Java
$ sudo apt-get update
$ sudo apt-get install default-jdk -y
Execute the below commands — navigate to /opt directory by changing directory:
$ cd /opt
Download Nexus
$ sudo wget http://download.sonatype.com/nexus/3/nexus-3.22.0-02-unix.tar.gz
Extract Nexus
$ sudo tar -xvf nexus-3.22.0–02-unix.tar.gz
$ sudo mv nexus-3.22.0–02 nexus
Create a user called Nexus
sudo adduser nexus

give some password may be as admin, but do remember.
Keep entering enter for all other values and press y to confirm the entries.
Give permission to Nexus user
sudo chown -R nexus:nexus /opt/nexus
sudo chown -R nexus:nexus /opt/sonatype-work
sudo vi /opt/nexus/bin/nexus.rc
change run_as_user=”nexus”
Modify memory settings
sudo vi /opt/nexus/bin/nexus.vmoptions
Add all the below changes the file with below yellow highlighted entry:

Configure Nexus to run as a service
sudo vi /etc/systemd/system/nexus.service
Copy the below content
— — — — — — — — — — — — — — — — — — — — — — — — — —
[Unit]
Description=nexus service
After=network.target[Service]
Type=forking
LimitNOFILE=65536
User=nexus
Group=nexus
ExecStart=/opt/nexus/bin/nexus start
ExecStop=/opt/nexus/bin/nexus stop
User=nexus
Restart=on-abort
[Install]
WantedBy=multi-user.target
— — — — — — — — — — — — — — — — — — — — — — — — — —
Now Start Nexus
$ sudo systemctl enable nexus
$ sudo systemctl start nexus
$ sudo systemctl status nexus
If it says stopped, review the steps above and you can troubleshoot by looking into Nexus logs by executing below command:
$ tail -f /opt/sonatype-work/nexus3/log/nexus.log

It should say Nexus is running..If you Nexus stopped, review the steps above.
Press control C to come out of the above window.
Once Nexus is successfully installed, you can access it in the browser by
URL — http://public_dns_name:8081 OR http://localhost:8081

Now click on Sign in, enter admin as user name and password by executing below cat command.
cat /opt/sonatype-work/nexus3/admin.password
Now change admin password as AXXX@YY3

Now click next, do not check Enable anonymous access.

Click Finish.
Now login with user name/password is admin/AXXX@YY3