Installing Java

update packages ก่อน

$ sudo apt update

ติดตั้ง Java JDK 11 (openjdk)

$ sudo apt install default-jdk

แต่ถ้าจะติดตั้ง Java 8 ใช้คำสั่ง

sudo apt install openjdk-8-jdk

โปรแกรมจะติดตั้งอยู่ที่ /usr/lib/jvm/java-11-openjdk-amd64/bin/

$ ls -l /usr/lib/jvm/java-11-openjdk-amd64/bin/java*
-rwxr-xr-x 1 root root 14560 ม.ค.  20 16:07 /usr/lib/jvm/java-11-openjdk-amd64/bin/java
-rwxr-xr-x 1 root root 14608 ม.ค.  20 16:07 /usr/lib/jvm/java-11-openjdk-amd64/bin/javac
-rwxr-xr-x 1 root root 14608 ม.ค.  20 16:07 /usr/lib/jvm/java-11-openjdk-amd64/bin/javadoc
-rwxr-xr-x 1 root root 14576 ม.ค.  20 16:07 /usr/lib/jvm/java-11-openjdk-amd64/bin/javap

ตรวจสอบการติดตั้งบน Ubuntu 20.04.6

$ java --version
openjdk 11.0.18 2023-01-17
OpenJDK Runtime Environment (build 11.0.18+10-post-Ubuntu-0ubuntu120.04.1)
OpenJDK 64-Bit Server VM (build 11.0.18+10-post-Ubuntu-0ubuntu120.04.1, mixed mode, sharing)

$ javac --version
javac 11.0.18

ตรวจสอบการติดตั้งบน Ubuntu 22.04.2

$ java --version
openjdk 11.0.18 2023-01-17
OpenJDK Runtime Environment (build 11.0.18+10-post-Ubuntu-0ubuntu122.04)
OpenJDK 64-Bit Server VM (build 11.0.18+10-post-Ubuntu-0ubuntu122.04, mixed mode, sharing)

$ javac --version
javac 11.0.18

Managing Java

ใช้คำสั่ง update-alternatives

$ update-alternatives --help
Usage: update-alternatives [<option> ...] <command>

Commands:
  --install <link> <name> <path> <priority>
    [--slave <link> <name> <path>] ...
                           add a group of alternatives to the system.
  --remove <name> <path>   remove <path> from the <name> group alternative.
  --remove-all <name>      remove <name> group from the alternatives system.
  --auto <name>            switch the master link <name> to automatic mode.
  --display <name>         display information about the <name> group.
  --query <name>           machine parseable version of --display <name>.
  --list <name>            display all targets of the <name> group.
  --get-selections         list master alternative names and their status.
  --set-selections         read alternative status from standard input.
  --config <name>          show alternatives for the <name> group and ask the
                           user to select which one to use.
  --set <name> <path>      set <path> as alternative for <name>.
  --all                    call --config on all alternatives.

<link> is the symlink pointing to /etc/alternatives/<name>.
  (e.g. /usr/bin/pager)
<name> is the master name for this link group.
  (e.g. pager)
<path> is the location of one of the alternative target files.
  (e.g. /usr/bin/less)
<priority> is an integer; options with higher numbers have higher priority in
  automatic mode.

Options:
  --altdir <directory>     change the alternatives directory.
  --admindir <directory>   change the administrative directory.
  --log <file>             change the log file.
  --force                  allow replacing files with alternative links.
  --skip-auto              skip prompt for alternatives correctly configured
                           in automatic mode (relevant for --config only)
  --quiet                  quiet operation, minimal output.
  --verbose                verbose operation, more output.
  --debug                  debug output, way more output.
  --help                   show this help message.
  --version                show the version.

You can have multiple Java installations on one server. You can configure which version is the default for use on the command line by using the update-alternatives command.

$ sudo update-alternatives --config java

ถ้ามี java ตัวเดียวก็จะขึ้นประมาณนี้

$ sudo update-alternatives --config java
There is only one alternative in link group java (providing /usr/bin/java): /usr/lib/jvm/java-11-openjdk-amd64/bin/java
Nothing to configure.

แต่ถ้ามี java หลายตัว ก็จะแสดงให้เราเลือก

javac ก็เหมือนกัน ใช้คำสั่ง

$ sudo update-alternatives --config javac

Setting the JAVA_HOME

$ sudo nano /etc/environment

At the end of this file, add the following line, and to not include the bin/ portion of the path: (หา path ได้ด้วยคำสั่ง update-alternatives)

JAVA_HOME="/usr/lib/jvm/java-11-openjdk-amd64"

JAVA_HOME="/usr/lib/jvm/java-8-openjdk-amd64"

Modifying this file will set the JAVA_HOME path for all users on your system.

Save the file and exit the editor.

Now reload this file to apply the changes to your current session:

$ source /etc/environment

Verify that the environment variable is set:

$ echo $JAVA_HOME

Link

• How To Install Java with Apt on Ubuntu 22.04 | DigitalOcean

ดู help ของคำสั่ง apt

$ apt --help
apt 2.4.8 (amd64)
Usage: apt [options] command

apt is a commandline package manager and provides commands for
searching and managing as well as querying information about packages.
It provides the same functionality as the specialized APT tools,
like apt-get and apt-cache, but enables options more suitable for
interactive use by default.

Most used commands:
  list - list packages based on package names
  search - search in package descriptions
  show - show package details
  install - install packages
  reinstall - reinstall packages
  remove - remove packages
  autoremove - Remove automatically all unused packages
  update - update list of available packages
  upgrade - upgrade the system by installing/upgrading packages
  full-upgrade - upgrade the system by removing/installing/upgrading packages
  edit-sources - edit the source information file
  satisfy - satisfy dependency strings

See apt(8) for more information about the available commands.
Configuration options and syntax is detailed in apt.conf(5).
Information about how to configure sources can be found in sources.list(5).
Package and version choices can be expressed via apt_preferences(5).
Security details are available in apt-secure(8).
                                        This APT has Super Cow Powers.

Update and Upgrade packages

update list of available packages

$ sudo apt update

list packages ที่สามารถอัพเกรดได้

$ apt list --upgradable

upgrade the system by installing/upgrading packages

$ sudo apt upgrade

ทำคำสั่ง apt update และต่อด้วย apt upgrade ด้วยการใช้คำสั่ง &&

When using the && command, the second command will be executed only when the first one has been succcefully executed.

$ sudo apt update && sudo apt upgrade

Install or Remove package

install packages

$ sudo apt install <package_name>

remove packages

$ sudo apt remove <package_name>

Remove automatically all unused packages

$ sudo apt autoremove

reinstall packages

sudo apt reinstall <package_name>
sudo apt reinstall lighttpd

hold a package ด้วย apt-mark

sudo apt-mark hold <package_name>
sudo apt-mark hold sudo

unhold a package ด้วย apt-mark

sudo apt-mark unhold <package_name>
sudo apt-mark unhold sudo

Other

show package details

To show or see information about the given package(s) including its dependencies, installation and download size, sources the package is available from, the description of the packages content and much more:

$ apt show <package_name>
$ apt show sudo

List package dependency

apt depends <package_name>
apt depends sudo

search in package descriptions

apt search php
apt search mysql-5.?
apt search mysql-server-5.?
apt search httpd*
apt search ^apache
apt search ^nginx
apt search ^nginx$

apt search ค้นหาใน package descriptions ทำให้ได้ข้อมูลเยอะเกิน หา pakcage ที่ต้องการยาก ให้ลองใช้ apt list แทน

apt list
apt list | more
apt list | grep foo
apt list | grep php7-

apt list nginx
apt list 'php7*'

List all installed packages

apt list --installed
apt list --installed | grep <package_name>

Ref

• apt Command Examples for Ubuntu/Debian Linux – nixCraft (cyberciti.biz)