In this post, I will show you how you can easily manage Java jar applications with Systemd service. Systemd is a system and service manager for Linux. It is now the default init system for a number of Distributions including Ubuntu 20.04/18.04, Debian 10/9, CentOS 8/7, Arch Linux e.t.c.
In this deployment, I have a Jar file located under a /opt/prod/directory. As a rule of thumb, we need to add a system user which will run the application with systemd.
Step 1: Create an Application User and group
Start by creating a system group for the user.
sudo groupadd -r appmgrNext, we create a system user jvmapps with the default group:
sudo useradd -r -s /bin/false -g appmgr jvmappsConfirm user created and if with the correct group:
$ id jvmapps
uid=992(jvmapps) gid=986(appmgr) groups=986(appmgr)Step 2: Create Systemd Service
We can now create a systemd service file to manage our application. You need to create this file as root user.
sudo vim /etc/systemd/system/myapp.serviceIt will have content like below:
[Unit]
Description=Manage Java service
[Service]
WorkingDirectory=/opt/prod
ExecStart=/bin/java -Xms128m -Xmx256m -jar myapp.jar
User=jvmapps
Type=simple
Restart=on-failure
RestartSec=10
[Install]
WantedBy=multi-user.targetSet User to the one created earlier, and WorkingDirectory to the directory with a jar file.
-Xms128m and -Xmx256m are used to set the minimum and maximum memory that the application can use.
When done with the change, give the user and group ownership permissions for the Project Directory:
sudo chown -R jvmapps:appmgr /opt/prodStep 3: Start Java Application service with systemd
The next thing to do is start the application service, but first, reload systemd so that it knows of the new application added.
sudo systemctl daemon-reloadOnce reloaded, start the service:
sudo systemctl start myapp.serviceTo check the status, use:
$ systemctl status myappSample output:
$ systemctl status myapp
● myapp.service - Manage Java service
Loaded: loaded (/etc/systemd/system/myapp.service; enabled; vendor preset: disabled)
Active: active (running) since Fri 2018-08-24 11:12:23 EAT; 23h ago
Main PID: 23220 (java)
CGroup: /system.slice/myapp.service
└─23220 /bin/java -Xms128m -Xmx256m -jar myapp.jar
Aug 25 10:50:00 server1 java[23220]: # Duration: 1000 µs
Aug 25 10:50:00 server1 java[23220]: # Total number of fields classified 0, 0 failed
Aug 25 10:50:00 server1 java[23220]: # ---------------------------------------------------------------
Aug 25 10:50:00 server1 java[23220]: # Completed step 'classify-tables'
Aug 25 10:50:00 server1 java[23220]: # Start: 2018-08-25T07:50:00.258Z
Aug 25 10:50:00 server1 java[23220]: # End: 2018-08-25T07:50:00.259Z
Aug 25 10:50:00 server1 java[23220]: # Duration: 1000 µs
Aug 25 10:50:00 server1 java[23220]: # Total number of tables classified 3, 0 updated
Aug 25 10:50:00 server1 java[23220]: #################################################################
Aug 25 10:50:00 server1 java[23220]: 08-25 10:50:00 INFO sync.util :: FINISHED: Analyze data for mysql Database 2 'Ch... (8 ms)
Hint: Some lines were ellipsized, use -l to show in full.You can also enable the service to start on server boot:
$ sudo systemctl enable myapp Created symlink from /etc/systemd/system/multi-user.target.wants/myapp.service to /etc/systemd/system/myapp.service.
To restart the application, use:
sudo systemctl restart myappMore Java learning:
Udemy.com
Conclusion
You now have a Java Application being managed by Systemd. Replicate the same procedure for all other services you need to manage using Systemd init. Hope this was helpful, for any issues, let me know through the comments section.
Other guides:
Best Books for Learning Java Programming
Install Metabase with Systemd on Debian
How to Install Metabase with Systemd on Ubuntu
