On CentovaCast server, icecast is run as user ccuser, to run icecast, you need to enable shell for this user. By defult, this user have shell access disabled.
ccuser:x:1001:1001::/usr/local/centovacast:/bin/false
running icecast manually maybe useful when you want to debug some issue with icecast.
To enable bash shell for user, run
chsh --shell /bin/bash ccuser
Login as user ccuser
su - ccuser
Now start icecast with
/usr/local/icecast/bin/icecast -c /usr/local/centovacast/var/vhosts/USER_HERE/etc/server.conf
Beofore you manually start icecast from terminal, make sure you stop icecast by logging into user in Centova Cast control panel.
See Centova Cast