First check nologin exists in /etc/shells

$ cat /etc/shells

if nologin is not found then append

# echo "/usr/sbin/nologin" >> /etc/shells

To set a user’s shell to nologin

# usermod <username> -s /sbin/nologin

# usermod ilugc -s /sbin/nologin

regards,

T.Dhanasekar