Look in the httpd.conf file for the line that starts with "User" that
defined the user that Apache is going switch to running as. Check that
the user that is listed is a valid user on the server.But if apache was running before..that means either the user might have got removed / httpd.conf got edited somehow ?
# If you wish httpd to run as a different user or group, you must run
# httpd as root initially and it will switch.
# User/Group: The name (or #number) of the user/group to run httpd as.
# . On SCO (ODT 3) use "User nouser" and "Group nogroup".
# . On HPUX you may not be able to use shared memory as nobody, and the
# suggested workaround is to create a user www and use that user.
# NOTE that some kernels refuse to setgid(Group) or semctl(IPC_SET)
# when the value of (unsigned)Group is above 60000;
# don't use Group #-1 on these systems!
if httpd -t or configtest showing such and error then it should somewhere in the config file/ If it is not listing in the httpd.conf file, then are you sure that there is not preconfig files included inside httpd.conf file.
This error mostly comes when we terminate a domain from cpanel server and it will not removed the config entries correctly.
grep bad /var/cpanel/accounting.log
if you get the domain name then try
grep -irl domainname/username /etc/ This will give in case any other config files included with httpd.conf have such entry..try to hash it if found any...