be set when invoking the pager, and the pager shall disable commands that open or create new files or start
           new subprocesses. When $SYSTEMD_PAGERSECURE is not set at all, pagers which are not known to implement secure mode will not be used. (Currently only less(1) implements secure mode.)

           Note: when commands are invoked with elevated privileges, for example under sudo(8) or pkexec(1), care must be taken to ensure that unintended interactive features are not enabled. "Secure" mode for the pager may
           be enabled automatically as describe above. Setting SYSTEMD_PAGERSECURE=0 or not removing it from the inherited environment allows the user to invoke arbitrary commands. Note that if the $SYSTEMD_PAGER or $PAGER
           variables are to be honoured, $SYSTEMD_PAGERSECURE must be set too. It might be reasonable to completely disable the pager using --no-pager instead.

       $SYSTEMD_COLORS
           Takes a boolean argument. When true, systemd and related utilities will use colors in their output, otherwise the output will be monochrome. Additionally, the variable can take one of the following special values:
           "16", "256" to restrict the use of colors to the base 16 or 256 ANSI colors, respectively. This can be specified to override the automatic decision based on $TERM and what the console is connected to.

       $SYSTEMD_URLIFY
           The value must be a boolean. Controls whether clickable links should be generated in the output for terminal emulators supporting this. This can be specified to override the decision that systemd makes based on
           $TERM and other conditions.

       $LISTEN_PID, $LISTEN_FDS, $LISTEN_FDNAMES
           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.

       For further environment variables understood by systemd and its various components, see Known Environment Variables[7].

KERNEL COMMAND LINE
       When run as the system instance, systemd parses a number of options listed below. They can be specified as kernel command line arguments which are parsed from a number of sources depending on the environment in which
       systemd is executed. If run inside a Linux container, these options are parsed from the command line arguments passed 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 and from the "SystemdOptions" EFI variable (on EFI systems) instead. Options from /proc/cmdline have higher priority. The following
       variables are understood:

       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 initrd, while the one that is not prefixed only in the main system.

       systemd.dump_core
           Takes a boolean argument or enables the option if specified without an argument. If enabled, the systemd manager (PID 1) dumps core when it crashes. Otherwise, no core dump is created. Defaults to enabled.

       systemd.crash_chvt
           Takes a positive integer, or a boolean argument. Can be also specified without an argument, with the same effect as a positive boolean. If a positive integer (in the range 1–63) is specified, the system manager
           (PID 1) will activate the specified virtual terminal when it crashes. Defaults to disabled, meaning that no such switch is attempted. If set to enabled, the virtual terminal the kernel messages are written to is
           used instead.