I found out the degraded service: It is smartmontools.service
root@rk3318-h96max:/dev# systemctl --failed
UNIT LOAD ACTIVE SUB DESCRIPTION
● smartmontools.service loaded "failed failed" Self Monitoring and Reporting Tech
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.
Further investigation suggested that it appears the EMMC (where I installed Armbian) cannot be scanned by smartmontools.
root@rk3318-h96max:/dev# systemctl status smartmontools.service
× smartmontools.service - Self Monitoring and Reporting Technology (SMART) Daemon
Loaded: loaded (/lib/systemd/system/smartmontools.service; enabled; preset: enabled)
Active: failed (Result: exit-code) since Thu 2022-08-18 09:00:19 HKT; 22min ago
Docs: man:smartd(8)
man:smartd.conf(5)
Process: 2333 ExecStart=/usr/sbin/smartd -n $smartd_opts (code=exited, status=17)
Main PID: 2333 (code=exited, status=17)
Status: "No devices to monitor"
CPU: 194ms
Aug 18 09:00:19 rk3318-h96max smartd[2333]: smartd 7.3 2022-02-28 r5338 [aarch64-linux-5.15.60-rockchip64] (local build)
Aug 18 09:00:19 rk3318-h96max smartd[2333]: Copyright (C) 2002-22, Bruce Allen, Christian Franke, www.smartmontools.org
Aug 18 09:00:19 rk3318-h96max smartd[2333]: Opened configuration file /etc/smartd.conf
Aug 18 09:00:19 rk3318-h96max smartd[2333]: Drive: DEVICESCAN, implied '-a' Directive on line 21 of file /etc/smartd.conf
Aug 18 09:00:19 rk3318-h96max smartd[2333]: Configuration file /etc/smartd.conf was parsed, found DEVICESCAN, scanning devices
Aug 18 09:00:19 rk3318-h96max smartd[2333]: In the system's table of devices NO devices found to scan
Aug 18 09:00:19 rk3318-h96max smartd[2333]: "Unable to monitor any SMART enabled devices. Try debug (-d) option. Exiting... "
Aug 18 09:00:19 rk3318-h96max systemd[1]: smartmontools.service: Main process exited, code=exited, status=17/n/a
Aug 18 09:00:19 rk3318-h96max systemd[1]: smartmontools.service: Failed with result 'exit-code'.
Aug 18 09:00:19 rk3318-h96max systemd[1]: Failed to start Self Monitoring and Reporting Technology (SMART) Daemon.
I did some google search, and this discussion suggested that Smartmontools does not support EMMC.
Suppose I should just disable this service, if it's no use to EMMC where I installed Armbian.