Sometimes you try to run ng serve command in my project it produce the below error. ERROR in ngcc is already running at process with id xxxx. To resolve the error try deleting your ngcc_lock_file in the path from node_modules.
rm node_modules/@angular/compiler-cli/ngcc/ngcc_lock_file
For Angular 9 and above version, the lock file to delete is:
rm node_modules/@angular/compiler-cli/ngcc/__ngcc_lock_file__
Note : I had the same issue and I deleted that file and it started working for me.