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snk
Asked: 2010-03-18 07:03:59 +0800 CST

Linux `alternatives --config` without user input

  • 772

I am writing a RHEL kickstart script, and in my %post, I need to install a JRE.

Basically, the current setup involves me needing to manually go in after first boot and set the newly installed JRE as the default using the alternatives --config command. Is there a way for me to pass arguments to alternatives so I don't have to manually pick the correct JRE?

java centos kickstart

4 Answers

  1. Best Answer

    Does your version have --set?

    --set name path
    Set the program path as alternative for name. This is equivalent to --config but is non-interactive and thus scriptable.

    • 22

  2. You can use alternatives --auto <name> to automatically select the highest priority option.

    An example:

     alternatives --install  /usr/lib/jvm/jre-1.6.0-openjdk.x86_64/bin/javac javac /usr/java/latest/bin/javac 10
 alternatives --install /usr/bin/javac javac /usr/java/latest/bin/javac 20
 alternatives --auto javac

    Would select the higher priority version (20) /usr/java/latest/bin/javac

    • 2

  3. Use grep:

    update-alternatives --set java $(update-alternatives --list java | grep java-8)

    or

    update-alternatives --set java $(update-alternatives --list java | grep java-11)
    • 1

  4. You may use the script below.
    You should configure the path for java "/bin" directory and a number for each version according to your system.

    #!/bin/bash
# update-java script

# Supported versions from the script. You may add more version numbers according to your needs.
supported_versions=( 8 11 )

# Validate that an argument has been given
if [ -z "$1" ]; then
    echo -e "No argument given. You should set as first argument the preferred java version.\nAvailable values: ${supported_versions[@]}"
    exit
fi

# Java "/bin" of each version. Be careful, each path should have the same index with the supported_versions array.
version_path=( "/usr/lib/jvm/jdk1.8.0_171/bin" "/usr/lib/jvm/java-11-openjdk-amd64/bin")

# Configure the alternatives
found=0
for i in "${!supported_versions[@]}"; do
    if [[ ${supported_versions[$i]} -eq $1 ]]; then
        update-alternatives --set java ${version_path[$i]}/java
        update-alternatives --set javac ${version_path[$i]}/javac
        found=1
    fi
done

# If a wrong version number has been given
if [ $found -ne 1 ]; then
    echo "You didn't provide a version of: ${supported_versions[@]}"
fi

    If you save the script with name "update-java", then set the executable permission, you will be able to run like below.

    $sudo update-java 12
You didn't provide a version of: 8 11
$sudo update-java
No argument given. You should set as first argument the preferred java version.
Available values: 8 11
$sudo update-java 11
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