systemd, init

systemd system and service manager

systemd [OPTIONS...]

init [options] {command}

When run as first process on boot (PID 1), acts as init system that brings up and maintains userspace services.
If called as init and a PID that is not 1, executes telinit and passes command line arguments unmodified.
That means init and telinit are mostly equivalent when invoked from normal login sessions. See telinit(8)

When run as system instance, interprets the configuration file system.conf, otherwise user.conf. See systemdsystem.conf(5)
--test Determine startup sequence, dump it and exit. debugging
--dump-configuration-itemsunderstood in unit definition files.
--unit= Set default unit to activate on startup. defaults default.target.
--system|--user --system, even if the process ID is not 1, i.e. systemd is not run as init process.
--user even if the process ID is     1.
For debugging. booting and maintaining a full system
--system mode, but PID not 1. is not supported
--system is only useful with --test.
--dump-coreon crash only as system
--crash-shell on crash only as system
--confirm-spawn no effect when run as user instance.
--show-status=true|false while booting. no effect as user
--log-target= console| journal| syslog| kmsg| journal-or-kmsg| syslog-or-kmsg| null.
--log-level= numerical log level or emerg| alert| crit| err| warning| notice| info| debug
--log-color=true|false Highlight important log messages. If argument omitted, default true.
--log-location= Include code location in log messages.
--default-standard-output=
--default-standard-error=
for all services and sockets, see systemd.exec(5) ).
inherit| null| tty| journal| journal+console| syslog| syslog+console| kmsg| kmsg+console.
If argument omitted --default-standard-output=journal and --default-standard-error=inherit.
-h, --help
--version

CONCEPTS

systemd provides a dependency system between various entities called "units" of 12 different types.
Units encapsulate various objects that are relevant for system boot-up and maintenance. The majority are configured in unit configuration files, whose syntax and basic set of options is described in systemd.unit(5),
some are created automatically from other configuration, dynamically from system state or programmatically at runtime.
Units may be "active" (meaning started, bound, plugged in, ..., depending on the unit type, see below), or "inactive" (meaning stopped, unbound, unplugged, ...), in the process of being activated or deactivated, i.e. between the two states (these states are called "activating", "deactivating"). < br> "failed" which is very similar to "inactive" entered when the service failed (process returned error code on exit, or crashed, or an operation timed out). the cause will be logged,

unit types

Service , start and control daemons see systemd.service(5).
Socket encapsulate local IPC or network sockets, for socket-based activation. systemd.socket(5), socket-based activation Target group or provide well-known synchronization points during boot-up, see systemd.target(5).
Device expose kernel devices may be used to implement device-based activation. see systemd.device(5).
Mount control mount points in the file system, see systemd.mount(5).
Automount provide automount capabilities, for on-demand mounting of file systems as well as parallelized boot-up. See systemd.automount(5).
Snapshot temporarily save the state of the set of systemd units, which later may be restored by activating the saved snapshot unit. systemd.snapshot(5).
Timer units are useful for triggering activation of other units based on timers. You may find details in systemd.timer(5).
Swap similar to mount units and encapsulate memory swap partitions or files of the operating system systemd.swap(5).
Path activate other services when file system objects change or are modified. See systemd.path(5).
Slice group units which manage system processes (such as service and scope units) in a hierarchical tree for resource management purposes. See systemd.slice(5).
Scope similar to service units, manage foreign processes . See systemd.scope(5).
Units are named as their configuration files. systemd.special(7).

systemd knows various kinds of dependencies, including positive and negative requirement dependencies (i.e. Requires= and Conflicts=) as well as ordering dependencies (After= and Before=). NB: ordering and requirement dependencies are orthogonal. If only a requirement dependency exists between two units (e.g. foo.service requires bar.service), but no ordering dependency (e.g. foo.service after bar.service) and both are requested to start, they will be started in parallel. It is a common pattern that both requirement and ordering dependencies are placed between two units. Also note that the majority of dependencies are implicitly created and maintained by systemd. In most cases, it should be unnecessary to declare additional dependencies manually, however it is possible to do this.

Application programs and units (via dependencies) may request state changes of units. In systemd, these requests are encapsulated as 'jobs' and maintained in a job queue. Jobs may succeed or can fail, their execution is ordered based on the ordering dependencies of the units they have been scheduled for.

On boot systemd activates the target unit default.target whose job is to activate on-boot services and other on-boot units by pulling them in via dependencies. Usually the unit name is just an alias (symlink) for either graphical.target (for fully-featured boots into the UI) or multi-user.target (for limited console-only boots for use in embedded or server environments, or similar; a subset of graphical.target). However, it is at the discretion of the administrator to configure it as an alias to any other target unit. See systemd.special(7) for details about these target units.

Processes systemd spawns are placed in individual Linux control groups named after the unit which they belong to in the private systemd hierarchy. (see cgroups.txt[1] for more information about control groups, or short "cgroups"). systemd uses this to effectively keep track of processes. Control group information is maintained in the kernel, and is accessible via the file system hierarchy (beneath /sys/fs/cgroup/systemd/), or in tools such as ps(1) (ps xawf -eo pid,user,cgroup,args is particularly useful to list all processes and the systemd units they belong to.).

systemd is compatible with the SysV init system to a large degree: SysV init scripts are supported and simply read as an alternative (though limited) configuration file format. The SysV /dev/initctl interface is provided, and compatibility implementations of the various SysV client tools are available. In addition to that, various established Unix functionality such as /etc/fstab or the utmp database are supported.

systemd has a minimal transaction system: if a unit is requested to start up or shut down it will add it and all its dependencies to a temporary transaction. Then, it will verify if the transaction is consistent (i.e. whether the ordering of all units is cycle-free). If it is not, systemd will try to fix it up, and removes non-essential jobs from the transaction that might remove the loop. Also, systemd tries to suppress non-essential jobs in the transaction that would stop a running service. Finally it is checked whether the jobs of the transaction contradict jobs that have already been queued, and optionally the transaction is aborted then. If all worked out and the transaction is consistent and minimized in its impact it is merged with all already outstanding jobs and added to the run queue. Effectively this means that before executing a requested operation, systemd will verify that it makes sense, fixing it if possible, and only failing if it really cannot work.

Systemd contains native implementations of various tasks that need to be executed as part of the boot process. For example, it sets the hostname or configures the loopback network device. It also sets up and mounts various API file systems, such as /sys or /proc.

For more information about the concepts and ideas behind systemd, please refer to the Original Design Document[2].

Note that some but not all interfaces provided by systemd are covered by the Interface Stability Promise[3].

Units may be generated dynamically at boot and system manager reload time, for example based on other configuration files or parameters passed on the kernel command line. For details see the Generators Specification[4].

Systems which invoke systemd in a container or initrd environment should implement the Container Interface[5] or initrd Interface[6] specifications, respectively.

DIRECTORIES

       System unit directories
           The systemd system manager reads unit configuration from various directories. Packages that want to install unit files shall
           place them in the directory returned by pkg-config systemd --variable=systemdsystemunitdir. Other directories checked are
           /usr/local/lib/systemd/system and /lib/systemd/system. User configuration always takes precedence.  pkg-config systemd
           --variable=systemdsystemconfdir returns the path of the system configuration directory. Packages should alter the content of
           these directories only with the enable and disable commands of the systemctl(1) tool. Full list of directories is provided in
           systemd.unit(5).

       User unit directories
           Similar rules apply for the user unit directories. However, here the XDG Base Directory specification[7] is followed to find
           units. Applications should place their unit files in the directory returned by pkg-config systemd
           --variable=systemduserunitdir. Global configuration is done in the directory reported by pkg-config systemd
           --variable=systemduserconfdir. The enable and disable commands of the systemctl(1) tool can handle both global (i.e. for all
           users) and private (for one user) enabling/disabling of units. Full list of directories is provided in systemd.unit(5).

       SysV init scripts directory
           The location of the SysV init script directory varies between distributions. If systemd cannot find a native unit file for a
           requested service, it will look for a SysV init script of the same name (with the .service suffix removed).

       SysV runlevel link farm directory
           The location of the SysV runlevel link farm directory varies between distributions. systemd will take the link farm into
           account when figuring out whether a service shall be enabled. Note that a service unit with a native unit configuration file
           cannot be started by activating it in the SysV runlevel link farm.

SIGNALS

SIGTERM serializes its state, reexecutes itself and deserializes the saved state again. like systemctl daemon-reexec. systemd user managers will start the exit.target unit when this signal is received. like systemctl --user start exit.target.
SIGINT will start the ctrl-alt-del.target unit. This is mostly equivalent to systemctl start ctl-alt-del.target. systemd user managers treat this signal the same way as SIGTERM.
SIGWINCH start the kbrequest.target unit. This is mostly equivalent to systemctl start kbrequest.target. This signal is ignored by systemd user managers.
SIGPWR start the sigpwr.target unit. like systemctl start sigpwr.target.
SIGUSR1 try to reconnect to the D-Bus bus.
SIGUSR2 log its complete state in human readable form. The data logged is the same as printed by systemctl dump.
SIGHUP Reloads the complete daemon configuration. like systemctl daemon-reload.
SIGRTMIN+0 Enters default mode, starts the default.target unit. like systemctl start default.target.
SIGRTMIN+1 Enters rescue mode, starts the rescue.target unit. like systemctl isolate rescue.target.
SIGRTMIN+2 Enters emergency mode, starts the emergency.service unit. like systemctl isolate emergency.service.
SIGRTMIN+3 Halts the machine, starts the halt.target unit. like systemctl start halt.target.
SIGRTMIN+4 Powers off the machine, starts the poweroff.target unit. like systemctl start poweroff.target.
SIGRTMIN+5 Reboots the machine, starts the reboot.target unit. like systemctl start reboot.target.
SIGRTMIN+6 Reboots the machine via kexec, starts the kexec.target unit. like systemctl start kexec.target.
SIGRTMIN+13 Immediately halts the machine.
SIGRTMIN+14 Immediately powers off the machine.
SIGRTMIN+15 Immediately reboots the machine.
SIGRTMIN+16 Immediately reboots the machine with kexec.
SIGRTMIN+20 Enables display of status messages on the console, as controlled via systemd.show_status=1 on the kernel command line.
SIGRTMIN+21 Disables display of status messages on the console, as controlled via systemd.show_status=0 on the kernel command line.
SIGRTMIN+22, SIGRTMIN+23 Sets the log level to "debug" (or "info" on SIGRTMIN+23), as controlled via systemd.log_level=debug (or systemd.log_level=info on SIGRTMIN+23) on the kernel command line.
SIGRTMIN+24 Immediately exits the manager (only available for --user instances).
SIGRTMIN+26, SIGRTMIN+27, SIGRTMIN+28, SIGRTMIN+29 Sets the log level to "journal-or-kmsg" (or "console" on SIGRTMIN+27, "kmsg" on SIGRTMIN+28, or "syslog-or-kmsg" on SIGRTMIN+29), as controlled via systemd.log_target=journal-or-kmsg (or systemd.log_target=console on SIGRTMIN+27, systemd.log_target=kmsg on SIGRTMIN+28, or systemd.log_target=syslog-or-kmsg on SIGRTMIN+29) on the kernel command line.

ENVIRONMENT

       $SYSTEMD_LOG_LEVEL
           systemd reads the log level from this environment variable. This can be overridden with --log-level=.

       $SYSTEMD_LOG_TARGET
           systemd reads the log target from this environment variable. This can be overridden with --log-target=.

       $SYSTEMD_LOG_COLOR
           Controls whether systemd highlights important log messages. This can be overridden with --log-color=.

       $SYSTEMD_LOG_LOCATION
           Controls whether systemd prints the code location along with log messages. This can be overridden with --log-location=.

       $XDG_CONFIG_HOME, $XDG_CONFIG_DIRS, $XDG_DATA_HOME, $XDG_DATA_DIRS
           The systemd user manager uses these variables in accordance to the XDG Base Directory specification[7] to find its
           configuration.

       $SYSTEMD_UNIT_PATH
           Controls where systemd looks for unit files.

       $SYSTEMD_SYSVINIT_PATH
           Controls where systemd looks for SysV init scripts.

       $SYSTEMD_SYSVRCND_PATH
           Controls where systemd looks for SysV init script runlevel link farms.

       $LISTEN_PID, $LISTEN_FDS
           Set by systemd for supervised processes during socket-based activation. See sd_listen_fds(3) for more information.

       $NOTIFY_SOCKET
           Set by systemd for supervised processes for status and start-up completion notification. See sd_notify(3) for more
           information.

KERNEL COMMAND LINE

When run as system instance systemd parses a number of kernel command line arguments[8]:
       systemd.unit=, rd.systemd.unit=
           Overrides the unit to activate on boot. Defaults to default.target. This may be used to temporarily boot into a different
           boot unit, for example rescue.target or emergency.service. See systemd.special(7) for details about these units. The option
           prefixed with "rd."  is honored only in the initial RAM disk (initrd), while the one that is not prefixed only in the main
           system.

       systemd.dump_core=
           Takes a boolean argument. If true, systemd dumps core when it crashes. Otherwise, no core dump is created. Defaults to true.

       systemd.crash_shell=
           Takes a boolean argument. If true, systemd spawns a shell when it crashes. Otherwise, no shell is spawned. Defaults to false,
           for security reasons, as the shell is not protected by any password authentication.

       systemd.crash_chvt=
           Takes an integer argument. If positive systemd activates the specified virtual terminal when it crashes. Defaults to -1.

       systemd.confirm_spawn=
           Takes a boolean argument. If true, asks for confirmation when spawning processes. Defaults to false.

       systemd.show_status=
           Takes a boolean argument or the constant auto. If true, shows terse service status updates on the console during bootup.
           auto behaves like  false until a service fails or there is a significant delay in boot. Defaults to true, unless quiet is
           passed as kernel command line option in which case it defaults to auto.

       systemd.log_target=, systemd.log_level=, systemd.log_color=, systemd.log_location=
           Controls log output, with the same effect as the $SYSTEMD_LOG_TARGET, $SYSTEMD_LOG_LEVEL, $SYSTEMD_LOG_COLOR,
           $SYSTEMD_LOG_LOCATION environment variables described above.

       systemd.default_standard_output=, systemd.default_standard_error=
           Controls default standard output and error output for services, with the same effect as the --default-standard-output= and
           --default-standard-error= command line arguments described above, respectively.

       systemd.setenv=
           Takes a string argument in the form VARIABLE=VALUE. May be used to set default environment variables to add to forked child
           processes. May be used more than once to set multiple variables.

       quiet
           Turn off status output at boot, much like  systemd.show_status=false would. Note that this option is also read by the kernel
           itself and disables kernel log output. Passing this option hence turns off the usual output from both the system manager and
           the kernel.

       debug
           Turn on debugging output. This is equivalent to systemd.log_level=debug. Note that this option is also read by the kernel
           itself and enables kernel debug output. Passing this option hence turns on the debug output from both the system manager and
           the kernel.

       -b, emergency
           Boot into emergency mode. This is equivalent to systemd.unit=emergency.target and provided for compatibility reasons and to
           be easier to type.

       single, s, S, 1
           Boot into rescue mode. This is equivalent to systemd.unit=rescue.target and provided for compatibility reasons and to be
           easier to type.

       2, 3, 4, 5
           Boot into the specified legacy SysV runlevel. These are equivalent to systemd.unit=runlevel2.target,
           systemd.unit=runlevel3.target, systemd.unit=runlevel4.target, and systemd.unit=runlevel5.target, respectively, and provided
           for compatibility reasons and to be easier to type.

       locale.LANG=, locale.LANGUAGE=, locale.LC_CTYPE=, locale.LC_NUMERIC=, locale.LC_TIME=, locale.LC_COLLATE=, locale.LC_MONETARY=,
       locale.LC_MESSAGES=, locale.LC_PAPER=, locale.LC_NAME=, locale.LC_ADDRESS=, locale.LC_TELEPHONE=, locale.LC_MEASUREMENT=,
       locale.LC_IDENTIFICATION=
           Set the system locale to use. This overrides the settings in /etc/locale.conf. For more information see locale.conf(5) and
           locale(7).

       For other kernel command line parameters understood by components of the core OS, please refer to kernel-command-line(7).

SOCKETS AND FIFOS

       /run/systemd/notify
           Daemon status notification socket. This is an AF_UNIX datagram socket and is used to implement the daemon notification logic
           as implemented by sd_notify(3).

       /run/systemd/shutdownd
           Used internally by the shutdown(8) tool to implement delayed shutdowns. This is an AF_UNIX datagram socket.

       /run/systemd/private
           Used internally as communication channel between systemctl(1) and the systemd process. This is an AF_UNIX stream socket. This
           interface is private to systemd and should not be used in external projects.

       /dev/initctl
           Limited compatibility support for the SysV client interface, as implemented by the systemd-initctl.service unit. This is a
           named pipe in the file system. This interface is obsolete and should not be used in new applications.
SEE ALSO
       The systemd Homepage[9], systemd-system.conf(5), locale.conf(5), systemctl(1), journalctl(1), systemd-notify(1), daemon(7), sd-
       daemon(3), systemd.unit(5), systemd.special(5), pkg-config(1), kernel-command-line(7), bootup(7), systemd.directives(7)

NOTES
        1. cgroups.txt https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt

        2. Original Design Document http://0pointer.de/blog/projects/systemd.html

        3. Interface Stability Promise http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise

        4. Generators Specification http://www.freedesktop.org/wiki/Software/systemd/Generators

        5. Container Interface http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface

        6. initrd Interface http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface

        7. XDG Base Directory specification http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html

        8. If run inside a Linux container these arguments may be passed as command line arguments to systemd itself, next to any of the
           command line options listed in the Options section above. If run outside of Linux containers, these arguments are parsed from
           /proc/cmdline instead.

        9. systemd Homepage http://www.freedesktop.org/wiki/Software/systemd/

systemd 215                                                                                                                   SYSTEMD(1)
pi-0-roof:/home/dgerman > 

/etc/systemd > ls -1
bootchart.conf
journald.conf
logind.conf
network
ntp-units.d
resolved.conf
system
system.conf
timesyncd.conf
user
user.conf



/etc/systemd/system LSS=/lib/systemd/system autologin@.service dbus-org.bluez.service LSS/bluetooth.service dbus-org.freedesktop.Avahi.service LSS/iavahi-daemon.service default.target LSS/multi-user.target bluetooth.target.wants: bluetooth.service LSS/bluetooth.service dhcpcd.service.d: dhcpcd5 LSS/dhcpcd.service getty.target.wants getty@tty1.service LSS/getty@.service getty@tty1.service.d: noclear.conf halt.target.wants: hwclock-save.service LSS/hwclock-save.service rpi-display-backlight.service LSS/rpi-display-backlight.service multi-user.target.wants: avahi-daemon.service LSS/avahi-daemon.service cron.service LSS/cron.service dhcpcd.service LSS/dhcpcd.service hciuart.service LSS/hciuart.service regenerate_ssh_host_keys.service LSS/regenerate_ssh_host_keys.service remote-fs.target LSS/remote-fs.target rsyslog.service LSS/rsyslog.service ssh.service LSS/ssh.service sshswitch.service LSS/sshswitch.service poweroff.target.wants: hwclock-save.service LSS/hwclock-save.service rpi-display-backlight.service LSS/rpi-display-backlight.service rc-local.service.d: ttyoutput.conf reboot.target.wants: hwclock-save.service LSS/hwclock-save.service rpi-display-backlight.service LSS/rpi-display-backlight.service sockets.target.wants: avahi-daemon.socket LSS/avahi-daemon.socket sysinit.target.wants: fake-hwclock.service LSS/fake-hwclock.service syslog.service LSS/rsyslog.service

rsyslog.service

[Unit] Description=System Logging Service Requires=syslog.socket Documentation=man:rsyslogd(8) Documentation=http://www.rsyslog.com/doc/ [Service] Type=notify ExecStart=/usr/sbin/rsyslogd -n StandardOutput=null Restart=on-failure [Install] WantedBy=multi-user.target Alias=syslog.service