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6th chunk of `init.man`
83925f24d1f0a0cf23f1d3a9e0424d570c66041aba9b2ee30000000100000fac
         This signal is ignored by systemd user managers.

       SIGPWR
           When this signal is received the systemd manager will start the sigpwr.target unit. This is mostly equivalent to systemctl start sigpwr.target.

       SIGUSR1
           When this signal is received the systemd manager will try to reconnect to the D-Bus bus.

       SIGUSR2
           When this signal is received the systemd manager will log its complete state in human-readable form. The data logged is the same as printed by systemd-analyze dump.

       SIGHUP
           Reloads the complete daemon configuration. This is mostly equivalent to systemctl daemon-reload.

       SIGRTMIN+0
           Enters default mode, starts the default.target unit. This is mostly equivalent to systemctl isolate default.target.

       SIGRTMIN+1
           Enters rescue mode, starts the rescue.target unit. This is mostly equivalent to systemctl isolate rescue.target.

       SIGRTMIN+2
           Enters emergency mode, starts the emergency.service unit. This is mostly equivalent to systemctl isolate emergency.service.

       SIGRTMIN+3
           Halts the machine, starts the halt.target unit. This is mostly equivalent to systemctl start halt.target --job-mode=replace-irreversibly.

       SIGRTMIN+4
           Powers off the machine, starts the poweroff.target unit. This is mostly equivalent to systemctl start poweroff.target --job-mode=replace-irreversibly.

       SIGRTMIN+5
           Reboots the machine, starts the reboot.target unit. This is mostly equivalent to systemctl start reboot.target --job-mode=replace-irreversibly.

       SIGRTMIN+6
           Reboots the machine via kexec, starts the kexec.target unit. This is mostly equivalent to systemctl start kexec.target --job-mode=replace-irreversibly.

       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
           Sets the service manager's log level to "debug", in a fashion equivalent to systemd.log_level=debug on the kernel command line.

       SIGRTMIN+23
           Restores the log level to its configured value. The configured value is derived from – in order of priority – the value specified with systemd.log-level= on the kernel command line, or the value specified with
           LogLevel= in the configuration file, or the built-in default of "info".

       SIGRTMIN+24
           Immediately exits the manager (only available for --user instances).

       SIGRTMIN+25
           Upon receiving this signal the systemd manager will reexecute itself. This is mostly equivalent to systemctl daemon-reexec except that it will be done asynchronously.

           The systemd system manager treats this signal the same way as SIGTERM.

       SIGRTMIN+26
           Restores the log target to its configured value. The configured value is derived from – in order of priority – the value specified with systemd.log-target= on the kernel command line, or the value specified with
           LogTarget= in the configuration file, or the built-in default.

       SIGRTMIN+27, SIGRTMIN+28
           Sets the log target to "console" on SIGRTMIN+27 (or "kmsg" on SIGRTMIN+28), in a fashion equivalent to systemd.log_target=console (or systemd.log_target=kmsg on SIGRTMIN+28) on the kernel command line.

ENVIRONMENT
       The environment block for the system manager is initially set by the kernel. (In particular, "key=value" assignments on the kernel command line are turned into environment variables
Title: Systemd Signal Handling and Environment
Summary
Systemd reacts to a variety of signals. SIGPWR starts sigpwr.target, SIGUSR1 attempts to reconnect to the D-Bus bus, SIGUSR2 logs the manager's complete state, and SIGHUP reloads the daemon configuration. Several real-time signals (SIGRTMIN+n) trigger specific actions such as entering different modes (default, rescue, emergency), halting, powering off, or rebooting the machine. Some real-time signals trigger immediate actions like halting, powering off, or rebooting. Other real-time signals control the display of status messages on the console, the service manager's log level, cause immediate exit, re-execution, or control the log target. The environment block for the system manager is initially set by the kernel.