Welcome to the community, and thanks for your question! This issue/error can happen for so many reasons, so it’s important to know the cause.
Please which guide did you follow for the DHIS2 installation, and what version of DHIS2 are you trying to install? Other helpful info is the versions for Java and PostgreSQL database in your OS?
Make sure you created the DHIS2 user and gave the permissions using ‘chown’ to the DHIS2 configuration file. Finally, please send the Tomcat servlet catalina.out log