Create separate users in Linux for running applications

The why? Why to create separate users for different applications in Linux

I won't copy/paste or restate the answers already present in the different forums. Instead I am going to quote the answers directly here for reference.

I prefer to have each application service run as its own user in order to have as much isolation between them as possible. If any part of the system gets broken or compromised I'd like to localise the damage as much as possible.

Source

When deploying a production service in Linux you want to configure it as securely as possible. Ideally, you will create a unique Linux user for each service and give them only read and write permission to the exact files they need. You can go even further and create a "system" user that has no home directory, no login shell, and no password. This prevents the user from being able to login and does not provide a home directory for them to store files. If the service was ever compromised this limits the actions an attacker can take with the user running the service.

Source

Technically, it makes no difference, but in the real world it turns out there are long term benefits in keeping user and software accounts in separate parts of the numeric space.
Mostly, it makes it easy to tell what the account is, and if a human should be able to log in.

Source

Next, how to create separate users in Linux for different applications. (For ubuntu click here)

In a fresh linux system we only have a single root user. But using the credentials of the root user is potentially dangerous as the user is allowed to do anything. In order to limit the damage a super privileged user can inflict on the system we create separate users for running different applications, scripts, or databases.

1. As a root user run:

   adduser newuser
   

   Or run the command with sudo.

2. Enter the password for the user and other details.

3. Optional: add the user to the Sudo group
   This allows the user to gain root access when called with the sudo prefix.

   usermod -aG sudo newuser
   

   Or run the command with sudo.

For more details see this

• Switching to the newly created user

su - newuser

Example: Creating user for Tomcat in Ubuntu

1. Create a non-root user to run Tomcat. First create a group called tomcat that runs the server

sudo groupadd tomcat

and

sudo useradd -s /bin/false -g tomcat -d /opt/tomcat tomcat

This creates a new tomcat user, makes it a member of the tomcat group and assigns it a home directory of /opt/tomcat and disables log in to the account.

Full docs on tomcat installation here and here.
Updated link to tomcat installation.