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).