Process - Service

A service is a process that:

• runs continuously in the background
• are started by the operating system when the system starts.

It's declared and managed by the OS init system. With the init system, you may:

• start / stop a service
• get a list of all currently running services
• …

It is used remotely through some remote interface, either synchronous or asynchronous (eg web service, messaging system, RPC, or socket.)

• Windows - Services

• SystemD - Services
• Linux - Service client

A service is identified:

• on the network by:
  • its endpoint (host + port: network address)
  • and socket (network address and protocol - TCP/UDP)
• on the application level by its scheme (application protocol)

For instance, if you known that there is a service on the port 80, you would expect it to be:

• a HTTP/Web server (because this is the default HTTP port
• over TCP (because HTTP works generally over it)