systemd-debug-generator — Generator for enabling a runtime debug shell and masking specific units at boot
/usr/lib/systemd/system-generators/systemd-debug-generator
systemd-debug-generator is a generator
    that reads the kernel command line and understands three
    options:
If the systemd.mask= or rd.systemd.mask=
    option is specified and followed by a unit name, this unit is
    masked for the runtime, similar to the effect of
    systemctl(1)'s
    mask command. This is useful to boot with
    certain units removed from the initial boot transaction for
    debugging system startup. May be specified more than once.
    rd.systemd.mask= is honored only by initial
    RAM disk (initrd) while systemd.mask= is
    honored only in the main system.
If the systemd.wants= or
    rd.systemd.wants= option is specified
    and followed by a unit name, a start job for this unit is added to
    the initial transaction. This is useful to start one or more
    additional units at boot. May be specified more than once.
    rd.systemd.wants= is honored only by initial
    RAM disk (initrd) while systemd.wants= is
    honored only in the main system.
If the systemd.debug_shell or
    rd.systemd.debug_shell option is
    specified, the debug shell service
    "debug-shell.service" is pulled into the boot
    transaction and a debug shell will be spawned during early boot.
    By default, /dev/tty9 is used, but a specific tty can also be set,
    either with or without the /dev/ prefix.
    Note that the shell may also be turned on persistently by enabling it with
    systemctl(1)'s
    enable command.
    rd.systemd.debug_shell= is honored only by initial
    RAM disk (initrd) while systemd.debug_shell is
    honored only in the main system.
systemd-debug-generator implements
    systemd.generator(7).