anacron.service

    can be used to execute commands periodically, with a frequency specified in days.
    When executed, Anacron reads a list of jobs from a configuration file, normally /etc/anacrontab
    ExecStart=/usr/sbin/anacron -dsq

apport.service

    Documentation=man:systemd-sysv-generator(8)
    a generator that creates wrapper .service units for SysV init[1] scripts in /etc/init.d/* at boot and when configuration of the system manager is reloaded.
    ExecStart=/etc/init.d/apport start
    
    # journalctl -b -u apport.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:08:09 CST. --
    9月 26 09:17:35 eric-vm-dev systemd[1]: Starting LSB: automatic crash report generation...
    9月 26 09:17:39 eric-vm-dev apport[837]:  * Starting automatic crash report generation: apport
    9月 26 09:17:40 eric-vm-dev apport[837]:    ...done.
    9月 26 09:17:40 eric-vm-dev systemd[1]: Started LSB: automatic crash report generation.

grub-common.service

    Documentation=man:systemd-sysv-generator(8)
    ExecStart=/etc/init.d/grub-common start
    
    # journalctl -b -u grub-common.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:08:09 CST. --
    9月 26 09:17:35 eric-vm-dev systemd[1]: Starting LSB: Record successful boot for GRUB...
    9月 26 09:17:39 eric-vm-dev grub-common[874]:  * Recording successful boot for GRUB
    9月 26 09:17:41 eric-vm-dev grub-common[874]:    ...done.
    9月 26 09:17:41 eric-vm-dev systemd[1]: Started LSB: Record successful boot for GRUB.

avahi-daemon.service

    Avahi mDNS/DNS-SD Stack
    BusName=org.freedesktop.Avahi
    ExecStart=/usr/sbin/avahi-daemon -s

containerd.service

    Documentation=https://containerd.io
    ExecStart=/usr/bin/containerd
    
    # journalctl -b -u containerd.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:08:09 CST. --
    9月 26 09:17:50 eric-vm-dev systemd[1]: Starting containerd container runtime...
    9月 26 09:17:50 eric-vm-dev systemd[1]: Started containerd container runtime.

cron.service

    Description=Regular background program processing daemon
    is started automatically from /etc/init.d on entering multi-user runlevels
    ExecStart=/usr/sbin/cron -f $EXTRA_OPTS
    
    # journalctl -b -u cron.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:08:09 CST. --
    9月 26 09:17:36 eric-vm-dev systemd[1]: Started Regular background program processing daemon.
    9月 26 09:17:36 eric-vm-dev cron[901]: (CRON) INFO (pidfile fd = 3)
    9月 26 09:17:37 eric-vm-dev cron[901]: (CRON) INFO (Running @reboot jobs)

dbus.service

    the D-Bus message bus daemon
    D-Bus is first a library that provides one-to-one communication between any two applications, dbus-daemon is an application that uses this library to implement a message bus daemon. 
    Multiple programs connect to the message bus daemon and can exchange messages with one another.
    ExecStart=/usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only

irqbalance.service

    Description=irqbalance daemon
    EnvironmentFile=-/etc/default/irqbalance
    ExecStart=/usr/sbin/irqbalance --foreground $IRQBALANCE_ARGS
    
    # journalctl -b -u irqbalance.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:08:09 CST. --
    9月 26 09:17:35 eric-vm-dev systemd[1]: Started irqbalance daemon.

kerneloops.service

    Description=Tool to automatically collect and submit kernel crash signatures
    EnvironmentFile=-/etc/default/kerneloops
    Type=forking
    ExecStartPre=/usr/sbin/kerneloops --test
    ExecStart=/usr/sbin/kerneloops $DAEMON_ARGS
    
    # journalctl -b -u kerneloops.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:08:09 CST. --
    9月 26 09:17:35 eric-vm-dev systemd[1]: Starting Tool to automatically collect and submit kernel crash signatures...
    9月 26 09:17:39 eric-vm-dev systemd[1]: kerneloops.service: Found left-over process 880 (kerneloops) in control group while starting unit. Ignoring.
    9月 26 09:17:39 eric-vm-dev systemd[1]: This usually indicates unclean termination of a previous run, or service implementation deficiencies.
    9月 26 09:17:39 eric-vm-dev systemd[1]: Started Tool to automatically collect and submit kernel crash signatures.

networkd-dispatcher.service

    Description=Dispatcher daemon for systemd-networkd
    ExecStart=/usr/bin/networkd-dispatcher $networkd_dispatcher_args
    # Load /etc/default/networkd-dispatcher
    EnvironmentFile=-/etc/default/%p
    
    # journalctl -b -u networkd-dispatcher.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:15:07 CST. --
    9月 26 09:17:39 eric-vm-dev systemd[1]: Starting Dispatcher daemon for systemd-networkd...
    9月 26 09:17:50 eric-vm-dev networkd-dispatcher[1077]: WARNING: systemd-networkd is not running, output will be incomplete.
    9月 26 09:17:50 eric-vm-dev systemd[1]: Started Dispatcher daemon for systemd-networkd.

NetworkManager.service

    attempts to make networking configuration and operation as painless and automatic as possible by managing the primary network connection and other network interfaces, 
    like Ethernet, WiFi, and Mobile Broadband devices.
    Type=dbus
    BusName=org.freedesktop.NetworkManager
    ExecReload=/usr/bin/dbus-send --print-reply --system --type=method_call --dest=org.freedesktop.NetworkManager /org/freedesktop/NetworkManager org.freedesktop.NetworkManager.Reload uint32:0    
    ExecStart=/usr/sbin/NetworkManager --no-daemon
    
    # journalctl -b -u NetworkManager.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:15:07 CST. --
    9月 26 09:17:39 eric-vm-dev systemd[1]: Starting Network Manager...
    9月 26 09:17:48 eric-vm-dev NetworkManager[1056]: <info>  [1632619068.5956] NetworkManager (version 1.10.6) is starting... (for the first time)
    9月 26 09:17:48 eric-vm-dev NetworkManager[1056]: <info>  [1632619068.5968] Read config: /etc/NetworkManager/NetworkManager.conf (lib: 10-dns-resolved.conf, 20-connectivity-ubuntu.conf, no-mac-addr-change.conf) (run: 10-globally-managed
    9月 26 09:17:48 eric-vm-dev NetworkManager[1056]: <info>  [1632619068.8560] manager[0x56062bf0e060]: monitoring kernel firmware directory '/lib/firmware'.
    9月 26 09:17:48 eric-vm-dev NetworkManager[1056]: <info>  [1632619068.8561] monitoring ifupdown state file '/run/network/ifstate'.
    9月 26 09:17:50 eric-vm-dev NetworkManager[1056]: <info>  [1632619070.1030] hostname: hostname: using hostnamed
    9月 26 09:17:50 eric-vm-dev NetworkManager[1056]: <info>  [1632619070.1031] hostname: hostname changed from (none) to "eric-vm-dev"
    9月 26 09:17:50 eric-vm-dev NetworkManager[1056]: <info>  [1632619070.1037] dns-mgr[0x56062bf29940]: init: dns=systemd-resolved, rc-manager=symlink, plugin=systemd-resolved
    9月 26 09:17:50 eric-vm-dev NetworkManager[1056]: <info>  [1632619070.1042] manager[0x56062bf0e060]: rfkill: WiFi hardware radio set enabled
    9月 26 09:17:50 eric-vm-dev NetworkManager[1056]: <info>  [1632619070.1043] manager[0x56062bf0e060]: rfkill: WWAN hardware radio set enabled
    9月 26 09:17:50 eric-vm-dev systemd[1]: Started Network Manager.
    ......

ondemand.service

    Description=Set the CPU Frequency Scaling governor
    ExecStart=/lib/systemd/set-cpufreq

plymouth-quit-wait.service

    Description=Hold until boot process finishes up
    ExecStart=-/bin/plymouth --wait
    
    # journalctl -b -u plymouth-quit-wait.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:17:01 CST. --
    9月 26 09:17:50 eric-vm-dev systemd[1]: Starting Hold until boot process finishes up...
    9月 26 09:18:29 eric-vm-dev systemd[1]: Started Hold until boot process finishes up.

plymouth-quit.service

    Description=Terminate Plymouth Boot Screen
    ExecStart=-/bin/plymouth quit

rsync.service

    Description=fast remote file copy program daemon
    ExecStart=/usr/bin/rsync --daemon --no-detach

rsyslog.service

    a system utility providing support for message logging.  
    Support of both internet and unix domain sockets enables this utility to support both local and remote logging.
    ExecStart=/usr/sbin/rsyslogd -n
    
    # journalctl -b -u rsyslog.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:17:01 CST. --
    9月 26 09:17:35 eric-vm-dev systemd[1]: Starting System Logging Service...
    9月 26 09:17:37 eric-vm-dev rsyslogd[848]: imuxsock: Acquired UNIX socket '/run/systemd/journal/syslog' (fd 3) from systemd.  [v8.32.0]
    9月 26 09:17:37 eric-vm-dev rsyslogd[848]: rsyslogd's groupid changed to 106
    9月 26 09:17:37 eric-vm-dev rsyslogd[848]: rsyslogd's userid changed to 102
    9月 26 09:17:37 eric-vm-dev rsyslogd[848]: [origin software="rsyslogd" swVersion="8.32.0" x-pid="848" x-info="http://www.rsyslog.com"] start
    9月 26 09:17:39 eric-vm-dev systemd[1]: Started System Logging Service.
    9月 26 09:22:34 eric-vm-dev rsyslogd[848]: [origin software="rsyslogd" swVersion="8.32.0" x-pid="848" x-info="http://www.rsyslog.com"] rsyslogd was HUPed

systemd-logind.service

    a system service that manages user logins
    User sessions are registered with logind via the pam_systemd(8) PAM module.
    See logind.conf(5) for information about the configuration of this service.
    ExecStart=/lib/systemd/systemd-logind
    
    # journalctl -b -u systemd-logind.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:17:01 CST. --
    9月 26 09:17:35 eric-vm-dev systemd[1]: Starting Login Service...
    9月 26 09:17:35 eric-vm-dev systemd-logind[838]: New seat seat0.
    9月 26 09:17:35 eric-vm-dev systemd-logind[838]: Watching system buttons on /dev/input/event0 (Power Button)
    9月 26 09:17:35 eric-vm-dev systemd-logind[838]: Watching system buttons on /dev/input/event1 (AT Translated Set 2 keyboard)
    9月 26 09:17:39 eric-vm-dev systemd[1]: Started Login Service.
    9月 26 09:17:57 eric-vm-dev systemd-logind[838]: New session c1 of user gdm.
    9月 26 10:14:37 eric-vm-dev systemd-logind[838]: New session 2 of user eric.

systemd-networkd.service

    a system service that manages networks. It detects and configures network devices as they appear, as well as creating virtual network devices.
    ExecStart=!!/lib/systemd/systemd-networkd

systemd-user-sessions.service

    a service that controls user logins through pam_nologin(8). After basic system initialization is complete, it removes /run/nologin, thus permitting logins. 
    Before system shutdown, it creates /run/nologin, thus prohibiting further logins.
    ExecStart=/lib/systemd/systemd-user-sessions start
    
    # journalctl -b -u systemd-user-sessions.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:17:01 CST. --
    9月 26 09:17:50 eric-vm-dev systemd[1]: Starting Permit User Sessions...
    9月 26 09:17:50 eric-vm-dev systemd[1]: Started Permit User Sessions.

thermald.service

    Description=Thermal Daemon Service
    Type=dbus
    SuccessExitStatus=1
    BusName=org.freedesktop.thermald
    ExecStart=/usr/sbin/thermald --no-daemon --dbus-enable
    
    # journalctl -b -u thermald.service
    -- Logs begin at Mon 2019-06-03 16:58:43 CST, end at Wed 2021-09-29 13:17:01 CST. --
    9月 26 09:17:35 eric-vm-dev systemd[1]: Starting Thermal Daemon Service...
    9月 26 09:17:39 eric-vm-dev thermald[873]: NO RAPL sysfs present
    9月 26 09:17:39 eric-vm-dev thermald[873]: 13 CPUID levels; family:model:stepping 0x6:2a:7 (6:42:7)
    9月 26 09:17:39 eric-vm-dev thermald[873]: Polling mode is enabled: 4
    9月 26 09:17:39 eric-vm-dev thermald[873]: Thermal DTS: No coretemp sysfs found
    9月 26 09:17:39 eric-vm-dev systemd[1]: Started Thermal Daemon Service.
    9月 26 09:17:40 eric-vm-dev thermald[873]: Thermal DTS or hwmon: No Zones present Need to configure manually
    9月 26 09:17:40 eric-vm-dev thermald[873]: No thermal sensors found
    9月 26 09:17:40 eric-vm-dev thermald[873]: THD engine start failed

getty-static.service

    getty on tty2-tty6 if dbus and logind are not available
    ExecStart=/bin/systemctl --no-block start getty@tty2.service getty@tty3.service getty@tty4.service getty@tty5.service getty@tty6.service

getty@tty1.service

    a generator that automatically instantiates serial-getty@.service on the kernel console(s), if they can function as ttys and are not provided by the virtual console subsystem.
    ExecStart=-/sbin/agetty -o '-p -- \\u' --noclear %I $TERM