http://forums.debian.net/viewtopic.php?f=10&t=136952&p=669344#p669344

After a large system update ...

|# systemctl restart fancontrol.service
Job for fancontrol.service failed because the control process exited with
error code.
See "systemctl status fancontrol.service" and "journalctl -xe" for details.
# systemctl status fancontrol.service -l
â fancontrol.service - fan speed regulator
   Loaded: loaded (/lib/systemd/system/fancontrol.service; enabled; vendor
preset: enabled)
   Active: failed (Result: exit-code) since Sat 2018-03-17 12:15:49 CET;
3s ago
     Docs: man:fancontrol(8)
           man:pwmconfig(8)
  Process: 27786 ExecStartPre=/usr/sbin/fancontrol --check (code=exited,
status=1/FAILURE)

Mar 17 12:15:49 leon-host systemd[1]: Starting fan speed regulator...
Mar 17 12:15:49 leon-host fancontrol[27786]: Loading configuration from
/etc/fancontrol ...
Mar 17 12:15:49 leon-host fancontrol[27786]: Some mandatory settings
missing, please check your config file!
Mar 17 12:15:49 leon-host systemd[1]: fancontrol.service: Control process
exited, code=exited status=1
Mar 17 12:15:49 leon-host systemd[1]: Failed to start fan speed regulator.
Mar 17 12:15:49 leon-host systemd[1]: fancontrol.service: Unit entered
failed state.
Mar 17 12:15:49 leon-host systemd[1]: fancontrol.service: Failed with
result 'exit-code'.

telling exactly which "|||mandatory settings" would be very helpfull| !!!
At least which variable, and, recommend in which conf file it should be set.

|-- System Information:
Debian Release: 9.4
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.9.0-6-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8),
LANGUAGE=en_GB:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages fancontrol depends on:
ii  init-system-helpers  1.48
ii  lsb-base             9.20161125

fancontrol recommends no packages.

fancontrol suggests no packages.

This bug still exists in buster.

uname -a:
Linux Pythagoras 4.18.0-3-amd64 #1 SMP Debian 4.18.20-2 (2018-11-23) x86_64 GNU/Linux

lsb_release:
Distributor ID: Debian
Description:    Debian GNU/Linux 10 (buster)
Release:        10
Codename:       buster

journalctl -b | grep -C 2 fancontrol:
Dez 28 04:38:21 Pythagoras /usr/sbin/gpm[905]: *** info [daemon/startup.c(131)]:
Dez 28 04:38:21 Pythagoras /usr/sbin/gpm[905]: Started gpm successfully. Entered daemon mode.
Dez 28 04:38:21 Pythagoras fancontrol[830]: Loading configuration from /etc/fancontrol ...
Dez 28 04:38:21 Pythagoras kernel: vboxdrv: loading out-of-tree module taints kernel.
Dez 28 04:38:21 Pythagoras kernel: vboxdrv: Found 8 processor cores
Dez 28 04:38:21 Pythagoras kernel: vboxdrv: TSC mode is Invariant, tentative frequency 1595984291 Hz
Dez 28 04:38:21 Pythagoras kernel: vboxdrv: Successfully loaded version 6.0.0 (interface 0x00290007)
Dez 28 04:38:21 Pythagoras fancontrol[830]: Common settings:
Dez 28 04:38:21 Pythagoras fancontrol[830]:   INTERVAL=10
Dez 28 04:38:21 Pythagoras fancontrol[830]: Settings for hwmon1/device/pwm1:
Dez 28 04:38:21 Pythagoras fancontrol[830]:   Depends on hwmon2/device/temp1_input
Dez 28 04:38:21 Pythagoras fancontrol[830]:   Controls hwmon1/device/fan1_input
Dez 28 04:38:21 Pythagoras fancontrol[830]:   MINTEMP=50
Dez 28 04:38:21 Pythagoras fancontrol[830]:   MAXTEMP=75
Dez 28 04:38:21 Pythagoras fancontrol[830]:   MINSTART=150
Dez 28 04:38:21 Pythagoras fancontrol[830]:   MINSTOP=150
Dez 28 04:38:21 Pythagoras fancontrol[830]:   MINPWM=150
Dez 28 04:38:21 Pythagoras fancontrol[830]:   MAXPWM=250
Dez 28 04:38:21 Pythagoras cron[752]: (CRON) INFO (Running @reboot jobs)
Dez 28 04:38:22 Pythagoras kernel: VBoxNetFlt: Successfully started.
--
Dez 28 04:38:24 Pythagoras systemd[1]: Started Login Service.
Dez 28 04:38:24 Pythagoras systemd[1]: Started WPA supplicant.
Dez 28 04:38:24 Pythagoras fancontrol[1012]: Loading configuration from /etc/fancontrol ...
Dez 28 04:38:24 Pythagoras systemd[1]: Started Bluetooth service.
Dez 28 04:38:24 Pythagoras systemd[1]: Started RealtimeKit Scheduling Policy Service.
--
Dez 28 04:38:25 Pythagoras NetworkManager[779]: <info>  [1545968305.0040] manager[0x563c910f5030]: monitoring kernel firmware directory '/lib/firmware'.
Dez 28 04:38:25 Pythagoras NetworkManager[779]: <info>  [1545968305.0041] monitoring ifupdown state file '/run/network/ifstate'.
Dez 28 04:38:25 Pythagoras fancontrol[1012]: Common settings:
Dez 28 04:38:25 Pythagoras fancontrol[1012]:   INTERVAL=10
Dez 28 04:38:25 Pythagoras systemd[1]: Starting OpenBSD Secure Shell server...
Dez 28 04:38:25 Pythagoras systemd[1]: Started Permit User Sessions.
Dez 28 04:38:25 Pythagoras systemd[1]: Starting Simple Desktop Display Manager...
Dez 28 04:38:25 Pythagoras fancontrol[1012]: Settings for hwmon1/device/pwm1:
Dez 28 04:38:25 Pythagoras fancontrol[1012]:   Depends on hwmon2/device/temp1_input
Dez 28 04:38:25 Pythagoras fancontrol[1012]:   Controls hwmon1/device/fan1_input
Dez 28 04:38:25 Pythagoras fancontrol[1012]:   MINTEMP=50
Dez 28 04:38:25 Pythagoras fancontrol[1012]:   MAXTEMP=75
Dez 28 04:38:25 Pythagoras fancontrol[1012]:   MINSTART=150
Dez 28 04:38:25 Pythagoras fancontrol[1012]:   MINSTOP=150
Dez 28 04:38:25 Pythagoras fancontrol[1012]:   MINPWM=150
Dez 28 04:38:25 Pythagoras fancontrol[1012]:   MAXPWM=250
Dez 28 04:38:25 Pythagoras systemd[1]: Started vboxautostart-service.service.
Dez 28 04:38:25 Pythagoras systemd[1]: Started vboxballoonctrl-service.service.
--
Dez 28 04:38:25 Pythagoras dbus-daemon[777]: [system] Activating via systemd: service name='org.freedesktop.hostname1' unit='dbus-org.freedesktop.hostname1.service' requested by ':1.7' (uid=0 pid=779 comm="/usr/sbin/NetworkManager --no-daemon ")
Dez 28 04:38:25 Pythagoras systemd[1]: Starting Hostname Service...
Dez 28 04:38:25 Pythagoras fancontrol[1012]: Device path of hwmon1 has changed
Dez 28 04:38:25 Pythagoras fancontrol[1012]: Device path of hwmon2 has changed
Dez 28 04:38:25 Pythagoras fancontrol[1012]: Device name of hwmon1 has changed
Dez 28 04:38:25 Pythagoras fancontrol[1012]: Device name of hwmon2 has changed
Dez 28 04:38:25 Pythagoras fancontrol[1012]: Configuration appears to be outdated, please run pwmconfig again
Dez 28 04:38:25 Pythagoras systemd[1]: fancontrol.service: Main process exited, code=exited, status=1/FAILURE
Dez 28 04:38:25 Pythagoras systemd[1]: fancontrol.service: Failed with result 'exit-code'.
Dez 28 04:38:25 Pythagoras systemd[1]: cgmanager.service: Service RestartSec=100ms expired, scheduling restart.
Dez 28 04:38:25 Pythagoras systemd[1]: cgmanager.service: Scheduled restart job, restart counter is at 2.
--
Dez 28 05:13:48 Pythagoras lircd-0.10.1[1180]: Error: No /sys/class/rc/ devices found
Dez 28 05:13:49 Pythagoras systemd[1]: Starting fan speed regulator...
Dez 28 05:13:49 Pythagoras fancontrol[3748]: Loading configuration from /etc/fancontrol ...
Dez 28 05:13:49 Pythagoras fancontrol[3748]: Common settings:
Dez 28 05:13:49 Pythagoras fancontrol[3748]:   INTERVAL=10
Dez 28 05:13:49 Pythagoras fancontrol[3748]: Settings for hwmon1/device/pwm1:
Dez 28 05:13:49 Pythagoras fancontrol[3748]:   Depends on hwmon2/device/temp1_input
Dez 28 05:13:49 Pythagoras fancontrol[3748]:   Controls hwmon1/device/fan1_input
Dez 28 05:13:49 Pythagoras fancontrol[3748]:   MINTEMP=50
Dez 28 05:13:49 Pythagoras fancontrol[3748]:   MAXTEMP=75
Dez 28 05:13:49 Pythagoras fancontrol[3748]:   MINSTART=150
Dez 28 05:13:49 Pythagoras fancontrol[3748]:   MINSTOP=150
Dez 28 05:13:49 Pythagoras fancontrol[3748]:   MINPWM=150
Dez 28 05:13:49 Pythagoras fancontrol[3748]:   MAXPWM=250
Dez 28 05:13:49 Pythagoras systemd[1]: Started fan speed regulator.
Dez 28 05:13:49 Pythagoras fancontrol[3825]: Loading configuration from /etc/fancontrol ...
Dez 28 05:13:49 Pythagoras fancontrol[3825]: Common settings:
Dez 28 05:13:49 Pythagoras fancontrol[3825]:   INTERVAL=10
Dez 28 05:13:49 Pythagoras fancontrol[3825]: Settings for hwmon1/device/pwm1:
Dez 28 05:13:49 Pythagoras fancontrol[3825]:   Depends on hwmon2/device/temp1_input
Dez 28 05:13:49 Pythagoras fancontrol[3825]:   Controls hwmon1/device/fan1_input
Dez 28 05:13:49 Pythagoras fancontrol[3825]:   MINTEMP=50
Dez 28 05:13:49 Pythagoras fancontrol[3825]:   MAXTEMP=75
Dez 28 05:13:49 Pythagoras fancontrol[3825]:   MINSTART=150
Dez 28 05:13:49 Pythagoras fancontrol[3825]:   MINSTOP=150
Dez 28 05:13:49 Pythagoras fancontrol[3825]:   MINPWM=150
Dez 28 05:13:49 Pythagoras fancontrol[3825]:   MAXPWM=250
Dez 28 05:13:49 Pythagoras fancontrol[3825]: Device path of hwmon1 has changed
Dez 28 05:13:49 Pythagoras fancontrol[3825]: Device path of hwmon2 has changed
Dez 28 05:13:49 Pythagoras fancontrol[3825]: Device name of hwmon1 has changed
Dez 28 05:13:49 Pythagoras fancontrol[3825]: Device name of hwmon2 has changed
Dez 28 05:13:49 Pythagoras fancontrol[3825]: Configuration appears to be outdated, please run pwmconfig again
Dez 28 05:13:49 Pythagoras systemd[1]: fancontrol.service: Main process exited, code=exited, status=1/FAILURE
Dez 28 05:13:49 Pythagoras systemd[1]: fancontrol.service: Failed with result 'exit-code'.
Dez 28 05:13:49 Pythagoras lircd[1180]: lircd-0.10.1[1180]: Error: No /sys/class/rc/ devices found
Dez 28 05:13:49 Pythagoras lircd-0.10.1[1180]: Error: No /sys/class/rc/ devices found