After Upgrading Apache from 2.2 to 2.4 following error occurred.

Apache Error: Invalid command ‘User’, perhaps misspelled or defined by a module not included in the server configuration

Apache Error Message:

AH00526: Syntax error on line xxx of /etc/httpd/conf/httpd.conf
Invalid command ‘User’, perhaps misspelled or defined by a module not included in the server configuration
httpd.service: main process exited, code=exited, status=1/FAILURE

Solution:

Load the module mod_unixd in Apache configuration file.
To load this module just add the following line in the httpd.conf

LoadModule unixd_module modules/mod_unixd.so