Starting httpd: AH00526, DocumentRoot must be a directory

Starting httpd: AH00526: Syntax error on line 121 of /etc/httpd/conf/httpd.conf:
DocumentRoot must be a directory

Check what exactly says the line in config:

cat /etc/httpd/conf/httpd.conf | awk 'NR==121'

This can output something like:

DocumentRoot "/var/www/html"

Check a little bit of range of this line:

cat /etc/httpd/conf/httpd.conf | awk 'NR>=101&&NR<=141'

For CentOS please try change file SELinux security context:

chcon -R -h -t httpd_sys_content_t /var/www/html

Start again httpd daemon:

cd /etc/init.d
./httpd start

Source:
https://stackoverflow.com/questions/14786881/apache-restart-causes-documentroot-must-be-a-directory-even-though-it-is-a-dire