Which network ports are reserved by the Linux Operating System?

For the Linux Operating system, there are 3 different kinds of network service ports:

• The Well Known Ports (0-1023) – which are reserved for the operating system and core services.
• The Registered Ports (1024-49151) – which can be used by applications, specific services, and users.
• The Dynamic and/or Private Ports (49152-65535)

There is a standard list of these network service port assignments for Linux documented at:
https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml

The Well Known Ports are listed in the /etc/services file on the OS. Specific ports used by applications etc can be added to the /etc/services file.