Debian 8 Jessie
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[1] Confirm services like follows.
# display the list of services which are running

systemctl -t service

UNIT                               LOAD   ACTIVE SUB     DESCRIPTION
acpid.service                      loaded active running ACPI event daemon
atd.service                        loaded active running Deferred execution scheduler
console-setup.service              loaded active exited  LSB: Set console font and keymap
cron.service                       loaded active running Regular background program processing daemon
dbus.service                       loaded active running D-Bus System Message Bus
systemd-user-sessions.service      loaded active exited  Permit User Sessions
udev-finish.service                loaded active exited  Copy rules generated while the root was ro

LOAD   = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB    = The low-level unit activation state, values depend on unit type.

35 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.

# display auto-start settings for services

systemctl list-unit-files -t service

UNIT FILE                              STATE
acpid.service                          disabled
atd.service                            enabled
autovt@.service                        disabled
bootlogd.service                       masked
bootlogs.service                       masked
urandom.service                        static
user@.service                          static
x11-common.service                     masked

128 unit files listed.
[2] Stop and turn OFF auto-start setting for a service if you don'd need it. (it's Atd as an example below)
systemctl stop atd

systemctl disable atd