installed. So, we need to to:
sudo apt-get install default-jre
As result, Java Runtime Environment (JRE) will be installed. When we want to install Java Development Kit (JDK), which is needed for compilling Java-app (for example, Apache Ant, Apache Maven, Eclipse and IntelliJ IDEA) we need to do:
sudo apt-get install default-jdk
Now, Java is installed.
Installing OpenJDK 7 (optionally)
sudo apt-get install openjdk-7-jre
After execution Java Runtime Environment (JRE) will be installed. For Java Development Kit (JDK), we execute:
sudo apt-get install openjdk-7-jdk
Installing Oracle JDK (optionally) Oracle JDK is an official JDK but, now, Oracle doesn't support it like default for installation in Ubuntu.
We can install it by apt-get but before we need to execute next commands:
sudo apt-get install python-software-properties
sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
Later, we have to choose needed version and execute:
For Oracle JDK 6
sudo apt-get install oracle-java6-installer
For Oracle JDK 7
sudo apt-get install oracle-java7-installer
For Oracle JDK 8
sudo apt-get install oracle-java8-installer
For Oracle JDK 9
sudo apt-get install oracle-java9-installer
Managing of Java (optionally) When we have some version Java installed we can choose one of them as default:
sudo update-alternatives --config java
As result we will see something like this:
There are 2 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-7-oracle/jre/bin/java 1062 auto mode
1 /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java 1061 manual mode
2 /usr/lib/jvm/java-7-oracle/jre/bin/java 1062 manual mode
Press enter to keep the current choice[*], or type selection number:
We can see it on the screen:
The same action we can do to choose the compiler (javac):
sudo update-alternatives --config javac
This command can be used to choose other java componenst, for example, like: keytool, javadoc and jarsigner.
Installing "JAVA_HOME"
To be installed **JAVA_HOME**:
sudo update-alternatives --config java
Result like:
There are 2 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-7-oracle/jre/bin/java 1062 auto mode
1 /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java 1061 manual mode
2 /usr/lib/jvm/java-7-oracle/jre/bin/java 1062 manual mode
Press enter to keep the current choice[*], or type selection number:
As we can see the paths for java will be:
/usr/lib/jvm/java-7-oracle
/usr/lib/jvm/java-6-openjdk-amd64
/usr/lib/jvm/java-7-oracle
Now, we need to copy one of the ways and paste it into:
/etc/environment:
sudo nano /etc/environment
In the file we are going to add a path(where YOUR_PATH - is path for desired version of java, for example: "/usr/lib/jvm/java-7-oracle"):
JAVA_HOME="/usr/lib/jvm/java-7-oracle"
On the screen:
Now, we need to reboot this file:
source /etc/environment
To check it we can:
echo $JAVA_HOME
On the screen:
When we have, now, input way("/usr/lib/jvm/java-7-oracle" in our example) it will be means we do it sucessfully. In other way we need to be more attentive and check all these steps once.
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