Enumerate

All Systems

cat /etc/services	Display network services
service --status-all	Shows all services
ps aux | grep [service_name]	Lists processes related to a specific service.
netstat -tlpn | grep [service_name]	Shows network connections used by a service.
ss -tulnp	Another command to display active network connections and associated services

Systemd (most modern distributions):

systemctl	Lists units for systemd, implicitly including services.
systemctl list-unit-files	Lists all available systemd unit files, including services.
systemctl list-units	Shows currently running services and their status.
systemctl list-units --type=service --all	Lists all systemd services, including active and inactive.
systemctl status [service_name]	Displays detailed information about a specific service.
systemctl enable/disable [service_name]	Enables or disables a service for automatic startup.

SysV init (older distributions):

/etc/init.d	Directory containing service scripts.
ls /etc/init.d	Lists all service scripts in the directory.
service --status-all	Displays the status of all services.
service [service_name] status	Checks the status of a specific service.
service [service_name] start/stop/restart	Starts, stops, or restarts a service.
chkconfig --list	Lists all services and their runlevel settings.

Upstart (rarely used now):

status [service_name]	Shows the status of a specific service.
stop [service_name]	Stops a service.
start [service_name]	Starts a service.
initctl list	Lists all running Upstart jobs.